Abstract:
The solubilities of Np(Ⅳ) in deionized water and groundwater were measured by oversaturation method at 30℃ and 60℃ and pH around 8.20. Na
2S
2O
4 was added to keep the oxidation state of Np(Ⅳ) unchanged. The solubilities of Np(Ⅳ) in deionized water and groundwater are found to be (3.4±1.0)×10
-9 mol/L and (1.0±0.3)×10
-8 mol/L respectively at 30℃, and (1.9±0.6)×10
-8 mol/L and (3.7±0.5)×10
-8 mol/L at 60℃. The solubilities of Np(Ⅳ) in deionized water and groundwater increase as temperature increasing. The thermodynamic data at zero ionic strength were calculated at experiment condition by using the “Specific Ion Interaction Theory (SIT)”. The solubility-controlling solids in deionized water and groundwater are identified as Np(OH)
4(am) by thermodynamic calculation. The dominant aqueous species are deduced to be Np(OH)
4(aq) in deionized water, Np(OH)
4(aq) and Np(CO
3)
2(OH)
22- in groundwater.