Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention rela-tes to a process for treating sul-
phated lead compounds for recovering metallic lead therefrom
and, concurrently therewith, a high-purity sulphate, and an
installa-tion for performing said process.
The process of the presen-t inven-tion is par-ticularly
suited to the trea-tmen-t of sulphated lead compounds coming from
acidic storage batteries with lead electrodes, which are exhaus-
ted ("electrode pastes").
Many a process is known for recovering metallic lead
from the "exhausted pastes" and from the sludges of the exhausted
batteries; for example, pyrometallurgical processes are commonly
known, in which the sulphated lead deriva-tives, mostly lead sul-
phate and lead sulphide, are thermally reduced to metallic lead.
Serious objections against such processes are, on the one hand,
the necessi-ty of using reagents, such as iron and pyri-te ashes,
or slag forming compounds, such as soda or lime, at hiyh -tempera-
tures, and, on the other hand, -the fac-t that a high percentage
of -the sulphur which is contained in the startiny materials is
converted into noxious s~llphurous gases which, i discharged
2r~ into the atmosE)here, cause ecological damage. I-t is thus
imperative to install purification systems in which the exhausted
sulphurous gases are subjected to scrubbing, for example with
alkaline solutions, based on lime or ammoniacal solutions.
It is apparent that this is a serious source of expendi-ture due
-to the capi-tal and running cos-ts of such purification systems,
so that this technology has grea-t limitations.
3r)
/
~
I-lydrometallurgical processes such as those disclosed
by the U.S. Patents 3,8~33,3~8 and 4,119,219 are alsQ known.
These patents describe processes in which the materials which
contain lead sulpha-te are treated with a solution of ammonium
carbonate to give lead carbonate and ammonium sulphate, the
lat-ter being recovered for use as a fertilizer. Typical draw-
backs of such processes are, however, the formation of ammoniacal
gases and thus the processing conditions are hazardous and the
necessity is felt of having specially designed systems available
for concentrating the ammonium sulphate solu-tions and recovering
the reactants, so -that such processes are also economically
objec-tionable.
The RI 3123 of the Bureau of Mines (U.S. Department
of the Interior) describes the use of calcium hydroxide for con-
ver-ting lead sulphate into lead hydroxide. Concurrently, in-
soluble calcium sulphate is formed so -that it becomes necessary
to carry out a reducing rnelting of the mixture thus obtained in
the presence of a large amount of a "flux" such as a mixture of
sodiurn chloride and potassium ch]oride.
A:LthoucJh the temperature at which such a reductlon
is :Iow, the great mass of substances to be melted makes -the pro-
cess of doubtful acceptance from an economical standpoint. More-
over, additional treatments are required to recover the fluxes.
Britich Patent l,535,025 discloses the dissolu-tion of
a "spent paste" which contains lead oxides and sulphates in-to
an alkaline electrolyte, in the presence of sucrose so as to
form a complex with lead, the solu-tion thus obtained being -then
electrolyzed with insoluble anodes to recover metallic lead.
3G
i,
I~his process is also bo-th intricate and economic~ally
objectionable.
U.S. Patent 4,018,567 describes an apparatus which is
ratller intricate and is intended for the separation of -the
several component par-ts of acidic lead storage batteries.
In order to form, together with the finer particles of
the active mass of -the storaye battery, the thick me~ium which is
required for making the lighter component parts, such as the
separators and ~he casings, buoyant, while sinking the me-tallic
component parts, such as bridge-poles and grids, the British
Patent uses a solution o:E sodium carbonate. The Patent mainly
discloses an intricate device for hydraulically and mechanically
separating -the several component parts involved, but does not
give any adequate suggestions as to -the procedure for making
the recovery sys-tem for -the several components economically
advantageous: this cou]d be done by a system which, in addition
to a satisfactory recovery of the me-tal, would concurren-tly
provide a complete and advan-tageous recovery of -the sulphated
compounds, -that which would also preven-t the ecological damage
due to their scatteri.ng i.n the environment.
It can thus be apprecia-ted that the processes as adop-
-ted heretofore for recovering metallic lead from i-ts sulphated
compounds involve problems which are predominantly health-
hazard problems and economic disadvantage problems due to the
processing conditions.
3~
~.~
/ '
This invention overcomes -the problems encountered with
the processes of -the prior art in this field. According to the
presen-t invention there is provided a process for -treating
sulphated lead compounds, more particularly those coming from
spen-t storage batteries, to recover both me-tallic leacl and a
high-purity sulphate, which comprises subjecting said sulphated
compounds to leaching wi-th sodium carbonate in aqueous solution,
collecting on a fil-ter the lead carbonate precipita-te thus ob-
tained from the dissolved sodium sulphate, subjecting -the lead
carbonate to reduction to metallic lead, separating the sodium
sulphate by crystallization from the filtrates and recycling
the crystallization mother liquors to the leaching stage.
The present inven-tion further provides an installa-tion
for performing the process referred to above, said installation
comprising a reactor for carrying out -the leaching of said sul-
phated lead compounds with sodium carbona-te, means Eor feeding
the reactants to the reactor, means for carrying out -the fi]tra-
tion of the liquor exiting the reactor, a kiln for the thermal
reduction of ]ead carbonate to give metallic lead, crys-talliza-
tion vats for separating the sod:iurn su:Lpahte from -the filtra-tes
and rneans for recycling the crystallization mother liquors to
said reactor.
