Exploration of the arsenic removal performance fluctuation using H2S from highly acidic wastewater in copper smelting

With continuous impelling of the Belt and Road Initiative, China has been cooperating with Belt and Road (B&R) countries in copper smelting. The large amount of highly acidic wastewater generated in copper smelter that is rich in arsenic (As) should be removed prior to recovery. The sparged H2S is used for As precipitation in the actual treatment, but is among the first found to be defective in performance fluctuation. This phenomenon is evidenced in this study that As concentrations of 60% samples obtained from the sulfuration tank are above the enterprise upper limit of 20 mg/l. Consistent with the performance fluctuation, our laboratorial investigation shows that the maximum As removal efficiency is only about 50%. Based on this issue that existed in the actual copper smelting, the inherent mechanism is explored. Experiments show that the H2S escape and As2S3 re -dissolution are two main reasons, which are other meaningful findings of this study. The limited height of sul-furation tank leads to the incomplete utilization of sparged H2S. The existing Cu2+ causes up to 21.5% of the generated As2S3 to be re-dissolved. Strategies are put forward from two aspects to favor the As removal, namely increasing the height of sulfuration tank to extend the contact between H2S and wastewater, and timely discharge of precipitated sludge to prevent As2S3 re-dissolution. This study provides China's solution to promote cleaner production in copper smelters, which benefits the copper smelting industry in both China and B&R countries.