IMPROVEMENTS IN THE TREATMENT OF ORES OF LEAD AND ZINC, AND OTHER METALS.
Year: 1880

page_text: LETTERS PATENT to James Cochran Stevenson, M.P., of Westoe, in the
County of Durham, Alkali Manufacturer, and James Graham Tatters, of the
same Place, Analytical Chemist, for an Invention of "IMPROVEMENTS IN
THE TREATMENT OF ORES OF LEAD AND ZINC, AND OTHER METALS.".
PROVISIONAL SPECIFICATION left by the said James Cochran Stevenson
and James Graham Tatters at the Office of the Commissioners of Patents on
the 18th October 1880.
JAMES COCHRAN STEVENSON, M.P., of Westoe, in the County of Durham, Alkali
Manufacturer, and JAMES GRAHAM TATTERS, of the same Place, Analytical
Chemist. "IMPROVEMENTS IN THE TREATMENT OF ORES OF LEAD AND ZINC,
AND OTHER METALS."
This Invention is applicable to the treatment of blue stone and other ores in
which the sulphides of lead and zinc are combined together with or without other
metals such as copper and silver.
After the ore has been ground and calcined in order to drive off its sulphur it
is treated and agitated with weak hydrochloric acid without boiling, and in
quantity equivalent as nearly as possible to dissolve the zinc without dissolving
the other metals.
From this solution oxide of zine may be precipitated by lime, or the zinc may
be obtained in other combinations by other suitable known means. The residue
after the separation of the zinc may be used for the production of lead and silver
by ordinary metallurgic processes.
This residue may also be treated with hydrochloric acid with the aid of heat so
as to convert the lead and other metals into chlorides. The mixture of chlorides
and gangue is boiled down and dried and calcined in a furnace at a heat sufficient
to drive off the excess of acid and render insoluble the iron present.
The calcined mass is treated with cold water to remove chloride of zinc, which
may have been formed from any zinc which had resisted the treatment with weak
acid. Such chloride of zinc is added to the bulk previously produced.
Chloride of lead free from iron may be then separated from the mass or gangue
by water or solutions of alkaline, or earthy chlorides, or by other known means.
The chlorides of copper and silver in solution may be treated by any known means
for the separation of these metals.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent, and
of an Order of the Lord Chancellor, filed by the said James Cochran
Stevenson and James Grahain Tatters in the Great Seal Patent Office on the
27th July 1881.
JAMES COCHRAN STEVENSON, M.P., of Westoe, in the County of Durham, Alkali
Manufacturer, and JAMES GRAHAM TATTERS, of the same Place, Analytical Chemist.
"IMPROVEMENTS IN TITE TREATMENT OF ORES, OF LEAD, AND ZINC, AND OTHER
METALS."
This Invention is applicable to the treatment of blue stone and other ores in
which the sulphides of lead and zinc are combined together with or without other
metals, such as copper and silver.
After the ore has been ground and calcined to drive off its sulphur it is
treated and agitated with weak hydrochloric acid without boiling, and in quantity
equivalent as nearly as possible to dissolve the zinc without dissolving the other
metals..
We find that hydrochloric acid which contains from 5 to 10 per cent. of real
acid is suitable for this purpose, and that while an excess of acid is required an
excess of 30 per cent. above the quantity which will combine with the zinc to be
dissolved is sufficient.
The action of the acid on the ore causes a rise of temperature of 6 to 20 degrees
of Fahrenheit's thermometer, varying with the quantity of zinc oxide, which is
dissolved, but artificial heat is not employed.
In this way all the oxide of zinc is dissolved with the aid of agitation, but the
zinc which through imperfect calcination remains in the ore as sulphide is not
attacked, and we find that very little copper and practically no iron or lead or
silver is dissolved. The excess of acid in the solution must not be neutralized,
as we find that it is required in order that the zinc solution may settle clear.
To aid the dissolving by agitation we prefer to carry on the operation in a box
or covered cistern of wood or cast iron, revolving on a shaft which passes through
the box or cistern at two corners diagonally opposite each other.
This vessel is
provided with a watertight door by which it may be filled and emptied.
The operation should occupy less than an hour, and when it is completed the
solution and the undissolved ore are discharged together into a vessel underneath
where the mixturo settles clear, and from which the solution may be run or siphoned.
The undissolved ore which we call the lead residue is after washing removed for
further treatment..
From the zinc solution copper if present may be thrown down by metallic zinc
and then oxide of zinc may be precipitated by lime. Or the zinc may be obtained
in other combinations by other suitable known means.
The lead residue may if desired be used for the production of lead and silver by
ordinary metallurgic processes.
The second part of our Invention relates to the treatment of this lead residue,
and is applicable also to the treatment of a like residue, which remains after the
extraction of the zinc from the ore by means of weak sulphuric acid as sometimes
practised. We first apply bydrochloric acid with the aid of heat so as to convert
the lead and other metals into chlorides, and then we render any iron which is
present insoluble by calcining the mixed chlorides and gangue.
For this purpose we prefer to use a similar arrangement to that which is known
as the pan and drier for the decomposition of common salt by sulphuric acid in
alkali works.
The hydrochloric acid should be as strong as possible, and considerably in excess
of the quantity which can enter into combination with the metals and other soluble

page_text: ingredients in the lead residue. The acid is run into the cast iron pan (which
may be lined with fire bricks or lumps), and the lead residue also is put into the
pan. The heat of the furnace assists the solvent action of the acid, and evaporates to
a pasty condition the chlorides and gangue, after which the mass is thrown onto
the adjacent hearth and calcined to a heat just sufficient to drive off the excess of
acid and decompose the salts of iron, and so render the iron insoluble. The silica
in the ore is rendered insoluble at the same time, and the gangue is rendered more
easy of separation in the subsequent treatment.
The calcined mass is then treated with cold water to remove chloride of zinc,
which may have been formed from any zinc which had resisted the treatment
with weak acid. Such chloride of zinc (after the precipitation by zine of any
copper which the solution may contain) is added to the bulk previously
produced.
Chloride of lead free from iron is then separated from the mass by boiling water
or by solution of alkaline, or earthy chlorides, or by other known means, and
silver if present may be separated by any known means.
Having now described our improvements, and the method of carrying out the
same, we claim,-
First. The treatment of calcined blue stone or similar ore with hydrochloric
acid so proportioned in quantity and adjusted as to strength and temperature, as
herein before described, that the oxide of zinc may be dissolved whilst the oxide
of load is left in the residue.
Second. The further treatment of the said or like residue first with hydrochloric
acid, converting the metals into chlorides, and then by calcination, rendering the
iron insoluble, as herein described.
In witness whereof, I, the said James Cochran Stevenson, have hereunto set
my hand and seal, this Thirteenth day of July, in the year of our Lord
One thousand eight hundred and eighty one.