AN IMPROVED PROCESS FOR TREATING COPPER PYRITES, COPPER BLENDES, AND OTHER SULPHURETTED COPPER ORES WHICH CONTAIN IRON
Year: 1873

page_text: LETTERS PATENT to Joseph Anthony Dixon, of Glasgow, in the
County of Lanark, North Britain, Writer, for the Invention of
"AN IMPROVED PROCESS FOR TREATING COPPER PYRITES, COPPER BLENDES,
AND OTHER SULPHURETTED COPPER ORES WHICH CONTAIN IRON."-A com-
munication from abroad by Thomas Henry Cobley. of Turin, in
the Kingdom of Italy, Chemist.
Sealed the 12th December 1873, and dated the 11th September 1873.
PROVISIONAL SPECIFICATION' left by the said Joseph Anthony Dixon
at the Office of the Commissioners of Patents, with his Petition,
on the 11th September 1873.
6
I, JOSEPH ANTHONY DIXON, of Glasgow, in the County of Lanark,
North Britain, Writer, do hereby declare the nature of the said In-
vention of AN IMPROVED PROCESS FOR TREATING COPPER PYRITES, COPPER
BLENDES, AND OTHER SULPHURETTED COPPER ORES WHICH CONTAIN IRON," the
same being a communication to me from abroad by Thomas Henry
Cobley, of Turin, in the Kingdom of Italy, Chemist, to be as follows,
that is to say :-.

page_text: associated With the copper.
These ores may be divided into two classes, the first class being those
sulphuratted ores which contain sufficient sulphur to support com.
bustion, and supply the means of roasting the ore without other fuel;
and the second class being those sulphuretted ores which contain an
amount of sulphur insufficient for maintaining self combustion.
Before applying the process constituting this Invention to the treatment
of the first class of these ores, the ores are first roasted. The ore after
having been roasted is then crushed by any convenient means to the
ordinary fineness of ores intended for dressing, and it is classified according
to size in a sizeing or classifying machine. The crushed and sized ore is
then lixiviated with water and slimed in the ordinary manner. ° In the
roasted ores or cinders the copper exists in three forms, sulphide,
sulphate, and oxide.
In the process of lixiviation the sulphate being soluble in water is
dissolved in the lixivium, and so also is the persulphate of iron which
is formed during the roasting from the iron present in the crude ore.
The sulphide of copper existing in the roasted and crushed ore. being
insoluble, is found on lixiviation in the slime, consisting of granules of a
dense and apparently crystalline character. These granules are washed
out, collected, and dried in the ordinary way, and as they are highly
concentrated require no further operation to make them ready for the
market as copper regulus.
The oxides of copper which are also formed in the roasting, though
insoluble in water alone arc rendered soluble and gradually become
dissolved by the persulphate of iron contained in solution (as herein-
before stated) in the water of lixiviation, according as that water
gradually acquires, by its repeated application to successive batches
of calcined ore lexiviated in it, the quantity of persulphate of iron
required to disolve the oxides. The oxides so dissolved are precipitated
from the solution in the manner herein-after mentioned together with
the copper originally existing as sulphate in the calcined ore.
The oxide of iron formed during calcination remains in a state of
fine division in the waste slimes after washing, and may be used for
making protosulphide of iron as herein-after set forth.

page_text: The liquor used for lixiviation containing the soluble salts of copper
and iron is used over and over again in lixiviating successive batches of
crushed ore until it is sufficiently strong for the precipitating process:
con-..
After precipitation of the copper the acid liquor left, which still
tains the persulphate of iron in solution may be used over and over
again in the lexiviation of fresh batches of roasted ore, the solubility of
the copper oxides in the calcined ore being dependent on the quantity
of persulphate of iron present in the lixivium.
The residual slime or deposit remaining after lixiviation and sliming is
thoroughly washed SO that the last crop of soluble copper may be
obtained therefrom, and the concentrated. insoluble copper remaining
therein may also be recovered in the shape of powder by sieving the
liquors. The resulting liquor containing the last crop of soluble copper
is added to the precipitating vat and subjected to the precipitating
process.
When the lixivium is sufficiently strong for applying the precipitation
process it is discharged into a precipitating vat, and the copper con-
tained in solution in it is precipitated therefrom by the addition.
thereto of sulphuretted hydrogen which may be obtained cheaply from
the ores themselves in the following manner:-Waste fine particles of
unroasted pyrites ore, those for example, resulting from the breaking of
the ore,
are intimately mixed with the fine slimes of oxide of iron
resulting from the washing and sliming operations herein-before men-
tioned. The proportion of about 100 parts of pyrites to 30 parts of
slimes is a convenient proportion for the mixture, but the proportion
varies according to the amount of sulphur in the pyrites and the per
centage of iron in the slimes.
The mixture is calcined in closed pots until the condition of the
pyrites is changed by the iron added thereto as oxide, having withdrawn
from the pyrites its "extra equivalent" of sulphur, and the whole or
great erportion of the oxide and persulphide of iron (Fe S 2) in the
whole mass has been converted into protosulphide of iron (Fe S).
This protosulphide of iron is used for the production of the sulphuretted
hydrogen required for precipitation.
Another method of preparing the protosulphide of iron for this purpose
is by driving off by sublimation the extra equivalent of sulphur from
the pyrites, and the sublimed sulphur may be recovered by conden-

