IMPROVEMENTS IN SEPARATING GOLD AND SILVER FROM LEAD CONTAINING THE SAME
Year: 1872

page_text: -LETTERS PATENT to John Henry Johnson, of 47, Lincoln's Inn Fields,
in the County of Middlesex, Gentleman, for the Invention of
"IMPROVEMENTS IN SEPARATING GOLD AND SILVER FROM LEAD CONTAINING
THE SAME."-A communication from abroad by Clement Roswag-
and Alfred Nicolle Pauville, both of Paris, in the Republic of
France.
PROVISIONAL SPECIFICATION left by the said John Henry Johnson
at the Office of the Commissioners of Patents, with his Petition,
on the 31st January 1872.
I, JOHN HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County
of Middlesex, Gentleman, do hereby declare the nature of the said
Invention for "IMPROVEMENTS IN SEPARATING GOLD AND SILVER FROM LEAD
CONTAINING THE SAME," a communication to me from abroad by Clement
Roswag and Alfred Nicolle Pauville, both of Paris, in the Republic of
France, to be as follows:-
This Invention consists of the neculiar metallurgical processes herein-

page_text: after described, which have for their object the extracting, from argenti-
ferous or auriferous lead, of the precious metal contained therein, whether
silver or gold, or both, by the aid of any metallic reagent, such as zinc,
magnesium, aluminium, or the alloys of these two latter metals -with
zinc, and, lastly, by mercury.
Hitherto the zinc employed as a reagent has been positively lost, for
zinc in the condition of oxide (zinc white), or in the condition of
sulphate or chloride, cannot be considered as recovered. The latter two
products especially are commercially useless, and are the necessary
residuum of any treatment of rich 'scum with a cheap mineral acid
(chlorhydric or sulphuric acid). By regenerating the zinc however, or
any other metallic reagent performing the same functions, the Inventors
are enabled, first, to desilverize lead at the same cost, whatever pro-
portion of the precious metal it may contain; and, secondly, to effect an
enormous reduction in the net cost of desilverizing.
The method herein-after, described has this twofold object, and forms
the subject of this Invention. It moreover embraces two novel sub-
stitutes for zinc which had not hitherto been employed for this purpose,
viz., magnesium and aluminium, as also the alloys of these metals
with zinc. All these conditions are fulfilled by the aid of a single agent,
viz., mercury, which is also regenerated.
In seeking a substitute for the reagent zinc the Inventors first of all
tried magnesium which is so closely similar to it. This metal effects the
desilverization rapidly and perfectly, but it is costly; it is still more
oxydizable than zinc, and it is not so favourable to the operation of
desilverizing as aluminium. Aluminium desilverizes less rapidly; the
incorporation of the lead is also well effected by the aid of the box which
has already been used for the introduction of the zinc at the bottom of
the boiler containing the pig lead in fusion at a dull red heat.
A mixture of zinc and aluminium öffers many advantages. The
essential features therefore of this part of the Invention are the appli-
cation and use of magnesium or aluminium, either separately or alloyed
with zinc, in the treatment of pig lead with a view to desilverizing the
same; also the treatment with mercury of the rich scum; whether such
scum be obtained by the metals above mentioned and their alloys with
zinc, or by zinc alone; and in the last case whether oxydised or not.

