Preparation Of Bagasse Biochar And Its Adsorption Of Cu²⁺,Pb²⁺and Zn²⁺

Biochar has a good ability to remove heavy metals and other contaminants from aqueous solutions,and its research and application in the environmental field has gradually attracted attention.In this study,Guangxi local agricultural waste bagasse was used as biomass raw material,and bagasse biochar(BC300,BC400,BC500 and BC600)was prepared at different pyrolysis temperatures of 300℃,400℃,500℃ and 600℃.The basic characteristics of bagasse biochar prepared at different pyrolysis temperatures were investigated.The adsorption properties and adsorption mechanism of bagasse biochar on single metal and multi-metal systems such as Cu2+,Pb2+ and Zn2+ were investigated.The main findings are as follows:(1)The surface of biochar prepared at four pyrolysis temperatures has oxygen-containing functional groups such as C-OH and C=0;the pHPZc of BC300,BC400,BC500 and BC600 are respectively 0.3.4,4.03,and 4.39;BC300 and BC400 have lower total specific surface area,BC500 is dominated by mesoporous structure,BC600 has a certain specific surface area,and forms a pore structure dominated by micropores.(2)The adsorption of Cu2+,Pb2+ and Zn2+ by BC300,BC400,BC500 and BC600 is a chemical adsorption process;the adsorption of Cu2+,Pb2+ and Zn2+by BC600 is the highest and the adsorption of multi-molecular layer;the adsorption of Cu2+ and Zn2+ by BC600 is dominated by the coordination of oxygen-containing functional group C=0;while the adsorption of Pb2+ by BC600 is mainly electrostatic,and involves ion exchange and coprecipitation.(3)In the ternary system,the selectivity sequence of BC600 for three heavy metal ions is consistent with the order in the single metal ion system,both of which are Pb>Cu>Zn.The analysis shows that the selectivity sequence of biochar on heavy metal ions is related to the nature of heavy metal ions.The larger the atomic weight,hydrolysis constant,ionic radius and electronegativity of heavy metal ions,the more easily heavy metal ions are adsorbed by biomass carbon.However,under the competitive system,Pb2+ adsorbed on BC600 by electrostatic action is easily inhibited by Cu2+ which is bonded to BC600 by coordination,while the adsorption of Zn2+ by coordination is less affected by other ions,it is indicated that the difference in adsorption mechanism of heavy metal ions by BC600 also affects the adsorption behavior of heavy metal ions in the competitive system.