Monomethylolated Thiourea – Sawdust as a New Adsorbent for Removal of Hg (II) from Contaminated Water: Equilibrium Kinetic and Thermodynamic Studies

Abstract

Sawdust (SD), a very low cost material, has been utilized as adsorbent material for the removal of Hg (II) from aqueous solutions after treatment with mono methylol thio urea (MMTU) in presence of zinc chloride as catalyst to form MMTU-SD. The reaction of MMTU-SD was carried out under different conditions including MMTU/ SD molar ratio, catalyst concentration, and reaction time and temperature. The MMTU-SD samples were characterized by estimating the nitrogen content. The ability of MMTU-SD to adsorb Hg (II) was investigated by using batch adsorption procedure. The effects such as pH, contact time, adsorbate concentration and adsorbent dosages on the adsorption capacity were studied. Langmuir, Freundlich, Temkin, and Redlich–Peterson isotherm models were applied in the adsorption studies at different temperatures. The experimental data were analysed using different adsorption kinetic models viz., the pseudo-first and second-order equations, Bangham's equation,intraparticle diffusion, Elovich and Bhattacharya–Venkobacha models. Results show that the pseudo-second-order equation provides the best correlation for the adsorption process. The adsorption experiments indicated that the MMTU-SD particles have great potential for the removal of Hg (II) from aqueous solution. The maximum adsorption capacity (Q_max) of the MMTU-SD towards Hg (II) ions was found to be 1000, 1000, and 1100 mg/g at 30, 50, and 60°C, respectively. Similarly, the Freundlich constant, n values were found to be 4.258944, 4.492363, and 5.293806 at 30, 50, and 60°C, respectively. The thermodynamics constants of the adsorption process: ΔH, ΔS and ΔG were evaluated.