Interaction of Nonideal, Multicomponent Solid Solutions With Water: A Simple Algorithm to Estimate Final Equilibrium States

Interaction of minerals with water frequently yields a dissolution‐coprecipitation process in which foreign ions incorporate into the solid structure substituting for the major ion. Coprecipitation often controls the transport and fate of harmful ions in the environment. Geochemical modeling and experimental studies of these aqueous‐solid solution (AQ‐SS) processes are typically performed using pure minerals. However, the host minerals could be binary solid solutions and the study of their interaction with a third dissolved ion would require considering ternary solid solutions (TSS). Here we present a simple algorithm (AQ‐TSS) implemented in PHREEQC to estimate equilibrium in AQ‐SS systems involving nonideal ternary solid solutions. The three binary joints are considered separately. Nonregular solid solutions are treated by combining regular models defined for specific ranges of composition. The algorithm has been tested successfully by comparing the results obtained by AQ‐TSS with those obtained using PHREEQC with the same binary nonideal solid solutions. Key Points Multicomponent solid solution‐aqueous solution modeling Mineral‐water interface Ternary nonideal solid solution end points