Improvements in the Production of Chlorine and Refined Lead, and in the Recovery of the Silver the Lead Contains.
Year: 1893

page_text: Date of Application, 8th Apr.: 1893
Complete Specification Left, 8th Feb., 1894-Accepted, "th Apr., 1894
PROVISIONAL SPECIFICATION.
Improvements in the Production of Chlorine and Refined Lead, and
in the Recovery of the Silver the Lead Contains.
'
I, FARNHAM MAXWELL LYTE of 60, Finborough Road, London, S.W.,
Analytical Chemist, do hereby declare the nature of this invention to be as
follows:-
-
This invention relates to a process for the industrial production of chlorine and
refined lead and the, recovery of any associated silver. It is a conjoint process
for the production of purified lead chloride together with its electrolysis when in
the fused state.
The process comprises the production of lead oxide, the conversion of lead
sulphate or of lead oxide or oxychloride into lead chloride, the separation and
recovery of the silver which may be associated with the lead or lead compound
treated, and the electrolysis of the lead chloride when in a fused state for the
evolution of chlorine and refined lead.
By the treatment of lead sulphate, with hydrochloric acid or with a strong
solution of a chloride to which hydrochloric or sulphuric acid has been added and
heating the mixture to a temperature above 70° to 80° C. or by boiling lead
sulphate with a saturated solution of magnesic chloride, lead chloride is produced.
The lead sulphate may be formed from lead oxide by treating the latter with
sulphuric acid in the manner hereafter described for treating lead oxide with
hydrochloric acid.
Lead chloride may be formed from lead oxide or oxychloride by grinding it with
an excess of aqueous hydrochloric acid, say, in the proportion of about 238 to
242 gallons of acid at 28° Tw. (or a proportionate amount of.a weaker or stronger
acid) per ton of lead oxide.
The operation of grinding is distinguishable from all other modes of treatment
by the fact that, under ordinary circumstances, the particles of lead oxide are liable
to become coated with sparingly-soluble lead chloride, so that the lead oxide
becomes protected from further action unless this coating be removed which is
effectually done by the friction of the grinding operation.
The grinding may be performed in a pan which must be made of, or protected
by, a material not acted on by the acid or the chloridès of lead or silver with
which it may be exposed to contact. For instance, the bottom of the pan may be
made of stone and the sides may be made of stoneware, vulcanized fibre, copper-
cased lead or iron, provided the metal surfaces be protected by an acid-resisting
paint or enamel. The grinding may be performed by edge runners furnished with
suitable scrapers, say, of ebonite, or a form of flat mill may be used if the ironwork
be properly protected.
The yellow lead oxide is to be preferred for this mode of treatment on account
of its greater porosity due to its not having been fused and consequent more ready
attackability, but litharge will also answer perfectly well. Metallic lead even will
be acted on by bydrochloric acid especially if the acid be hot and strong, or if the
lead be granulated and alternately exposed to the air and the action of the acid
and be frequently turned over.
Any silver compound associated with the lead salt or oxide treated will be
chloridized and may be lixiviated out of the lead chloride (formed by either of the
above described methods of treatment) with strong hydrochloric acid, or with a

