Study On Chemical Leaching Cadmium And Other Metals Contaminated Soil With GLDA

Soil heavy metal pollution is one of the important environmental problems.Accumulation of heavy metal wastes,atmospheric dry and wet precipitation,and sewage irrigation will aggravate soil heavy metal pollution.It seriously threatens the survival of animals,plants and microorganisms in the soil,even cause health risks to humans through the food chain.In order to reduce the risk of heavy metals contaminated soil,effective remediation technologies need to be studied.N,N-bis(carboxymethyl)-L-glutamic acid(GLDA)is biodegradable and is a new generation of environmentally friendly chelatior.The soil column leaching with GLDA was used to remediate Cd and other metal-contaminated soils,and the remediation efficiency of dynamic continuous leaching and the effect of leaching on the physical and chemical properties of the soil were investigated,so as to provide scientific basis for application of GLDA in chemical leaching of heavy metals contaminated soil.In order to optimize the elution conditions,the effects of GLDA concentration,pH and extraction time on the removal efficiencies of Cd Pb,and Zn were investigated under shaking extraction conditions.Under the original pH condition of the GLDA solution,the removal rate of heavy metals is positively correlated with the concentration of GLDA within the concentration range of 0.5-10 mmol/L.When the concentration of GLDA exceeded 10 mmol/L,the removal efficiencies of Cd,Pb,and Zn tended to be stable.The removal rate of Cd,Pb,and Zn by GLDA at a concentration of 10 mmol/L reached 57.7%,23.9%,and 7.7%,respectively.The removal efficiencies of GLDA on Cd and Zn had no obvious trend with the increase of pH(3-10).The removal efficiency of GLDA on Pb gradually decreased with the increase of pH.The removal efficiencies of Cd,Pb and Zn by GLDA increased with the reaction time.After 60 minutes,the removal rate increased slowly and then stabilized,which means that heavy metals in the soil can be desorbed in a short time,which is beneficial to conduct soil column experiments.In order to evaluate the practical application of GLDA chemical leaching,the GLDA soil column leaching experiment was carried out.Under soil column leaching,GLDA with concentration of 10 mmol/L and pH=6.1 leached out 61.7%,22.3%,and 28.3% of Cd,Zn,and Pb,reduced the acid extractable and reducible metals significantly,and the metals in the soil were more stable after leaching,which effectively reduced the migration of metals and environmental risks.FeS can precipitate Cd and other metals in the leaching liquid,which can realize the recovery and utilization of GLDA,and the regenerated and fresh GLDA demonstrated similar Cd,Pb,and Zn extraction capacities,which were 56.5%,18.2%,16.4%and 53.8%,17.9%,and 18.1% respectively.Using water to wash the soil after GLDA leaching can reduce the amount of GLDA and residual GLDA.The soil properties after GLDA leaching were evaluated.GLDA leaching increased soil pH and available phosphorus content,and leached part of soil available potassium.From the results of soil particle composition and SEM characterization,GLDA leaching resulted in a decrease in the proportion of soil sand particles and an increase in clay and powder particles,and the soil texture changed from sandy to sandy loam.The effect of GLDA leaching on soil structure and texture is worthy of attention,and further research is needed to find ways to reduce these effects.