Recovery of gold(III) ions by a chitosancoated magnetic nano-adsorbent

The monodisperse chitosan-coated Fe₃O₄ nanoparticles with a mean diameter of 13.5 nm and 4.92 wt% chitosan were used as an anionic magnetic nano-adsorbent for the recovery of Au(III) ions from aqueous solutions. It was found that Au(III) ions could be fast and efficiently adsorbed, and the adsorption capacity increased with the decrease in pH due to the protonation of the amino groups of chitosan. The adsorption data obeyed the Langmuir equation with a maximum adsorption capacity of 59.52 mg/g (1210 mg/g based on the weight of chitosan) and a Langmuir adsorption equilibrium constant of 0.066 l/mg. From the studies on the adsorption kinetics and thermodynamics of Au(III) ions, it was found that the adsorption process obeyed the pseudo-second-order kinetic model. Furthermore, the time required to reach the equilibrium was significantly shorter than those using the micro-sized adsorbents due to the large available surface area.