The Effect Of Clay Minerals On Remediation Of Cd Contaminated Soils

At present,the form of farmland soil heavy metal pollution has become increasingly serious,including cadmium?Cd?pollution is the most common,especially in the cities and industrial and mining areas surrounding.Because of the heavy metal Cd with mobility strong,easily absorbed by plants and other characteristics,Cd contaminated soil problem attracting widespread attention.Clay minerals content passivation repair measures governance farmland soil heavy metal Cd pollution is the most commonly used method,there have been many cases of demonstration application.But the long-term effect of clay minerals content repair Cd contaminated soil and side effect,is also need to pay attention to and research problem.This study on sepiolite and palygorskite as passivation materials,by adding the Cd element,soil pollution of heavy metal Cd in situ remediation of pot experiment,the effects of two kinds of clay minerals in different amount of change of maize Cd content,soil pH and effective state Cd content,to characterize the repair effect.At the same time design soil column leaching test,the simulation of different frequency under the condition of rainfall and rainfall intensity precipitation,to exert different proportion sepiolite processing of soil heavy mentals in the soil column Cd along with the migration characteristics of runoff effects,analysis to drench filtrate and soil pH,Cd in the total amount and the changing rule of the effective state Cd content,to study the migration characteristics.?1?Under the condition of two kinds of Cd contaminated soil,it is more economical and effective to reduce the content of Cd in the stem and leaf of the plant,which is suitable for the growth of crops and the degree of toxicity to crops.The amount of different conditions in two kinds of clay minerals,the maize plant height with the increase of Cd concentration decreased significantly in different periods,the same trend,and the maize growth period,two kinds of clay minerals influence on plant height,and the application level of Cd.Compared with the control group without adding clay minerals,two kinds of clay minerals in different proportions could increase the biomass of crops,but did not reach a significant level.The content of Cd in the aboveground parts of maize plants increased with the increase of Cd content in the soil,and the distribution of the content of the maize kernel was corn grain.?2?The change of soil pH value is an important factor for clay minerals to repair Cd contaminated soil.0?10 cm soil surface pH values were higher than the 10?20 cm layer,and with the increase of the amount of applied two kinds of clay minerals increased;according to the different ratio of applying two kinds of clay minerals cound reduce the available Cd content in soil,and the difference was significant?P<0.05?.The increase of soil pH value can change the existing form of Cd in the soil,which can reduce the migration and bioavailability of Cd,and alleviate the damage and harm of Cd to corn and soil.?3?Soil column leaching test,different ratio of soil column leaching after applying sepiolite,8 pillars of water holding capacity of the order of C1H1>C1H2>C2H3>C1H3>CK1>C2H1>C2H2>CK2;the pH value of leachate is between 6.5?8.0.The leaching intensity will affect the infiltration rate,the greater the leaching intensity,the greater the infiltration rate,while the Cd content in the leachate will be reduced.The content of Cd in the soil column of sepiolite was lower than thatof the control group at the two levels of Cd contaminated soil,and the leaching rate of Cd in leachate was the largest when the applied amount was 1%and 1.5%,respectively.?4?Two kinds of Cd contaminated soil,compared with the control group,the effect of Cd content on Cd contaminated soil in different depth of applying different proportions of sepiolite significantly?P<0.05?;and there are different degrees of heavy metal Cd vertical downward migration phenomenon.The control group of Cd contaminated soil in 20?30 cm layer(Cd layer of the original content in soil was 0.46 mg kg^-1)Cd content were 0.90 mg kg^-1 and 1.82 mg kg^-1,increased by 0.44 mg kg^-1 and 1.36 mg kg^-1,The different proportion of sepiolite was applied after the repair,can effectively inhibit the downward migration of heavy metal Cd,two kinds of soil Cd pollution level in 1%and 1.5%respectively,applying sepiolite to inhibit soil Cd downward migration was reduced to 0.50 mg kg^-1 and 0.44 mg kg^-1.?5?The potting soil leaching toxicity test analysis:The content of Cd in the 10?20cm layer was higher than that on the surface of 0?10cm?except ClA2?,which indicated that the heavy metal Cd contaminated soil still had downward migration after cultivation or clay mineral passivation treatment.Applied clay minerals remediation of Cd contaminated soil,alleviate the leaching amount of leaching toxicity of Cd content,no significant effect on 2 mg kg^-1 Cd in contaminated soil,but 5 mg kg^-1 Cd contaminated soil effect is remarkable,and the amount of attapulgite is 1.5%,the maximum response of soil Cd leaching amount of 0?10cm layer of shadow,a decrease of 0.132 ug L^-1?33.8%?;sepiolite applied quantity of 1.5%,the greatest impact on the 10?20cm soil Cd leaching amount,reduced 0.213 ug L^-1?46.0%?.