Covellite (CuS) as a novel adsorbent for the direct removal of As(III) and As(V) simultaneously from groundwater

ABSTRACT

Covellite (CuS) synthesized by precipitation method using sodium sulfide as the precipitant efficiently adsorbs As(III) and As(V) from water in 4–9 pH range. The adsorption does not require any pretreatment step for the oxidation of As(III) into As(V). The process of sorption entails the precipitation of copper arsenate, Cu₃(AsO₄)₂, formed due to the reaction between As species and CuS, in the crystalline surface moiety of covellite. The existence of As(V) in the adsorbed state is ascertained chemically by exploiting the selective extraction of As(V) in aqueous and As(III) in nonpolar solvents. The conversion of As(III) to As(V) occurs by a disproportionation reaction induced by sulfhydryl group formed as a result of the protonation of S atoms of CuS in the aqueous medium. The process of adsorption is fast and the adsorption follows the Freundlich isotherm for both As species. Cu₃(AsO₄)₂ is soluble in mild acidic solutions and its quantitative desorption is affected in <2.0 pH HCl. In column experiments, CuS (2 g) reduced the concentration of As in 9 L groundwater spiked with 200 μg/L As to <10 μg/L. In brief, covellite has good attributes of an adsorbent and is a candidate material for As remediation technologies.

KEYWORDS:

• Arsenic remediation
• arsenic (iii)
• arsenic (v)
• copper sulfide
• adsorbent
• groundwater

Acknowledgements

The authors thank Dr. A. K. Tyagi, Associate Director, Chemistry Group, BARC, Mumbai, for his support. The authors also thank Shri A. A. Sukumar for EDS and XRD measurements. The discussions and suggestions with Dr. R. Verma are gratefully acknowledged.