Thermodynamics of Indium Dissolution Behavior in FeO-Bearing Metallurgical Slags

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INDIUM (In) represents a minor percentage of the earth’s crust. Its concentration is comparable to that of silver, which is about 0.1 mass ppm, and ranges from 50 to 200 ppb in the earth’s crust. The average indium content in zinc deposits ranges from less than 1 to 100 ppm.[1] Indium is usually produced as a minor by-product in the lead and zinc smelting and refining processes. It is a rare and valuable metal that is used in a variety of industrial applications, such as liquid crystal displays (LCDs), semiconductors, low-temperature solders, infrared photodetectors, and solar cells.[2–4] Indium production has declined from over 600t in 2007 to around 520t in 2009.[5,6] In 2009, China produced just over half of the total world indium output. Because the demand for indium is increasing, an interest in recycling In-containing materials has developed. Indium is most commonly recovered from indium tin oxide sputtering targets, LCD screens, and other sources.[7,8] Recently, pyrometallurgical recycling of Incontaining materials has been issued in view of ‘Urban Mining’ due to the high cost and scarcity of indium.[9,10] The literature contains only three experimental studies of pyrometallurgical processing. Johnson et al.[11] measured the distribution of In between molten Pb and SiO2-CaO-MgO-FeO-PbO-Al2O3 slag at 1473 K YUN SOON HAN, Graduate Student, and JOO HYUN PARK, Professor, are with the Department of Materials Engineering, Hanyang University, Ansan 426-791, Korea. Contact e-mail: [email protected] Manuscript submitted April 28, 2014. Article published online October 15, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B

(1200 °C) under an oxygen partial pressure of pO2 ¼ 1012 atm using a CO-CO2 gas mixture. The In distribution ratio (Lm/s In ) between metal and slag, i.e., [mass pct In]metal/(mass pct In)slag, was approximately increased by increasing the basicity 50. The Lm/s In (=(CaO+MgO)/SiO2) and was independent of the FeO/SiO2 ratio.[11,12] Another study, performed by Hoang and Swinbourne,[12] examined the In distribution between molten Pb and FeO-CaO-SiO2-8 mass pct Al2O3 slag at pO2 ¼ 1012 to 1010 atm. The Lm/s In was a function of the FeO/SiO2 ratio and was independent of the CaO/ SiO2 ratio, and the highest In distribution ratio occurred for slag richest in FeO.[12] Because these two studies tested improvements of indium recovery under lead smelting conditions, the results are hard to apply directly to the pyro-recycling treatment of In-containing materials. Moreover, the experimental results for the effect of slag composition on indium dissolution behavior in FeO-bearing metallurgical slags are controversial, as mentioned above. Finally, these experiments did not establish an indium dissolution mechanism. Therefore, we recently investigated the indium dissolution mechanism in synthetic CaO-SiO2-Al2O3 slag under a strongly reducing atmosphere, i.e., pO2 ¼ 1017 to 1016 atm, at 1773 K (1500 °C).[13,14] CaObearing slags have compositions close to blast furnace slags (BFS) and ladle furnace slags (LFS).

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