Study On Migration Characteristics Of La And Pb In Black Soil And Remediation Of La And Pb Contaminated Soil By Phosphorus And Montmorillonite Modified Biochar

With the continuous progress of social industrialization in our country,more and more pollutants were discharged into the environment we live.As an important part of the ecosystem,soil always plays a very important role.In recent years,due to the irrigation of heavy metal wastewater and the extensive application of rare earth fertilizers,soil was seriously polluted by heavy metals and rare earth metals.Lanthanum（La）and lead（Pb）,as typical rare earth metals and heavy metals,existed in large quantities in the black soil of Northeast in China,which seriously posed a huge threat to the surrounding environment.However,the migration mechanism of La and Pb in black soil under different environmental factors was still unclear,and the remediation technology for La and Pb co-contaminated soil also needed to be developed urgently.In this study,the soil column experiment was used to simulate the migration behavior of La and Pb in black soil under different environmental factors,and the Hydrus1D model was used to fit and predict their migration.On this basis,using garbage biochar as a matrix,red phosphorus and montmorillonite were used to modify biochar,and phosphorus and montmorillonite co-doped biochar（P-M-BC）was synthesized by ball milling.The research results are as follows:（1）The influence of different environmental factors on the migration of La and Pb in black soil is as follows:dry-wet cycle>freeze-thaw cycle>mechanical dispersion.With the increase of soil depth,the migration ability and migration content of La and Pb become more and more weak.The content of La and Pb in the 5-10 cm soil layer could reach 27.3 mg/kg and 58.5 mg/kg respectively after seven freeze-thaw cycles;and the content of La and Pb in the 5-10 cm soil layer could reach 27.3 mg/kg and 58.5 mg/kg respectively after seven dry-wet cycles.Under the action of exogenous forces（freezing tension,water gravity,etc.）,the migration ability of La and Pb will be enhanced.The simulation results of Hydrus1D showed that the soil column simulation was similar to the migration of La and Pb in the actual soil.After 20 freeze-thaw cycles,the content of La and Pb in the 5-10 cm soil layer will still increase,but the increase amplitude was very low.Meantime,the contents of La and Pb in the lower soil hardly changed,and there was no migration occurred in the lower soil;while under the condition of mechanical dispersion,La and Pb no longer migrate after a period of time.（2）The adsorption experiment in water showed that the synthesized P-M-BC had an excellent adsorption effect on La³⁺and Pb²⁺ions in the water.The initial p H value,adsorption time and adsorption temperature will affect the adsorption results.The optimum p H for the adsorption of La³⁺by P-M-BC was 4,and the equilibrium time was 90 min;the optimum p H for the adsorption of Pb²⁺was 5,and the adsorption equilibrium time was 240 min.The kinetics results showed that the adsorption process of La³⁺and Pb²⁺by P-M-BC was more suitable to be simulated by the Avrami kinetic fitting model,indicating that the adsorption process of La³⁺and Pb²⁺ions by P-M-BC included both physical and chemical adsorption process.The isotherm results showed that the Langmuir fitting model was more suitable for fitting the adsorption process of La³⁺and Pb²⁺by P-M-BC at different temperatures.The maximum adsorption amount of Pb²⁺by P-M-BC was 345mg/g at 20 ^oC and La³⁺by P-M-BC at 50 ^oC was 382 mg/g.（3）Soil remediation experiments showed that in the process of P-M-BC remediation of La and Pb co-contaminated soils,the material dosage,soil moisture content and soil p H will affect the remediation effect of P-M-BC.For the actual black soil,P-M-BC showed excellent remediation ability under the condition of 2%dosage,40%soil moisture content,and p H around 7.The contents of DTPA-extractable La and Pb in the soil were respectively decreased by 29.9%and45.5%.