| In recent years,heavy metal pollution in soil has received extensive attention from scholars at home and abroad.Cadmium,one of the five toxic elements,accumulates in the soil and is easily absorbed by crops.It affects the growth of crops and the quality of agricultural products,and then harms human health through the food chain.Therefore,it is imperative that cadmium-contaminated soil be restored and treated.As an organic-inorganic hybrid material,razor calm shell powder is widely used in the field of environmental remediation for its wide range of sources and low cost and availability.In this research,through the indoor incubation test,the aragonite shell powder was selected as the passivation agent to study the distribution and transformation of soil Cd in different concentrations of Cd pollution,exploring its repair mechanism,so as to achieve the recycling of waste,harmLess,reducing the use of the shell and provided an important basis for the exploration of more practical passivation agent for soil stabilization repair.The main results are as follows:(1)The addition of razor calm shell powder reduced the available Cd content of soil to varying degrees in all three contaminated soils.With the increase of the proportion of razor calm shell powder and the increase of the activation temperature of razor calm shell heat,the decreasing effect was obvious.It shows that the application of razor calm shell powder can indeed change the bioavailability of cadmium in soil and greatly reduce the content of available Cd in soil.For high-concentration Cd pollution,800 °C heat-activated razor calm shell powder treatment is better than the others,while for the medium-low pollution degree soil,all three can significantly reduce the effective Cd content in the soil,and the difference between the treatments is not significant,and the result may be related to the nature of the passivating agent,particle size,pH and other factors.However,considering the cost,it is best when the natural razor calm shell powder addition is 5%.(2)With the addition of razor calm shell powder,the exchangeable content increased first,then decreased,and then stabilized.In comparison,the 800℃ calcined razor shell powder(ES1~ES5)treatment had the most obvious effect on the exchangeable cadmium in middle contaminated soil.(3)The correlation analysis of soil pH and exchangeable cadmium content showed thatthere was a significant or extremely negative correlation between soil cadmium content and pH during the whole culture period,indicating that pH is a key factor affecting the migration and transformation of heavy metals.(4)After 60 days for adding the razor shell powder cultured,Cd chemical speciation occurred in the soil compared with the control group.The contents of exchangeable cadmium in all treatment groups were significantly reduced,and carbonate-bound Cd,Fe-Mn oxide-bound,residual cadmium content and organic-bound Cd were all increased to some extent.With the increase of the proportion of razor calm shell powder,Various formations of cadmium contents had gradually reduced or increased.However,the effects of different razor calm shell treatments on the cadmium content in different forms were different.The contribution rate of cadmium form from available state to potential or unusable state conversion is: 800℃ calcined razor shell powder> 600℃ calcined razor shell powdwe>natural razor calm shell powder.(5)when different razor calm shell powder were added to the soil,pH increased in defferent levels,and with the increase in the proportion of increase.There were differences among shell powder treatments,but the pH were all significantly higher than CK.The ES1~ES5 treatments showed a significant decrease trend,and compared with the initial period of culture,the pH decreased by 4~5 units after 60 days of culture.The rest of the treatments showed an increase and then decrease and finally stabilized with the culture time changing.The pH range was between 7 and 9. |
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