Axel König

Heats of crystallization of potassium chloride and magnesium chloride hexahydrate from aqueous solutions at 298.15 K. A critical review

Abstract Published data on the heats of crystallization from aqueous solutions of potassium chloride and magnesium chloride hexahydrate are critically reviewed and compared with those evaluated from solubility and activity data. The recommended values of the heats of crystallization are −13.8±0.1 kJ mole−1 for KCl and −15.8−0.3+2.8 kJ mole−1 for MgCl2·6 H2O. A test of the mutual consistency of data for dissolution heats, temperature dependence of solubility and concentration dependence of activity and/or osmotic coefficient is a side-issue of the review.

Production of Crystal Suspensions for Granulation Processes

One possibility for the transformation of a melt into a convenient to handle and easy to store solid formis the dropforming process. During this process, themelt is first separated into small dropswhich are then solidified due to rapid cooling. If the feed is a crystal suspension (melt with crystal seeds) rather than a pure melt, the time needed for the solidification process can be significantly reduced and the inner structure of the solid drops (pastilles) can be improved. A new technique is presented for the continuous production of crystal suspensions in an ultrasound field. A melt flow is supercooled and then irradiated acoustically in an ultrasound cell. By this means a nucleation process is started and a fine crystal suspension produced. The mechanism of power ultrasound on the nucleation is in the case of the organic substances tested a secondary nucleation mechanism which is mainly due to acoustic cavitation.

Enthalpy of crystallization of potassium chloride from aqueous solutions at temperatures between 0 and 100°C

Abstract Enthalpies of crystallization of potassium chloride from aqueous solution were calculated using the description of thermodynamic properties recently derived by Holmes and Mesmer on the basis of the Pitzer model and Silvester and Pitzer correlations. Published experimental data were compared with those evaluated from the above model for the temperature range 0–100°C. Similar data for magnesium chloride hexahydrate are discussed.