page_text: In effecting the treatment of the rich scum or dross resulting from
the preceding operations by mercury or amalgamation, the said scum is
first skimmed off and deposited on a metal plate after having been
eliquated, that is to say, after as much lead as possible has been
separated by fusion at a low temperature in a cast-iron boiler. The
scum has a granular appearance, and may be readily crushed with a
shovel on the plate when warm. In this manner it is reduced to a
finely pulverized state; it is then caused to pass through a sieve, the.
lumps that do not pass being introduced again into the boiler, and the
operation repeated. This pulverization may also be effected when the
scum is in a heated state, in a machine similar to a coffee mill. The
finely pulverized substance is introduced into an amalgamating cask, or
into any suitable form of churn or mixer. Water is added, by pre-
ference acidulated with a little nitric acid and old scrap iron, in order to
effect the beating up of the mixture with the mercury which has been
previously introduced into the cask or churn. It is desirable to operate
with warm water. Salt water (warm) containing a large quantity of
salt may also be employed. The amalgamation is effected by the rapid
rotation of the cask. If the scum contains aluminium this will not
amalgamate, but zinc, silver, and lead will unite with mercury.
By adding a sufficient dose of mercury to the bath, when it is ascer-
tained that the amalgamation is complete, the aluminium powder is
collected with a ladle and re-melted in a crucible; the aluminium is thus
immediately regenerated, and may be used again. The amalgam dis-
solved in the excess of mercury is passed through a chamois skin or
a woollen strainer; the mercury in excess which filters under pressure
from the skin or the woollen strainer is re-collected, and may be used
again, this being a primary partial recovery of the positive reagent.
The amalgam in a state of consistence, cleared as much as possible of
the droplets of free mercury, is in addition to the latter metal composed
of lead, zinc, and silver; it is in fact a triple or ternary amalgam. It is
left to dry in the air without fire. When it is in the pulverulent state
it is charged in small portions into an eliquative apparatus, which
consists essentially of a vessel composed of sheet metal provided with a
cover and an inclined bottom, such vessel having an opening in front
over a lateral gutter. As soon as the bottom of this vessel is heated the
lead amalgam more fusible than the zinc rolls down and descends into
the gutter, whence it is received into a special vessel. This amalgam

page_text: contains nearly all the silver of the scum. The zinc amalgam, which
has remained on the bottom in a pulverulent state is again amalgamated,
in order to complete the separation of what silver it may still contain.
After having been again re-filtered and re-cliquated it furnishes, 1st, a
fresh dose of argentiferous lead amalgam, which is added to that of
the primary cliquation; and, 2ndly, a pulverulent poor zinc amalgam.
When the whole mass of scum has been thus treated two separate and
distinct lots are obtained, videlicet, 1st, very rich argentiferous lead in
the state of amalgam (a); 2ndly, zinc slightly argentiferous in the
state of amalgam (6). The separation having thus been effected, the two
vessels containing the two lots a and b are placed separately in a retort
for distilling mercury per descensum, or in any other distilling apparatus,
such as a receiver provided with shelves, for example :-
The result given by the distillation is,―
=;
1st. Metallic mercury resulting from the two amalgams a and b 1
collected at the lower part of the retort in a vessel, ad hoc, filled
with water; the mercury employed for the amalgamation will be thus
totally regenerated.
2ndly. A very pure argentiferous lead containing the whole of
the silver in the vessel a. By the cupellation of this small portion of 1
lead, which will not be 100th of the lead operated upon there will
be obtained the pure silver or gold, or the mixture of the two precious
metals if they both exist at the same time in the lead subjected to
the operation of separation.
3rdly. Zinc poor in silver in the state of sponge in the vessel b.
By incorporating it with tar, and melting the whole in a crucible,.
regenerated metallic zinc will be obtained capable of serving for
a fresh operation, at which it will restore if required what little:
silver it may still retain. By adding a small quantity of lead to the
crucible, which does not offer any inconvenience, as the zinc is to be
subsequently incorporated with this metal in a fresh operation of desil-
verizing, the zinc sponge may be readily collected in a bottom. The
tar with which it is mixed for the purpose of re-melting prevents the
zinc oxidizing, to which it is very liable when in a finely divided state,
it may however be used even in this state for desilverizing in the pig
lead, by which the necessity for re-melting the zinc will be obviated.
The essential features of the new method therefore consist in re-
generating,―

