| Cadmium pollution in farmland has become one of the prominent environmental issues in China.Remediation of soil cadmium contamination includes physical remediation,bioremediation,chemical remediation,and joint remediation.Among them,in-situ chemical passivation remediation has the advantages of low cost,easy operation,and quick response.It is a method that is widely used and has a good effect.One,but there are still problems such as poor stability of passivation effects.Therefore,this study selected two typical cadmium-contaminated paddy soils in Hunan Province-red-yellow mud(total cadmium content 0.73mg/kg)and Masha mud(total cadmium content 0.59mg/kg)as the research object,and select the main current passivation Materials,including five types of calcium oxide(YHG),calcium carbonate(TSG),biochar(SWT),silicon calcium fertilizer(GGF),and polyferric sulfate+calcium oxide(J+YHG),adopting simulated leaching of indoor warming rainfall In the method,after the passivation material was added to the cadmium-contaminated soil,four times of high-temperature cultivation(promoting ion exchange)and simulated rainfall leaching were alternated to monitor the changing patterns of soil pH,runoff liquid water-soluble cadmium,calcium,magnesium,etc.Then,a pot experiment was conducted with paddy-passivation + simulated leaching and control(passivation without leaching)soil in rice cultivation to monitor changes in cadmium,soil available cadmium,and exchangeable calcium and magnesium in brown rice in order to identify different types of passivation materials.The Stability and Mechanism of Cadmium Passivation in Soils.The main findings are as follows:1.Different passivation materials can significantly increase the pH of red-yellow mud and Masha mud,but the performance in different soils varies.In the red-yellow soil,YHG had the best pH-elevation effect.Only the passivation,passivation and simulated leaching increased soil pH by 0.67 and 0.48 units,respectively(P<0.05).In the Masha soil,the pH of the GGF treatment increased.The best results were obtained.Only the pH of passivation treatment,passivation + simulated leaching treatment increased by 1.37,0.84 units(P<0.05).The effects of different passivation materials on the stability of the two contaminated soils are also different.Among them,the TSG treatment has the best stability for the pH of the red-yellow soil,followed by the GGF treatment,and the two passivation materials increase the pH.The stability rates were 0.79 and 0.78,respectively.The best pH stabilization rate for the Masha soil was YHG treatment,followed by GGF.The stability rates of the two passivation materials for increasing soil pH were 0.77 and 076,respectively.2.Different passivation materials can significantly reduce the effective Cd content of red-yellow mud and Masha mud soil.YHG treatment had the best effect on Cd reduction in red-yellow soil.Only the passivation treatment,passivation and simulated leaching treatment decreased soil available Cd by 44.3% and 35.5%,respectively(P<0.05),and YHG treatment reduced soil.The stability of effective Cd was 0.80,which was superior to other passivated materials.GGF treatment had the best effect on reducing soil available Cd in Masha mud soil and the best Cd stability rate was.The stability rate of reducing soil available Cd was 0.94.Only the passivation treatment,passivation + simulated leaching treatment decreased soil available Cd content by 40.1% and 37.7%,respectively(P<0.05).3.Different passivation materials can significantly reduce the Cd content in different parts of rice.The effect of different passivation materials on the reduction of Cd content in different parts of rice is better than that of passivation + simulated leaching treatment.In the red-yellow soil,YHG treatment had the best effect on decreasing the Cd content of brown rice.The Cd content of brown rice with only passivation treatment,passivation + simulated leaching treatment decreased significantly by 38.5% and 27.7%,respectively(P<0.05);In the soil,GGF treatment had the best effect on reducing the Cd content of brown rice.Only Cd content of brown rice with passivation treatment,passivation + simulated leaching treatment decreased by 43.6% and 30.4%,respectively(P<0.05).Different types of soil,the effect of the application of passivation materials also showed different performance.The J+YHG treatment had the best stability for decreasing the Cd content of brown rice in the red-yellow soil,and the stability of the Cd reduction in brown rice was 0.95.The GGF treatment had the best stability for decreasing the Cd content of the brown rice in the Masha soil.The reduction rate of Cd was 0.70.In the red-yellow and Masha soils,compared with the control treatment,YHG and GGF treatments significantly increased the contents of Ca and Mg in brown rice.The contents of Fe,Mn,and Zn in different parts of rice were expressed as stems and leaves> Root system> The trend of brown rice.4.During 4 simulated leaching periods,YHG treatment and J+YHG treatment can significantly reduce the Cd content in red runoff soil runoff during the entire 4simulated leaching periods,and the runoff liquid in J+YHG treated Cd The content ofCd has been in a relatively stable state,indicating that its effect on curing Cd in red-yellow soil is better than other passivation treatments.In the Masha mud soil,GGF treatment can significantly reduce the Cd content in the runoff solution of the red-yellow soil during the entire four simulated leaching periods.The Cd content in the SWT-treated runoff fluid was at all four simulated leaching losses.A more stable state indicates that its effect on curing of Cd in red-yellow soil is better than other passivation treatments.Considering the treatment cost,technical effect and its stability,the effect of calcium oxide on the viscous red-yellow mud of Quaternary red soil is the best,and the application of silicon-silica fertilizer on sandy sand granite is best. 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