Improvements in the Extraction of Zinc from Ferruginous Liquors, specially applicable to the Treatment of the Spent Liquors of Copper Works.
Year: 1896

page_text: PROVISIONAL SPECIFICATION.
Improvements in the Extraction of Zinc from Ferruginous Liquors,
specially applicable to the Treatment of the Spent Liquors of
Copper Works.
We JOSIAH RIGBY WYLDE, Alkali Manufacturer JOSIAH WYCKLIFFE
KYNASTON, Analytical Chemist, and JOHN BROCK, a Director of the United
Alkali Company Limited, all of G11 Exchange Buildings, Liverpool, in the
County of Lancaster do hereby declare the nature of this invention to be as
follows:-
In the process for obtaining copper in the wet way from burnt cupreous ores, the
calcined ore, still containing some sulphur, is ground up with common salt and the
mixture is furnaced until the copper is rendered soluble in water or in weak
hydrochloric acid. The roasted material is then withdrawn from the furnace and
conveyed to vats wherein it is drenched with water or weak acid and the copper
salt washed out. The solution of copper so obtained is first treated for the removal
of silver, if any be present, and then run into vats containing scrap iron and heated
with steam. The copper is thus precipitated and the iron enters into solution.
The ferrous solution drained from the precipitated copper is the "spent" liquor
above referred to. It often contains considerable quantities of zinc, also in much
larger quantities ferrous chloride, sodium chloride and as the principal constituent,
sodium sulphate. There are also usually traces of copper, arsenic, and nickel.
Previous attempts to extract the zinc from these solutions have failed for the
reason that the processes adopted involved the prior removal of the iron by methods
more or less costly.
According to our invention by the new and improved process hereinafter
described we are able to extract the zinc directly and completely, leaving all the
iron in solution and we obtain the zinc in such a form that it is easily converted
into zinc oxide available for the production of the metal by the usual distillation
process or for use as zinc white.
As is well known, it is not possible to precipitate zinc from solutions containing
free mineral acids by means of hydrogen sulphide, and from neutral solutions of
the inorganic salts of ziuc hydrogen sulphide either fails to effect precipitation or
the precipitation is very incomplete, because the acid liberated by the sulphuretted
hydrogen redissolves the zinc sulphide.
Now we have found that if a base is present in a neutral zinc-solution, capable
of entering into combination with the acid at the moment of its liberation that
then hydrogen sulphide precipitates zinc completely from solutions containing
ferrous salts.
If a solution of caustic alkali, or milk of lime or magnesia, be added to such
neutral solution of mixed ferrous and zinc chlorides just equivalent to the amount
of zinc salt, present, there is produced a precipitate of mixed ferrous and zinc
hydrates and if hydrogen sulphide be then passed into the solution the zinc is
precipitated as sulphide, some of the ferrous hydrate previously thrown down by

page_text: the addition of the base being redissolved, but the zinc sulphide is contaminated
with some ferrous hydrate.
If instead of the caustic solutions or mixtures above mentioned, a carbonate of
an alkaline earth or magnesia or even zinc carbonate be added to such neutral
solution, no change is produced, but when hydrogen sulphide is then passed in, the
zinc is precipitated as sulphide, and the iron remains in solution.
Our improvements in the extraction of zinc from these "spent " liquors consist
then in adding to the liquor, preferably immediately after it leaves the copper vats
and while it is at a temperature of about 150° Fahr., sufficient of a carbonate of an
alkaline earth or magnesia or zinc carbonate to neutralize any free acid that may
be present and then to add such further quantity of a carbonate as is equivalent to
the zinc contained in the liquor under treatment, and then to pass into the liquor
hydrogen sulphide. The reactions that ensue are shewn by the following example
in which calcium carbonate is used.
calcium sulphate simultaneously formed.
The form of calcium carbonate which we prefer is the waste product of the
Chance sulphur recovery process. It is sufficiently pure for the purpose and its
fine state of division renders it very effective, but any other finely divided carbonate
of lime may be used.
After the solution has been freed from excess of sulphuretted hydrogen by the
addition of some fresh liquor, the precipitate of mixed zinc sulphide and calcium
sulphate is collected on a filter bed and washed as perfectly as possible with water
in order to free it from the ferrous chloride. It is then removed to a still similar
in construction to the ordinary Weldon chlorine still and treated with hydrochloric
acid in sufficient quantity to decompose and dissolve the zinc sulphide. The
hydrogen sulphide evolved is used for the treatment of another batch of "spent
liquor as already described. The calcium sulphate remains for the most part
undissolved, and any traces of copper and arsenic also remain insoluble.
The solution of zinc chloride thus obtained may be used for any purpose but we
prefer to treat it as follows:-
The solution of zinc chloride is heated, and the zinc precipitated by the
addition of milk of lime in form of zinc hydrate which when washed, dried, and
calcined is available as zinc white or for reduction to metallic zinc in the
ordinary way.
If the precipitate of zinc sulphide and calcium sulphate have not been washed
free from the ferrous chloride before being treated with the hydrochloric acid it is
necessary, for the removal of the iron, to treat the solution of zinc chloride with a
solution of bleaching powder in sufficient quantity to convert the iron to the ferric
state and then to add calcium carbonate in slight excess, when the iron is removed
as insoluble ferric hydrate. The zinc oxide may then be obtained, as before
described, of a pure white colour.
Dated this 15th day of May 1896
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.

