Mineral Liberation of Magnetite-Precipitated Copper Slag Obtained via Molten Oxidation by Using High-Voltage Electrical
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INTRODUCTION
COPPER smelter slag is the main solid waste generated from copper smelting. Owing to recent overcapacity of the cement industry, which has the highest demand for copper slag, secondary reuse and hence technology development of recycling, has become essential.[1] Metal extraction has always been a focus in the study of its reutilization, and many processes have been developed, including mineral processing (flotation) and pyro- and hydro-metallurgical ways.[2] The high cost and environmental concerns retard the large-scale practical applications of copper slag.[3] The isothermal transformation process[4] of copper slag revealed that high temperatures have a significant effect on magnetite incubation or nucleation. We proposed a molten oxidation process, which is based on directly blowing oxidizing gas onto/into the molten slag, which is an exothermic reaction (low-energy input achieved) immediately after copper smelting. During the process, most of the iron values are designed to be transformed into magnetite through controlling the oxygen partial pressure, thereby allowing downstream selective recovery of magnetite concentrate and low-iron-bearing tailing for specific purposes. During the molten oxidation process,[5] at various oxygen partial pressures, the relationship between the magnetite and the hematite was found to be a trade-off. Low-oxygen partial pressures were conductive for the
YONG FAN, PD Researcher, ETSURO SHIBATA and TAKASHI NAKAMURA, Professors, and ATSUSHI IIZUKA, Assistant Professor, are with the Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Sendai 980-8577, Japan. Contact e-mail: [email protected] Manuscript submitted April 16, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS B
precipitation of magnetite. In particular, the use of 1 vol pct oxygen resulted in significant dependence of magnetite precipitation and limited the occurrence of hematite. However, the study was conducted via a milligram scale experiment by using an infrared furnace. In general, studies of mineral liberation and separation must be performed on gram-scale slag samples, owing to the experimental. Therefore, in the present study, gram-scale slag samples were prepared in the first place by using an electric furnace. Based on our proposal, molten oxidation under 1 vol pct oxygen was performed to realize magnetite precipitation. Afterward, the preroasted magnetite-precipitated copper slag was used for mineral liberation and separation experiments. Mineral liberation plays a vital role in the entire recycling process, and it is the key to improving the downstream separation effects. The conventional crushing technology such as jaw crushers, double rolls, gyratory, and cone crushers, which are capable of reducing the ore lumps from several hundreds of mm to several mm, and the grinding technology such as a ball mill and a rod mill could reduce the crushed fragments into a micron scale for further processing. High-voltage (HV) electrical pulses can be also used for the l
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