page_text: 1st. The mercury used for the treatment of the rich scum, whether
oxydised or not.
2ndly. The argentiferous lead which contains the whole of the
silver that the zinc has extracted from the pig lead, and which in a
small proportion entered into the composition of the scum after its
eliquation.
3rdly. The zinc which has served as the extractor, or in lieu thereof
the aluminium and magnesium which have performed the same func-
tions, either separately or alloyed with zinc. Aluminium when employed
alone is separated, as before stated, in the operation of amalgamation.
All that has been herein-before stated with respect to silver is per-
fectly applicable to gold, and to the alloy of these two precious metals
when they are found together in the lead to be desilverized.
SPECIFICATION in pursuance of the conditions of the Letters Patent
filed by the said John Henry Johnson in the Great Seal Patent
Office on the 30th July 1872.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
HENRY JOHNSON, of 47, Lincoln's Inn Fields, in the County of
Middlesex, Gentleman, send greeting.
.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
etters Patent, bearing date the Thirty-first day of January, in the year
of our Lord One thousand eight hundred and seventy-two, in the 35th
year of Her reign, did, for Herself, Her heirs and successors, give
and grant unto me, the said John Henry Johnson, Her special license
that I, the said John Henry Johnson, my executors, administrators, and
assigns, or such others as I, the said John Henry Johnson, my executors,
administrators, or assigns, should at any time agree with, and no others,
from time to time and at all times thereafter. during the term therein
expressed, should and lawfully might make, use, exercise, and vend,
within the United Kingdom. of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN SEPARATING
GOLD AND SILVER FROM LEAD CONTAINING THE SAME,' a communication to me
from abroad by Clement Roswag and Alfred Nicolle Pauville, of Paris,
"

page_text: in the Republic of France, upon the condition (amongst others) that I,
the said John Henry Johnson, my executors or administrators, by an
instrument in writing under my hand and seal, should particularly
describe and ascertain the nature of the said Invention, and in what
manner the same was to be performed, and cause the same to be filed
in the Great Seal Patent Office within six calendar months next and
immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said John Henry Johnson, do hereby
declare the nature of the said Invention, and in what manner the same
is to be performed, to be particularly described and ascertained in and
by the following statement, reference being had to the accompanying
Drawings, and to the letters and figures marked thereon, that is to
say:
This Invention consists of the peculiar metallurgical processes herein-
after described, which have for their object the extracting from argenti-
ferous or auriferous lead of the precious metal contained therein, whether
silver or gold, or both, by the aid of any metallic reagent, such as zinc,
magnesium, aluminium, or the alloys of these two latter metals with
zinc, and, lastly, by mercury.
The primordial process, as old as metallurgy itself for separating
silver or gold from lead is cupellation. By reason of the costliness of
this operation, which consists in oxidizing the rich lead, it can only be
applied to lead containing a certain quantity of fine metal, sufficient to
pay the expences of the operation.
Hugh Lee Pattinson, of Newcastle, invented about forty years since a
process for the desilverization of poor lead, which process is known as
the crystallization method. This had been and is still universally
employed through a concentration (by crystallization) of the silver in a
small portion, videlicet, about one-tenth of the lead operated upon; only
a small fraction of the argentiferous or auriferous lead is submitted to
cupellation.
Karsten, a skilful German metallurgist, discovered the curious pro-
perty which zinc possesses of removing the silver and gold from lead
when the latter contains a given proportion of zinc. The discovery in
question was not put into immediate operation. It was first however
commercially applied by Mr. Parkes at the Llanelly Works, and for it he
obtained Letters Patent; the silver was extracted from lead by running

