A new method for determining Gibbs energies of formation of metal-carbonate solid solutions: 1. The Ca[sub x]Cd[sub 1-x]CO[sub 3](s) system at 298 K and 1 bar

Journal Article · Sat Oct 01 04:00:00 EDT 1994 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(94)90333-6· OSTI ID:6766513

Rock, P A; Walling, E M; Casey, W H; McBeath, M K ^[1]

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1. Univ. of California, Davis, CA (United States)

New thermodynamic data are presented for mixing of calcite (CaCO[sub 3](s)) and otavite (CdCO[sub 3](s)) to form Ca[sub x]Cd[sub 1-x]CO[sub 3](s) solutions. A reversible equilibrium was achieved between the aqueous solution and the metastable solid solution using electrochemical double cells and a new electrode of the third kind. Evidence that the cell reactions are reversible includes demonstration of Nernstian response to changes in electrolyte composition and an absence of significant hysteresis in cell current-voltage and current-temperature (10-35[degrees]C) plots. The authors observe negative excess Gibbs energies for mixing on the order of 0 to -6.6 kJ[center dot]mol[sup [minus]1]; these magnitudes are sensitive to uncertainties in the estimates of [Delta]G[sub f][degrees][CdCO[sub 3](s)]. The double-cell method is potentially useful in other systems where, through incorporation of impurities, the activity of the CaCO[sub 3](s) is not unity relative to the standard state of the pure, well-crystallized, endmember mineral. It remains to be seen whether the double cell method is equally useful for systems, such as the Ca[sub x]Mg[sub 1-x]CO[sub 3](s) or Ca[sub x]Sr[sub 1-x]CO[sub 3](s) solid solutions, that have variable and positive excess Gibbs energies, but some of the same advantages would apply.

• DOE Contract Number: FG03-92ER14307
• OSTI ID: 6766513
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 58:20; ISSN GCACAK; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
CADMIUM CARBONATES
CADMIUM COMPOUNDS
CALCITE
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHEMICAL REACTIONS
DISPERSIONS
ENERGY
FORMATION FREE ENTHALPY
FREE ENTHALPY
MINERALS
MIXTURES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SOLID SOLUTIONS
SOLUTIONS
THERMODYNAMIC PROPERTIES