A novel method for preparing an As(V) solution for scorodite synthesis from an arsenic sulphide residue in a Pb refinery

摘要

A novel method has been proposed to prepare an arsenate (As(V))-containing solution for scorodite formation using an arsenic (As) sulphide residue obtained from a Pb refinery. Preparation of the As(V) solution from the As sulphide residue included As oxidation leaching by alternating addition of a highly concentrated sodium hydroxide (c-NaOH 600 g/L) solution and hydrogen peroxide (H2O2) at 70 degrees C. This method gave an As leaching efficiency of up to 99% (total % recovery of As up to 90%), while at the same time, other metals could be recovered effectively (e.g., 95% Pb, 97% Cd, 90% Zn, and 96% Cu). Further oxidation and removal of the remaining arsenite (As(III)) in the leached filtrate by H2O2 indicated that the oxidation efficiency of oxidizing As (III) to As(V) was up to 99%. The As(V) solution produced by this process was suitable for As(V) fixation as scorodite. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the starting materials and output solids. The results showed that the major As phase in the As-containing compound of the initial As sulphide residue was As sulphide. Highly pure elemental sulphur (total % recovery of S up to 30%) was generated during the S(-II) elimination process, and the scorodite from the As(V) fixation process was highly crystalline. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray absorption near edge structure spectroscopy (XANES) were employed to characterize the intermediate filtrate of the process. The results showed that the intermediate filtrate was a multiphase mixture containing As(III), arsenate, sulphate, thio-arsenate, thio-sulphate and polysulphides (S-n(2-)). The produced scorodite showed good As stability in the TCLP and at pH 3 (0.47 mg/L), pH 5 (0.26 mg/L), and pH 7 (3.41 mg/L) in a 10-day short-term stability test.