Mechanism study of the effect of copper ions on the stability of As(III) sulfuration precipitation in acidic copper smelting wastewater.

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Sulfide precipitation is considered as a very efficient method for removing arsenic from actual copper smelting acidic wastewater. However, the arsenic removal process can be affected by copper ions. This study focuses on the mechanism of copper ions' influence on the stability of As(III) sulfuration precipitation. Sulfuration reaction experiments are carried out using Na2S in three different simulated highly acidic wastewaters with initial As(III) concentrations of 2000mg/L (LAs), 5000mg/L (MAs), and 10000mg/L (HAs), and the implications of processes variables of S/As ratio and copper concentration on the stability of As(III) sulfuration precipitation are discussed. The results show that the As(III) sulfuration precipitation is significantly affected by copper ions in the LAs reaction systems, whereas in the MAs and HAs reaction systems, which can be noticeably affected by copper ions only when the S/As is not greater than 1.5 (≤ 1.5), i.e., when the amount of Na2S is insufficient. Person correlation analysis also demonstrates a remarkable negative correlation (correlation coefficient is around - 0.96) between the S/As ratio and copper ion concentration on As(III) removal efficiency in the LAs reaction systems. The effect of copper ions on As2S3 is further investigated, and it is detected that copper ions cause approximately 3.3% of the precipitated As2S3 to be re-dissolved. This study proves that copper ions not only compete with As(III) for S2-, but also cause the precipitated As2S3 to re-dissolve. Therefore, in the actual manufacturing process, it is essential to control not only the sulfiding dose, but also the copper ions. This study provides a specific reference for actual enterprises to sulfurize As(III) from highly acidic wastewater and is of great significance for controlling actual industrial processes.