Sorption of palladium-thiocyanate complexes onto polyurethane foam from aqueous solution using radiotracer technique

The sorption of palladium-thiocyanate complex onto polyurethane foam (PUF) has been investigated and optimized from aqueous solution of different pHs (1-10) and of acids of varied concentration (0.01-0.5 M). Maximum sorption (∼99%) of palladium (9.4 × 10^-5 M) in the presence of thiocyanate (1.25 × 10^-2 M) ions has been achieved from 0.1 M hydrochloric acid solution within 5 min equilibrating time. The variation of palladium concentration (1.03 × 10^-4 - 1.16 × 10^-3 M) data were subjected to different sorption isotherms. The data followed both Freundlich and Dubinin-Radushkevich (D-R) isotherms very well, but Langmuir isotherm is not obeyed at very low concentration. The Freundlich parameters 1/n = 0.54 ± 0.02 and of C_m = 35 ± 7 mmol g^-1 have been evaluated, whereas D-R isotherm yields β = -0.003277 ± 0.000193 kJ² mol^-2, X_m = 1.01 ± 0.16 mmol g^-1, and of E = 12.3 ± 0.35 kJ mol^-1. The Langmuir isotherm gives the value of Q = 0.27 ± 0.08 mmol g^-1 and of b = (2.83 ± 0.06) × 10⁴ L mol^-1. The temperature variation (15-55°C) studies have given values of ΔH = -48.9 ± 2.5 kJ mol^-1, ΔS = -127.3 ± 8.2 J mol^-1 K^-1, and of ΔG = -25.2 kJ mol^-1 at 298 K. Among the ions tested, thiourea, cyanide, thiosulphate, molybdate, nitrite, and Fe(II) reduce the sorption significantly (31-70%).