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 ϫ 10 Ϫ2 min. Ϫ1 The variation of equilibrium constant K c with temperature (15-50°C) yields values of ⌬H ϭ Ϫ64 Ϯ 4.6 kJиmol Ϫ1 , ⌬S ϭ Ϫ192.6 Ϯ 15.6 Jиmol Ϫ1 иK Ϫ1 , and ⌬G ϭ Ϫ8.71 kJиmol Ϫ1 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 ϫ 10 Ϫ4 to 1.20 ϫ 10 Ϫ3 M follow Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherms. Freundlich parameters 1/n ϭ 0.35 Ϯ 0.02 and A ϭ 0.85 Ϯ 0.2 mmolиg Ϫ1 , Langmuir constants Q ϭ (5.54 Ϯ 0.12) ϫ 10 Ϫ5 molиg Ϫ1 and b ϭ (3.55 Ϯ 0.74) ϫ 10 4 dm 3 иmol Ϫ1 and D-R isotherms ␤ ϭ Ϫ0.002999 Ϯ 0.000189 kJ 2 иmol Ϫ2 , C m ϭ 10.66 Ϯ 0.16 ϫ 10 Ϫ4 molиg Ϫ1 and E ϭ 12.9 Ϯ 0.4 kJиmol Ϫ1 have been evaluated. The possible sorption mechanism of cobalt-thiocyanate complex onto PUF is also discussed.

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The batch kinetics of silver sorption at the tracer level onto manganese dioxide along with the thermodynamic parameters from dilute nitric and perchloric acid solutions are described. The values of AH, AS, and AG found from both acid solutions are similar. The sorption equilibrium constant, Kc, has been calculated at different temperatures between 288 and 308 K. Tests of different isotherms have shown that the sorption data fit very well to the Freundlich and Dubinin-Radushkevich (D-R) models at different temperatures. The thermodynamic data indicate the endothermic nature of silver sorption onto the oxide. The sorption capacity in the 0.23-0.77 mmol/g range and a mean free energy of sorption of about 11.5-15.4 kJ/mol have been found by using the D-R approach. The values of B and the correlation factor (r) have been determined by using the D-R isotherm. These values are comparable with those reported earlier for other sorption systems.