Ion-Exchange Processes between Surface Layer and Core of Reverse Micelles of NaAOT+Tergitol NP-4 during Evaporation Crystallization of KNO₃

Liquid extraction and microdroplet probing of the composition of reverse microemulsions (NaAOT+Tergitol NP-4, NaAOT, and Tergitol NP-4 in n-decane) with aqueous salt solutions (KNO3, NaNO3, and KNO3+NaNO3) were used to determine the distribution of Na+ and K+ between the surface layer and the micelle core in the processes of evaporation crystallization of KNO3 and NaNO3 salts. It is shown that, at high content of NaAOT, K+ cations in micelle core are virtually completely replaced by Na+ and no crystallization of KNO3 in NaAOT micelles is observed. At low content of NaAOT in mixed micelles and small solubilization capacity (less than 1 vol %) partial exchange takes place and crystallization of KNO3 begins from a mixture of KNO3+NaNO3 salts. During crystallization, micelle cores become depleted in potassium nitrate, which causes reverse exchange of K+ cations, associated with AOT–, for Na+ contained in the micelle core. As a result, mainly KNO3 crystallizes in mixed micelles.