Summary
Effects of salinity and low temperature on the removal of dissolved contaminant metals from water by an iminodiacetic acid (IDA) ion-exchange resin, Amberlite IRC748, were investigated under batch equilibrium conditions. As expected for ions retained by chelation, the efficiency of the resin was reduced with low temperature. The efficiency of the resin increased with salinity: increasing salinity (from 0% seawater) reduces protonation of the resin, lowering solution pH into the optimum pH range for the retention of contaminant metal ions. Selectivities of the divalent matrix cations, Ca2+ and Mg2+ were decreased with increasing salinity: this is attributed to a shift to an ion-exchange retention mechanism for these ions, which is favoured at lower solution pH. At low salinity, the selectivity for Ca2+ and Mg2+ was decreased at low temperature, however at higher salinities, selectivity was unaffected by low temperature. This is consistent with the proposal of a shift from a chelation to an ion-exchange mechanism for these ions.