Risk Assessment Of Heavy Metals In Sediments Of Xijiang River Basin And Study On Adsorption Capacity Of Soil To Arsenic And Cd

Heavy metal is one of the important pollutants in river sediment and agricultural soil,and the problem of heavy metal pollution is becoming more and more serious.The sources of heavy metals include human factors and natural factors.In this paper,the environmental behavior of soil and sediment in geological high background area is studied.The adsorption capacity of heavy metals As,Cd)in Yubu Village in Xijiang River basin under high geological background was studied,and the morphology and infrared analysis of soil samples before and after heavy metals adsorption were carried out.Taking the sediments in Xijiang River basin As the research object,the physical and chemical properties,heavy metal content and morphology of the sediments were analyzed.The risk assessment method was used to assess the Cd,As and Pb in the sediments,and the results were As follows:1)The p H of sediments in Xijiang River basin was basically weakly alkaline7.04≤p H≤8.59),and the p H of S9 sampling point was weakly acidic p H=6.02).The average content of organic matter was 1.98%,and the content of carbonate was about7.55%.The spatial distribution of the total amount of heavy metals As,Cd,Pb)in the sediments of Xijiang River basin indicates that the pollution of heavy metals in Diao River basin is particularly serious.Using BCR method to extract the morphology of heavy metals,it was found that Pb and As mainly existed in the form of F4 residual state)in the xijiang River basin,accounting for 47.04%and 39.94%of the total,respectively.Heavy metals Cd existed in the form of F1 exchangeable state/carbonate state),accounting for 44.81%of the total.2)The risk assessment results of enrichment factor index EF),geo-accumulation index I_geo),ecological risk index RI,E_rⁱ)and improved risk index MRI)all indicate that the Diao River Basin is at a high level of ecological risk.Spearman correlation analysis,principal component analysis PCA)and redundancy analysis RDA)were similar to physical and chemical properties of heavy metals Cd,Pb and As in sediments.This indicates that Cd and As in this area are mainly from mining industry,and Pb may be partly affected by other factors.3)The p H of the soil was 7.42,the organic matter content was about 4.10%,and the carbonate content was about 7.17%.Soil organic matter plays a positive role in adsorption of As and Cd.The smaller the soil particle size,the stronger the adsorption capacity.The adsorption effect of soil on Cd increases with the increase of p H,while the adsorption effect of As does decrease with the increase of p H.When p H increases from3 to 9,the adsorption amount of Cd increases by 182.7 mg/Kg,while the adsorption amount of As decreases by 165.7 mg/Kg.The solid-liquid ratio of adsorption As was1:25;g:m L),the solid-liquid ratio of adsorption Cd was 0.8:25;g:m L).After adding organic acids for 24 h,the heavy metal content in the solution was analyzed respectively,and it was found that the adsorption capacity of the samples with CH₃COONa was significantly lower than that with Na₃C₂O₄and C₆H₅Na₃O₇,indicating that CH₃COONa had a greater inhibition effect on adsorption.4)The Langmuir equation and Freundlich equation were used to fit the adsorption isotherms of As and Cd,and the results showed that the Langmuir model had better fitting results.The As and CdΔG<0 adsorption reaction can occur spontaneously,ΔH>0indicates that the soil heavy metal adsorption reaction is endothermic reaction.Quasi-first-order and quasi-second-order fitting of dynamic data show that As and Cd all conform to quasi-second-order dynamic model.5)BCR method was used for morphological extraction of heavy metals from soil.The As and Cd in soil samples in front of the adsorption mainly exists in the form of the F4 residue),and the adsorption of heavy metals As in the soil mainly in F1exchangeable/carbonate combined with state)and F2 iron manganese oxide combined with state)form,while the heavy metal Cd to F1 exchangeable/carbonate combined with state)and F3 organic matter and sulphide combination state)in the form of.Fourier Transform Infrared Spectroscopy was used to detect the soil before and after adsorption of heavy metals,and significant changes were found,indicating that heavy metals interact with functional groups in the soil.