An Improved Process for Producing Basic Lead Salts and Obtaining Certain Bye Products.
Year: 1893

page_text: Date of Application, 13th July, 1893
Complete Specification Left, 11th Apr., 1894-Accepted, 12th May, 1894
PROVISIONAL SPECIFICATION.
An Improved Process for Producing Basic Lead Salts and Obtaining
Certain Bye Products.
We, Dr. GEORGE LUNGE, Professor of Chemistry at The Polytechnicum,
Zurich, Switzerland, and CECIL HENRY MAXWELL-LYTE, of 60, Finborough
Road, London, S. W. Esquire, do hereby declare the nature of this invention to be
as follows:
This invention relates to a process of conjointly producing basic lead salts from
crude pig lead and obtaining certain bye products by a continuous cycle of
operations wherein the lead is oxidised, lead nitrate is formed by dissolving the
oxide of lead, and is then decomposed by a soluble salt in the presence of some free
base for the production of a basic lead salt which is insoluble or but sparingly
soluble in the nitrate which is also produced by the decomposition, this nitrate
being then decomposed to regenerate nitric acid for the production of more lead
nitrate from a fresh batch of oxide of lead while, if the soluble salt which was used
have an alkali base the whole of the base of the alkali nitrate is recovered as
caustic alkali in solution which may either be evaporated for sale or be partially
acidified for use over again as the soluble salt.
It is to be understood that the invention may be employed for the production of
basic salts of lead other than the carbonate as well as of inixtures of basic salts of
lead, but as the production of basic carbonate of lead is the principal object of the
process we will describe the invention as applied to the manufacture of this
particular salt, it being understood that where caustic soda and sodium salts are
referred to potash and potassium salts are included.
We proceed as follows:-Crude pig lead is oxidized to form litharge which is
dissolved in nitric acid to form lead nitrate. Any silver, copper, and other metallic
impurities that may have been present in the crude lead are now eliminated from
the lead nitrate by the addition of finely divided metallic lead, whereby the silver
and some other metallic impurities are precipitated along with finely divided lead
forming ultimately rich silver lead as a bye product of the process.
The purification of the lead nitrate is only required if crude pig lead has been
used to form the lead oxide and by this means the cost of refining the lead is saved
at the same time that a valuable bye product is obtained, but it is of course to be
understood that although, for economical reasons, crude lead would be used the
process is not limited in this respect as it will be obvious that litharge made from
refined lead might be used although with less advantage.
To the solution of pure lead nitrate produced as above described, caustic soda
and carbonate of soda are added in the proper proportions for precipitating from
the lead nitrate the whole of the lead as basic lead carbonate which precipitates,
and leave pure sodic nitrate. The relative proportions of the best commercial
carbonate and of the best commercial caustic alkali are respectively 67% and 33%
but these proportions are by no means imperative. They may be varied as desired
according to the amount of base or hydrate that is to be imparted to the lead
carbonate.
The complete precipitation of nitrate of lead by carbonate of soda and caustic
soda will take place in the cold, but it may be found more practical on a large scale
to assist this precipitation by the application of heat which may also render the
precipitate more dense. The solution of sodic nitrate is separated from the
precipitate by decantation and filtration and whilst being evaporated to dryness is
mixed and stirred with such a quantity of ferric oxide as will prevent the fusing or
Buxing of the sodic nitrate when the latter is heated and so maintain the mass in a

page_text: porous condition throughout the operation next described. The mass is then
heated to an incipient red heat in a retort of, say, iron or earthenware and is at the
same time subjected to the chemical action of a mixed current of heated air and
steam (at, preferably, the same temperature as that of the mass) which is caused to
pass through the mass whose porosity permits of its easy permeation by the mixed
current of heated air and steam whereby nitrous fumes are evolved for conversion
into nitric acid at a much lower temperature than would be possible if only external
heat were applied, or if the fluxing of the mass into a mixed solid and liquid
condition were permitted. In this way the temperature of the decomposition is kept
sufficiently low to avoid the splitting up of the nitrous fumes into constituents
unconvertible into nitric acid.
The proportion of ferric oxide (if "purple ore" be used) should be two parts by
weight thereof, or more, to one part of nitrate of soda but the proportion of ferric
oxide may be varied according to the kind used, its physical state, and degree of
division. It must always be sufficient not only to prevent any fluxing of the mass
but also to ensure a sufficiently low temperature of decomposition to avoid the
splitting up of the nitrogen oxides too far for recovery as nitric acid. When the
mixed current of heated air and steam is passed through the heated mass as above
described, a true chemical action takes place by which the nitrate of soda is entirely
converted into ferrite of soda with evolution of nitrous fumes, only a very small
proportion of the oxides of nitrogen being destroyed, most of the nitric acid corre-
sponding to the nitrate of soda being recovered by air and water in a "Lunge plate
tower or other suitable apparatus in the usual way. The quantity of steam in the
mixed current is regulated in such manner that the recovered nitric acid is not too
weak and the quantity of air is kept in due excess for reconverting the lower oxides
of nitrogen into nitric acid in the "Lunge tower." The nitric acid thus regenerated
is used for dissolving a fresh batch of litharge and the ferrite of soda is decomposed
by heating into ferric oxide for use with a fresh batch of nitrate of soda, and a
solution of caustic alkali which may be partly carbonated by gassing with carbonic
acid for precipitating basic lead carbonate from a fresh batch of lead nitrate, or may
be partly used with more carbonate of soda for that purpose and partly sold as
caustic soda after evaporation in the usual way.
""
The reactions taking place in this process may be expressed as follows, the
desilverization of the lead being omitted to avoid complication:-
G. LUNGE,
C. H. MAXWELL-LYTE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents.

