Phase Formation in Extraction of Metals from Aqueous Salt Solutions with Polyethylene Glycol: 2. Polyethylene Glycol-Water Binary System

The experimental data on water activity in PEG solutions as influenced by the PEG concentration and its molecular weight were analyzed in terms of the polymer solution theory. This analysis shows that nonideality of PEG-water solutions is mainly caused by the athermal effect, namely, by a large difference in the size of water and PEG molecules which, according to Flory theory, causes the increase in the entropy of mixing. The influence of van der Waals interactions and hydration on the solution nonideality was also considered. The PEG hydration number is 2 at the critical temperature of formation of the two-phase system and increases to 4 at lower temperatures. Adequate simulation of the nonideality of the systems concerned is reached with the finite value of the coordination number. In spite of weakness of the van der Waals interactions in the PEG-water systems, their contribution to the nonideality is sufficient to provide a two-phase system. The phase diagrams of the PEG-water system at elevated temperatures are discussed. © MAIK Nauka/Interperiodica 2002.