IMPROVEMENTS IN THE TREATMENT OF COPPER PYRITES AND OTHER ORES OF COPPER
Year: 1876

page_text: LETTERS PATENT to Thomas Henry Cobley, of Dunstable, in the County
of Bedford, Chemist, and Joseph Anthony Dixon, of Glasgow, in the County
of Lanark, North Britain, Writer, for the Invention of " IMPROVEMENTS IN
THE TREATMENT OF COPPER PYRITES AND OTHER ORES OF COPPER."
Sealed the 26th May 1876, and dated the 28th March 1876.
PROVISIONAL SPECIFICATION left by the said Thamas Henry Cobley and
Joseph Anthony Dixon at the Office of the Commissioners of Patents on the
28th March 1876.
THOMAS HENRY COBLEY, of Dunstable, in the County of Bedford, Chemist, and
JOSEPH ANTHONY DIXON, of Glasgow, in the County of Lanark, North Britain,
Writer. IMPROVEMENTS IN THE TREATMENT OF COPPER PYRITES AND OTHER
ORES OF COPPER."
"
This Invention which relates to improvements in the treatment of copper
pyrites and other ores of copper is partly a development of the Invention described
in the Specification filed in pursuance of Letters Patent granted to the said
Joseph Anthony Dixon and numbered 2981, A.D. 1873.
Copper ores containing sulphur in the ordinary condition and proportions in
which it occurs in copper pyrites may in practising this Invention be generally
roasted by the combustion of their own sulphur, but when the pyrites or other
sulphuretted ores are too poor in sulphur to permit of such treatment they are
then roasted by the heat of some extrinsic fuel, or they may be mixed with other
combustible materials richer in sulphur so as to supplement their own deficiency in
sulphur and supply the requisite fuel.
The object we have in roasting the ores is to obtain as large a quantity as
possible of the copper in a soluble state by converting the sulphides of copper into
sulphate, with the purpose of afterwards separating the dissolved copper from its
solution by precipitation in manner after mentioned. To attain this end we
conduct the roasting slowly with a free access or current of atmospheric oxygen
to the ore and at or about a low red heat, rising gradually to a medium red
heat.
Although the treatment herein-after described may be applied to ore roasted in
small lumps we decidedly prefer it to be previously granulated. For this purpose
the raw ore is preferably first broken with a stone crusher or equivalent machine
Disine 101

page_text: into cubes or fragments of a suitable size and then ground with edge runners into
a powder, which need not, so far as roasting is concerned, be dust, but should
rather be gritty or granular, so that the mass of it shall be somewhat porous
and permeable to the oxygen while in the furnace. When the ore is in lumps
or very large grains, the copper in the central parts is either converted into
sulphide instead of sulphate of copper, or if the central parts are sulphatized the
exterior is apt to be reduced from sulphate to oxide. The proper degree of granu-
lation is that which at a moderate heat, as before described, permits of uniform
sulphatization through and through the granule, for which reason the granule
must not be too large, and which also permits of the free permeation of the oxygen
through the mass of granules during roasting, for which reason the granules must
not be too small. The size of granule will vary with the natural density and
other physical characters of the ore, and cannot be fixed to a precise figure. Too
powerful a current of oxygen to the roasting mass is to be avoided as tending
to raise the temperature too high and hurry the roasting, whereby there is
occasioned fusion or "clinkering" of the ore, causing waste of the sulphur of the
iron pyrites through the formation of protosulphide of iron and of other more
refractory iron sulphides, and particularly of magnetic sulphide and oxide of iron,
the presence of which latter magnetic bodies always indicates something improper in
the burning, either too great leat or too rapid roasting, or, on the other hand,
obstruction to the access of sufficient oxygen to portions of the ore.
The presence
of this magnetic sulphide and oxide may be readily ascertained by washing or
sliming a small portion of the roasting ore in powder, and applying a magnet to
the residue when the magnetic particles will adhere to the magnet. The specific
gravity of these magnetic particles is so near that of copper sulphide that it is
very difficult or almost impossible to separate them to any considerable extent
by washing or vanning. When it is intended, as in the Specification of Joseph
Anthony Dixon, herein-before referred to, to concentrate any part of the copper
as sulphide by these methods, the formation of such magnetic particles must be
carefully avoided with a view to successful washing or vanning.
Our object in the present process is to dispense with washing or vanning
altogether or as much as possible. Care must also be taken in whatever kind of
furnace the roasting of the ore is conducted, either at first or in a second roasting
as after mentioned, that no carbon or carbonic oxide comes into contact with the
roasting ore, because burning carbon and carbonic oxide tend to reduce the sulphate
of copper as fast as it forms by abstracting oxygen from it. To avoid the contact
of carbon and carbonic oxide with the roasting ore we prefer, where carbon is
used as fuel, to roast the ore in what is commonly known as a blind furnace, in
which the compartment containing the ore is protected from the access of the
flame and vapours of combustion into its interior. Time as well as access of
oxygen is required for the forination of sulphate of copper and therefore slow
roasting is preferable to rapid roasting. The temperature and duration of time
proper for the formation of copper sulphate in the roasting of pyrites may be
regulated according to the following principles: The sulphate of copper forms
best at a temperature at or about that which decomposes sulphate of iron into
oxide, but of course below that which decomposes the copper sulphate itself into
oxide. It requires a considerable temperature, a strong or full red heat, to
decompose the sulphate of copper and reduce it entirely to oxide. On the other
hand the iron pyrites associated with the copper forms in the process of roasting
a sulphate of iron at a heat below that required for the formation of copper
sulphate, and the said sulphate of iron is reduced to oxide at a temperature at which
copper sulphate remains unaffected, and in the same way if there be alumina in
the ore the sulphate of alumina which is formed is reduced to oxide by a
temperature rather below that which effects the reduction of the sulphate of
iron.
While it is not desirable to attempt to roast the ores so as entirely to reduce
the iron therein to oxide, the comparative quantity of soluble iron which appears in

page_text: the test tube from time to time on lixiviating small portions of the roasting ore and
treating the lixivium with ammonia will after a little experience of the particular
ore be of considerable assistance in the conduct of the roasting. Too low a tempe-
rature will form much soluble iron and little or no soluble copper, and as the proper
temperature and length of roasting are approached the appearance of soluble iron
will diminish while the formation of soluble copper up to a certain point increases;
but, on the other hand, if the temperature be carried too high both soluble iron and
soluble copper will diminish and disappear. In roasting large quantities of ore in
numerous furnaces at once it will not be practicable to apply this test to all at the
same time, nor to conduct the roasting by testing, but what we wish to be under-
stood as suggesting is that with any given ore the frequent application of the test
combined with observation of the temperature and time required by that ore to
show the formation and then the diminishing of soluble iron, will enable the
operator after a little experience to know the habit of the ore, and the best way of
roasting it. This test will not supersede the need of care, watchfulness, and judg-
ment, but it will materially assist then. Another rule which will be found useful
is to withdraw a small portion of ore from time to time out of the furnace, and to
ascertain the amount of sulphurous acid being evolved from it as it comes out. If
there is much sulphurous acid coming off the ore is not yet sufficiently roasted, but,
on the other hand, the roasting should be discontinued before sulphurous acid entirely
ceases to be evolved. The ore should be stirred and turned over every quarter of an
hour or oftener while roasting. About 4 to 6 hours should suffice for an ordinary
charge of 10 cwts. of powdered raw pyrites ore, but in, this matter the operator
should be guided by the appearances above described and not by the length of time.
The finer the powder the less will be the time required, and the temperature will
also not require to be quite so high; and it is also to be kept in view that within
the limits of the directions herein-before given a somewhat lower heat continued
for a longer time will effect the same results as a higher heat applied for a shorter
time. The charge after roasting should be allowed to cool slowly, unless where it
is cooled by drawing the red cinder into water or acid liquor. We find that if the
ore is mixed with lime, as herein-after described, less time and a somewhat lower
heat are required for proper roasting. We find it also advantageous after the ore
has been very finely ground to intimately mix it with hydrated aluminous earth or
with calcic hydrate, either in the proportions of lime to sulphur specified in the
Specification of the said Joseph Anthony Dixon before referred to or in the shape of
milk of lime, and in the inferior proportion of lime to sulphur herein-after specified
in regard to ores of copper disseminated through limestone rocks, and to make it up
with sufficient water loosely into small porous rolls or pipes, balls, bricks, or lumps
as small as convenient so as to permit of sulphatization through and through,
some moisture in the balls while being roasted being also advantageous in promoting
the sulphatization of the copper. The presence of moisture in the ore while being
roasted is always conducive to sulphatization. These balls, bricks, or other shaped
lumps after roasting are very friable, and are broken up into very fine powder before
going into the lixiviating vats. If an ore is poor in sulphur it is advantageous to
supplement the natural quantity of sulphur in it not only for the sake of burning it
as before mentioned, but also for the sake of more perfect sulphatization of the
copper. This may be done by adding to it, either in balls or bricks or in loose
intermixture, powdered iron pyrites, pyrites smalls, or other sulphuretted mineral
or other combination, or compound of sulphur which at a temperature below that
which would reduce copper sulphate to oxide will give up its sulphur or sulphuric
acid to help the sulphatization of the copper without leaving behind any alkaline or
other oxide which would decompose the sulphate of copper in the subsequent
lixiviation. If self combustion be the object the material added will be a com-
bustible sulphide, and such sulphide is also suitable for promoting sulphatization,
especially if it contains moisture. For this latter purpose sulphates may also be
employed, such as sulphate of alumina or the acid liquor formed in the processes of
lixiviation and precipitation. The magma or precipitated mixture formed by adding
A 2

page_text: lime to the said acid liquor will also form a suitable compound for this purpose.
It may sometimes also be suitable to add to the powdered ore raw ore already
burned before calcination or recalcination, a solution of nitrate of soda, and to pass
through the ores so mixed with nitrate of soda while roasting the sulphurous acid
from other roasting ores, so as to promote the sulphatization of the copper, and in
this case the nitrous fumes may be utilized for the manufacture of sulphuric acid.
The object of the fine grinding of the ore before roasting is to permit the fire and
the oxygen to have readier access to the sulphur and copper, but there being on the
other hand a tendency in finely pulverized ore to coking or condensation while
roasting, which obstructs the access of air, stirring or some other arrangement for
securing free access of oxygen to all the particles during the roasting must in that
case be had recourse to.
Although pulverization of the ore before the first roasting is preferred, it is not
absolutely necessary, and a great part of the copper may be extracted in the form
of sulphate by the operations now to be detailed from copper pyrites which has
been roasted for the first time in lumps of considerable size, and with inadequate
observance of the proper conditions for the formation of sulphate; but such ill
roasted ores require much greater labour to treat than ores properly roasted, and
generally require further treatment, as herein-after described, supplementary to the
lixiviation with water and acid liquor which is immediately herein-after described.
The ore being roasted, it is then lixiviated, and the most essential requisite to
lixiviation and extraction of the copper as sulphate is minute division of the
particles of the ore to be lixiviated. The finer the division of the particles the
inore perfect is the action of the solvent, whether water or the acid or precipitate
Jiquors after mentioned, and the more complete the exhaustion of the copper in the
soluble form; we therefore grind the roasted orc or cinders as fine as possible.
The grinding is efficiently performed by employing a pair of French burr stones,
such as are used for grinding lime; the cinder, which proper burning renders very
friable, being then easily reduced by these to great fineness and evenness of grain.
The roasted ore should be ground fresh; it is then perfectly dry and grinds better.
A disintegrator. may be used to grind the ore instead of burr stones. The lixivia-
tion is also greatly promoted by the application of the solvent hot (hot water being
less easily saturated with sulphate of copper than cold water is), and by continuous
commotion of the particles of the ore through the body of the liquid while under
the action of the solvent. The heating and the agitation may be effected by the
aid of steam injected into the vats during lixiviation or any other convenient
methods of heating and agitating may be applied. We also before lixiviating
moisten the finely ground cinder in mass, with the acid or precipitate liquor before
mentioned and keep it under cover.
In this state it developes heat, and an extra formation of sulphate of copper
goes on spontaneously within the mass, and a very slight addition of precipitate 1
or acid liquor to the moisture greatly promotes this action. Advantage may be
taken of this to advance the sulphatization of the ores while they are waiting for
lixiviation.
A succession or series of washings is preferable, especially with badly roasted
ores, each washing or lixivium so soon as it shows a good deep blue in a test tube
upon the addition of ammonia being allowed to settle, and the clear liquor is then
run or syphoned off into the precipitating tank and replaced by a fresh liquor, and
so on until the last liquor after a considerable time shows on testing that no more
soluble copper is being extracted.
The cyanide of potassium test, or any other well-known readily applicable test,
will enable the operator to determine how much of the whole copper has been
got out in solution, and what further treatment is required to render it all soluble.
Water alone will generally with even badly burned ores take out about one half
of the copper, and a larger proportion, if the ores have been properly burned.
most cases water will still leave a certain per-centage of undissolved copper in the
pulverized ore, which residuum may be rendered soluble and extracted to a very
In

