| The environmental damage caused by heavy metals pollution has gradually received attention from all parties.Under the action of human activities and the natural environment,pollutants are constantly enriched in the soil,and the heavy metals concentration in the polluted areas has exceeded the purification capacity of the soil.At the same time,the contaminated area is gradually expanded through runoff and rainfall,which threatens the health of animals and plants and humans in the cycle of the ecological chain.Therefore,studying the adsorption and migration rules of heavy metals pollutants in soil and the permeability characteristics of contaminated soil are great significance for detecting the scope of heavy metal pollution,evaluating pollution hazards and environmental governance.This paper takes four typical heavy metal pollutants Cr(Ⅵ),Cd(Ⅱ),Pb(Ⅱ)and Ni(Ⅱ)as research objects.The experiment uses the GDS environmental soil flexible wall permeability test system to measure the relevant parameters of saturated-unsaturated polluted soil permeability and analyzes the permeability characteristics of polluted soil.Explore the soil adsorption mechanism of heavy metals through static adsorption experiments and X-ray spectroscopy.Based on the one-dimensional soil column migration experiments of heavy metal contaminated water,combined with permeation and adsorption experiments,the migration process of heavy metals in the soil is studied to evaluate the scope of heavy metal pollution.The conclusions are summarized as follows:(1)Heavy metals pollutants affect the internal structure of the soil,causing changes in the permeability coefficient.Unsaturated penetration and saturated penetration of heavy metals contaminated soil have the same law,and the permeability distribution is Cr(Ⅵ)>Cd(Ⅱ)> Ni(Ⅱ)> Pb(Ⅱ).The permeability coefficient is inversely related to the confining pressure and positively related to the top water pressure and the osmotic pressure.(2)Heavy metals pollutants have physical and chemical adsorption with clay particles.When the mass ratios of Cd(Ⅱ),Pb(Ⅱ)and Ni(Ⅱ)pollutants to clay are not greater than1/1600,1/200,and 1/1000,respectively,the pollutants can be completely adsorbed.The adsorption kinetics curves of clay for heavy metal pollutants all conform to the pseudo-second-order kinetic model,and clay adsorbs Pb(Ⅱ)pollutants fastest and Ni(Ⅱ)pollutants for the slowest.Temperature can promote the adsorption of Ni(Ⅱ),Cd(Ⅱ)and Pb(Ⅱ)pollutants by clay,and can inhibit the adsorption of Cr(Ⅵ)pollutants,and temperature factors need to be considered during the repair process.At an ambient temperature of 25℃,the adsorption capacity distribution pattern of single-layer heavy metal pollutants is Pb(Ⅱ)> Ni(Ⅱ)> Cd(Ⅱ)> Cr(Ⅵ).(3)With the increase of pollution concentration,the migration and infiltration depth of heavy metals pollutants increased,but it is stable within 4320 h.Heavy metals pollutants are concentrated in the surface layer of the soil,and the residual concentration gradually decreases with the deepening of the soil layer.Although the contamination concentration is150 mg/L,the stable migration depths of Cd(Ⅱ),Pb(Ⅱ)and Ni(Ⅱ)are 85.1348,81.7292 and 85.1348 cm,however,according to the limited concentration value of the Soil Environmental Quality Specification,it is recommended that the repair depth of Pb(Ⅱ)and Ni(Ⅱ)pollutants is 0-10 cm,and the repair depth of Cd(Ⅱ)pollutants is 0-20 cm.(4)Combining soil penetration and pollutant adsorption and migration,the laws of different heavy metal pollutants are as follows: Pb(Ⅱ)is susceptible to adsorption with soil,and pollutants accumulate severely at 30 cm on the surface of the soil,and the permeability coefficient of the polluted soil is low;Ni(Ⅱ)has a long migration path,and has a long adsorption time with the soil;Cd(Ⅱ)aggregates severely at 40 cm on the surface of the soil and has a short adsorption time;Cr(Ⅵ)has the fastest migration in soil,low soil adsorption efficiency,and high permeability coefficient of contaminated soil. |
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