Thermodynamic properties of copper carbonates ? malachite Cu2(OH)2CO3 and azurite Cu3(OH)2(CO3)2

Abstract

Abstract. The thermodynamic properties of the copper carbonates malachite and azurite have been studied by adiabatic calorimetry, by heat-flux Calvet Calorimetry, by differential thermal analysis (DTA) and by thermogravimetric (TGA) analysis. The heat capacities, C o of natural malachite and azurite have been measured between 3.8 and 300 K by low-temperature adiabatic calorimetry. The heat capacity of azurite exhibits anomalous behavior at low temperatures. At 298.15 K the molar 8298.15 heat capacities C ~ and the third law entropies o are 228.5 _+ 1.4 and 254.4 _+ 3.8 J mol-1 K-1 for azurite and 154.3+0.93 and 166.3• K -1 for malachite. Enthalpies of solution at 973 K in lead borate (2PbO'BzO3) have been measured for heat treated malachite and azurite. The enthalpies of decomposition are 105.1 +__ 5.8 for azurite and 66.1 +_ 5.0 kJ tool-1 for malachite. The enthalpies of formation from oxides of azurite and malachite determined by oxide melt solution calorimetry, are -84.7 + 7.4 and -52.5 __+ 5.9 kJ mol-1, respectively. On the basis of the thermodynamic data obtained, phase relations of azurite and malachite in the system Cu 2 + -HzO-CO2 at 25 and 75 ~ have been studied.

The molar heat capacity of hydrous copper chloride: atacamite Cu2Cl(OH)3

“…In the temperature range (4 to 10.5) K we observed a small anomaly in the heat capacity of atacamite with a maximum at T = 8.6 K. A similar phenomenon was found for a synthetic sample at temperatures below 8 K by Kawaji et al (17) Recent studies (22) of the magnetic susceptibility of synthetic atacamite revealed the existence of a relaxation phenomenon below T = 8 K identical to that in spin glasses. We discovered anomalies in the heat capacities of other Cu-minerals such as azurite, (1) broshantite, (3) and dioptase. (4) We assumed these anomalies were connected with antiferromagnetic ordering of the magnetic moments of Cu 2 + ions as the temperature decreased.…”

“…Thermodynamic modelling allows one to determine the optimum parameters of oxidized mineral sulfurization in technical hydrothermal conditions and to establish the quantitative equilibrium composition of solid, liquid, and gaseous components of the system. We have performed thermodynamic modelling of the equilibrium composition in the hydrothermal systems of (oxidized copper mineral + sulfur + water) for Udocan copper deposits (1,2) on the basis of new thermodynamic data obtained by us earlier.…”

“…This work was preceded by our experimental investigations of thermodynamic properties of copper minerals of oxidized ore deposits including malachite, (1) azurite, (1) chrysocolla, (3) broshantite, (4) and dioptase. (5) We chose natural minerals with compositions closest to the theoretical ones for the investigation.…”

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

“…Richardson and Brown (16) determined the standard enthalpy of formation of malachite by employing solution calorimetry in hydrochloric acid at T = 298.15 K. Kiseleva et al (17) obtained the standard enthalpies of formation of malachite and azurite from decomposition experiments in a drop calorimeter at T = 973 K. In addition, the standard entropies, S o m , of these minerals were derived from low-temperature measurements of the heat capacity by Kiseleva et al (17) Robie and Hemingway (18) (15) as well as Kiseleva et al (17) entered the thermodynamic database of Robie and Hemingway. (18) Using this data set, (18) the partial pressure of carbon dioxide for the equilibrium between malachite and tenorite (CuO) in an aqueous medium is predicted to be 0.32 MPa at T = 323.15 K. Applying the thermodynamic quantities given by Kiseleva et al (17) results in p(CO 2 ) = 5.20 MPa at T = 323.15 K. However, it will be shown in this work that tenorite can be transformed into pure malachite at p(CO 2 ) = 0.084 MPa and T = 323.15 K, which clearly disproves the prediction using the values listed in references 17 and 18. As the thermodynamic data for CuO are consistent with the JANAF tables (19) and are regarded to be fairly reliable, some of the literature values for the thermodynamic quantities of copper carbonates must be wrong.…”

Structural Alterations in Mechanically Activated Malachite

“…Frost et al studied thermal decomposition of malachite and azurite by means of thermal, mass spectrometric, and infrared emission analyses and concluded that decomposition phenomenon occurred in six overlapping stages that dier in temperature [1]. Thermodynamic properties of copper carbonates were studied by Kiseleva et al [9] and thermogravimetry of mechanically activated malachite and physical mixture of malachite and calcite were studied by Wieczorek-Ciurowa et al [10] to illuminate the mechanism for further process. Nowadays malachite have been although still used for production of copper, in ancient time it was used as pigments in manuscripts, glasses and glaze [1].…”