New Slag for Nickel Matte Smelting Process and Subsequent Fe Extraction
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I.
INTRODUCTION
IN the nickel pyrometallurgical process, large amounts of slag with high iron oxide content are produced. Take Jinchuan Nonferrous Metal Co. (JNMC) as an example; 1.6 million tons of residual slag with about 40 pct Fe is discharged annually. The accumulated deposit of nickel residual slag will be up to 41 million tons this year.[1,2] The nickel residue slag contains not only plenty of Fe and gangue components, but also small amounts of nickel, copper, cobalt and other valuable metals. Therefore, it has great potential to become a recycled secondary resource. However, how to use it properly is still a problem. To date, most of these residues have been stockpiled. This causes environmental problems and wastes valuable metal components. Therefore, it is essential to find an effective way to use these residues.[1,3,4] Relevant work had found that the iron phase in nickel residues is mainly in the form of 2FeOÆSiO2, which is JUNXUE ZHAO, ZHONGYU ZHAO, YARU CUI, RUIMENG SHI, WENDAN TANG, XIAOMING LI, and NAN SHANG are with the School of Metallurgical Engineering, Xi’an University of Architecture and Technology, Xi’an 710055, P.R.China. Contact e-mail: [email protected]; [email protected] Manuscript submitted June 7, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS B
produced by SiO2 addition as flux during slag formation in the nickel smelting process.[1–3] Due to the poor magnetic separation character and reducibility, it is difficult to extract iron from the residual slag and use it effectively. Much work had been done on the recovery of Fe from residual slag produced by the smelting process.[4–9] In these works, the direct reduction and smelting reduction processes were usually used to extract the Fe or ferrosilicon alloy. But, in fact, there has been no substantive breakthrough because of the poor reducibility of 2FeOÆSiO2 and the lower Fe content in residue slag; as a result, enormous amounts of slag are produced in the smelting reduction process. To make sure the direct reduction or smelting reduction process can be carried out, it can consume large amounts of calcium flux and energy, making the process economically unfeasible. Therefore, a practicable process needs to be found to solve the above-mentioned problems and make full use of nickel residual slag.
II.
PRACTICAL FLOW SHEET ANALYSIS AND POSSIBLE BREAKTHROUGH
A. Flow Sheet of the Nickel Flash Smelting Process in JNMC The flow sheet of nickel flash smelting (Outokumpu nickel smelting furnace) at JNMC is shown in Figure 1. Two kinds of nickel residual slags are produced in the flash smelting process, piling up to 0.63 million tons per year. In addition, about 0.92 million tons of residual slag are produced per year from another process, i.e., the oxygen top-blowing furnace (Ausmelt nickel smelting furnace), with a similar chemical composition of nickel residual slags. The chemical composition of the residual slag in JNMC nickel flash smelting is listed in Table I; the main components are Fe, MgO and SiO2, and the main phase is (Fe,Mg)2SiO4 (about 71.
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