Improvements in Methods of Treating Lead Ores.
Year: 1894

page_text: Date of Application, 15th May, 1894-Accepted, 21st July, 1894
COMPLETE SPECIFICATION.
Improvements in Methods of Treating Lead Ores.
I, AMBROSE GEORGE FELL of No. 200 West 130 Street in the City, County
and State of New York, United States of America, Chemist, 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 :-
.
My invention relates to the chemical reduction of the ores of lead, such as those
known under the names: galena (native sulphide) anglesite (native sulphate)
cernsite (native carbonate) and kerasin (native chlorocarbonate) with the view of
ultimately converting the lead in the ore into merchantable oxide (impure or pure
litharge) and lead salts, such as the acetate and nitrate.
In order that my method may be more readily understood, I will state how I
prefer to carry out my invention in the treatment of galena, which is one of the
more common and abundant ores of:lead.
The ore is crushed or ground and freed as far as possible from foreign matter.
This may be done with any of the usual mechanism employed for crushing, ores,
and forms no part, properly speaking, of my invention.
T
First step. In a suitable tank adapted to be heated, and preferably a shallow
tank lined with lead and provided with a hood to carry away the gases, I put
about 300 gallons of water, acidulated with 820 pounds of sulphuric acid of 66° B.
and 590 pounds of commercial muriatic acid (which contains about 236 pounds of
real hydrochloric acid), and I add to this acid liquid 450 pounds of sulphate of
soda..
Heat is applied to the tank containing the above mixture and to the mixture are
added about 2000 pounds of the crushed ore.
11
Decomposition of the ore ensues with evolution of sulphuretted hydrogen and
other gases. The operation is maintained for from two to six hours, dependent on
the temperature to which the mixture is raised which should not exceed 218° F. If
the mixture be stirred, the operation will be greatly facilitated. I find about four
hours to be the average time required for the operation, which will terminate about
thirty minutes after the evolution of sulphuretted hydrogen ceases, at which time I
add to the mixture at least as much water as that originally employed, (namely
300 gallons) and the mass is then well stirred and allowed to settle.
After settling, the clear liquid is drawn off and the sedimentary solid matter in
the tank washed with clean water until it is reasonably freed from acid. This
sedimentary lead compound will now have lost its metallic appearance and will
appear as a bluish, heavy mass, friable when dry and consisting principally of
sulphur and chlorine compounds of lead.
Second step. The lead compound resulting from the above treatment is next
agitated or mixed (in the same tank if desired) with a solution of sal-soda (mono-
carbonate of soda), and the mixture heated moderately up to say 150° F., or, if the
soda solution be hot when mixed with the lead compound, then no further heating
will be required. The strength of this sal-soda solution is immaterial (about 150 B.
answers very well); it is only necessary that it should not be too weak which
would retard the process.
The proportion of sal-soda required will vary somewhat even with the same
class of ore, but usually about 1500 pounds will suffice for the quantity of ore
ore under
treatment, that is 200 pounds of galena.
1.
The operation will be complete as soon as the solution in the tank furnishes to
the usual turmerio test a permanent alkaline reaction.

page_text: :
The mixture should be thoroughly stirred or agitated and allowed to settle, when
the clear liquid, a solution of soda salts, will be drawn off.
The resultant lead compound presents an appearance similar to that from the
first step but is lighter in tint, and its composition has been materially changed.
The next step in the treatment of the lead compound will depend upon what the
lead is to be converted into; if into a fine merchantable oxide the next step will
be as follows :-
Third step. The lead compound derived from the second step, as above, is mixed
with about 140 pounds of nitric acid, then dried and then subjected to the action
of heat which will vary in intensity according to the kind of oxide desired. For
ordinary litharge, a temperature of about 800° F., continued for about two hours,
will suffice for the other oxides the temperature and duration will be varied
proportionately, as will be understood by those skilled in the art.
In lieu of nitric acid, an equivalent amount of a nitrate may be employed as an
equivalent, nitrate of soda or nitrate of lead serving the purpose very well. If any
other nitrate than the nitrate of lead be employed, the product will have to be
washed and dried after roasting, but if the acid, or nitrate of lead be used, this will
not be necessary..
If, instead of an oxide, it is desired to convert the lead into a soluble salt of lead,
the lead compound will be treated with a solvent correspondent to the salt desired.
For example, if a nitrate is desired, I proceed as follows
Fourth step: To the lead compound of the second step is added nitric acid
diluted with about its weight of water and action goes on until the acid is
neutralised, or very nearly so.
The solution obtained is evaporated to dryness to obtain the salt. As this salt,
lead nitrate, contains no water of crystallisation, and no purification is necessary,
there is no advantage in crystallising the salt out of the solution.
If another salt than a nitrate is required, as an acetate, for example, a similar
course will be pursued. In the latter case acetic acid will be employed, and the
acetate crystallised out of the solution.
..:
In case the lead ore treated is argentiferous, or has in it other precious metals,
these will remain concentrated in. the undissolved' residuum from the foregoing
fourth step, and this residuum may be treated for their recovery by any of the
known methods.
The sulphuretted hydrogen evolved in the first step of the process may be
collected and converted into sulphuric acid for use in the process, in which event
the concentration of the acid, will be avoided as it may be used in its diluted
condition as obtained from the ordinary sulphuric acid chambers.
In a like manner the solution drawn off at the termination of the first step of
the process may be employed in lieu of a fresh solution in operating on a fresh lot
of ore, with the addition of free acid.
I have described my method as applied to the treatment of galena, but the other
ores of lead may be treated in substantially the same manner, the only variation
necessary to note being the proportion of ore treated. Of galena, about 2000 pounds,
as stated, will be the proportion; of. anglesite, about 3600 pounds; of cerussite,
about 2200 pounds.
I employ heat in the first step of the process to hasten the operation; the process
may as well be carried on at the normal temperature, but it will be very much.
slower.
In lieu of the hydrochloric acid, I may use in the first step of the process a
chloride; and' in lieu of the sulphate of soda in that s
t step of the process I may use
an equivalent sulphate.
:
In lieu of sal-soda, I may use in the second step of the process an alkali or an
alkaline earth as an equivalent or another carbonate.
.:
,
While I do not limit myself to the exact proportions employed in the process,
have given those that I prefer. It is best not to use an excess of hydrochloric acid,
or its equivalent. chloride, in the first step, as it will form soluble lead chlorides
[!]

