Coacervation characteristics of nonionic surfactants and their application to metal separation

Phase-separation characteristics of aqueous solutions containing a nonionic surfactant, polyoxyethylene nonyl phenyl ether, have been studied from viewpoints of equilibrium and history. The surfactant aggregates to make a small coacervate phase from the solution at a temperature above its cloud point, which increased with increasing HCl concentration. A phase diagram relating the composition of the surfactant-rich phase to the aqueous phase was constructed with a variety of the concentrations of HCl and NaCl, as a function of the temperature difference between the settling medium and the cloud point. The effects of operating parameters on the phase-separation history were also examined, and it was found that more hydrophobic surfactant allows the phase-separation to slow. Moreover, the application of the surfactant system to metal separation was demonstrated for the recovery of gold(III) and gallium(III) from HCl medium.