Improvements in the Production of Chlorine conjointly with the Purification of Lead and the Recovery of Silver.
Year: 1891

page_text: Date of Application, 16th Oct., 1891
Complete Specification Left, 13th Aug., 1892-Accepted, 15th Oct. 1892
PROVISIONAL SPECIFICATION.
Improvements in the Production of Chlorine conjointly with the
Purification of Lead and the Recovery of Silver.
We, FARNHAM MAXWELL LYTE, Analytical Chemist, and CECIL HENRY
MAXWELL LYTE, Esquire, both of 60, Finborough Road, London, S.W., do
hereby declare the nature of this invention to be as follows:-
Our invention has mainly for its object the manufacture of pure lead chloride
with a view of producing chlorine and pure lead therefrom by the electrolytical
process described in a former application for Letters Patent, made by one of us,
dated the 6th day of March 1891 No. 4068.
For this purpose we take a solution of any soluble chloride, such as calcic or
magnesic chloride, and precipitate lead chloride therefrom by the addition of a
soluble salt of lead, such as lead nitrate.
out.
We will assume that we are treating the waste (mixed calcic and sodic chloride)
liquors of the ammonia-soda process, obtained by driving off the ammonia by
means of lime in the usual way. These liquors are boiled down until a point is
reached at which, on cooling, all the sodic chloride they contain will crystallize
A practically pure calcic chloride is thus obtained from which lead chloride
is precipitated by the addition of a solution of lead nitrate, preferably hot. The
resulting nitrate of lime in solution is, after separation from the lead, evaporated
to dryness and heated in a decomposing pan or other suitable apparatus, such as a
revolving furnace, to, say, a low red heat whereby all or most of the nitric acid
will be driven off as nitrous fumes which are to be condensed in the usual way into
nitric acid. Should any nitrate of lime remain undecomposed, it may be washed
out of the lime residue and added to the next batch of nitrate of lime to be decom-
posed. In this manner, practically all the nitric acid is eventually recovered for
use over again in the production of more nitrate of lead and all the lime is also
employed over again for producing more calcic chloride by driving off the ammonia
from the ammonic chloride liquors of the ammonia-soda process.
The mixed calcic and sodic chloride liquors of the ammonia-soda process may
also be converted into maguesic chloride for treatment with lead nitrate, and this
we perform by the Schaffner and Helbig process which consists in mixing "soft-
burnt" magnesia with the calcic chloride (freed from sodic chloride) and "gassing"
with carbonic acid. In this way magnesic chloride is obtained in solution with a
precipitate of calcic carbonate. This magnesic chloride is now treated with nitrate
of lead for the production of chloride of lead and the resulting nitrate of magnesia
decomposed by heat similarly to the nitrate of lime. Or the nitrate of magnesia
may first be converted into an oxy-salt by the addition of a further quantity
of "soft-burnt " magnesia in order to facilitate the evolution of the nitrous
fumes.
86
By soft-burnt" magnesia is meant oxide of magnesium which has not been
heated to above a low-red heat and the residue in the pan after the decomposition
of the nitrate of magnesia will answer very well for this purpose.
Instead of treating a soluble chloride with a soluble salt of lead, as above
described, hydrochloric acid may be evolved by the addition of nitric acid to the
soluble chloride this hydrochloric acid being then employed for the production of
chloride of lead by adding it to a soluble salt or an oxide of lead.
In preparing a soluble salt of lead for the above purposes, we repeatedly,
alternately expose granulated or finely divided lead to the action of the air and of
acetic or weak nitric acid, thus forming acetate or nitrate of lead, or oxide of lead
may be dissolved in either of these acids. Or metallic lead may be dissolved in

page_text: strong nitric acid-the nitrous fumes evolved being caught and regenerated as
nitric acid for use over again. In the precipitation of acetate of lead with free
hydrochloric acid, we preferably employ a basic acetate, precipitating out only the
base with the hydrochloric acid and thus leaving a neutral acetate for the dissolving
of a further quantity of lead-in this way, loss of acetic acid is avoided. The
advantage of forming a soluble salt of lead by repeatedly exposing finely divided
metallic lead to the alternate action of weak acid and air is that all the impurities,
such as silver, etc., will precipitate out of the solution and therefore the chloride
formed from this pure soluble salt of lead will on electrical decomposition yield a
chemically-pure lead. The process thus becomes in part one for the purification
of lead, enabling us to employ impure lead and recover the silver while at the
same time we obtain pure lead for sale, as our alternate product.
