(Solid + solute) phase equilibria in aqueous solution. XIII. Thermodynamic properties of hydrozincite and predominance diagrams for (Zn2++ H2O+ CO2) (original) (raw)
Related papers
The Journal of Chemical Thermodynamics, 2002
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 ± 0.10), f G o m {Cu 2 (OH) 2 CO 3 } = (−903.3 ± 1.2) kJ · mol −1 , f H o m {Cu 2 (OH) 2 CO 3 } = (−1067.1 ± 3.4) kJ · mol −1 , S o m {Cu 2 (OH) 2 CO 3 } = (166.3 ± 2.5) J · mol −1 · K −1 ; and azurite (T = 298.15 K): log K 0 ps0 (azu.) = (6.30 ± 0.10), f G o m {Cu 3
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2002
Synthetic malachite, hydrozincite and five monophasic mixed copper–zinc hydroxycarbonates have been studied by Fourier transform infrared (FTIR) spectroscopy at ambient and liquid nitrogen temperature in the region of 4000–400 cm−1. The analysis of the spectra reveals that the samples containing up to 20% zinc retain the malachite lattice, thus forming solid solutions. The inclusion of zinc ions in malachite reflects on the positions and intensity of the bands corresponding to the internal modes of the carbonate ion, to the OH librations and to the MeO interactions. For example, the higher and the lower frequency components of ν3 shift to higher and lower frequencies, respectively. The intensity of the bands corresponding to ν2 decreases with the zinc content increase. The spectrum of the sample Cu1.31Zn0.69(OH)2CO3 become diffuse and ill-resolved in the region of the MeO interactions (region below 600 cm−1) and the corresponding bands are shifted to lower frequencies due to the weaker ZnO interactions as compared with those of the copper ions. The internal modes of the carbonate ions in hydrozincite and aurichalcite are assigned and discussed taking into account the site symmetry and factor group symmetry. The OH and OD stretches (matrix-isolated HDO molecules) and the hydrogen bond strengths are interpreted in terms of MeO interactions (synergetic effect), hydrogen bond angles and different hydrogen bond acceptor strengths of the oxygen atoms from the carbonate ions. It proves that the hydrogen bonds in hydrozincite are stronger as compared with those in malachite, irrespective of both the larger hydrogen bond lengths and the weaker ZnO interactions in hydrozincite due to the higher hydrogen bond acceptor strength of the non-coordinated oxygen atom and the formation of bifurcated hydrogen bonds.
Critical assessment and thermodynamic modeling of the Cu–Fe–O system
Calphad, 2013
A self-consistent thermodynamic description of the Mg-Ca-Zn ternary system has been obtained in this work. Four ternary intermetallic compounds (IM1, IM2, IM3 and IM4) and binary compounds with extended ternary solubility have been included in the modeling. Binary compounds, CaZn 11 and CaZn 13 in the Ca-Zn system have been re-modeled by compound energy formalism (CEF) to accommodate recently reported ternary solubility ranges. Also Mg 2 Ca in the Mg-Ca system has been re-optimized. Among the ternary intermetallic compounds, IM1 and IM3 having complex solubility ranges have also been modeled using compound energy formalism, whereas IM2 and IM4 have been considered as stoichiometric phases. Modified quasi-chemical model (MQM) has been used to model the liquid phase in the system. To investigate the behavior of the system and to verify the consistency of the thermodynamic model with experimental results, key samples with 4 at% and 6 at% Ca concentration were prepared and characterized with differential scanning calorimeter (DSC). Various vertical sections, liquidus projection and isothermal section at 608 K, in the Mg-Ca-Zn system have been calculated and found to be in good agreement with the experimental data.