page_text: Improvements in the Extraction of Zinc from Ferruginous Liquors,
specially applicable to the Treatment of the Spent Liquors of
Copper Works.
We, JOSIAH RIGBY WYLDE, Alkali Manufacturer, JOSIAH WYCKLIFFe
KYNASTON, Analytical Chemist and JOHN BROCK, a Director of the United
Alkali Company, Limited, all of G 11 Exchange Buildings, Liverpool, in the
County of Lancaster, 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:-
In the process for obtaining copper in the wet way from burnt cupreous ores, the
calcined ore, still containing some sulphur, is ground up with common salt and the
mixture is furnaced until the copper is rendered soluble in water, or in weak acid.
The roasted material is then withdrawn from the furnace and conveyed to vats
wherein it is drenched with water or weak acid and the copper washed out. The
solution of copper so obtained is first treated for the removal of silver, if any be
present, and then is run into vats containing scrap iron and heated by steam. The
copper is thus precipitated and the iron enters into solution. The ferrous solution
or spent liquor drained from the precipitated copper often contains considerable
quantities of zinc, also, in much larger quantity, ferrous chloride, sodium chloride
and as the principal constituent, sodium sulphate. There are also usually traces of
copper, arsenic, nickel and cobalt.
Previous attempts to extract the zinc from these spent liquors have failed for
various reasons. Some have failed because the processes have involved the prior
removal of the iron by methods so costly as to be prohibitive whilst others in
which hydrogen sulphide has been proposed as the precipitant, have failed, because
the precipitation by this agent is very incomplete, the precipitate itself is slimy
and unworkable and of no value, and the sulphur of the hydrogen sulphide used
is lost.
This invention is based upon the discovery that, if a substance such as calcium
carbonate be present in a neutral zinc solution it is capable of neutralizing the acid
at the moment of its liberation, and then hydrogen sulphide precipitates zinc
completely from solutions containing ferrous salts and that the hydrogen sulphide
used can be advantageously regenerated from the zinc precipitate and used over
and over again indefinitely for the treatment of fresh quantities of ferruginous
liquor, replacing from time to time slight mechanical or other loss. The calcium
carbonate which is a waste product of the Chance sulphur process is well adapted
for the purpose of this invention but any other finely divided calcium carbonate
may be used.
The reaction which takes place is expressed as follows:
In carrying out this invention, the ferruginous liquor is introduced into covered
flag-stone cisterns, which may be of a construction, similar to that of the well
known Weldon-chlorine stills. It is preferred to employ a series of three of these
cisterns, two to be in operation whilst the other is being discharged of its contents
and refilled with ferruginous liquor.
Into each of the cisterns filled up to say within 12 to 18 inches of the cover with

