Speciation characterization of arsenic-bearing phase in arsenic sulfide sludge and the sequential leaching mechanisms

Abstract

Arsenic sulfide sludge (ASS) is a kind of deleterious waste which contains various valuable metallic elements, such as Re and Pb, which are always associated with arsenic-bearing phases in ASS. The leaching speed and efficiency of valuable elements may depend on the phase constitution. Here, we proposed a sequential leaching method to thoroughly understand the constitution of arsenic-bearing phase and the distribution of valuable elements in ASS. The results show that five major arsenic-bearing phases exist in ASS: amorphous As₂S₃, crystalline As₄S₄, As₂O₃, and As atoms dissolved into the lattice of PbS and PbSO₄ phases. Re is mainly distributed in As₂S₃ and As₄S₄ phases. During the leaching process, the dissolution of As₂O₃ particles and As₂O₃ layers on the surface of As₂S₃/As₄S₄ particles occurs first. Then, the reaction between As₂S₃/As₄S₄ particles and copper sulfate happens. The order of leaching sequence is As₂O₃, amorphous As₂S₃ and crystalline As₄S₄. The majority of Re element exists in the solution while almost all Pb element remains in the solid residues, which is beneficial for the separation and purification valuable elements individually. This work not only detailed determines the arsenic-bearing species, but also provides significant theoretical bases for extracting valuable elements from ASS.

Keywords: Arsenic sulfide sludge; As-bearing species; Phase constitution; Sequential leaching process; Valuable elements.