Adsorption isotherms and thermodynamic profile of Co(II)-SCN complex uptake on polyurethane foam

Sorption of cobalt(II)-thiocyanate complex onto polyurethane foam (PUF) has been investigated in detail with respect to the equilibrating time between Co(II)-thiocyanate complex in solution and foam, and concentrations of cobalt(II) and sorbent. The sorption was optimized with respect to the composition of electrolyte. Maximum sorption has been achieved from 0.1 M HCl solution containing 0.5 M SCN after 10 minutes of shaking time. The kinetics and thermodynamics of sorption are studied in detail. The kinetics follow a first-order rate equation with the rate constant, k, = to 9.57 x 10(-2) min.(-1) The variation of equilibrium constant K-c with temperature (15-50 degrees C) yields values of Delta H = -64 +/- 4.6 kJ.mol(-1), Delta S = -92.6 +/- 15.6 J.mol(-1), and Delta G = -8.71 kJ.mol(-1) at 298 K. The sorption of Co(II)-thiocyanate onto PUF in the presence of common anions and cations has also been measured. The sorption data studied in the concentration range of Co(II) 1.12 x 10(-4) to 1.20 x 10(-3) M follow Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. Freundlich parameters 1/n = 0.35 +/- 0.02 and A = 0.85 +/- 0.2 mmol.g(-1), Langmuir constants Q = (5.54 +/- 0.12) x 10(-5) mol.g(-1) and b = (3.55 +/- 0.74) x 10(4) dm(3).mol(-1) and D-R isotherms beta = -0.002999 +/- 0.000189 kJ(2).mol(-2), C-m = 10.66 +/- 0.16 x 10(-4) mol.g(-1) and E = 12.9 +/- 0.4 kJ.mol(-1) have been evaluated. The possible sorption mechanism of cobalt-thiocyanate complex onto PUF is also discussed.