Improvements in the Treatment of Zinc-bearing Ores for Obtaining Zinc and other Metals therefrom.
Year: 1898

page_text: Improvements in the Treatment of Zinc-bearing Ores for Obtaining
Zinc and other Metals therefrom.
I, SHERARD OSBORN 'COWPER-COLES, of 39, Victoria Street, Westminster, in the
County of London, Engineer, do hereby declare the nature of this invention
to be as follows;-
This invention relates to the treatment of zinc-bearing ores for obtaining
therefrom zinc and other metals they contain.
Hitherto the attempts that have been made to extract the metals from these
ores, especially when they are of a complex character, have not been satisfactory;
a large percentage of the metals being lost during the treatment of the ores.
It is the chief object of this invention to provide a process whereby the metals
can be recovered from the ores without the great loss which has been incidental
to processes hitherto used. The said process is especially applicable to the treat-
ment of sulphide ores of the kind obtained from Broken Hill (which contain
zinc, lead, silver and a small quantity of gold) but is nevertheless also applicable
to the treatment of zinc bearing ores generally, such for example as zinc blende
which may in some cases contain, in addition to the zinc, varying quantities of
lead or copper or both.
According to this invention I crush the ore and then subject it to a "dead
roast," so as to convert the sulphides present in the ore into sulphates or oxides
or both. I then leach it as hereinafter described to remove the zinc and in cases
where copper is present I remove the copper from the leaching solution and
afterwards electrolyze such solution for the recovery of the zinc therefrom.
When lead or silver or both are present I leach the residue to obtain the lead,
and afterwards leach the residue again to obtain the silver. In describing this
invention I will take for example the sulphide ores of Broken Hill.
I crush the ore to such a degree of fineness that it will pass through a sieve
containing about 1600 meshes per square inch. I then subject the ore to a dead
roasting operation, so as to convert the zinc sulphide into zinc sulphate and
zinc oxide. To facilitate the roasting it is advantageous, when dealing with such
an ore as that instanced, to add zinc blende, copper sulphide ores, or tin ores,
or tailings, as these prevent the adhesion of the ore, and enable a dead roast
to be obtained, which would not otherwise be the case. During roasting, the
ore is kept constantly stirred, for which purpose a hollow rake through which air
is blown can be used with advantage. The ore after being roasted is placed in
a reciprocating or revolving screen and the fine dust withdrawn by the exhaust
of a centrifugal fan or other suitable device, the dust being delivered directly
into a leaching vat, so that the metal or metals present may be leached out as
hereinafter described.

page_text: The remainder of the ore is placed in leaching vats which have false bottoms
covered with filtering cloths or the like to constitute a filter bed. I commence
the leaching with a weak solution of hot or cold diluted sulphuric acid; say
one containing not more than 1 oz. of free sulphuric acid to 1 gallon of water.
The acid combines with the oxides of the zinc and the copper to form sulphates.
A current of electricity may be passed through the charge during leaching, for
which purpose I may employ an insoluble anode, placed beneath the ore, and a
cathode, surrounded by a porous protector, placed above the ore.
The zinc sulphate solution containing copper sulphate and a little or no free
acid is drawn off from beneath the filter bed in the vats and is passed through
a body or bed of zinc and carbon or iron and carbon or both, on which bed the
copper is deposited and may be recovered as a fine powder by washing.
The zinc sulphate solution after it has been brought up to the desired strength
as hereinafter described and freed from copper is then passed through electro-
lyzing cells, through which the electrolyte is circulated. In these cells are ver-
tically revolving cast iron discs serving as the cathodes; lead plates being
employed for the anodes. The iron discs are slowly rotated and are provided
with fillets of wood which can be detached to allow of the removal of the deposited
zinc in the form of segments when such zinc has attained the desired degree
of thickness. The current density employed varies from 15 to 20 amperes; a
convenient voltage at the terminals of the electric generator being from 100
to 150 volts, the voltage at the terminals of the cells varying from 1 to 2 volts.
Zinc dust can be readily and economically made by varying the chemical or
electrical conditions or both so that the zine is deposited in a spongy form on the
revolving cathodes and removed by scrapers placed against the face thereof.
To obtain an effectual extraction of zinc from the ore it is advisable, after
leaching, to thoroughly wash out the remaining soluble zinc salts with hot water.
If this weak wash were allowed to mix with the electrolyte it would dilute the
latter too much, and therefore it is preferably run into an evaporating pan which
can be heated by the waste heat from the roasting furnace. The zinc sulphate
thus produced in the evaporating pan may be treated by any suitable process
for the production of zinc white therefrom."
The electrolyte after being electrolyzed as above stated is returned to the
leaching vat, a further quantity of acid being added to the solution. I find that
a solution containing 1 oz. of free sulphuric acid and from 20 to 30 ozs. of zinc
sulphate or thereabouts to the gallon of water, dissolves the zinc and copper
leaving behind in the residue the other metals such as silver, lead and iron,
which may be present.
The lead remaining in the residue is leached out by means of a solution of
caustic soda, the lead being recovered from this solution by electrolysis. After
the caustic soda solution has been used a number of times for leaching out the
lead, it becomes partly converted into silicate and carbonate of soda. Lime
may be added to the solution or the ore to re-form caustic soda or the solution
may be suitably treated for the production of white lead or lead sulphate by a
process that forms no part of my present application for patent. The carbonate
of soda obtained during the production of the white lead may be used for con-
verting the zinc in the sulphate solution into zinc carbonate which is subsequently
converted into zinc oxide by the application of heat.
The silver and any gold there may be present in the residues after the removal
of the lead, can be extracted by means of a weak solution of cyanide of potassium.
I wish it to be understood that I do not limit myself to the precise treatment
nor to the details thereof hereinbefore stated.
Dated this 10th day of March 1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.

