Uranium(VI) solubility in carbonate-free WIPP brine

Abstract

Abstract The solubility of uranium(VI) was determined in WIPP-relevant brines as a function of pCH+ and ionic strength, in the absence of carbonate. Carbonate concentration was below 2 × 105 M, measured using the gas chromatography method. In the absence of carbonate, the uranium(VI) solubilities were about  × 106 M in GWB at pCH+ ≥7 and about  × 108– × 107 M in ERDA-6 brine at pCH+ ≥8. Solubility of uranium(VI) was also measured in NaCl media at the same levels as in ERDA-6 brine. The data established a uranium solubility that was 10–100 times lower than published results from Diaz-Arocas and Grambow [13], and they are in good agreement with modeling results and other literature data [11,12]. In the absence of carbonate, hydrolysis was the main complexation and precipitation mechanisms for uranium(VI) solubility at high ionic strength and pC H+ ≥7. However, the effect of borate complexation was noticeable at pCH+ ∼8–9.