Preparation Of Acid Modified Biochar And Its Inhibition Effect On Lanthanum Polluted Soil

With the increasing demand for rare earth resources,a large amount of waste residues and tailings accumulated over the years generated in the process of mining and extraction make La enter the ecosystem through natural action,posing a threat to the local ecological environment.Therefore,it has become a hot and difficult problem to explore the effective resistance and control technology,release precipitation,migration and transformation mechanism in rare earth mining area.At the same time,based on the application potential of biomass as an effective way for rare earth waste treatment,this study took acid-modified corncob charcoal（HCC）as raw material to investigate the effect of single factor on La adsorption,and combined with characterization analysis and mathematical model fitting to explore the adsorption mechanism and behavior.Exogenous La soil was used as the test soil,and HCC was added through sampling physical and chemical analysis,laboratory simulation test and other means to compare the change characteristics of La morphology.On this basis,a column simulation test was carried out to investigate the variation of La content in leachate,the vertical migration rule of soil La,the influence of material stability and the variation of La occurrence in soil under no/freeze-thaw action.The main conclusions are as follows:（1）La adsorption efficiency of HCC was 3.8 times higher than before.The influence degree of La³⁺adsorption by single factor test was ranked as follows:Initial concentration of La³⁺>p H>dosage of HCC>ionic strength.The increase of H⁺inhibited the adsorption of La³⁺by HCC.With the increase of dosage of HCC and ionic strength,the adsorption capacity of the biochar for La³⁺first increased and then decreased.The La³⁺adsorption process of HCC was mainly controlled by chemical action,and was accompanied by complex reactions such as surface adsorption and water film diffusion,which was a spontaneous endothermic reaction.The quasi-second-order kinetics and Temkin model are more suitable to describe the whole adsorption process.The simulated maximum adsorption capacity is 142.46 mg/g,and the material loss rate is 28.36%after 5 desorption.（2）After the addition of HCC,the exogenous La in the soil was dominated by residue,humus and amorphous oxide adsorbent state,while the endogenous La was dominated by residue and carbonate binding state.Under acid rain leaching,the p H of soil（exogenous/endogenous La）in control group and experimental group decreased and increased,respectively,and the concentration of La³⁺in endogenous/exogenous La soil leachate decreased by 83.97%and 65.80%.After the end of leaching,the rare earth element La migrated from the experimental group was reduced by 30.97%and 28.90%compared with the control group.HCC effectively inhibited La migration in soil through surface complexation and other functions.（3）The initial adsorption rate of HCC under freeze-thaw treatment was relatively slow at the 5th and 10th cycles,and the equilibrium adsorption capacity decreased to 36.08%of the original adsorption capacity at the 10th cycles.The HCC structure was destroyed after the10th freeze-thaw,and the adsorption process was controlled by molecular diffusion.With the increase of freeze-thaw frequency,soil p H first increased,then decreased and finally stabilized.Soil organic matter has increased to a certain extent.From the perspective of proportion analysis,X3 decreases from 8.01%to 7.2%,the release of X1,X4 and X5increases,and the proportion of X6 decreases from 63.97%in the first freeze-thaw cycle to58.27%,which proves that under the action of freeze-thaw,the residual state will be released and converted into other chemical forms,and the total amount of La decreases by 7.39%.It was proved that HCC had a certain inhibition effect on La under freeze-thaw.Compared with passivation,La content in soil decreased by 53.18%,which may be caused by the interference of external temperature on soil and the damage of the internal structure of HCC itself.