Arsenic Removal from Contaminated Water Using the CaO–SiO₂–FeO Glassy Phase in Steelmaking Slag

Arsenic is a highly toxic element, and its removal is crucially important. To remove As from water, Fe-based materials have shown high As removal capacities. From the perspective of low removal cost, steelmaking slag is a potential material because it is rich in iron oxides. However, due to insufficient dissolution of Fe in water, the potential effects of iron oxides in As removal from steelmaking slag have not been completely revealed. In this study, a CaO–SiO₂–FeO glassy phase, which allows Fe to be easily dissolved in water, was used to remove As from solution. With pH lower limit of 4 and the addition of an oxidizer (KMnO₄), a high As removal ratio was obtained with a final As content of lower than 0.1 mg/L. The removal mechanism was found to be the adsorption of As on the precipitated FeOOH. When using the glassy phase to remove As, control of pH and oxidation/reduction potential was necessary to dissolve Fe and Ca, and to form FeOOH as the adsorbent. In addition, because the Si dissolved from glassy phase could have a polymerization effect that improves the permeability and stability of FeOOH, the As removal rate increased in the presence of Si. The adsorption kinetics was found to obey a pseudo-second-order model, and chemisorption was the rate-controlling step. The adsorption capacity estimated from the Langmuir isotherm was about 28.17 mg/g-glassy phase, which was much higher than the values previously reported while using steelmaking slag.