Preparation of biochar derived from rice straw residue after extraction of humic acid and its adsorption capacity for Cr(Ⅵ)in water
Biochar was prepared by co-pyrolysis of rice straw residue after extraction of humic acid humic acid(ER)and industrial tailings(TR),and was applied to the adsorption of Cr(Ⅵ)polluted water.The main pyrolysis and adsorption factors were analyzed,and the adsorption mechanism was preliminarily explored.Results show that the optimal pyrolysis and adsorption conditions of biochar are 700 ℃,ER∶TR=2∶1,dosage of 1 g/L and pH=2.Under these conditions,when the initial concentration of Cr(Ⅵ)is less than 30 mg/L,the removal rate of Cr(Ⅵ)can reach 99％in only 5 min.The adsorption process of biochar conforms to Langmuir isotherm e-quation,and the saturated adsorption capacity is 27.05 mg/g.The quasi-second-order kinetic equation could reflect the adsorption process of biochar very well,which is mainly chemisorption.Cr(Ⅵ)is firstly adsorbed onto the surface of biochar under electrostatic action,then Cr(Ⅵ)is reduced to Cr(Ⅲ)on the surface of biochar by elemental carbon or H+in solution,and finally Cr(Ⅲ)is com-plexed with functional groups on the surface of biochar.
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