Study On Stability Of Immobilization Effect Of Cadmium In Typical Paddy Soil

The in-situ immobilization technology of heavy metals do not remove heavy metals cadmium?Cd?from contaminated soil.Soil environment,crop growth and other factors are bound to affect the stability of the immobilization materials and the immobilization product activation of Cd.So the long-term stability of the immobilization effect is the key to the successful implementation and popularization of the in-situ immobilization technology of heavy metals.This paper studies the effect of aging effect on the adsorption stability of paddy soil Cd after application of sepiolite and biochar,the change of soil Cd morphology and the persons correlation about the change of paddy soil Cd,iron?Fe?,manganese?Mn?,copper?Cu?and zinc?Zn?,and leading to the following conclusions:?1?The effect of applying sepiolite and biochar on the form of Cd in the soil was studied by BCR continuous extraction method.The studies show that the soil Cd morphology was in the process of dynamic change,and the aging effect made it eventually tend to equilibrium.The application of sepiolite and biochar can significantly increase the soil pH and weakened the bioavailability of paddy soil Cd.However,during the re-release stage of the stable Cd in the soil,the change trend of the soil pH was relatively stable.The research has shown that the re-release process of stable Cd in the soil is divided into two categories:?a?the stable Cd in the immobilization product was converted to the bioavailability Cd in the soil again;?b?the interaction between the soil conditioner and the soil components leading to the soil stable Cd was converted to the bioavailability Cd in soil.?2?Apply the concepts of definite integral and deviation to construct the Immobilization Efficiency Index?Index of Immobilization Proportion,IP?and the Immobilization Stability Index?Index of Immobilization Stability,IS?to evaluate the immobilization effect of paddy soil Cd.The greater the IP value which means the greater the average passivation efficiency,the better the passivation stability of the passivation material;the IS which refers to the stability of the passivation effect of the passivation material tends to 1,it shows the worse the passivation stability and efficiency;Whereas when it tends to0,the passivation effect would be more stable.Compared with the passivation curves of the passivation materials?sepiolite and biochar?,the passivation efficiency and passivation stability of biochar were better than sepiolite at 0-19 d,during the period of 0-19 d,The IP and IS of biochar are higher than sepiolite(IP^[HS,0-19]=0.69>IP^[HB,0-19]=0.34,IS^[HS,19-308]=0.60<IS^[HB,0-19]=0.88),the result was consistent with the conclusion of the passivation curve comparison;by constructing the passivation efficiency index and passivation stability index,the comparison method has been changed from two-dimensional to one-dimensional,which was more convenient comparative analysis.In the process of soil cultivation of 308days,there were immobilization stage,immobilization stabilization stage,stable Cd re-releasing stage and a re-immobilization stage of soil Cd;Applying the extraction method of diethyl triamine penttacetic acid?DTPA?,The effects of sepiolite and biochar on the adsorption stability of soil Cd were studied.From the aspects of immobilization efficiency and immobilization stability,different paddy soil types?Hechi,Xiangtan and Shaoguan paddy soil?,different soil conditioning agents?sepiolite,Biochar?,there were significant differences in the release of stable Cd in the soil.In Applying sepiolite of Hechi soil treatment?HS?,Applying biochar of Hechi soil treatment?HB?,Applying sepiolite of Xiangtan soil treatment?XS?,Applying biochar of Xiangtan soil treatment?XB?,Applying sepiolite of Shaoguan soil treatment?SS?and Applying biochar of Shaoguan soil treatment?SB?,the immobilization stability of soil Cd in Xiangtan rice field was better than Hechi and Shaoguan(IS^[XS-0-308]=0.16<IS^[HS-0-308]=0.50<IS^[SS-0-308]=0.70;IS^[XB-0-308]=0.16<IS^[SB-0-308]=0.60<IS^[HB-0-308]=0.88),the immobilization efficiency of sepiolite is better than biochar(IP^[HB-0-308]=1.6<IP^[HS-0-308]=10.5;IP^[SB-0-308]=6.5<IP^[SS-0-308]=8.9;IP^[XB-0-308]=8.1<IP^[XS-0-308]=10.7).?3?The persons correlation analysis of the changes of Cd,Fe,Cu and Zn in the paddy soils of Hechi,Xiangtan and Shaoguan after the application of sepiolite and biochar was studied and the results indicated that because of the soil parent material of different paddy soil,its correlation difference was obvious.Compared with the application of sepiolite,the correlation between the paddy soil Cd,Fe and Mn morphological changes was stronger after applying biochar.during soil cultivation of 308 days,there was no competitive adsorption relationship between soil Cd,Zn and Cu.