Adsorption and thermodynamic characteristics of Hg(II)-SCN complex onto polyurethane foam

The sorption of Hg(II) in the presence of sodium thiocyanate solution onto polyurethane (PUR) foam, an excellent sorbent, has been investigated in detail. Maximum sorption of Hg(II) is achieved from 0.1 M hydrochloric acid solution containing 7.5 x 10(-2) M sodium thiocyanate in 5 min. The sorption data followed both Freundlich and Langmuir adsorption isotherms. The Freundlich constants 1/n and sorption capacity, C-m, are evaluated to be 0.44 +/- 0.02 and (3.86 +/- 0.89) x 10(-5) mol g(-1). The saturation capacity and adsorption constant derived from Langmuir isotherm are (6.88 +/- 0.28) x 10(-5) mol g(-1) and (5.6 +/- 0.37) x 10(4) dm(3) mol(-1) respectively. The mean free energy (E) of Hg(II)-SCN sorption onto PUR foam computed from D-R isotherm is 12.4 +/- 0.3 kJ mol(-1) indicating ion-exchange type mechanism of chemisorption. The variation of sorption with temperature yields thermodynamic parameters of Delta H = -30.7 +/- 1.2 kJ mol(-1), Delta S = -70.1 +/- 4.1 J mol(-1) K-1 and Delta G = -9.86 +/- 0.77 kJ mol(-1) at 298 It. The negative value of enthalpy and free energy reflects the exothermic and spontaneous nature of sorption. On the basis of the sorption data, sorption mechanism has been proposed. (C) 1999 Elsevier Science B.V. All rights reserved.