Study On The Passivation Effect Of Different Soil Conditioners On Heavy Metals In Compound Contaminated Soil

The report of geochemical survey on Chinese arable land in 2015showed that the cultivated land with severe and moderate heavy metal pollution was nearly 35 million mu,and the cultivated land with slight and light pollution was nearly 79 million mu,and the survey included nearly 14 hundred billion mu of cultivated land（about 68 percent of the total cultivated land area in China）.The polluted arable land was dominated by Hunan,Jiangxi,Fujian and Guangdong province in the south of China.And the acidification of soil in Fujian province was also more serious,and soil acidification increases the risk of soil heavy metal pollution.Therefore,it is necessary to take measures to control the pollution risk of heavy metals in cultivated land,and the pollution situation is imminent.In recent years,it has been found that soil conditioners not only contain rich mineral elements,but also have more alkaline substances,which can retain water and fertilizer in the soil while reducing the biological effectiveness of heavy metals.This study discussed in five aspects:different soil conditioners repairing heavy metal compound polluted soil,and the effects of soil conditioners on the bioavailability of cadmium,zinc,copper,nickel,and lead,and the migration of five heavy metal elements in the soil-brassica juncea system,and effects of yield and quality of brassica juncea,and characterization analysis of different conditioner materials,main passivation mechanism of conditioners.The purpose is to provide practical reference for improving the quality of agricultural products and the popularization and application of remediation technologies for agricultural soils polluted by heavy metals.The main conclusions of this study are as follows:（1）The addition of different conditioners could effectively increase soil p H（M field and N field）.After the application of different soil conditioners,the yield of brassica juncea in the M field was increased from 0.1%to 34.3%.The yield of brassica juncea in the N field increased in the range of-12.1%to 39.7%.（2）In the analysis of the effects of conditioners on the available states of heavy metals,different conditioners effectively reduced the content of DTPA extraction state of Cd,Pb,Zn,Ni,Cu in soils（M field and N field）.Conditioner A has the most reduction in DTPA-Pb and DTPA-Cu with a decrease of 26.0%and 23.2%respectively,while the decrease of DTPA-Cd,DTPA-Zn and DTPA-Ni by conditioner G was the largest with decreases of 21.0%,46.5%and 48.7%respectively in the M field.The conditioner G showed the largest decrease in DTPA-Cd,DTPA-Cd,DTPA-Zn,DTPA-Ni and DTPA-Cu,with the decrease of39.4%,39.6%,50.6%,73.0%and 32.9%respectively in the N field.Generally speaking,the proportion of effective heavy metal reduction in lightly compound contaminated soil（N field）is greater than the proportion of effective heavy metal reduction in severely compound contaminated soil（M field）.（3）Basing on the test and analysis of heavy metals enriched in brassica juncea by conditioners,different conditioners reduced the concentrations of five heavy metals in Cd,Pb,Zn,Ni,and Cu（M field）.The decrease of Cd and Pb in brassica juncea was the most with decreases of 50.0%and 75.0%respectively,and the lowest concentrations of Zn,Ni and Cu in brassica juncea after the treatment of conditioner G,conditioner F and conditioner D,and with decreases of 41.0%,48.0%and26.8%respectively.Different conditioner reduced Cd,Pb,Zn in brassica juncea（N field）,while conditioner B increased the concentration of Ni and conditioner C and conditioner F increased the concentration of Cu in brassica juncea.The treatment of conditioner A,conditioner B,conditioner C,conditioner D,conditioner E,conditioner F and conditioner G decreased Cd the most（33.3%）in brassica juncea,and the largest decreases of Pb,Zn,Ni and Cu were those treatments of conditioner A,conditioner F,conditioner G and conditioner D in brassica juncea respectively.（4）In the evaluation of adding different conditioners to enrich heavy metals in brassica juncea,all the conditioners reduced Cd-BAF,Pb-BAFand Ni-BAF（M field）.Conditioner C and conditioner E increased Zn-BAF,conditioner A and conditioner G increased Cu-BAF,but other treatments decreased.The addition of different conditioners all reduced Cd-BAF,Pb-BAF,Zn-BAF and Ni-BAF in brassica juncea（N field）.Treatments have no effect,except for conditioner B and conditioner G,which increased Cu-BAF in brassica juncea by 0.01.After treatment with conditioner A,the QIAP value of brassica juncea was the lowest,and with decreases of 37.2%and 22.9%respectively（M and N fields）.After treatment with conditioner D,the brassica juncea QIAP value was the highest,and with declines of 18.6%and 8.3%respectively.The addition of different conditioners all reduced mustard QIAP.This showed that different conditioner treatments have improved mustard varieties.（5）The analysis of physical and chemical properties of the seven conditioners found that the concentration of seven conditioners’Cd,Pb,Hg,As,and Cr did not exceed the limit values of the national standard23349-2009,and could be used to repair the soil in M and N fields.Electron microscopy analysis showed that conditioner A,conditioner B,conditioner E and conditioner G were mostly small particles and massive;Conditioner C was microporous,and Conditioner D was spherical and the surface was covered with small protrusions;Conditioner F was spherical and shell-shaped.The ingredients in the conditioners are mainly Ca CO₃、Ca Mg（CO₃）₂、Si O₂and Ca O,and the particle size is mostly large pores（>50 nm）.The conditioner materials mainly reduced the activity and bioavailability of five heavy metals in the four aspects of ion exchange,surface adsorption,surface precipitation and ion antagonism in the soil,and reduced the absorption of heavy metals by brassica juncea.It was proposed to recommend Conditioner A as the conditioning agent for promotion and application in the next step of the experiment.