This invention has as its object a process for recovering pure lead
and absolutely lead-free ecological slags, which can be reused as waterproofing,
by melting the lead oxide and sulfate of worn-out batteries.
Processes are known for recovery of pure lead by melting the lead
oxide and sulfate of worn-out batteries for motor vehicles and other uses.
They generally use carbon and iron as reducing agents.
Although the reaction between carbon and iron is exothermic, the energy
balance of said known processes is not very encouraging since on the whole a notable
amount of thermal energy is required for the reaction.
A further serious drawback of said known processes consists in the
fact that the slags that are obtained from the melting, still contain about 3%
of lead and since lead is a poison, they constitute an ecologically unacceptable
waste, which creates serious drawbacks when the tons of slags are considered that
are produced annually in all the countries of the world.
The process according to the invention completely eliminates the above
mentioned drawbacks since it makes it possible to recover all the pure lead present,
with notable reduction of the energy used and with slags that are absolutely free
of lead and are not toxic of harmful.
Said slags, subsequently treated, can further be used as waterproofing
of grounds, avoiding transmission of polluting substances to the water-bearing
Said process is characterized by the use, during melting of the lead
bioxide and sulfate, of a catalyst with a base of a carbonate of alkali or alkaline-earth
metals and potassium and aluminum silicates.
Calcium carbonate (CaCO&sub3;) is preferred as the carbonate.
From the practical viewpoint, said catalyst is obtained by using white
marble (calcium carbonate) sawdust and granite sawdust.
Actually, granite contains: quartz (SiO&sub2;), orthoclase (KAlSi&sub3;O&sub3;)
and muscovite: Al&sub3;KH&sub2;(SiO&sub4;)&sub3;.
With the catalyst according to the invention, the separation of the
lead is total and the slags are completely free of it, but not only that, but
given the presence of silicates in soluble form, they constitute, when further
treated, a waterproofing of notable efficiency, which can be used among others,
as has already been said, for waterproofing of grounds at the water-bearing strata.
The attached scheme represents the various phases of the process which,
among others, makes it possible in a way known in the art to recover the plastic
parts and the sulfuric acid solution of said treated batteries.
As can be seen from said scheme, 1 indicates the storage of the worn-out
batteries, 2 the mechanical separation of sulfate (3) and of the lead parts 4
constituting the support frames of the active material and the connections of the
plates of the batteries. 5 is the separation of the plastic (containers) and separators
of the plates; 6, the active solutions.
The lead sulfate obtained: PbSO&sub4;, at a temperature of about 10000,
of melting (3), is separated into lead bioxide (PbO&sub2;)(10) and into anhydride
SO&sub2; (7) which is an energetic reducing agent.
To the lead bioxide PBO&sub2; (10) and possible sulfate PbSO&sub4;
still present there are added (at 11) the marble and granite sawdust and reducing
agent (SO&sub2;) (15) coming from 7 and an optional further reducing agent (Fe,
C, S, etc.), thus obtaining the totality of Pb (at 16) and slags (12) absolutely
free of lead and reusable as ecological waterproofing agents.
The percentage of marble sawdust can be about 2.5-6 % by weight of
the PbSO&sub4; to be treated, that of the granite about 1-3 by weight of the PbSO&sub4;.
It is provided that said catalysts can be melting and reducing additives
of known type without going outside the scope of protection of the patent.