The Study Of Chemical Washing Remediation Of Cadmium And Lead Contaminated Farmland Soils And The Disposal Of Leaching Wastewater

In recent years,China's regional farmland soil pollution,especially heavy metal pollution,has become increasingly serious,which affects the rural environment security,agricultural products quality and humanbody health.Compared with the mild heavy metal contaminated soil,the area of the mid-high contaminated farmland soil is small,but the risk of ecology and food chain is great danger.On the one hand,it will reduce crop yield and quality,result in heavy metal content in crops seriously overweight,affect humanbody health;On the other hand,it may migrates through various means to the surrounding soil and groundwater.Therefore,for mid-high contaminated soil,the effective control and remediation is one of the focuses of the current soil pollution prevention and control works.In this article,we take cadmium and lead contaminated farmland soil as the research subject,systematically study the soil column leaching by composite chemicals and the disposal of leaching water,building a model of soil ex-situ washing remediation.The main contents are as follows:?1?Simulated soil column leaching experiment in laboratory using FeCl₃ and three kinds of organic acid?citric acid,malic acid and tartaric acid?were conducted to study the composite leaching agent dosage,the leaching times and the migration of chemical forms of Cd and Pb before and after soil washing.The results showed,FeCl₃ and citric acid washed 1 time?750 mL?,FeCl₃ and malic acid washed 1 time?750 mL?,FeCl₃ and tartaric acid washed 3 times?600mL?,the removal rate was optimal.Heavy metal fractionation experiments showed that the main form of Cd in contaminated soil was exchangeable,carbonate bound and iron?manganese?oxidation state,and the main form of Pb was organic and residual.?2?Simulated wastewater adsorption experiment is to study the adsorption characteristics of biochars,examining the influence of the biochars mass,solution initial pH values,adsorption time and the co-existing ions.The results indicated,when Cd²⁺ concentration was 10 mmol·L^-1,the amount of biochars was 80 mg,wastewater initial pH was 6.0,the adsorption rate was 95.5%under 25? and 15 min shaking time;When Pb²⁺ concentration was 100 mmol·L^-1,the amount of biochars was 150 mg,wastewater initial pH was 6.0,the adsorption rate was 95.5%under 25? and 15 min shaking time.At the meantime,the adsorption rate reduced to some extent as the co-existing ion concentration increased.The Langmuir model could describe the isothermal adsorption behavior of biochars better at the temperature of 15,25 and 35?.Also,the adsorption experiment was an endothermic reaction.?3?For the soil column leaching waste water,a purification method using alkaline precipitation combined biomass carbon adsorption was concluded.First,we add 2%hydrogen peroxide solution at 25?.Then we adjust pH to 12.2 and separate the precipitation.3.75 g·L^-1 biochars were uesd to adsorb wastewater under the condition of 25? and 6.0 pH values.The results of Cd concentration was 0.07 mmol·L^-1,Pb concentration was 0.20 mmol·L^-1 which was in line with the national wastewater discharge standards...