Phase Equilibrium Studies of Iron Silicate Slag in the Liquid/Spinel/White Metal/Gas System for Copper Converting Proces
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ch the matte (Cu-FeS) produced from the smelting process is further oxidized into the blister copper (98.5 to 99.5 wt pct Cu, O < 1 wt pct and S < 0.1 wt pct), accounts for one key step in the pyrometallurgical copper-making process. The converting process is mostly performed in the Peirce-Smith converter, and operates as a batch process in the temperature range 1473 K to 1573 K (1200 C to 1300 C).[1–3] Generally, the converting process can be divided into two stages: slag-forming stage and copper (blister)-making stage. In the slag-forming stage,[2–4] FeS from the matte is oxidized to FeO and Fe3O4, which form slags with the added flux, while S turns into SO2. The product of this stage is impure Cu2S (contains low Fe content, Fe < 1 wt pct), generally named as white metal.[2,3] The second stage involves the further oxidation of Cu2S to produce blister. In the converting
YONGQI SUN, MAO CHEN, and BAOJUN ZHAO are with the School of Chemical Engineering, The University of Queensland, Brisbane 4072, Australia. Contact e-mail: [email protected] ZHIXIANG CUI is with the Dongying Fangyuan Nonferrous Metals, Dongying 257000, P.R. China. LEONEL CONTRERAS is with the National Copper Corporation of Chile, Huefanos 1270, Santiago, Chile. Manuscript submitted October 30, 2019. Article published online February 18, 2020. 426—VOLUME 51B, APRIL 2020
process, SiO2 is commonly added as the fluxing agent to form iron silicate slags with the iron oxides. Due to the high oxygen potentials in the converting processes, the converting slags normally contain high contents of dissolved copper oxides, which is dominantly present as Cu2O.[1–3] In most of the industrial operations, the slags are tapped out of the Peirce-Smith converter at the end of the slag-forming stage, and the high Cu-containing converting slags will be cleaned through different slag cleaning processes.[5,6] Converting slags with low Cu content will significantly reduce the load of the slag cleaning process, and receive dramatic financial benefits. The properties of the converting slags are also important to control the impurities of the blister, and corrosion of the furnace refractories. In the slag-forming stage of the converting process, nowadays, the slags are in contact with white metal and SO2-containing gas atmosphere, while solid spinel may be present in the slags. The slags and gas compositions, and operating temperature control the spinel solid proportion, and concentration of Cu2O in the slags. Therefore, it is vital to investigate the slag chemistry to obtain the optimum liquidus temperature, and Cu2O content of slags to have an operatable fluidity of slags, and low copper content in the slags. However, a few studies were focused on the phase equilibria in the silica primary phase field,[7,8] and the gas compositions (P(O2) and P(SO2)) were not accurately controlled. No experimental study has been found in the spinel primary phase field with fixed gas compositions. In the present study, the phase equilibria of iron silicate slags were investigated under the convertin
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