Abstract:
Sorption and transport behaviors of arsenite on aquifer materials was investigated. Three types of aquifer materials; sandy clay loam, clay loam, and loamy sand were used. This research consisted of two experimental sections batch and column experiments. Batch experiment was conducted to examine the effectiveness and ability of soil sample for arsenite sorption at varying pH of 4, 7, and 10. The competitive adsorption of typical ions .i.e., bicarbonate and phosphate, was also investigated. Arsenite transport through soils were studied in the column. The experimental results were compared with the simulated results from the computer program HYDRUS2D. The batch experiments results showed that the sorption ability of arsenite in clay loam is more than sandy clay loam and loamy sand. The adsorption isotherm for arsenite adsorption can be modelied by Langmuir sorption isotherm. Bicarbonate ion did not effect arsenite adsorption. However; phosphate ion suppressed the arsenite sorption significantly. The tracer column experimental results ascertained that dispersion coefficient was 2.89x10⁻³ cm²/s for sandy clay loam, 2.71x10⁻³ cm²/s for clay loam, and 1.05x10⁻² cm²/s for sandy loam. Arsenite adsorption decreases with increasing pH in both batch and column studies. Adsorption of arsenite was highest with clay loam follow by sandy clay loam and loamy sand, respectively. Moreover, the results of the competitive ion were reducing the adsorption ability of arsenite on the soil sample, especially phosphate ion highly affected on reducing the adsorption ability of arsenite. While the ratio of the competitive ions were not effect on the adsorption ability of arsenite. The simulation by HYDRUS2D program compared with the results from the experiments elucidated the results from the column test in the clayey loam at initial pH10 were most agreeable to the estimation by HYDRUS2D. Nevertheless, the simulation of sandy clay loam, clay loam, and loamy sand at the initial pH4 and 7 failed to predict the transport behaviors because of the nature of non-equilibrium sorption in real aquifer materials.