Mechanism And Application In Remediation Methods Of Heavy Metal-Contaminated Soil

Heavy metal contamination in soil is seriously threating the grain production and food safety,constraining the sustainable development of the economy and society.Accordingly,specific prevention and control methods as well as remediation techniques must be developed.Action plan for prevention and cure of soil pollution will be introduced and fully implemented in years,which may set higher requirements for the technological level of our national soil remediation industry.There exist huge demands for soil remediation techniques in our country but proprietary techniques are few in number.In addition,key technology and equipment are relatively backward and are mostly imported from abroad.New remediation techniques of typical heavy metalcontaminated industrial sites and farmland in our country has been studied and implemented for engineering application in this research,which proved to be effective and is of great practical significance to the guarantee of soil environment safety and public health.The results of this study are as follows:(1)A new microwave-enhanced green elution technique has been proposed in this study,which meets the urgent demand for remediation of heavy metalcontaminated sites,addresses the issue of lack of available domestic technical equipment,is environmentally friendlier and has higher treatment efficiency.Microwave has been introduced to soil eluting remediation and a new way of microwave-enhanced green elution remediation technique applicable to heavy metalcontaminated soil has been presented.①EDTA and citric acid were mixed as eluant to treat the soil of industrial sites contaminated with Pb and As.Compounding conditions were as follows:0.01mol/L EDTA,0.1mol/L citric,water-soil ratio of 10:1 and 400W microwave elution for 10min.Removal rates of Pb and As in soil were 81.32%and 61.32%respectively.② Recycling technology of the eluant was further studied and resin 201 with high absorption effect(Pb and As concentrations in the eluant were only 7.35mg/kg and 5.38mg/kg respectively)was selected out.Such a resin can be directly used in eluant recycling.③ Based on above lab experiments,the first domestic microwave-enhanced soilremediation eluting equipment was designed and developed.Removal rates of Pb and As in soil were 70.42%and 63.52%respectively.in 30 minutes.Secondary pollution can also be avoided through the recycling technology of eluants.(2)Stabilizing agent with coconut shell biochar as the core material was compared with other materials according to farmland soil security requirements and in situ stabilized remediation technique of heavy metal-contaminated alkaline farmland.① Inactivation effect of heavy metals became more obvious with the addition of stabilizing agent.Coconut shell bio-char is more effective than other seven stabilizers.2.0%coconut shell bio-char in soil stabilized up to 99.08%of available Cd,and could remain the bio-available Cd at a relative low level for more than 250 days.In addition,the application of coconut shell bio-char also promoted the wheat growth and decreased Cd concentrations in wheat.1.5%coconut shell bio-char in soil decreased the Cd concentrations in root and shoot by 60.04%and 58.07%respectively when compared with the control group.By speciation analysis,coconut shell bio-char showed its ability in transforming Cd from the bio-available form to the stable form in soil.It decreased the proportion of water-soluble and exchangeable forms of Cd and increased that of organic-bound and residual forms.② On the basis of lab researches,coconut shell biochar was applied to cadmiumcontaminated alkaline farmland and the results were consistent with those of lab experiments.Compared with control groups,effective state of cadmium in soil reduced by 90.52%,with 42.12%,34.15%and 25.36%respectively in wheat root,shoot and grain.The chosen coconut shell biochar as stabilizing agent can not only realize longterm remediation of heavy metal-contaminated alkaline farmland but also significantly improve soil structure,increase soil fertility,and promote wheat yield.