A method for activity calculations in saline and mixed solvent solutions at elevated temperature and pressure: A framework for geological phase equilibria calculations.
MetadataShow full item record
Quantitative thermodynamic calculations that involve aqueous fluids have proved difficult because of the complexity of the interactions that occur within the fluids. Existing thermodynamic models are difficult to apply to mixed solvent or highly saline solutions at P >0.3 GPa and T >300 C. This work constructs a method for activity-composition calculations in saline, mixed solvent, supercritical aqueous solutions. Mixing is formulated on a mole-fraction scale in terms of a set of independent end-members that describe composition and speciation within the solution. The ideal mixing term takes speciation into account and avoids problems with the common ion effect. Non-ideal interactions are represented by an activity coefficient term that combines a limited form of Debye-Hckel and a van Laar formulation. This approach, referred to as the DH-?ASF model, is thermodynamically valid over a wide range of P, T and fluid composition. The value of the model lies in its broad applicability, and small number of calibration parameters. Experimental data from the literature for the systems NaCl-H2O, KCl-H2O, H2O-SiO2-CO2, H2O-NaCl-CO2, H2O-NaCl-SiO2 and for H2O-albite melts have been used to calibrate the DH-ASF model. Calculations were performed using Thermocalc, computer software that calculates equilibria for mineral-based chemical systems. 1 The model represents the data to within experimental error in most cases.Conditions modelled include pressures between 0.2 and 1.4 GPa, temperatures between 500 and 900 C, and xH2O from 0.1 to 1. Calibrated parameters are consistent with expectations based on the conceptual model for the fluid, and are relatively insensitive to changes in pressure and temperature for most examples. The DH-ASF model is thermodynamically valid for a range of P-T conditions that includes pressures from 0.1 to 2 GPa and temperatures from 200 to 1000 C. A lack of experimental data restricts calibration of the model for many end-members. However, it may be possible to neglect parameters associated with end-members present in small amount. In this case, or with new experimental data for calibrations, the DH-ASF model allows previously inaccessible geological systems and processes to be modelled.
The link to the journal’s home page is: http://www.elsevier.com/wps/find/journaldescription.cws_home/212/description#description. Copyright © 2006 Elsevier B.V. All rights reserved
Showing items related by title, author, creator and subject.
The effect of CO2 on the speciation of RbBr in solution at temperatures to 579 degrees C and pressures to 0.26 GPaEvans, Katy; Gordon, R.; Mavrogenes, J.; Tailby, N. (2009)Carbon dioxide- and salt-bearing solutions are common in granulite, ore-forming and magmatic environments. The presence of CO2 affects mineral solubilities, fluid miscibility, and viscosity and wetting properties, and ...
The dissociation mechanism and thermodynamic properties of HCl(aq) in hydrothermal fluids (to 700 °C, 60 kbar) by ab initio molecular dynamics simulationsMei, Y.; Liu, W.; Brugger, J.; Sherman, D.; Gale, Julian (2018)HCl is one of the most significant volatiles in the Earth’s crust. It is well established that chloride activity and acidity (pH) play important roles in controlling the solubility of metals in aqueous hydrothermal fluids. ...
Amiri, Amirpiran (2013)The alumina industry provides the feedstock for aluminium metal production and contributes to around A$6 billion of Australian exports annually. One of the most energy-intensive parts of alumina production, with a strong ...