page_text: considerable extent by lixiviating the ore with the acid liquors from which_copper
has been precipitated, and which are to be preserved for this purpose. Even a
slight degree of acidity in the liquor, whether derived from the addition of a little
free sulphuric acid or from the sulphuric acid and acid salts generated in the said
liquors in the processes of precipitation and lixiviation will be found to produce a
marked effect.
The said processes of precipitation and lixiviation will produce an abundant
supply of such acid liquors always increasing in strength.
These liquors we desig
nate by the name of precipitate liquors, and they are to kept and used over and
over again in lixiviating the successive batches of ore, and for use in the other ways
herein-before and herein-after described.
In regard to the use of the various ferric and ferrous sulphate salts or liquors,
which are produced throughout the process herein described, it is to be observed
that in calcining the ores as herein-before described, or in re-calcining the residues
as herein-after described, it will always be more advantageous to use for admixture
with them as a sulphatizing material a ferric sulphate or sulphate of the peroxide
of iron, whether neutral or basic, in preference to an equal quantity of the ferrous
sulphate, because in the furnace the ferrous salt gives off a large proportion of its
sulphur as sulphurous acid, and not as undecomposed sulphuric acid, not in fact
giving off any, or any considerable quantity of sulphuric acid, until the ferrous
oxide of the base is converted after evolution of sulphurous acid into ferric oxide,
whereas any sulphate of ferric oxide, basic or neutral, gives off its acid in the form
of sulphuric acid.
The liquid drawn from the precipitating tank after precipitation should, therefore,
be used as a sulphatizing agent only after it has by exposure to the air become as
far as possible converted into persulphate, and the ochreous deposit which accom-
panies the peroxidation of the ferrous salt, and which is also a peroxide salt, though
basic, may be used along with the peroxidized liquor for sulphatizing roasting ores
or residues, particularly when the latter have been over roasted.
It will readily
be understood that ferric sulphates with larger proportions of acids to the base are
preferable as sulphatizing admixtures to the more basic ferric sulphates.
The liquor in the precipitating tank after the precipitation by sulphuretted
hydrogen will consist largely of ferrous sulphate, which should be allowed before use
again as a lixiviating liquor to absorb oxygen from the air in the cold, in order to
convert it as much as possible into persulphate of iron. There will also be present
after precipitation soine free sulphuric acid from the precipitation of the cupric
sulphate, and from any excess of free sulphuretted hydrogen not decomposed in the
process by the cupric sulphate or by any persulphate of iron present before precipitation.
On returning the liquor over a fresh batch of roasted ore the persulphate of iron will
on boiling or strong heating (unless the solution be nearly saturated with it) decom-
pose into persulphate, basic ferric sulphate, and free sulphuric acid, and will so decom-
pose all the more readily, and with formation of more basic sulphate and free sulphuric
acid the more dilute it is. The free sulphuric acid is of importance in dissolving the
copper. In the lixiviation and other steps of the process there is formed a con-
siderable quantity of basic ferric sulphates, which are insoluble in water, and these
on being somewhat strongly ignited give off undecomposed sulphuric acid, and
therefore form good sulphatizing materials to mix with ores about to be roasted.
In calcining ores, or in recaleining the residues if the latter have been previously
slimed, the basic sulphates (yellowish-brown, or orange coloured substances when
moist) may be mixed with the ores or residues as well suited to promote sulphatiz-
ation, and all the ochreous basic sulphates of iron which will be found throughout
the process should be preserved and used for this purpose, either alone or together
with the other auxiliaries before or after mentioned. Of course the unslimed
residues will contain these basic sulphates which will promote the object of the
recalcination. If the lixiviating liquors in the early periods of working the process,
or the acid liquor left after the earlier precipitations at the start of the process, be
not strong enough, they may be strengthened by the addition of a small quantity o

page_text: free sulphuric acid, but this will not be necessary, except at the start. If water and
sulphuric acid is used for lixiviation the liquors may be used about 10° to 15° of
Twaddle, or 1050 to 1075 specific gravity, water being unity. The precipitate
liquors may be used of much greater specific gravity. The acid solvent liquor should
be applied with the aid of heat and agitation as before described, and will require
generally to be kept longer in contact with the ore, in order to extract the remaining
copper than the water in the earlier washings of the same batch of ore required to
be. By testing from time to time it will be ascertained when the liquor has taken
up sufficient copper to be fit for precipitating, when it should be run off into the
precipitating tank, and replaced by fresh acid liquor, containing no copper, and the
action of the acid or precipitate liquor as directed will be continued until the whole,
or at least the greater part of the copper is extracted by the solvent. The remainder
of the copper may ultimately be extracted without further treatment by piling the
residues containing it on proper beds, and allowing the air and moisture to find
access into the mass, and collecting the liquor exuding from the heaps, but in
general further treatment of the residues as herein-after described will be advisable.
It is sometimes advantageous to lixiviate with the acid or precipitate liquors from
the commencement of the lixiviation without commencing first with water for the
carlier washings. The grinding. for lixiviation, and the lixiviation itself may also
go on together, the roasted ore being put with water, or with acidified or precipitate
liquor, into an apparatus similar to the "Mexican arrastra" or the apparatus in
which flints are ground, for the manufacture of pottery, and ground therein. If
this mode is adopted a regulated flow of water or liquor into and over the edge of
the vessel holding the ore in process of trituration may be so arranged as during the
grinding to float away or slime off the oxide of iron. The liquor after flowing over
the edge of the vessel is conveyed through a succession of slime pits, in which the
finely divided oxide of iron will settle, the finest particles furthest from the grinding
apparatus, and the supernatant liquor which will hold the soluble copper is carried
back again until strong enough for precipitation, and the precipitate liquor used for
lixiviating and sliming fresh quantities. The insoluble copper which may have
been formed in the roasting being of greater specific gravity than the oxide of iron
will remain in a concentricated condition in the grinding vessel, or not go farther
than the nearest slime pits, and this if not found to be concentrated, or if it be not
desired by vanning and dressing to concentrate it to a sufficient degree of
strength for smelting as sulphide of copper, may be lixiviated over again with
precipitate liquor and heat, or may be further treated in the method now about to
be described.
Where the residues, either after lixiviation with water or with the precipitate or
acid liquor before mentioned, are still found to contain a considerable proportion of
undissolved copper (as in cases of bad burning), the residues, after having been first
slimed in a washing machine such as "Frue's Patent vanning machine," or in
slime pits, so as to wash away as much as possible of the oxide of iron and other
matters than the copper, and being by this process much reduced in bulk, are
subjected to calcination, or they may be calcined without sliming. If there is much
magnetic or other sulphide of iron present along with the copper, no additional
sulphur may be necessary to effect the sulphatization of the remaining copper in
this calcination, but it will generally be of advantage to add to the material to be
calcined some sulphatizing compound as above described in order to supply sulphur
or sulphuric acid to sulphatize the copper. The residues moist with the persulphate
liquor in which they have been undergoing lixiviation may be transferred into the
furnace and recalcined without any further sulphatizing auxilary. Or the residues
may be mixed in suitable quantities with and well distributed. through other ores
about to undergo the process of roasting for the first time, and calcined along with
them. The calcination is conducted with an oxidizing fire, and with the other pre-
cautions hercin-before specified with reference to the original roasting, but a shorter
time and somewhat lower temperature will generally be sufficient, especially if lime
be mixed with the ore. Or the residues may be mixed with hydrated aluminous

page_text: carth or the precipitated magma herein-before described, or with calcic hydrate as
herein-before and after described, and then calcined. Very badly burned ores may
be ground and recalcined without attempting any previous lixiviation. After
recalcination the recalcined ore will be lixiviated as before. If the pulverized roasted
ore has not been slimed before or during lixiviation the residues are slimed in
the ordinary way after all the copper has been extracted so as to recover the finely
powdered oxide of iron.
The successive lixivia after the fine powder has been allowed to settle in the vat,
so that only clear liquor shall run off, are run into the precipitating tank, and when
a sufficient quantity of liquor has been collected it is then precipitated by means of
sulphuretted hydrogen obtained in manner described in the Specification of Joseph
Anthony Dixon herein-before referred to, or precipitation is effected by the other
methods therein mentioned. In addition to the methods therein described of pro-
curing bisulphide of magnesium for the generation of sulphuretted hydrogen it may
also be obtained by passing sulphuretted hydrogen into a vessel containing an alkaline
or earthy hydrate, preferably hydrate of magnesia diffused or suspended in water,
when bisulphide of magnesium or other polysulphide of the hydrated base employed
will be formed. In this way a great deal of superfluous and waste sulphuretted
hydrogen which might otherwise be lost may be conveniently stored up for future
use, and in the case of bisulphide of magnesium in a form which we find to be more
suitable than any other. The bisulphide of magnesium or other polysulphide ought
to be preserved in covered vessels. By boiling the bisulphide of magnesium it
gives off all its sulphuretted hydrogen in a copious and regular stream, depositing
hydrate of magnesia alone, which can be used over again to form fresh bisulphide of
magnesium as before, and so on continuously; or being treated with the acid liquor
the hydrate will give sulphate of magnesia for mixing with the yellow liquor in
order to give bisulphide of magnesium in that way. Instead of using a poly-
sulphide of calcium per se along with kieserite or sulphate of magnesia to form
bisulphide of magnesium, as described in the Specification of Joseph Anthony
Dixon referred to, tank waste, gas waste, or soda waste ("blue billy"), or any
other form of sulphide of calcium or substance containing it in a considerable
proportion may be put (preferably pulverized) into a tank along with kieserite or
sulphate of magnesia, and left to stand covered with a layer of water, stirring
occasionally to admit air, and it is advantageous that a inoderate warmth be
applied. In a few days the supernatant liquor will acquire a greenish yellow
colour and be fit for use in the boiler as a source of sulphuretted hydrogen. A
method of procuring sulphuretted hydrogen in some respects less suitable than the
above, but which may sometimes be more convenient, is to put the sulphide of
calcium, or an alkaline or carthy sulphide, or polysulphide, into the boiler or any
other vessel with water, adding vegetable or organic matter rich in hydrogen, as
leaves, sawdust, chips and shavings of wood, particularly beechwood shavings, pine
needles, and the like, and to let the mixture stand for a few days, the vessel being
kept closed. On applying heat to the boiler containing the mixture a considerable
quantity of sulphuretted hydrogen will be obtained. It will help the evolution of
the sulphuretted hydrogen if a little acid is added to the liquor, and stream of
carbonic acid gas passed into the boiler which contains any alkaline or earthy
sulphide or polysulphide will also facilitate the disengagement of sulphuretted
hydrogen. Care should be taken not only when using this but also when using
any of the other methods of generating sulphuretted hydrogen described or referred
to, to prevent by means of a dome on the pipe leading from the boiler into the
precipitating vat, or by some equivalent mechanical arrangement for trapping them,
any of the lime, alkali, or vegetable matter, or of the liquor itself, being carried over
with the sulphuretted hydrogen into the precipitating tank. The precipitation
being completed and the precipitate allowed to settle, the supernatant liquor so
long as it comes off quite clear, may be run or syphoned off and kept for use, as the
precipitate liquor herein-before mentioned. The remaining moist precipitate con-
sisting of sulphide. of copper is then run off.into filters, barrels, or receivers

