Autori: V. W. Trusdale and C. Sebu

Editorial: Aquat Geochem , 19, p.39-56, 2013.

Rezumat:

Following a recent suggestion of a new rate equation specifically for the batch
dissolution of salts in solutions containing a common ion, this paper describes an analytic
solution to its integration. The equation has been tested by dissolving 250 lm gypsumrock
particles in water (26.7 g l-1) containing various mixtures of sodium and calcium
chlorides, all at an ionic strength of 0.060 M. The model fitted the experimental curves
very well and showed that the dissolution slowed slightly overall when the initial calcium
concentration was increased from 0 to 0.020 M. The dissolution curves were also modelled
as a simple exponential, whence the fit was comparable to that with the new equation, with
the exponential rate constant varying between 0.025 and 0.019 (±0.0004) for 0 and
0.020 M initial calcium concentration, respectively. Conventional Electrolyte theory from
thermodynamics is used to show that the new equation is an inevitable consequence of
modelling the net rate of dissolution in terms of a back reaction that is first order with
respect to the dissolved substance, as per the recently described Shrinking Object model.
Moreover, it is shown how the simple exponential model (which is a well-used plot in
dissolution kinetics) provides the linear end-member to an infinite number of curvilinear
plots of rate of dissolution versus reaction progress developed by the new model—it is the
special case where common ion is absent. The results are now judged good enough to
identify a generic batch dissolution rate equation for all salts dissolving without significant
complication from either contaminants or their own gaseous species, as in calcium carbonate
dissolution.

Cuvinte cheie: Dissolution  Dissolution kinetics  Batch dissolution  Shrinking Object model  Gypsum  Rate equation  Common ion effect  Electrolyte theory  Analytic integral