Experimental study of nickel solubility in sulfidic groundwater under anoxic conditions

This paper presents the results from an experimental study of the nickel solubility in sulfidic groundwater under anoxic conditions. The waters used were natural groundwater from Olkiluoto and synthetic saline groundwater, to which sulfide had been added. Two sulfide concentrations, 3.1 (.) 10(-6) M and 9.4 (.) 10(-5) M, were used. The possible influence of ferrous iron on the nickel concentration was also studied by adding small amounts of iron chloride, which yielded ferrous iron concentrations of 1.8(.)10-5 M or less. The initial nickel concentrations in the water samples were 1.0(.)10(6) M and 1.0(.)10(-3) M. The nickel concentrations were determined using Ni-63 and liquid scintillation counting. The duration of the experiments was 177 days. The results for the waters differed markedly. The nickel concentration in the natural groundwater decreased in all samples to roughly 10% of the initial value. The nickel concentration in the synthetic groundwater was found to decrease in those samples having initial sulfide and nickel concentrations of 9.4(.)10(-6) M and 1.0(.)10(-6) M, respectively. The nickel concentration was in this case reduced to about 1% of its initial value. For the other synthetic groundwater samples, the nickel concentration remained at its original initial level. The variation of the ferrous iron concentration did not have any observable effect on the measured nickel concentrations.