page_text: Improvements in the Treatment of Zinc-bearing Ores for Obtaining
Zinc and other Metals therefrom.
I, SHERARD OSBORN COWPER-COLES, of 39, Victoria Street, Westminster, in the
County of London, Engineer, do hereby declare the nature of this invention
and in what manner the same is to be performed, to be particularly described
and ascertained in and by the following statement:-
This invention relates to the treatment of zinc bearing ores for obtaining
therefrom zinc and other metals they contain.
Hitherto the attempts that have been made to extract the metals from these
ores, especially when they are of a complex character, have not been satisfactory,
a large percentage of the metals being lost during the treatment of the ores.
It is the chief object of this invention to provide a process whereby the metals
can be recovered from the ores without the great loss which has been incidental
to processes hitherto used. The said process is especially applicable to the treat-
ment of sulphide ores of the kind obtained from Broken Hill (which generally
contain zinc, lead, silver and a small quantity of gold) but is nevertheless also
applicable to the treatment of zinc bearing ores generally, such for example as
zinc blende which sometimes contains, in addition to the zinc, varying quan-
tities of lead or copper or both.
66
According to my invention. the ore is first crushed to such a condition that it
will pass through a sieve of about 1300 meshes to the square inch. It is then
heated to a dead roast" in any suitable furnace so as to convert the zinc
sulphide into zinc sulphate or zinc oxide or both. To facilitate this roasting
I add from 25 % to 50% of zinc blende to prevent the adhesion of the particles
of the ore and enable an effectual dead roast to be obtained, which would not
otherwise be the case. Instead of the zinc blende I may if found convenient
employ copper sulphide ore, or tin ore or tailings thereof. I prefer however to
employ the zinc blende on account of its more economical working. During the
roasting, the ore is kept constantly stirred, for which purpose a hollow rake
through which air is blown can be used with advantage.
After the ore has been roasted as above explained it is then washed with water
& the water so used is conducted to an evaporating pan. The ore is then placed
in a reciprocating or revolving screen to separate the fine dusty portion there-
from, the coarse portion being placed in one series of leaching vats and the fine
dusty portion in another series of leaching vats so that each portion can be
independently treated by my process. A centrifugal fan or other appropriate
device may be provided for removing the fine dusty portion and depositing it
into the leaching vats. The leaching vats into which the coarse particles are
placed are provided with false bottoms covered with filtering cloths or the like
to form a filter bed. The ore having been placed in the vats I then proceed
to treat it with various leaching solutions for removing the metals.
I commence with a weak solution of sulphuric acid containing not more than
1 oz. of free sulphuric acid to each gallon of water. This solution is admitted
to the leaching vats from suitable elevated tanks, the acid in the solution com-
bining with the oxides of the zinc and the copper to form sulphates. While
this leaching operation is proceeding and in order to hasten the process a current
of electricity may be passed through the mass of ore in the vats, for which
purpose may employ an insoluble anode placed beneath the ore, and a zinc
cathode, surrounded by a porous protector, placed above the ore.
This solution after passing through the ore contains zinc sulphate, copper sul-
phate and a little or no free acid, and is allowed to flow from the space beneath

