Determination of Aqueous Mickel-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 NaClO_4 background electrolyte. The Ni-oxalate data were interpreted in terms of a single Niox(aq) complex having log K_1 values for Ni~(2+) + ox~(2+) (mutually impiles) 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 deg C. Specific ion-interaction theory (SIT) was used to obtain log K_1 deg = 5.17 +- 0.05 (95% confidence level and DELTA_(omega) = -0.23 +- 0.15) at I.S. = 0. The Ni-carbonate studies were carried out an p[H] values of 7.5, 8.5 and 9.6 in 0.5 Mol-L~(-1) NaClO_4/NaHCO_3 solutions. The NiCO_2(aq) species was the dominant complex in the [CO_3~(2-)] concentation ranges studied at all three p[H] values. A log K_1 = value for Ni~(2+) + CO_3~(2+) (mutually impiles) NiCO_3(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 deg = 4.2 +- 0.3 (95% confidence level and DELTA_(omega) = -0.26 +- 0.04). The data allowed upper bound values for the complexation constants for NiHCO_3~+ and Ni(CO_3)_2~(2-) to be estimated. i.e., log K deg < 1.4 for Ni~(2+) + HCO_3~- (mutually impiles) NiHCO_3~+, and log K_2 deg < 2 for NiCO_3(aq) + CO_3~(2-) (mutually impiles) Ni(CO_3)_2~(2-), respectively.