418 The present study proposed that a remediation method combining montmorillonite and limestone (CaCO3) improved arsenic removal from groundwater, and its mechanisms were evaluated. The arsenic sorption capacity of Mnt alone was limited to 10 µg/g-Mnt, whereas the coexistence of CaCO3 significantly enhanced the capacity to a maximum of 150 µg/g-Mnt. This result indicated a remarkable synergistic effect between the two natural minerals. Characterization of the adsorbent confirmed that physicochemical properties and microstructure played crucial roles in the performance enhancement. In the removal mechanism, Ca2+ released from CaCO3 were intercalated into the Mnt interlayers, resulting in expanded interlayer spacing and a shift in surface charge (zeta potential) from negative to positive/neutral. It is inferred to suppress electrostatic repulsion between Mnt and arsenate ions (AsO4 3-), thereby facilitating access to adsorption sites. Specifically, the presence of CaCO3 induced a structural transition in Mnt from an Edge-Face (E-F) to a Face-Face (F-F) orientation. Regarding field implementation, the adsorbed arsenic was strongly stabilized and was not released even under anoxic conditions (DO < 1 mg/L) typical of groundwater. Although coexisting sulfate ions tended to reduce the removal efficiency, this study demonstrated the potential of using low-cost and environmentally friendly minerals for the development of sustainable water treatment systems. REFERENCES [1] Shaji, E., Santosh, M., Sarath, K. V., Prakash, P., Deepchand, V., & Divya, B. V. (2021). Arsenic contamination of groundwater: A global synopsis with focus on the Indian Peninsula. Geoscience Frontiers. 12(3), 101079. [2] Naujokas, M. F., Anderson, B., Ahsan, H., Aposhian, H. V., Graziano, J. H., Thompson, C., & Suk, W. A. (2013). The broad scope of health effects from chronic arsenic exposure: update on a worldwide public health problem. Environmental Health Perspectives. 121(3), 295-302. [3] Nordstrom, D. K. (2002). Worldwide occurrences of arsenic in ground water. Science. 296(5576), 2143-2145. [4] Paikaray, S. (2015). Arsenic geochemistry of acid mine drainage. Mine Water and the Environment. 34(2), 181-196. [5] Johnson, D. B., & Hallberg, K. B. (2005). Acid mine drainage remediation options: a review. Science of the Total Environment. 338(1-2), 3-14. [6] Skousen, J., Zipper, C. E., Rose, A., Ziemkiewicz, P. F., Nairn, R., McDonald, L. M., & Kleinmann, R. L. (2017). Review of passive systems for acid mine drainage treatment. Mine Water and the Environment. 36(1), 133-153.
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