page_text: which are objectionable for various reasons, one of which is that they are not so
readily convertible into insoluble compounds by the action of sodium sulphate as
are the lead oxychlorides produced when a smaller proportion of hydrochloric acid
is employed.
The bluish, slate colored compound from the first step of the process is of a
complex nature, varying according to the ingredients used, their proportions, the
temperature employed and the duration of the treatment; it consists of sulphates,
basic-sulphates oxychlorides and double salts formed by the combination of these,
together with some unconverted ore. The precise interchange of elements and
composition of the products cannot be accurately stated, but as the general
compound is basic in its reaction under chemical tests, it is concluded that its
compounds are as I have stated. But the variations in its composition do not
materially interfere with its successful treatment in the second step of the process,
which has, as a resultant, another complex lead compound. This latter consists in
the main of sub- or basic-carbonates, chloro-carbonates, sulphur compounds and
combinations of these, with some unconverted ore as distinct from a carbonate as
the product of the first step is distinct from a sulphate. This lead compound from
the second step, which is somewhat lighter in shade or colour when dry, than that
from the first step, and of which from 75% to 90% is soluble in nitric or acetic
acid with which it is treated in the fourth step, although complex, produces a pure
salt, as the portions insoluble in the solvent used are inert both to the solvent and
the salt, and go into the residue, thus enabling the operator to obtain therefrom a
purer salt than can be obtained directly from the commercial oxides and carbonates
now used for the production of such salts. This residue, which consists mainly of
undecomposed and partially decomposed ore, and such small percentages of silver
or other precious metal, as exist in the ore, may be allowed to accumulate until a
sufficient quantity is obtained to make a charge of ore, when it can be treated
precisely as herein described; thus the precious metal will be concentrated
conveniently and without extra expense.
The lead compound produced by the second step may be converted into an
impure oxide by heat alone and without the aid of nitric acid or an equivalent
nitrate, and this oxide, being more economically produced, may have a market
value owing to its lower cost, and, when treated with a solvent as described in the
third step of the process, yield corresponding lead salts, but a good commercial
oxide such as that obtained from ordinary carbonate cannot be obtained from it
by heat alone, as this low oxide thus produced has mixed with it some undecom-
posed lead salts, sulphides and unconverted ore. By the treatment with nitric
aoid or nitrate and roasting, it is convertible into any of the commercial forms of
oxide. Before, however, its treatment for conversion into an oxide by the third
step, the silver in it should be extracted, and this may be done after the first step
by any of the known methods for the extraction of silver chloride, the silver at that
stage of the process being in the form of a chloride. I prefer to employ for the
extraction of the silver a hot concentrated solution of sodium chloride, from which
solution the silver chloride is afterward precipitated by dilution with water and the
metallic silver obtained therefrom by digesting the chloride with scraps of copper,
iron, or zinc. Where the object is to form a soluble salt of lead and not an oxide,
the silver in the ore, if any, may be concentrated as before explained.
Lead ores, such as galena, for example, usually contain some iron, zinc, copper
and silver. In the treatment by the first step, all of these metals are converted
and dissolved out except the silver, and are drawn off with the liquid; hence only
the silver need be considered if the object is to produce a pure oxide. If gold is
present, this also will remain in the residuum.
I havé described my process as I prefer to carry it out, but would now add I do
not wish to be limited to the particular agents employed in the first step. The
essential agent in this step is a solution or mixture containing free sulphuric acid.
For the muriatic acid or equivalent chloride, nitric acid or equivalent nitrate may
be employed. I prefer the muriatic acid only on the score of economy. Sulphuric

