Kinetic Investigation of Silica Gel Chemically Modified by Ethylenediamine Bis(Methylene Phosphonic Acid) for Adsorption of Au(Iii)

Abstract

A novel hybrid material, silica gel chemically modified by ethylenediamine bis(methylene phosphonic acid) (denoted as SH-E-P), has been developed, and FT-IR analysis demonstrated that methylene phosphonic acid groups had been grafted successfully onto the surface of the silica gel. A detailed kinetic investigation of the adsorption of Au(III) onto SH-E-P is reported in this study. The results showed that SH-E-P could reach its saturation adsorption capacity within 4h, with an excellent adsorption capacity for Au(III) of 453.83 mg g⁻¹ when the initial solution concentration was 2.0 mmol L⁻¹ at 35°C. Moreover, the adsorption kinetics can be closely modelled by a pseudo second-order rate equation. The thermodynamic parameters ΔG, ΔH and ΔS were - 19.52 kJ mol⁻¹, 4.84 kJ mol⁻¹, and 79.43 J K⁻¹ mol⁻¹, respectively. It can be concluded that the adsorption of Au(III) on SH-E-P is a spontaneous, endothermic process controlled by film diffusion, which results in its higher adsorption capacity at higher temperatures.