409 LIMESTONE AND MONTMORILLONITE FOR ARSENIC REMEDIATION IN GROUNDWATER: A PERFORMANCE EVALUATION *H. Yodoya1, Y. Shimada1, H. Matsumoto1, K. Mitsuhashi1, H. Iwai2, Y.O. Zubair3, C. Tokoro2,4 1Nittetsu Mining Co., Ltd., 8-1 Hirai, Hinode-machi, Nishitama-gun, Tokyo 190-0182, Japan (*Presenting author: h-yodoya@nittetsukou.co.jp) 2 Department of Resources and Environmental Engineering, Faculty of Science and Engineering, Waseda University, 169-8555 Tokyo, Japan 3Sustainable Energy & Environmental Society Open Innovation Research Organization, Waseda University, Shinjuku, Tokyo 169-8555, Japan 4Department of System Innovation, Faculty of Engineering, The University of Tokyo, 113-8656 Tokyo, Japan ABSTRACT Arsenic contamination in groundwater is a serious environmental problem for public health. Sources of contamination include geological factors, historical mining activities, and the presence of arsenic-bearing minerals. Long-term treatment is required to reduce concentrations before the water enters the public water supply. Thus, even if the arsenic level is below that of the mine water, reduced treatment costs are needed. In this study, we propose a treatment technique for arsenic-contaminated groundwater using natural minerals, limestone, and montmorillonite, which are relatively inexpensive and have a low environmental impact. Although montmorillonite alone adsorbed 10 µg/g montmorillonite arsenic, the amount of adsorbed arsenic in combination with limestone increased significantly to a maximum of 150 µg/g montmorillonite, indicating that limestone has a synergistic effect in increasing the sorption capacity. SEM observations showed that the coexistence of montmorillonite and limestone resulted in a layered montmorillonite aggregate structure that increased the surface area available for arsenic. It was also confirmed that these aggregates adhere to the surface of the limestone. The zeta potential of the combined mixture showed that as the amount of limestone added increased, the absolute value of the negative surface charge originally held by the montmorillonite decreased. The increase in the interlayer distance of montmorillonite was recorded from the XRD analyses. The results thus suggested that the Ca2+ dissolved from the limestone was incorporated into the montmorillonite, stimulating a layer-to-layer structure of the montmorillonite, and sorbed on the negatively charged face of the minerals. As a result, it would provide an effective positively charged stacking face for AsO4 3- adsorption, by weakening the repulsion between the mineral and AsO4 3-. This adsorption process reaches equilibrium in about 2 hours and is highly effective in treating anoxic environments (DO<1mg/L) such as groundwater. The proposed material is expected to be used as a cost effective and environmentally friendly treatment for the removal of arsenic in groundwater.
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