Retention and thermodynamic characteristics of mercury(II) complexes onto polyurethane foams

Polyurethane foams (PUF) loaded with crystal violet and some onium cations were successfully employed for the retention of mercury(II) traces present in aqueous media. The kinetics and thermodynamics of the sorption of mercury(II) ions onto PUFs have been studied. The sorption of mercury(II) ions onto PUF follows a first-order rate equation which results as k = 0.25 +/- 0.01 min(-1). The sorption data followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R)-type sorption isotherms. The D-R parameters were beta = -0.0123 +/- 0.0002 mol(2)/kJ(2), K-DR = 90 +/- 5 mumol/g and E = 6.38 kJ/mol. The negative values of DeltaH and DeltaS may be interpreted as the exothermic chemisorption process and indicative of the faster chemisorption of the HgBr3- complex sorbed onto the active sites of the sorbent. Quantitative retention and recovery (99.5 +/- 2.1) of mercury(II) ions in water at less than or equal to5 ppb level by the foam columns were achieved. The HETP, the number (N) of the theoretical plates, the breakthrough and the critical capacity of the mercury(II) uptake by the foam column were found to be 0.65 +/- 0.01, 155 +/- 4.1 mm, 10.8 and 8.1 mg/g, respectively, at 5 cm(3)/min flow rate. A retention mechanism based on the sorption data has been proposed. This mechanism involves both absorption related to solvent extraction and an added component for surface adsorption. (C) 2003 Elsevier Science B.V. All rights reserved.