Solid–solute phase equilibria in aqueous solution. XVI. Thermodynamic properties of malachite and azurite—predominance diagrams for the system Cu 2 + – H2 O– CO 2
✍ Scribed by Wolfgang Preis; Heinz Gamsjäger
- Publisher
- Elsevier Science
- Year
- 2002
- Tongue
- English
- Weight
- 267 KB
- Volume
- 34
- Category
- Article
- ISSN
- 0021-9614
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✦ Synopsis
The thermodynamic properties of the copper carbonates malachite, Cu 2 (OH) 2 CO 3 , and azurite, Cu 3 (OH) 2 (CO 3 ) 2 , have been obtained from solubility measurements as a function of temperature as well as ionic strength of aqueous perchlorate media. First, solubility constants have been determined from T = 288.15 K to T = 338.15 K at constant ionic strength, I = 1.00 mol • kg -1 NaClO 4 . Second, solubility experiments have been carried out from I = 1.00 mol • kg -1 to I = 3.00 mol • kg -1 NaClO 4 at constant temperature, T = 298.15 K. All experimental data have been evaluated by application of the optimization routine of ChemSage, yielding an internally consistent set of thermodynamic properties for malachite (T = 298.15 K): log K 0 ps0 (mal.) = (6.34 ± 0
; and azurite (T = 298.15 K): log K 0 ps0 (azu.) = (6.30 ± 0.10
• K -1 . Whereas these results confirm the literature data for the standard molar entropies, new values for the standard molar enthalpy of formation of malachite and azurite are recommended. Moreover, the phase relations in the ternary system Cu 2+ -H 2 O-CO 2 are discussed by the construction of twodimensional as well as three-dimensional predominance diagrams.