Adsorption of As(III) to schwertmannite: impact factors and phase transformation

The phase transformation of Schwertmannite (SCH) can significantly affect the interface behavior and toxic effect of As(III). Previous studies have predominantly focused on pollutants adsorption by SCH on a long-time scale (such as 30 days), without paying attention to the adsorption characteristics within shorter time frames (e.g., within 24 h). This work compared the adsorption characteristics of As(III) on three synthesized SCHs under various environmental conditions. The adsorption of As(III) by M-SCH (SCH synthesized by KMnO₄ oxidation method) and Y-SCH (SCH synthesized by ethanol modification method) were governed by physical adsorption, while that of H-SCH (SCH synthesized by H₂O₂ oxidation method) was dominated by chemisorption. Acidity, selected ions (NO₃^-, Ca²⁺, CO₃^2-, and PO₄^3-), fulvic acid (FA), and Sb(III) adversely impacted the As(III) adsorption by SCHs. Furthermore, alkalinity, selected ions and FA induced the phase transformation of SCHs to iron hydroxide, while no transformation was observed in the presence of Sb(III) and Cr(VI). The iron hydroxide observed in this study is presumed to represent an intermediate stage in the transformation of SCH into goethite. These findings enhance our comprehension of the transformation process of SCH to goethite and provide scientific insights for SCH utilization in immobilizing As(III) in water.