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 MgCO 3 ) 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 ( W Ad0 / V ), As valence, and the initial As and Si ( C Si0 ) concentrations. In some cases, As removal improved at relatively low C Si0 ; however, overall performance decreased with increasing C Si0 for all Mg-based adsorbents. Moreover, compared with Mg(OH) 2, the performance of MgO and MgCO 3 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 MgCO 3 , the amount of As removed by coprecipitation with secondarily generated Mg(OH) 2 aggregates was inferred to decrease with increasing C Si0 , because higher C Si0 lowered the solution pH. Overall, MgO and Mg(OH) 2 can function effectively as adsorbents for As treatment when W Ad0 / V is appropriately selected, considering the range of Si concentrations typically found in groundwater.