page_text: the pig lead into molten zinc, and skimming off the rich scum or dross
which was formed, and afterwards distilling it in order to regenerate the
zinc. This process was complicated, and was only really practicable in
those countries where coal and refractory clays were exceedingly cheap.
In One thousand eight hundred and fifty-four Letters Patent were
obtained in Spain by one of the communicators of this Invention for the
desilverization of pig lead with zinc, by treating the lead with the aid of
boxes containing the zinc reagent immersed at the bottom of the boiler,
the lead in such boiler receiving a gyratory motion, which was imparted
to it by the aid of a vertical axis provided with wings. The rich scum
was treated by laying under it a stratum of lead, and submitting it to a
scorification or oxydation of zinc, or in lieu thereof with any one of the
mineral acids, nitric, sulphuric, or chlorhydric.
Numerous improvements were successively made on this method,
which is known as the zinking process, and a number of Letters Patent
therefore were obtained in various countries by one of the communi-
cators of this Invention. The whole of this method, which however has
effected a saving of fifty per cent. over the process of crystallization, iş
deficient in a capital point, videlicit, the zinc employed as a reagent was
positively lost, for zinc in the condition of oxide (zinc white), or in the
condition of sulphate or chloride, cannot be considered as recovered.
The latter two products especially are commercially useless, and are the
necessary residuum of any treatment of rich scum with a cheap mineral
acid (chlorhydric or sulphuric acid). An improvement was therefore
required in the method of regenerating the reagent, for this would at
once still further reduce the net cost of desilverization by twenty-five
per cent.
The direct actual expenses (independently of the cost of refining the
lead, cupellation of the rich lead, reduction, and other similar items) are
about thirteen or fourteen shillings per ton, of which, for lead containing
a small proportion of silver, and consequently requiring but one per
cent. of the reagent, the zinc and the other acid reagents cost at least
six or seven shillings. This proportion of zinc reagent is applicable to
lead which contains from three-fourth to seven-eighths of an ounce of
silver per hundredweight. The quantity of zinc reagent increases
according to the proportion of silver; half hundredweight is required
for lead containing two and three-quarter ounces of silver per hundred-
weight

page_text: When the pig lead contains a certain large proportion of silver, the
crystallization process and the present process of desilverization with
zinc, are equivalent the one to the other. This is in fact the principal
reason why the rich lead of the coast of Spain is still desilverized in
England by Pattinson's process, which has survived only on this account.
By regenerating the zinc therefore, or any other metallic reagent per-
forming the same functions, the Inventors are enabled, first, to desil-
verize lead at the same cost, whatever proportion of the precious metal it
may contain; and, secondly, to effect an enormous reduction in the net
cost of desilverizing.
The method herein-after described has this twofold object, and forms
the subject of this Invention. It moreovor embraces two novel sub-
stitutes for zinc, which have not hitherto been employed for this purpose,
videlicet, magnesium and aluminium, as also the alloys of these metals
with zinc. All these conditions are fulfilled by the aid of a single agent,
videlicit, mercury, which is also regenerated.
In seeking a substitute for the reagent zine, in the extraction of
silver from lead, the Inventors first of all tried magnesium, which is so
closely allied to it. This metal effects the desilverization rapidly and
perfectly, but it is costly; it is still more oxydizable than zinc, and is
not so favorable to the operation of desilverizing as aluminium.
Aluminium desilverizes less rapidly; the incorporation of the lead is
also well effected by the aid of the box which was designed and used by
one of the communicators of this Invention for the introduction of the
zinc at the bottom of the boiler containing the pig lead in fusion at a dull
red heat.
°
Figure 6 of the Drawings hereunto annexed shews a box for con-
taining the desilverizing metal or alloy. This box is used in the following
manner: The ingot (whether zinc or other metal or alloy) is intro-
duced into the box A; the perforated cover B is caused to descend,
and then by sliding the rod E, the solid cover C is also brought down.
In this position the rod which slides in the eye N is at the level n; the
wedge Q is then inserted, which tightens and secures it. The box is
then immersed in the boiler containing the lead, and when it is desired
to allow the zinc to escape it is simply necessary to withdraw the
wooden wedge Q, which retained it at the bottom of the box. The
zinc then passes through the holes in the cover B, and rises in the
boiler to the surface, conducting the silver there in the state of scum.

