Physicochemical Rationale for the Method of Extractive Crystallization of Salts Based on the Analysis of the Phase Diagrams of Salt–Water–Amine Ternary Systems

Criteria for selecting the best antisolvent among aliphatic amines: dipropylamine, diisopropylamine, and triethylamine were developed. The phase behavior of 14 salt–water–amine ternary systems was analyzed, including salts with different solubilities and salting-out abilities (sodium and potassium formats; sodium, potassium, and cesium nitrates; lithium and sodium chlorides; potassium bromide and iodide). The temperature dependences of the composition of the critical solution were determined for the majority of systems, and isothermal phase diagrams were constructed for all of them. The compositions of the equilibrium phases of the monotectic state were used to calculate the yield of salt crystals depending on the antisolvent concentration and temperature. The optimum conditions for the process can be determined based on the analysis of the phase diagrams of systems in a certain temperature range. The revealed tendencies in extractive crystallization made it possible to significantly reduce the amount of experimental work to find the best conditions for extracting the salts from aqueous solutions and to propose a research algorithm. The algorithm makes it possible to reduce the experiment by 6–8 times and to carry out an express assessment of the effectiveness of an antisolvent for a particular salt without phase selection and their chemical analysis.