Application Of Potassium Permanganate Modified Peanut Shell Biochar In Remediation Of Cadmium Contaminated Farmland Soil

With the continuous progress and development of society,the soil quality problems caused by the process of urbanization and industrialization are worrying.According to the“National Survey Bulletin of Soil Pollution Status”in 2014,about 10 million hectares of arable land in my country are polluted,accounting for about 19%of all arable land;about82.4%of all contaminated land is caused by heavy metals,of which heavy metals Cadmium pollution accounts for up to 7%.Cadmium in the environment has the characteristics of easy migration and accumulation.It enters the human body directly or indirectly through the food chain and other channels,and eventually accumulates in the internal organs and bones of the human body,causing great harm to the human body.In order to improve the ecological environment,prevent soil pollution,protect public health,promote the construction of ecological civilization,and promote sustainable economic and social development,my country formulated the“Law of the People’s Republic of China on the Prevention and Control of Soil Pollution”in 2018.The methods of remediation of heavy metal contaminated soil mainly include electric remediation technology,chemical leaching technology and chemical passivation technology.Because chemical passivation technology has the advantages of low price and easy availability,quick operation,it is often used to repair soil contaminated by heavy metals.The key to chemical passivation technology is to choose a suitable passivator.Biochar is often used as a soil passivator because of its good stability,abundant functional groups and huge specific surface area.Not only that,biochar can also improve the storage capacity of soil carbon.In order to enhance the adsorption capacity and passivation effect of biochar,it is necessary to modify the biochar.In this thesis,peanut shell biochar was prepared at two pyrolysis temperatures.The peanut shell biochar was modified with different concentrations of potassium permanganate.The structure and surface chemical characteristics of the modified peanut shell biochar were analyzed by BET,XRD,FTIR,SEM-EDS and XPS.The modified material with the best adsorption capacity was screened,and the influence of different conditions on the adsorption of cadmium by the biochar before and after the modification was analyzed.The adsorption characteristics of the biochar on cadmium were studied through batch experiments.In addition,soil cultivation experiments were conducted on cadmium-contaminated soil in Nanjing and Lanping to study the effect of peanut shell biochar application on soil properties and cadmium forms,in order to provide a practical basis for the treatment of heavy metal pollution in water and soil.The test results obtained are as follows:（1）The peanut shell biochar prepared at 350℃and 600℃was modified,and MnO_xwas loaded on the peanut shell biochar.The specific surface area and pore size analyzer,scanning electron microscope with energy spectrum,Fourier transform infrared spectrometer,X-ray diffractometer and energy spectrum analyzer were used to characterize the modified peanut shell biochar.The results showed that the surface structure of the modified peanut shell biochar was more loose,and the existence of manganese could be detected.The more potassium permanganate was added,the higher the content of manganese was.When the pyrolysis temperature was 350℃,the modified peanut shell biochar successfully added Mn-O groups,but when the pyrolysis temperature was 600℃,Mn-O groups were not added.Using X-ray photoelectron spectroscopy,it can be analyzed that potassium permanganate is reduced to MnO_xwhen preparing modified peanut shell biochar.Based on various characterization results,a suitable modified peanut shell biochar was finally screened out,that is,the peanut shell biochar prepared at 350℃was modified with a 0.3 mol·L^-1potassium permanganate solution.（2）Potassium permanganate modified peanut shell biochar can increase the adsorption capacity of cadmium.Under the conditions of pH 6.0,solid-liquid ratio of 0.5 g·L^-1,temperature of 45℃,reaction time of 24 h,and initial concentration of 200 mg·L^-1,the modified peanut shell biochar achieves the best adsorption capacity.The isothermal adsorption process conforms to the thermodynamic Langmuir model,that is,the adsorption process is homogeneous single-molecule adsorption.The saturated adsorption capacity of modified peanut shell biochar is 95.00 mg·g^-1,which is 41 times larger than that of unmodified peanut shell biochar.The adsorption kinetics is more in line with the quasi-two kinetic model,and the correlation coefficient R²>0.9989.Sodium nitrate solutions with different pH values were used to desorb the modified peanut shell biochar after Cd²⁺adsorption,and the desorption rate did not exceed 6.91%,indicating that potassium permanganate modified peanut shell biochar had better stability after Cd²⁺adsorption.In the cyclic adsorption and desorption test with nitric acid,the third adsorption capacity is67.75 mg·g^-1,the adsorption capacity is reduced by 15%compared with the first time,indicating that the biochar can be recycled.（3）The effects of adding modified and unmodified peanut shell biochar soil pH and cadmium forms in Nanjing and Lanping were investigated.The results showed that unmodified peanut shell biochar could adjust the pH of the two soils.The peanut shell biochar increased the soil pH in the two places.For Nanjing soil,unmodified peanut shell biochar can effectively reduce the proportion of acid-soluble cadmium in the soil,while modified peanut shell biochar can increase the proportion of cadmium residue content in the soil.For the Lanping soil,the modified peanut shell biochar not only effectively reduce the acid-soluble content of cadmium in the soil,but also increase the proportion of the residue content of cadmium.The modified peanut shell biochar is beneficial to Lanping heavy metals.Contaminated soil has a better passivation effect.