Interaction of arsenic(III) and arsenic(V) on manganese dioxide: XPS and electrochemical investigations

Abstract

Manganese dioxide (MnO₂) synthesized by solid-state reaction was characterized and sorption of As(III) and As(V) on it was studied in batch mode using ⁷⁶As radiotracer. Arsenic removal efficiency was ∼98 % in the pH range of 3–9. Solvent extraction study indicated that >95% of arsenic is present as As(V) after sorption. A new electrochemical method was developed for explaining the arsenic–manganese interactions. Cyclic voltammetry and chronopotentiometry measurements were carried out which indicated the difference in the interaction of As(III) and As(V) with MnO₂. X-ray Photoelectron Spectroscopy (XPS) was carried out in which the 3p_3/2 binding energy peak of As(III) and As(V) standards was compared with the binding energy peaks observed for arsenic sorbed on manganese dioxide. The binding energy peaks of arsenic on MnO₂ were matching with that of As(V), irrespective of the oxidation state of arsenic taken for sorption. The study confirmed that irrespective of the initial oxidation state, arsenic was sorbed on MnO₂ as As(V); during the oxidation of As(III) by MnO₂, manganese was reduced to Mn(II) and the Mn(II) formed during sorption was sorbed on the surface creating fresh surface promoting further sorption. Based on the observations, a mechanism of sorption has been proposed.

Keywords:

• Sorption mechanism
• arsenate
• arsenite oxidation
• manganese dioxide

Acknowledgments

The authors thank Dr. P. D. Naik, Associate Director, Chemistry Group & Head, Analytical Chemistry Division, BARC for his support. The authors thank Dr. R. Tewari, Shri Sanjay Kumar, MSD, BARC and Dr. Raghumani N., Chemistry Division, BARC for their help during TEM measurements. The authors also thank the operation crew of Dhruva reactor for their support during sample irradiation for radiotracer preparation.

Disclosure statement

No potential conflict of interest was reported by the authors.