page_text: COMPLETE SPECIFICATION.
An Improved Process for Producing Basic Lead Salts and Obtaining
Certain Bye Products.
We, Dr. GEORGE LUNGE, Professor of Chemistry at The Polytechnicum,
Zurich, Switzerland, and CECIL HENRY MAXWELL-LYTE of 60, Finborough
Road, London, S.W., Esquire, 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 of conjointly producing basic lead salts from
crude pig lead and obtaining certain bye-products by a continuous cycle of
operations wherein the lead is oxidised, lead nitrate is formed by dissolving the
oxide of lead, and is then decomposed by a soluble salt in the presence of some
free base for the production of a basic lead salt which is insoluble or but sparingly
soluble in the nitrate which is also produced by the decomposition, this nitrate
being then decomposed to regenerate nitric acid for the production of more lead
nitrate from a fresh batch of oxide of lead while, if the soluble salt which was
used have an alkali base the whole of the base of the alkali nitrate is recovered as
caustic alkali in solution which may either be evaporated for sale or be partially
acidified for use over again as the soluble salt.
It is to be understood that the invention may be employed for the production of
basic salts of lead other than the carbonate as well as of mixtures of basic salts
of lead, but as the production of basic carbonate of lead is the principal object of
the process we will describe the invention as applied to the manufacture of this
particular salt, it being understood that where caustic soda and sodium salts are.
referred to, potash and potassium salts are included.
We proceed as follows: Crude pig lead is oxidized to form litharge which is
dissolved in nitric acid to form lead nitrate. Any silver, copper, and other metallic
impurities that may have been present in the crude lead are now eliminated from
the lead nitrate by the addition of finely divided metallic lead, whereby the silver
and some other metallic impurities are precipitated along with the finely divided
lead forming ultimately rich silver lead as a bye product of the process.
The purification of the lead nitrate is only required if crude pig lead has been
used to form the lead oxide and by this means the cost of refining the lead is
saved, at the same time that a valuable bye product is obtained but it is of course
to be understood that, although for economical reasons crude lead would be used,
the process is not limited in this respect as it will be obvious that litharge made
from refined lead might be used although with less advantage.
To the solution of pure lead nitrate produced as above described, caustic soda
and carbonate of soda are added in the proper proportions for precipitating from
the lead nitrate the whole of the lead as basic lead carbonate which precipitates
and leaves pure sodic nitrate. The relative proportions of the best commercial
carbonate and of the best commercial caustic alkali are respectively 67% and 33%!
but these proportions are by no means absolute. They may be varied as desired
according to the amount of base or hydrate that is to be imparted to the lead
carbonate.
The complete precipitation of nitrate of lead by carbonate of soda and caustic
soda will take place in the cold, but it may be found more practical on a large
scale to assist this precipitation by the application of heat which may also render
the precipitate more dense. The solution of sodic nitrate is separated from the
precipitate by decantation and filtration and whilst being evaporated to dryness is
mixed and stirred with such a quantity of. ferric oxide as will prevent the fusing.
or fluxing of the sodic nitrate when the latter is heated and so maintain the mass
in a porous condition throughout the operation next described. The mass is then
L

