Hydrothermal Treatment of Arsenic Sulfide Residues from Arsenic-Bearing Acid Wastewater

Arsenic sulfide residue (ASR), a by-product from the treatment of arsenic-bearing acidic wastewater, is abundantly generated but not properly disposed of in China. The utilization of such high-content arsenic waste residue is limited by the market. The traditional methods of stabilization/solidification (S/S) by lime cement or iron salt have a large mass/volume addition, high dumping cost and secondary pollution risk. In this paper, hydrothermal technology was used to treat three kinds of ASRs obtained from different smelters to minimize waste. The leaching toxicity and chemical speciation of the generated products was also evaluated by TCLP and BCR analyses. It was found that the hydrothermal treatment could greatly reduce the volume and moisture content of the ASRs. TCLP tests showed that the leachability of arsenic and heavy metals significantly decreased after the treatment. According to the BCR analysis, most of the unstable As, Cd and Cr transformed into a residual fraction. Finally, XRD, SEM, Raman and XPS techniques were carried out to reveal the mechanism. As a result, hydrothermal treatment can efficiently achieve the dehydration, volume reduction and stabilization/solidification of ASRs.