page_text: sation. The protosulphide of iron, together with a quantity of water,
or of water strengthened with the acid liquor remaining in the pre-
cipitating vat after the copper has been thrown down is then put into a
vessel, which is connected on the one hand with the precipitating vat
by pipes or tubes arranged so as to convey the sulphuretted hydrogen,
when generated in the form of gas from the protosulphide of iron and
water into the precipitating vat. and is also connected on the other
hand by pipes or tubes with a retort or set of retorts in which as herein-
after mentioned sulphuric acid is generated in the state of vapour, and
which last mentioned pipes or tubes are intended to convey the sul-
phuric acid in vapour as it is generated into the vessel containing the
protosulphide of iron and water with the object of disengaging from the
latter sulphuretted hydrogen gas.
The sulphuric acid is generated from the persulphate of iron (obtained
from the liquors themselves) by enclosing the persulphate in fire-clay
tubes, cylinders, or retorts, connected by pipes as herein-before
mentioned, with the vessel containing the protosulphide of iron and
water, and by subjecting the persulphate in these retorts to a iem-
perature high enough to drive off the sulphuric acid in fumes or vapour
through the pipes into the vessel containing the protosulphide of iron
and water.
When the sulphuric acid is driven off from the persulphate of iron,
oxide of iron remains as a residue, and it may be economised by mixing
it with pyrites to make protosulphide of iron, as herein-before
mentioned.
As the sulphuric acid vapour passes through the pipes into the vessel
containing the protosulphide of iron and water, sulphuretted hydrogen
is disengaged therein in the form of gas, and is allowed to escape through
the other set of pipes or tubes into the precipitating vat until pre-
cipitation is complete. The disengagement of the sulphuretted hydrogen
leaves persulphate of iron in solution in the liquor, and this persulphate
may be crystallized and used again for making sulphuric acid, or it may
be used for strengthening the lixivium for dissolving the oxides in the
roasted ore.
The sulphuretted hydrogen gas on being conveyed into
the pre-
cipitating vat holding in solution the soluble portions of the calcined
ore throws down the whole of the copper held in solution therein in the

page_text: "
form of a powdered regulus of copper. When the precipitation is com-
pleted the precipitate is allowed to settle, and is afterwards deprived of
its moisture by pressure, and it may then either be smelted or converted
into salts of copper.
The liquor remaining in the vat after precipitation contains sulphate.
of iron, sulphuretted hydrogen, and sulphuric acid, and the sulphuretted.
hydrogen is by exposure to the atmosphere gradually converted into
sulphuric acid. In order to utilize the free sulphuric acid therein the
liquor may he advantageously employed to act on the protosulphate of.
iron and water for the disengagement of sulphuretted hydrogen, as
herein-before explained, or to strengthen the lixivium for fresh batches
of ore. If the ore contains any proportion of silver or gold these metals
are during calcination associated with the sulphide of copper, and are
found in the sulphide washed out in granules in the process of sliming.
The second part of this Invention which is called the lime or
"calcium process" is applicable to the second class of ores herein-before
described as consisting of sulphurets of copper too poor in sulphur to be
capable of supporting self combustion; it is as follows:-
The per centage of sulphide of copper present in the ores to be treated,
and the per centage of sulphur existing in the ore in other forms than
that of sulphide of copper having been ascertained there is added to the
quantity of copper ore to be treated, sufficient calcium, hydrate, or
ordinary caustic lime to represent the equivalent of the base of the
sulphur compounds, minus the copper sulphide existing in the quantity
of ore to be operated on. The proportional quantities of copper ore and
caustic lime so ascertained are then ground or pulverised and intimately
mixed together with water to the consistency of a paste in a pug mill or
its equivalent. The paste is then formed into pipes, bricks.
or balls.
which are dried or burned, or the mixture may without being formed
into shapes be burned upon the hearth of a furnace.
The calcination requires an oxidising fire, and a temperature not
higher than that of a dull red heat.
In the calcination the lime takes the excess of sulphur and forms an
insoluble sulphate of lime. The copper sulphate into which the sulphide
of copper is chiefly converted is soluble in water, and any oxide of
copper which may be formed may be dissolved by the action of per-
sulphate of iron in the manner herein-before described.

