Study On Biochar Remediation Effect And Mechanism Of Cadmium Pollution Of Typical Farmland In Jiangsu Province

Through previous research,it has been found that soil cadmium pollution is an outstanding problem in Yixing City,Jiangsu Province.The reason for this is the commercial cadmium pigment used in the paint industry.The typical commercial cadmium pigment include cadmium yellow and cadmium red,among which the main components of cadmium yellow are CdS.The main components of cadmium red are CdS and CdSe.Due to the severe cadmium pollution in the local soil,it is urgent to carry out soil cadmium pollution remediation technology.Because of its large specific surface area,good adsorption performance,biochar can be used as an excellent soil remediation agent.However,the mechanism of biochar for cadmium-contaminated soil remains unclear.This project takes a typical region of Cd contaminated soil as the research object,using biochar as the soil remediation agent,using potted plants and greenhouse cultivation experiments as experimental methods to simulate the remediation process of Cd pollution,using continuous extraction methods and ICP-MS to analyze the morphological changes of soil Cd.The correlations between soil physicochemical properties and the morphologies of Cd were evaluated by using Pearson correlation coefficient,focusing on the environmental behavior of CdS and CdSe in the process of bioremediation.The intrinsic relationship between the morphological changes of soil Cd and its bioavailability reduction behavior;the mechanism of the research on the change of morphological transformation of Cd in the rhizosphere environment;the analysis of the characteristics of the rhizosphere environment,the occurrence and transformation of Cd and the behavior of Cd reduction.The interrelationships of rhizosphere environment,occurrence and transformation of Cd and then elucidate the mechanism of biochar remediation of soil Cd pollution.The research results of this thesis will provide scientific basis for soil Cd pollution control,and have important scientific significance for understanding the soil environmental behavior of CdS and CdSe in depth.To this end,we carried out a simulated remediation experiment of cadmium-contaminated,and obtained the following main results:(1)A multi-layer lattice root box was used to construct a 2-10 mm gradient spatial micro-domain from the plant roots.The farmland soil was used as the test soil.Wheat was used as the test plant and grown under 1000 mg kg-1 Cd stress for 3 months to measure wheat in vivo.Cd concentration.The results showed that the concentrations of roots in wheat grown in CdS-added soil and in CdSe-added soil were 15.57 mg kg-1 and 4.72 mg kg-1,respectively,0.29 mg kg-1 and 0.19 mg kg-1 in the stem,indicating that CdS was more easily absorbed by wheat.Continuous extraction method was used to extract Cd in different spatial micro-domain soils.The results showed that in the soil with CdS added,the exchangeable Cd concentration was the lowest,accounting for 0.01-0.49%,the concentration of those bounds to organic matter was the highest,accounting for 89.3-94.0%,and the residual was the second large occurrence form,accounting for 5.12 to 10.12%.The distribution pattern of CdSe in soil was similar to that of CdS,but the concentration difference was obvious.The lowest was exchangeable concentration,accounting for 0.02-0.94%,the highest concentration was those bounds to organic matter,accounting for 64.71-67.39%.The residual was the second large occurrence form,with a concentration of 29.54.-34.03%,indicating that CdSe was more stable.(2)A multi-layer grid root box was used to construct a 2-10 mm gradient spatial micro-domain from the plant roots.The farmland soil was used as the test soil and wheat was used as the test plant.After adding biochar to the soil,the bioavailability of CdS and CdSe in the soil could be effectively reduced.Among them,the roots and stems of wheat grown in the soil with CdS added were reduced by 52.2%and 37.9%,respectively.The concentration of Cd in the roots and stems of CdSe-added soil were reduced by 18.0%and 21.1%,respectively.The addition of biochar to tested soil could significantly change the form of CdS in the soil.Biochar effectively reduced the exchangeable Cd concentration,the reduction rate was 5.9-92.3%,and the reduction rate in the rhizosphere soil was 14.1%,which increased the concentration of those bounds to Fe-Mn oxide and the organic matter.The effect of residual had no obvious rule.In the CdSe-added soil,biochar could effectively reduce the exchangeable Cd concentration,the reduction rate was 11.8-88.3%,and the reduction rate in the rhizosphere soil was 11.8%.Biochar increased the concentration of those bounds to Fe-Mn oxide bound state and organic matter,and had no obvious effect on the residual state.(3)A multi-layer lattice root box was used to construct a 2-10 mm gradient spatial micro-domain from the plant roots.Wheat was used as a test plant,and ionized Cd was used as a cadmium pollution source.Biochar was used for soil remediation.For the Cd-contaminated farmland soil,biochar can also effectively weaken the bioavailability of Cd.The greater the amount of biochar added,the more significant the effect of weakening.When adding 1%and 3%biomass carbon,the bioavailability of Cd in wheat roots and stems decreased by 21.2%,22.9%,21.8%,and 37.9%.After 3 months of cultivation in the greenhouse,continuous extraction method was used to extract Cd in different spatial micro-domain soils.The results showed that biomass carbon could effectively reduce the concentration of exchangeable Cd in the soil.When the dosage was 1%and 3%,the reduction rate reached 28.2-44.1%and 49.2-61.3%,with the amount of biomass carbon.Biochar could increase the concentration of those bounds to carbonate and the Fe-Mn oxide.The concentration of those bounds to organic matter was significantly increased,and it could increase 121.6-338.9%and 308.7-722.5%,and can also increase the residual state.(4)Biochar can fix ion state Cd by passivation,adsorption,reduce the exchangeable Cd concentration and inhibit the mobility of Cd to reduce its bioavailability.Biochar can affect the form of Cd in soil by changing soil pH and organic matter concentration,affecting the distribution of CdS and CdSe in soil.Specifically,the correlations between the exchangeable state,those bounds to carbonates and iron-manganese oxide and the soil pH were significant,and the correlation between those bounds to organic matter and the soil organic matter was more significant.For the residual,there was no significant correlation with changes in soil pH and organic matter concentrations.