It is common knowledge that all traditional lead recycling processes contemplate smelting, which is a highly polluting, expensive and inefficient process. This is due to the use of furnaces which work at very high temperatures (about 1300°C) and are extremely polluting (one of the most polluting processes on earth).
After several years of research and fine tuning of the technology, STC S.r.l., an engineering company located in South of Italy, has realized a pilot plant able to regenerate about 2 t/d of lead oxides starting from exhausted lead paste without involving pyrometallurgical processes.
The system is based on a process, patented by the company, which employs ammonium carbonate for the transformation of lead sulphate into lead carbonate. Although the mentioned reaction has been known for many years, in this case the adopted engineering expedients allowed to achieve yields close to 100%. A lead paste treatment, where the drying temperature is higher than the PbCO3 decomposition temperature, leads to the formation of oxide, a compound that is easily leached in the following step. It is possible to reprecipitate high purity lead carbonate thanks to an ingenious recovery system. The following heat treatment leads to the production of pure lead oxides of different types: litharge, massicot or minium which might be used both for the production of active material for batteries (starter and traction batteries), and for any other use this pure compound is thought for (ceramic, glass and rubber industries, etc). The by-product deriving from the whole cycle, ammonium sulphate, is a fertilizer to be sold and used for agricultural applications. Both the abatement of pollution caused by old systems and the final production of a fertilizer confirm the green essence of this cycle.
Furthermore, an experimental batch of about 1000 starter batteries (see figure 2) has been produced with the hydro-metallurgical Lead Oxide Regeneration technology proposed by STC. After several tests, it has been proved that the obtained batteries containing the regenerated nanostructured oxides have a greater capacity and a longer life than those produced with traditional processes.
In other words, this technology makes it possible to have a remarkable economic saving, a virtually non-existent environmental impact and the possibility to supply battery producers with oxides that are ready for the production of new batteries with better characteristics than the traditional ones.
Now, the next step for STC is the construction of an industrial plant that will demonstrate to the scientific community and to all main actors of the energy storage sector the great potential of its process.