Qian Liang,Linhua Jiang,Ning Duan,Fuyuan Xu,Hongping He
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 H 2 S 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 H 2 S escape and As 2 S 3 re-dissolution are two main reasons, which are other meaningful findings of this study. The limited height of sulfuration tank leads to the incomplete utilization of sparged H 2 S. The existing Cu 2+ causes up to 21.5% of the generated As 2 S 3 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 H 2 S and wastewater, and timely discharge of precipitated sludge to prevent As 2 S 3 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.
Sulfidation is recognized as a competitive method to remove arsenic from copper smelting waste acid. However, despite its ability to shed As(Ⅲ) efficiently, the sulfidation driven by S(-Ⅱ) supersaturation levels generates fine particles that severely hamper subsequent solid-liquid separation. In this study, the results manifest that expanding S(-Ⅱ) dosage and downgrading acidity (i.e., H 2 SO 4 concentration) can foster As(Ⅲ) removal, but diminish the particle size distribution of As(Ⅲ) sulfides. Based on the diffusion-growth model, except for in-situ CuS and CdS, concomitant anions and cations decelerate As(Ⅲ) sulfide settling. This is attributed to enhanced negative charges on the particle surface. In pursuit of better settling performance of As(Ⅲ) precipitate, a strengthening strategy of As 2 S 3 crystal seed and polyacrylamide(PAM) flocculant is proposed, where the preparation of As 2 S 3 crystal seed from arsenic waste complies with the green recycling-production standards. By involving 10 g/L As 2 S 3 crystal seed as heterogeneous nucleation and 5 ml/L PAM flocculant as framework support, the settling velocity of As(Ⅲ) sulfide is boosted by approximately 170%, delivering valuable guidance for reinforcing gravity settling performance in thickener processes.
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