AN IMPROVED METHOD OF AND APPARATUS FOR TREATING LOW CLASS AND OTHER ORES FOR OPMAINING CORDED AND SILVED THEREFROM
Year: 1874

page_text: LETTERS PATENT to Thomas Clarke, M.D., of Ladyfield, Wilmslow,
in the County of Chester, for the Invention of "AN IMPROVED
METHOD OF AND APPARATUS FOR TREATING LOW CLASS AND OTHER ORES FOR
OPMAINING CORDED AND SILVED THEREFROM
"
Sealed the 5th February 1875, and dated the 30th September 1874.
PROVISIONAL SPECIFICATION left by the said Thomas Clarke at
the Office of the Commissioners of Patents, with his Petition, on
the 30th September 1874.
I, THOMAS CLARKE, M.D., of Ladyfield, Wilmslow, in the County of
Chester, do hereby declare the nature of the said Invention for "AN
IMPROVED METHOD OF AND APPARATUS FOR TREATING LOW CLASS AND OTHER ORES
FOR OBTAINING COPPER AND SILVER THEREFROM," to be as follows:-
Low class copper and silver ores containing, say 2 per cent. of copper,
and 4 to 8 ounces of silver a ton, after having been ground to such
fineness that the particles are not larger than a pin's head, are first

page_text: roasted to drive off any sulphur, arsenic, or antimony they may contain,
and which may be collected in the usual way.
The ores are then to be again ground to extreme fineness (the finer
the better) and intimately mixed with 7 per cent. of common salt (but
varying according to the amount of copper and silver in the ores) and
the copper and silver converted into chlorides in the usual way.
Sufficient care, however, is not generally taken in this process, and the
object is to obtain a perfect chloridisation. If the heat is too prolonged
insoluble sub-chloride of copper will be formed and some chloride
volatilized. A jet of steam should also be introduced over the surface
of the ores towards the end which makes the combination of the chlorine
and silver more certain, and by condensation of vapours tends to retain
the silver, otherwise a large proportion of the metal in it is said to be
lost. This seems founded on the fact that the change has been observed
to be much facilitated if at the moment of union the sodic chloride is in
a slightly moistened state.
When the chloridisation is considered perfect the ore is placed in a
square or circular tank formed of fire-brickwork and lined cither with
coarse glass, slabs of slate, cement, or perhaps better still white glazed
tiles set in cement, the last is to be preferred.
The wooden tanks hitherto employed soon become useless as they
are unable to bear either the strain of the weight or the heat. All the
wooden implements used, such as shovels, rakes, and similar articles
should be of pitch pine, the resin therein serving to resist the action of
the liquid. This first series of tanks may be about 10 feet in diameter,
and from 2 to 3 feet deep, probably four, such tanks might be suffi-
cient for forty tons of calcined ore a day. Two small tramways, one
above the tank to bring the ore, and the other below to remove it to be
dressed for tin, and can be easily arranged and save much labour.
Immediately below this scries is another row of 4 square tanks similarly
constructed, say 5 feet square and 4 feet deep, capable of holding 600
gallons of liquid. Instead of 4 such tanks it is probable that two would
be equally serviceable, each of which might be 6 fect square and 4 feet
deep, holding 864 gallons each, as this plan for 40 tons of calcined ore
requires 1600 gallons of liquid. In this second series is placed a
solution of common salt, to which has been added from 1 ounce of
hyposulphite of soda to, the gallon, according to-the- richness or

page_text: peculiarities of the ore. This solution is kept moderately hot by steam
being blown into it.
When the ore is placed in the first tank and spread over it the hot
solution in the second is pumped on it and allowed to run back again
through one or more glazed earthenware pipes from the bottom of the
first tank, but having the orifices properly protected with filters to
prevent the ore passing through. The solution is constantly stirred and
mixed with the ores by wooden rakes either moved by land or revolved
by machinery. When by this process the chlorides from ten tons of ore
are found to be all dissolved (as may be ascertained by testing the ore)
which may take half an hour, and the concentrated solution is liquor all
filtered into the second tanks, it is allowed to settle until it is quite
clear, which may take 15 or 20 minutes, it then passes into the pre-
cipitating tank No. 3, of which there perhaps need only be one, say 8 or
9 feet square and 4 feet deep, holding 2000 gallons.
It must be observed that the chloride of copper is very readily soluble
in water. The difficulty is with the chloride of silver, and which is with
difficulty soluble in salt solution alone. Even with the hyposulphite of
soda added, 1 ounce of the solution should be allowed for every grain
of argentic chloride. It is also important that any sediment remaining
in No. 2 should be put back again into No. 1 so as to be subsequently
treated again with the next batch of ore, and so that no silver may be
lost. When then the concentrated solution has passed into the precipi-
tating tank, bars of wrought iron or scrap iron are placed on wooden
shelves or supports and the solution kept hot in the way already men-
tioned. Footmoor pig iron will do, and the grey better than the white,
but wrought should be employed if possible.
It is very important now, 1stly, that the solution should be kept as
far as possible of uniform temperature; 2ndly, that it should be.fre-
quently agitated; 3rdly, that the precipitate should be swept off the
iron as it accumulates; and 4thly, that the air should be excluded as
much as possible. When the copper and silver are all precipitated they
will form a dark brown powder, consisting of metallic copper and silver,
and probably some sulphides of these metals with free sulphur, leaving
a perfectly free liquid above of a slightly green hue. The precipitate is
then washed a few times with hot water, collected, dried, and at once
fused in a blast furnace or a modified Bessemer's. An alloy of almost

