XXV INTERNATIONAL MINERAL PROCESSING CONGRESS (IMPC) 2010 PROCEEDINGS / BRISBANE, QLD, AUSTRALIA / 6 - 10 SEPTEMBER 2010 263 INTRODUCTION Precious metals, such as gold and platinum, apart from the traditional uses, have found new applications in electronics, chemical and environmental catalyses, medicine and life sciences, hydrogen storage and separation, and other industrial applications (Lam, Fong and Yeung, 2007) in recent years. Considering this growing demand coupled with the declining resources available, efficient recovery of precious metals from secondary sources (ie electronic wastes and spent catalysts) and primary sources, such as leach liquors, has become an important technology and research interest. The hydrometallurgical technique still remains as a standard method for metal extraction from ores and is substantially considered in many metal recycling processes where metal contents are usually present in minimum amounts, due to its simpler operation, lower cost requirement, and relatively well-purified products with minimal loss of target metals (Lam, Fong and Yeung, 2007; Wiraseranee et al, 2008). Precious metals, especially Au, are usually extracted from their ores using cyanide. Although cyanide is an effective leaching agent, its use poses threat to mankind and the environment due to its toxicity. Due to this, safer and more environmental-friendly leaching agents, such as chloride and thiosulfate solutions, have been developed and introduced as alternatives to the toxic cyanide (Aylmore, 2005). Separation and recovery of the dissolved precious metals in the 1. Division of Solid Waste, Resources and Geo-Environmental Engineering, Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan. Email: richard@eng.hokudai.ac.jp 2. Professor, Division of Sustainable Resources Engineering, Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan. Email: hiroyosi@eng.hokudai.ac.jp 3. Assistant Professor, Division of Solid Waste, Resources and Geo-Environmental Engineering, Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan. Email: itomayu@eng.hokudai.ac.jp 4. Professor, Division of Solid Waste, Resources and Geo-Environmental Engineering, Graduate School of Engineering, Hokkaido University, Kita 13, Nishi 8, Kita-ku, Sapporo 060-8628, Japan. Email: tunekawa@eng.hokudai.ac.jp RECOVERY OF PRECIOUS METALS FROM CHLORIDE SOLUTION BY MAGNETITE R Alorro 1 , N Hiroyoshi 2 , M Ito 3 and M Tsunekawa 4 ABSTRACT The development of environmental-friendly lixiviants as alternatives to cyanide and the increasing recycling activities to recover precious metals from waste materials have prompted researchers to find efficient methods and alternative sorbents to recover precious metals, such as Au and Pt, from aqueous solutions. This study explored the use of magnetite (Fe 3 O 4 ) as a sorbent to recover Au and Pt from chloride solutions. Magnetite is a semiconductor and has the capability of transferring electrons both within the solid state and across the solid-liquid interface and has the ability to reduce metal species on its surface. The sorption of AuCl 4 - and PtCl 6 2- from NaCl solution on commercial grade magnetite powder was investigated by batch-sorption experiments. The effects of pH, contact time, NaCl concentration and precious metal concentration on the recovery were studied. Sorption experiments revealed that magnetite exhibited selectivity towards other metals with the strongest affinity for Au. Both Au and Pt recoveries showed similar pH dependence curves, with peaks at pH 6 - 7. At this pH range, a maximum of 4.4 μmol Au/g Fe 3 O 4 and 3.0 μmol Pt/g Fe 3 O 4 were recovered after 24 h at an initial metal concentration of 0.05 mol/m 3 . Increasing the initial precious metal concentration increased the Au and Pt uptake amount by magnetite. It was also observed that the recovery decreased with high NaCl concentrations. The SEM images of the magnetite particles after the treatment showed that gold, which was confirmed by the EDX analysis, agglomerated and were deposited on Fe 3 O 4 surface. Keywords: precious metals, magnetite, hydrometallurgy, sorbent