Sorption and thermodynamic behavior of zinc(II)-thiocyanate complexes onto polyurethane foam from acidic solutions

The uptake of Zn(II)-SCN complex onto polyurethane foam (PUF) has been investigated in detail with respect to different composition and variable concentration of electrolyte, zinc, thiocyanate ions and PUF, and equilibration time. The sorption data followed both Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms over the entire concentration range of zinc investigated whereas Freundlich sorption isotherm is obeyed upto 13.6·10^-3M concentration. The Langmuir constants Q = 202±7 μmole·g^-1 and of b = (1.78±0.31.10⁴ dm³·mole^-1 and of D-R paraneter X_m = 493±1 μmole·g^-1, β = activity coefficient = -0.028±0.0002 and of sorption energy E = 13.2±0.5 kJ·mole^-1 and Freundlich constants 1/n = 0.42±0.03 and c_m = 6.47±1.7 mmole·g^-1 were evaluated. The influence of temperature variation on sorption have yielded ΔH = -77.5± 2.9 kJ·mole^-1, ΔS = -5±0.09 J·mole^-1·K^-1 and ΔG = -6.67±0.05 kJ·mole^-1. The effect of common anions and cations on the sorption has been examined. Sulphate, ascorbate and bromide ions enhances the sorption to some extent whereas nitrite, Pb(II), Fe(III), Al(III), Cu(II) and Co(II) decrease to sorption significantly. A possible mechanism has been envisaged for Zn(II)-SCN sorption onto PUF.