Improvements in the Treatment of Solutions of Ores Containing Zinc for the Recovery of Zinc as Oxide.
Year: 1896

page_text: Date of Application, 23rd July, 1896
Complete Specification Left, 21st Apr., 1897-Accepted, 29th May, 1897
PROVISIONAL SPECIFICATION.
Improvements in the Treatment of Solutions of Ores Containing
Zinc for the Recovery of Zinc as Oxide.
I, ALEXANDER MELVILLE CLARK, of the Firm of A. M. & Wm. Clark of
53, Chancery Lane in the County of Middlesex, Fellow of the Chartered Institute
of Patent Agents, do hereby declare the nature of this invention (a communication
to me by Edgar Arthur Ashcroft of Newcomnien Street, Newcastle, in the Colony
of New South Wales, Electrical Engineer,) to be as follows:-
The object of this invention is to obtain zinc oxide from ores or solutions
containing zinc, in a cheaper and more convenient manner than heretofore. It is
well known that the recovery of zinc from ores or solutions presents great difficulty
because its more easily formed salts are not easily decomposed, are volatile, or
present other hampering tendencies. I have discovered that these difficulties can
be obviated and that zinc can be economically recovered from ores or solutions in
the form of zinc oxide by the following process.
The zinc being first obtained in solution as sulphate or chloride, the addition of
zinc oxide to such solution will precipitate their zinc contents together with that
of the added oxide in compounds known as basic zinc salts. The composition of
these basic salts varies with the condition of production but their most general
composition is:-ZnSO4 +3 ZnO + H2O or ZnCl. + 3 ZnO + H₂O. These basic
salts may be converted into zinc oxide much more readily than the corresponding
neutral salts and as zinc oxide is the agent I employ for the production of the
basic salts a suitable proportion of the zinc oxide finally produced can be again
used for the treatment of fresh quantities of zinc solution thus making the process
cyclical. The balance of zinc oxide not required for the treatment of further
solutions is available for disposal in any of the various commercial industries in
which zinc oxide is used, notably it can be reduced to metal by retorting in
distillation furnaces or by electrolytic processes. The sulphuric acid can also
be recovered from the basic zinc salts and again used cyclically for obtaining the
solutions of sulphate of zine from the ores.
In applying this process to the treatment of zinc-bearing ores, I prefer to operate
as follows:-The zinc is first obtained in solution from roasted ores by means of
sulphuric acid and the solution is heated to between 80 and 100 degrees Centigrade
and brought to a strength of about 200 grammes per litre more or less. Zinc
oxide is then added to the hot solution in the proportion of about 2 gramines of
zinc as oxide for every gramme of zinc in the solution. The mixture is then
intimately mixed by stirring in a grinding pan or other suitable apparatus and in a
short time the mixture will become pasty owing to the formation of basic salts and
the absorption of the water of solution. The pasty mass is then converted into zinc
oxide by either of the following methods:-
First. It can be heated to a strong red heat in a muffle or other furnace until
the sulphuric acid is driven off leaving the zinc oxide residue. The resultant
gases can be collected and reconverted in lead chambers into sulphuric acid for
use again.
Second. The decomposition of the salts can be facilitated and effected at a much
lower temperature by intimately mixing carbon, preferably in the form of finely
powdered charcoal, with the pasty mass in the proportion of about one-twentieth of

page_text: the weight of the zinc to be recovered from the solutions and subjecting the mixture
to a uniform temperature corresponding to a few degrees below the melting point.
of aluminium metal, sulphurous acid gases are disengaged and can be converted into
sulphuric acid in lead chambers.
Alternatively the zinc sulphate solution may be used weaker; it is then heated,
put into agitators, and zinc oxide being added in suitable proportion it is stirred
until the reaction has taken place. The basic salt is then collected and separated
by filtration or other means from the remaining liquor which need not be entirely
freed of zinc and can be used over again for leaching fresh ore after the addition
of sulphuric acid. The precipitate is then dried and converted into zinc oxide by
either of the methods described above.
Although I have confined the foregoing description of my process to zinc
sulphate solutions, other zine salts, such as zinc chloride, re-act with zinc oxide in
a similar manner and may in some cases be employed with advantage.
Datad this 23rd day of July 1896
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
Improvements in the Treatment of Solutions of Ores Containing
Zinc for the Recovery of Zinc as Oxide.
I, ALEXANDER MELVILLE CLARK of the Firm of A. M. & Wm. Clark of
53, Chancery Lane in the County of Middlesex, Fellow of the Chartered Institute
of Patent Agents, do hereby declare the nature of this invention (a communication
to me by Edgar Arthur Ashcroft of Newcommen Street, Newcastle, in the
Colony of New South Wales, Electrical Engineer,) 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 obtain zinc oxide from ores or solutions
containing zine, in a cheaper and more convenient manner than heretofore.
It is well known that the recovery of zinc from ores or solutions presents great
difficulty, because its more easily-formed salts are not easily decomposed, are
volatile or present other hampering tendencies. It has been discovered that
these difficulties can be obviated and that zinc can be economically recovered
from ores or solutions, in the form of zinc oxide, by the following process:-
The zinc being first obtained in solution (for instance as sulphate) the addition
of zinc oxide to such solution will precipitate the zinc contents together with that
of the added oxide in compounds known as basic zinc salts. The composition of
these basic salts varies with the conditions of production, but their composition is
indicated by the following formula
ZnSO, +3 ZnO + H₂O
These basic salts may be converted into zinc oxide much more readily than the
corresponding neutral salts, and as zinc oxide is the agent I employ for the
production of the basic salts, a suitable proportion of the zine oxide, finally
produced, can be again used for the treatment of fresh quantities of zinc solution,
thus making the process cyclical. The balance of zine oxide not required for
the treatment of further solutions is available for disposal in any of the