page_text: acid alone does not attack the ore with vigour, but when some other acid is added as
an intermediate agent the conditions are at once changed. Moreover, the process
may be effected without the aid of the sulphate of soda, but it will proceed much
slower. The addition of the sulphate greatly accelerates the process. Therefore,
so far as this first step is concerned, I do not wish to be limited to the admixture of
muriatic acid or its equivalent with the sulphuric acid, nor do I wish to be limited
to the use of the sulphate.
My process, it will be understood, does not deal with a definite lead compound,
but with an ore, containing a number of compounds and very variable in composition
and at no time during the process do I reduce the lead to a metallic state or produce
or operate upon either lead sulphate or lead carbonate, per se,
I an well aware that the reagents I employ, namely, sulphuric acid, alkalis and
heat, have been before used for purifying crude oxides of iron, copper, cobalt and
nickel, and especially the latter, with a view of obtaining pure metallic nickel,
and this I make no claim to. In such process, the nickel oxide remains unchanged,
the only object of the treatment being to remove foreign substances, such as
sulphate of lime, magnesia and silica.
I do not treat metallic oxides at all but native salts as distinguished from oxides,
and in fact only lead ores which are native lead salts. These salts are decomposed
by the reagents and not in a limited or proper sense purified only by the treatment.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is-
1. The herein described method of treating native lead salts or ores direct for
the production of merchantable lead compounds, which consists in first decomposing
the ground lead ores and converting the lead therein into insoluble lead salts by
subjecting said ore to the action of an acid solution containing free sulphuric acid,
then separating the lead salts from the solution and subjecting them, under the
influence of a moderate heat, to a compound containing an alkaline base for a time,
and finally separating the insoluble lead salts from this solution.
2. The herein described method of treating native lead salts or ores direct for
the production of merchantable lead compounds, which consists in first decomposing
the ground lead ores and converting the lead therein into insoluble lead salts by
subjecting said ore to the action of an acid solution containing free sulphuric acid,
then separating the lead salts from the solution and subjecting them, under the
influence of a moderate heat, to a compound containing an alkaline base for a time,
then separating the insoluble lead salts from this solution and finally roasting said
salts.
3. The herein described method of treating lead ores direct for producing lead
oxides, which consists in first subjecting the ground ore for a time to the action of
an acid solution containing free sulphuric acid and separating the undissolved
residue from the solution of soluble salts, then removing any silver that may be
contained in the said residue, then subjecting the residue, with heat, to a solution
of a compound containing an alkaline base, for a time, and removing the solution
of soluble salts, and then roasting the undissolved residue.
4. The herein described method of treating lead ores direct for the production of
lead oxides, which consists in first subjecting the ground ore for a time to the action
of an acid solution containing free sulphuric acid and separating the undissolved
residue from the solution of soluble salts, then subjecting said residue for a time to
the action of a solution of a compound containing an alkaline base, with heat, and
separating the undissolved residue from the solution of salts, and then mixing with
the residue nitric acid or nitrate, drying and roasting.
5. The herein described method of treating lead ores direct for the production of
lead oxides which consists in first subjecting the ground ore for a time to the action
of an acid solution containing free sulphuric acid and separating the undissolved
residue from the solution of soluble salts, then removing any silver that may be

page_text: contained in the said residue, then subjecting said residue for a time to the action
of a solution of a compound containing an alkaline base, with heat, and separating
the undissolved residue from the solution of salts, and then mixing with the residue:
nitric acid or nitrate, drying and roasting.
6. The herein described method of treating lead ores direct, for the production
of soluble salts, which consists in first subjecting the ground ore for a time to the
action of an acid solution containing free sulphuric acid and separating from the
undissolved residue the solution of salts, then subjecting said undissolved residue to
the action of a compound containing an alkaline base for a time, with moderate
heat, and separating the solution of salts from the undissolved residue; and
finally subjecting the residue to the action of a solvent, and by crystallisation or
evaporation, recovering from the solution the lead salt.
7. The herein described method of treating ores containing lead sulphide direct
for the production of lead oxides or salts, which consists in first mixing together
the ground ore, sulphuric acid, another inorganic acid, as muriatic or nitric acid, a
sulphate, and water, then heating the mixture until the evolution of sulphuretted
hydrogen practically ceases, and then drawing off the solution of salts; second,
subjecting the undissolved residue to the action of a solution of an alkaline
carbonate, with moderate heat, until the mixture shows a permanent alkaline
reaction, and then separating the solution from the undissolved residue.
1004
WM. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicant.