| A large amount of acid wastewater and waste residue is produced in the process of mining uranium,which contains toxic and harmful substances like large heavy metal and radionuclide etc. That can cause a serious pollution to the surrounding soil and groundwater.This article chose the surrounding paddy soil and red soil from a south uranium mine tailings reservoir as objects of study. The objectives of content of uranium(U) and soil organic matter(SOM) in the paddy soil and the correlation between them were approached both by field survey and lab analysis.We researched U adsorption properties befor and after the removal of SOM and the effect of initial pH, initial U concentration, temperature and adsorption time by static adsorption experiment, based on which, contribution of SOM in the process of the soil adsorbing U and the ionic U adsorption mechanism were studied. The main conclusions were as follows:(1)Lab analysis results showed that the order of SOM and U content in the study area was:the paddy soil > red soil, rhizosphere soil > surface soil; Both U and SOM content decreased with soil depth deepening in the range of soil depth of 0-100 cm;U content in soil increased with SOM content and decreased with the lower.(2)The correlation analysis between SOM content and U content have been studied. The results showed that the correlation coefficient of U and SOM reached 0.5-1.0, which had significant correlation, and the SOM and U content in the rhizosphere soil is in significant correlation at the 0.01 level, the rest of the other layers were significantly correlated at the0.05 level, which suggested that SOM could promote U adsorpting, and the adsorption capacity of SOM was proportional to its U content under natural conditions.(3)Static adsorption experiments results showed that U adsorption was of the most significant with the initial pH,and followed by time, The adsorption rate was reducing with the increase of the initial U concentration.but the temperature had no significant effect on theadsorption of U when it’s in the range of 5~35℃. Adsorption equilibrium was reached at25℃ and pH at 4-5 and the adsorption time reached 8h, on the time of which the adsorption capacity of paddy soil after removal of SOM decreased about 18%~19%, the red soil decreased about 13%~14%. The contribution of SOM to U adsorption was about 22%~23%and 15% for paddy soil and red soil,respectively. The contribution rate was consistent with the order of SOM content,which indicated that the higher the content of SOM, the stronger the adsorption capacity of U was. SOM had a strong complexation adsorption effect on U,which could effectively reduce the migration activity of U, and promote the adsorption of U.The order of these two soils on their adsorption capacity of U was paddy soil > Red Soil.(4)Adsorption mechanism analysis showed that, the basic structure of soil remained unchanged after adsorption.The main radical groups of SOM included C-O, C-N, C-H,-OH,N-H, which could work together with the radical groups of Si-O, C=O, C=C in soil to form a strong complex with2?2UO, and enhance the electrostatic adsorption of U on the soil; SOM could affect the soil particle size, and then affect its adsorption capacity; The isothermal adsorption curve types of the paddy soil and red soil before and after the removal of SOM were type II, the pore structures were parallel plate slit shaped opening pores having narrow pore size distributions that belonged to mesoporous materials.After removal of SOM, the specific surface, pore volume and pore size of paddy soil and red soil decreased, that resulted in the adsorption capacity decreasing, mainly due to the effect of SOM; Paddy soil and red soil’s adsorpting U process was dominated by surface adsorption of molecular monolayer,Accompanied by physical adsorption and chemical adsorption interaction and its adoption behavior more in line with the Langmuir isothermal adsorption equation and Pseudo-second-order model; This was an exothermic adsorption process which could be spontaneously occur at room temperature and adpting U mainly through ion exchange and precipitation,the former reaction contains mainly electrostatic adsorption and interparticle diffusion, and the latter includes oxidation reduction reaction,complexation reaction, and chelate reaction and so on. |
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