Sorption of traces of silver ions onto polyurethane foam from acidic solution

The sorption of traces of silver ions onto polyurethane foam (PUF) has been investigated in detail. Maximum sorption of silver (K-d = 6109 cm(3) g (-1), %sorption > 97.5%) has been achieved from 1 M nitric acid solution after equilibrating silver ions with similar to 29 mg PUF for 20 min. The kinetics and thermodynamics of the sorption of silver ions onto PUF have also been studied. The sorption of silver ions onto PUF follows a first-order rate equation, which results as 0.177 min(-1). The variation of sorption with temperature yields the values of DeltaH = - 56.1 +/- 3.2 kJ mol(-1) DeltaS = - 159.7 +/- 10.5 J mol(-1) K-1 and DeltaG = - 8.68 +/- 0.09 kJ mol(-1) at 298 K with a correlation factor gamma = 0.9919. The sorption data were subjected to different sorption isotherms. The sorption follows Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The values of Langmuir isotherms Q = 65.3 +/- 1.5 mu mol g(-1) and b = (4.79 +/- 1.16) x 10(4) dm(3) mol(-1) have been evaluated for Langmuir sorption constants, whereas the Freundlich sorption isotherm gives the value lin = 0.12 +/- 0.02 and A = 0.15 +/- 0.03 mmol g(-1). The D-R parameters computed were beta = - 0.000817 +/- 0.000206 mol(2) kJ(-2), X-m = 76.8 +/- 8.7 mu mol g(-1) and E = 24.7 +/- 3.2 kJ mol(-1). The influence of common ions on the sorption was also examined. It is observed that Hg(II), thioura, Al(III), thiocyanate and thiosulphate reduce the sorption, whereas Cu(II), citrate and acetate ions enhance the sorption significantly. It can be concluded that PUF may be used to remove traces of silver ions from its very dilute solutions or for its preconcentration from aqueous acidic solutions. (C) 2001 Elsevier Science B.V. All rights reserved.