Am在两种不同地下水中的种态分布及溶解度分析

利用自主编写的地球化学计算软件CHEMSPEC分析了Am在北山地下水和我国西南某地下水中的种态分布,并计算了Am在这两种地下水中的溶解度,考察了pH、Eh、不同离子以及硅的存在等对种态分布的影响。结果表明,Am在这两种地下水中均以正三价存在,随pH值的不同Am的种态会发生较大的变化,在偏酸性条件下,主要以AmSO+4、Am(SO4)-2及Am3+的形式存在,在中性至弱碱性条件下,以AmCO+3的形式存在,强碱性条件下,则基本转化为Am(OH)3;当北山地下水中有Si存在时,在pH=6.5~9.7范围内,Am的主要种态为AmSiO(OH)2+3;不同离子的浓度变化对Am的种态分布会产生一定影响,其影响顺序为HCO-3F-SO2-4Cl-。pH和HCO-3对Am溶解度的影响较大,随着地下水pH的升高,Am的溶解度逐渐减小。Am在两种地下水中的溶解度分别为2.01×10-7 mol/L(北山地下水pH=7.56、Eh=164mV)、1.60×10-7 mol/L(西南地下水pH=7.50、Eh=0mV)。

Prediction of the Species and Solubility of Am in Two Different Groundwaters

The speciation and solubility of americium in Beishan groundwater and Southwest China groundwater were calculated using a newly developed geochemical model CHEMSPEC by Peking University. Influences of pH, Eh, different ions and presence of Si on the speciation were investigated. The results indicate that americium exists as trivalent Am(Ⅲ) in the two different groundwaters and the species significantly changes with pH values. Under acidic conditions, americium mainly exists as AmSO⁺₄, Am(SO₄)^-₂ and Am³⁺. While in neutral or weak alkaline conditions, the main species is AmCO⁺₃. When the solution is in strong alkaline condition, most of americium exists as Am(OH)₃. When Si is present in the Beishan groundwater, the main species is AmSiO(OH)²⁺₃ in the pH range of 6.5-9.7. The concentration of different ions also have an influence on the speciation distribution of americium, and in the order of HCO^-₃>F^->SO^2-₄>Cl^-. The solubility of americium is greatly affected by pH and HCO^-₃ concentration. When pH value increases, the solubility of americium decreases. The solubility of americium in Beishan groundwater (pH=7.56, Eh=164 mV) and Southwest China groundwater (pH=7.50, Eh=0 mV) are 2.01×10^-7 mol/L and 1.60×10^-7 mol/L, respectively.