Efficient removal of As, Cu and Cd and synthesis of photo-catalyst from Cu-smelting waste acid through sulfide precipitation by biogenic gaseous H₂S produced by anaerobic membrane bioreactor

The proper disposal of Cu-smelting waste acid (CSWA) is a major challenge in sulfide ores pyrometallurgy industry due to its high content of H₂SO₄, extremely high concentration of As and multiple toxic metals. The neutralization precipitation using cheap CaO is the most widely used process in tackling CSWA. However, a large amount of hazardous wastes covering As and other heavy metals which requires further disposal is generated, and the valuable H₂SO₄ cannot be reused. Herein, anaerobic membrane bioreactor (AnMBR) is used to continuously produce gaseous H₂S for sulfide precipitation of the refractory CSWA and simultaneous fabrication of photo-catalyst for the first time. The 200L AnMBR respectively gained the highest total H₂S production of 6.41 g/h and the highest gaseous H₂S production of 5.05 g/h under the optimal conditions, being 3–9 times higher than previous reports by other types of bioreactors. And the sulfide precipitation triggered by the maximum gaseous H₂S of 5.05 g/h harvested almost 100 % removal for Cu, As and Cd from CSWA within a short time from 0.35 to 3.69 days. Moreover, the phase 1 precipitate covering Cu-S compounds displayed an efficient photo-catalytic activity. The sulfide precipitation by AnMBR showed an application potential in tackling the refractory CSWA and fabrication of valuable nanoparticle photo-catalyst.