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Cobalt solubility at elevated temperatures in Co–CoO buffered solutions at fixed pH
Goldschmidt Conference Abstracts 2006
Characterising geochemical processes using the d34S and d18O of sulfate in groundwater D.M. KIRSTE1,2, P.
DE
Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME), Australia 2 Department of Earth and Marine Sciences, Australian National University, Australia (Dirk.Kirste@ anu.edu.au; SWelch@ ems.anu.edu.au) 3 Geoscience, Australia ([email protected])
Introduction Developing predictive numerical models of hydrogeochemical systems requires an understanding of the physical and chemical processes affecting the composition of the water. Physical processes like mixing and evaporation can be reasonably well defined using the chemical data, but redox sensitive chemical processes are more difficult to quantify. Applying the isotope chemistry of dissolved sulfate to characterise and even quantify these redox processes enhances the capabilities of numerical modelling, in particular those associated with acid mine drainage, acid sulfate soils and sulfide mineral exploration. This work describes how the stable isotopes of sulfur and oxygen in sulfate can be used to characterise geochemical processes and thereby improve reactive transport models.
Discussion Groundwater, pore water and surface water from a number of areas in Australia have been used to determine the sources of sulfur in acid sulfate susceptible systems. Sulfate reduction, and sulfide oxidation commonly dominate the chemical processes controlling sulfur in a groundwater system. Bacterial sulfate reduction (BSR) can be recognised by the effect on the d34S and d18O of sulfate. Both ratios increase as the lighter isotope is removed through dissimilatory bacterial reduction. Oxidation of sulfides occurs through two processes, one involving molecular oxygen (O2) and the other involving oxidised iron (Fe3+). The different pathways result in considerable differences in the oxygen isotopic composition of the produced sulfate. Surface water and some groundwater from the Loveday basin in SA show evidence of evaporation and BSR, while the near surface pore waters, although similarly evaporated, contain sulfate that predominantly originates from sulfide oxidation. Sulfate in groundwater from several other regions has isotopic compositions that indicate sulfide oxidation involving either the O2 or the Fe3+ pathways. The implications are that the sulfate history can be understood through isotopic analysis and that this can be used in geochemical models to trace chemical processes. doi:10.1016/j.gca.2006.06.648
Cobalt solubility at elevated temperatures in Co–CoO buffered solutions at fixed pH
CARITAT1,3, S. WELCH1,2
1
A321
S.A. KISSIN1, C. NORMAND2, S.A. WOOD2 1
Department of Geology, Lakehead University, Canada ([email protected]) 2 Department of Geology, University of Idaho, USA (charlesn@ uidaho.edu; [email protected]) Although abundant data on the solubility of cobalt at 25 °C are available (Baes and Mesmer, 1976), there is little experimental data on cobalt solubility at higher temperatures. Hydrothermal cobalt arsenide minerals are abundant in Ni–Co arsenide-native Ag (five-element) deposits and occur as minor constituents of unconformity-type uranium and sandstone-type uranium deposits. Cobalt sulfide minerals are abundant in some stratiform copper deposits and occur as minor minerals in some Mississippi Valley-type Pb–Zn deposits. A series of experiments was carried out using a large-capacity autoclave with a sampling system such that reaction progress could be monitored. The reaction was buffered by Co(metal) + CoO, and pH was fixed at the start of the run at 4.75 by use of the acetate buffer system. Runs were made at 50 °C intervals from 100 to 300 °C. Cobalt solubility at 100 °C in 0.02 M acetate buffer was found to agree with previous work (Dinov et al., 1993). It was found, however, that increasing acetate concentration to 0.05 M significantly increased solubility at 100 and 150 °C, apparently as the result of acetate complex formation. Runs at higher temperatures apparently did reach equilibrium; however, a trend of increased solubility with increasing temperature was observed.
References Baes, C.F., Mesmer, R.E., 1976. The Hydrolysis of Cations. Wiley, New York. Dinov, K., Matsuura, C., Hiroishi, D., Ishigure, K., 1993. Nucl. Sci. Eng. 113, 207–216. doi:10.1016/j.gca.2006.06.649
Characterising geochemical processes using the d34S and d18O of sulfate in groundwater D.M. KIRSTE1,2, P.
