Crystallization Behavior of Copper Smelter Slag During Molten Oxidation
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INTRODUCTION
IN the copper smelting industry, nearly 30 million tons of smelter slag is estimated to be produced every year in the world.[10] The recent overcapacity of the cement industry in the developed markets has been causing increasingly serious concern, thereby necessitating the urgent utilization of slag. Most of the slag in developing countries is dumped without being fully recycled, which causes serious environmental pollution and is a huge waste of resources. Copper slag is composed mainly of iron silicates [(Fe, Al, Ca, Mg,)x SiOy] obtained by smelting copper concentrate and silica flux. One of the most important criteria for the utilization of this secondary resource is the recovery of iron from the slag matrix, which has a concentration of nearly 40 mass pct that could effectively decrease the volume of the dumped slag. Several lab-scale studies have been performed for recycling iron from copper slag, such as the multistage grinding-mineral process, smelting reduction, sulfation method, and many hydrometallurgical methods.[2] In the current study, the molten oxidation process followed by crushing and magnetic separation is shown to be a more sustainable approach that is based on directly blowing oxidizing gas onto the molten slag after
copper smelting. During this process, most of the nonmagnetic iron components were designed to be transformed into magnetite, which allows selective recovery of iron-bearing and non-iron-bearing slag constituents for specific purposes. In a previous study,[3] the time–temperature–transformation diagram of copper slag was obtained for the isothermal transformation into magnetite precipitates between 993 K and 1493 K (720 C and 1220 C) under the atmosphere of air. Further, it was observed that, under isothermal procedures, high temperature was an effective factor for magnetite incubation or nucleation. Therefore, in the current study, the crystallization behavior during the molten oxidation process was studied to better understand the relationship between magnetite and hematite precipitations. Furthermore, the crystal morphology was examined using a laser microscope and Raman imaging system to understand the iron oxide transformation, and the distribution of impurities such as Cu, Zn, As, Cr, and Pb were complemented with scanning electron microscopy and energy dispersive spectroscopy. In addition, the reaction mechanism was investigated with a focus on the oxidation processes.
II. YONG FAN, Doctoral Student 3rd Year, is with the Graduate School of Environmental Studies, Tohoku University, 6-6-20 AramakiAza-Aoba, Aoba-Ku, Sendai, 980-8579, Japan. ETSURO SHIBATA and TAKASHI NAKAMURA, Professors, ATSUSHI IIZUKA, Assistant Professor, Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Aobaku, Sendai, 980-8577, Japan. Contact e-mail: [email protected]. ac.jp Manuscript submitted March 3, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
EXPERIMENTAL
The chemical composition of copper slag from a smelting furnace used in
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