Preparation Of Cotton Straw Biochar Based On Microbial Fermentation Method And The Adsorption Performance Of Uranium

Cotton straw is one of the important agricultural by-products and an important biomass resource in in agricultural production.With the massive planting of cotton,cotton straw waste exists extensively.The traditional methods of utilizing cotton straw mainly include straw turnover,burning,etc.,which cause related environmental pollution problems directly.So,it is imprtant to convert the straw into high value-added products.Converting cotton stalks into biochar is an important resource utilization approach.However,the preparation process of traditional biochar has limited due to high cost,high pollution,and low selectivity.In this thesis,a simple microbial fermentation method was used to decompose cotton straw biomass,combining with hydrothermal carbonization（HTC）to prepare high value-added Calcium phosphate functionalized cotton stalk biochar（CSB）and cotton subshell biochar（CHB）to achieve high-efficiency separation of uranium.Additionally,the effects of fermentation,doping on the elements,morphology,and functional groups of cotton straw biomass were investigated systemly.The main conclusions are as follows:（1）By using an efficient fermentation pretreatment strategy,Calcium phosphate functionalized CSB was prepared.The results showed that the Calcium content of CSB was increased from 4.94 mg·g^-1 to 23.40 mg g^-1,and the adsorption capacity of U（VI）could reach528.8 mg·g^-1.The adsorption isotherms of CSB for U（Ⅵ）fit the Langmuir model,and the adsorption kinetics fit the pseudo-second-order kinetic model,respectively.Compared with the unfermented biochar,the CSB prepared by fermentation method had the advantages of good selectivity and high adsorption rate of U（VI）.（2）The Calcium phosphate functionalized CHB was efficiently prepared by introducing exogenous Calcium salts.The results confirmed that more phosphate groups were immobilized on the surface of biochar by hydrothermal carbonization.The CHB has a superior ability for U（VI）separating(952.7 mg·g^-1),which is more than 3 times that of the unfermented Calcium phosphate-functionalized CHB(283.1 mg·g^-1).And the CHB could reach the adsorption equilibrium within 5 min.Further mechanistic studies indicated that the adsorption of U（VI）by Calcium phosphate-functionalized CHB was mainly controlled by ion exchange and surface complexation.In summary,this project has prepared cotton straw biochar based on Calcium phosphate functionalization efficiently by a simple microbial fermentation pre-treatment method,and realized cotton straw biochar with high enrichment and separation ability for uranium-containing wastewater.In addition,this preparation method is expected to be further extended to similar biochar preparation to realize comprehensive utilization of resources.