Transformation behavior of the morphology, structure and toxicity of amorphous As2S3 during hydrothermal process

Abstract

Arsenic sulfide sludge (ASS) is a typical hazardous waste in the non-ferrous smelting industry. In our previous study, ASS was effectively stabilized by hydrothermal treatment. However, the mechanism of hydrothermal stabilization is still unclear. Amorphous As2S3 is the main component of ASS. Therefore, in this work, the hydrothermal transformation behavior of amorphous As2S3 precipitated with NaAsO2 and Na2S·9H2O under acidic aqueous was investigated for a better understanding of hydrothermal stabilization process of ASS. It was found that under the conditions of 210 °C, initial pH 2 and solid-to-liquid (S/L) ratio 1:5, amorphous As2S3 floc gradually transformed to spherulitic particles and showed aggregation behavior with the extension of hydrothermal duration. The spherulitic particles were identified as orpiment, which was the crystalline arsenic mineral in the nature. Moreover, the As leaching concentration of hydrothermal products decreased remarkably with the transformation from amorphous As2S3 to orpiment. Under certain hydrothermal conditions, the As leaching concentration of amorphous As2S3 can be reduced from 139.4 mg/L to less than 5 mg/L. Hence, the mineralization from amorphous As2S3 to orpiment was the significant reason for the stabilization of arsenic sulfide during hydrothermal treatment. This paper provided a theoretical support for the hydrothermal stabilization of ASS.