Investigation of Aqueous Biphasic Polyethylene Glycol Systems for the Selective Liquid/Liquid Extraction of Dissolved Metal Ions

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This proposal is concerned with using aqueous biphasic salts composed of polyethylene glycol (PEG) and an inorganic salt to separate dissolved metal ions. When PEG and salt are added to water, the solution separates into two distinct layers; one phase is rich in PEG and the other in salt. Metal ions dissolved in this system preferentially dissolve in the PEG rich phase, and hence ion separation can be effected by simply dissolving polymer and salt in a metal-containing aqueous stream, and then separating the phases. The variables which affect the metal partitioning are the pH, salt selection, PEG concentration, temperature and distance from the critical point (i.e. the polymer/salt composition at which two phases first appear). Several critical areas are proposed for study: (i) In previous research, the PI has demonstrated in a series of batch experiments, that technetium in the form of TcO4- can be extracted into the PEG rich phase using carbonate (K2CO3) and sulphate ((NH4)2SO4 without the need of a complexing agent. The PI intends to study this novel result further, and to build on this discovery by finding a method to strip the metal ions from the PEG-rich phase and complete the separation process. Several methods will be tested including ion exchange, and oil-water batch extraction with the PEG as the aqueous phase. (ii) Optimize particular biphasic systems (SO42-,CO32-, PO43- or alkmaline media) for the selective removal of Tc or Cr (in the form of CrO41-). (iii) Base-Side extraction of alkali and alkaline earth metal ions from synthetic waste solutions of high alkalinity and high nitrate concentration. (iv) Biphasic systems for the removal of toxic metal cations using inorganic anions to form extractable complex anions of metals. (v) Organic separations in biphasic systems (vi) f-element extraction using a combination of aqueous biphase and water soluble extractant.