镎在北山地下水中的溶解行为分析

237 Np是高放废物地质处置库安全评价中的关键核素之一,其环境化学行为受到人们的重视。本工作利用化学种态分析软件CHEMSPEC计算了Np在北山地下水中的溶解度,并研究了氧化还原电位Eh值、pH值、总碳酸根离子浓度等对溶解度的影响。结果表明,Np的溶解度范围为8.19×10-8~3.29×10-3 mol/L。Eh值对溶解度的影响最为显著。当Eh=0.089V或更小时,Np的沉淀为NpO2,溶解度较小;当Eh=0.346V或更大时,Np的沉淀为NaNpO2CO3或NpO2OH,溶解度较大。Np的溶解度随pH值的变化趋势与其沉淀形式密切相关。当pH=7.25时,对于NpO2和NpO2OH沉淀,增加总碳酸根离子浓度使得Np的溶解度增加;对于NaNpO2CO3沉淀,增加总碳酸根离子的浓度会使Np的溶解度降低。

Solubility Analysis of Neptunium in Beishan Groundwater

²³⁷Np is one of the key radionuclides for the safety assessment of high-level radioactive waste repository. The environmental chemistry of neptunium is concerned. In this work, the solubility of neptunium in Beishan groundwater was analyzed by CHEMSPEC. The influences of redox potential Eh, pH, and the total carbonate concentration on solubility were investigated. The results indicate that the solubility range of neptunium in Beishan groundwater is 8.19×10^-8-3.29×10^-3 mol/L. Neptunium would precipitate in the form of NpO₂ and the solubility would be lower in reducing environment. The precipitation would change to be NaNpO₂CO₃ or NpO₂OH in oxidation environment and the solubility would be higher. The influence of pH on solubility depends on the speciation of precipitation. For NpO₂ and NpO₂OH, the solubility would increase with the total carbonate concentration at pH=7.25. For NaNpO₂CO₃, the solubility of neptunium would decrease with the increase of the total carbonate concentration at pH=7.25.