Journal of Alloys and Compounds, 2009
The thermal behaviour of individual and mixed solids, with different molar ratios, of basic copper carbonate and ammonium metavanadate was reported. The pure and mixed solids were thermally treated at 300, 500, 750 and 1000 • C. The thermal products at various calcination temperatures were characterized by means of thermal analyses (TG-DTG-DTA), X-ray diffraction (XRD) and electron spin resonance (ESR) techniques. The catalytic activity of all solids was measured using hydrogen peroxide decomposition at 30, 40 and 50 • C. The results revealed that pure basic copper carbonate decomposed to CuO at 300 • C and to Cu 2 O at temperature above 950 • C, where as pure ammonium vanadate decomposed to (NH 4) 2 V 6 O 16 and NH 4 V 4 O 10 as an intermediate compound at 250 and 350 • C before the formation of V 2 O 5 at 450 • C. CuO enhanced the formation of V 2 O 5 at 300 • C. A series of copper vanadate phases were detected, Cu 5 V 2 O 10 , Cu 2 V 2 O 7 and Cu 3 V 5 O 4 , for the mixtures 3Cu:1V, 1Cu:1V and 1Cu:3V preheated at 750 • C, respectively. These phases were formed as a result of solid-solid interactions between copper and vanadium oxides. The calcination temperature and the composition of the Cu-V mixtures affect the degree of crystallinity and pattern intensities of different phases detected at treatment temperatures ranged between 300 and 1000 • C. The catalytic activity of mixed CuO-V 2 O 5 was found to be greater than that of single oxides obtained at the same calcination temperatures. This might be attributed to increase in the concentration of active sites by creation of new ion pairs. No measurable catalytic activity was observed for all solids calcined at 750 and 1000 • C. This might be attributed to restriction of catalytically active constituents.
Phase equilibria of the MgO-Cu 2O-CuO system
Mater Res Bull, 1997
Phase equilibria of the MgG-C@-CuO system have been determined in air at temperatures ranging from 850 to 1100°C. The starting compositions ranged from 0 to 100% Mg in (Mgl,Cu,)O. CuO was quite soluble in MgO. The solubility of CuO in MgO at 85O"C was about 9% and at i050°C was about 20%. The only known ternary Guggenito phase had a composition of CuzMg03. The Guggenite phase exists in three forms, namely, Guggenite A (GA, orthorhombic, space group Pmmn(59)), Guggenite B (GB, orthorhombic, space group I(O)), and Guggenite X (Gx, monoclinic). Guggenite A was obtained as a single phase in air at xcuo = 67% (i.e., 67% CuO and 33% MgO) and 1OOO'C. It undergoes a phase transition to the Gdggenite X phase when it is heated above 1050°C. The Guggenite B phase was obtained in a mixture at XC"O = 75% and at temperatures above 1050°C. MgO was not found to be soluble in CuO. For samples with XC"O 2 67%, the Guggenite A phase coexisted with tenorite (CuO, monoclinic) at temperatures I 1000°C and above 1021°C, it was in equilibrium with cuprite (CUZO, cubic). For CuO compositions between 20% and 67%, a mixture of Guggenite A phase and the periclase phase (MgO, cubic) was obtained at temperatures I 1000°C. The decomposition of CuzMgOs (Guggenite A) phase was determined at several oxygen partial pressures and the Gibbs free energy of formation of this phase was also calculated. cop~risht Q 1997 Hsevier scren~e ~td
Geochimica et Cosmochimica Acta, 2014
The incorporation of cobalt in mixed metal carbonates is a possible route to the immobilisation of this toxic element in the environment. However, the thermodynamics of (Ca,Co)CO 3 solid solutions are still unclear due to conflicting data from experiment and from the observation of natural occurrences. We report here the results of a computer simulation study of the mixing of calcite (CaCO 3 ) and spherocobaltite (CoCO 3 ), using density functional theory calculations. Our simulations suggest that previously proposed thermodynamic models, based only on the observed range of compositions, significantly overestimate the solubility between the two solids and therefore underestimate the extension of the miscibility gap under ambient conditions. The enthalpy of mixing of the disordered solid solution is strongly positive and moderately asymmetric: calcium incorporation in spherocobaltite is more endothermic than cobalt incorporation in calcite. Ordering of the impurities in (0001) layers is energetically favourable with respect to the disordered solid solution at low temperatures and intermediate compositions, but the ordered phase is still unstable to demixing. We calculate the solvus and spinodal lines in the phase diagram using a sub-regular solution model, and conclude that many Ca 1Àx Co x CO 3 mineral solid solutions (with observed compositions of up to x = 0.027, and above x = 0.93) are metastable with respect to phase separation. We also calculate solid/ aqueous distribution coefficients to evaluate the effect of the strong non-ideality of mixing on the equilibrium with aqueous solution, showing that the thermodynamically-driven incorporation of cobalt in calcite (and of calcium in spherocobaltite) is always very low, regardless of the Co/Ca ratio of the aqueous environment.
