Abstract
Studies on the direct reduction of carbon-bearing pellets made from discarded copper slag have been conducted in this paper. They include the influences of reduction coal content, limestone content, industrial sodium carbonate content, reduction temperature, reduction time and layers of carbon-bearing pellets on reduction effect. Finally, the optimum conditions have been obtained. The pilot scale experiment results show that the optimum conditions are the mass proportion of discarded copper slag, reduction coal, limestone and industrial sodium carbonate of 100:25:10:3, the reduction temperature of 1280 °C for the reduction time of 35 min, three layers (approximately 42 mm) of carbon-bearing pellets—this was the basis on which the pilot tests in a rotary hearth furnace (RHF) were conducted. The iron products obtained from the pilot tests under such conditions have an iron grade of 90.35% with an iron recovery rate of 89.70%. The mechanism research based on the analysis results of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) indicates that fayalite (2FeO·SiO2) and magnetite (Fe3O4) in the copper slag are reduced into metallic Fe in the direct reduction (DR) process, and the mass and heat transfer become stronger from the bottom to the top layer of the pellets, resulting in a rising iron recovery rate.
Highlights
At present, copper production in China mainly comes in a pyrometallurgical process
Mixed with the reducing agent and the additives, the copper slag is made into the carbon-bearing pellets (12–16 mm), which should be dried before being charged into a rotary hearth furnace (RHF)
The early tests indicated when◦ C, one layer ofthe pellets were under roasting, thecause highest reduction temperature could only be keptthat at 1200 because higher temperature could pellets melting, temperature could onlyto bethe keptRHF
Summary
Copper production in China mainly comes in a pyrometallurgical process. Generally, for one ton of copper, 2.2 tons of discarded copper slag is generated, and in China, the amount of discharging copper slag exceeds 10 million tons per year [1], with the accumulated amount of copper slag over the years exceeding 120 million tons [2]. The above researches, whichrates areintechnically feasible, beenmodification done onlyareintoo thelow, bench test of the iron recovery direct beneficiation andhave oxidative whereas laboratory, but a lack of industrial equipment to process copper slag with coal-based. Production environment, while the rotary kiln for the DR process is usually applied in large-scale to the above researches, which are technically feasible, have been done only in the bench test of the laterite laboratory, nickel orebut reduction, which has negative effects on operation due to ringlet formation resulting a lack of industrial equipment to process copper slag with coal-based DR in large scale. The tunnel kiln features a low capacity, high energy consumption, and a severe production environment, while theobject rotaryofkiln for In the processthe is basic usually in domestic copper smelting plant as the study. Experimental and pilot plant tests have been conducted following the RHF DR and grinding/magnetic separation process flow, and the reduction mechanism has been analyzed
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