Application of δ-MnO₂ and biochar materials in an arsenic-contaminated groundwater

Two activated biochar materials, peanut char (δ-MnO₂ /A-PC) and corn char (δ-MnO₂ /A-CC), were used to treat an arsenic solution containing 97.5% As(III) and 2.5% As(V). After reacting with δ-MnO₂ /A-PC for 24 h, 18.8% of As(III) and 35.4% of As(V) remained in the solution, revealing that some As(III) was oxidized to As(V) and the other was removed by adsorption. However, δ-MnO₂ /A-CC caused the solution to retain 15.6% of As(III) and 41.7% of As(V) under the same conditions, indicating that δ-MnO₂ /A-CC had higher oxidation for arsenic species than δ-MnO₂ /A-CC. Adsorption capacities for δ-MnO₂ /A-PC and δ-MnO₂ /A-CC to arsenic were 1.50 and 1.53 mg/g in a solution with 0.5 ppm As(III), respectively. After coating with δ-MnO₂ , the proportion of mesopore surface areas of δ-MnO₂ /A-CC increased from 33.3% to 79.0%, but their mesopore volumes increased from 67.6% to 89.4%. Fourier-transform infrared spectroscopy and X-ray diffraction analyses demonstrated that δ-MnO₂ was coated onto the surfaces of the biochars. The 600°C-ACC had a higher specific surface area, 221 m² /g, than the δ-600°C-APC, 81.5 m² /g; δ-MnO₂ /A-CC could attach more Mn (38.2%) than δ-MnO₂ /A-PC (27.8%). The elemental analysis revealed that δ-MnO₂ /A-PC and δ-MnO₂ /A-CC had similar carbon contents of 26.2%. PRACTITIONER POINTS: The δ-MnO₂ /biochar adsorbent can oxidize As(III) into As(V) in the groundwater. δ-MnO₂ /biochar adsorbed large amounts of As(III) and As(V). Adsorbent that contains more δ-MnO₂ has a higher oxidation capacity. The δ-MnO₂ /biochar made from corn stalks could combine with more δ-MnO₂ .