Sorption of arsenic on manganese dioxide synthesized by solid state reaction

Abstract

Arsenic in groundwater is a major concern in many parts of the world and suitable sorbents are required for removal of arsenic from ground water. Removal of arsenic from groundwater has been studied using manganese dioxide, synthesized by solid state reaction of manganese acetate with potassium permanganate. Manganese dioxide was characterized by X-ray diffraction (XRD), zeta potential, surface area, particle size measurements and thermal analysis. XRD measurement showed that the manganese dioxide had α-MnO₂ structure. Sorption of As(III) and As(V) on manganese dioxide was studied by radiotracer technique using ⁷⁶As radio isotope. Arsenic removal efficiency for both As(III) and As(V) at concentration of 2 mg L⁻¹ was ∼99% in the pH range of 3–9. The sorption capacities for As(III) and As(V) were ∼60 mg g⁻¹. Kinetic studies showed that the equilibrium was reached within 30 s. Arsenic sorbed on manganese dioxide was present as As(V) irrespective of initial oxidation state. The presence of Ca²⁺, Mg²⁺, Cl⁻ and SO₄²⁻ up to a concentration of 1000 mg L⁻¹ had no significant effect on arsenic sorption. The sorption of arsenic decreased significantly in the presence of phosphate and bicarbonate anions above 10 mg L⁻¹. Arsenic sorbed on manganese dioxide was desorbed by 0.1M NaOH. Arsenic was effectively removed by manganese dioxide from groundwater samples collected from arsenic contaminated areas of West Bengal, India.

Keywords:

• Arsenic, sorption, manganese dioxide, ⁷⁶As radioactive tracer, ground water

Acknowledgments

The authors are grateful to Dr. A. K. Tyagi and Mr. R. Shukla for XRD measurements, Dr. Sanjukta A. Kumar and Ms. Shailaja Pandey for ICP-MS analysis, Dr. Naina Raje for thermal analysis and Dr. M. B. Kakade for zeta potential measurements. The authors are also thankful to the operation crew members of Dhruva reactors for their cooperation during neutron irradiations. The authors thank Dr. D. P. Chowdhury, Mr. J. Datta, Mr. S. Dasgupta, Mr. A. A. Mallick and Mr. D. Bhattacharya for their help during groundwater sample collection from West Bengal, India.