Study On The Mechanism Of γ-Cyclodextrin Biochar For Reducing Heavy Metals In Agricultural Water

Long-term input of low concentrations of heavy metals from agricultural water into the soil can result in cumulative toxicity,causing serious soil heavy metal contamination and ultimately affecting human health.However,the treatment of heavy metal pollution is currently a major challenge and is mostly post-pollution remediation.Therefore,in this paper,with the starting point of preventing the import of heavy metals into soil from agricultural water,ensuring the pre-safety of agricultural water and reducing the risk of soil heavy metal contamination,a total of six newγ-cyclodextrin biochar and its magnetic biochar were prepared at three temperatures（300°C,500°C and 700°C）,involving three heavy metals(Pb²⁺,Cu²⁺and Cd²⁺),and the biochar was studied for The physical and chemical properties,p H effects,kinetics,isothermal adsorption and competitive adsorption of the six biochar were investigated for their adsorption effects on heavy metal ions in polluted water in both single and Pb-Cu binary systems.The main conclusions of this thesis are as follows:（1）The maximum theoretical adsorption capacities ofγ-cyclodextrin biochar（BC）for lead,copper and cadmium contaminated irrigation water were 296.590 mg/g,180.422mg/g and 119.878 mg/g respectively,which exceeded the adsorption capacities of most types of biochar.γ-cyclodextrin biochar was prepared to improve its surface carboxyl functional group content,aromatization and carbonization,which enhanced its structural stability and electron feeding capacity.The preparation ofγ-cyclodextrin biochar improved the stability of the structure by increasing its carboxyl functional group content,aromatization and carbonization,and the electron feeding capacity.The adsorption of Pb²⁺,Cu²⁺and Cd²⁺in irrigation water byγ-cyclodextrin biochar is in accordance with the quasi-secondary kinetic fitting equation and the Langmuir isothermal adsorption model.It is an adsorption process in which the internal adsorption of biochar organic components and the fixation（dominance）of conjugated aromatic structure,the complexation of surface functional groups,precipitation and cation exchange and other mechanisms work together.（2）The maximum theoretical adsorption amount of magneticγcyclodextrin biochar on lead,copper and cadmium polluted irrigation water can reach 189.850 mg/g,143.931mg/g,and 71.825 mg/g,respectively.The magnetic modification ofγcyclodextrin by Fe Cl₃·6H₂O shows that the magnetization effect of the magneticγcyclodextrin biochar prepared successfully is obvious,the magnetization efficiency can be as high as 98%,and the stability of the benzene ring skeleton structure is improved.The adsorption mechanism of magneticγcyclodextrin biochar on heavy metals(Pb²⁺,Cu²⁺,Cd²⁺)of contaminated irrigation water is the same as that of cyclodextrin biocharγ.（3）The adsorption of Pb²⁺,Cu²⁺and Cd²⁺in the composite system can be balanced faster than that of a single system,and the adsorption rate has been further improved.By analyzing and comparing the maximum theoretical adsorption amount of each index fitting in the competitive adsorption test of lead-copper polluted irrigation water,we have concluded that compared with a single system,lead-copper ions can coexist in a binary composite system to produce mutual antagonism,resulting in different degrees of reduction of each index,but in the binary composite system,magnetic biochar shows a stronger affinity for copper ions and can still maintain a high adsorption amount.The functional groups,organic components and conjugated aromatic structure of BC and MBC together determine the adsorption performance of heavy metals,and their adsorption of lead,copper and cadmium in agricultural polluted water is better than that of adsorbents such as biomass carbon,carbon nanotubes and modified graphene.The findings of this thesis can provide a theoretical basis for the application of BC and MBC in preventing the import of heavy metals into soil in agricultural water and reducing the accumulation of heavy metal pollution in soil and agricultural development.