Adsorption and Miscible Displacement of Arsenic Derived from Arsenopyrite in Soils.

Arsenic and its compounds which cannot be mobilized easily when it is immobile is also found in conjunction with sulfur in minerals such as arsenopyrite (AsFeS), realgar, orpiment and enargite can be found naturally on earth in small concentrations are used in the production of pesticides, herbicides, and insecticides. In this investigation we observed the leaching of arsenic in soils amended with several levels of gravel size of arsenopyrite collected from a road construction site. Saturated hydraulic conductivity playing a crucial role in mobility of soil substances was slightly increased with increasing mixing ratios of arsenopyrite as well as and increasing particle size. The results of pH measured from effluent showed that pHs were increased by approximately max. 4, 1.1, and 1.5 units compared with for pHs of influent for 3, 6.64, and 9, respectively. The cumulative amount of As recovered from the effluent were decreased in the order of the influent pHs of 3, 6.64, and 9 in silty clay and sandy loam, respectively. However, the total amount of As from was silty clay significantly lower than those of sandy loam, indicating that adsorption As was much greater than that in sandy loam due to clay content. Adsorption kinetics of As(V) in silty clay and sandy loam under various solution pHs showed that approx. 80 % of As from solution phase was disappeared, indicating that As adsorption was instant reaction onto the surface of charged clay and organic matter. However, the instant adsorption was distinctive with decrease in pH of solution. For breakthrough curves, we found that the pore volumes of water to reach the relative concentration 1 was greater in silty clay than those of sandy loam, meaning that clay content influenced the transport of As in soil in addition to soil pH.