某铀尾矿库下游地下水中U形态特征研究

以某铀尾矿库下游地下水为研究对象,分析该地下水水化学成分的基础上,采用PHREEQC软件模拟在不同pH值、pe值条件下U赋存形式及饱和指数(SI)间的变化关系。结果表明:研究区地下水中U主要以UO_2(CO_3)_3~(4-)、UO_2(CO_3)_2~(2-)、UO_2CO_3、(UO_2)_2CO_3(OH)_3~-、UO_2(OH)_2、UO_2(OH)_3~-等形态存在,其中UO_2(CO_3)_3~(4-)所占比例最大,平均高达87.64%。pH值是影响铀存在形态的重要因素,UO_2CO_3在pH=5时含量最高,在pH>5后,UO_2CO_3、UO_2SO_4和UO_2~(2+)含量逐渐下降;UO_2(CO_3)_2~(2-)在pH=6时达到峰值后随pH值增加而递减,在pH>6后具有高络合常数的UO_2(CO_3)_3~(4-)占绝对优势。随着pe值的增加,U~(6+)摩尔浓度不变,而U~(4+)浓度增加。SI结果显示,在该研究区水文地球化学背景下,随着pH值、pe值的改变,地下水中的UO_2SO_4、UO_2CO_3、UO_2(OH)_2均处于溶解状态。

Morphological Characteristics and Health Risk Assessment of Heavy Metals and Radionuclides in Groundwater of a Uranium Tailings Reservoir

Based on the analysis of chemical composition of uranium tailings, the PHREEQC software is used to simulate the relationship between the uranium forms and the saturation index (SI) under different pH and pe values. Results showed that UO2(CO3)4- 3,UO2(CO3)2- 2,UO2CO3,(UO2)2CO3(OH)- 3,UO2(OH)2 and UO2(OH)- 3 were main existence forms of uranium of groundwater in the study area, and UO2(CO3)4- 3 accounts for the largest proportion, with an average as high as 87.64%. The pH value is an important factor affecting the existence of uranium. UO2CO3 has the highest content at pH=5. UO2CO3,UO2SO4 and UO2+ 2contents gradually decreased after pH>5. UO2(CO3)2- 2 decreases with increasing pH value after reaching the peak value at pH=6, and UO2(CO3)4- 3with high complexation constant was dominant after pH>6. With the increase of pe, the concentration of U6+ remains unchanged, while U4+ increases. SI results show that under the hydrogeo chemical background of this research area, UO2SO4, UO2CO3 and UO2(OH) 2 in groundwater are dissolved with the change of pH and pe values.