Study On Leaching Remediation Of Heavy Metal Contaminated Farmland Soil And Field Application

The rapid development of the industrial society has brought side effects that are difficult to ignore.Wastewater and metal waste residues from industrial and mining enterprises not effectively treated have caused a large number of soils to be contaminated by heavy metals,and even severely endangered human health.The release of the State Council's"Action Plan for Soil Pollution Prevention and Control"showed the country's emphasis on the determination and control of heavy metal pollution in the soil.Among the numerous heavy metal remediation treatment technologies,the soil leaching and remediation technology has the characteristics of simple operation process,high remediation efficiency,and the ability to permanently remove heavy metal from the soil,which has been paid wide attention by researchers.In the actual environment,the research on the pollution remediation of single heavy metal elements can not meet the needs,and there are many kinds of heavy metals in the actual soil.At the same time,the traditional single reagent leaching and extractions have their limitations.Therefore,this study took a farmland soil polluted by heavy metals containing Cd,Pb,Cu,and Zn as the research goal.GLDA and Fe Cl₃ were selected as research reagents according to the relevant properties of the leaching reagents,to investigate the influence of single leaching reagent concentration,liquid-solid ratio and leaching time on the leaching efficiency,and analyze the morphological composition and distribution of heavy metals in the soil before and after leaching;Then screen the compound reagents with different concentration combinations,and perform five repeated leaching and compound leaching morphological analysis before and after.Finally,the actual field test was applied to verify the actual effect of the compound leaching agent,and the feasibility of popularizing and applying the leaching agent and application technology was discussed.The main conclusions are as follows:?1?GLDA and EDTA have similar effects on the removal efficiency of Cd,and GLDA has good degradability,and is suitable as an efficient leaching agent to replace EDTA,Fe Cl₃ also have a good elution effect,and the two are selected as leaching agents for further research.?2?When the concentration of GLDA and Fe Cl₃ were 0.05 mol/L and 0.50 mol/L respectively,the best leaching effect was obtained.the removal rate of Cd,Pb,Cu and Zn elements of GLDA shows that increased at the beginning and then decreased when increasing the eluent concentration,and the removal rate of four elements of Fe Cl₃ increased greatly.The removal rate of both leaching agents increased rapidly within 10 minutes after the start of leaching,and the reaction was basically balanced after 120 minutes.The removal of heavy metals by GLDA depends on the chelation of heavy metals in the weak acid extracted state,and the removal mechanisms of Fe Cl₃ includes cation replacement,hydrolytic acidification,chloride complexation.The weak acid extraction and oxidizable states of heavy metals are reduced after leaching.?3?The screening results of the combination leaching combination show that the best combination of GLDA and Fe Cl₃ is the combination of 0.01 mol/L GLDA and 0.50 mol/L Fe Cl₃,and the removal efficiency of the four heavy metal elements Cd,Pb,Cu and Zn Reached 70.75%,42.17%,84.72%and 92.08%respectively.The removal rate of heavy metal with compound leaching agent GF was significantly improved.After repeated washings,the removal rates of Cd,Pb,Cu and Zn were increased greatly,especially Pb with more residues.?4?The compounding reagent GF combines the strong chelation of GLDA and chloride ions as well as the hydrolytic acidification of iron ions.The combination of the two can not only extract the weak acid-extracted heavy metals,but also disturb the combination of soil and heavy metals,promote the dissociation of heavy metals in the reducible state and oxidizable state,and transform them into the extractable state,and even have a certain effect on the residual metal.After leaching with the compound reagent GF,the soil alkaline nitrogen,available phosphorus and available potassium decreased by 33.6%,6.5%and 53.6%respectively.The effect of leaching on the nutrient properties of the soil can be supplemented by the application of agricultural fertilizers.?5?On the three field application tests,the first one was manually stirred and rinsed with a small square of 1 square meter,the removal rate of Cd was 19.60%;the second extended the field of the test field to 1 acre,using agricultural machinery mixing and mixing,Cd The removal rate reached 33.01%;after the third rinse,the water was washed multiple times to improve the repair efficiency,and the removal rate of Cd reached 37.05%.In-situ leaching repair technology plus economical and environmentally friendly reagents,the average repair cost per acre is about13,000 yuan.The combination of new complex leaching reagents developed in this study can effectively improve the removal efficiency of heavy metals.Considering the application test results and remediation cost in actual soil,it has the feasibility of popularizing large-scale remediation.