Abstract
Mass transfer during the alteration of phlogopite in Ca-bearing acid aqueous solution was studied in laboratory. The experiment was undertaken in two systems; one is a batch system regarded as a closed system and the other is a batch-flow system corresponding to a quasi-open system. The dissolution of phlogopite occurs incongruently and the priority in dissolution is in turn ; K≥Al≥Si≥Mg>Fe in the batch system. On the basis of kinetic examination, it is inferred that the dissolution of K and Mg is controlled by a diffusion process. The activation energy of their dissolution is evaluated to be 9.4 kcal/mol·deg in the batch system and the corresponding estimate in the batch-flow system is nearly the same in the magnitude. Phlogopite alters to vermiculite and/or phlogopite /vermiculite interstratified phase with the progress of alteration. In response to the alteration of phlogopite, the change of its chemical composition, especially the content of the interlayer K+, shows a difference particular to each system. The interlayer K+ decreases continuously in the process of alteration in the batch-flow system and as a result phlogopite alters into vermiculite. On the other hand, in the batch system the vermiculite formed earlier regains K+ from the ambient solution. This results in the formation of interstratified phlogopite/vermiculite from vermiculite.