F. MAXWELL.LYTE,
C. H. MAXWELL LYTE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent 'Agents.
COMPLETE SPECIFICATION.
Improvements in the Production of Chlorine conjointly with the
Purification of Lead and the Recovery of Silver.
We, FARNHAM MAXWELL LYTE, Analytical Chemist, and CECIL HENRY
MAXWELL LYTE, Esquire, both of 60, Finborough Road, London, S.W., 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 :-
Our invention relates to the production of chlorine, conjointly with the purifica-
tion of lead and the recovery of silver therefrom.
According to one part of the invention the process, so far as concerns the
purification of lead and the production of lead chloride for electrolytical decom-
position into chlorine and refined lead, consists in forming pure lead nitrate as
hereafter mentioned, decomposing a soluble chloride with the lead nitrate thus
forming lead chloride and a nitrate, then decomposing the nitrate thus formed to
produce nitric acid, oxidising metallic lead (which has been freed from zinc) and
dissolving the lead oxide in the nitric acid, recovering silver and forming pure
nitrate of lead with which to continue the operation, the base of the nitrate from
which the nitric acid has been recovered being available for treating more raw
material from which the soluble chloride to be treated is obtained.
The soluble chloride to be thus treated may either be calcic or magnetic chloride,
the former obtained from the waste chloride liquors of the ammonia-soda process,
and the latter obtained either from the same, or from a native source.
Assuming that calcic chloride (contained in the mixed calcic and sodic chloride
liquors obtained in the ammonia-soda process by driving off the ammonia by. means
of lime in the usual way) is to be decomposed directly with lead.nitrate, we proceed
as follows-
The mixed chloride liquors are to be first concentrated by boiling until, on
cooling, practically all the sodic chloride will crystallize-out: Torthe calcic
chloride thus obtained a sufficient quantity of lead nitrate in (preferably hot)
solution is added to cause complete double decomposition whereby lead chloride is
precipitated and nitrate of lime remains in solution. This nitrate of lime will
contain some lead chloride in solution which will not precipitate out on cooling but
by adding some of the base of the nitrate of lime solution in the form of, say,
milk of lime, the chloride remaining in solution will precipitate out as oxychloride
of lead.

page_text: Or any other suitable base may be used such as lead oxide (preferably lead
hydrate), magnesia, or caustic soda for example.
The nitrate of lime after separation from the lead chloride is to be evaporated
to dryness and decomposed at a low red heat in any suitable apparatus such as a
decomposing pan or a muffle furnace so as to drive off nitrous fumes which are to
be caught oxidised and condensed into nitric acid in the usual way, say by a Lunge
plate tower. Aby nitrate or nitrite of lime that may remain undecomposed may
be washed out of the lime residue and added to the next batch of nitrate of lime
to be evaporated and decomposed so that practically all or nearly all the nitric acid
is eventually recovered. This nitric acid is used over again for the production of
more nitrate of lead (for decomposing more calcic chloride) by oxidising metallic
lead (which has been freed from zinc) and then dissolving the lead oxide in the
nitric acid.
All the silver and other metallic impurities remaining in the metallic lead (after
elimination of zinc) will, if in solution, precipitate out of the nitrate of lead, on
the addition thereto of spongy or finely divided lead and therefore the lead chloride
formed from this nitrate as above described will on electrolytical decomposition as
hereafter described yield a pure metallic lead.
