Aluminium clay regulates oxidation dissolution mechanism of pyrite by solid film passivation layer and S, Fe, Al, Si speciation transformation

Mining operations metallic sulfur minerals expose to oxidizing conditions, resulting in the production of acidic mine drainage (AMD). This work investigates how the inclusion of aluminous clay (AC) influences the speciation changes of sulfur (S), iron (Fe), aluminum (Al), and silicon (Si) on the surface of pyrite while it undergoes the bio-oxidative dissolution process. The results show that adding a small amount of AC (≤4.0 g/L) promotes the bio-oxidation of pyrite. Conversely, the addition of a larger amount of AC (>4.0 g/L) inhibits the oxidation of pyrite. The oxidation process of pyrite conforms to the "polysulfide-thiosulfate" complex oxidation pathway. The breakdown of AC involves the consumption of H⁺ ions and the release of Al³⁺ ions. This process contributes to changes in hydrochemical composition, facilitating the hydrolysis of Fe³⁺ and Al³⁺ to create a secondary mineral layer on the pyrite's surface. This in turn, encourages the formation of FeS_n or Fe_1-xS. These findings suggest the potential to control the oxidative dissolution of pyrite by regulating the formation of a solid film passivation layer. This work gives a new insight into devising strategies aimed at remediation and treatment, presenting avenues to mitigate environmental pollution caused by AMD.