Mineralogical Magazine, 2011
The relative stabilities of the copper/zinc solid solutions of hydroxyl sulphates, carbonates, nitrates, chlorides and bromides were studied by attempting their preparation using a variety of methods. All of the naturally occurring solid solutions except rosasite were obtained as single phases. Rosasite crystallized in a mixture with malachite and calcium carbonate during a room temperature preparation from calcium carbonate, copper nitrate and zinc nitrate. The solid solution with the antlerite stoichiometry [endmember Cu3SO4(OH)4] as well as the nitrates were not produced by the methods employed. All of the natural polymorphs of Cu2(OH)3Cl were obtained and a new method for the preparation of botallackite is reported. Botallackite was found to be stable in solution for over a year, contrary to previous reports. A bromine-bearing analogue of botallackite was prepared. Compounds were characterized by X-ray diffractometry, which was used to determine the unit-cell parameters, and by ...
Experimental determination of the phase equilibrium in the Mg–Cu–Ca ternary system at 350 °C
Journal of Alloys and Compounds, 2020
Hydroquinone (HQ) forms organic clathrates in the presence of various gas molecules in specific thermodynamic conditions. For some systems, clathrate phase equilibrium and occupancy data are very scarce or inexistent in literature to date. This work presents experimental results obtained for the CO 2 −HQ, CH 4 −HQ, and N 2 − HQ clathrates, in an extended range of temperature from about 288 to 354 K. Formation/dissociation pressures, and occupancies at the equilibrium clathrate forming conditions, were determined for these systems. Experiments showing the influence of the crystallization solvent, and the effect of the gas pressure on HQ solubility, were also presented and discussed. A good agreement is obtained between our experimental results and the already published experimental and modeling data. Our results show a clear dependency of the clathrate occupancy with temperature. The equilibrium curves obtained for CO 2 −HQ and CH 4 −HQ clathrates were found to be very close to each other. The results presented in this study, obtained in a relatively large temperature range, are new and important to the field of organic clathrates with potential impact on gas separation, energy storage, and transport.
Phase relations and thermodynamic properties of condensed phases in the system calcium-copper-oxygen
Chemistry of Materials, 1993
The isothermal sections of the phase diagram for the system Ca-Cu-0 at 1073 and 1223 K have been determined. Several compositions in the ternary system were quenched after equilibration, and the phases present were identified by optical microscopy, X-ray diffraction, and electron probe microanalysis. Two ternary compounds Ca2CuO3 and Cao.8&uO1.9s were identified at 1073 K. However, only Ca2CuO3 was found to be stable a t 1223 K. The thermodynamic properties of the two ternary compounds were determined using solid-state cells incorporating either an oxide or a fluoride solid electrolyte. The results for both types of cells were internally consistent. The compound C~O .~& U O~.~~, which can also be represented as Ca15Cu18035, has been identified in an earlier investigation as Cao.828CuOz. Using a novel variation of the galvanic cell technique, in which the emf of a cell incorporating a fluoride electrolyte is measured as a function of the oxygen potential of the gas phase in equilibrium with the condensed phase electrodes, it has been confirmed that the compound Cao.828CuO1.93 (Ca15Cu18035) does not have significant oxygen nonstoichiometry. Phase relations have been deduced from the thermodynamic data as a function of the partial pressure of oxygen for the system Ca-Cu-0 a t 873, 1073, and 1223 K.