DETERMINATION OF EQUILIBRIUM-CONSTANTS OF ALKALINE-EARTH METAL-ION CHELATES WITH DOWEX A-1 CHELATING RESIN

A complexation chemistry model is applied to chelating ion-exchange sy stems and a method is presented for the determination of equilibrium c onstants for metal ion chelates with these resins. Protonation constan ts for the iminodiacetic based chelating resin Dowex A-1 were determin ed from potentiometric pH-data. Equilibrium constants were determined for 1:1 beryllium, magnesium, calcium, strontium and barium chelates w ith the resin in a wide pH range by measuring the concentrations of re spective metal ions in the aqueous phase with direct current plasma at omic emission spectrometry (DCP-AES). A batch technique was used for t he equilibrium experiments. At pH below 7 protonated 1:1 species were also found to be formed with the resin. From the obtained equilibrium constants, theoretical distribution coefficients were calculated as fu nction of pH for respective metal ion resin system.