Kinetics and thermodynamic characteristics of cadmium(II) sorption from water using procaine hydrochloride physically impregnated polyurethane foam

A fast and selective method for cadmium(II) removal from water by procaine hydrochloride (PQ+·Cl−) immobilized polyurethane foam (PUFs) sorbent was developed. The method was based upon formation of [CdI4]−2aq in the test aqueous KI solution and subsequent extraction by PQ+·Cl− treated PUFs. The sorption of Cd2+ ions followed first order equation with an overall rate constant of 0.132 ± 0.033 min−1. The values of ΔH and ΔS were −41.54 ± 0.9 kJ mol−1 and −144.58 ± 3.1 J mol−1 K−1, respectively with a correlation factor of 0.998. The thermodynamic parameters (ΔH, ΔS and ΔG) suggest that the sorption was spontaneous and exothermic process. The negative value of ΔS provides indication of moderate sorption of [CdI4]2− ion associate and ordering of the ionic charges without compensatory disordering of the sorbed species onto the sorbent. Cadmium(II) sorption is mainly dominated by absorption related to “solvent extraction” and an added component for “surface adsorption”. PQ+·Cl− treated PUFs packed column was also tested for preconcentration of trace concentrations of cadmium(II) species in various water samples. The retained Cd species were successfully recovered with dilute HNO3 (1.0 mol L−1) and subsequently analyzed by ICP-OES. Thus, the proposed sorbent packed column provides efficient removal of traces of cadmium(II) ions from water samples. The method could be extended for preconcentrate of trace and ultra trace cadmium species from large samples onto PUF packed column and subsequently analyzed. Indeed, the developed method could be satisfactorily applied to the determination of trace Cd ions in natural water.