Immobilization of Arsenate in Artificially Contaminated Kaolinite by the Addition of Magnesium Oxide-based Materials

Abstract

Soil contamination by arsenic is becoming a serious environmental problem worldwide. In this study, a series of experiments were performed to deepen the understanding on the behavior of arsenate in the water-kaolinite-MgO system, with the final objective of evaluating the use of MgO-based materials as an arsenate immobilization agent in soils. Leaching tests performed with leaching solutions of various pH levels and ionic concentrations at a solidliquid ratio of 1:10(w/v)showed that the addition of sufficient amount of MgO effectively immobilized arsenate below 0.01 mg-As/L(the permissible level for leaching tests in Japan)against the exposure to pH 4.0 acid rain for 100 years. Also, experiments using diffusion cells demonstrated that the arsenate desorbed from kaolinite was quickly re-immobilized by MgO addition. These experimental results overall demonstrate that the addition of MgObased materials is a quite effective soil treatment for quick immobilization of arsenate, and that the immobilization effectiveness is long-lasting against exposure to acid rain. However, the MgO dosage needs to be carefully determined considering the decreased capability of kaolinite as an arsenate adsorbent at high pH conditions.