Column solid-phase extraction of heavy metal ions on a high surface area CeO2 as a preconcentration method for trace determination

The adsorption of heavy metal cations on two CeO2 samples, (C-1, 204 m(2) g(-1), prepared by hydrolysis of Ce(NH4)(2)(NO3)(6), and C-2, 123 m(2) g(-1), synthesized by hydrolysis-oxidation of Ce(NO3)(3)), has been investigated. Studies on (i) adsorption kinetics, (ii) pH curves, (iii) adsorption isotherms, (iv) adsorption capacities and (v) the nature of the sorption sites have been performed. Quantitative sorption of Cd2+, Co2+, Cu2+, Mn2+, Pb2+ and Zn2+ has been detected at pH greater than or equal to 7. On the basis of IR spectra of adsorbed CO, it has been concluded that the adsorption sites represent coordinatively unsaturated Ce4+-O2- pairs at the ceria surface. All of the adsorbed ions may be eluted by HNO3 and EDTA and the CeO2 sample preserves its sorption properties after this procedure. Optimal conditions for simultaneous and quantitative solid-phase extraction of the most common heavy-metal ions are proposed. A column system for preconcentration is developed. Conditions for quantitative and reproducible elution and subsequent atomic absorption spectrometry are established. The system has been tested with some analytes of particular environmental importance (Cd, Co, Cu and Ph) in river and waste waters.