page_text: perforated at the bottom and sides, and lined with cloth, through which it will
drain itself free of the greater part of the remaining liquor (which is also to be kept
for use as herein-before mentioned), and afterwards it may be dried and solidified
still further by a press, such as Needham and Kite's clay press for drying potter's
material, or by such a press as is used for drying alizarine paste, or in a centrifugal
hydro-extractor, or by any other convenient mode of applying pressure or power for
this purpose, and it may be transferred either without or after such pressure into a
shallow pan or drying vat with a steam chamber (provided with a steam trap)
below the vat, or below and around it, and be dried therein by steam heat. Owing
to the quantity of sulphur present, and to the fine state of division in which the
precipitate exists, it is very inflammable at a comparatively low point of ignition,
and drying by fire heat direct is not desirable. Unless pure sulphate of copper is
required the precipitate should not be left in the moist state exposed to the air, as
there then takes place a gradual formation of sulphate of cupric oxide. Ignited out
of contact with the air the dry precipitate may be converted with evolution of half
its sulphur in the form of sulphurous acid (which may be utilized in various well
known ways) into the disulphide or subsulphide of copper, thus forming a rich regulus
of copper, and by adding an excess of charcoal, urging the heat and admitting the
air, this regulus may be reduced, with evolution of the remaining sulphur or most of
it in the form of sulphurous acid, to rough copper or a very rich regulus.
There are certain forms of occurrence in which copper (sometimes in the form of
subsulphide, grey copper, purple or peacock ore, and other rich forms, and sometimes
also in the form of pyrites more or less mixed with particles or patches of richer
ore,) is found disseminated in particles or patches through large masses of lime-
stone, rock, or other rock formations, as, for example, at Acton Vale, in Canada.
Ores of this class we treat in the following manner:-We burn the limestone in-
pregnated with ore as in the ordinary method of burning limestone so as to drive
off the carbonic acid from the lime and to disintegrate the rock and render it more
friable, as well as to increase the difference of specific gravity between the limestone
and the copper ore. With sandstone or siliceous rocks of a clayey origin or
metamorphic character the addition of lime as after mentioned will be found of
advantage in breaking up the rock, which should be pulverized before burning, and
calcined at a low heat. The roasted limestone or rock and the ore are then, if not
already, ground to the degree of fineness suitable for treatment in Krom's air
concentrator, by which the limestone or other rocky particles are blown away and
separated from the denser particles of the copper ore, and the latter are concentrated
into a greater state of richness. When the copper is in the form of subsulphide,
purple or peacock or other rich ore, the ore after concentration may be smelted into
inetallic copper. When the ore disseminated through limestone rock is altogether
or principally copper pyrites, if the quantity of unseparated lime left after the
blowing does not vary inaterially from the proportions of copper, sulphur, and lime
mentioned in the second part of the Specification of Joseph Anthony Dixon herein-
before recited, in which he describes a lime process, the residue left after the air
concentration may be treated by affusing the lime with water so as to hydrate it,
and it may then be roasted and treated as the mixture of copper ore and calcic
hydrate is directed to be treated in the said Specification or as ores mixed with
lime are directed to be treated in the preceding parts of the present Specification.
If the lime be in excess of the proportion of lime to sulphur mentioned in the said
Specification, the ground limestone and ore may be mixed with ground iron pyrites
or other ground sulphur-holding copper ores which do not contain lime, so as to
supplement the sulphur to the extent required to convert the hydrated lime on
burning into sulphate of lime and the copper into sulphate of copper in the manner
mentioned in the said Specification or in this Specification. If only a small quantity
of lime remains in the blown ore of less amount than what the sulphur present
would be able to convert into sulphate of lime besides converting the copper into
sulphate of copper, this small quantity will do no harm. The blown ore in that
case should be atlused with water and stirred about so as to render the lime some-

page_text: what fluid like milk of lime, and so more thoroughly to distribute it among the
particles of the copper ore, and the ore so mixed with milk of line will be roasted
in manner before described and lixiviated. We find generally that the presence of
a small quantity of lime in the shape of milk of lime or hydrated lime along with
any pyrites, ore, or residues of lixiviation to be roasted, even though the lime be
much less in proportion to the sulphur present than the proportion described in the
Specification herein-before referred to is of great advantage in promoting the oxidiza-
tion of the cupric sulphides, and particularly of the undissolved portions of the ore
which have escaped sulphatization in the first roasting. But in all cases the sulphur
should be in some excess as compared with the lime, or should be supplemented so
as to be in excess to ensure the conversion of the whole hydrate of lime into sulphate
of lime and leave no lime free, which would have a tendency to precipitate the
copper from the liquor in the process of lixiviation. Sulphide of calcium or the
magina before described or other sulphur holding compounds such as are herein-
before described may also be used. If the rock through which copper pyrites is
disseminated as before described is not limestone and no limestone has been used
with it in burning or no lime remains in it after blowing, then after the burning
and concentrating as aforesaid it may be treated in the mode above described with
reference to ordinary copper pyrites.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Thomas Henry Cobley and Joseph Anthony Dixon in the Great Seal
Patent Office on the 27th September 1876.
THOMAS HENRY COBLEY, of Dunstable, in the County of Bedford, Chemist, and
JOSEPH ANTHONY DIXON, of Glasgow, in the County of Lanark, North Britain,
Writer. "IMPROVEMENTS IN THE TREATMENT OF COPPER PYRITES AND OTHER
ORES OF COPPER."
Our said Invention, which relates to improvements in the treatment of copper
pyrites and other ores of copper, is partly a development of the Invention described
in the Specification filed in pursuance of Letters Patent granted to the said Joseph
Anthony Dixon, and numbered 2981, A.D. 1873.
The general nature and objects of the process which we herein-after describe in
detail in the first part of this Specification are as follows:-By roasting copper
pyrites ore or cinder in fine powder in manner and under the conditions after-
mentioned, we convert a large proportion of the sulphide of copper contained
therein into sulphate of copper in the furnace, and the rest which escapes
sulphatization in the furnace into cupric oxide (Cu O), with the purpose of
converting this cupric oxide also into sulphate by the action of a solvent acid
liquor formed from the ores themselves as after mentioned. We so roast as to avoid
as far as possible leaving any copper in the form of sulphide or cuprous oxide,
the former being almost insoluble, and the latter difficultly and only partially
soluble in the said acid solvent, while cupric oxide is readily soluble therein,
especially in fine division. We so regulate the roasting that the iron sulphides of
the charge are converted first into ferrous sulphate, and then into basic ferric
sulphates, including bisulphate (Fe, O., 2 SO), and the greater portion of the
sulphuric acid of the latter is, by continued roasting, liberated in the furnace,
(leaving the iron as peroxide) and aids in sulphatizing a portion of the cupric oxide,
and also, as after mentioned, in converting copper sulphide and cuprous oxide into
cupric oxide; but we allow a convenient proportion of the iron sulphates to escape
conversion into peroxide with a view to the formation of the said solvent liquor in
lixiviating the ore. The liquor originally formed, consisting chiefly of ferrous
sulphate, and if clay be present in the roasted ores, also of some sulphate of
alumina, (Al, O., 3 SO) comes in the course of the process to contain in considerable
quantity persulphate of iron, or so-called neutral ferric sulphate (Fe, O. 3 SO,) and

page_text: free SO. The persulphate is formed partly by the incidental or purposed exposure
of the ferrous sulphate to heat and air in the course of the process as after mentioned;
partly by the action of the free sulphuric acid on the basic ferric sulphates
produced in the furnace and otherwise, and in the peroxide of iron, and also by the
action of the free acid and air on the ferrous sulphate in the pickling of the ore
as after mentioned, and partly by the resolution of the bisulphate into a bibasic
sulphate and persulphate by water and heat. The free SO, is formed partly by the
decomposition of the persulphate, by boiling as after mentioned, partly by the
liberation of free SO, in the precipitation of the cupric sulphate as sulphide, and
partly, as after mentioned, by the conversion of sulphuretted hydrogen into free
acid by heat in the presence of water in the precipitating tank. We lixiviate the
roasted powder at boiling heat, partly because soine of the sulphates formed in
roasting are somewhat difficult of solution in water, and the heat aids the solvent
power of the liquor (whether water or the acid solvent mentioned) and enables us
to perform the lixiviation more rapidly and with smaller quantities of liquor,
the cupric and other sulphates requiring also much less hot water to dissolve them
than they require of cold; and partly because ebullition forms sulphuric acid in
the liquor by decomposing persulphate of iron into free acid and terbasic ferric
sulphate, and so increases the solvent power of the liquor; and partly also because
where the ore contains silver which we wish to recover, the sulphate of silver formed
in the roasting is only soluble in boiling, but not in cold water, and is readily
soluble in a boiling solution of ferric sulphate, its solubility being also promoted
by the presence of the free sulphuric acid in the solution of ferric sulphate. Heat
also contributes, while thus promoting the precipitation of basic iron sulphates, to
prevent the precipitation of any basic copper sulphate, and it also promotes the
conversion of any ferrous sulphate into persulphate. We lixiviate therefore with
the aid of heat, and, in the first instance, until the said acid solvent forms in sufficient
strength (which soon happens) with boiling water, whereby we obtain an acid
solution of the cupric sulphate and of the soluble iron sulphates. As the boiling
is continued the bisulphate of iron is decomposed into persulphate and a basic
sulphate, and a certain proportion of free sulphuric acid is also formed by the decom-
position of the ferric persulphate present into free acid and basic sulphates, partly
soluble and partly insoluble. The proportion of free sulphuric acid thus formed
is greater, and is formed at a lower heat, in proportion as the persulphate in the
liquor is dilute, which it will be at the outset. The action of this acid liquor
converts the cupric oxide, and also any cuprous oxide or metallic copper formed by
careless roasting into cupric sulphate, which is dissolved. The persulphate of iron
in the liquor converts not only cupric oxide, but also metallic copper and cuprous
oxide, and even to some extent disulphide of copper (Cu³ S) into cupric sulphate,
though in the case of cupreous oxide there appears to be decomposition of the water
and liberation of hydrogen which, in stutu nascenti, interferes with the complete
sulphatization, probably forming sulphite. The action of sulphuric acid even in a
dilute state completely converts cupric oxide (Cu 0) into cupric sulphate, but
unless there be also free access of air is not so complete on metallic copper and
cuprous oxide as on cupric oxide. It is always desirable therefore to have a
considerable quantity of persulphate present, which, however, the action of the
free acid on the peroxide of iron and other reactions above mentioned, will always
secure. The ferrous sulphate also converts cupric oxide into cupric sulphate with
formation of ferrous sulphate, and of some basic sulphate of iron, but there is also
in this case a liberation of hydrogen. If there is any sulphate of alumina present,
it also, in consequence of the weak affinity of its acid for its base, is readily
decomposed by cupric oxide with formation of cupric sulphate. The imperfect
action of the solvent liquor on cuprous oxide, cupric and cuprous sulphites, and
metallic copper, we obviate by means after described, so as to get the whole copper
into solution as cupric sulphate. Having obtained the copper in solution, we then
(unless we first recover the silver as after mentioned) separate the copper in the
form of sulphide of copper (Cu S) by precipitation with sulphuretted hydrogen

