Terri L. Woods

Use of oxidized copper minerals as environmental indicators

Abstract The distribution of the basic copper salts malachite (Cu 2 (OH) 2 CO 3 ), brochantite (Cu 4 (OH) 6 SO 4 ), and paratacamite (Cu 4 (OH) 6 Cl 2 ) is determined by the chemical composition of the waters in which copper is found. A previous study of these minerals indicated that they respond rapidly to changes of solutions from one field of stability to another and that conversions of these phases from one to the other leaves an indication (in the form of remnant low magnification textures) of the previous stable phase that permits evaluation of changing environmental conditions. Comparison of the theoretical distribution of these phases (using activity-activity diagrams) with their observed occurrences reveals good agreement between predicted and actual assemblages. Malachite is predicted to be the stable phase in equilibrium with most surface and ground waters including seawater, and such is observed to be the case. Brochantite and paratacamite are observed more frequently than malachite as corrosion products of copper exposed to atmospheric precipitation and the diagrams predict that these copper salts will often supersede malachite as the stable phase in this environment.

CALCULATED AQUEOUS-SOLUTION-SOLID-SOLUTION RELATIONS IN THE LOW-TEMPERATURE SYSTEM CAO-MGO-FEO-CO2-H2O

Abstract A method of estimating an aqueous-solution composition from that of solid-solutions believed to be in equilibrium with it is derived. The low-temperature ternary Ca-Fe-Mg phase relations of the rhombohedral carbonates are investigated using this method, and their phase diagrams at 25 and 150°C are calculated. Algebraic manipulations of equilibrium constant equations representing dissolution of the carbonates yield equations for the phase boundaries separating calcite from an ankerite-dolomite solid-solution and an ankerite-dolomite solid-solution from a siderite-magnesite solid-solution. A value for the free energy of formation of ankerite is estimated (−1818.0 ± 0.8 kJ/mol, 25°C) from compositions of natural coexisting carbonates. Necessary compositional information for the carbonates was derived from the relatively unmetamorphosed Early Proterozoic Marra Mamba Banded Iron-Formation of the Hamersley Basin of Western Australia. The method yielded information on the a Fe 2+ a ca 2+ and a Mg 2+ a ca 2+ ratios of the solutions that deposited the carbonates of the Marra Mamba. The method suggests a depositing solution for the carbonates of the Lower Marra Mamba Iron-Formation significantly richer in iron than was likely to have been the case for Early Proterozoic seawater.

Adherence of sulfide mineral layers produced by corrosion of copper alloys

Abstract Sulfiding corrosion of copper alloys can occur from microbiologically induced corrosion (MIC) mechanisms involving sulfate reducing bacteria (SRB) or from exposure to bulk waters containin...