Study On Removal Of Soil Cadmium By Biosurfactant And Modified Peanut Shell

In recent years,due to China’s rapid economic and social development,human production activities and high background values in some areas,the situation of Cd pollution in farmland in China is not optimistic,and a safe and efficient soil remediation method is urgently needed.Peanut hulls are a wide range of agricultural and forestry wastes.Using them as raw materials to prepare adsorbent materials not only turns waste into treasure,but also has low cost.At the same time,biosurfactants have a good solubilizing effect on soil heavy metals,the combined application of the two in the rehabilitation of Cd-contaminated farmland can quickly reduce the degree of soil pollution from the total amount,and has broad development prospects.In this study,peanut shells from agricultural and forestry wastes were used as raw materials,and modified peanut shells with good Cd²⁺adsorption properties were obtained through modification with potassium permanganate（KMnO₄）,the surface morphology,specific surface area,crystal structure and functional groups of peanut shell before and after modification were characterized by modern detection techniques,and the adsorption characteristics of peanut shell before and after modification were compared and analyzed.Through the static adsorption test,the adsorption effect of modified peanut shell on Cd²⁺under different KMnO₄ solution concentration,modification time and impregnation ratio was discussed,and isothermal adsorption and adsorption kinetics were also studied.In addition,the compounding ratio between three different biosurfactants was studied through a single factor test,and the effects of the concentration of the extract solution and the extraction time on the removal of Cd in the soil were discussed.Finally,the bio-surfactant compounding system was used to extract the Cd in the soil,and the modified peanut shell was used to adsorb and treat the extract solution to analyze the changes of the soil properties before and after the restoration,so as to form a combined technology for efficient repair of farmland Cd-contaminated soil.The main conclusions obtained in this study are as follows:（1）The biosurfactant compounding results showed that the pH of the extract solution of the tea saponin（TS）/sodium lauryl sulfate（SDS）compounding system was maintained at acidity,and the effect of Cd extraction was the best.Keeping the concentration of extraction solution and extraction time constant,when the mass ratio of TS to SDS is 2:1,the removal rate of soil Cd is the highest,reaching 52.17%.When analyzing the effect of the concentration of the extraction solution and the extraction time on the effect of soil extraction,it was found that with the increase of both,the extraction effect was significantly improved.When the concentration reached 5%and the extraction time was 24 h,the best removal rates was 58.33%.（2）The results of Cd content in the soil after pre-leaching showed that the TS/SDS compound extract can effectively remove the total Cd and effective Cd content in the soils with high,medium and low pollution levels.The total Cd content of the three polluted soils decreased by 50.27%,42.45%,and 41.59%,respectively;the effective Cd content decreased by 61.42%,52.41%,and 41.00%,respectively.After analyzing the change of Cd morphology in the soil after treatment,it was found that the TS/SDS compound extract could significantly reduce the acid extraction and reducible state of Cd in the soil,thereby reducing its bioavailability.（3）Through response surface optimization analysis,it was found that the significant order of influence on the adsorption amount of modified peanut shell was the impregnation ratio of peanut shell to KMnO₄ solution>modification time>KMnO₄solution concentration.The optimal modification conditions of peanut shell are:KMnO₄solution concentration of 2.5%,modification time is 10 hours,and the impregnation ratio of peanut shell to KMnO₄ solution is 1:21.Under this condition,the surface of the modified peanut shell is rough,forming a large number of cracks and pores,the specific surface area and average pore volume are increased,and the average pore diameter is reduced.At the same time,MnO₂ is formed on the surface of the peanut shell,and the original crystal structure is destroyed.More functional groups were exposed,which significantly improved the adsorption properties of peanut shells.（4）Isothermal adsorption test results show that the Langmuir equation can better describe the adsorption process of Cd²⁺by modified peanut shells,and the maximum adsorption capacity of Cd²⁺by modified peanut shells at 15°C,25°C,and 35°C are 30.46mg·g^-1,31.22 mg·g^-1,and 34.52 mg·g^-1.Fitting the adsorption kinetic data found that the quasi-second-order kinetic model is more suitable for the adsorption of Cd²⁺by modified peanut shells,and the adsorption process is mainly based on chemical adsorption.（5）The results of adsorption of Cd in the modified peanut shell extract showed that the modified peanut shell can efficiently adsorb Cd in the soil extracts of three pollution levels,and the adsorption rate of Cd is the largest in the range of 0 to 5 h.When the adsorption time reached 12 h,the adsorption of Cd in the extract by the modified peanut shell was basically completed.