page_text: pure copper and silver will be formed and almost void of any iron. The
great value of this plan of obtaining copper and silver from low class
ores is not only in the perfection of the arrangement as to the form,
position, and constitution of the tanks, but it is especially by the addition
of the hyposulphite of soda to the salt solution. This is perfectly
original, never having been suggested or tried, as the Inventor believes,
before. It is possible that the chloride of ammonium may be also added
with good effect.
The effect of the hyposulphite added to the brine solution is peculiar
and extraordinary :—
(1st.) Being the special solvent of the chloride of silver it aids
materially in collecting it and preventing any being lost.
2nd. It prevents the oxidation of the iron in a very remarkable
manner, the oxygen passing apparently to the salt instead of to the iron,
and so the sulphate of iron remains undecomposed. In the brine solution
the difference is striking.
3rd. From this cause the sulphate given, sulphate of soda, &c., may
be made articles of commerce and become a source of profit.
4th. With the hyposulphite added the waste of iron is prevented, and
so the process becomes much more economical.
5th. Heat is not so much essential as in the brine process.
6th. While the precipitation is equally rapid the precipitate is purer,
requiring less washing, and being heavier it deposits more quickly and
firmly.
2
7th. Being free from iron it is not only purer, but it is more readily 2
fused.
In the precipitation from the salt solution a great quantity of oxide
of iron is produced, which not only complicates the whole process, but
makes the washing very troublesome. The waste of iron is greater and
the chloride of silver is less perfectly dissolved.
3

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Thomas Clarke in the Great Seal Patent Office
on the Sth February 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
CLARKE, M.D., of Ladyfield, Wilmslow, in the County of Chester, send
greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirtieth day of September, in the year
of our Lord One thousand eight hundred and seventy-four, in the
thirty-eighth year of Her reign, did, for Herself, Her heirs and suc-
cessors, give and grant unto me, the said Thomas Clarke, Her special
license that I, the said Thomas Clarke, my executors, administrators,
and assigns, or such others as I, the said Thomas Clarke, my
executors, administrators, and assigns, should at any time 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 METHOD OF AND APPARATUS FOR TREATING LOW CLASS AND OTHER
ORES FOR OBTAINING COPPER AND SILVER THEREFROM," upon the condition
(amongst others) that I, the said Thomas Clarke, my executors or
administrators, by an instrument in writing under my, or their, or one
of their hands and seals, 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.
NOW KNOW YE, that I, the said Thomas Clarke, do hereby declare
the nature of the said Invention, and in what manner the same is to
be performed, to be particularly described and ascertained in and by
the following statement thereof, that is to say :-
The ores or minerals to be treated, after having been ground to the
requisite degree of fineness, are first roasted to drive off any volatile
substances (such as arsenic, sulphur, or antimony,) which they may
contain, and which may be collected in the usual way. The ore is then
to be mixed with a quantity of common salt, say, in the ratio of about