page_text: ;
.
,
strong solution of an alkaline chloride.or of a suitable alkalino-earthy chloride, not
with calcic chloride, of course, if sulphuric acid be present. The silver chloride
may be precipitated as metallic silver by filtering the solution in which it is
contained through spongy or finely divided lead or by otherwise bringing the
silver chloride into intimate contact with this or any other metal electro-positive
to silver. Warming the lixiviate after its withdrawal from the lead chloride
accelerates the reduction of the silver, especially if lead be the reducing metal
employed.
Instead of lixiviating out the silver chloride from the lead chloride, the silver
may be reduced in admixture with the latter and be separated therefrom by fusion
over a bath of metallic lead in a closed vessel and by repeating this operation over
the same bath with successive batches of argentiferous lead chloride, the lead of
the bath may be enriched with silver to any desired extent and finally withdrawn
as rich silver lead for recovery of the silver by cupellation.
The oxidation of crude lead to form litharge may-be-conveniently and cheaply
performed by blowing in a basic-lined Bessemer converter into which the lead is
introduced after having been heated to a little above its melting point. The lead
then takes fire and is oxidised by its own combustion and the oxide fuses and
attains a very high temperature, there remaining unoxidised only a small quantity
of metallic lead into which nearly all the silver which the crude lead contained
becomes concentrated whilst the silver contained both in the litharge and the fume
may be extracted down to the very last trace by means of spongy or finely divided
lead as above mentioned.
+
The method of oxidising crude lead above described is particularly applicable for
the purpose of this process by reason of the large amount and the purity of the
litharge produced, the rapidity with which the oxidation of several tons of lead
may be, performed, and the small consumption of fuel and labor. In the ordinary
method of lead smelting, the litharge would need to be again reduced to metallic
lead but this is not necessary in this process the litharge being what is required.
The lead chloride in whichever of the above described ways it may be produced,
should.it still be contaminated by any lead sulphate, lead oxide, or other foreign
insoluble material may be purified by solution in hot water and crystallization by
cooling, the heat given off being reabsorbed by means of a kind of regenerative
arrangement into the water of solution, so that with but little additional heat the
same water may be continually employed in dissolving fresh chloride. Anyway it
is to be washed, dried, fused, and electrolytically decomposed when in the fused
state for the production of refined lead and chloride.
An important improvement consists in preventing the oxidation of the lead
chloride during its fusion by the introduction within the chamber of the cell
containing the lead chloride of a gas, which has no action on carbon or on fused
lead chloride such as chlorine or nitrogen so as to expel any air from which the
lead chloride would otherwise be liable to absorb oxygen and so become converted
into an oxychloride, and as the dissolved oxide becomes electrolysed at a lower
voltage than the chloride with evolution of oxygen a waste of power would occur,
the same number of ampères being consumed in the production of the oxygen as
for the production of over twice its weight of chlorine.
Dated this 8th day of April 1893.
'

page_text: COMPLETE SPECIFICATION.
Improvements in the Production of Chlorine and Refined Lead, and
in the Recovery of the Silver the Lead Contains.
I, FARNHAM MAXWELL LYTE of 60, Finborough Road, London, S.W.,
Analytical Chemist, 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:―
This invention relates to a process for the industrial production of chlorine and
refined lead and the recovery of any associated silver, the process being based
essentially on the production of purified lead chloride and its électrolysis when in
the fused state.
The process comprises the conversion of lead oxide or oxychloride into lead
chloride, the separation and recovery of the silver which may be associated with
the lead compound treated, and the electrolysis of the purified lead chloride when
in a fused state for the evolution of chlorine and production of refined lead.
The invention also comprises an important improvement whereby oxidation of
the lead chloride in course of fusion at the commencement of the electrolytic
operation is prevented.
Lead chloride is to be formed from lead oxide or oxychloride by grinding it with
an excess of aqueous hydrochloric acid, say, in the proportion of about 233 gallons
of acid at 34° Tw. (or a proportionate amount of a weaker or stronger acid) per
ton of lead oxide.
The operation of grinding is distinguishable from all other modes of treatment
by the fact that under ordinary circumstances the particles of lead oxide are liable
to become coated with sparingly-soluble lead chloride so that the lead oxide
becomes protected from further action unless this coating be removed, which is
effectually done by the friction of the grinding operation.
The grinding may be performed in a pan which must be made of, or protected
by, a material not acted on by the acid or the chlorides of lead or silver with which
it may be exposed to contact. For instance, the bottom of the pan may be made.
of stone, say granite, and the sides may be made of stoneware, vulcanized fibre,"
copper-cased lead or iron, provided the metal surfaces be protected by an acid-
resisting paint orʼenamel.
The grinding may be performed by edge runners furnished with suitable scrapers,
say, of ebonite or lignum vitæ, or a form of flat mill, such as represented in
sectional elevation and plan in Figures 1 and 2 of the accompanying drawings,
forming part of this Specification, may be used if the ironwork be properly
protected. In these figures, A is a stoneware pan, B are stone mullers carried
round by the cross-arms and stay-rods of a frame C revolving on a centre D and
resting by rollers at their outer ends on a circular railway E outside the pan
supported by adjusting screws F to enable the grinding action of the mullers B to
be regulated.
The yellow lead oxide is to be preferred for this mode of treatment on account
of its greater porosity, due to its not having been fused, and consequent more ready
attackability, but litharge will also answer perfectly well.
Any silver associated with the lead salt or oxide treated will be chloridized' and
may be lixiviated out of the lead chloride (formed by either of the above described
methods of treatment) with strong bydrochloric acid or with a strong solution of
an alkaline chloride or of a suitable alkalino-earthy chloride. The silver chloride
may be precipitated as metallic silver by filtering the solution in which it is
contained through spongy or finely divided lead; or by otherwise bringing the silver
chloride in solution into intimate contact with this or any other metal electro-
positive to..silver. Warming the lixiviate after its withdrawal from the lead

