| The Soil Pollution Prevention and Control Action Plan issued by the State Council clearly stated that in soil prevention and control actions,supervision of pollution sources should be strengthened,soil pollution prevention should be done well,pollution prevention and control of industrial and mining,agriculture and livestock and poultry industry should be strengthened,water quality management of irrigation water should be strictly controlled,and pollution of domestic garbage should be reduced.Therefore,this study carried out the idea of combination of prevention and cure of soil pollution,and based on the modified peanut shell biochar（MBC）obtained by the research group in the previous study,which had a good removal effect on ammonia nitrogen in the solution,through the analysis of modified peanut shell charcoal applied before and after the change of soil property,in batch equilibrium adsorption experiment and soil column leaching experiment,on the basis of combination of adsorption kinetics and isothermal adsorption curve and the physical and chemical properties characterization results,revealed the adsorption characteristics and mechanism of ammonium in MBC treated soil,and the relevant prediction parameters of ammonia transport in soil were obtained by the Hydrus-1D model fitting based on equilibrium and non-equilibrium models,could in the effective utilization of waste resources and reduced or avoided the risk of ammonium pollution in soil and groundwater.The main research results of this paper were as follows:（1）Before and after incubation,the soil particle size distribution was 3-5nm and the specific surface area was similar,and the adsorption type was all multi-layer chemisorption.Compared with the control soil,the p H value of MBC（1%,3%,5%and10%）soil increased by 0.41,1.27,2.22 and 2.84 units on average,respectively,and the CEC value of the control soil was 17.3 cmol·kg-1,belonging to the medium fertility preserving soil.After a period of incubation,the CEC value of all the MBC treated soils increased to more than 20 cmol·kg-1,and the TOC content of the soil was significantly augmented by MBC addition.In contrast to nature soil,the TOC value of 10%MBC treated soil augmented by 85.31%,and other application ratios（1%-5%）increased by28.81%-38.95%.（2）With the increase of initial ammonium from 15 mg·L-1 to 100 mg·L-1,the adsorption capacity of ammonium in control soil and 10%MBC treated soil increased from 0.16 mg·g-1 and 0.21 mg·g-1 to 0.51 mg·g-1 and 0.90 mg·g-1,respectively.The removal rate of ammonium decreased from 43.05%and 61.47%to 20.55%and 39.68%,respectively.At an initial concentration of 100 mg·L-1,compared with the control soil,the specific adsorption capacity of ammonium in the MBC（1%,3%,5%and 10%）treated soil increased from 0.51 mg·g-1 to 0.53 mg·g-1,0.64 mg·g-1,0.74 mg·g-1 and 0.90 mg·g-1,respectively,while the removal ratios were increased by 3.89%,28.95%,50.95%and93.04%,respectively.（3）The Freundlich and the quasi-second-order equation were suitable for describing the adsorbent process of ammonium in the MBC treated soil.The adsorption effect of soil treated by MBC was greatly improved,and the adsorption process tended to be multi-layer adsorption with rate-limiting steps as chemisorption.（4）Based on the analysis of modern instruments such as Scanning Electron Microscope-Energy Dispersive Spectrometer,Fourier Transform infrared spectroscopy and BET specific surface area measurement,combined with the previous analysis of the mechanism of MBC adsorption on ammonium,it was inferred that the adsorption of ammonium in MBC treated soil was mainly through chemical multi-molecular layer adsorption,which mainly consisted of ion exchange and oxygen-containing functional group complexation,and the mechanism of physical adsorption was small（5）The adsorption breakthrough curves of ammonium in soil columns with different MBC dosages（1%,3%,5%and 10%）were basically the same.In contrast to nature soil,when the MBC dosages were 3%,5%and 10%,the specific adsorption capacity increased from 1.17 mg·g-1 to 1.20 mg·g-1,1.31 mg·g-1,1.46 mg·g-1 and 0.90 mg·g-1,respectively.In addition,when the MBC application ratio is 10%,the breakthrough volume of upper layer and lower layer increased by 5.56%and 8.73%,respectively,compared with that of mixed layers.This indicated that the layered application method of MBC could enhance the inhibition effect of soil ammonium transport rate.（6）Based on the equilibrium and non-equilibrium models of the Hydrus-1D,it was found that the non-physical equilibrium region had little influence on the transport process of ammonium in the soil column,which was mainly a chemical non-equilibrium transport process.Sensitivity analysis of key parameters of solute transport fitting showed that(（9） has the greatest influence on NH4+-N breakthrough curve.As an environmentally friendly material with the advantage of treating waste with waste,MBC could improve the soil physical and chemical properties,enhanced the chemical adsorption capacity of the soil to ammonium,and then inhibited the migration behavior of ammonium in the soil.The application amount and adding method of MBC will affect the migration behavior of ammonium in the soil,so the above factors should be taken into consideration when applying MBC to the soil environment.Solute transport parameters obtained by Hydrus-1D fitting,especially in the non-equilibrium TSM model,were of great significance for evaluating and predicting the risk of soil ammonium pollution and selecting appropriate remediation strategies.MBC technology was different from other post-treatment technologies for soil pollution,had the forward-looking advantage of combining prevention with control.Therefore,this technology could reduce the possible environmental pollution risks of agricultural land,industrial and mining land and landfill sites,provided innovative ideas for the harmless management and operation of land under environmental risk conditions,and properly handled the contradictions among resources,environment and economy,which was of great significance for promoting the development of various industries. |
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