page_text: the filter bed of the leaching vats to a body or bed composed of fragments of zinc
and carbon or iron and carbon or both. As the solution passes slowly through
such body or bed it deposits thereon the copper it contains, which is subsequently
recovered by any appropriate washing operation.
The aforesaid leaching solution is passed a number of times through the vats
containing the ore, fresh sulphuric acid being added thereto in the small quan-
tities already mentioned, each time it is returned to the vats, until the solution
contains approximately 1 oz. of free sulphuric acid and from 20 to 30 ozs. of
zinc sulphate to each gallon of water. When the solution has attained such
strength and has been freed from the copper it contains, as described above, it
is then electrolytically treated in electrolyzing cells. These cells may be provided
with cathodes composed of vertically revolving cast iron discs and with anodes
composed of lead plates. The iron discs are slowly rotated during the electro-
lytic action and are provided with fillets of wood which can be detached to allow
of the removal of the deposited zinc in the form of segments when such zinc
has attained the desired degree of 'thickness. The current density employed
varies from 15 to 20 amperes per square foot; a convenient voltage at the
terminals of the electricity generator being from 100 to 150 volts, and at the
terminals of the cells from 1 to 2 volts.
Instead of zinc plates, zinc dust can be readily and economically obtained by
varying the chemical or electrical conditions or both, so that the zinc is deposited
in a spongy form on the revolving cathodes and removed by scrapers placed
against the face thereof.
The aforesaid zinc sulphate solution, after being electrolytically treated to
remove the zinc therefrom and after its strength has been adjusted to the requisite
strength of 1 oz. of sulphuric acid to each gallon of water as aforesaid, is then
returned to a suitable tank or chamber ready for leaching another charge of the
ore.
In order to obtain an effectual extraction of zinc from the ore, it is advisable,
after the aforesaid leaching has been effected, to thoroughly wash out, with hot
water, the soluble zine salts that remain in the mass of ore in the leaching vats.
This weak wash should not be passed into the electrolytic cells containing the
zinc sulphate solution, as it would dilute the latter too much and therefore I
prefer that it should be conducted to an evaporating pan which may be same
as that into which the water used for washing the ore is run. This pan is heated
by the waste heat from the roasting furnace or otherwise. The zinc sulphate
thus obtained in the evaporating pan can be treated by any suitable process for
the production of zinc white therefrom.
The ore in the vats having by the above described treatment been freed of
most of the zine and copper it contains, is now further leached with a solution,
containing about 30 ozs. of caustic soda to each gallon of water. This solution
is passed a number of times through the ore in the leaching vats and takes up the
lead which such ore contains. The resulting sodium plumbate solution is then
passed into an electrolyzing cell and electrolytically treated to deposit the lead.
The repeated use of the solution for leaching out the lead from the ore, causes
it to become partly converted into silicate and carbonate of soda. I therefore
add freshly burned lime to the said solution or to the ore, in sufficient quantities
to re-form caustic soda, care being taken not to add too much lime.
The sodium plumbate solution instead of being electrolytically treated as
aforesaid, may be treated, for the production of white lead by conducting it to a
receiver or chamber to which carbonic acid gas is supplied under pressure whereby
the lead is converted into lead carbonate and hydrate and the caustic soda into
carbonate of soda. The carbonate of soda may be used for converting the zinc
in the sulphate solution resulting from the first leaching treatment of the ore,
into zine carbonate which is subsequently converted into zine-white by the appli-
cation of heat.
o
The ore in the leaching vats having now been freed of its lead as well as its

page_text: zinc and copper, is then treated in any well known manner with cyanide of
potassium solution to remove the silver and any gold that may be present in
the ore.
The aforesaid fine dusty portion or tailings of the ore are treated in an
analogous manner to that already described with respect to the other portion of
the ore, except that as already stated they are treated separately and in vats
specially provided for them.
Having now particularly described and ascertained the nature of my said
invention and in what manner the same is to be performed, I declare that what
I claim is:
1. In the treatment of complex zinc ores such as those known as Broken Hill
ore and the like the admixture with the ore prior to its roasting of a quantity
of zinc blende, copper ore, tin ore or tailings thereof, substantially in the pro-
portions stated and for the purpose set forth.
2. In a process in which a complex ore containing zinc and copper is leached
with a solution of sulphuric acid the recovery of the copper from the said leaching
solution by passing it through a body or bed of zinc and carbon or iron and carbon
or both substantially as described.
3. The recovery from a solution containing a mixture of suitable salts of zinc
and copper of metallic copper by passing the solution through a body or bed
of zinc and carbon or iron and carbon or both substantially as described.
4. A process of treating mixed ores of zinc, copper, lead, silver and the like
consisting of first roasting the ore with or without the addition thereto of zinc
blende prior to roasting, then washing the ore with water and running the wash
into an evaporating pan, then treating the ore with a dilute solution of sulphuric
acid removing the zinc and copper, then again, washing the ore with water and
also running the wash into the evaporating pan, then treating with a solution
of caustic soda and removing the lead, then treating with potassium cyanide to
remove the silver and gold, substantially as described.
5. A process of treating mixed ores of zinc, copper, lead, silver and the like
consisting of first roasting the 'ore, with or without the addition thereto of zinc
blende prior to roasting, then washing the ore with water and running the wash
into an evaporating pan, then treating the ore with a dilute solution of sulphuric
acid removing the zine and copper, then again washing the ore with water and
also running the wash into the evaporating pan, then treating with a solution
of caustic soda and removing the lead substantially as described.
6. A process of treating mixed ores of zinc, copper, lead, silver and the like
consisting of first roasting the ore, with or without the addition thereto of zinc
blende prior to roasting, then washing the ore with water and running the wash
into an evaporating pan, then treating the ore with a dilute solution of sulphuric
acid, then again washing the ore with water and also running the wash into the
evaporating pan, then separating the zinc and copper by passing the solution
through a bed of zinc and carbon or iron and carbon or both substantially as
described.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.