page_text: various commercial industries in which zinc oxide is used; notably it can be
reduced to metal by retorting in distillation furnaces or by electrolytic processes.
The sulphuric acid can also be recovered from the basic zine salts and again
used cyclically for obtaining the solutions of sulphate of zinc from the ores.
In applying the process to the treat:nent of zinc-bearing ores, I prefer to operate
as follows:-
The zinc is first obtained in solution from roasted ores by means of sulphuric acid
and the solution is heated to between 80 and 100 degrees Centigrade, and brought
to a strength of about 200 grammes per litre more or less. Zinc oxide is then
added to the hot solution in the proportion of about 2 grammes of zinc as oxide for
every gramme of zinc in the solution.
The mixture is then intimately mixed by stirring in a grinding pan or other
suitable apparatus: in a short time the mixture will become pasty, owing
to the formation of basic salts and the absorption of the water of solution.
The pasty mass is then converted iuto zinc oxide by either of the following
methods:-
First. It can be heated to a strong red heat in a muffle or other furnace until
the sulphuric acid is driven off, leaving the zinc oxide residue. The resultant
gases can be collected and reconverted in lead chambers into sulphuric acid for use
again.
Second. The decomposition of the salts can be facilitated and effected at a much
lower temperature by intimately mixing carbon, preferably in the form of finely-
powdered charcoal, with the pasty mass in the proportion of about one-twentieth of
the weight of the zinc to be recovered from the solution, and subjecting the mixture
to a uniform temperature corresponding to a few degrees below the melting point
of aluminium metal. Sulphurous acil gases are disengaged, and can be converted
into sulphuric acid in lead chambers.
Alternatively the zinc sulphate solution may be used weaker. It is then heated,
put into agitators, and, zinc oxide being added in suitable proportion, it is stirred
until the reaction has taken place. The basic salt is then collected and separated
by filtration or other means from the remaining liquor, which need not be entirely
freed of zinc and can be used over again for leaching fresh ore after the addition
of sulphuric acid. The precipitate is then dried and converted into zinc oxide by
either of the methods described above.
Although I have confined the foregoing description of the process to zinc
sulphate solutions other zinc salts, such as zinc chloride, react with zinc oxide in a
similar manner and may in some cases be employed with advantage, a suitable
farther process being chosen for treating the basic salt so produced.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
I claim is :-
1. In the treatment of zinc sulphate in solution, the converting of basic sulphate
obtained as herein decribed into zine oxide by intimately mixing therewith carbon
(preferably as powdered charcoal) in approximately the proportion stated and
heating the mixture approximately to the temperature specified substantially as
described and for the purposes specified.
2. The herein described process for the treatment of ores or solutions containing
zinc consisting in :-
(a) Obtaining by known methods solutions of zinc sulphate of a strength
approximately as stated;
(6) Adding zinc oxide in quantities approximately as specified and stirring
the mixture in a suitable apparatus until a pasty consistency is obtained;
(c) Treating the resulting product for the production of zinc oxide, either by
strongly heating it in a furnace, or by first intimately mixing with it carbon
(preferably as powdered charcoal) in the proportion approximately as
stated, and finally heating the mixture in a furnace at a uniform temperature

page_text: approximately as specified for the purpose of converting it into zine
oxide, sulphuric or sulphurous acid gas being disengaged in either casc,
all substantially as described and for the purposes specified.
3. The herein described process of treating zinc ores, which consists in
obtaining from the said orcs solutions of basic zinc salts, mixing the said basic
salts with carbon, and heating the mixture to produce zinc oxide, substantially as
set forth.
Dated this 21st day of April 1897.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.