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621920 
Journal Article 
Leaching of gold and palladium with aqueous ozone in dilute chloride media 
Viñals, J; Juan, E; Ruiz, M; Ferrando, E; Cruells, M; Roca, A; Casado, J 
2006 
Yes 
Hydrometallurgy
ISSN: 0304-386X 
81 
2 
142-151 
Abstract: The recycling of gold and palladium from metallic scraps can be carried out by ozone-leaching at ambient temperature and low (∼0.1 M) H+ and Cl− concentrations. Rh and Pt remain un-reacted, whereas metals such as Cu, Ni, Ag, can be previously eliminated through O2/H+ and O2/O3/H+ leaching pretreatments. Gold and palladium are dissolved in O3/Cl−/H+ with formation of AuCl4 − and PdCl4 2−. Leaching studies showed a passive region, basically located at <0.01 and <0.05 M Cl− for Au and Pd, respectively. In the non-passive region, rates were only slightly dependent on either H+ and Cl−. Secondary formation of chlorine or hypochlorous acid was negligible at ≤0.1 M Cl−. Kinetics appeared to be controlled by mass transfer of O3(aq) to the solid–liquid interface, showing first order dependency with respect to [O3]aq. Rates increased with temperature up to about 40 °C, but decreased at higher temperatures due to the fall in the O3 solubility. The ozone mass transfer coefficients showed an activation energy <20 kJ/mol. Gold leaching rate gradually diminished for pH>2, as consequence of the influence of the [H+] on transfer control. The electric power consumption associated with O3 generation was in the range 4–8 kWh/kg metal leached. [Copyright 2006 Elsevier] Copyright of Hydrometallurgy is the property of Elsevier Science Publishers B.V. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) 
LEACHING; PALLADIUM; AIR -- Pollution; SOLUTION (Chemistry)