page_text: In case of insoluble oxides being produced by: over calcination or
accidental addition of too much lime, it is advantageous to wash those
out either with the acid liquor containing the persulphate already
mentioned, or with perchloride of iron which may be produced by adding
the requisite quantity of hydrochloric acid to the oxide, or more con-
veniently to the sub or the basic sulphate of iron, both of which may be
obtained from the pyrites by the well known methods.
After the calcination is complete the ore is crushed, sized, lixiviated,
and slimed with water (in this case preferably with hot water), and
washed out with the acid liquors containing persulphate of iron, as
herein-before mentioned in relation to the first head of this Invention.
The acid lixivium and washings both hold the soluble sulphate of
copper and dissolves any oxide of copper that may have been formed.
The precipitation of these from their solution is carried out in the same
manner as that herein-before described in relation to the first part of
this Invention.
If the ore is sufficiently rich in copper, the bricks or pieces may after
the calcination be put into a blast furnace and smelted with the addition
of the necessary flux into metallic copper.
SPECIFICATION in pursuance of the conditions of the Letters Patent
filed by the said Joseph Anthony Dixon in the Great Seal Patent
Office on the 11th March 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOSEPH
ANTHONY DIXON, of Glasgow in the County of Lanark, North Britain,
Writer, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Eleventh day of September, in the
year of our Lord One thousand eight hundred and seventy-three, in
the thirty-seventh year of Her reign, did, for Herself, Her heirs and suc-
cessors, give. and grant unto me, the said Joseph Anthony Dixon, Her
special license that I, the said Joseph Anthony Dixon, my executors,
administrators, and assigns, or such others as I, the said Joseph Anthony
Dixon, my executors, administrators, or assigns,
should at any time

page_text: agree with, and no others, from time to time and at all times thereafter
during the term therein expressed, should and lawfully might make,
use, exercise, and vend. within the United Kingdom of Great Britain
and Ireland, the Channel Islands, and Isle of Man, an Invention for
"AN IMPROVED PROCESS FOR TREATING COPPER PYRITES. COPPER BLENDES, AND
OTHER SULPHURETTED COPPER ORES WHICH CONTAIN IRON," a communication to
me from abroad by Thomas Henry Cobley, of Turin, in the Kingdom
of Italy, Chemist, upon the condition (amongst others) that I, the said
Joseph Anthony Dixon, my executors or administrators, by an instru-
ment in writing under my hand and seal, should particularly describe and
ascertain the nature of the said Invention, and in what
manner the
same was to be performed, and cause the same to be filed in the Great
Seal Patent Office within six calendar. months next and immediately
after the date of the said Letters Patent.
the
NOW KNOW YE, that I, the said Joseph Anthony Dixon, do hereby
declare the nature of the said Invention, and in what manner
same is to be performed, to be particularly described and ascertained in
and by the following statement, that is to say:―
The said Invention relates to the treatment of the sulphuretted ores of
copper commonly called cupreous pyrites, and sometimes also called
copper blende being sulphurets of copper containing a sulphuret or
sulphurets of iron, or iron pyrites associated with the copper.
These ores may be divided into two classes, the first class being those
sulphuretted ores which contain sufficient sulphur to support combustion,
and supply the means of roasting the ore without other fuel, the second
class being those sulphuretted ores which contain an amount of sulphur
insufficient for maintaining self combustion.
Before applying the processes constituting this Invention to the
treatment of the first class of these ores, the ores are first roasted en
masse, care being taken that the pieces are not too large, the most
convenient sizes being not over one or two cubic inches capacity, or
even less, according to the nature of the ores so as to permit of thorough
roasting to the centre.
The sufficiency of the roasting may be easily known by the formation
at the interior of the pieces of a kernel of cupreous sulphide, and a little
observation of the behaviour of the particular ore fn regard to the