page_text: ferruginous liquor preferably taken as it leaves the copper precipitating tanks at a
temperature of about 150° Fahrenheit sufficient calcium carbonate to neutralize
any free acid that may be present is first introduced and then a further quantity of
calcium carbonate is added as nearly as possible equivalent to but not exceeding
the zinc chloride contained in the liquor, molecule for molecule. There is then
blown into the mixture in the first of the series of cisterns (preferably by means
of a gas pump) hydrogen sulphide gas. The gas which remains unabsorbed in
this first cistern is conveyed by a connecting pipe between the two cisterns to the
bottom of the second cistern and in passing through the mixture in this second
cistern, the hydrogen sulphide escaping from the first cistern is completely, or
almost completely, absorbed. Each of the cisterns is fitted with the usual or any
suitable arrangement for comminuting and distributing the gas so as to bring it
into intimate contact with the mixture. When the contents of the first cistern are
saturated with hydrogen sulphide, the gas supply is cut off and conveyed directly
to the second cistern and from this to the third cistern of the series which latter
has in the meantime been charged with ferruginous liquor and the required quantity
of calcium carbonate. In like manner, when the second cistern becomes saturated
with hydrogen sulphide, the supply is diverted to the third cistern and from this to
the first cistern which has in the meantime been emptied and recharged as before
described. The reactions which take place in the precipitating cisterns result in
the production of a mixed precipitate of zinc sulphide and calcium sulphate in
equivalent or approximately equivalent proportions and the whole of the zinc
contained in the ferruginous liquor is removed from the solution.
When commencing operations the required supply of hydrogen sulphide is
conveniently obtained by treating alkali waste (a crude calcium sulphide) with
hydrochloric acid which may be done in a Weldon still of the ordinary construction.
But when a sufficient supply of the mixed precipitate of zinc sulphide and calcium
sulphate has been obtained, this zinc mud is substituted for the alkali waste and
the zinc sulphide being thus decomposed yields the hydrogen sulphide required to
precipitate the zinc from a further batch of ferruginous liquor and thus the zinc
mud from previous operations yields continuously the hydrogen sulphide required
for carrying out this invention.
When a batch of ferruginous liquor has been saturated with hydrogen sulphide
in the manner herein-before described, and the gas supply cut off, a sufficient
quantity of fresh ferruginous liquor is added to the batch to remove the excess of
hydrogen, and the batch is then allowed to stand at rest for say an hour when the
precipitate will have subsided. The clear liquor is then drawn off, and the zine
mud run to a filter bed, which may be of any ordinary or suitable construction, and
when the liquor has drained through, sufficient water is run upon the precipitate to
wash it as perfectly as possible from the ferrous solution.
The crude zine precipitate retained by the filter is removed therefrom and, as
hereinbefore described, is transferred to the Weldon-still for treatment with
hydrochloric acid so as to obtain the hydrogen sulphide required for the precipi-
tation of the zinc from another batch of ferruginous liquor. The zinc sulphide
having thus been completely decomposed and the hydrogen sulphide driven off,
there remains in the still a solution of zinc chloride and the calcium sulphate for
the most part undissolved. The contents of the still are run to a filter bed upon
which the calcium sulpbate remains and the solution of zinc chloride passes
through and may be used for any purpose for which it can be employed.
If it be desired to obtain the zinc as oxide suitable for reduction to metallic zinc
in the ordinary way, the solution of zinc chloride is transferred to a suitable
vessel and heated to boiling by means of steam. Milk of lime is then added in
slight excess so as to render the solution alkaline which may be determined by the
use of tumeric paper. The precipitate of zinc hydrate so obtained is collected,
washed, dried, and calcined and the resulting oxide is available for any desired
purpose such as for reduction to metallic zinc in the usual way.
If the precipitate of zinc sulphide and calcium sulphate has not been washed free

page_text: from the ferrous chloride before being treated with hydrochloric acid and if it be
desired to obtain a zinc oxide of high purity, the solution of zinc chloride containing
iron is treated with a solution of bleaching powder in sufficient quantity to convert
the iron to the ferric state and then calcium carbonate in slight excess is added.
The iron now becomes insoluble and is removed by subsidence or by filtration.
The solution of zinc chloride thus purified is then decomposed by the addition of
milk of lime as hereinbefore described.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. The extraction of zinc from ferruginous liquors by treating the said liquors
with hydrogen sulphide in the presence of a sufficient quantity of calcium carbonate
to neutralize any free acid which may be present or which may be liberated by such
treatment.
2. In a process as claimed by Claim 1, and for use in the precipitation of zinc
from further quantities of ferruginous liquor the reproduction of the hydrogen
sulphide required in this process by treating with hydrochloric acid the zinc sulphide
obtained in a previous operation of the said process.
3. The process as a whole consisting in treating ferruginous liquors containing
zinc with hydrogen sulphide in the presence of calcium carbonate dissolving the
sulphide of zinc in hydrochloric acid for the regeneration of hydrogen sulphide
for re-use, and treating the resulting chloride of zinc solution either with lime only
or first with bleaching powder and then with lime, all substantially as hereinbefore
explained.
Dated this 15th day of February 1897.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.