The removal of arsenic from water with natural and modified clinoptilolite

The presence of increased arsenic concentrations in Eastern Croatia is a consequence of the geological composition of the soil. Because of its known harmful effects, arsenic removal is of high importance and adsorption represents an attractive and economically efficient approach to arsenic removal. The use of zeolites obtained from the Donje Jesenje deposit, Croatia (CZ) and the Zlatokop deposit in Vranjska Banja, Serbia (SZ) in Na- and Fe-Na-modified forms was investigated in order to effectively remove arsenate and arsenite from aqueous solutions. The adsorption kinetics of arsenic was studied as a function of the initial arsenate and arsenite concentrations (30-300 mu g . L-1), equilibration time (3-48 h), pH (5-10) and in the presence of sulfate and phosphate at initial concentrations of 0.2-0.5 mg . L-1. In order to estimate sorption constants designating the sorption capacity and affinity of the zeolites samples, the experimental results were fitted to the Langmuir and Freundlich sorption isotherms. Desorption tests conducted with 1-3 mol . L-1 HCl indicated that arsenate sorption was irreversible. The results obtained indicated that use of the Serbian zeolite in the Fe-Na-modified form (Fe-Na-SZ) was favourable for arsenate removal from water containing up to 30 mu g As . L-1.