Heavy Metal Pollution Of Biofilm In The Uranium-rich Coal Mining Area And Environmental Dissolution Behavior Of Uranium Mineraks

This study first investigated the heavy metal pollution of biofilms in the rivers in the typical uranium-rich coal mining area,Yili,and special attention was paid to the spatial distribution of uranium pollution in the investigated area.Then,the environmental biofilm samples were studied for their uranium release behaviors under different water chemistry conditions.To specifically explore the dissolution performance,a micron-sized U₃O₈ particle?U₃O₈ microparticles,U₃O₈ MPs?was prepared in laboratory as model uranium mineral and then used in a series of leaching experiments.Finally,the interaction between U₃O₈ MPs and dissolved organic matter?DOM?in the aquatic environment was investigated via the fluorescence quenching tests.The results obtained are presented as follows:?1?Ag,Sb,W and Bi were found to be the most leading heavy metal pollutants in the biofilms of Yili area in contrast with other heavy metals,followed by Li,Ti,V,Cr,Fe,Rb,Sr,Ag,Cd,Sb,Ba,W,Tl,Pb,Bi and U.The heavy metal pollution with Ag and As in biofilms was more closely related to human activities.The Mn-and Sr-pollution in biofilms showed a very high correlation.Among all the studied rivers in the cities and counties of Yili area,Chabuchar County suffered the most severe heavy metal pollution in biofilms.?2?The uranium pollution in biofilms of Yili area mainly distributed in the central part of Chabuchar County.Generally,the uranium content in biofilms was higher near the coal mining area than in the non-coal mining area.?3?The carbonate ion(CO₃^2-)was found to promote the release of uranium from environmental biofilms.Laboratory-simulated dissolution experiments based on the environmental biofilm samples showed that the dissolved U in the solution reached87.55?g/L after 72 h's test at the initial carbonate concentration of 5 mmol/L;and the value reached 262.88?g/L after 72 h of dissolution at the initial carbonate concentration of 10 mmol/L.?4?pH is a key environmental factor affecting the dissolution of U₃O₈ MPs.Experimental results denote that about 63.64%and 15.69%of uranium was dissolved at very low pHs?such as pH2?and very high pHs?such as pH=12?,respectively.In the tested pH range,the lower the pH was,the higher the dissolution of U₃O₈ MPs was observed.?5?Under high pH conditions?i.e.pH=12?,CO₃^2-could promote the dissolution of uranium in U₃O₈ MPs,but the effect was weak due to the competition between OH^-and CO₃^2-.?6?Under low pH conditions?i.e.pH=2?,PO₄^3-could significantly inhibit the dissolution of U₃O₈ MPs.Uranium had a very strong affinity to PO₄^3-.About 53.95%of uranium was released at 0?mol/L of PO₄^3-in solution while the release decreased to around 44.97%,36.1%,34.1 and 30.38%at 10?mol/L 100?mol/L,230?mol/L and600?mol/L of PO₄^3-,respectively.?7?Three different types of DOM,fulvic acid?FA?,humic acid?HA?and DOM extracted from soils respectively,can inhibit the release of U from U₃O₈ MPs by adsorbing on the surface of U₃O₈ MPs.?8?According to the fluorescence quenching of FA,HA and DOM extracted from soils by U₃O₈ MPs,the studied DOM has limited binding sites for its complexation with U₃O₈ MPs.The binding capacity of FA with U₃O₈ MPs was slightly higher than that of HA.In the aquatic environment with complex DOM,the DOM competed for the complexation and adsorption with U₃O₈ MPs.