The Influence Of Aluminum Trichloride Modified Biochar On Fluoride And Cadmium Bioavailability In Tea Garden Soils

With the advancement of social industrialization,the pollution of fluorine and cadmium in the soil of tea gardens in China has become increasingly serious,which not only harms the soil-tea tree ecosystem,leads to the degradation of the soil of tea gardens and the decline of the yield and quality of tea,but also endangers human health through direct contact and enrichment of the food chain.Biochar is a kind of high temperature anaerobic pyrolysis of porous carbon materials,has a large specific surface area,surface functional groups rich,high carbon content,carbon sequestration ability and stability greatly,can effectively influence of fluorine,cadmium in soil biological effectiveness,gradually become a new soil repair material.Therefore,an AlCl₃-modified corn stalk biochar（AlCl₃-BC）was prepared in this paper.The morphology and structure of AlCl₃-BC were characterized by XRD,FTIR,XPS,SEM,BET and Zeta potential.At the same time,the adsorption effect and adsorption mechanism of AlCl₃-BC on single and compound fluorine and cadmium in aqueous solution were investigated by adsorption experiments.In this study,the soil improvement effect of AlCl₃-BC on tea garden soil,and the effects of the forms,phytotoxicity and accumulation of fluorine and cadmium in the soil were investigated by selecting typical tea garden soils（Enshi and Huanggang）in Hubei Province.The main results are as follows:（1）As the amount of Al OOH on the surface of AlCl₃-BC increases,the negative charge content decreases,the surface area increases,and there are more Al-O functional groups,which increase the adsorption of F^-and Cd²⁺in the electrostatic interaction.At35℃,the adsorption capacity of AlCl₃-BC for F^-and Cd²⁺was the highest(81.65mg g^-1,153.78mg g^-1).The adsorption of F^-and Cd²⁺was more consistent with the quasi-first-order kinetic model,and the R²was close to 0.99.The isothermal adsorption data were consistent with the Langmuir and Freundlich models.The adsorption of F^-and Cd²⁺on biochar may be due to the combination of homogeneity and heterogeneity.In binary solutions of F^-and Cd²⁺,F^-and Cd²⁺have competitive adsorption on BC and Al Cl3-BC.（2）After the addition of biochar,the p H value of the tea garden soil increased by0.61（Enshi）and 0.56（Huanggang）,respectively,and other soil physical and chemical properties（effective cation exchange capacity e CEC,electrical conductivity,organic matter content,clay,aluminum oxide,manganese oxide）increased.The electrical conductivity increased significantly(Enshi:1.06 us cm^-1,Huanggang:0.36 us cm^-1).（3）Al modified biochar is helpful for the transformation of exchangeable and water-soluble F to residual F,mechanically bound F and Fe-Mn bound F in tea garden soil.It can promote the conversion of soil heavy metal Cd from exchangeable state to carbonate bound state,iron and manganese oxide bound state,organic bound state and residue state,and reduce the bioavailability and ecological toxicity of fluorine and cadmium.The presence of F inhibits the distribution of various forms of Cd,and vice versa.（4）After biochar was added,plant height of tea seedlings treated with different F and Cd treatments was generally increased by 0.4～0.9 cm.Compared with CK,and other growth indexes of tea seedlings（fresh weight,dry weight,total root length,total root area,total chlorophyll,carotenoids）were also increased to varying degrees,but root volume,root diameter and root branch had no significant changes.The content of fluoride and cadmium in the root of tea seedlings decreased by 33.1%～77.2%and1.2%～77.4%respectively.Under different concentrations of fluorine and cadmium,fluorine and cadmium had synergistic effects on the toxicity of tea seedlings,and their accumulation in the root of tea seedlings had mutual inhibition effects.Aluminum modified biochar can inhibit the accumulation of fluorine and cadmium in the root of tea seedlings to a certain extent,inhibit the toxicity of fluorine and cadmium to tea seedlings,and promote the growth of tea seedlings.