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, equal to 9.57 X 10^-2 min.^-1 The variation of equilibrium constant K(c) with temperature (15- 50°C) yields values of ΔH = -64 ± 4.6 kJ·mol^-1, ΔS = - 192.6 ± 15.6 J·mol^-1 ·K^-1, and ΔG = -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 l/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 10⁴ dm³·mol^-1 and D-R isotherms β = -0.002999 ± 0.000189 kJ²·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.