Rapid Separation of Copper Phase and Iron-Rich Phase From Copper Slag at Low Temperature in a Super-Gravity Field
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UCTION
COPPER slag, a main by-product produced in the conversion of copper matte during the copper pyrometallurgy process[1] is a secondary resource of Cu-Fe. The annual output of copper slag has increased to more than 1.5 million tons in China alone[2,3] with the rapid development of the copper industry. Moreover, a large amount of converter slag and leaching residue is produced in other steps of the copper pyrometallurgy process.[4,5] The copper slag from the traditional copper smelting process contains up to 4.5 wt pct of copper,[6,7] and about 50 wt pct of iron. The copper is dispersed in various phases, which are generally small and have a complex interfacial combination of copper phases[2,3]). Hence, less than 12 pct of the copper slag is generally used, while the remainder is discarded in landfill, resulting in a huge waste of valuable metal resources and severe environment pollution.[8]
XI LAN, JINTAO GAO, ZILI HUANG, and ZHANCHENG GUO are with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing, 100083 P.R. China. Contact e-mail: [email protected] Manuscript submitted September 15, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
Several technologies have been proposed to recover metal resources from copper slag, including physical separation,[9] hydrometallurgy,[10,11] and pyrometallurgy methods.[12] In the copper slag, various copper matte and metallic copper phases are present as fine droplets, while iron exists in the form of fine magnetite (Fe3O4) particles discretely distributed among the slag. The conventional beneficiation methods cannot easily and efficiently separate the copper and iron from the copper slag due to the fine phase microstructures.[9] Generally, mineral processing methods have been commonly employed for the pre-treatment of copper slag, rather than the direct recovery of metal resources from the slag.[13] In addition, hydrometallurgy methods for recovering copper resources from the copper slag can be classified according to the material used to leach the metals, e.g., sulfuric acid, chlorination, ammonia, and microbial leaching methods. The disadvantages of such methods, include the large amounts of leachate used, slow leaching rate, long production cycle, and environment pollution.[14] In pyrometallurgy methods, liquid-liquid separation of liquid metal and molten slag via ‘‘free sedimentation’’ has been used to separate copper resources from copper slag. However, the driving force generated by the difference in density between the liquid metal (e.g., copper-containing phases) and molten slag is insufficient to effectively overcome the large interfacial tension
between the two phases. Therefore, it is difficult to coalescence and subsequently separate the fine copper droplets from the slag melt under conventional conditions.[15] Moreover, the large amount of fine magnetite particles formed during cooling of copper slag increased the melting point and viscosity of the slag phase,[16] which hinder sedimentation of fine copper droplets. Hence,
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