Study of Phase Relations of ZnO-Containing Fayalite Slag Under Fe Saturation
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SECONDARY copper refers to all the non-primary copper resources, including metallurgical residuals, industrial wastes, and consumer scraps.[1] It was estimated that previous to 2014, up to 150 million tons of copper were landfilled as waste, and the end-of-life copper was generated at about 10 million tons per year.[2] Considering the continuously growing demand of the copper, production from secondary resources is of great importance. As a by-product of the secondary copper smelting process, an iron silicate-based slag (it is common that this slag also contains significant ZnO and traces of CaO and Al2O3) is formed in the smelter and has to be tapped out at the end of the process. The viscosity of the slag is utmost importance for the smooth operational practice. Numerous problems are introduced by the high viscosity of the slag, including high copper loss and the blocking of the tapping hole, which are often encountered in the secondary copper smelting process, especially for the high ZnO-containing slag. Although the effect of temperature and slag composition on the viscosity of FeO-SiO2 slag under iron saturation has been experimentally investigated,[3] the effect of ZnO additions on the viscosity of this slag has not been clarified. Moreover, as the slag viscosity is related to the slag composition and thereby to the phase relations (e.g., HUAYUE SHI and LIUGANG CHEN, Ph.D. Students, ANNELIES MALFLIET and PETER TOM JONES, Senior Researchers, BART BLANPAIN, Full Professor, and MUXING GUO, Senior Researcher Expert, are with the Department of Materials Engineering, KU Leuven, Leuven, Belgium. Contact e-mail: muxing. guo@mtm. kuleuven.be Manuscript submitted April 6, 2016. Article published online June 15, 2016. 2820—VOLUME 47B, OCTOBER 2016
whether the solid precipitation presents in the slag melt has a great influence on the viscosity), it is firstly important to know the thermodynamics of the slag system within the temperature range of the secondary copper smelting process. As the fundamental of most non-ferrous metallurgical slags, the binary system FeO-SiO2 was systematically investigated since the 1930s.[4] The phase relations in the Fe-Zn-O-Si system with iron saturation was recently experimentally investigated by Jak.[5] Based on the experimental data, the liquidus surface at the temperature range of 1473 K to 1873 K (1200 °C to 1600 °C) was calculated, showing the primary fields of fayalite, willemite, wustite, tridymite, and zincite. The ZnO‘‘FeO’’-CaO-SiO2 system at temperature range from 1273 K to 1573 K (1000 °C to 1300 °C) has been previously investigated at metallic iron saturation for CaO/ SiO2 = 0.33, 0.71, 0.93, and 1.2.[6,7] The effect of Al2O3 on the slag liquidus has been investigated with respect to a number of sections of the form ZnO‘‘FeO’’-(Al2O3 + CaO + SiO2) with (CaO + SiO2)/ Al2O3 weight ratios from 3.5 to 7.0 and CaO/SiO2 weight ratios from 0.55 to 0.93 in equilibrium with metallic iron.[8] The effect of Al2O3 was also reported by Zhao that it not only decreases the liquidus temperature of
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