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

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 β=−0.0123±0.0002 mol2/kJ2, KDR=90±5 μmol/g and E=6.38 kJ/mol. The negative values of ΔH and ΔS 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 ≤5 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 cm3/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.