page_text: KUTHICT WILL gurde ΤΟ une DEST SIZE TOP The
pieces or
the ore.
frustate the after
The roasting may be effected in mounds, circular, or pyramidal. or on
hearths consisting of three walls with a slightly inclined floor similar to
the Styrian hearths or German rost-stadel, or in any other suitable furnace.
The particular form of the furnace will depend to some extent on
whether the sulphurous acid driven off in the roasting is to be utilized or
not, and if so how care should be taken that the roasting is protected
against wind, otherwise fusion may set in and
operations which are herein-after specified. [ do not claim any
particular method of roasting as part of the process, but it is of
importance that the roasting of the ore should precede the grinding and
washing, as I find that there is a very considerable loss of sulphide of
copper if the ore is ground and washed before roasting, the particles of
sulphide being. by previous calcination rendered more dense and less
liable to be floated away and lost in the washing. The ore having been
roasted is then crushed by any convenient means to the ordinary fineness
of ores intended for dressing, and it is classified according to size in a
sizeing or classifying machine. The crushed and sized ore is then
lixiviated with water and slimed in the ordinary manner. In the roasted
ores or cinders the copper exists in three forms, videlicet, principally and
normally in the forms of sulphate and sulphide, and frequently also as
an accident of roasting in that of oxide of copper.
In the process of lixiviation the sulphate being soluble in water is
dissolved in the lixivium, and SO also is the sulphate of iron which is
formed during the roasting from the iron present in the crude ore.
The sulphide of copper existing in the roasted and crushed ore being
insoluble is found on lixiviation in the slime, consisting of granules of a
dense and apparently crystalline character. These granules are washed
out, collected, and dried in the ordinary way, and as they are highly
concentrated require no further operation to make them ready for the
market as copper regulus.
The oxide of copper which is also formed in the roasting though
insoluble in water alone is rendered soluble, and gradually becomes
dissolved by the sulphate of iron contained in solution (as herein-before
stated) in the water of lixiviation. according as that water gradually
acquires by its repeated application to successive batches of calcined ore

page_text: lixiviated in it the quantity of sulphate of iron required to dissolve the
oxide. The oxide so dissolved is precipitated from the solution in the
manner herein-after mentioned. together with the copper originally
existing as sulphate in the calcined ore.
The oxide of iron formed during calcination remains in a state of fine
division in the waste slimes after washing, and may be used for making
sulphide of iron as herein-after set forth."
The liquor used for lixiviation containing the soluble salts of copper,
and iron is used over and over again in lixiviating successive batches of
crushed ore, until it is sufficiently strong for the precipitating process.
After precipitation of the copper, the acid liquor left which still contains
the sulphate of iron in solution may be used over and over again in the
lixiviation of fresh batches of roasted ore, the solubility of the copper
oxide in the calcined ore being dependent on the quantity of sulphate of
iron present in the lixivium.
The residual slime or deposit remaining after lixiviation and sliming
is thoroughly washed, so that the last crop of soluble copper may be
obtained therefrom, and the concentrated insoluble copper remaining
therein may also be recovered in the shape of powder by ore dressing
machinery. For this purpose find it advantageous to use a machine
known as Huet and Geyler's "crible continue " or endless sieve, by
which the slimes are treated over and over again, and the last crop of
insoluble ore is recovered in powders of various sized grains varying in
per centage, according to the quality of the ore operated on, say
from 35% to 45%. The resulting liquor containing the
last crop of
soluble copper is added to the precipitating vat, and subject to the
precipitating process.
When the lixivium is sufficiently strong for applying the precipitation
process it is discharged into the precipitating vat, and the copper con-
tained in solution in it is precipitated therefrom by the addition thereto
of sulphuretted hydrogen, which may be obtained cheaply from the ores
themselves in the following manner:-Waste fine particles of unroasted
pyrites ore (those for example resulting from the breaking of the ore)
are intimately mixed with the fine slimes of oxide of iron resulting from
the washing and sliming operations herein-before mentioned.
The pro-
portion of about one hundred parts of pyrites to thirty parts of slimes is
convenient proportion for the mixture, but the proportion varies
a

page_text: according to the amount of sulphide in the pyrites and the per centage
of iron in the slimes.
The mixture is calcined in closed pots or in a closed reverberatory or
other suitable close furnace (the air being excluded and a little coal or
coke thrown in to maintain a reducing action in the furnace) until the
condition of the pyrites is changed by the iron added thereto, as oxide
having withdrawn from the pyrites its "extra equivalent" of sulphur, and
the whole or greater portion of the oxide and bi-sulphide of iron (Fe S2)
in the whole mass has been converted into monosulphide and proto-
sulphide of iron. This mono and protosulphide of iron (herein-after
called sulphide of iron) is used for the production of the sulphuretted
hydrogen required for precipitation.
Another method of preparing the sulphide of iron for this purpose is
by driving off by sublimation the "extra equivalent" of sulphur from
the pyrites, and the sublimed sulphur may be recovered by condensation.
The sulphide of iron, together with a quantity of water, is put into a
closed vessel connected on the one hand with the precipitating vat by
pipes or tubes arranged so as to convey the sulphurcited hydrogen when
generated in the form of gas from the sulphide of iron and water into
the precipitating vat, and is also connected on the other hand by pipes.
tubes, or flues with a retort от set of retorts, or muffle oven, in which.
as herein-after mentioned, sulphuric acid is generated in the state of
vapour, and which last mentioned pipes, tubes, or flues are intended to
convey the sulphuric acid in vapour as it is generated into the vessel
containing the sulphide of iron and water with the object of disengaging
from the later sulphuretted hydrogen gas.
The sulphuric acid is generated from the proto and sub sulphate of
iron, herein-after called sulphate of iron (obtained from the liquors
themselves), by enclosing the said sulphate in fire-clay tubes, cylinders,
or tubular retorts, connected by pipes, as herein-before mentioned, with
the vessel containing the sulphide of iron and water, and by subjecting
the sulphate of iron in these retorts to a temperature high enough to
drive off the sulphuric acid in fumes or vapour through the pipes into
the vessel containing the sulphide of iron and water.
The object of having these retorts tubular and of no greai diameter is
to permit of that high heat being more readily applied which is necessary
to drive off the sulphuric acid in Vabour. With this view the retort

