Lime additions to arsenic-containing wastes have been proven to be beneficial in reducing the mobility of dissolved arsenic, presumably through the formation of low-solubility calcium arsenates. Ho...

Arsenic immobilization by calcium arsenate formation

The stabilities of calcium arsenates at 23 ± 1°C

Removal and recovery of high levels of arsenic (As) in copper smelting wastewater present a great environmental challenge. A novel approach was investigated for the first time using TiO2 for As adsorptive removal from wastewater and subsequent spent adsorbent regeneration and As recovery using NaOH. EXAFS results demonstrate that As(III), as the only As species present in the raw water, does not form an aqueous complex with other metal ions. An average of 3890 ± 142 mg/L As(III) at pH 1.4 in the wastewater was reduced to 59 ± 79 μg/L in the effluent with final pH at 7 in the 21 successive treatment cycles using regenerated TiO2. Coexisting heavy metals including Cd, Cu, and Pb with concentrations at 369 mg/L, 24 mg/L, and 5 mg/L, respectively, were reduced to less than 0.02 mg/L. As(III) adsorption followed pseudosecond-order rate kinetics, and the adsorption behavior was described with the charge distribution multisite surface complexation model. Approximately 60% As(III) in the waste solution after the ...

Arsenic removal and recovery from copper smelting wastewater using TiO2.

Coprecipitation of arsenate with iron(III) in aqueous sulfate media: Effect of time, lime as base and co-ions on arsenic retention

Heavy metal removal from copper smelting effluent using electrochemical cylindrical flow reactor

The systems Ca(II)-As(III)-H2O and Ca(II)-As(V)-H2O were studied by equilibrating mixtures of calcium oxide and arsenious or arsenic acid solution at 25°C for one month. Where the pH of the final solution was likely to be greater than 8, care was taken to exclude atmospheric carbon dioxide. Chemical analysis of the final solid phases and the associated solution from each experiment for calcium and arsenic, together with X-ray diffraction analysis of the solids and an inspection of graphed relationships, indicated the existence of the compounds Ca(AsO2)2 and CaAsO2OH 1/2H2O in the system Ca(II)-As(III)-H2O; and Ca(H2AsO4)2, CaHAsO4 H2O, Ca3(AsO4)2 4H20 and Ca2AsO4OH 2H2O in the system Ca(II)-As(V)-H2O. The solubility and stability regions for these compounds were assessed as a function of pH, and solubility constants and conditional free energies of formation for each compound calculated from the solubility data obtained. A brief historical review of literature in which calcium arsenites and calci...

T. Nishimura

Papers

A Re-evaluation of the Solubility and Stability Regions of Calcium Arsenites and Calcium Arsenates in Aqueous Solution at 25°C