Removal of arsenic from ground water by manganese dioxide-coated sand

摘要

In a laboratory study, manganese dioxide-coated sand (MDCS), prepared by reacting potassium permanganate with manganese chloride under an alkaline condition and in the presence of sand, showed promise as a medium for use in small systems or home-treatment units in developing areas of the world, for removing arsenic(III) and arsenic(V) from ground water. In ten cycles of downflow column tests [bed depth 400 mm; empty-bed contact time 74 min; influent arsenic 0.5 mg As/L of arsenic(III) and 0.5 mg As/L of arsenic(V)], breakthrough bed volumes at the World Health Organization guideline value of 0.01 mg As/L for arsenic in drinking water were in the range of 153-185 per cycle. During regeneration (backwashing with 2 L of a 0.2 N sodium hydroxide solution), 85.0% of the removed arsenic was recovered in the first cycle, and 94.6-98.3% was recovered in subsequent cycles. A low-cost, simple home arsenic removal unit, containing 6 kg (4 L) of the MDCS medium and operated at 6 L/h, produced 740 and 700 L of water in two cycles of runs when the influent arsenic concentration was 0.5 mg As/L of arsenic(III) and 0.5 mg As/L of arsenic(V). No arsenic(III) or leaching of manganese from the medium was detected in the effluent. A detailed study addressing the effects of some important factors (water pH, concentration and type of competing anions, and cations) on the process is needed. The home arsenic removal unit should be subjected to field trials to assess the long-term effects on performance.