page_text: When the process is carried on upon a large scale a mume oven may
be substituted for the cylinders or retorts and connected with the vessel
containing the sulphide of iron and water by flues or other suitable
passages for conveying the sulphuric acid as it is generated into the said
vessel.
When the sulphuric acid is driven off from the sulphate of iron oxide
of iron remains as a residue, and it may be economically used by mixing
it with pyrites to make sulphide of iron, as herein-before mentioned.
°
As the sulphuric acid vapour passes through the pipes, flues, or
passages herein-before mentioned into the vessel containing the sulphide
of iron and water, sulphuretted hydrogen, is disengaged therein in the
form of gas, and is allowed to escape through the other set of pipes or
tubes into the precipitating vat until precipitation is complete. The
disengagement of the sulphuretted hydrogen leaves sulpliate of iron in
the liquor and this sulphate may be used again for making fresh
sulphuric acid, or it may be used for strengthening, the lixivium for
dissolving the copper oxide in the roasted orc.
The sulphuretted hydrogen gas on being conveyed into the precipi-
tating vat, holding in solution the soluble portions of the calcined ore,
throws down the whole of the copper held in solution therein in the
form of a sulphide in a high state of concentration and purity. When
the precipitation is completed the precipitate is allowed to settle, and is
afterwards deprived of its moisture by pressure, and it may then either
be smelted or converted into salts of copper.
to act
!
The liquor remaining in the vat after precipitation contains sulphate
In order to utilize
of iron, sulphuretted hydrogen, and sulphuric acid.
the free sulphuric acid in the liquor it may be advantageously employed
on the sulphide of iron and water for the disengagement of
sulphuretted hydrogen, as herein-before explained, or to strengthen the
lixivium for fresh batches of ore. If the ore contains any proportion of
silver or gold these metals are during calcination associated with the
sulphide of copper, and are found in the sulphide of copper and in gold.
washed out in granules in the process of sliming.

page_text: In order to prevent evasion of my Patent by the use of chemical equi-
valents, I observe that any other sulphate which will part with its
sulphuric acid under the influence of heat may be substituted for
sulphate of iron as a source of fuming sulphuric acid, as, for example.
sulphate of magnesia or kieserite, which would give off sulphuric acid in
fumes, and would leave in the retort magnesia, from which, by treating
it with the acid liquors from the precipitating vat. fresh sulphate of
magnesia could be formed and sulphuretted hydrogen could also be
disengaged from the proto-sulphide of iron and water by using, instead
of fuming sulphuric acid hydrochloric acid driven off from any of the
well-known sources. But the nse of any such chemically equivalent
processes will not be found so convenient as the use of sulphate of iron,
which I prefer.
'
.
There are also other methods which I use for obtaining and applying
sulphuretted hydrogen for precipitating the copper from the sulphate
solution thereof, herein-before mentioned, and which may, either from
the character of particular ores or the circumstances and resources of
particular localities, be found more convenient and advantageous than
the method herein-before described, and these alternative methods I now
proceed to describe.
Instead of producing sulphuretted hydrogen gas by the action of
fuming sulphuric acid on sulphide of iron and water, I produce sul-
phuretted hydrogen gas by boiling a solution of the bi-sulphide of
magnesium, so as to drive off sulphuretted hydrogen gas therefrom into
the precipitating vat in order to precipitate the copper as sulphide of
copper. Or I add a solution in water of bi-sulpide of magensium to the
solution from which the copper is to be precipitated, the sulphuretted
hydrogen disengaged in the latter solution on the addition of the said
bi-sulphide thereto precipitating the copper as sulphide of copper.
Bi-sulphide of magnesium produce for the said purposes by acting
on. a solution of sulphate of magnesia with poly-sulphide of calcium,
commonly known as the yellow liquor produced in the alkali manu-
facture, the result of the double decomposition ensuing between the
sulphate of magnesia and poly-sulphide of calcium being sulphate of
lime and the said bi-sulphide of magnesium.
The use of native sulphate of magnesia, commonly called kieserite,
sali can he conveniently
will
he
adopted where that form of the

