Acid/base and metal uptake properties of chelating and weak base resins

Purolite's weakly basic experimental resins with diethanolamine, morpholine , 2-vinylpyridine, mono-and bispicolylamine functionalities were evaluated with respect to their hydrogen, Zn, Ni, Cu and Cd uptake, and compared with Purolite's commercial chelating iminodiacetate, aminophosphonate and hydro xamic acid resins. Special attention was paid to the resin performances in acidic solutions. In general, diethanolamine, morpholine and 2-vinylpyridin e resins took up these metals poorly. Only cadmium was retained in acidic s olutions, probably as negatively charged chloride complexes. The chelating resins, with their weakly acidic groups, did not function in acidic solutio ns but worked well at pH 4 and above. The only resin that efficiently remov ed metals from acidic solutions was the bispicolylamine resin. Metal uptake values on this resin did not change appreciably in the pH range between 1 and 6. Maximum uptake values ranged between 0.6 and 1.7 mmol/g, being highe st for copper and lowest for nickel. Acid/base properties of the weakly bas ic resins did not correlate with their capability to take up metals from so lution: the results obtained did not support the initial assumption that th e weaker the resins are the better they take up metals in acidic solutions.