Study On Migration And Heavy Metal Adsorption Of Microplastics In Porous Media

The improper disposal of waste in some early landfills has resulted in leakage of MP,leading to serious pollution issues.These leaked MPs can penetrate into the surrounding soil of the landfills and spread to other environments via groundwater.The complex influencing factors within the landfill can alter the physicochemical properties of MP.MPs are capable of adsorbing heavy metals present in high concentrations in the landfill,thereby causing further contamination to the soil and ground water.To study the migration characteristics of MPs in soil and the effect of aging on the adsorption of heavy metals by MPs,this paper conducts transport experiments in porous media to simulate the breakthrough capacity of MPs under different influencing factors.A new method has been developed to resolve the issue of MP quantification in porous media experiments.MP were aged under different factors and the changes in their ability to adsorb heavy metals were studied.The main research results are as follows:（1）In order to achieve quantitative analysis of MPs in migration experiments,a new laboratory-based quantification method for MPs was established.The feasibility of constructing a standard curve method for MPs using ethanol dilution was studied,and the effect of ethanol-to-water volume ratio was discussed.The standard curves established in pure ethanol,ethanol-water volume ratios of 4:1,3:2,1:1 showed satisfactory parameters（R2>0.99）and recovery rates（80-120%）.For ethanol-water volume ratios of 2:3,1:4,the recovery rate parameters fluctuated significantly（RSD>20%）,and MPs were difficult to suspend and disperse in a pure water environment.The recovery rates and matrix effects under different interfering factors（p H,Na Cl,humic acid）and actual water body detection were within the range of 80-120%,indicating good resistance to interference and potential for practical application.The results showed that the inter-particle energy barriers of MPs were all greater than 15 KT,demonstrating good dispersion effects.（2）The migration characteristics of MPs in quartz sand porous media under different background solutions were studied,and the energy change relationship between MPs and quartz sand particles was analyzed.The migration rate of MPs increased with the rise in p H（from42.68%to 91.55%）,decreased with the increase in Na Cl concentration（from 53.59%to 9.77%）,and increased with the increase in humic acid concentration（from 53.59%to 92.39%）.The change in the energy barrier between MPs and quartz sand is consistent with the change in the migration rate of MP in quartz sand.Only when p H=9 and DOC=10,20 mg/L,the energy barrier is greater than 15 KT,under other conditions,MPs are prone to agglomerate with quartz sand,leading to sedimentation.（3）In order to study the changes in the adsorption characteristics of MPs due to aging under various factors,we aged MPs for 50 days using p H=4,9,humic acid=1000 mg/LDOC,and 30%H₂O₂,and studied the changes in the ability of differently aged MPs to adsorb heavy metals Cu（II）and Zn（II）.Compared to the original MP’ability to adsorb Cu（II）and Zn（II）,H2O2 aging increased the maximum adsorption capacity by approximately 118.51%and125.07%,respectively.Aging at p H=9 increased the maximum adsorption capacity by approximately 97.46%and 61.11%,p H=4 aging increased it by about 81.01%and 54.09%,and DOM aging increased it by about 8.64%and 6.49%.The kinetics of heavy metal adsorption conform to the pseudo-second order kinetic model,and the isotherm conforms to the Langmuir isotherm model.The ability to adsorb Cu（II）is greater than Zn（II）.Characterization results of MPs showed that aging changes the degree of surface wrinkling and damage of MPs to various extents,and also increases the proportion of oxygen-containing functional groups in MPs.This study employed ethanol and a turbidity meter for quantification,providing insights for the quantification of MPs in the laboratory.We established migration curves for MPs under various influences,offering a reference for studying the migration characteristics of MPs in different soil environments.Furthermore,we discussed the impact of different aging processes on the adsorption capacity of MPs,providing a reference for analyzing the effects of the actual environment on MPs.