If the chloride to be decomposed by lead nitrate be magnesic chloride it may
either be produced from the waste chloride liquors of the ammonia-soda process or
from native sources. If the former the calcic chloride (obtained by crystallizing
out the sodic chloride from the mixed calcic and sodic chloride liquors of the
ammonia-soda process) is converted into magnesic chloride by the Schaffner and
Helbig process which consists in mixing soft burnt" or hydrated oxide of
magnesium with the calcic chloride and "gassing" with carbonic acid whereby
magnesic chloride is obtained in solution with a precipitate of calcic carbonate.
This magnesic chloride after being separated from the precipitate is to be treated
with nitrate of lead (in exactly the same way us above described in regard to
calcic chloride) for the production of lead chloride and nitrate of magnesia. The
latter is to be decomposed with neat; and this decomposition is in some respects
facilitated by first converting the nitrate of magnesia into an oxy-salt by the
addition to it of "soft burnt" magnesia and in any case it yields nitric acid and
magnesia which being "soft burnt" may be hydrated by boiling in water and so
rendered fit for use over again to form more magnesic chloride whilst the nitric
acid is available for forming more lead nitrate.
If the magnesic chloride treated be obtained from a native source (Stassfurt
salts or sea-water for example) this magnesic chloride is simply dissolved and
decomposed by nitrate of lead the remainder of the operations being the same as
above described except that "soft burnt" magnesia will be in this case obtained as
a product.
According to the second part of the invention the process, so far as concerns' the
purification of lead and the production of lead chloride for electrolytical decom-
position, consists in forming lead nitrate or acetate, effecting the decomposition of
the lead nitrate or lead acetate (normal or basic) with hydrochloric acid to form
lead chloride nitric or acetic acid being liberated (or normal acetate of lead being
formed if basic acetate was used) treating lead oxide with the acid so liberated or
the acetate so formed (as the case may be) for the recovery of silver from lead and
further formation of normal or basic lead salt.
In carrying out the process we take commercial hydrochloric acid as made by
the Leblanc process or produced by decomposing magnesic chloride or oxychloride
by, say, Eschelmann-Pechiney's process whether the magnesic chloride so treated
has been obtained from a native source such as Stassfurt salts or from sea-salt
works or by converting the calcic chloride (obtained by crystallizing out the sodic
chloride from the waste chloride liquors of the ammonia-soda process) into
magnesic chloride by adding "soft burnt or hydrate of magnesia to the calcic
chloride and gassing" with carbonic acid according to the Schaffner and Helbig
process.
“

page_text: Assuming that the lead salt to be treated is the nitrate we add to it hydro-
chloric acid (obtained from any source) to form lead chloride weak nitric acid being
liberated. This weak nitric acid is used over again for the production of more
nitrate of lead, by oxidising metallic lead (which has been previously freed from
zine) and then dissolving the lead oxide in the weak nitric acid. All the silver
and other metallic impurities contained in the metallic lead after elimination of
the zinc will if in solution precipitate out of the nitrate of lead on the addition
thereto of spongy or finely divided lead and the lead chloride formed from this
nitrate will be pure, and will on electrolytic decomposition as hereafter described
yield pure metallic lead.
Assuming that the lead salt to be used is the acetate this is to be decomposed by
commercial hydrochloric acid to form lead chloride, and either form acetic acid if
the normal acetate was used or render the acetate normal if the basic acetate was
used. The acetic acid or the normal acetate (as the case may be) then used for
treating more lead oxide for the production of more normal or basic acetate (as
the case may be) for repeating the operation.
It will be found that on the formation of the acetate any silver the lead may
have contained will precipitate out and should there be any acetate of copper
formed the copper may be eliminated by the addition of finely divided metallic
lead leaving acetate of lead for treatment with hydrochloric acid. And the silver
and copper are similarly extracted if acetic acid be washed repeatedly over
granulated lead alternately with exposure to the air until it becomes a normal or
basic acetate.
Having described the various methods of producing the lead chloride, we will
now in continuation of the above in part described processes, describe the method
of decomposing the lead chloride into chlorine and refined metallic lead.