page_text: In other cases sulphate of magnesia may be conveniently and cheaply
prepared for the purposes of this process by treating magnesian lime-
stone or native carbonate of magnesia, known as magnesite, with the acid
liquors remaining after precipitation of the copper. The use of mag-
nesian limestone with the acid liquors will give sulphate of magnesia in
solution and a precipitate of sulphate of lime, which last may be eco-
nomised in forming poly-sulphide of calcium in manner. herein-after
mentioned.
Poly-sulphide of calcium I procure in several ways. one or other of
which may be found more convenient." according to circumstances. Thus
in the roasting of the pyrites ore, herein-before mentioned. I cover up
the burning ore with a layer of ordinary hydrated or caustic lime, or
carbonate of lime, or ordinary limestone, as on exposure of these sub-
stances to the fumes of burning sulphur they absorb sulphur, and yield
on .exposure to the air and water considerable quantities of poly-sulphide
of calcium or yellow liquor.
The formation of poly-sulphide of calcium may also be effected by
exposing tank waste, or gas lime waste, or any material of similar con-
stitution containing sulphides of calcium to the action of air and
moisture; or by calciuing together a quantity of pyrites ore with lime
or any of the compounds of lime or calcium herein-before mentioned,
such as, by preference, the sulphate of lime, and dissolving out the
poly-sulphide of calcium therefrom by means of water. The residue left,
after dissolving out the poly-sulphide of calcium, may itself be recalcined
with pyrites, as herein-before mentioned in order to obtain fresh poly-
sulphide of calcium or yellow liquor.
I have found that a mixture of six parts of burnt lime and fifteen
parts of ordinary pyrites calcined together in a reducing furnace answers
very well for the production of poly-sulphide of calcium.
In the double decomposition of poly-sulphide of calcium and sulphate
of magnesia to form bi-sulphide of magnesium care must be taken to
use a plentiful quantity of water. If too little water is used there is a
partial formation of mono-sulphide of magnesium and a loss of sulphu-
retted hydrogen, which escapes any sulphuretted hydrogen however
which may escape during the reaction I utilize by conveying it into the
solution from which copper is to be precipitated in order to secure its
being made sufficiently acid. And I here direct generally that the said
.

page_text: solution, containing as it does sulphate of iron as well as sulphate of
copper in solution, must be made and kept acid enough to redden litmus
paper, in order that sulphuretted hydrogen, whether immitted as gas or
produced in the liquor itself as aforesaid by the addition of bi-sulphide
of magnesium or by any other reagent, may precipitate the copper
without precipitating the iron, which would be liable to be precipitated
if the solution holding it became neutral or alkaline.
.
Having by the aforesaid or any other convenient means obtained the
poly-sulphide of calcium in solution of the requisite strength, I run it.
in order to form bi-sulphide of magnesium, into a tank containing
sulphate of magnesia in solution, and by double decomposition I obtain
bi-sulphide of magnesium, which remains in solution, and also sulphate
of lime, which subsides to the bottom as an insoluble precipitate. The
bi-sulphide of magnesium so formed is then run by a pipe provided with
a stop-cock from the tank in which it is produced into a boiler, in
which it is completely. decomposed by boiling partly into sulphuretted
hydrogen, which passes over from the boiler through another pipe into
the precipitating vat holding the copper solution, and partly into oxide
of magnesium, otherwise called caustic magnesia, which remains in the
boiler as an insoluble precipitate.
After the sulphuretted hydrogen driven over into the precipitating vat
has thrown down the copper, the supernatant acid liquor is pumped or
syphoned back into the boiler, in order to wash out, preferably with the
assistance of heat applied to the boiler, the magnesia left therein with
which it forms a solution of sulphate of magnesia, which is then run out
of the boiler by a cock provided for the purpose near the bottom of the
boiler into a settling vessel, from which after settling the solution of
sulphate of magnesia is pumped back again into the tank herein-before
mentioned, in which it is again treated with fresh poly-sulphide of
calcium or yellow liquor to form fresh bi-sulphide of magnesium, which
is boiled to produce sulphuretted hydrogen for precipitating the copper,
sulphate of magnesia being again formed, and treated with fresh yellow
liquor, and so on in continuo.
The boiler I prefer to use as convenient is a cylindrical boiler, so
formed as to have a fire-space open at both ends, and of convenient
diameter, extending from one end to the other of the axis of the cylinder.

