Adsorption and thermodynamic studies of Co(II) and Hg(II) on 2-nitroso-1-naphthol immobilized polyurethane foam using radiotracer technique

Abstract

Summary The sorption behaviour of Co(II) and Hg(II) on 2-nitroso-1-naphthol loaded polyurethane foam (PUF) was studied. The maximum sorption of 1.8×10-5M solution of Co(II) occurred at low pH range 3-7 and that of 3.11×10-5M solution of Hg(II) was sorbed at higher pH range 7-9. The maximum equilibrium was attained within twenty minute shaking time. The adsorption data followed the Freundlich and Langmuir adsorption isotherms successfully. The Freundlich constants 1/n and K f for Co(II) are 0.44 and 1.18×10-2mol g-1 and for Hg(II) are 0.38 and 8.67×10-4mol g-1 respectively indicate the surface heterogeneity. The Langmuir constants M and b are 2.6×10-4mol g-1 and 4.7×104L g-1 for Co(II) and 2.9×10-5mol g-1 and 7.6×104L g-1 for Hg(II) respectively. The sorption free energy (E) evaluated from Dubinin–Radushkevich (D–R) isotherm for Co(II) and Hg(II) are 12.7kJ mol-1 and 13.13kJ mol-1 respectively, which indicate the ion exchange type chemisorption of Co(II) and Hg(II) onto 2-nitroso-1-naphthol loaded PUF. The thermodynamics parameters ΔH, ΔS and ΔG have been evaluated. The change in enthalpy (ΔH) of Co(II) is 74.55kJ mol-1, indicates the endothermic sorption, while for Hg(II) is -25.28kJ mol-1, depicts the exothermic sorption. The effect of diverse anions on the sorption of Co(II) and Hg(II) has been studied which revealed that the sorption of Hg(II) was completely masked in the presence of bromide, tartrate, nitrite, EDTA, thiocyanate, cyanide, perchlorate, ascorbate and thiourea, whereas sorption of Co(II) was greatly affected in the presence of oxalate, EDTA, cyanide, citrate and ascorbic acid. The nature of sorption mechanism has been discussed. The 2-nitroso-1-naphthol loaded PUF has potential in radiochemistry to separate 203Hg(II) from 75Se(IV), and Co(II) from Ni(II) metal ions or vice versa.