page_text: from the iron (and from any zinc, nickel, cobalt, or manganese) in the solution. The
solution from which the copper has been precipitated is materially strengthened by
this process of precipitation as we conduct the same, a further quantity of free
sulphuric acid being formed therein, partly by the liberation of the sulphuric acid
of the cupric sulphate by the sulphuretted hydrogen, and partly because, as we
drive the sulphuretted hydrogen off from a boiling solution as after mentioned into
the precipitating tank, the hot sulphuretted hydrogen, and the steam accompanying
it, as it comes from the boiler, heat the solution containing the copper to a high
degree, and we take advantage of this to form at each precipitation more
sulphuric acid in the liquor by throwing in an excess of sulphuretted hydrogen,
which, in presence of water, oxidizes readily into sulphuric acid at a temperature
of between 100° and 120° F., and still more readily at from 100° to 212° F. This
liquor is next treated for the purpose of reconverting into persulphate the sulphate
of iron (now reduced to ferrous sulphate by the hydrogen of a portion of the
sulphuretted hydrogen having oxidized itself to water at the expense of the extra
oxygen of the ferric sulphate with precipitation of its sulphur along with the
copper sulphide), and is then brought back again to lixiviate fresh batches of ore at
boiling heat, whereby, in addition to the further accession of cupric and iron.
sulphates which it receives from the fresh batch of ore, there is a further formation
of free sulphuric acid from decomposition of a portion of the persulphate as before.
The liquor is further strengthened by going again through the process of precipitating
the copper of the fresh batch of ore with sulphuretted hydrogen, and by the excess
of sulphuretted hydrogen thrown in, and as it is always brought back again and
employed (with the requisite dilution, as occasion requires, with water or the steam
used to heat it during lixiviation) to lixiviate the successive batches of ore, we have
a solvent liquor constantly forming in the course of the process, and increasing in
strength and quantity as the process goes on, such liquor being capable of converting
into sulphate all the cupric oxide which escapes sulphatization in the roasting, and
being also specially suited as consisting of a mixture of persulphate of iron and
ferric sulphates with free sulphuric acid, to dissolve the silver sulphate and silver
oxide formed in the roasting, and even particles of metallic silver if there be silver
in the ore.
If there be silver in the ore it is to a considerable extent converted in
the roasting as we conduct it, and in presence of the copper and iron sulphates into
sulphate of silver, which dissolves in the said boiling acid liquor, from which it may
be precipitated by metallic copper before precipitating the copper from the solution
by sulphuretted hydrogen; the sulphate of copper formed by the action of the
metallic copper in decomposing the sulphate of silver being recovered as sulphide
on the precipitation of the copper, and its sulphuric acid liberated in the liquor.
The sulphide of copper is precipitated in fine division and mixed with more or less
free sulphur, by the aid of which it may be readily ignited on hot plates in the air,
the ignition driving off any arsenical impurities precipitated along with it, and
converting the precipitate into a rich regulus consisting nearly altogether of copper
oxide in a state of great purity. Prior to the lixiviation of the roasted powder,
and in case any cuprous oxide may have been left not oxidized in the roasting into
cupric oxide, we prefer to moisten the ore with, but so as not to submerge it in the
acid liquor with free access of air to and through it, allowing it to dry up as far as
it will in the air, by which treatment the cuprous oxide which, as is herein-after
more fully explained, would otherwise be partly converted into metallic copper and
cupric sulphate, is converted by the united action of the acid and the oxygen of the
air wholly into cupric sulphate, while the action of the acid solvent liquor on the cupric
oxide is at the same time being promoted so as to facilitate the subsequent lixiviation,
The dilute sulphuric acid in the liquor also acts at this period in converting the basic
ferric sulphates formed in the furnace, the ferrous sulphate and the ferric oxide
itself into persulphate of iron (Fe, O., 3 SO₁). The persulphate of iron of which con-
siderable quantities will crystallize from the concentrated liquors, as wbite anhydrous
crystals in the peroxidizing tank, especially when there is much free acid in the
liquor, and the basic ferric sulphates which are precipitated in considerable quantities

page_text: as ochreous deposits in the lixiviating tanks, and at other stages of the process have
the property of giving off sulphuric acid undecomposed on being heated to redness
in a retort, leaving fine peroxide of iron behind, and they may be used as supple-
mentary sources of sulphuric acid if required, either by mixing them with ores
about to be roasted or by driving off their acid from a retort, as mentioned, and
using it for any convenient purpose. The residual ore after lixiviation may be
slimed to recover the oxide of iron. The sulphuretted hydrogen which we use for
precipitation we obtain and apply according to any one of the methods explained
in the former Specification of the said Joseph Anthony Dixon herein-before men-
tioned, but preferably according to one of the said methods, viz., by roasting waste
copper pyrites ore or the iron pyrites which is generally found in its vicinity with
lime or lime compounds to form sulphide of calcium (Ca S) from which, by treatment
with air and moisture, we obtain bisulphide or bi-hydrosulphate of lime or calcium
(Ca 2 H, S), or a polysulphide of calcium (Ca, x H, S), whence, by admixture with
sulphate of magnesia we obtain, by double decomposition, sulphate of lime (which we
reduce by carbon again to Ca S for use as before) and bisulphide or bi-hydrosulphate
of magnesia, which by mere boiling at 212° Fa. gives off all its H. S for precipitation
and leaves behind in the boiler magnesia, from which with some of the acid liquor
formed as above, or sulphuric acid got from the ferric persulphate or basic sulphates,
as already mentioned, we reform sulphate of magnesia for use as before. In this way
we make the ore itself supply, in the course of the process itself, everything needed for
the extraction of the copper, except the stocks of lime and magnesia, which are used
over and over again without any but the unavoidable mechanical loss in handling, and
excepting also the fuel required for raising steam, or for occasionally heating retorts,
or for calcination or occasional recalcination of cinders or badly burned ores too
poor in sulphur for self-sustained combustion, where we do not roast them along
with other ores containing the necessary sulphur for roasting both together.
Having thus described in outline the general plan, objects, and methods of our
said process, we now proceed to describe it in detail.
>>
Copper pyrites consists of a combination of iron and copper sulphides, which may
be generally expressed by the formula Cu² S, Fe, S.; but there are frequently present
sulphides of copper with a larger proportion of sulphur to copper, as Cu S, and Cu S,
and also sulphides of iron with still greater complexity in the proportions of sulphur
and iron, as Fe, S or Fe S, or Fe, S, or Fe, S, besides combinations of two or more
of these forms, and portions of these are sometimes replaced by other sulphides, such
as those of zinc and arsenic. If an ore is rich in sulphur, as when much Fe S, is
present, a part of the sulphur is apt in the roasting to rise in vapour and burn on
the surface of the ore in the furnace with great evolution of heat, which renders it
difficult to control the temperature and other conditions of proper roasting, fre-
quently causing "sintering" or clinkering," or a sort of incipient fusion in the
mass, which tends, by preventing the access of oxygen from the air, to form
sulphides of iron and copper, and also cuprous oxide instead of sulphates and cupric
oxide. Besides, as the sulphides require in our burning to be roasted till the whole
sulphurous acid has disappeared from the furnace, too great an excess of sulphur
requiring to be roasted off at the low heat and with the care and labour which
roasting for our special purpose requires, results merely in prolonging the period of
the roasting and in an excess of the special care and labour attendant thereon. .It
is best, therefore, to give such ores a preliminary gentle roasting to drive off the excess
of this sulphur, and then to roast the residue for the special purposes of our pro-
cess, and such preliminary roasting may be in lumps of even size and in open heaps,
roasting cells, pit ovens, or on hearths with free but not too abundant access of air
through the mass, for fear of fusion from the great heat apt to develope itself if much
sulphur is present. And ores containing arsenic should be treated in the same way
by a gentle heat sufficient to expel the arsenic as arsenious acid, and sub-oxide without
such heat and access of air as would form arsenic acid and with such arsenical ores the
injection of water vapour or steam has been found beneficial as expelling the arsenic.
In roasting raw ores or cinders which retain a very large quantity of sulphur, a

page_text: convenient arrangement is to divide the furnace into two portions or compartments,
in the one of which the first part of the roasting, consisting in the expulsion of the
bulk of the sulphur, is conducted by the aid of direct heat from the furnace playing on
the ore, and in the other of which the roasting, after the sulphur has been reduced
in the first compartment to about 5 per cent., or thereby, may be finished by heat
applied to the outside of the compartment, so as to exclude carbon and carbonic oxide
for the reasons after mentioned from the ore. When this arrangement is adopted,
steam may be injected into the compartment in which the first part of the roasting
is conducted, and it will then be beneficial (especially when a free influx of atmo-
spheric air requires to be checked or moderated on account of its tendency, when
excess of sulphur is still present, to create too intense a heat) in assisting the
expulsion of the sulphur as sulphuretted hydrogen, and of the arsenic and antimony
present as sulphurets by disengaging their sulphur as sulphuretted hydrogen,
and the arsenic and antimony as volatile hydrosulphurets, oxysulphurets, and oxides
of arsenic and antimony. But the presence of steam or water vapour in contact.
with the ore is of no practical advantage in the later stage of roasting but is rather
to be avoided, because the excess of free sulphur produced by the contact of
sulphuretted hydrogen and sulphurous acid in the furnace tends, if there is any
want of air, to prevent the higher oxidation of the sub-oxide of copper, and to form
magnetic oxide of iron and sulphides of iron and copper, and to prevent the
sulphatization of the silver, and if there is, as there should be at this stage, a free
influx of air, the water vapour effects nothing in the way of oxidizing the sulphur
and the copper which atmospheric air will not effect in a better way and in a
shorter time and with less expenditure of fuel. The presence of a sufficient quantity
of sulphur, and especially in the form of a sulphide of iron, in or along with the ore
or cinder in the final roasting is necessary, however, not so much to maintain or ai
self combustion (for such poor ores or cinders may and generally must be roasted by
the help of some extraneous fuel), but principally for the formation of sulphurous,
and sulphuric acids in the furnace, because it is on their formation and reactions
inter se and on the ores during the roasting that the conversion of the sulphide of
copper and sub-oxide of copper into cupric sulphate and oxide mainly depends.
The metallic sulphides, roasted in fine powder at the lowest possible temperature at
which oxidation is capable of proceeding with the different sulphide metals in the
ore, and with free access of atmospheric air, give off their sulphur under the action
of the air and heat in the form of sulphurous acid, the metals assuming first the
lowest grade of oxidation of which they are susceptible; the sulphurous acid, by
the influence of the air and of contact with the roasting orc, is converted into
vaporous anhydrous sulphuric acid (SO,) which acts partly as a sulphatizing agent,
converting the oxides into sulphates, and partly as an oxidizing agent, giving up
its third atom of oxygen to convert other portions of the sulphides into oxides (tlic
sulphur of these sulphides consequently going off as sulphurous acid) and also to
raise the lower metallic oxides to a higher degree of oxidation. The free access of
atmospheric oxygen and the requisite temperature are thus essential. If air is
excluded the sulphurous acid is apt to oxidize itself into sulphuric acid at the cost
of the oxygen of the higher inetallic oxides and of the iron sulphates already formed,
and if the temperature of the furnace fall too low, both the influx and the
oxidizing action of the air and acid vapours may be so far arrested or weakened
as to conduce to the same results. It is we believe not so much by the direct
action of the atmospheric oxygen as by its indirect action through the formation
and action of sulphuric acid that sulphates and oxides are formed from the sulphides
and sub-oxides, and therefore such an amount of sulphur as will continually form
and keep the furnace always abundantly supplied with sulphuric acid until the
results aimed at are attained to the greatest possible extent is essential.
siderable proportion of sulphides of iron is always favourable to the successful
roasting of the copper sulphides, because the former give occasion to copious
formation of SO, and form sulphates which give up their SO, to the copper ore at a
temperature below that which would decompose the cupric sulphate; and the
A con-

