Thermodynamic analysis of solubility data on gaspeite

Solubility measurements are especially valuable for the determination of an internally consistent set of thermodynamic data for nickel carbonates. Other methods turned out to be less convenient. Thus the calorimetric determination of the dissolution enthalpy according to Reaction (V.106) is bound to be inaccurate, because the result depends to a high extent on the state of carbon dioxide. It is well known that keeping CO2 quantitatively either in solution or in the gas phase is quite difficult. 

Another method to determine thermodynamic data of nickel carbonate consists in the investigation of the decomposition equilibrium (V.107). Tareen et al. [91TAR/FAZ] determined the standard molar quantities of formation of gaspeite, NiC03(cr) from hydrothermal T, p decomposition data of this reaction, but probably overestimated the precision achieved AjG°= - (628.36 1.24) kJ-mol (-(632.3 6.0) kJ mol ), = - (703.38 + 1.24) kJ-mol (- (709.2 + 6.0) kJ-mol ). 

The numerical values in brackets have been found when the experimental results of [91TAR/FAZ] were re-evaluated according to the present state of the art, see Appendix A. 

The solubility data of synthetic NiC03 were thermodynamically analysed to obtain the respective standard molar quantities of formation AjG and A,// . An analogous set of equations was used as described in Section V.3.2.2.3 (Equations (V.41) - (V.44)). Solubility constants were extrapolated to infinite dilution using the Specific Ion-interaction Theory [97GRE/PLY2]. All calculations were based on auxiliary quantities which were either recommended by CODATA (see NEA TDB auxiliary data set) or recently critically evaluated (see Section V.2.1). 

The following set of reliable thermodynamic quantities has been derived [82GAM/REI], [98GAM/KON], [2002WAL/PRE]  

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