Stabilization mechanism of arsenic-sulfide slag by density functional theory calculation of arsenic-sulfide clusters

Stabilization of arsenic sulfur slag (As-S slag) is of high importance to prevent the release of deadly As pollutants into environment. However, the molecular understanding on the stability of As-S slag is missing, which in turn restricts the development of robust approach to solve the challenge. In this work, we investigated the structurestability relationship of As-S slag with adopting various As-S clusters as prototypes by density functional theory (DFT). Results showed that the configuration of S multimers-covering-(As2S3)n is the most stable structure amongst the candidates by the analysis of energies and bonding characteristics. The high stability is explained by orbital composition that the 4p-orbital (As) binding with 3p-orbital (S) decreases energy level of highest occupied molecular orbital (HOMO). Inspired from the calculations, an excess-S-based hydrothermal method was successfully proposed and achieved to promote the stabilization of As-S slag. Typically, the As concentration from the leaching test of stabilized As-S slag is only 0.8 mg/L, which is much lower than the value from other stabilized slag.