Adsorption of Au(III) in multi-metal systems Au/Cu/Ni on mercapto modified silica coated on magnetite (Fe 3 O 4 /SiO 2 -SH) has been studied. Fe 3 O 4 /SiO 2 -SH was synthesized via sol-gel process by using magnetite obtained through co-precipitation of Fe 2+ /Fe 3+ salt mixture with NH 4 OH as the precipitating solution, sodium silicate solution extracted from rice hull ash and 3mercaptopropyltrimethoxysilane (MPTMS) as the mercapto group source. Fe 3 O 4 /SiO 2 -SH was characterized with

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... er transform infrared (FTIR) spectrophotometer, X-ray diffraction (XRD) and ion chromatography for sulfur analysis. Optimization of Au(III) adsorption in a batch system was carried out as function of pH, contact time and ion concentration. Adsorption kinetics was evaluated with pseudo-first order and pseudo-second order models based on the data of contact time variation, while the adsorption isotherm was studied based on Langmuir and Freundlich models. The adsorbed metal ions Au(III), Cu(II) and Ni(II) quantitatively were calculated based on the difference of metal concentrations before and after adsorption analyzed with flame atomic absorbance spectrophotometer (FAAS). Results of characterization showed that Fe 3 O 4 /SiO 2 -SH has been successfully synthesized. Adsorption of Au(III) on Fe 3 O 4 /SiO 2 -SH slightly decreased with increasing the pH in a range of 2.0-6.0 and fits to pseudo-second order model with the rate constant of 1.37x10 -3 g mg -1 min -1 . Fe 3 O 4 /SiO 2 -SH shows a linear plot of Langmuir isotherm model with adsorption the capacity for Au(III) of 125 mg/g. Adsorption on multimetal systems shows that capacity of Au(III) on Fe 3 O 4 /SiO 2 -SH is higher than that of Cu(II) and Ni(II), and high selectivity for Au(III) toward Cu(II) and Ni(II) ions.