Arsenic Removal from Water Using Mg-Based Adsorbents in the Presence of Silicic Acid

Dissolved silicic acid (Si) in groundwater can reduce the As-removal performance of adsorbents used for treating contaminated water. However, its effects on Mg-based adsorbents remain largely unexplored. In this study, As-removal tests were conducted under various test conditions to evaluate the suitability of Mg-based adsorbents (MgO, Mg(OH)2, and MgCO3) for the purification of As-contaminated water in the presence of Si. As-removal performance varied significantly depending on the Mg-based adsorbent type and dosage (WAd0/V), As valence, and the initial As and Si (CSi0) concentrations. In some cases, As removal improved at relatively low CSi0; however, overall performance decreased with increasing CSi0 for all Mg-based adsorbents. Moreover, compared with Mg(OH)2, the performance of MgO and MgCO3 was more strongly affected by Si. This inhibition is attributed to competition between Si and As for adsorption sites on the adsorbent surface. Furthermore, for MgO and MgCO3, the amount of As removed by coprecipitation with secondarily generated Mg(OH)2 aggregates was inferred to decrease with increasing CSi0, because higher CSi0 lowered the solution pH. Overall, MgO and Mg(OH)2 can function effectively as adsorbents for As treatment when WAd0/V is appropriately selected, considering the range of Si concentrations typically found in groundwater.