page_text: An assay made with sodium proved that that metal does not effect the
desilverization.
An assay made with a mixture of zinc and aluminium shews that this
alloy offers many advantages; first, the zinc becomes less oxydizable;
secondly, the reagent reascends very rapidly in the interior of the boiler;
thirdly, the rich silver scum becomes very cleanly separated from the
impoverished lead. The mixture may be varied in any proportions, but
65 parts of zinc to 35 parts of aluminium have been found to answer
perfectly; with aluminium however in the proportion of onlyth of the
zinc the zinc works better than when used alone.
I shall now proceed to describe the treatment of the rich scum or
dross resulting from the preceding operations with mercury or amalga-
mation. I assume that the rich scum or dross resulting from the
preceding operations (zine alone, aluminium alone, magnesium alone, or
zinc and aluminium, or zinc and magnesium has been skimmed off, and
deposited on a metal plate after having been eliquated (that is to say),
after as much lead as possible has been separated by fusion at a low
temperature in a cast-iron boiler, the scum has a granular appearance,
and may be readily crushed with a shovel on the plate when warm. In
this manner it is reduced to a finely pulverized state; it is then caused
to pass through a sieve, the lumps that do not pass being inserted again
in the boiler, and the operation repeated. This pulverization, which
may be readily effected when the scum is in a heated state, may also be
neatly performed in a machine similar to a coffee mill. The finely
pulverized substance is introduced into an amalgamating cask similar
to those employed in the Halsbruike silver works, Saxony, for example,
or in the works of Hien-de-la-Encina, Spain. Any suitable churn may
be used if required.
Figure 7 shews one example of amalgamating cask. T is the cask,
which is mounted on a shaft R, S, carrying a wheel M, N, which is
provided with a handle 8. This shaft is carried in bearings P. The
cask is provided with a bung hole B, and its contents are run into a
funnel O, which conducts the amalgam and the mercury through the
passage X into the woolen strainer H for the purpose of filtering the
excess of mercury. The sediment escapes by the passage Z. Water is
added, by preference acidulated with a little nitric acid and old scrap
iron, in order to effect the beating up of the mixture. with the mercury

page_text: which has been previously introduced into the cask. It is desirable to
operate with warm water. Salt water, warm, containing a large
quantity of salt may also be employed. The amalgamation is effected
by the rotation of the cask very rapidly, according to the quantity
operated upon. If the scum contains aluminium this will not amalga
mate, but zinc, silver, and lead will unite with mercury.
.
By adding a sufficient dose of mercury to the bath, when it is ascer-
tained that the amalgamation is complete, the aluminium sediment is
collected with a ladle and re-melted in a crucible; the aluminium is thus
immediately regenerated, and may be used again. The amalgam dis-
solved in the excess of mercury is passed through a chamois skin or a
woollen strainer; the mercury in excess which filters under pressure
from the skin or the woollen strainer is re-collected, and may be used
again. This is a primary partial recovery of the definitive reagent.
The amalgam in a state of consistence, cleared as much as possible of
the droplets of free mercury, is in addition to the latter metal composed
of lead, zinc, and silver; it is in fact a triple or ternary amalgam. It is
left to dry in the air without fire. When it is in the pulverulent state it
is charged in small portions into an eliquative apparatus, an example of
which is shewn at Figures 1, 2, and 3 of the Drawing hereunto annexed,
which are respectively an elevation, longitudinal, vertical section and plan
of an eliquative apparatus for the separation of the amalgams of lead and
zinc. This apparatus is composed of a sheet metal case B provided with
a moveable cover A and an inclined bottom C, having cylindrical
canelures. The amalgam runs into the gutter D through the aperture O,
being guided by the lateral plane surfaces G; Q is the receptacle for the
amalgam, and P are the feet of the apparatus. In this arrangement a
very moderate degree of heat is applied to the bottom C of the apparatus.
It will be understood that any other arrangement meeting the same
conditions of slope or inclination would be equally suitable. As soon as
the bottom of this vessel is heated the lead amalgam, more fusible than
the zinc, rolls down and descends into the gutter, whence it is received
into the vessel Q. This amalgam contains nearly all the silver of the
scum. The zinc amalgam, which has remained on the bottom in a
pulverulent state, is again amalgamated in order to complete the sepa-
ration of what silver it may still contain. After having been again re-
filtered and re-eliquated it furnishes, first, a fresh dose of argentiferous
lead amalgam, which is added to that of the primary eliquation; and,

