Adsorption modeling and thermodynamic characteristics of uranium(VI) ions onto 1-(2-pyridylazo)-2-naphthol (PAN) supported polyurethane foam

The sorption of uranium(VI) ions onto PAN loaded PUF has been investigated. Quantitative sorption of uranium(VI) onto PAN loaded PUF was achieved after 30 minutes equilibration time from pH 7 buffer solution. The sorption data followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. Langmuir parameters Q = 45.3 ± 0.2 μmol g^-1 and b = (76.2 ± 0.2) × 10³ dm³ mol^-1, Freundlich constants 1/n = 0.21 ± 0.01 and K_F = 229 ± 21 μmol g^-1 and D-R parameters β = -0.0015 ± 0.00005 kJ ² mol^-2, X_m = 72.23 ± 3.11 μmol g^-1 and E = 18.3 ± 0.3 kJ mol^-1 have been evaluated. The variation of sorption data with temperature gives ΔH = 176 ± 5 kJ mol^-1, AS = 626 ± 17 J mol^-1 K ^-1 and ΔG = - 10.6 ± 0.7 kJ mol^-1 at 298 K. The positive value of enthalpy (ΔH) and negative value of free energy (ΔG) show endothermic and spontaneous nature of sorption respectively. A number of solvents were tested to elute the uranium-PAN complex from the PAN loaded PUF, only amine solvents and cyclohexanone have the capability to desorb the complex. The sorption mechanism has been discussed.