Research On The Adsorption Performance Of Heavy Metals Pb(?) And Cd(?) By Biochar And Modified Biochar

In recent years,the situation of heavy metal pollution has become more severe,and soil heavy metal pollution has seriously endan,gered human production and life due to its long-term,concealed and widespread nature.Because of its excellent structural properties,cheap and extensive biomass sources,biochar is often used as a remediation agent and modifier to be applied to contaminated soil.In this article,wheat straw and pine sawdust were selected as raw materials for biomass,combined with thermogravimetric,elemental,infrared spectroscopy,specific surface area,electron microscopy analyses.The chemical composition and structural composition of biochar with different pyrolysis temperatures were systematically studied.Based on the subsequent design of adsorption experiments,the adsorption performance of different biochars?M400,M500,M600,S400,S500,S600?on Pb and Cd at different pyrolysis temperatures,biochar dosage,initial pH,and initial concentration,respectively,coupled with isothermal adsorption model to explore the adsorption mechanism.In order to enhance the adsorption and conversion of biochar to heavy metal Pb and Cd pollutants,modification methods of phosphoric acid,potassium hydroxide,loaded Fe,microwave were utilized to optimize the structural properties of biochar.The enhancement effects of modified biochar?PM600,KM600,FeM600,BM600?on the adsorption and conversion of heavy metal Pb and Cd pollutants in the soil were studied.Due to simulate the addition of biochar in actual soil on the impact of migration and transformation of pollutants,soil-cultivation experiments was used to study the application potential of biochar addition in the field of actual soil remediation.The main conclusions and innovations obtained are as follows:?1?The relationship between elemental composition,pore structure,surface functional groups and preparation temperature of biochar made from wheat straw and pine wood chips of different biomass materials was investigated.The results showed that with the increase of the preparation temperature,the polar functional groups of biochar gradually decreased,the degree of aromatization gradually increased,and the microporous pore structure gradually increased.?2?In the adsorption experiment,with the increase of pyrolysis temperature,addition amount and initial solution pH of biochar,the adsorption of biochar to heavy metals Pb and Cd in the solution also increased significantly.The adsorption of biochar to Pb²⁺ is more in line with the Langmuir model,which shows that the adsorption of biochar to Pb²⁺ is largely consistent with the adsorption of monolayer.The adsorption of Cd²⁺ by wheat straw biochar is more in line with the Freundlich model,indicating that its adsorption of Cd²⁺ is multilayer adsorption.The Langmuir model can better characterize the adsorption of pine sawdust biochar on Cd²⁺,and the adsorption of Cd²⁺ is more in line with the monolayer type.?3?The effects of phosphoric acid,potassium hydroxide,loaded Fe,microwave and other modification methods on the structure,adsorption and conversion properties of wheat straw biochar were studied.The results show that phosphoric acid and iron-based modification can significantly enhance the adsorption and conversion ability of wheat straw biochar to heavy metal Pb and Cd pollutants.Microwave modification can unblock the surface attachments in the wheat straw biochar structure,and expose more active sites,thereby enhancing biochar's ability to adsorb and transform pollutants.Phosphoric acid modified biochar PM600 has the best adsorption and conversion effect on soil heavy metals Pb and Cd pollutants.?4?In the passivation experiment,the soil pH value first decreased due to the nature of the phosphoric acid modified biochar,and then slowly increased.In the soil contaminated by single heavy metals Pb and Cd,as the amount of biochar added and the cultivation time of biochar prolonged,the weak acid extractable content of heavy metals Pb and Cd decreased accordingly.Modified PM600 biochar has a good passivation effect on heavy metal contaminated soil.Considering the economic and passivation effects,the addition of 5%PM600 biochar is most suitable for the passivation of soil heavy metal Pb and Cd pollution.