As(III) Removal via Combined Addition of Mg- and Ca-Based Adsorbents and Comparison to As(V) Removal via Those Mechanisms

Damage to human health caused by As-contaminated water can be prevented using proper As-removal techniques, such as employing excellent arsenic adsorbents. In this study, the combined addition of Mg- and Ca-based adsorbents was investigated for the efficient removal of As from contaminated water. Following a previous study on As(V), As-removal tests targeting As(III) and several additional tests, including X-ray diffraction analysis, were conducted to clarify the mechanism of the improved performance of the combined-addition As removal. Similarly as for As(V), the combined additions of both MgCO 3 + CaO and MgCO 3 + Ca(OH) 2 improved As(III)-removal performance while inhibiting the leaching of base material components; however, they did not remove As(III) as effectively as As(V). The differences in the removal ratios of As(V) and As(III) in these combined additions were concluded to be primarily due to the different As-removal mechanisms. Mg(OH) 2 and CaCO 3 were generated, and As(III) was incorporated into the generated precipitate of Mg(OH) 2 but not into that of CaCO 3 . Conversely, As(V) was incorporated into both Mg(OH) 2 and CaCO 3 . Additionally, MgCO 3 + Ca(OH) 2 was evaluated as a more efficient combined-addition method because MgCO 3 + Ca(OH) 2 exhibited a higher As-removal ratio value than MgO + CaO. Proposals have been made to remove As(III) using activated carbon modified with heavy metals or transition elements, or concrete waste grafted with polymers, but these methods are complicated to prepare, costly, and involve the risk of leaching of harmful components. Adsorbents that use general Mg and Ca components as their base material do not contain such harmful components. The Mg- and Ca-based adsorbents are readily available and low-cost, and, best of all, there is no concern that they will leach harmful components. Therefore, widespread use of Mg- and Ca-based adsorbents as a measure against arsenic contamination could greatly contribute to a sustainable society.