Determination of Aqueous Nickel-Carbonate and Nickel-Oxalate Complexation Constants

摘要

An ion-exchange method was used to determine complexation constants for the Ni-oxalate and Ni-carbonate systems in a NaClO4 background electrolyte. The Ni-oxalate data were interpreted in terms of a single Niox(aq) complex having log K 1 values for Ni2+ + ox2− ⇔ Niox(aq) of 3.9 ± 0.1 (I.S. = 0.5 mol-L−1 p[H] = 7.1) and 4.4 ± 0.1 (I.S. = 0.1 mol-L−1 p[H] = 8.6) at 22 ± 1○C. Specific ion-interaction theory (SIT) was used to obtain log K 1 ○ = 5.17 ± 0.05 (95% confidence level and Δ ε = −0.23 ± 0.15) at I.S. = 0. The Ni-carbonate studies were carried out at p[H] values of 7.5, 8.5, and 9.6 in 0.5 mol-L−1 NaClO4/NaHCO3 solutions. The NiCO3(aq) species was the dominant complex in the [CO3 2−] concentration ranges studied at all three p[H] values. A log K 1 value for Ni2+ + CO3 2− ⇔ NiCO3(aq) of 2.9 ± 0.3 was deduced at I.S. = 0.5 mol-L−1. Extrapolating this value to zero ionic strength using the SIT approach yielded log K 1 ○ = 4.2 ± 0.3 (95% confidence level and Δε = −0.26 ± 0.04). The data allowed upper bound values for the complexation constants for NiHCO3 + and Ni(CO3)2 2− to be estimated, i.e., log K ○ < 1.4 for Ni2+ + HCO3 − ⇔ NiHCO3 +, and log K 2 ○ < 2 for NiCO3(aq) + CO3 2− ⇔ Ni(CO3)2 2−, respectively.