page_text: heated to an incipient red heat (temperature of about 500° C.) in a retort of, say,
iron or earthenware, and is at the same time subjected to the chemical action of a
mixed current of heated air and steam (at preferably the same temperature as that
of the mass) which is caused to pass through the mass whose porosity permits of
its easy permeation by the mixed current of heated air and steam, the effect of
the intimate contact of the heated air and steam with the mass and the internal
heating of the latter thus effected being that the temperature of decomposition is
lowered, so that whilst complete decomposition is effected nitrous fumes are evolved.
which are wholly, or almost wholly, convertible into nitric acid, at a much lower
temperature than would be possible if only external heat were applied, or if the
fluxing of the mass into a mixed solid and liquid condition were permitted, since
in either of these cases the temperature of the decomposition would not be kept
sufficiently low to avoid the splitting up of the nitrous fumes into constituents
unconvertible into nitric acid.
The proportion of ferric oxide (if "purple ore" be used) should be two parts
by weight thereof, or more, to one part of nitrate of soda, but the proportion of
ferric oxide may be varied according to the kind used, its physical state, and
degree of division. It must always be sufficient to prevent any fluxing of the
nass, so as to render the mass easily permeable by the heated air and steam,
the effect of which as above stated is to ensure a sufficiently low temperature
of decomposition to avoid the splitting up of the nitrogen oxides too far for
recovery as nitric acid. When the mixed current of heated air and steam is
passed through the heated mass as above described, a true chemical action takes
place by which the nitrate of soda is entirely converted into ferrite of soda with
evolution of nitrous fumes at such a temperature that nearly all of the nitric acid
corresponding to the nitrate of soda is recoverable by air and water in a
"Lunge
plate tower,' or other suitable apparatus, in the usual way, only a very small
proportion of the oxides of nitrogen being destroyed. The quantity of steam in
the mixed current is regulated in such manner that the recovered nitric acid is not
too weak and the quantity of air is kept in due excess for reconverting the lower
oxides of nitrogen into nitric acid in the "Lunge tower." The nitric acid thus
regenerated is used for dissolving a fresh batch of litharge, and the ferrite of soda
is decomposed by heating with water into ferric oxide for use with a fresh batch
of nitrate of soda, and a solution of caustic alkali which may be partly carbonated
by gassing with carbonic acid for precipitating basic lead carbonate from a fresh
batch of lead nitrate, or may be partly used with more carbonate of soda for that
purpose and partly sold as caustic soda after evaporation in the usual way.
The reactions taking place in this process may be expressed as follows, the
desilverization of the lead being omitted to avoid complication :
1. PbO PbO
2. PbO + 2 HNO,
=
Pb(NO3)2 + H₂O
2 PbСО, Pb(OH)2 + 6 NaNO3
3. 3 Pb(NO3)2 + 2 Na(OH) + 2 Na2CO3
3'
4. 6 NaNO, +3 Fе2O3 + 3 H₂O = 3 Na₂O, Fе, O + 6 HNO,
5. 3 Na,O, Fе,O₂ + 3 H₂O = = 6 Na(OH) + 3 Fe2O3.
The course of anamti

page_text: 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 producing a basic insoluble or sparingly
soluble salt of lead, and caustic alkali, which process consists in dissolving oxide
of lead in nitric acid, decomposing the nitrate of lead by a soluble salt of an alkali
in the presence of some free base, so as to produce the basic salt of lead required
and a pure nitrate, then forming by double decomposition of this nitrate with.
ferric oxide, by means of heat air and steam, nitric acid for use over again and
a ferrite corresponding in its base to that of the soluble salt used, then decom--
posing this ferrite into ferric oxide for use over again, and caustic alkali.
2. The herein described process of producing basic lead carbonate and caustic
alkali, which process consists in dissolving lead oxide in nitric acid, decomposing.
the lead nitrate by sodic carbonate and caustic soda, so as to form basic lead.
carbonate and pure sodic nitrate, then forming by double decomposition of this
nitrate with ferric oxide, by means of heat air and steam, nitric acid for use over
again and ferrite of soda and then decomposing this ferrite into ferric oxide and.
caustic soda, as specified.
3. The herein described process of producing a basic insoluble or sparingly
soluble salt of lead and caustic alkali conjointly with the recovery of silver as.
silver lead, and of nitric acid and ferric oxide for use over again, which consists
in oxidizing crude pig lead, converting the lead oxide into lead nitrate, precipi-
tating the silver from the lead nitrate with finely divided lead, forming the basic
salt of lead by addition of an alkaline carbonate and some free base, decomposing
the alkaline nitrate formed by means of ferric oxide, heat, air, and steam, decom-
posing the resulting ferrite into ferric oxide and caustic alkali, as specified.
4. The herein described process of producing basic lead salts and obtaining
certain bye products, substantially as specified.
Dated this 11th day of April 1801
GEORGE LUNGE,
C. H. MAXWELL LYTE,
By A. M. & Wm. Clark,
53, Chancery Lane, London, Chartered Patent Agents..