page_text: higher the grade of their sulphurization is the more abundant is the formation of
sulphate and the less the proportion of oxides of copper formed in the roasting.
We have found that the pyrites cinders remaining after the native pyrites ore has
been roasted in lumps for the manufacture of sulphuric acid, in the ordinary way,
and which usually contain about five per cent. of sulphur, can be roasted without
additional sulphur by the help of extraneous fuel so as to yield a very considerable
amount of cupric sulphate and cupric oxide, so that as much as (or more than) three-
fourths of the copper can be obtained in soluble form by careful roasting and
lixiviation with water, but when the proportion of sulphur is much below that
mentioned there is generally left a certain proportion of cupric and cuprous oxide
and of unoxidized copper sulphide, and a larger proportion of sulphur, about 8 or 10
per cent., would give much better results, though it may prolong the period of
roasting, which must be continued till there is no longer any smell of sulphurous
acid in the furnace. It is not necessary to lose the sulphur which does not combine
with the oxides as sulphate, for it may be carried, on passing out of the furnace as
SO, and SO, into the leaden chamber and converted into sulphuric acid in the
usual way or otherwise utilized in well known ways. Ores or cinders too poor in
sulphur should be mixed with ores richer in sulphur, or with other compounds
containing sulphur, and which will give it off at the moderate heat we employ, and
should be roasted along with them.
In order to attain our object, we observe in roasting pyrites ores or cinders the
following further conditions or precautions:-
(1.) We roast the ore (as a general rule and subject to the exceptions after
mentioned) at a low or dull red heat, a little above a black, or at just visible red
heat, or incipient redness, in the heart of the ore, as it is being turned over, and
never rising above a distinctly visible redness there. The surface when exposed to
a cooler draught of air entering from without will not show more than a glimmering
or commencing redness in the shaded light of the inner parts of the furnace.
(2) There must be a free and constant access of air or oxygen to the ore, and,
as far as possible, through its whole mass and to every individual particle of it.
It is to be observed, however, that if the atmospheric air be admitted direct from
without into the furnace it will cool down the surface of the ore, over which it
travels, and as the action of the air, and of the oxygen of the sulphuric acid
proceeds principally at the surface, and does not proceed at all, or at least so
energetically, when the temperature of the ore is reduced below a certain point,
it is necessary to obviate this cooling of the surface of the ore either by spreading
the powdered ore more thinly over the hearth of the furnace (when it is heated
from below), not over six inches at most, so as to let the heat penetrate to the
surface ore without unduly raising the heat of those portions of the ore lying
beneath, or, which is better and permits of a somewhat deeper body of ore being
laid on the hearth, to heat the atmospheric air before it comes into contact with
the surface of the ore, so that during the roasting the whole mass may, as nearly
as possible be kept at the same temperature, viz., generally that of a dull red, a
little above blackness, but raised at a particular point of the process a little
higher, as after mentioned, The air may be heated by being drawn or forced
into the roasting chamber through pipes or vessels heated in the furnace or flues
by which the roasting hearth is heated, or by other known means. There must
be provision made for regulating the draught so as not to burn too fiercely or
rapidly, as much sulphur with a strong draught is apt to do, nor should the
sulphurous and sulphuric acids formed in the furnace be quickly withdrawn from
it by a rapid draught, but they should be kept well in contact with the ore.
access of air to the underlying portions of the ore is attained mainly by continual
turning over of the ore so as to bring the under portions to the surface, and to
let in the air through the particles by moving and stirring the mass, either by
manual labour with rakes and plough-shaped tools that raise the ore, and let it fall
again in loose condition and turn it upside down, or such stirrers may be actuated
by mechanical power, or the end may be attained by the use of revolving furnaces,
The

page_text: such as Russel's or Stevenson's revolving furnaces for roasting alkali, or Oxland's
tin roasters, modified to suit this process by excluding direct flame from acting on
the ore, and provided with longitudinal ridges inside to catch the ore and then let
it fall, as the furnace revolves, in a broken shower, instead of sliding down the
sides in an unbroken cake with the same surface always uppermost, or Siemens'
revolving gas furnace may be employed with an oxidising flame maintained in
the cylinder. Or air may be forced in under and through the stratum of ore by
such an apparatus as Körting's injector. Raw ores or ores partly burned but
still containing a large excess of sulphur may be conveniently roasted in an
oscillating cylindrical furnace divided into three longitudinal compartments ex-
tending the length of the cylinder by two floors of fire-bricks arched across the
width of the retort. The upper floor on to which the ore on entering the retort
decends from the hopper is heated in the inside by the direct flame of the furnace
and gases of combustion which may be made either to enter the upper floor and
play along it and then down through a boxed or enclosed passage leading into the
third or lowest compartment, heating the middle compartment through its floor
or sole, or they may be made to enter at the lowest compartment, and after
playing along this and heating the floor of the mid compartment from its under
side may be drawn up the closed passage into the upper compartment and act
there directly on the ore. The ore after working its way by the movement of the
cylinder and a suitable slope of floor from the one end to the other of the uppermost
compartment drops through a boxed or enclosed passage separate from that through
which the flame and furnace gases pass into the mid compartment, which is pro-
tected from access of flame, furnace gas, and carbonaceous products of combustion,
and is practically a blind furnace or mufle oven. The ore being tolerably well
desulphurized by the direct action of the flaine and gases in the upper floor, works
along from one end of the mid compartment to the other (its floor being also
sloped to suit) and at the said other end it drops out into a suitable chamber or
flue, from which it is raked out. The roasting to remove the excess of sulphur is
thus performed by direct flame heat, and (if thought advisable) also with the aid of
injected steam in the upper compartment, and the proper or more peculiarly sul-
phatising portion of the roasting is completed in the blind oven below from which
carbon and carbonic oxide (CO) are excluded, and to which air from without should
be freely admitted by pipes or suitable openings. If the flame be admitted first
into the uppermost compartment the ore should be charged at the opposite end
from the furnace and be caused to run towards the flame and then drop into the
muffle compartment in which it will run in the opposite direction, and by ad-
mitting the flame and furnace gases into the uppermost and drawing them off
through the lowest compartment, the heat of the burning sulphur is added to that
of the furnace gases in heating the under side of the floor of the muffle compart-
ment. The cylinder will oscillate on axles at the centres of its two ends, and its
weight will be mainly borne by antifriction wheels beneath it. The powdered
orc when hot is so fluent that the top of the retort need not at its extreme points
of oscillation be depressed more than half a quarter of a circle on either side.
(3.) The roasting should be gradual, commencing at the low heat of that part
of the furnace furthest from the fire, and the charge should be raked forward from
the cooler into the hotter portions of the hearth, being continually turned over
in the process. If too strong a heat be applied at first (especially when there is
much sulphur and inefficient stirring) there are formed sintered or semi-fused
particles or small nodules containing Cu S and Cu O, while, if the temperature
be gradually raised and the stirring kept up (especially at the beginning when
sintering is most apt to set in), there will remain only a very little, if any,
Cu S.
(4.) Although the treatment herein-after described may be applied with com-
paratively successful results to ore roasted in small lumps, we decidedly prefer that
the ore or cinder be previously to roasting granulated, and we regard reduction
to granular powder as an indispensable part of proper roasting for our purpose

page_text: except in the case of very richly sulphuretted ores, which may be first subjected
to a preliminary roasting in manner already described, and then ground to powder
for re-roasting. The raw ore or lump cinder is preferably first broken with a
stone crusher or equivalent machine into fragments of suitable size, and is then
ground with edge runners, or still more finely and evenly (evenness of grain, which
is of great importance, being also attained by sieving and returning the portion of
the grist which does not pass through the sieve through the mill stones again) with
French burr stones into a powder, which need not, so far as roasting is concerned,
be dust, but should rather be gritty or granular, so that the mass of it shall be
somewhat porous, and permeable by the air, oxygen, and gascous sulphuric acid
while in the furnace. When the ore is in lumps, or very large grains, the copper
in the central parts of the lumps or grains is either converted into sulphide instead
of sulphate of copper, or if the central parts are sulphatized the exterior is apt
to be reduced from sulphate to cupric oxide, and from cupric oxide to suboxide,
or even to metallic copper. The proper degree of granulation is that which, at
a low heat as before described, permits of uniform sulphatization or oxidation
through and through the granule, for which reason the granule must not be too
large, and which also permits so far as possible, consistently with the requisite
fineness of grain of permeation or interpenetration of the oxygen through the
mass of granules, for which reason the granules must not be too small. The proper
size of granule will to some extent vary with the natural density and other physical
characters of the ore, and cannot be fixed to a precise figure; but it is better to be
too fine than too coarse, as the objection to its too great fineness may be obviated
by more assiduous stirring of the ore during roasting. In the case of silver holding
copper pyrites, ore, or cinder, the grain should be larger, as there is a certain loss
of silver mechanically carried away by the draughts, which is apt to increase with
too great fineness of pulverization. This loss is, however, not so great in a blind
furnace as in a reverberatory furnace.
(5.) Care must also be taken in whatever kind of furnace the roasting is con-
ducted that no carbon or carbonic oxide shall come into contact with or proximity
to the roasting ore (especially at these later stages of the roasting, when the greater
part of the sulphur has been burned off and sulphatization and oxidation of the
copper is proceeding), because burning carbon and carbonic oxide tend by abstract-
ing oxygen to reduce the sulphuric acid to sulphurous acid, and the SO, to sulphur
vapour, and to reduce the sulphate of copper and cupric oxide to sulphide and sub-
oxide respectively, or even to metallic copper, as fast as they form. To avoid the
injurious action of carbon and carbonic oxide in the furnace and on the roasting
ore, we prefer, where carbon in any solid form is used as fuel, to roast the ore in
what is commonly known as a blind furnace, or muflle oven, in which the compart-
ment containing the ore is protected from the access of the flame and other gaseous
and solid products of combustion into its interior, and this muffle furnace should be
provided with an arrangement for heating the atmospheric air which enters the
roasting chamber, because otherwise either the under parts of the ore on the hearth
of such a furnace are apt to be overheated, or the surface of the ore exposed to a
direct draught of air from without is apt to fall below the proper temperature. If
however it is preferred for this or other reasons to roast in a reverberatory
furnace by the direct action of the flame and gases of combustion on the ore, a
plentiful current or thick stratum of atmospheric air must be always kept up
between the burning carbonaceous matters and gases coming directly from the
burning fuel which will occupy the upper part of the furnace, and the ore on the
hearth, so as to form an atmospheric layer between them, which will perfectly
oxidize the carbon and carbonic oxide into the inert or innocuous carbonic acid,
before they reach the surface of the ore. We do not recommend the latter form of
furnace or mode of roasting for cinder poor in sulphur, though it may answer for
such crude ores and cinders as contain plenty of sulphur. Whereas in the Siemens'
revolving gas furnace and other furnaces, the oxidizing character of the flame can
be certainly maintained free from any admixture of carbonaceous particles, or the

page_text: presence of
any carbonic oxide, the contact of the flame and the ore will not only
not be objectionable, but advantageous as securing thorough roasting with less
expenditure of fuel than a muffle oven requires. In roasting raw ore or partially
roasted ore, which still retains a large amount of sulphur, the process may be
divided into two stages, in the first of which the bulk of the sulphur may be
driven off by the direct heat of the fuel, as in a common reverberatory furnace,
until the sulphur is reduced to about the proportion left in ordinary pyrites cinder,
when the ore will be transferred to another part of the furnace from which the
direct access of flame and carbonaceous gases is excluded, and the roasting finished
there by heat transmitted through the sides or sole plate of the furnace.
The temperature and duration of roasting, and certain further points requiring
to be attended to in the roasting, may be regulated according to the following
principles-The sulphate of copper forms best at a temperature below, and gradu-
ally rising up to that which decomposes the sulphate of iron into oxide, but of
course it must not rise to the strong or full red heat which is necessary to decom-
pose the copper sulphate itself. Cupric oxide, though it takes up SO in the
furnace, and is converted into cupric sulphate at and about or a little above the
same temperature at which iron sulphate is formed, is a stronger base than peroxide
of iron, and does not give off its sulphuric acid so readily, or at the same low red
heat, as the peroxide of iron. The iron pyrites in the ore first changes, at very low
red heat, into ferrous oxide and sulphurous acid, both of which are acted on by the
atmospheric air supplied to the furnace, the latter, in contact with the roasting ores,
becoming converted into sulphuric acid, while the former is partly converted, in the
first instance, into magnetic oxide (Fe O, Fc. O₁, or F'c, O₁), and thence, by the
oxidizing influence of the SO, and the air into ferric oxide or peroxide of iron
(Fe, O), with further evolution of sulphurous acid; and partly, by the same influ-
ence into ferrous sulphate which, at a little higher heat, or by longer ignition, passes
into basic ferric sulphates (Fe, O, SO₁ and Fe, O 2 SO,), also with evolution of
sulphurous acid, and these ferric sulphates soon after give off their sulphuric acid
undecomposed, leaving ferric oxide behind. The sulphuric acid so set free, together
with that continually forming and reforming from the sulphurous acid, and the
oxygen of the air, will act on any further undecomposed sulphide of copper or
iron as an oxidizing agent, and also on any copper oxide as a sulphatizing agent;
but it will not, at the higher heat, which has decomposed the ferric sulphates,
sulphatize the ferric oxide. On the other hand the SO, will continue to act
as a reducing agent on the cupric oxide (but not on the ferric oxide, seeing
that anhydrous ferrous oxide is unknown, and magnetic or ferroso-ferric oxide is
not to any great extent reduced from ferric oxide by SO, alone, or without carbon or
carbonic oxide in the furnace, at least if there be plenty of air present), and this
reducing action of the sulphurous acid will go on simultaneously with the oxidizing
action of the sulphuric acid until there is no longer any sulphurous acid being
formed, and consequently no longer any sulphuric acid. This period may be known
by the characteristic smell of sulphurous acid ceasing to be perceptible in the ore or
furnace, or in the draught coming through the furnace. At this point, if the
roasting has been properly conducted the whole or nearly the whole of the iron
will have given off its sulphuric acid, and will remain as ferric oxide, but the cupric
sulphate formned will not be decomposed. The rest of the copper will remain chiefly
as cuprous and cupric oxide. There may be and ought to be little or no copper in
the form of sulphide, because by the oxidizing action of the air, and of a sufficient
quantity of SO, there is nothing to hinder its perfect desulphurization, and the SO.
formed thereby has no tendency in presence of plenty of air to reconvert any part
of it into sulphide, although in the absence of air SO, tends to break up into SO.
and sulphur vapour, the latter of which is apt to reform sulphides. But as the
sulphuric and sulphurous acid are always (although it may be in different pro-
portions, inter se) present together in the furnace till both disappear together, and
as they continue till the last to exert their respective oxidising and reducing actions
on the copper oxides, it is found that they leave behind at the moment of their
B