page_text: 7 per cent., but this is to be proportioned to the amount of copper and
silver contained in the ore, and the copper and silver converted into
chlorides in any suitable furnace. The great object is to obtain a perfect
chlorodisation, and care should be taken that the heat is not too great or
too prolonged, as the chloride of copper will be decomposed into in-
soluble sub-chloride, and the chloride of silver into oxide, or actually
volatilised. A jet of steam may also be introduced over the surface of
the ore towards the end, which makes the combination of the chlorine
and silver more certain, and by condensation of the vapours tends to
prevent the escape of any chloride when formed. The ore then having
been chlorodised may be placed in an ordinary lixiviating tank made of
wood, but as these tanks are soon liable to become defective from the
strain and licat, a stronger circular tank, say, 10 feet in diameter and
2 or 3 feet deep, may be made of brickwork, and lined with boards or
slabs of coarse glass, slate, or tiles. The brickwork must be set in some
suitable cement to prevent leakage.
When a sufficient quantity of ore has been spread over the floor of
the tank a hot solution of common salt, to which has been added an
alkaline hyposulphite, preferably the hyposulphite of soda, as a special
solvent of chloride of silver, is poured upon it, and the salts of silver and
copper washed out by the ore being stirred by strong wooden or tinned
metal rakes, either turned by hand or by machinery. When the liquid
has been allowed to settle a little it passes by earthenware pipes (the
orifices being protected by any suitable filter to prevent the coarser
particles of the ore passing through) into a second series of tanks below
the first, and from thence when clear into a third series lower again,
containing scrap or other form of iron, where the silver and the copper
will be precipitated together. This well-known law has indeed been acted
upon for years in different parts of England for obtaining these metals
together from brine solutions alone. These tanks may be of any size,
and in such number as the requirements of the case suggest. The
solution may be kept hot in the different processes by means of the
customary steam jet, but superheated steam is much to be preferred.
The implements used, such as shovels, &c., should be of wood, pitch
pine perhaps being preferable, as the resin protects it. Two small tram-
ways should be constructed, one above and one below the lixiviating
tank, by which ore may be brought and removed, and so a great deal of
labour saved. The quantity of the alkaline hyposulphite to be-used is

page_text: determined by the amount of silver in the ore, but from one to two ounces
to the gallon of brine may be considered sufficient. It is important that
any sediment in the second series of tanks should be rewashed in the
first.
The scraps of iron in the third series of tanks may rest on wooden
bars a foot or so from the bottom, so that the precipitate may fall between
them and be kept purer. It is important that the liquid should be
agitated, be kept of a uniformly hot temperature, that the precipitate
should be swept off the iron occasionally, and that the air should be
excluded as far as possible to prevent any unnecessary oxidation of the
iron. The precipitate may be then washed with hot water, collected,
dried, and fused in a small blast furnace or a modified Bessemer's, and
run off into ingots. The value of this plan of obtaining copper and silver
from ores of different values is not only in the perfection of the arrange-
ment as to the form, position, and constitution of the tanks, but especially
in the addition of alkaline hyposulphites, and preferably the hyposulphite
of soda. The great difficulty in these cases is with the chloride of silver,
the chloride of copper being readily soluble even in cold water, which has
little or no effect on the chloride of silver; but a still greater value is
that as the hyposulphite will dissolve out the silver as a hot or cold
solution it gives me an alternative process; and, what is more important
still, it enables me to obtain the silver separate from the copper, and
which is what I strongly advise to be done. Besides, I am enabled to
treat the chlorodised ore in a cold state, so that it may be stored up for
months if need be before it is operated upon. To obtain the metal
separate then, or if much free acid has been generated (and which
interferes with the action of the hyposulphite) I first wash out all the
soluble salts and acid with cold water, and pass this solution into the
iron tank for the precipitation of the copper, and then dissolve the silver
chloride with a solution of hyposulphite of soda with or without salt, and
pass it into another tank containing sheets or other form of zinc or
copper, which will precipitate the silver.
The silver like the copper is precipitated all the more rapidly if the
solution be kept hot, and superheated steam may be used for this
purpose. So again if the ores to be treated are mainly silver ores, and
containing little or no copper, the solution may at once be passed into
the tank which contains zinc or copper without any previous lixiviation
except to remove any free acid and other impurities.

page_text: It is to be observed that any copper dissolved in precipitating the
silver is reclaimed by passing it into the iron tank.
Having now described the nature of my said Invention, and the
manner of carrying the same into effect, I would have it understood that
what I desire to claim is,-
1st. The special form and construction of the lixiviating tank, sub-
stantially in the manner and for the purposes herein-before set forth and
described.
2nd. The addition of an alkaline hyposulphite, preferably the hyposul-
phite of soda, to the brine solution as a special solvent of the chloride of 1
silver, substantially in the manner and for the purposes herein-before
set forth and described.
3rd. The ability to dissolve the silver in the chlorodised ore by the
solution of hyposulphite of soda when cold, which cannot be done by
even hot brine solution alone, substantially in the manner and for the 1
purposes herein-before set forth and described.
4th. The obtaining the silver separate from the copper by using zinc
or copper as a precipitating agent, substantially in the manner and for
the purposes herein-before set forth and described.
5th. The use of superheated steam in the precipitating tanks, whereby 2
the precipitation is hastened, substantially in the manner and for the
purposes herein-before set forth and described.
In witness whereof, I, the said Thomas Clarke, have hereunto
set my hand and seal, this Sixteenth day of January, in the
year of our Lord One thousand eight hundred and seventy- 2
five.
THOMAS CLARKE, M.D. (L.S.)