The fast recovery of gold(III) ions from aqueous solutions using raw date pits: Kinetic, thermodynamic and equilibrium studies

The recovery of Au(III) ions from aqueous solutions employing raw date pits (RDPs) has been systematically investigated in this paper. The morphology, the specific surface area, and the functional groups of RDPs were analyzed using scanning electron microscopy, the methylene blue adsorption method, and FT-IR spectra, respectively. The adsorption of Au(III) onto date pits was achieved quantitatively (90% ± 3.4%) after 90 min of shaking in an aqueous medium containing 0.5 mol L−1 HCl. The process of gold(III) ion recovery using RDPs was described by the adsorption coupled reduction mechanism which includes adsorption of Au(III) ions onto RDP surface, followed by the reduction of Au3+ to Au. The kinetic data were studied using pseudo-first order, pseudo-second order and intraparticle diffusion models, and was found to follow closely the pseudo-second order model. The batch equilibrium data fitted well to the Freundlich and Langmuir isotherm models, and maximum adsorption capacity of RDPs for Au(III) was 78 ± 1.1 mg g−1 at 298 K which was relatively large compared to some adsorbents recently reported. Thermodynamic parameters, namely ΔG, ΔH, and ΔS, showed that the adsorption of Au(III) onto RDPs is exothermic, spontaneous, and chemisorption at low temperature.