Competition of Various Ions Present in Shallow Aquifer Water in Respect of Arsenic Removal by Hydrated Ferric Oxide

Abstract

Iron-oxides have long been used as adsorbent in the arsenic filter materials. Little is known about the arsenic removal efficiency of these materials in the presence of other naturally occurring ions. Hydrated ferric oxide (HFO) based mesoporous material was prepared freshly in our laboratory by co-precipitating silicic acid and ferric oxyhydroxide from silicate and iron salt solutions. We carried out detailed laboratory experiments to understand how the effect of other ions such as iron, bicarbonate, ammonium and phosphate influence the adsorption of arsenic on HFO at neutral pH. It was found that arsenate and phosphate were in direct competition and the efficiency of the material decreased in the presence of aqueous phosphate. Also, the material can remove carbonate/bicarbonate effectively but arsenic removal efficiency decreases to nearly the same extent as observed for phosphate. The presence of iron in the solution interestingly increases the life time of HFO and hence the efficiency for the removal of arsenic. The results from our experiments suggest that it is essential to know the concentration of other ions along with arsenic in the contaminated tubewell water before it is subjected to adsorption filtration using HFO.