The lead chloride in whichever of the above described ways it may be produced
is to be collected, washed if necessary and dried, and is then to be fused in a
crucible or other suitable vessel and submitted to electrolysis whilst in the fused
condition in the manner hereinafter described. The electrolytic decomposition cell
may be a trough preferably of earthenware or enamelled iron and it may be heated
in a sand bath or directly by gas or other means whereby it may be maintained at
a constant temperature. In this vessel or cell are to be placed a number of plates,
say of carbon graphite or other suitable material unattackable by chlorine and
unaffected by the fused chloride in which they are immersed, said plates being
arranged like the plates of an ordinary galvanic battery, and being so connected
to the main conductors as to be alternately anodes and cathodes. Two or more
such cells may be used grouped by preference in series the cathode plates of the
one cell being coupled to the anode plates of the other cell whereby a more
economical production of chlorine may sometimes be obtained than by the use of a
single cell. This trough is closed by a cover which may be sealed for instance by
means of a liquid joint, or by a washer of asbestos card and provided with a pipe
to convey away the chlorine. The electrodes are so supported in the trough that
they do not touch one another or the metallic lead which collects in a molten
state at the bottom of the trough, sufficient space being left for the said metallic
lead (which results from the decomposition of the fused chloride) to flow beneath
the plates without touching them and so short circuiting them.
The bottom of the trough may slope towards one end where the molten metallic
lead will collect and whence it may be caused to run off spontaneously by a siphon
or other means.
The plates may pass through slots in the cover of the trough with which they
make gas-tight joints. They should not extend the full width of the trough in
order to allow the chlorine generated to flow past them to the chlorine outlet, and
they should be provided with external binding clips by which they may be coupled
respectively to the anode and cathode conductors. The overflow syphon is made
of earthenware or of iron enamelled externally and the overflow of the molten lead
8 caused by the pressure of the fused lead chloride in the tank, the bend of the

page_text: overflow pipe being at such a height that the level of the molten lead will remain
constant provided the fused chloride is kept at the same level. Suitable provision
should therefore be made for supplying the chloride to the tank without removing
the cover.
This may be done by introducing the chloride through a pipe passing
through the cover and sealed against the escape of chlorine by dipping into the
molten chloride in the trough. The level of the chloride can thus be kept constant
and the process rendered continuous.
The cathode plates may however be omitted and the molten lead made the
cathode, in which case sufficient lead for the purpose would be put into the trough
at the outset, enough always being retained to form a cathode of extended area,
the conductor connected with the negative terminal of the source of electricity
being in that case made of iron tinned to ensure good electrical contact with the
molten lead into which it is led. Whatever form of apparatus may be adopted
care should be taken that the areas of the exposed surfaces of the anode and
cathode should respectively correspond.
Owing to the exceptionally low resistance of fused lead chloride a large current
of low voltage, say two or three volts or less, may be employed the conductors and
dynamo being similar to those used in electroplating.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, we declare that what we
claim is :-
1. The herein described process of conjointly producing chlorine, purifying
metallic lead, and recovering silver, based upon the decomposition of a soluble
chloride such as herein specified by nitrate of lead, the said process consisting in
the following cycle of operations, viz. :-decomposing the soluble chloride with lead
nitrate to form lead chloride and a nitrate, decomposing (either in one or in a
succession of operations) the nitrate formed, oxidising metallic lead and dissolving
the lead oxide in the nitric acid to regenerate nitrate of lead, precipitating silver,
and decomposing the lead chloride electrolytically, all as herein specified.
2. The herein described process of conjointly producing chlorine, purifying lead,
and recovering silver, which consists in decomposing lead nitrate or acetate with
commercial hydrochloric acid however produced, to form lead chloride, treating
lead oxide with the nitric or acetic acid liberated or with the lead acetate produced
(or treating superficially-oxidised granulated lead with the acetic acid or lead
acetate), for the regeneration of the soluble lead salt and recovery of silver, and
decomposing the lead chloride electrolytically into chlorine and refined metallic
lead, all substantially as herein specified..
Dated this 13th day of August 1892.
F. MAXWELL LYTE,
C. H. MAXWELL LYTE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.