FREZCHEM: A geochemical model for cold aqueous solutions

doi:10.1016/j.cageo.2009.06.004

Computers & Geosciences

Volume 36, Issue 1, January 2010, Pages 10-15

https://doi.org/10.1016/j.cageo.2009.06.004 Get rights and content

Abstract

FREZCHEM is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions [up to ≈20 moles/kg(H₂O) (molality)] using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. This subzero temperature model has been extensively used to explore cold geochemical processes and/or limits for life in the Arctic, Antarctica, Europa, and Mars. FREZCHEM contains environmental pathways for simulating temperature change, evaporation, and pressure change. The objectives of this work were to (1) adopt a better mathematical algorithm to calculate chemical equilibrium, (2) develop a more user-friendly Internet version, and (3) develop an archive for various model versions. We adopted a Gibbs free energy mathematical algorithm that significantly reduced convergence problems that existed with older versions of this model. An Internet site was developed at http://frezchem.dri.edu that simplifies model access and is more user-friendly than pre-existing FREZCHEM versions. At this Internet site, FORTRAN codes and instructions for using various FREZCHEM versions are archived. This effort will make this unique theoretical research tool readily and easily available, even to occasional users, now and in the future.

Introduction

FREZCHEM (FREeZing CHEMistry) is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions [up to ≈20 moles/kg(H₂O) (molality)] using the Pitzer approach for the temperature range from <−70 to 25 °C and the pressure range from 1 to 1000 bars. This unique subzero temperature model has been extensively used to explore cold geochemical processes and/or limits for life in the Arctic (Elberling, 2001; Boike et al., 2008; Morin et al., 2008), Antarctica (Lyons et al., 2005), Europa (Kargel et al., 2000; Zolotov and Shock, 2001), and Mars (Morse and Marion, 1999; Gaidos and Marion, 2003). The consequences of evaporation and freezing of solutions and high pressures (e.g., beneath the surfaces of Mars and Europa) have been examined with FREZCHEM. See Marion and Kargel (2008) for multiple examples of Earth, Mars, and Europa cases. For the past several years, the FORTRAN code for this model was made freely available to interested scientists. Nevertheless, the continual updating, dissemination, and archiving of the model are problematic. For example, model programs are currently disseminated by G.M. Marion through programs archived on a personal computer. Archiving and dissemination from an Internet site would be a major improvement. Furthermore, and most importantly, earlier versions of this model have convergence problems. The objectives of this work were to (1) adopt a better mathematical algorithm to calculate chemical equilibrium, (2) develop a more user-friendly Internet version, and (3) develop an archive for various model versions. This effort will make this unique theoretical research tool readily and easily available, even to occasional users, now and in the future.

Section snippets

FREZCHEM model

FREZCHEM is an equilibrium chemical thermodynamic model parameterized for concentrated electrolyte solutions using the Pitzer approach (Pitzer, 1991, Pitzer, 1995) for the temperature range from <–70 to 25 °C and the pressure range from 1 to 1000 bars (Marion and Grant, 1994; Mironenko et al., 1997; Marion and Farren, 1999; Marion, 2001, Marion, 2002; Marion et al., 2003, Marion et al., 2006, Marion et al., 2009a, Marion et al., 2009b, Marion et al., 2008, Marion et al., 2005; Marion and Kargel,

Results and discussion

The Internet model is accessible at http://frezchem.dri.edu. Five options are available for controlling simulations. User instructions are posted at the Internet site that describes these options in detail. Option 1 refers to system cation–anion solution phase specifications. Users can specify total solution concentrations for Na, K, Mg, Ca, H, Fe(II), Cl, ClO₄, SO₄, carbonate alkalinity (HCO₃+2CO₃), and NO₃. These inputs must be in molal units [mol kg(H₂O)⁻¹], except for alkalinity that is in

Concluding remarks

FREZCHEM is in a continuing state of adding new chemical processes, chemical species, and their associated minerals (Table 4). For example, the latest addition to FREZCHEM is perchlorate chemistry (Version 13, Table 4); the resulting perchlorate paper is in submission to a technical journal. But meanwhile, we added perchlorate chemistry to the Internet site (Version 10, Table 4). So users have access to perchlorate chemistries that are currently highly relevant to the Mars Phoenix Mission (//phoenix.lpl.arizona.edu/index.php

Acknowledgement

Funding was provided by a NASA Mars Fundamental Research Program (MFRP) project, “FREZCHEM: An Aqueous Geochemical Model for Mars”.

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^☆: Code available from server at: http://frezchem.dri.edu.

¹: Tel.: +775 673 7330.

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FREZCHEM: A geochemical model for cold aqueous solutions☆

Abstract

Introduction

Section snippets

FREZCHEM model

Results and discussion

Concluding remarks

Acknowledgement

Geomorphology

Geochimica et Cosmochimica Acta

Icarus

Geochimica et Cosmochimica Acta

Geochimica et Cosmochimica Acta

Computers & Geosciences

Geochimica et Cosmochimica Acta

CALPHAD

Icarus

Geochimica et Cosmochimica Acta

Geochimica et Cosmochimica Acta

Geochimica et Cosmochimica Acta