Fractionation of aqueous sodium salts by liquid-liquid extraction in aqueous two phase systems

An important element in the work-up of brines is the separation of different ions present. Usually, energy consuming technologies, such as multi-stage evaporation, reverse osmosis, crystallization, and nanofiltration, are used to bring the composition of the brine to the required specification. Fractionation of salts by liquid-liquid extraction using thermo-responsive polymers is a novel concept. In the current study we have evaluated the fractional extraction of sodium chloride from brines containing sodium sulfate as well. Four different polymers (Dehypon® LS 54, PPG 425, Pluronic® L31 and Triton® X - 15) have been used. The quaternary systems of these polymers with water, sodium chloride and sodium sulfate have been obtained at 283.15 K and 298.15 K. From experiments at 298.15 K, it was concluded that the polymer Dehypon® LS 54 showed the most interesting combination of extracted sodium chloride yield and selectivity of sodium chloride over sodium sulfate. The polymer losses to the feed (brine) phase were limited. Collected extract phases were subjected to a temperature increase to 323.15 K, 333.15 K, 343.15 K, and 353.15 K in order to study the polymer recovery by temperature induced phase splitting. It was found that at higher temperature the miscibility gap increased strongly and limited amounts of polymer remained in the aqueous phase.