The conventional pirometallurgical process for the production of metallic lead is compared with two innovative clean processes: electrohydrometallurgical and alkaline smelting. The electrohydrometallurgical process consists on reducing the particle size of the lead compounds and leaching them with an acidic solution of ferric fluoroborate. In this step, lead is dissolved with the ferric being reduced to ferrous ions. The resulting solution from the leaching step is sent to the cathodic compartment of a diaphragm cell in which lead is deposited on a cathode of stainless steel, in compact and pure form. The solution that is depleted of lead ions is then sent to the anodic compartment of the same cell where a suitable anode oxidizes ferrous to ferric ions that turn back to the leaching step. The alkaline smelting process consists in feeding molten caustic soda, sulfur and lead compounds into a reaction reactor at temperature of 600-700°C. As a result metallic lead is obtained together with a melt containing sodium salts, metal sulfides and gangue. The melt is processed yielding gangue, metal sulfides, caustic soda and sulfur. These two last turn back to the reaction reactor. Both processes allow the recovery of valuable metals such as antimony, tin, sulfur and silver that in conventional process are losing in the slag. These innovate processes are ecologically cleaning processes without serious pollution of Pb and SO2. The obtained metallic lead is purer than that from conventional process and seldom contains any impurity.
Lead; electrohydrometallurgical process; alkaline smelting process and environment