page_text: sulphide is added, and the precipitation of the copper may be known to
iron rod or steel blade ceases after a short
be completed so soon as an
immersion in the liquor to
shew any traces of copper precipitated upon
it, or it may be known by testing a small portion of the liquor for the
presence of copper by ammonia.
The sulphide of copper precipitated by this method will probably not
be so pure as that precipitated by gaseous sulphuretted hydrogen passed
into the copper solution, but it will nevertheless be rich and pure
enough for the copper smelter. Care should be taken that the copper
solution be thoroughly acid before adding the bi-sulphide. In the event
of the copper
sulphide resulting from this method being found ΟΠ
settling down to be of a pasty consistency it may be got into a solid
transportable state by adding a small quantity of burnt lime as a drying
agent.
On precipitation of the copper by adding bi-sulphide of magnesium as
herein-before mentioned to the copper solution, the supernatant liquor
will contain sulphate of iron and sulphate of magnesia.
In order to convert the sulphate of magnesia remaining in the liquor
back again into bi-sulphide of magnesium, the supernatant liquor
remaining after the precipitated sulphide of copper has been separated
from it is treated with poly-sulphide of calcium (using an excess of such
poly-sulphide), which throws down as insoluble precipitates both the iron
in the form of bi-sulphide of iron, and the calcium in the form of
sulphate of lime, and at the same time. converts the sulphates of magnesium
into the bi-sulphide of magnesium which remains in solution, and is,
after settling. run off into the boiler and boiled.
as herein-before
mentioned to produce sulphuretted hydrogen. The residual mixture
of bi-sulphide of iron and sulphate of lime precipitated may be utilized
for forming fresh poly-sulphide of calcium by mixing it with additional
pyrites ore and calcining in a reducing fire.
I also avail myself in certain circumstances in order to produce
sulphuretted hydrogen of the peculiar property which the sulphate of
magnesia exhibits when brought in contact in strong saturated solution
with poly-sulphide of calcium, also saturated, of evolving sulphurretted
hydrogen, and depositing mono-sulphide of magnesium which is insoluble
in water; but the insoluble mono-sulphide of magnesium can be
removed or recovered from the sulphate of lime in the form of the

page_text: soluble bi-sulphide by means of a more dilute solution of poly-sulphide
of calcium or other soluble sulphide.
When poly-sulphide of calcium and sulphate of magnesia are used for
the immediate production of sulphurretted hydrogen both must be in a
state of strong saturated solution, but when they are used to form bi-
sulphide of magnesium the sulphate of magnesia should be used in a
diluted state, and the poly-sulphide need not be above a specific gravity
of 125 or 150 degrees Twaddel, the escape of sulphurretted hydrogen
will indicate that there is not enough of water present, or in other words
that the reagents are not used in a state of sufficient dilution.
Sulphuretted hydrogen may also be obtained from the poly-sulphide
of calcium itself by boiling it, but the whole sulphuretted hydrogen is
not driven off in boiling. To drive off the whole sulphuretted bydrogen
procurable from poly-sulphide of calcium it must be heated to redness
in a retort or furnace with access of steam. This will not generally be
found a convenient method, but may in special circumstances and when
poly-sulphide of calcium and steam can be abundantly obtained from
any cheap source.
Instead of sulphate of magnesia and poly-sulphide of calcium being
used to form bi-sulphide of magnesium as a source of sulphuretted
hydrogen or for direct use as a precipitant of copper it may in some
cases be found convenient to use sulphate of alumina and poly-sulphide
of calcium to produce the sesqui-sulphide of aluminium as the source of
sulphuretted hydrogen or as a direct precipitant. In this case alumina.
will be left in the boiler instead of magnesia, and the sulphate of alumina
and sesqui-sulphide of aluminium will be reformed instead of sulphate
of magnesia and bi-sulphide of magnesium. But the sulphate of alumina
will be found less manageable and under ordinary circumstances less
convenient than sulphate of magnesia.
as
"lime" or calcium
The second part of this Invention, which is called the
process," is applicable to the second class of ores herein-before described
as consisting of sulphurets of copper too poor in sulphur to be capable
of supporting self-combustion; it is follows: The per centage of
sulphide of copper present in the ores to be treated, and the per centage
of sulphur existing in the ore in other forms than that of sulphide of
copper having been ascertained, there is added to the quantity of copper
ore to be treated sufficient calcic hydrate or ordinary caustic linge to