page_text: final disappearance from the furnace a certain proportion of the copper oxides as
cupric, and a certain proportion as cuprous oxide. Some proportion of cuprons
oxide is thus almost inevitably left after the sulphurous and sulphuric acid gases
have ceased to be evolved or formed in the furnace. Keeping these various
reactions in view, we therefore commence at the lowest degree of temperature
herein before indicated, and gradually bring up the heat to incipient redness till
the evolution of SO, begins to diminish, and then we gradually raise it a little more,
but not higher than just distinctly visible red in order to drive off the sulphuric
acid of the ferric sulphates, the temperature being kept at this point until nearly
the whole of the iron sulphates have been decomposed, and this may be readily
known by lixiviating a small portion of ore withdrawn from the furnace in hot
water, and ascertaining the amount of soluble iron in the solution by any of the
well known tests convenient. We do not continue the roasting till the whole of
the ferric sulpliate is reduced to ferric oxide, partly because we require a certain
quantity of ferric sulphate to keep up our acid liquor, and partly to avoid the risk
of decomposing any of the cupric sulphate. When the proper point has been reached,
which a little experience of the habit of the ore, guided by testing, will soon teach
the operator to recognise, the heat should be lowered at once so as to stop the
liberation of any more SO, and after there is no longer any further smell of SO, in
the furnace the heat should be kept for a considerable period at a dull or incipient
red heat, so as not to decompose any more of the ferric sulphate and with active
stirring of the ore and free access of air in order to raise the cuprous oxide as far as
possible to the higher stage of oxidation by the influence of the air. The raising of
the whole of this Cu, O to the higher degree of oxidation is important, because in
the subsequent lixiviation with acid liquor, as already mentioned, neither the
sulphuric acid nor the persulphate of iron therein contained will convert cuprous
oxide wholly into cupric sulphate. There is formed by the action of SO, on Cu. O
partly cupric sulphate and partly metallic copper. Metallic copper again, and
dilute sulphuric acid, when the metal has not free access of air or oxygen, give rise
to little or no cupric sulphate, and though metallic copper and stronger acid do form
cupric sulphate, this is accompanied with formation at the same time of sulphurous
acid, which acting on other portions of the metallic copper out of contact of the
air forms partly sulphate of copper and partly sulphide of copper (which latter is not
acted on by the acid liquor), and acting on cupric and cuprous oxides gives rise to
cupric and cuprous sulphites, which with hot water and sulphuric acid again
decompose partly into cupric sulphate and partly into further quantities of SO,,
metallic copper, cuprous oxide, and a small quantity of copper sulphide. On the
other hand, though cuprous oxide is not at once wholly converted into cupric
sulphate by persulphate of iron, and cupric and cuprous sulphides are to some extent
formed in the first instance which decompose as already explained, yet the metallic
copper, which is the chief disadvantageous product of the decomposition, is con-
verted into cupric sulphate by the action of the persulphate of iron without the
formation of any other byeproduct than ferrous sulphate, and even the copper
sulphide is, though less completely, converted by it into cupric sulphate. From
these complicated reactions, all of which may be traced back to the presence of the
cuprous oxide left in the roasted ore, there is thus a larger or smaller portion of the
copper which is apt to escape, being converted into the soluble condition by the acid
liquor, and might be lost in the residues of lixiviation. We therefore endeavour, as
the first and best means of obviating this inconvenience as much as possible, to
perfect and complete the oxidation of the copper to its highest degree in the furnace
by exposure to heat and free air or oxygen at the end of the roasting after the
reducing action of the sulphurous acid has ceased, in manner already mentioned.
But in case any cuprous oxide still remains, which might in contact with sulphuric
acid and when out of the free reach of air in the lixiviating vats, give rise to the
series of reactions above mentioned, we take advantage before lixiviating of the fact
that metallic copper, especially in very fine particles is under the united action of
dilute SO, and of air or oxygen freely admitted, or other suitable oxidizing agent,

page_text: and especially with the aid of heat, entirely converted into cupric sulphate without
any formation of SO, or consequent formation of copper sulphites or sulphide. We
therefore, previous to lixiviation, prefer to moisten the roasted ore with plentiful
affusion of the acid liquor, consisting of persulphate of iron and free sulphuric acid,
and expose the same to the action of air or oxygen, either by turning it frequently
over or placing it in a tank with a false bottom finely perforated and forcing air or
oxygen up through the loose moistened mass, and we allow it to dry up as far as it
will. At first it tends to set into hard lumps, but after standing for some time it
loosens and disintegrates, and is then in the most suitable condition for being
lixiviated. In this process the sulphurous acid or hydrogen (formed as already
mentioned) is partly oxidized by the remaining persulphate and partly by the air
or oxygen, so that there is no formation or a smaller formation of the cupric or
cuprous sulphites or copper sulphide, which would otherwise result in manner above
explained if air and oxygen were not supplied. Air may be forced up through
the mass by Körting's air compressing and injecting machines or other similar
contrivances, and if pure oxygen or a highly oxygenized air is preferred, the former
may be obtained by M. Tessier du Motay's method of producing oxygen from the
atmosphere by means of sodic hydrate, manganic acid, and steam, in which the solid
reagents always renew themselves and are perpetually efficient, and the latter still
more conveniently by M. Mallet's mechanical method of obtaining air with a high
per-centage of oxygen through the medium of water. The injection of atmospheric
air or oxygen into the liquors during lixiviation will further the same object as
forcing them through the loosely packed and merely moistened ores, and will besides
hasten the extraction of the copper salts.
It is well known that alumina is a very weak base, forming with sulphuric acid,
and other strong acids, combinations which are themselves powerfully acid, the strong
acid in the combination being not at all saturated and requiring for saturation just
about as much alkali or base as if there were no alumina present at all, and the
alums and sulphate of alumina dissolve metals with evolution of hydrogen as readily
or almost as readily as free sulphuric acid. There are various known methods by
which hydrated aluminous earths, such as decomposed trachytes and shales con-
taining a notable per-centage of available alumina, may be converted (after roasting)
by the action of sulphurous acid, water, and air into sulphate of alumina. In cases
where such alumina is readily procurable we utilize the waste sulphurous acid from
the roasting ores by forming crude sulphate of alumina, and using a strong solution
of it as pickling liquor for the roasted ores, or even, if need be, for lixiviating or
assisting in lixiviating the roasted ores, and the liquor so formed may be used over
and over for lixiviating successive batches of ore or in strengthening the other
solvent liquor before described. The same solution may also be used instead of
sulphate of magnesia for adding to yellow liquor to liberate sulphuretted hydrogen,
as mentioned in the previous Specification of the said Joseph Anthony Dixon.
We have found it advantageous with many ores and cinders to mix them intimately
before roasting with hydrated aluminous earth or clay, and in the case of highly
sulphuretted ores roasted raw (but not of cinders unless they contain excess of
sulphur) to mix with calcic hydrate either in the proportions of lime to sulphur,
specified in the Specification of the said Joseph Anthony Dixon before referred to,
or in the shape of milk of lime, and in the inferior proportion of lime to sulphur
hercin-after specified in regard to ores of copper disseminated through limestone
rocks. The mixture may be either made up with sufficient moisture loosely into
small porous bricks, pipes, balls, or lumps, as small as convenient, so as to permit of
sulphatization and oxidation through and through, or better still, to roast the mix-
ture in loose powder, which avoids the risk of unequal roasting. Lime is especially
useful in breaking up silicate ores, and should be mixed with the ground ore in the
state of fresh calcined limestone, and he hydrated after being mixed, as it exerts in
the act of hydration or slaking an especial action in reducing the crystalline silicates
to the amorphous condition. We find that with highly sulphuretted ores, roasted
in the raw state, the calcic hydrate by absorbing and retaining the sulphur as sul-
B 2

page_text: phate of lime hastens the period of roasting, and we find also that under certain
circumstances at least lime appears to act as an oxidizing agent on sulphides, or it
may induce oxidation by preventing sintering; but lime must not be used in such
quantities that the sulphur present will not be sufficient besides sulphatizing the
iron and copper to convert the whole quantity of lime used into sulphate or sul-
phide, as then it would decompose the cupric sulphate in the process of lixiviation.
Clay or aluminous earth appears to act by forming at a very low temperature
sulphate of alumina from the sulphurous and sulphuric acid formed in the roasting
of the sulphides, and it gives off its sulphuric acid again undecomposed, and with some-
what greater facility than the sulphates of iron, and sulphate of alumina, as already
mentioned, is also decomposed by cupric oxide in lixiviation with formation of cupric
sulphate. Where there is plenty of sulphur in the copper ore, and a deficient proportion
of iron, sulphide clay is a valuable addition to the charge, for the reasons stated.
It is also advantageous, if any cheap sulphates are to be had, which give off their
sulphuric acid at the temperatures prescribed by us, and which would not leave any
alkaline or other oxide which would decompose cupric sulphate in the subsequent
lixiviation to add such sulphates to ores or cinders poor in sulphur. A considerable
quantity of persulphate of iron, and of basic ferric sulphates, and often of sulphate
of alumina, will be formed in the course of carrying on this process, which may be
utilized in this way, and if it be an object to form sulphate of silver, these ferric and
ferrous sulphates should always be added to the charge, as well as any sulphate of
alumina that may have crystallized out in the tanks, and clay or hydrated aluminous
earth is also of advantage. In roasting for silver the temperature towards the latter
part of the roasting should be raised to a moderate red heat, but so as not to decom-
pose the cupric sulphate and the ferric and ferrous sulphate, and sulphate of alumina
should be added to the charge at the commencement of this period, and stirred well
through the ore. We prefer the basic ferric salts and the sulphate of alumina for
that purpose to the ferrous salt, as the former give off their sulphuric acid to the
silver undecomposed. As inagnetic oxide of iron and cuprous oxide reduce the
sulphate of silver, which forms the final raising of the temperature, and addition of
ferric salts or sulphate of alumina in order to complete the sulphatization of the
silver is most beneficially made after these have been as far as possible converted
by the previous roasting into peroxide of iron and cupric oxide. If a silver-
holding copper ore contain little iron pyrites, iron pyrites should be added before
roasting, so as to provide an abundant supply of SO, without decomposition of
the cupric sulphate. It will also be of advantage while a stock of ground
ore or cinder is awaiting burning to affuse it with acid liquor, and let it
stand till it dries up and disintegrates from the lumpy condition in which
it will exist immediately after being moistened, as this is found to expedite the
subsequent process of roasting. It may sometimes also be advantageous both for
sulphatizing copper and silver to carry the fumes of sulphuric acid from richer
ores through poor ores or cinders moistened and mixed with a saturated solution of
from 1 to 2 per cent. of nitrate of soda before the roasting, or to treat the roasted
and moistened ore in this way before lixiviation. In lixiviating the roasted ore it
is important to have it in finely divided condition. The finer the division the more
perfect is the action of the solvent liquor. If the orc or cinder has not been pre-
viously ground or sufficiently ground it must be ground finely and evenly with
burrstones, as before directed. We also for the reasons already mentioned (and
also because heat tends to convert any ferrous sulphate formed into persulphate)
lixiviate with hot water, or hot acid liquor, and we keep up a continuous com-
motion and agitation of the fine particles of ore through the body of the liquor, or
what is the same thing, we force the liquor up through the ore, heating by a coil of
steam pipe or otherwise under the false bottom of the vat. The finely powdered
ore is very ready to settle into a dense cake, the interior of which escapes the
action of the solvent and of the air, if it is attempted to force the liquor down into
or through it. The heating and the agitation may be best effected at once by the
injection of steam into the vats through perforated pipes suitably disposed therein