DE
Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME), Australia 2 Department of Earth and Marine Sciences, Australian National University, Australia (Dirk.Kirste@ anu.edu.au; SWelch@ ems.anu.edu.au) 3 Geoscience, Australia ([email protected])
Introduction Developing predictive numerical models of hydrogeochemical systems requires an understanding of the physical and chemical processes affecting the composition of the water. Physical processes like mixing and evaporation can be reasonably well defined using the chemical data, but redox sensitive chemical processes are more difficult to quantify. Applying the isotope chemistry of dissolved sulfate to characterise and even quantify these redox processes enhances the capabilities of numerical modelling, in particular those associated with acid mine drainage, acid sulfate soils and sulfide mineral exploration. This work describes how the stable isotopes of sulfur and oxygen in sulfate can be used to characterise geochemical processes and thereby improve reactive transport models.
Discussion Groundwater, pore water and surface water from a number of areas in Australia have been used to determine the sources of sulfur in acid sulfate susceptible systems. Sulfate reduction, and sulfide oxidation commonly dominate the chemical processes controlling sulfur in a groundwater system. Bacterial sulfate reduction (BSR) can be recognised by the effect on the d34S and d18O of sulfate. Both ratios increase as the lighter isotope is removed through dissimilatory bacterial reduction. Oxidation of sulfides occurs through two processes, one involving molecular oxygen (O2) and the other involving oxidised iron (Fe3+). The different pathways result in considerable differences in the oxygen isotopic composition of the produced sulfate. Surface water and some groundwater from the Loveday basin in SA show evidence of evaporation and BSR, while the near surface pore waters, although similarly evaporated, contain sulfate that predominantly originates from sulfide oxidation. Sulfate in groundwater from several other regions has isotopic compositions that indicate sulfide oxidation involving either the O2 or the Fe3+ pathways. The implications are that the sulfate history can be understood through isotopic analysis and that this can be used in geochemical models to trace chemical processes. doi:10.1016/j.gca.2006.06.648
Cobalt solubility at elevated temperatures in Co–CoO buffered solutions at fixed pH
CARITAT1,3, S. WELCH1,2
1
A321
S.A. KISSIN1, C. NORMAND2, S.A. WOOD2 1
Department of Geology, Lakehead University, Canada ([email protected]) 2 Department of Geology, University of Idaho, USA (charlesn@ uidaho.edu; [email protected]) Although abundant data on the solubility of cobalt at 25 °C are available (Baes and Mesmer, 1976), there is little experimental data on cobalt solubility at higher temperatures. Hydrothermal cobalt arsenide minerals are abundant in Ni–Co arsenide-native Ag (five-element) deposits and occur as minor constituents of unconformity-type uranium and sandstone-type uranium deposits. Cobalt sulfide minerals are abundant in some stratiform copper deposits and occur as minor minerals in some Mississippi Valley-type Pb–Zn deposits. A series of experiments was carried out using a large-capacity autoclave with a sampling system such that reaction progress could be monitored. The reaction was buffered by Co(metal) + CoO, and pH was fixed at the start of the run at 4.75 by use of the acetate buffer system. Runs were made at 50 °C intervals from 100 to 300 °C. Cobalt solubility at 100 °C in 0.02 M acetate buffer was found to agree with previous work (Dinov et al., 1993). It was found, however, that increasing acetate concentration to 0.05 M significantly increased solubility at 100 and 150 °C, apparently as the result of acetate complex formation. Runs at higher temperatures apparently did reach equilibrium; however, a trend of increased solubility with increasing temperature was observed.
References Baes, C.F., Mesmer, R.E., 1976. The Hydrolysis of Cations. Wiley, New York. Dinov, K., Matsuura, C., Hiroishi, D., Ishigure, K., 1993. Nucl. Sci. Eng. 113, 207–216. doi:10.1016/j.gca.2006.06.649