page_text: with
represent the equivalent of the base of the sulphur compounds, minus
the copper sulphide existing in the quantity of ore to be operated on.
The proportional quantities of copper ore and caustic lime so ascertained
are then ground or pulverized, and intimately mixed together
water to the consistency of paste in a pug mill or its equivalent. The
paste is then formed into pipes, bricks, or balls, which are dried or
burned, or the mixture may without being formed into shapes be burned
upon the hearth of a furnace.
The calcination requires an oxidising fire and a temperature not higher
than that of a red heat.
In the calcination the lime takes the excess of sulphur and forms an
insoluble sulphate of lime; the copper sulphate, into which the sulphide
of copper is chiefly converted, is soluble in water, and any oxide of
copper which may be formed may be dissolved by the action of sulphate
- of iron in the manner herein-before described. The proportioning of
the equivalents so as not to add an excess of caustic lime and the careful
regulation of the fire are intended to promote the conversion of as much
as possible of the copper into the form of the soluble sulphate, and to
avoid as much as possible the formation of oxides.
.
or
In case of insoluble oxides being produced by over calcination
accidental addition of too much lime it is advantageous to wash these
out with the acid liquors containing the sulphate already mentioned.
After the calcination is complete the bricks, pipes, or balls containing
the roasted ore and lime are crushed to powder, lixiviated and slimed
with water (in this case preferably with hot water), and the residium
washed out thoroughly with the acid liquors containing sulphate of
iron, as herein-before mentioned in relation to the first head of this
Invention.
The acid lixivium and washings both hold the soluble sulphate of
copper and dissolve any oxide of copper that may have been produced.
The precipitation of these from their solution is carried out in the same
manner as that herein-before described in relation to the first part of
this Invention. Or the treatment may be so arranged that in the process
of calcination of the mass a supply of sulphuretted hydrogen or of
poly-sulphide of calcium may be obtained at a low cost by first con-
ducting the calcination in a furnace with a reducing fire, and as soon as
sulphide of calcium is formed in the mass (which may be easily known

page_text: by any ordinary test) either injecting a jet of steam into the furnace to
draw off sulphuretted hydrogen through suitable exits provided for the
purpose, and communicating with the precipitating vat, or removing the
mass from the furnace at this stage, and extracting the poly-sulphide
of calcium therefrom by water as herein-before described, subsequently
returning the residue into the furnace, and the roasting will be con-
tinued after getting off the sulphuretted hydrogen or the poly-sulphide
as the case may be with an oxidising fire until the copper is converted
into sulphate as herein-before mentioned, the sulphuretted hydrogen or
poly-sulphide of calcium so obtained will be applied to precipitate the
copper as sulphide in manner herein-before directed.
Having now described and particularly ascertained the nature of the
said Invention, and the manner in which the same is or may be used or
carried into effect, I would observe in conclusion that what I consider
to be novel and original, and therefore claim as the Invention secured
to me by the herein-before in part recited Letters Patent is,-
First. The several alternative processes herein-before described in the
first part of this Specification, but not the separate steps thereof, except
in combination as a process for treating copper ores, and except the
separate steps herein-after specially claimed.
Second. The formation of poly-sulphide of calcium by exposing lime,
carbonate of lime, or limestone to the fumes of the roasting sulphuretted
ores, and by calcining the compounds of lime or calcium herein-before
mentioned with pyrites ore, all as herein-before described.
Third. The formation of bi-sulphide of magnesium as herein-before
described and the use of the same as a source of sulphuretted hydrogen
for the purpose of precipitating copper and the precipitation of copper
by adding a solution of bi-sulphide of magnesium to the solution to be
precipitated, both as herein-before described.
Fourth. The formation of the sesqui-sulphide of aluminium and its
use as a source of sulphuretted hydrogen, as herein-before described.
Fifth. The generation of sulphuretted hydrogen for the precipitation
of copper by bringing a saturated solution of sulphate of magnesia into
contact with a saturated solution of poly-sulphide of calcium, and the
conversion of the mono-sulphide of magnesium thereby produced into
the soluble bi-sulphide by the use of a dilute solution of poly-sulphide of
calcium, as herein-before described.

page_text: Sixth. The use of calcic hydrate or lime in reducing sulphuretted ores
of copper, poor in sulphur, in the manner heréin-before in the second
part of this Specification escribed, and also the method of procuring
sulphuretted hydrogen and poly-sulphide of calcium directly from the
mass in the process of calcining such ores of copper with lime, as hercin-
before described.
In witness whereof, I, the said Joseph Anthony Dixon, have to
this my Specification, set my hand and seal, the Sixth day of
March One thousand eight hundred and seventy-four.
J. A. DIXON. (L.S.).