Arsenic recovery from water containing arsenite and arsenate ions by hydrothermal mineralization

Recovery of arsenic as precipitate of natural mineral from model wastewater containing various initial concentrations and oxidation states of inorganic arsenic oxoanions was investigated by hydrothermal mineralization treatment. The treatment is an earth-mimetic method to produce natural minerals by hydrothermal treatment using Ca(OH)2 as a mineralizer. The treatment of model wastewater containing arsenate ion or mixed aqueous solution of arsenate and arsenite ions by using Ca(OH)2 mineralizer and H2O2 oxidizer was found to precipitate arsenate apatite which is a natural mineral containing high concentration of arsenic. The feature of this treatment was independent on the initial concentration and the oxidation state of arsenic regardless of mixed ratio of arsenate and arsenite ions. Arsenic concentration in the treated-water at the optimum treatment conditions was 0.02 mg/dm3, when treated for the aqueous solution containing 1-2000 mg/dm3 of arsenate or arsenite ions. The precipitate obtained by this treatment was a kind of natural mineral (Johnbaumite), which could be easily reused as resources of arsenic compounds. Therefore, the present hydrothermal mineralization treatment with the Ca(OH)2 mineralizer is an effective technique to recover arsenic from aqueous media.