PRELIMINARY RESULTS UPON CRYSTALLIZATION OF THE CALCITE-SPHEROCOBALTITE SOLID SOLUTION

Abstract

The (Ca,Co)C03-H20 system was studied at 25 °C using both precipitation experiments and crystallization in silica gel in order to examine the thermodynamic properties and crystallization of the solid solution. Near the CaC03 endmember, unit cell parameters and volume of the solid phase show an almost linear variation, while near the C0CO3 endmember, the growth of a phase of low crystallinity prevented those calculations. A detailed Fourier Transform Infrared Spectroscopy (FTIR) assigned this phase to a cobalt carbonate hydrate (CoCO}nH20). The fact that cell volumes are plotted above the line that corresponds to the theoretical cell volumes of the two endmembers, indicates positive value of excess volume of mixing (VE), and consequently a non-ideal solid solution. Nucleation under conditions of high supersaturation in gels showed that in all the cases the degree of cobalt incorporation in crystals was low with an average value of cobalt mole fraction (XC0CO3) around 0.03 while -even in the Co-rich zones- this value never exceeded the upper limit of 0.2. Crystal morphologies also exhibited a wide variety of forms as a function of aqueous phase composition.