No abstract

The process of transforming hydromagnesite to magnesite is analysed in the context of the theory of solvent-mediated transformations. A series of experiments at 120, 150 and 180ºC with different heating times was designed to determine, by powder X-ray diffraction, the amount of magnesite generated as a function of time. The aqueous-phase composition was monitored by inductively coupled plasma-mass spectrometry and carbonate alkalimetry. From the analytical data, the evolution of saturation indexes with respect to both phases was determined using the geochemical code PHREEQC. Finally, two different methods were applied to obtain the activation energy of the process and a TTT (TemperatureTransformation-Time) graph was constructed to define suitable conditions in which to obtain magnesite.

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.