Adsorption behaviour of Hg(II) from acetate medium onto PAR-imbedded polyurethane foam

The sorption behaviour of a 2.46 × 10^-5 M solution of Hg(II) on 4-(2-pyridylazo)resorcinol (PAR)-loaded polyurethane foam (PUF was investigated. Optimum sorption was observed from acetate medium at pH 6 with the maximum equilibration time being 30 min. The kinetic data indicated an intraparticle diffusion process with sorption being first order. The rate constant k was 0.053 min^-1. The classical Freundlich and Langmuir adsorption isotherms were tested. The Freundlich constants 1/n and K_f were determined as 0.40 and 1.07 × 10^-3 mol/g, respectively, and the Langmuir constants 'M' and 'b' were 3.84 × 10^-5 mol/g and 3.5 × 10⁴ dm³/mol, respectively. A sorption free energy (E) of 12.9 kJ/mol indicated chemisorption. The numerical values of the thermodynamic parameters ΔH, ΔS and ΔG indicated that sorption was spontaneous and exothermic in nature. The Scatchard equation was tested as a means of evaluating the binding sites of PUF with Hg(II). The stability constants for sorption were determined and the sorption mechanism was discussed.