Mathematics – Logic
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59..851m&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 59, Issue 5, pp.851-866
Mathematics
Logic
7
Scientific paper
Tellurium occurs in trace amounts in a wide range of geological environments, the most important of which are epithermal ore deposits that contain precious- and base-metal telluride minerals. The behaviour of Te in hydrothermal fluids is poorly known, making it difficult to understand the formation of these types of deposits. This paper reviews the existing information for aqueous Te species and reports the derivation of their thermodynamic properties from 25 to 350°C. Free energies of formation at 25°C were derived mainly from experimental data and estimated at higher temperature using new experimental data for the solubility of tellurite (TeO 2 ) up to 80°C and isocoulombic techniques. The stabilities of aqueous Te species were then predicted as a function of temperature, redox, acidity, and total tellurium concentration. For conditions typical of many ore-forming liquids telluride and tellurite species are predicted to be the most important Te species. Under relatively reduced (e.g., magnetite-stable) and acid to neutral pH conditions, the most important species are predicted to be H 2 Te (aq) and HTe - . In more oxidized (hematitestable) environments, H 3 TeO 3 + , H 2 TeO 3 , and HTeO 3 - predominate. There is a polymeric species (Te 2 2- ) that may be important under some conditions, but its stability is limited by the solubility of native Te and dependent on total Te concentration. At temperatures between 100 and 300°C, it is predicted to be stable at pH greater than approximately 8 and oxygen activities near and below the Te -II /Te IV boundaries. At even higher pH (>10 to 12) Te 2- and Te0 3 2- predominate. The most oxidized Te species, the tellurates (H 6 TeO 6 , H 5 Te0 6 - , and H 4 TeO 6 - ) may be important at low temperature (<50°C) and high oxygen activity (e.g., atmospheric), although circumstantial evidence suggests they are not stable under geological conditions. Tellurium concentrations expected in hydrothermal fluids are low (less than 10 ppb at 300°C), based on solubility calculations for native Te (acid to neutral pH, range of oxygen activity at magnetite-hematite ± 6 log units). The solubility of native Te increases with oxidation and reduction away from a minimum near magnetite-hematite (at 300°C). pH has no effect at neutral to acid conditions, except under oxidized conditions and low pH (<2) where H 3 TeO 3 + is stable. At high pH (>7 or 8) the solubility of native Te increases with increasing pH regardless of the oxygen activity. Measured Te concentrations in experiments on the solubility of hessite + native Te + chlorargyrite in HCl solutions at 300°C are much higher (1's to 1000's of ppm) than predicted (10's to 100's of ppb) and may be evidence for unknown Te species (e.g., metal-tellurium complexes or aqueous Te in other valence states). The low predicted concentrations of aqueous Te may also indicate that vapour-phase transport of Te is important in the formation of telluride-bearing epithermal ore deposits.
No associations
LandOfFree
Thermodynamic properties of aqueous tellurium species between 25 and 350° does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Thermodynamic properties of aqueous tellurium species between 25 and 350°, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermodynamic properties of aqueous tellurium species between 25 and 350° will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-885474