Study on metastable zone width and crystal growth of a ternary system: case study MgCl2·6H2O·1,4-dioxane

The recovery of MgCl2 from brines and salt lakes by solvate crystallization as MgCl2·6H2O·1,4-dioxane with 1,4-dioxane was investigated. The metastable zone (MSZ) of MgCl2·6H2O·1,4-dioxane in the MgCl2-6H2O-1,4-dioxane system was studied using an IR probe in small scale (12 mL) and an ultrasound velocity probe in large scale (120 mL). It was experimentally observed that small scale (12 mL) nucleation experiments were not reproducible, whereas large scale (120 mL) experiments presented reliable results. The solubility data of the two polythermal methods were compared with a published isothermal method. The influence of volume on MSZW measurements is explained in detail. Crystal growth rates were also determined at different temperatures and supersaturation levels using a microscopic cell. To correlate the measured growth rate with species concentrations in solution, a simple empirical approach was proposed. The correlation presented is of interest for the calculation of growth rates when designing crystallization processes to separate the MgCl2·6H2O·1,4-dioxane from salt brines.