Copper Smelting Slag Cleaning in an Electric Furnace by Using Waste Cooking Oil
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INTRODUCTION
THE process of smelting combined with converting is becoming the main technology for blister copper production. Modern smelting technology injects oxygen-enriched air into the melt for efficient production of high-grade matte, and magnetite is inevitably precipitated in the melt as a result, leading to the increase in copper content of the slag.[1] Therefore, copper slag cleaning is a critical process to reduce copper loss and improve copper recovery simultaneously. Copper slag cleaning using the flotation method and/or in an electric furnace is widely adopted in industrial production.[2–5] The flotation method has the advantages of low energy consumption and low copper content in the slag,[4] but the waste liquid treatment after flotation has always been an issue. Due to the simple process and high production efficiency, copper slag cleaning in an electric furnace is also favored in the copper industry.[3] Local conditions (including the economic and environmental strategy), practical experience and smelting furnace characteristics should be considered for selecting the slag cleaning method.
YONGGANG WEI is with the State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, P.R. China. Contact email: [email protected] TIFU ZHANG is with the Yimen Copper Co., Ltd., Yuxi 651100, P.R. China. BO LI and SHIWEI ZHOU are with the Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, P.R. China. Manuscript submitted May 20, 2020; accepted September 22, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
The ISASMELT furnace is a typical representative smelting technology, which has the characteristics of continuous production and periodic discharge of matte. Because the matte and slag are tapped simultaneously from the same taphole, the slag cleaning furnace becomes the necessary equipment to promote separation of the matte from the slag. Too much magnetite content in the slag is the critical factor to hinder the matte particle settling,[1] which makes it necessary to add an appropriate amount of reductant to the melt during the process of slag cleaning in the furnace. Based on the physicochemical reaction of the melt, the process of copper slag cleaning in an electric furnace could be divided into two steps: reduction and settling. In the reduction stage, excessive magnetite is reduced to provide favorable conditions for the settling. Natural gas, coal, coke, petro-diesel, ferrosilicon, etc., were used as reductants to realize the objective conventionally,[2] all with different degrees of success. In terms of resource characteristics, non-renewability seems to be their common defect, and they would emit additional environmentally unfriendly gases (CO2, SO2) during the reduction process. Furthermore, the ash in the coal and coke also enters the slag phase to increase the slag amount, and the total copper loss is increased as a result. The use of biomass energy as an alternative s
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