Improved Process for Treating Mixed Sulphide Ores.
Year: 1897

page_text: Date of Application, 19th Oct., 1897-Accepted, 20th Nov., 1897
Communicated from abroad by ERNEST CUMMINGS KETCHUM, of 10 Rutland
Square, Boston, in the County of Suffolk, and State of Massachusetts, U.S.A.,
Electrical Engineer].
Improved Process for Treating Mixed Sulphide Ores.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of The Agency for Foreign
Patent Solicitors, 322, High Holborn, in the County of Middlesex, 6, Lord Street,
Liverpool, and 6, Bank Street, Manchester, both in the County of Lancaster,
and Lower Temple Street, Birmingham, in the County of Warwick, Civil
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:-
My invention has for its object to provide an improved process by means of
which the lead and zinc which are contained in mixed sulphide ores may be
extracted commercially at a lower cost than by any other means or process known
to me. My invention is fully set forth in the following description and the novel
features thereof are pointed out and clearly defined in the claims at the end of this
specification.
For the purpose of more clearly setting forth my improved process I have made
reference in the following description to the accompanying drawings, in which
at Fig. 1 I have shown a diagram illustrative of the apparatus by means of which
my process is practised. Fig. 2 is a detail hereinafter referred to. Fig. 3 is a
diagrammatic view showing a modified arrangement of the apparatus shown
Fig. 1, reference to which will hereafter be made.
In practising any process I first break the ore into fine particles by means of a
crushing mill or similar device. The ore is then concentrated in any well known
manner, if concentration is necessary. I then subject the ores that have been thus
crushed to heat in a reverberatory or other roasting furnace of any well known
construction. In the roasting process which goes on in the furnace it is important
that as nearly as possible what is known as a dead roast" should be obtained.
In the roasting process the sulphides are changed to oxides, practically all the
sulphur being driven off in the form of sulphur dioxide which is saved in the
well known manner and which is particularly fitted for the manufacture of sul-
phuric acid. After the ore has been roasted a fraction of a per cent. of sulphur
will remain in the form of sulphate of zinc, and another fraction in the form of
undecomposed sulphide of zinc. I then preferably leach the roasted ores with
water which serves to remove the slight trace of sulphate of zinc. This step is,
however, not absolutely necessary to the successful practising of my process.
then place the ore which has been thus treated in vats, indicated at 1 in the
accompanying drawing, containing mechanical agitators indicated at 111 which
may be of any well known construction, and subject it to the action of a dissolving
fluid containing caustic alkali in solution. This solution contains preferably
about twenty-five per cent. of alkali, but the precise, percentage may be varied
somewhat. While the ore is in the said solution in the dissolving vats, the
I

page_text: solution is kept at about 210° Fahrenheit, that is the temperature is kept as high
as possible without boiling the solution. The effect of this solution on the ore is
to dissolve both the lead and the zinc contained therein forming from the lead and
zinc what may be described as plumbate of potash and zincate of potash, that is
to say, if potash be employed as the caustic, or corresponding soda salts if soda
is used. These terms, however, are, in my opinion, somewhat misleading, since
the lead and zinc may be regarded as being present in the solution of caustic
alkali in the form of oxide of lead and oxide of zinc. If there is iron in the ore
it remains as ferric oxide in the residue or tailings. The silver will also remain
in the tailings, generally as metallic silver, and the copper will remain as cupric
oxide. All other metals will also remain in the tailings with the iron and silver,
and may be recovered by subjecting the tailings to treatment in any well known
manner for the recovery of these metals.
The solution of caustic alkali which contains, as above stated, oxide of lead and
oxide of zinc, is then caused to flow through pipes 14 into a series of tanks or vats
indicated at 2 and 4 in the accompanying drawings which are preferably of iron and
are connected by means of glass or earthenware tubing, or equivalent non-corrosive
insulating material. Each of the said tanks contains sets of anodes and cathodes
which may be of well known construction and which are in the circuit of an
electric current, the conducting wires being shown at 3. The first tanks indicated
at 2, of the series of tanks, are the tanks in which the lead oxide contained in the
solution will be decomposed by the electric current, the decomposition resulting
in the production of caustic potash or soda and metallic lead, the latter being in
the form of crystals or spongy masses which are deposited on the cathode side,
while oxygen is freed at the anode. The oxygen thus freed may be saved as a
by-product if desired.
The electro-motive-force to which the solution in these tanks, indicated at 2,
is subjected is substantially about one and eight-tenths volts. This current will
decompose the lead oxide, but will not affect the zinc oxide which requires a
current of a higher electro-motive force, namely about two and one-tenths volts.
The lead, which is deposited on the lead cathodes in the form of small crystals
or spongy masses, as above stated is raked off at intervals and subjected to pres-
sure in a hydraulic press or the like, and is thus condensed and formed into small
pigs.
To ensure satisfactory results, I employ a cup shown at 10, which is preferably
made from asbestos cloth or earthenware. An anode 11 of platinum or other
insoluble conducting material may be employed, the said anode being placed in
the said cup. Inside the cup I place a solution of pure caustic, that is a caustic
solution free from lead, or the like. The anode 11 is immersed in this pure
caustic solution and outside the cup 10 within the cell is the caustic solution
which contains the lead and zinc, as above stated. By this arrangement I prevent
the formation of a peroxide of lead at the anode and this is undesirable for the
efficient working of my process.
The caustic solution containing the zinc oxide which, as above stated, will not
be affected by the electric current in the lead tanks, indicated at 2, flows on into
the tanks indicated at 4, it being understood that the tanks are so arranged with
reference to each other that the liquid will pass by gravity from one tank to the
adjacent one. In the tanks indicated at 4 à current is applied having a higher
electro-motive-force, namely, about two and one-tenths volts, and this effects a
decomposition of the zinc oxide, metallic zinc being deposited on the zinc cathode
in a hard mass. The zinc cathode thus covered may be melted up and formed
into pigs of zinc. After a zinc cathode is thus covered with a deposit of metallic
zinc a small piece thereof may be taken and rolled out into a thin sheet to form a
new cathode to replace the one removed. The anodes employed in all the tanks
are of insoluble conducting material such as carbon or platinum. As previously
stated, however, I do not confine myself to the use of any specific electrical
apparatus, since apparatus of well known construction may be employed.

