Model for the decomposition of carnallite in aqueous solution

• Model parameters are obtained by the quaternary diagram of the NaCl–KCl–MgCl2–H2O.
• Model was established based on the principle of mass conservation for MgCl2.
• The amount of water and yield of KCl for carnallite are investigated.
• This research provides the theoretical basis for producing KCl from carnallite.

Carnallite is a double salt (KCl·MgCl2·6H2O or KMgCl3·6H2O), which is a common source of potassium chloride (KCl). It is treated with a mother liquor containing magnesium chloride (MgCl2), KCl and sodium chloride (NaCl), and then KCl and NaCl precipitate in the mother liquor solution. The amount of water and the temperature are the two crucial factors for the decomposition of carnallite in aqueous solution. Because of the lack of research on the decomposition process of carnallite, the yield and quality of the KCl produced are limited. In this study, we develop a model for the decomposition of carnallite based on the multi-temperature quaternary diagram of the NaCl–KCl–MgCl2–H2O system and the principle of mass conservation for MgCl2. The model is verified using experimental and literature data for different types of carnallite: normal, Mg-rich, Na-rich, and (Mg and Na)-rich. The proposed model predicts the amount of water required for decomposition of carnallite and the yield of KCl very well for normal and Mg-rich carnallite (within 2%), for Na-rich and (Mg and Na)-rich carnallite (within 8%), and for ancient evaporite carnallite in Laos (within 2%).