Abstract
Simulations of microcline weathering reactions (in closed system and reacting with a HCl solution of pH =4, at 25° C and 50° C) are formulated with the more recent versions of the computer codes EQ3/6, CHILLER, PHREEQE YHARPHRQ. The calculated reaction paths are strongly dependent of the thermodynamic constants for mineral equilibria but almost insensitive to variations in the speciation reactions enclosed in those codes for the selected conditions of simulation. Changes in the thermodynamic values for the mineral equilibria lead to important numerical differences in the predicted mass transfers, solution compositional parameters and also affect the number of secondary minerals involved in the simulation. So, differences in the thermodynamic data can induce variations in reaction path calculations as important as those produced by changes in the initial conditions of simulation. In spite of efforts on database updating, model sensitivity to mineral equilibrium constants is important and it must be taken into account in reaction path modeling of microcline weathering process.
Highlights
A HCl solution of pH = 4, at 25° C and 50° C) are formulated with the more recent versions of the computer codes EQ3/6, CHILLER, PHREEQE YHARPHRQ
The calculated reaction paths are strongly dependent of the thermodynamic constants for mineral equilibria
insensitive to variations in the speciation reactions enclosed in those codes for the selected conditions
Summary
En este trabajo se comparan los resultados de las versiones más recientes de los códigos de modelización termodinámica EQ3/6, CHILLER, PHREEQE Y HARPHRQ en la simulación de un proceso de alteración de microlina (con HCl diluido en agua pura a pH =4, en condiciones de sistema cerrado y a temperaturas de 25 y 50° C). Los resultados de la simulación presentan una marcada dependencia de las constantes de equilibrio mineral, siendo apenas afectados por las diferencias en las constantes de las reacciones de especiación consideradas por cada código. Los distintos valores de las constantes de equilibrio mineral que intervienen en el proceso provocan apreciables diferencias en las transferencias de masa y en los caracteres composicionales de la solución calculados por los códigos; e incluso llegan a afectar al número de minerales secundarios en los que se resuelve la simulación. A pesar de los esfuerzos realizados en el refinamiento y mejora de las bases de datos de los códigos, existen todavía importantes diferencias en los valores de las constantes de equilibrio mineral consideradas; circunstancia que se traduce en un importante grado de dependencia de los resultados respecto a esos parámetros en la simulación del proceso mediante cálculos de pautas de reacción.
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