Research On Aqueous Hg²⁺ Adsorption By Different Sulfurized Biochar And Associated Mechanism

The waste discharged by human activities which contained mercury has been seriously polluted the water environment in China.Mercury has a characteristic of biological enrichment and it can permanently stay in human bodies through the food chain,which can cause an irreversible damage on nervous system.For this study,different kinds of sulfurized biochar will be respectively modified with mercaptoacetic acid and sublimed sulfur on the original corn stalk biochar（BC）.The optimized adsorbents are required to have simple and environmentally friendly preparation process and highly removal efficiency to aqueous Hg²⁺.The results of well-selecting experimentation showed that the adsorption effect of BC is worse with higher preparation temperature.For thio-modification biochar（TBC）,the modification effect is worse with higher preparation temperature of its raw BC as well.For biomass-based sulfurized biochar（SBC）and biochar-based sulfurized biochar（BCS）,SBC mainly has higher adsorption effect than BCS under the same preparation condition,and of which the adsorption effect is worse with higher preparation duration with the same preparation temperature.Moreover,the adsorption effect of SBC and BCS showed first rise and then fall with higher preparation temperature with the same preparation duration.Therefore,BC-kind material prepared with 2 h at 300℃（BC300）,TBC-kind material prepared by BC300,BCS-kind material prepared with 15 min at 450℃（LBCS450）and SBC-kind material prepared with 15 min at 450℃（LSBC450）were chosen as the optimized materials of this study.SBC has the highest adsorption capacity(268.45 mg g^-1)than any other optimized adsorbents such as BC,TBC and BCS.The results showed that BCS had the largest sulfur content,specific surface area and total pore volume.Thiol group（-SH）has been found on TBC and abundant sulfur-containing chemical bonds have been found on both BCS and SBC.These sulfur-containing species on the adsorbents can enhance the remove effects of Hg²⁺.The sorption kinetic and isotherm experiments were conducted to study the removal performance of aqueous Hg²⁺from the optimized adsorbents.The experiments results showed that the optimized adsorbents can get the best adsorption effect with pH value of 8.0 and the results of kinetic experiments can be well fitted with pseudo-second-order kinetic model.The isotherm of BC and TBC conformed to the Langmuir model while the BCS and SBC conformed to the Freundlich model.This study shows that the thiol groups on TBC300,the S-containing groups,including the C=C bonds,C=S bonds,O=S=O bonds in sulphate,S-containing bonds in sulfoxide and sulphone,C-S bonds on alkyl and C-S bonds on thiophene,on BCS and SBC as well as the oxygen-containing groups such as hydroxyl and carboxyl groups on SBC can effectively improve the material adsorption performance.In summary,SBC possesses large quantities of oxygen-containing and sulfur-containing functional groups and has the strongest adsorption effect on aqueous Hg²⁺.This green sulfurized biochar prepared by low-cost agricultural wastes with a simplified preparation method can be used as a highly-efficient adsorbent with excellent physical and chemical properties.