Kinetics of crystallization of potassium chloride from aqueous solutions at 30 °C

Abstract

The aim of this work is to usr a diffusion layer model for the determination of individual rate constants of reaction and diffusion step of KCI at 30 "C. Crystal growth rate ~v a s measured by travelling microscope technique. From thc measured valiies of tho mean linear growth rate the resulting individual rat.e constants and the rffcctiverwss factors (GARSIDE) are cvaluated as a fiirictioii of the driving force and of t h c flow velocity of solution. The significance of diffusional and surface rcactioii resistances against mass t raiisfer is discussed in relation to t h e cxperirnental coiidit>ions used.Gcgenstand der vorliegendrn Arbeit, ist die Anwendung des L)iffusio~~sschichtlrlodells zur Ermitt lung der Konst.ant>en des Diffusionsund Reaktionsschrittes des Kristalltvachstiims von KCI bei 30 "C. Die Krist,allw-achstumsgeschwindigkeit wiirde mittels hlikroskop a m Einzelkristall grmessen. Aus diesen Werten werden die individuellen Konstanten des Diffusions-und des Reaktionsschrittes und deren Effektivitatsfaktoren als Funktion der Triebkraft und der Anstromgeschwindigkeit ermittelt.

Growth kinetics of potassium chloride—I: Pure aqueous solutions

“…Some literature data, calculated from correlations developed for similar experimental conditions, were also included in the same plot after being converted to the thermodynamic scale. The trend of the overall growth data was nearly first-order with respect to the driving force, in accordance with the findings of the large majority of authors [1][2][3][7][8][9][10][11].…”

“…(9) is fitted to the raw growth data, different sets of constants satisfy the minimization criterion used for the regression, albeit pointing to contradictory conclusions as shown by Ko¨nig and Emons [3]. The analysis of the influence of temperature and of relative solid-liquid velocity can, however, shed some light on the relative importance of the rate controlling mechanisms.…”

“…The issue of the growth rate controlling mechanism of potassium chloride is still to date an unresolved one, a fact that is clearly illustrated in the literature by the identical number of opinions defending the diffusional mass transfer [1,2,5] or a first-order surface-reaction [3,8,9] as the preponderant mechanism. The assessment of the relative importance of these two steps based on the usual linearized form of the equation that combines both contributions [18]:…”

“…The crystallization of potassium chloride from pure aqueous solutions has been studied by a number of authors using direct and indirect measurement techniques, e.g., single-crystal [1][2][3], fluidized bed crystallizer [4][5][6], mixed suspension mixed product removal (MSMPR) crystallizer [7], seeded controlled cooling batch crystallizer [8], unseeded desupersaturation runs [9][10][11][12], etc. Because growth rates depend on supersaturation, as well as on temperature and relative solid-liquid velocity, the use of different setups or operating conditions might, to a certain extent, explain the lack of agreement between the published results.…”

Crystal Growth Rate of KCl in the KCl–MgCl2–H2O System Based on MSE Modeling

“…A number of researchers have studied the crystal growth process of KCl, and several crystal growth mechanisms have been proposed in the literature. − Sarig et al have measured the growth rates of KCl crystals in cooling solutions. The range of the average overall measured growth rates was 0.6–1.5 × 10 –7 m·s –1 .…”