ION-EXCHANGE ON RESINS WITH TEMPERATURE-RESPONSIVE SELECTIVITY .1. ION-EXCHANGE EQUILIBRIUM OF CU2+ AND ZN2+ ON IMINODIACETIC AND AMINOMETHYLPHOSPHONIC RESINS

The ion-exchange equilibrium of Cu2+ and Z(2+) from sulfate solutions at pH = 1.9 on iminodiacetic (IDA) and aminomethylphosphonic (AMP) res ins has been studied in the temperature range between 10 and 80 degree s C. The values of the equilibrium separation factor alpha for Zn-Cu e xchange demonstrate a strong temperature dependence in the case of IDA resin, while for AMP this dependence is pronouncedly much weaker. A d ecrease of alpha at elevated temperatures has been observed for both i on exchangers. The absolute alpha(Zn)(Cu) values for IDA resin lie wit hin between 83.0 (at 10 degrees C) and 30.0 (at 80 degrees C). In the case of AMP resin, alpha values have been shown to vary from 1.67 to 1 .4 in the same temperature interval. It has been shown that thermostri pping with stock solution at 20 degrees C from IDA resin pre-equilibra ted with the same solution at 60 degrees C leads to selective desorpti on of Cu2+, while under the same conditions AMP resin is selectively r eleasing Zn2+. Thermodynamic interpretation of the temperature depende ncies of the separation factors obtained on IDA resin has been shown t o allow a comparison of the properties of the ion exchanger with those of iminodiacetic acid in homogeneous solution.