page_text: or they may be effected by heat externally applied to the vessel, and by stirrers, or
by effecting the lixiviation in a revolving or oscillating vessel having steam
introduced through the axis or trunnion on which the vessel rotates or oscillates.
The injection of air or oxygen into the liquors is also advantageous, and when
steam is used for heating the use of a Körting's air compressor and injector will be
convenient and economical. Or the same action of air in co-operation with the
solvent liquor in lixiviation may be secured by running the liquor from one
lixiviating vessel into a second, and a third or more, leaving the ore still moist with
acid liquor to the free action of the air for some time, at the same time stirring it
and turning it over, and if need be, blowing air or oxygen in through a false bottom,
and then returning the liquor back over the circuit again, thus exposing each
tankful to the alternate action of acid liquor, and atmospheric air or oxygen until
the copper is extracted. It is not necessary that the solvent liquor should be highly
concentrated; on the contrary, dilute sulphuric acid acts more energetically on
copper oxide, and less energetically on iron oxide, while more strongly concentrated acid
dissolves too large a proportion of iron oxide.
On the other hand the more dilute
test
the solution is the persulphate is more readily and abundantly, and at a lower
temperature decomposed into free acid and basic sulphate, so that the proper
proportion of persulphate in the liquor is not kept up. A succession of washings,
preferably with alternate exposure to free air, is advisable, especially with badly
roasted ores, each wash so soon as it shows a good blue with ammonia in
tube, or shows a considerable amount of saturation with soluble copper on testing
with cyanide of potassium or any other readily applicable test, being allowed to
settle, and the clear liquor, after the ore has settled being run off into the pre-
cipitating tank, and replaced by a fresh liquor, and so on until the last liquor shows
on testing it after being a reasonable time in contact with the ores that no more
soluble copper is being extracted. The later washings will require a longer period
than the earlier, because in the first the ready formed cupric sulphate is readily
dissolved, while in the later it is the oxides of copper that are being attacked by
the acid, a process which requires more time to perfect itself.
Whatever traces of undissolved copper the residues of the ore after lixiviation
may contain may be recovered in several ways. If the residual copper is not large
it inay be recovered without further treatment than piling the residues containing
it on proper beds, and allowing the air and moisture to find access into the mass and
collecting from time to time the liquor exuding from the heaps, but if the residual
or unexhausted copper be considerable, as in the case of improperly roasted or
lixiviated ores, it may be the residues after having been first slimed in a washing
machine or in slime pits so as to wash away as much as possible of the oxide of iron
and basic sulphates of iron, and being by this process much reduced in bulk, are
subjected to calcination or re-roasting, or they may be re-roasted without previous
sliming. If there is much magnetic or other sulphide of iron present no additional
sulphur may be necessary to effect the sulphatization of the remaining copper in this
re-roasting; but it will generally be of advantage to add some sulphatizing material.
The residues moist with the persulphate or acid liquor in which they have been
undergoing lixiviation may after drying up and disintegration be transferred to the
furnace without any further auxiliary, or they may be mixed in suitable quantities with
and well distributed thoughout other ores or cinders containing sufficient sulphur for
both, and roasted with them. All the directions as to the first roasting are applicable to
a re-roasting. Sometimes when ore or cinders have not been ground, or not sufficiently
ground before roasting, the grinding for lixiviation and the lixiviation itself may go
on together, the roasted ore being put with water or acid liquor into an apparatus
similar to a Mexican arrastra, or the apparatus in which flints are ground for the
manufacture of pottery, and ground therein. A regulated flow of water or liquor
into and over the edge of the vessel holding the ore in process of lixiviation may be
so arranged as during the grinding to float away or slime off the oxide of iron.
The liquor after flowing over the edge of the vessel is for this last purpose con-
veyed through a succession of vats or slime pits, in which the finely divided oxide,

page_text: of iron will settle, the finest particles furthest from the grinding apparatus, and the
supernatant liquor, which will hold the soluble copper, is carried back again
until strong enough for precipitation, and the precipitate liquor used for lixiviating
and sliming a fresh quantity. The insoluble copper being of greater specific gravity
than the peroxide of iron will remain in a concentrated condition in the grinding
vessel, or not go farther than the nearest slime pits, and this if not found to be
concentrated, or if it be not not desired by vanning and dressing to concentrate it to
a sufficient degree of strength for smelting, may be re-roasted with or without
other ores or sulphur holding materials, as above described.
If silver exists in the ore the sulphate of silver formed in the roasting is separated
from the solution while it is still hot by metallic copper as cement silver before
precipitating the copper. Cuprous oxide being apt to precipitate silver in metallic
condition from its sulphate solutions great care should be taken in the roasting and
by pickling, as aleady mentioned, to raise the cuprous oxide into cupric oxide
when silver is to be recovered, and for this purpose it is also advisable to add to
the ore in the pickling of it a solution of nitrate of iron, which may be well enough
prepared for this purpose by adding nitrate of soda to sulphate of iron.
In lixiviating the roasted ore the successive washings after the fine powder has
settled and only clear liquor runs off is decanted, or if need be run through filtering
vessels into the precipitating tank, and the copper is precipitated as sulphide by
sulphuretted hydrogen obtained and applied in manner described in the Specifi-
cation of the said Joseph Anthony Dixon, herein-before referred to, or by any of
the other methods therein mentioned. It is evident, that precipitation by iron
might be substituted, but the strong persulphate of iron and free sulphuric acid
would occasion a great consumpt of iron, or else the liquor, if partially neutralized
in the ordinary way, would be less available for dissolving the copper in the
lixiviation of subsequent batches of roasted ore; the advantage of being able to
strengthen the liquor by the conversion of surplus sulphuretted hydrogen into free
acid would be lost, nor will precipitation by iron be either so cheap or give so pure a
product, the precipitate being usually mixed with iron and basic ferric sulphates.
The liquor if left awaiting precipitation for any considerable length of time in
contact with the air is apt to deposit difficultly soluble crystals of persulphate of
iron, and also basic, ferric salts, which would contaminate the copper subsequently
precipitated in the same vessel, and therefore in such a case the liquor, if it is to be
kept for any time, should be kept in separate tanks, and then run into the precipi-
tating tank immediately before precipitation. There may also in such a case take
place the precipitation of basic sulphates of copper, which are sometimes produced
in lixiviation, either by the presence of oxide of zinc in the ore, which reacts on
the cupric sulphate, or by the mutual action of cupric oxide and concentrated cupric
sulphate on each other. These basic sulphates are less liable to be precipitated
froin a hot solution, and are redissolved in the acid liquor on heating, but they
may, in the case of keeping the liquor long in separate tanks before precipitation,
be left behind and lost. Where there is zinc in an ore this source of loss should be
watched and provided against.
In addition to the methods described in the Specification above referred to, of
procuring bisulphite of magnesium, it may also be obtained by passing sulphuretted
hydrogen into a vessel containing an alkaline or carthy hydrate, preferably hydrate
of magnesia diffused or suspended in water, when bisulphide of magnesium or a
polysulphide of the other hydrated base employed will be formed. In this way a
great deal of superfluous and waste sulphuretted hydrogen, which might otherwise
be lost, may be conveniently stored up for future use, and, in the case of bisulphide
of magnesium, in a form which we find to be more suitable than any other. The
bisulphide of magnesium or other polysulphide ought to be preserved in covered
vessels. By boiling the bisulphide of magnesium it gives off all its sulphuretted
hydrogen in a copious and regular stream, depositing hydrate of magnesia alone,
which can be used over again to form fresh bisulphide of magnesium as before, and
so on continuously; or being treated with the acid liquor the hydrate will give

page_text: sulphate of magnesia for mixing with the yellow liquor in order to give bisulphide
of magesium in that way. Instead of using a polysulphide of calcium per se along
with kieserite or sulphate of magnesia to form bisulphide of magnesium, as described
in the Specification of Joseph Anthony Dixon referred to, tank waste, gas waste,
or soda waste "(blue billy) " or any other form of sulphide of calcium, or substance
containing it in a considerable proportion, may be put (preferably pulverized) into a
tank along with kicserite or sulphate of magnesia, and left to stand covered with a
layer of water, stirring occasionally to admit air, and it is advantageous that
a moderate warmth be applied. In a few days the supernatant liquor will acquire a
greenish yellow colour, and be fit for use in the boiler as a source of sulphuretted
hydrogen. A method of procuring sulphuretted hydrogen in some respects less
suitable than the above, but which may sometimes be more convenient, is to put
the sulphide of calcium or an alkaline or earthy sulphide or polysulphide into the
boiler or any other vessel with water, adding vegetable or organic matter rich in
hydrogen, as leaves. sawdust, chips and shavings of wood, particularly beechwood
shavings, pine needles, rich vegetable humus and the like, and to let the mixture
stand for a few days, the vessel being kept closed. On applying heat to the boiler
containing the mixture a considerable quantity of sulphuretted hydrogen will be
obtained. It will help the evolution of the sulphuretted hydrogen if a little liquid
acid is added to the liquor, or a stream of carbonic or other acid gas passed into a
boiler which contains any alkaline or earthy sulphide or polysulphide will also
facilitate the disengagement of sulphuretted hydrogen. Care should be taken not
only when using this, but also when using any of the other methods of generating
sulphuretted hydrogen described or referred to, to prevent by means of a dome on
the pipe leading from the boiler into the precipitating vat, or by some equivalent
mechanical arrangement for trapping them, any of the lime, alkali, or vegetable
matter, or of the liquor itself being carried over with the sulphuretted hydrogen
into the precipitating tank. Sulphide of lime for generating yellow liquor may
also be obtained by calcining in a reducing furnace, along with one-third of its
weight of charcoal, sulphate of lime, or the mixture of sulphate and sulphite left
after decomposing yellow liquor with sulphate of magnesia, or after driving off
sulphuretted hydrogen from yellow liquor.
In countries where wood fuel is abundant the furnaces both for making sulphide
of calcium and for roasting the ores may advantageously be constructed to burn
wood gas, and in that case pyroligneous acid may be collected by well known
means and utilized for liberating sulphuretted bydrogen from the polysulphide of
calcium. The crude pyroligneous acid or black liquor as it is called when mixed
with yellow liquor will disengage sulphuretted hydrogen, and will at same time
forin crude acetate of lime, which can then, after gentle roasting to expel empy-
reumatic oils and other impurities, be converted by distillation with sulphuric acid
into acetic acid and sulphate of lime in the ordinary way, and the sulphate of lime
will serve over again for forming sulphide of calcium by roasting it in a reducing
furnace with about 1/3 of its weight of charcoal or more, or with carbonic oxide gas.
In conducting the precipitation by sulphuretted hydrogen it will always be easy
to increase the free sulphuric acid in the liquor if required, by allowing an excess
of sulphuretted hydrogen to flow into the liquor over and above what is required to
precipitate all the copper, and what is necessarily expended in reducing persulphate
to ferrous sulphate and sulphur as already explained. The persulphate may be
renewed in the liquor by the action of the free acid on the peroxide of iron, and on
basic ferric sulphates, of both of which there will always be sufficient quantities left
in the residues of lixiviation. The ferrous sulphate will also be converted into
persulphate in well known ways, as by the liquor being run into broad flat ponds
and exposed to the air, or air may be injected into it. Heating and division into
fine spray or rain (either by passing the liquor through thorns or by breaking it up
into spray by cylinders armed with bristles revolving therein while a free current of
air passes through the spray, or by allowing steain at a pressure of about two