page_text: The
After the oxides of lead and zinc have thus been decomposed and removed, the
caustic solution may be returned into the dissolving tank to be used over again.
After frequent use the caustic solution becomes impaired, probably by reason of its
slow conversion into carbonate through carbon dioxide in the atmosphere.
solution which is thus impaired is useless for this purpose to the extent of the
presence of the carbonate. Since also there may be a slight amount of silica present
in the ores, there is apt to be a slow formation of silicate of soda which impairs the
value of the caustic solution in the same manner as does the presence of carbonate.
A caustic solution when impaired by the presence of carbonate and silicate may be
restored by boiling with caustic lime. It is therefore not a difficult matter to
restore the impaired caustic solution.
The decomposition by electrolytic action is carried on in the presence of heat
in all cases.
It is therefore desirable that all the tanks in the system' should be
kept heated to over 200°. Any well known arrangement for applying heat may
be employed.
In practising my process, it is not essential that the caustic solution should,
after the lead has been removed pass directly from the last of the series of lead
tanks to the first of the series of zinc tanks 4, since the lead tanks and zinc tanks
may be arranged in independent groups, as is indicated in the diagrammatic view
shown in Fig. 3. In an apparatus having this latter arrangement, after the lead
has been removed, which in all cases must precede the removal of the zinc, the
caustic solution containing the zine alone will be returned to the dissolving tank
or tanks, indicated at 1, from which it passes again into the receiving vat 15 and
thence is permitted to flow through the zinc tanks 4 where the zine is removed.
The direction of flow of the solution is indicated by the arrows in said Fig. 3, and
at 17, 17, in said figure are indicated pumps which may be employed to cause a
flow of the said caustic solution. At 111 are indicated mechanical agitators which
are located within the dissolving vats and which may be of any well known con-
struction. I preferably employ agitators which comprise a vertical shaft 112,
provided with means for causing rotation thereof, said shaft being provided with
horizontally projecting arms or paddles 113 by means of which the contents of
the vat may be stirred up or mechanically agitated.
In Fig. 1 the pipes 14 lead from vats I to a receiving vat 15 from which the
solution passes into the tanks 2 and 4. The pipe 16 leads from the last tank 4
to the vats 1, a pump 17 being employed to occasion a flow of the liquid.
Having now particularly ascertained and described the nature of my said
invention and in what manner the same is to be performed as communicated to
me by my foreign correspondent I declare that what I claim is:-
1. The process of treating mixed sulphide ores containing lead and zinc, which
consists in first roasting the ores, then subjecting the roasted ores to the action
of a solution of caustic alkali in the presence of heat to remove from the ores the
lead and zinc, then subjecting the caustic solution containing the lead and zinc
to electrolytic action in the presence of heat to remove the lead, in a cell or cells
in which the anode is immersed in a solution that is free from lead and that also
is separated by a porous medium from the electrolyte containing the lead and zine
and finally subjecting the solution in which the zinc remains to electrolytic action,
also in the presence of heat, to remove the zinc, employing electric currents of
different electro motive force in effecting the successive decompositions, as set
forth.
2. The process of treating mixed sulphide ores containing lead and zinc, which
consists in first roasting the ores, then subjecting the roasted ores to the action
of a solution of caustic alkali in the presence of heat to remove from the ores the
lead and zinc, then subjecting the caustic solution containing the lead and zinc
to electrolytic action in one or more cells to remove the lead, the anodes of which
cells are immersed in a volume of pure caustic solution which is separated by a

page_text: porous medium from the electrolyte containing the lead and zinc, and then sub-
jecting the caustic solution or electrolyte containing the zinc only, to electrolytic
action in one or more cells to remove the zinc, substantially as set forth.
Dated this 19th day of October 1897.
W. P. THOMPSON & Co.,
322 High Holborn, London, W.C., Patent Agents for the Applicant.