Effects Of Freeze Thaw Cycle Ageing And High Temperature Ageing On Adsorption Of Cadmium,Copper And Atrazine By Biochar

Biochar,a carbonaceous solid material that is produced via pyrolytic decomposition of raw biomass,is receiving increasing attention for soil remediation,carbon sequestration and soil improvement due to its unique prospective,such as high specific surface area,well-developed pore structure,rich diversity of surface functional groups and high carbon stability.Specifically,biochar for soil amendment would go through the long-term geochemical weathering processes,called ageing,in the environment,which eventually contributed to the changes of biochar properties,as well as the adsorption performance for various pollutants in soil remediation.At present,the effect of aging on the physical and chemical properties of biochar,especially on different pollutants,and its mechanism are not clear.In this study,corn straw and rice husk were used as raw materials to prepare different kinds of biochar by oxygen limited pyrolysis at different temperatures（350,500,and 650℃）.The effects of different raw materials and pyrolysis temperatures on the adsorption of heavy metals Cd²⁺,Cu²⁺and organic pollutants atrazine by biochar were studied.The effects of different ageing treatment and ageing time on the physicochemical properties and adsorption performance of biochar were systematically studied by various characterization methods and adsorption experiments.The results showed that for fresh corn straw biochar,the adsorption capacity of Cd²⁺,Cu²⁺increased with pyrolysis temperature increasing,while that of atrazine decreased.For fresh rice husk biochar,the adsorption capacity of both Cd²⁺,Cu²⁺and atrazine increased with pyrolysis temperature increasing.After freeze-thaw cycles and high-temperature ageing,the C content of biochar decreased,while the O content and O/C,（O+N）/C value increased,indicating that the polarity and hydrophilicity of biochar enhanced during ageing.The ageing process would also increase biochar surface functional groups（e.g.,-OH,C=O,and C-O-C）.These changes in physical and chemical properties further affect the adsorption behavior of biochar for heavy metals Cd²⁺,Cu²⁺and atrazine.As ageing time increasing,the adsorption performance of biochar for pollutants showed fluctuation.The short-term ageing improved biochar adsorption capacity for heavy metals.However,the long-term ageing inhibited biochar adsorption capacity for Cd²⁺and Cu²⁺.Similarly,the adsorption capacity of corn straw biochar for atrazine decreased,while the adsorption capacity of rice husk biochar for atrazine increased with ageing time increasing.This indicated that the adsorption mechanism of biochar for pollutants is complex,which is affected by many factors,such as raw materials,ageing methods,ageing time and pollutant types,etc.The results from this study reveal the adsorption mechanism of biochar on pollutants under different ageing methods and ageing time conditions,suggesting that we need to comprehensively consider the changes of physical and chemical properties of biochar and the performance of fixed pollutants when we use biochar in long-term soil remediation.