page_text: atmospheres to escape into the centre of a flow of the liquor, or by any other suitable
and known contrivance) will both promote the peroxidation.
The precipitated copper sulphide mixed with free sulphur is separated from the
liquor by being allowed to settle, and the supernatant liquor so long as it runs
quite clear may be syphoned or run off. The moist precipitate remaining is then
run off through filters, being barrels or other similar vessels, perforated at the sides
and lined with cloth, through which it will drain itself free of the greater part of
the remaining liquor (which is also to be kept for use as herein-before mentioned),
and afterwards it may be dried and solidified further by a press, such as Needham
and Kites' clay press for drying potters material, or such a press as is used for
drying alizarine paste, or in a centrifugal hydro-extractor, or by any other econo-
mical mode of applying pressure or power to this purpose, and it may be transferred,
either without or after such pressure, into a shallow pan or drying vat with a steam
jacket or chamber, above or below, and around the vat, and be dried therein by
steam heat. It contains a good deal of free sulphur, and being in fine division is
extremely combustible at a low temperature, and should not be dried by flame heat
applied to the vessel containing it, unless it is wished to ignite it. The free sulphur
may be sublimed or extracted by sulphide of carbon, which may be recovered and
used over again by well known methods. If left in moist state in contact with
air it is slowly converted into cupric sulphate. If roasted with exclusion of all air,
except what is absolutely necessary for combustion of the sulphur, it will pass into
subsulphide, and (with or without pulverized carbon, and with somewhat more
air and a moderate heat), into a rich regulus consisting principally of metallic
copper and oxides of copper. In this roasting, any arsenical compounds which may
have got into the liquor and passed into the precipitate as an arsenical sulphide,
will be driven off, and the application of steain will be of great service in aiding
the volatization. From the fine state of division in which the precipitated copper
exists after the sulphur has been driven off, and from its great purity, it may be
very readily converted into cupric sulphate, according to any of the known methods.
If the precipitate, especially in its moist and uncompressed state and mixed with
neid liquor, be mixed with sawdust or other organic matter, and burned on the
hearth of a close furnace with exclusion of air, a large quantity of sulphuretted
hydrogen may be procured, and this will be promoted by passing steam through it,
and this sulphuretted hydrogen may either be put to immediate use in precipitating
a fresh quantity of copper liquor, or inay be stored up in the form of bisulphide of
magnesium for future use, as already described, and the residue of the precipitate
will form a rich regulus.
There are certain forms of occurrence in which copper (sometimes in the form of
subsulphide, grey copper, purple, or peacock ore, and other rich forms, and some-
times also in the forin of pyrites, more or less mixed with particles or patches of
richer ore) is found sparsely disseminated in particles or patches throughout large
masses of limestone, rock, or other rock formations, such as clay and shales, as, for
example, the copper, limestone, and shale at Acton Vale, in Canada. Ores of this
class we treat in the following manner, and this constitutes the second part of our
Invention and of this Specification-We burn the limestone impregnated with ore
so as to drive off the carbonic acid from the lime, and to disintegrate the rock and
render it more friable, as well as to increase the difference of specific gravity
between the limestone and the copper ore. Before burning, the copper ore is, as a
rule, very friable, and apt in the process of grinding or crushing the rock which
carries it to be reduced to very fine powder, which is not capable of being recovered
by water-jigging or other form of water separation from its gangue. The roasting
renders the copper ore tougher or denser, and not so liable to fall into fine powder
or dust. If there is much clay in the linestone the burning should be at a moderate
heat, and the limestone is preferably slaked or hydrated afterwards. If wood is
used as the fuel for burning the limestone it is not advisable to mix the wood with
the lime as there is then a tendency to flux the lime and render portions of it

page_text: vitreous. In any case it is more advantageous to burn the lime by the hot gases
of combustion, as in the mode of burning flare kiln lime. With certain pure lime-
stones, hydration, after burning and before grinding and blowing as after mentioned,
will be found to increase the separability of the copper from the other particles;
but no more water must be used than is absolutely required to causticize the
lime, the subsequent operation of blowing herein-after described requiring its
material to be blown to be as free as possible from hydroscopic moisture. The
particles of limestone not carrying copper disintegrate after burning even by
air slacking or absorption of moisture from the air much more readily than
the portions carrying copper, and after slacking a considerable part of the copper
holding lime may be separated froin the rest by riddling or similar mechanical
separation. With sandstone or silicious rocks of a clayey origin or metamorphic
character, the addition of fresh burned lime, as after-mentioned, will be found
of advantage in breaking up the rock, which should be pulverized before burning,
and calcined at a low heat. In mixing lime with the ores we prefer to add
the lime dry or unslaked to the ores and to hydrate it in contact with the ores, as
the lime is especially effective in decomposing the silicates during the act of
hydration or slaking, and it should then be allowed to dry up in the air for some
time before roasting. In treating copper holding shales or rocks consisting of
silicates of alumina or clay the clay should be desiccated or gently roasted at a
temperature sufficiently low to facilitate the disintegration, and at the same time to
avoid that permanent induration and recontraction of volume which takes place in
clay at a red heat. The roasted limestone or rock and the ore (being kept quite
dry for the subsequent operations) are then, if not already, ground to the degree of
fineness suitable for a mode of treatment, by which the limestone or other rocky
particles are blown away and separated from the denser particles of the copper ore,
and the latter are concentrated into a greater state of richness. This process of
separating the particles of copper froin the other material by blowing may be
performed for many purposes sufficiently well by using with such small adjustments
as are obvious an ordinary pair of fanners, or the machine used for separating
wheat from chaff, or by allowing the powdered material to fall in a thin stratum or
cascade at a regulated speed through a sufliciently strong draught or current produced
by a chimney or other known means in a suitable flue or passage. But the most
perfect instruments for dry concentration by air with which we are acquainted is that
known as Krom's Patent air concentrator, made by Mr. Krom, of New York, which
may be also operated by a jet of dry steam. When the copper is in the form of
subsulphide, purple, or peacock, or other rich ore, the ore after concentration may be
smelted into metallic copper, or otherwise disposed of according to known means.
When the ore disseminated through limestone is altogether or principally copper
pyrites, if the quantity of unseparated lime left after the blowing does not vary ma-
terially from the proportions of copper, sulphur, and lime, mentioned in the second part
of the Specification of Joseph Anthony Dixon herein-before recited, in which he describes
a lime process, the residue left after the air concentration may be treated by affusing
the lime with water so as to hydrate it, and it may be then roasted and treated as
the mixture of copper ore and calcic hydrate is directed to be treated in the said
Specification, or as ores mixed with lime are directed to be treated in the preceding
parts of the present Specification. If the lime be in excess of the proportion of
lime to sulphur, mentioned in the said Specification, the ground limestone and ore
may be mixed with ground iron pyrites or other ground sulphur holding copper
ores which do not contain lime, so as to supplement the sulphur to the extent
required to convert the hydrated lime on burning into sulphate of lime and the
copper into sulphate of copper, in the manner mentioned in the said Specification or
in this Specification. If only a small quantity of lime remains in the blown ore, and
that of less amount than what the sulphur present would be able to convert into
sulphate of lime besides converting the copper into sulphate of copper, this small
quantity will do no harm. The blown ore in that case should be affused with
water and stirred about so as to render the lime somewhat fluid, like milk of lime,

page_text: and so more thoroughly to distribute it among the particles of the copper ore, and
the ore so mixed with milk of lime will be roasted in manner before described and
lixiviated. We find generally that the presence of a small quantity of lime in the
shape of milk of lime or hydrated lime along with any pyrites, orc, or residues of
lixiviation to be roasted even though the lime be much less in proportion to the
sulphur present than the proportion described in the Specification herein-before
referred to, is of great advantage in promoting the oxidation of the cupric sulphides,
and particularly of the undissolved portions of ore which have escaped sulphatization
in the first roasting. But in all cases the sulphur should be in some excess as
compared with the lime, or should be supplemented so as to be in excess to ensure
the conversion of the whole hydrate of lime into sulphate of lime, and leave no lime
free, which would have a tendency to precipitate the copper from the liquor in the
process of lixiviation. If the rock through which copper pyrites is disseminated as
before described is not limestone, and no limestone has been used with it in burning,
or no lime remains in it after blowing, then after the burning and concentrating as
aforesaid it may be treated in the modes above described with reference to ordinary
copper pyrites.
Having now described and particularly ascertained the nature of our said
Invention, and the system, mode, or manner in or under which the same is or
may be used, or carried into practical effect, we would observe in conclusion that
what we consider to be novel and original, and therefore claim as the Invention
secured to us by the herein-before in part recited Letters Patent is
First. The process herein-before in the first part of this Specification described,
or a process substantially the same, which process consists essentially of a com-
bination of the methods or alternative methods herein-before described, of (1),
roasting copper pyrites, ores, or cinders, either with or without the addition of
alumina, or the other auxiliary substances herein-before mentioned, preferably in
fine division at low heat, with an oxidising fire, and with the other conditions and
precautions herein-before described, so as to convert the copper, as far as possible,
into cupric sulphate, and to raise the rest of the copper which is not sulphatized
in the furnace as far as possible to the highest grade of oxidation; (2) lixiviating
so as to dissolve the cupric sulphate so formed, and at the same time to convert
the rest of the copper into sulphate by means of an acid solvent liquor, formed,
kept up, and renewed from the ores and materials themselves in the course of the
process, as in the case of the liquor, consisting mainly of sulphate of iron and free
sulphuric acid, herein-before described, and applied as herein-before described, or
by means of an acid solvent liquor consisting of sulphate of alumina formed from
the waste fumes of the roasting ore, and applied as herein-before described, or by
means of a combination of said liquors, such lixiviation being conducted either
with or without, but preferably with, the pickling of the roasted ore or cinder
in manner set forth with either or both of said liquors previous to lixiviation;
(3) precipitating with sulphuretted hydrogen prepared and applied in manner
herein-before described or referred to as described in the previous Specification
herein-before mentioned; and (4) in the case of silver holding copper ores applying
the same methods of roasting, pickling, and lixiviation with the various modi-
fications herein-before described to the recovery of the silver simultaneously with
applying them to the recovery of the copper. But we do not claim separately or
otherwise than in combination as steps of our process, nor otherwise than with
the particular modifications set forth, the forming of cupric sulphate by roasting
at a low temperature, either in powder or lump, nor the forming it by the action
on oxide of copper of sulphuric acid or sulphates of iron or alumina, hot or cold,
not formed as we form the same, nor the preparation or application of sulphuretted
hydrogen so far as the same are described in the said previous Specification.
nor except in so far as the same are conducted in the way herein-before described
or referred to, nor do we claim the method of recovering the silver, except as
incidental to and in connection with the copper process. We do, however, claim
separately the method of forming, keeping up, and renewing the said acid solvent

page_text: liquor, consisting mainly of sulphate of iron and free sulphuric acid, in manner
herein-before described, and the application of the same, as also the application of
the said sulphate of alumina liquor formed as herein-before described, and of any
combination of said liquors to the pickling and lixiviation of copper ores and cinders
wherever sulphate and oxides of copper are formed in the treatment of such ores or
cinders, although the treatment may be so conducted as also to produce some
sulphide of copper along with them.
And we claim also the method of roasting copper pyrites, ore, or cinder with clay
or aluminous earth in manner herein-before described for the purpose of assisting in
the formation of cupric sulphate in the furnace, and in the formation of a solvent
liquor for sulphatizing copper oxides; and we claim the use of lime as herein-before
described for expediting the desulphurization of raw ores and cinders containing
much sulphur.
Second. The process in the second part of this Specification described for treating
copper ores disseminated throughout limestone and other rocks.
In witness whereof, I, the said Joseph Anthony Dixon, on behalf of myself
and the said Thomas Henry Cobley, have hereunto set my hand and seal,
this Twenty-fifth day of September, One thousand eight hundred and
seventy-six.
JOSEPH ANTHONY DIXON. (L.S.)