REMOVAL OF As(V) CONTAMINATED WATER BY A COMBINATION OF ZERO-VALENT IRON COATED SAND AND IRON OXIDE-COATED SAND USED IN PERMEABLE REACTIVE BARRIER

Abstract

This research aims to evaluate the removal efficiency of As(V) contaminated in groundwater in different reactive materials under acidic and neutral conditions by using column experiments. Six columns were set up for As(V) removal efficiency with three different materials, used as the reactive barrier media packed in columns, under different pH (e.g., pH 4 and 7) conditions. The reactive materials consist of pure sand (control column), iron oxide coated sand (IOCS) and the combination of IOCS and zero-valent iron coated sand (ZVICS). According to column experiments, the descending orders of removal capacity (mg As/g) under pH 4 and 7 by combination of ZVICS and IOCS, IOCS and sand are: 0.0328 mg As/g > 0.024 mg As/g > 0.014 mg As/g as well as 0.0135 mg As/g > 0.0115 mg As/g > 0.0064 mg As/g, respectively. The results of column experiments showed that the removal of As(V) increase with decreasing pH. The pHzpc of sand, IOCs and ZVICS-IOCS (i.e., 5±0.03, 7±0.02 and 7.5±0.3) affect to removal capacity of As(V) on different reactive materials. Moreover, that coating sand with iron oxide and zero-valent (ZVI) cause an increase of pore site, causing specific surface areas appear to be more available for the As(V) sorption. The SEM images and the corresponding EDX spectrum of acid-washed natural sand, IOCS and ZVICS with IOCS before and after finished As(V) transport through columns at pH 4 and pH 7 found As(V) adsorption onto all reactive material. The results of microwave digestion indicated that the As(V) retained on the mixing of ZVICS and IOCS more than IOCS and sand column. The mechanism of As(V) adsorption onto sand at pH 4 and pH 7 correspond to the uniform (equilibrium) solute transport model. On the contrary, IOCS and ZVICS-IOCS at pH 4 and pH 7 correspond to chemical non-equilibrium two-site model (TSM).