The present invention will be further il~ustrated by
way of the accompanying drawing, which is a flow diagram of the
process according to a preferred embodiment of the invention.
~ _
/
Referring to the diagram, a "spen-t pas-te" of exhausted
storage batteries, which mainly contains lead sulphaté, is char-
ged at 11 into a reactor 12, ~or example a vat having heating
and stirring means, which is also fed at 13 and 14 with an
aqueous solution of Na2CO3 of medium strength. The "spent
paste" charged at 12 is obtained by separating the paste from
the remaining component parts of the s-torage ba-tteries by any
appropriate method, for example as disclosed in the U.S. Patent
Nos. 3,456,886 and 3,614,003.
In the reactor 12, which is maintained at a tem-
6.
perature be-t~Yecn 30C and 40C with stirring for about
one hour, the leaching stage is carried out, so -that
a double-excl)ange reaction tal<es place hetw~en the
reacting salts, the result being the formation of lead
carbonate in the iform of an insolubl.e precipitate, and
v~ry
1 the formation of sodium su].phate which is oxtrcmcly so-
luble in ho-t tvater and which thus remains disso~.ved
therei.n. ~nee tne reaction has been eompleted, the
mixture thus obtained is -fed to a filtration stage 15,
1~ such as a -filter-press, to separate the precipi.tate
from the solution. At -the exit from this stage,ther.e
is obtained at 16, a solid which contains the derivati~
ves, main~y lead earbonatc, of the learl ch~rge coming
from 11. The solids are dried at 17 and fed at 18 tV a
stage Or reduction, in a Iciln to wh;.eh coa]. .Ls -fecl dt
19 in the necessary amount (rouc)h].y 4% of the soli.d<; by
we:Lgllt ),
~rom the reduetion k-;.ln, whien is Maintcli.ned at
about 900C for one hour, ra-.Y metallic lead is drawn at
20, The fil-tra-te 219 coming -from ttle filtration stage
15, contains the as-produced sodium sulphate and the
unreacted sodium carbonate from the leaching stage.
The filtrate is collectcd in crys-ta].li~ati.on vats 22,
~/hercin, by merely allowlncJ the liquor to cvol at room
temperature, crystals of decahydrous sodlurn sulphate
can gro~,. On completi.on of crystalli~ati.on, the mo-
theJ li~uors 23 e~.i.tin(J 22 are recycled to the reactor
12 for the sutJsc~lent step.
The crystals of sodium sulphate coming from the vats
22 are strained by centrifugation at 2~, collec-ted at 25 and
subjected at 26 -to drying in a low-tempera-ture air-s-tream to
give a high-purity anhydrous sodium sulphate which can be used
for enamel coatings or glass mills direc-tly and without requir-
ing any fur-ther purification s-teps.
The process allows the conversion of -the s-tar-ting sul-
pha-ted lead compounds into two recovered products having a high
quality, such as raw metallic lead and pure anhydrous sodium
sulphate, without being affected by any of the difficulties dis-
cussed above relatively to -the prior ar-t in this field.
The vi.rtually to-tal conversion of the charged lead
into its non-sul.phated compounds, mainly PbCO3, allows a kiln
reduction to be effected with times which are much shor-ter and
at temperatures which are mus-t lower -than those in the hitherto
conven-tional processes of reduction of lead sulphate (or sul-
phide), and, above all, no fluxes or slag-:Eormers are required.
In the process according to this invention on compari-
son wi.th conventional pyrometa].lurgical procedures, the potential
output of the reduction k:iln is irnproved by about 15%, the dura-
tion of the refractory liners of -the kiln is ex-tended by abou-t
60%, the formation of fumes and slags is reduced by about 65%,
the lead losses by scattering in the fumes and slags is reduced
by about 50%, and finally, the power consumption is reduced
by about 30%.
3~
-- 7 --
~9¢~
Above all, -the process according to this lnvention,
by providing for the -total conversion of the sulphated lead com-
pounds into lead carbonate prior to -the redcution stage, pre-
vents, in the latter stage, the emission of sulphurous gases,
which, conversely, was invariably experienced in all those pro-
cesses in which sulphated lead compounds were reduced. The
starting sulphur, not only is no more scattered in the a-tmos-
phere in the form of noxious gases, but, conversely, is conver-
ted, in its turn, into a high-purity compound, that is sodium
sulphate, the commercial value of which can be estimated to be
such as to balance the processing costs for the added reac-tants.
An additional, considerable advan-tage afforded by -the
process of the invention is that the sodium sulphate exiting the
processing run, inasmuch as it crystallizes with 10 mols of
water per mol of salt, considerably reduces the amount of water
in use, whereby the recycling of -the mo-ther liquors of the pro-
cess is faci.litated and the possibility of any water pollu-tion
in -the environment of the installa-tion is dras-tically reduced~
The process according to -this invention allows the
lead contained in sulpha-ted lead res:idues to be recovered with
a mini.rnum loss of metal, a maximum economical effi.ciency and a
substantial reduction of any risk of pollu-tion of the environ-
ment.
-- 8
/
The presen-t inven-tion thus affords a clean technology
which is adap-ted to -the treatment of all the sulphatea compounds
of lead. The process can advantageously be adopted, no-t only to
-the treatment of spent pastes and sludges from exhausted lead
storage ba-tteries to which it is particularly adap-ted, but also
-to the trea-tment of sulphur-containing lead fumes and ores,
after an appropriate sulphation of -the materials -to be processed.
.~...
