Removal and reuse of arsenic from arsenic-bearing purified residue by alkaline pressure oxidative leaching and reduction of As (V)

Arsenic removal from arsenic-bearing purified residue by alkaline pressure oxidative leaching (APOL) and reduction of arsenate in solution to arsenite by sulfur dioxide gas was studied. The effects of different parameters including NaOH concentration, oxygen partial pressure, temperature, liquid/solid ratio, and leaching time for the extraction of arsenic were investigated based on thermodynamic calculation. The optimum leaching conditions have been established as: 2.5 mol/L of NaOH concentration, 0.5 MPa of oxygen partial pressure, 120 degrees C of temperature, 4 mL/g of liquid/solid ratio and 3.0 h of time. Under these conditions, the leaching rates of arsenic, zinc and nickel respectively reached 94.47%, 19.90% and 12.66%, while copper and cobalt were hardly leached out, achieving the selective removal of arsenic from the arsenic-bearing purified residue. The reduction of As(V) in solution was optimized by orthogonal experimental design method, and the effects of experimental parameters including initial pH, reduction temperature (T), flow rate of SO2(F), and reduction time (t) on reduction of As(V) were investigated. The results show that the optimum reduction parameters were 4 of initial pH, 30 degrees C of temperature, 60 mL/min of SO2 flow rate and 2.5 h of time. Based on these conditions, the reduction rate of As (V) reached 92.95%.