Biochar is rich in both organic carbon and inorganic components. Extensive work has attributed the high sorption ability of biochar to the pore structure and surface chemical property related to its organic carbon fraction. In this study, three biochars derived from dairy manure (DM-biochar), sewage sludge (SS-biochar), and rice husk (RH-biochar), respectively, were evaluated for their SO₂ sorption behavior and the underlying mechanisms, especially the role of inherent inorganic constituents. The sorption capacities of SO₂ by the three biochars were 8.87-15.9 mg g^-1. With the moisture content increasing from 0% to 50%, the sorption capacities increased by up to about 3 times, mainly due to the formation of alkaline water membrane on the biochar surface which could promote the sorption and transformation of acidic SO₂. DM- and SS-biochar containing larger mineral constituents showed higher sorption capacity for SO₂ than RH-biochar containing less mineral components. CaCO₃ and Ca₃(PO₄)₂ in DM-biochar induced sorbed SO₂ transformation into K₂Ca(SO₄)₂·H₂O and CaSO₄·2H₂O, while the sorbed SO₂ was converted to Fe₂(SO₄)₃·H₂SO₄·2H₂O, CaSO₄·2H₂O, and Ca₃(SO₃)₂SO₄·12H₂O in SS-biochar. For RH-biochar, K₃H(SO₄)₂ might exist in the exhausted samples. Overall, the chemical transformation of SO₂ induced by biochar inherent mineral components occupied 44.6%-85.5% of the total SO₂ sorption. The results obtained from this study demonstrated that biochar as a unique carbonaceous material could distinctly be a promising sorbent for acidic SO₂ removal in which the inorganic components played an important role in the SO₂ sorption and transformation.

Daxuan Huang

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