| With the increasing activities of human industrial production,soil heavy metal pollution is becoming more and more serious,especially heavy metal cadmium(Cd)pollution,which has become a research hotspot in the field of soil environment.In this paper,the reclaimed soil of Panyi Mine was taken as the research object,and the basic properties of the soil were determined.The Cd contaminated soil was artificially simulated by adding different concentrations of exogenous Cd solution to the soil,and the morphological changes of Cd after exogenous Cd entered the soil were studied by using the Tessier five-step continuous extraction method.Different concentrations of malic acid and citric acid were added to the soil to study the morphological changes of Cd in the soil,revealing the morphological transformation and distribution of Cd under the conditions of changing soil pH,soil temperature,soil particle size and soil aging time,providing a theoretical basis for predicting the migration and transformation of heavy metal Cd in soil.The main conclusions of the study are as follows:(1)Cd in reclaimed soil of Panyi Mine mainly exists in residual form,followed by exchangeable Cd > Fe-Mn oxide bound Cd > organic bound Cd > carbonate bound Cd.When the exogenous Cd concentration in soil gradually increased,the Fe-Mn bound and exchangeable forms became the main forms of Cd in soil.(2)In reclaimed soil,low concentrations of citric acid and malic acid had no significant effect on the content of Cd in various forms.The addition of malic acid and citric acid to artificially simulated Cd-contaminated soil increased the contents of exchangeable Cd and carbonate-bound Cd,decreased the contents of other forms,promoted the transformation of difficult-to-use bound Cd to active Cd,and increased the bioavailability of Cd.With the increase of exogenous Cd concentration and low molecular organic acid concentration,this effect is more obvious;the difference is that citric acid is conducive to promoting the increase of exchangeable Cd content,while malic acid promotes the transformation of other forms to carbonate-bound Cd..(3)Under the influence of citric acid and malic acid solution with different pH(2.3 to 9.0),the content of exchangeable Cd decreased with the increase of pH value,and the content of the remaining four Cd forms increased gradually.When soil pH was7,malic acid was beneficial to increase Cd activity.(4)Under the experimental temperature of 5°C to 25°C,with the increase of culture temperature,under the action of citric acid and malic acid,the content of carbonate bound Cd and exchangeable Cd increased significantly,and the content of other forms of Cd decreased gradually.Both organic acids increased the bioavailability of Cd in soil at elevated temperature.(5)In soils with different particle sizes(18-100 mesh),with the decrease of soil particle size,the content of bioavailable Cd increased gradually,the percentage of potential bioavailable Cd decreased significantly,and the residual Cd was basically unaffected.The decrease of soil particle size increased the activation effect of citric acid and malic acid on Cd.(6)Under the action of organic acids,during the early aging period(one week),the contents of carbonate-bound Cd and exchangeable Cd increased gradually,while the contents of other forms of Cd decreased continuously,and the activity of Cd in soil increased.After one week of aging,with the extension of aging time,active Cd in soil gradually transformed into strong binding Cd,reducing the activity of heavy metal Cd in soil.This study clarified that the content change and morphological distribution of Cd in reclaimed soil under the influence of citric acid and malic acid mainly existed in morphology and variation law,which provided a scientific basis for predicting the migration and transformation of Cd in reclaimed soil,and also provided a theoretical basis for phytoremediation of Cd pollution in reclaimed soil.Figure[31]Table[10]Reference[133]... |
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