Sorption of arsenic on manganese dioxide synthesized by solid state reaction

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 alpha-MnO2 structure. Sorption of As(III) and As(V) on manganese dioxide was studied by radiotracer technique using As-76 radio isotope. Arsenic removal efficiency for both As(III) and As(V) at concentration of 2mg L-1 was similar to 99% in the pH range of 3-9. The sorption capacities for As(III) and As(V) were similar to 60mg g(-1). Kinetic studies showed that the equilibrium was reached within 30s. 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 1000mg L-1 had no significant effect on arsenic sorption. The sorption of arsenic decreased significantly in the presence of phosphate and bicarbonate anions above 10mg 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.