page_text: operation, at which it will restore what little silver it may still retain.
By adding a small quantity of lead to the crucible, which does not offer
any inconvenience, as the zinc is to be subsequently incorporated with
this metal in a fresh opération of desilverizing, the zinc sponge may be
readily collected in a bottom. The tar, with which it is mixed for the
purpose of re-melting, prevents the zinc oxydizing, to which it is very
liable when in a finely divided state: It may however be used even in
this state for desilverizing in the pig lead, by which the necessity for
re-melting the zinc will be obviated.
operation, at which it will restore what little silver it may still retain.
By adding a small quantity of lead to the crucible, which does not offer
any inconvenience, as the zinc is to be subsequently incorporated with
this metal in a fresh opération of desilverizing, the zinc sponge may be
readily collected in a bottom. The tar, with which it is mixed for the
purpose of re-melting, prevents the zinc oxydizing, to which it is very
liable when in a finely divided state: It may however be used even in
this state for desilverizing in the pig lead, by which the necessity for
re-melting the zinc will be obviated.
The essential features therefore of the new method of treating the
amalgams consist in regenerating, —
First. The mercury used for the treatment of the rich scum.
Secondly. The argentiferous lead which receives the whole of the
silver that the zinc has extracted from the pig lead, this latter metal
entering in a small proportion into the composition of the scum after its.
eliquation.
Thirdly. The zinc which has served as the extractor, or in lieu thereof
the aluminium and magnesium which have performed the same func-
tions, either separately or alloyed with zinc. Aluminium when employed
alone is separated, as before stated, in the operation of amalgamation.
All that has been herein-before stated with respect to silver is per-
fectly applicable to gold, and to the alloy of these two precious metals
when they are found together in the lead to be desilverized.
I may add in conclusion that it has not hitherto been proposed to
subject the rich scum from the operation of desilverizing by zinc to
amalgamation, because as mercury combines equally well with the three
metals which constitute the scum, videlicit, silver, zinc, and lead, no
means of separation could be seen. This is in fact one of the causes
which have prevented amalgamation being applied to silver ores which
contain these metals in a certain proportion, a fact which is well known
to metallurgists. But in performing the operation of amalgamation, in
order to separate the aluminium in the assays made by the present
Inventors, the aluminium not being amalgamable, they had the oppor-
tunity of discovering this unsuspected curious property which admits of
the separation of the amalgam of zinc from the amalgam of lead,
videlicit, that the latter melts at the lower temperature, and forms a

page_text: semi-metal exceedingly fusible. When it is cold it has the brilliant
appearance of silver; it is eminently fragile. The amalgamated zinc on
the contrary withstands and remains dry and pulverulent at the same
low temperature, which does not exceed one hundred and twenty degrees
centigrade.
Another property equally fortunate, and which completes the success
of the method, is that the amalgam of lead which is so fusible combines
with the amalgam of silver, which becomes separated from the amalgam
of zinc, leaving the latter impoverished.
Having now described and particularly ascertained the nature of the
said Invention, and the manner in which the same is or may be used
or carried into effect, I would observe in conclusion that what I con-
sider to be novel and original, and therefore claim as the Invention
secured to me by the herein-before in part recited Letters Patent is,―
First. The treating of argentiferous and auriferous lead with mag-
nesium or aluminium, either separately or alloyed with zinc, for the
purpose of separating gold and silver therefrom.
Secondly. The treating of the rich scum or dross resulting from any
of the preceding operations with mercury for the purpose of effecting
the separation of silver and gold therefrom, as herein-before described.
Thirdly. The treating with mercury of the rich scum or dross resulting
from the treatment of argentiferous and auriferous lead with zinc for
the purpose of effecting the separation of silver or gold, as herein-before
described.
In witness whereof, I, the said John Henry, Johnson, have to this
my Specification set my hand and seal, the Thirtieth day of Julv