GEM-Selektor geochemical modeling package: revised algorithm and GEMS3K numerical kernel for coupled simulation codes

Abstract

Reactive mass transport (RMT) simulation is a powerful numerical tool to advance our understanding of complex geochemical processes and their feedbacks in relevant subsurface systems. Thermodynamic equilibrium defines the baseline for solubility, chemical kinetics, and RMT in general. Efficient RMT simulations can be based on the operator-splitting approach, where the solver of chemical equilibria is called by the mass transport part for each control volume whose composition, temperature, or pressure has changed. Modeling of complex natural systems requires consideration of multiphase-multicomponent geochemical models that include nonideal solutions (aqueous electrolytes, fluids, gases, solid solutions, and melts). Direct Gibbs energy minimization (GEM) methods have numerous advantages for the realistic geochemical modeling of such fluid-rock systems. Substantial improvements and extensions to the revised GEM interior point method algorithm based on Karpov's convex programming approach are described, as implemented in the GEMS3K C/C++ code, which is also the numerical kernel of GEM-Selektor v.3 package (http://gems.web.psi.ch). GEMS3K is presented in the context of the essential criteria of chemical plausibility, robustness of results, mass balance accuracy, numerical stability, speed, and portability to high-performance computing systems. The stand-alone GEMS3K code can treat very complex chemical systems with many nonideal solution phases accurately. It is fast, delivering chemically plausible and accurate results with the same or better mass balance precision as that of conventional speciation codes. GEMS3K is already used in several coupled RMT codes (e.g., OpenGeoSys-GEMS) capable of high-performance computing.

Effect of temperature and aluminium on calcium (alumino)silicate hydrate chemistry under equilibrium conditions

“…Thermodynamic modelling was performed in the GEM Selektor v.3 software (http://gems.web.psi.ch/) [26,27] using the PSI/Nagra 12/07 thermodynamic database [28], which is updated from [29] via the inclusion of two additional dissolved (alumino)silicate species, and the CE M D ATA 0 7 thermodynamic database [9,10,[30][31][32][33][34][35] updated to include recently published data for Al(OH) 3 and hydrogarnet phases [24,36]. Solubility products (K so ) for C-(A-)S-H, and effective saturation indices (SI*) for relevant solid phases, were calculated from experimental data obtained here.…”

“…Activities of Ca 2+ (aq) , SiO 3 2-(aq) , AlO 2 -(aq) , OH -(aq) and H 2 O (l) were determined in GEMSelektor (http://gems.web.psi.ch/) [26,27]; the OH -concentration was matched to the measured pH values. The results of these calculations, for the hypothetical C-(A-)S-H endmembers, are shown in Figure 9.…”

The optimal windows for seismically-enhanced gold precipitation in the epithermal environment

“…The GEMS geochemical modeling software (Kulik et al, 2012) was used to compute dissolved gold concentration in hydrothermal fluids under epithermal conditions. As the gold (2014) was used.…”

Preparation, characterization and thermodynamic properties of Zr-containing Cl-bearing layered double hydroxides (LDHs)

“…Firstly, by applying GEMS-Selektor v.3. code [26,27] with built in Nagra-PSI thermodynamic database [18] and by using chemical analyses of aqueous solutions, the speciation of dissolved metals, activities and chemical potentials of relevant components (i.e., Mg 2+ , Al 3+ , Zr 4+ , OH − , Cl − ) have been calculated. Then the statement which says that: "Gibbs free energy of the system at equilibrium is minimum, and chemical potentials of the components are the same at each phase" allowed to calculate the molar Gibbs free energies from chemical potentials and from stoichiometric coefficients in Table 1 according to equation:…”

“…of Zr-containing LDHs with the help of thermodynamic modeling [26,27]; 2) to develop the provisional scheme of Zr-substitution in the hydrotalcite structure.…”