Enhanced removal of As(III) and Cd(II) from wastewater by alkali-modified Schwertmannite@Biochar

Pollution by As(III) and Cd(II) co-contaminated wastewater has become a severe environmental issue. In this study, the composite Schwertmannite@Biochar (Sch@BC) was successfully synthesized using a biological method and modified by alkali, after which its effectiveness in removing As(III) and Cd(II) was investigated. Results showed that the adsorption capacity for As(III) and Cd(II) was significantly improved by alkali-modified Schwertmannite@Biochar (AM-Sch@BC) obtained from the system with a mass ratio of FeSO4 ⋅ 7H2O to biochar of 20:1. At pH = 7.00, when both As(III) and Cd(II) concentrations were 1 mg/L and the adsorbent (AM-Sch@BC) dosage was 1 g/L, the removal efficiency of As(III) and Cd(II) increased from ∼80% to 90% and from <10% to 75%, respectively, by 1.1 and 7.5 times, compared with Sch@BC. A co-adsorption experiment revealed that AM-Sch@BC could effectively remove As(III) and Cd(II) when pH was 6.00–8.00. When both As(III) and Cd(II) concentrations were 1 mg/L, adsorbent (AM-Sch@BC) dosage was 1 g/L, 100% removal efficiency of As(III) within 1 h, and 70% removal efficiency of Cd(II) after 12 h. Sch@BC, after alkali modification, the –OH content and specific surface area (SSA) in the adsorbent increased significantly, which is perhaps the main reason for its efficient removal of As(III) and Cd(II).