Improved Process for the recovery of Zinc from Refractory Zinc Bearing Ores.
Year: 1898

page_text: Date of Application, 21st Feb., 1898-Accepted, 14th May, 1898
COMPLETE SPECIFICATION.
Improved Process for the recovery of Zinc from Refractory Zinc
Bearing Ores.
I, JOHN JONES, of No. 18, Brunswick Street, East Melbourne, in the Colony of
Victoria, Australia, 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:
-
. The object of this invention is to provide an economic and efficient process
whereby zinc is recovered from its ores. I first obtain a mixed solution of sulphate
of zinc and sulphate of ammonia and this subject to electrolysis for the deposi-
tion of the zinc. The essential feature in the electrolytic treatment being that the
catholyte solution is kept in a slightly acid state and is not allowed to become
either too acid or to become alkaline so that a continuous deposit of zinc is obtained
which is not redissolved by the solution.
The zinc bearing ore is first roasted to sulphate sulphite or oxide, the zinc is then
leached out of the roasted ore by water (as sulphate) or by an acid solution, the
solution of zinc thus obtained is next to be freed from its iron and other impurities
this may be accomplished by any well known means but I prefer to employ an
absorbing tower of ordinary construction in which the solution is subjected to pro-
ducer gases containing ammonia whereby iron and some other impurities are pre-
cipitated the solution in this case being subjected to the gas in the tower for a
limited time only so as not to allow of the precipitation of the zinc. Any
manganese will remain in solution with the zinc and provision is made (as here-
after) for its removal.
After purification the solution has added to it sulphate of ammonia in sufficient
quantity to supply the ammonium ions to the catholyte of the electrolytic cell as
hereafter described and the mixed solution of sulphate of zinc and sulphate of
ammonia is then to be treated by electrolysis.
I prefer to obtain the mixed solution of sulphate of zinc and sulphate of ammonia
in the following manner-The purified solution of sulphate of zinc has free acid
added to it preferably ten to twenty-five per cent., it is then led to an absorbing
tower similar to that employed for purifying the zinc solution and in which it is
subjected to gases as before. The gases are generated in an apparatus in which
water gas or producer gas or both are made such gas being made so that very little
tar will be carried with the gases while the ammonia will not be destroyed,
the free acid in the zinc sulphate solution will thus be caused to combine with the
ammonia contained in the gases so as to form sulphate of ammonia whilst the
mixed solution of sulphate of ammonia and sulphate of zinc will be conducted to
the electrolytic cell or battery. The gases from the producer (thus freed from
ammonia) may be conducted from the tower and employed as fuel for the engines
operating the dynamos or be conducted to the furnace employed in roasting the
ore, or used for other like purposes..
The mixture of sulphate of zinc and sulphate of ammonia is allowed to flow into
the electrolytic vats each cell of which is divided into two compartments by means

page_text: of a porous septum on one side of this septum an anode of metal or other conductor,
preferably lead, is used and on the other side a cathode of metal or conductor pre-
ferably zinc is placed. The mixture of sulphate of zinc and sulphate of ammonia
is allowed to flow into the anode compartment while either acid zinc sulphate or
acid zinc sulphate and sulphate of ammonia flows into the cathode compartment
the added sulphate of ammonia being for the purpose of producing ammonium ions
in the catholyte and also hardening the zinc coat as it is deposited. The action
will therefore be as follows: On the electric current being applied to the anode and
cathode zinc is deposited on the cathode and ammonium liberated in catholyte the
ammonium combining with the free acid of catholyte forming sulphate of ammonia
and thereby the free acid is kept from accumulating round or near the cathode
surface so as to prevent the re-dissolving of the deposited zinc.
SO, is liberated at the anode which combining with the H₂ of the water forms
sulphuric acid.
The zinc being thus deposited and the catholyte solution becoming less acid by
the passage of SO, ions to the anode, and ammonium ions to the cathode, the
catholyte would in time become alkaline, so that fresh acid must be supplied to the
catholyte either by the inflowing acid zinc sulphate or by adding fresh acid, or
allowing some of the contents of the anode chamber to flow into the cathode
chamber, thus making and maintaining the solution sufficiently acid for the con-
tinued deposition of the zinc.
In lieu of solution flowing from anolyte to catholyte it might be arranged to
flow to next anode compartment or from catholyte to next cathode compartment
of a series and fresh acid solution added to the catholyte as required to maintain it at
a low degroe of acidity, while sulphate of ammonia is added to the anolyte solution
in sufficient quantity to maintain the passage of the ammonium ions to the
catholyte so that practically the whole of the zinc will be deposited while a solution
of sulphate of ammonia will be formed in the cathode compartment.
Any manganese that may not have been previously eradicated is partly pre-
cipitated at the anode by a little fine carbon or hydro-carbon which is added to the
anolyte solution for the purpose of reducing the permanganates or permanganic
acid formed and thereby precipitating them as lower oxide.
At the end of the process there will be a solution of sulphate of ammonia, con-
taining some sulphate of zinc in the cathode chamber, and a solution of sulphuric
acid containing a little sulphate of zinc, in the anode chamber together with a
little iron, manganese, or other impurities which might not have been previously
completely extracted. The sulphuric acid can be used again for leaching the ore,
and the sulphate of ammonia solution can be used again in the electrolytic cells,
or otherwise.
In lieu of the employment of sulphates in the herein described process I may
employ chlorides.
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. In a process for treating refractory zinc ores.
Passing a mixture of sulphate of zinc and sulphate of ammonia into the anode
compartment of an electrolytic cell (which is divided into two compartments by
means of a porous septum) while either acid zinc sulphate alone or acid zine
sulphate and sulphate of ammonia are passed into the cathode compartment of
same so that the zinc contained in the solution is deposited at the cathode while.
the liberated ammonium combines with the free acid of catholyte so as to form
sulphate of ammonia and whereby the catholyte solution is maintained at a low
degree of acidity substantially as and for the purposes set forth.
2. In a process for treating refractory zinc ores.
Adding to the herein described catholyte during electrolytic action acid zine
sulphate or fresh acid, or otherwise allowing some of the contents of the anode

page_text: chamber to flow into the cathode chamber in sufficient quantity to maintain the
solution in a slightly acid state whilst sulphate of ammonia is added to the anolyte
substantially as and for the purposes set forth.
3. In a process for treating refractory zinc ores.
Adding to the herein described anolyte solution a little fine carbon or hydro-
carbon for the purpose of reducing the permanganates or permanganic acid formed
and thereby precipitating them as lower oxides substantially as and for the pur-
poses set forth.
4. The complete process for treating refractory zinc ores for the recovery of the
zinc which consists in leaching the zinc from roasted ore freeing the solution thus
obtained from its iron and some other impurities adding to the solution sulphate
of ammonia and conducting the mixed solution to the anode compartment of an
electrolytic vat having an acid solution in its cathode compartment substantially
as and for the purposes described.
Dated this 21st day of February 1898.
J. JONES,
Per W. H. Beck,
Agent, 115, Cannon Street, London, E.C.