Alternation Mechanism of Lead Sulfate toward Lead Sulfide under Sulfuric Acid Conditions

Abstract

Rapid metasomatism of lead sulfide toward lead sulfate under acidic conditions is a geochemical phenomenon that can access the immobilization route of toxic heavy lead; however, the molecular mechanism has not yet been elucidated. Here, we succeeded in studying the alternation mechanism of galena to anglesite under sulfuric acid conditions by an extended mechanistic theory of nucleation, where diffusion and reactions of molecules at mineral interfaces are taken into consideration. There exist large nanovoids with a size of ∼6 Å at the interfaces acting as diffusion pathways of solution molecules with an activation energy of ∼0.1 eV. In addition, protons available in solution readily react with interior surfaces of the above-mentioned nanovoids because of close interaction involving an energy cost of ∼0.2 eV. The diffusive nature and reactive nature of solution molecules at the mineral interfaces govern the anglesite formation, triggering off a low energy cost of ∼0.3 eV under sulfuric acid conditions.