As a mineral resource, Antimony (Sb) has been widely used in various industrial products. However, excessive antimony in the soil and water environment can cause pollution and is harmful to human beings. The adsorption of Sb(III) and Sb(V) on Mn-coated biochar using batch experiments was studied in this paper. Mn-coated biochar was simply synthesized through the reaction of biochar with different MnSO4 concentrations in aqueous solution. It is confirmed the successful coating of Mn on the surface of the biochar from SEM and XRD analysis. It is showed that MnSO4 modification greatly increased the particle size of the original biochar by Laser particle size analyzer and the specific surface area of Mn-coated biochar is smaller than the untreated biochar by BET analysis.
The effects of initial Sb concentration, pH, reaction time, and temperature at different concentrations on the adsorption of Sb(III) and Sb(V) were investigated in this research. Kinetic studies indicated that Sb(III) and Sb(V) reached an adsorption equilibrium within 12 hours. Both for biochar and Mn-coated biochar, sorption kinetic data better follows the pseudo second-order model (R2>0.80). The adsorption data of Sb(III) and Sb(V) at 283 K, 298 K, and 313 K are fitted well by both Freundlich (R2>0.76) and Langmuir (R2>0.76) isotherms. At 298 K, the maximum sorption capacity for Sb(III) calculated from Langmuir model are 0.3231 mg/g for biocharand 1.5590 mg/g for Mn-coated biochar. The maximum sorption capacity for Sb(V) calculated from Langmuir model are 0.2238 mg/g for biochar and 1.2567 mg/g for Mn-coated biochar. The thermodynamic parameters (ΔG0>0, ΔH0>0, and ΔS0>0) are calculated from the temperature dependence, illustrating that the adsorption processes of Sb(III) and Sb(V) are endothermic. From the LC–AFS date of Sb(III) aqueous solution, It is showed that the oxidation of Sb(III) occurred on a time scale of minutes and Sb(III) was oxidized to Sb(V) as soon as the reaction began. The sorption process of Mn-coated biochar was pH independent. It is indicated that physical adsorption and chemical adsorption of biochar occurred together, reflected in ion exchange and redox reaction. Strong chemisorptive binding of Sb to biochar surfaces is further confirmed from FTIR and XPS.
By this study, MnSO4 modification is a simple and effective method to increase the sorption capacity of biochar. The process is simple and easy to operate, and the synthesized material shows delightful sorption property for Sb(III) and Sb(V).