page_text: chloride accelerates the reduction of the silver especially if lead be the reducing
metal employed.
Instead of lixiviating out the silver chloride from the lead chloride, the silver
may be reduced in admixture with the latter and be separated therefrom by fusion
over a bath of metallic lead in a closed vessel and by repeating this operation over
the same bath with successive batches of argentiferous lead chloride, the lead of
the bath may be enriched with silver to any desired extent and finally withdrawn
as rich silver lead for recovery of the silver by cupellation.
If litharge is used, the oxidation of crude lead to form the litharge may be
conveniently and cheaply performed by blowing in a basic-lined Bessemer converter
into which the lead is introduced after having been heated to a little above its
melting point. The lead then takes fire and is oxidised by its own combustion and
the oxide fuses and attains a very high temperature, there remaining unoxidised
only a small quantity of metallic lead into which nearly all the silver which the
crude lead contained becomes concentrated whilst the silver contained both in the
litharge and the fume may be extracted down to the very last trace by means of
spongy or finely divided lead as above mentioned.
The method of oxidising crude lead above described is particularly applicable
for the purpose of this process by reason of the large amount and the purity of the
litharge produced, the rapidity with which the oxidation of several tons of lead
may be performed and the small consumption of fuel and labor.
The lead chloride, however it may be produced, should it still be contaminated
by any lead oxide or other foreign insoluble material, may be purified by solution
in hot water and crystallization by cooling, the heat given off being reabsorbed, by
means of a kind of regenerative arrangement, into the water of solution, so that
with but little additional heat the same water may be continually employed and
re-employed in dissolving fresh chloride.
The purified lead chloride is to be washed, dried, fused, and electrolytically
decomposed when in the fused state for the production of refined lead and chlorine.
The electrolytic decomposition of the fused lead chloride is effected preferably
in a cell such as represented in Figure 3 of the drawings, wherein A is an iron
pan set over a furnace M, B a bell of earthenware or plumbago supported in the
pan A, its upper end being provided with a removable cover B and its lower end
sealed by dipping into metallic lead L; E are anodes of hollow carbon with a
fusible metallic core, preferably, in this case, of lead in which the terminal
conductors are embedded, F is the inlet through which lead chloride may be
supplied to the cell during the electrolytic operation, G' is the outlet for chlorine,
His the cathode terminal dipping in the molten lead L which forms the cathode
and runs off at D.
The bell B would have its mouth sealed by a preliminary melting of the lead L
which may then be allowed to solidify after which lead chloride C, in crystals, is
charged into the bell B, its cover B¹ being removed for the purpose.
At the commencement of the operation the bell chamber B after being sealed
and charged with lead chloride would under ordinary circumstances contain air
and the lead chloride whilst undergoing fusion therein would be liable to absorb
oxygen and so become converted into an oxychloride. As the dissolved oxide-
becomes electrolysed at a lower voltage than chloride, with evolution of oxygen,
a waste of power would occur as the same number of ampères would be consumed
in the production of this oxygen as for the production of over twice its weight of
chlorine. To avoid this action, I prevent the oxidation of the lead chloride during
its fusion by displacing all the air contained in the chamber B of the cell, by
means of a gas which has no action on fused lead chloride or on carbou. The gas
employed is preferably chlorine but nitrogen may be used.
Suppose a number of cells, such as shewn in Figure 3, to be used. These would
be connected in series by pipes G G', that is to say the bell B of one to the bell B
of the next and so on for any convenient number, the exit pipe from the last cell
dipping in water. Then supposing the operation to be commenced in the first cell

page_text: of the series by fusing the chloride and putting on the current, the chlorine
therein generated would displace the air in the other cells and thus the whole
series would be filled with chlorine before the chloride in those cells is fused. The
chloride in all the other cells would be fused and the electrolysis of the whole
commenced.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, I declare that what I
claim is:
1. The conjoint process for the production of chlorine and refined lead, which
consists in the formation of lead chloride by grinding lead oxide or oxychloride
with hydrochloric acid, extracting any associated silver in either of the ways
described, and then electrolysing the fused lead chloride, as described.
2. The method of forming lead chloride which consists in grinding lead oxide or
oxychloride with hydrochloric acid, substantially as specified.
3. In the electrolytic decomposition of fused lead chloride, the method of
preventing the oxidation of the chloride at the commencement of the operation,
which consists in displacing the air in the cell by an inert gas before fusing the
lead chloride.
Dated this 8th day of February 1004
F. MAXWELL LYTE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.