Abstract
An experimental study on the phase equilibrium and the liquidus isotherms for the PbO-ZnO-CaO-SiO2-Fe2O3 system with CaO/SiO2 in 1.1 and PbO/(CaO+SiO2) in 2.4 weight ratios, respectively, was carried out in the temperature range 1100-1300oC (1373-1573 K). High temperature phases were determined by the equilibrium-quenching method. Results are presented in the form of pseudo-ternary sections Fe2O3-ZnO-(PbO+CaO+SiO2). X-Ray diffraction (XRD) and SEM-EDS results showed that the phase equilibria in this system are dominated by the high melting temperature spinel and zincite phases. It was observed that if the system is at a temperature below 1300oC and the total (Fe2O3 + ZnO) is greater than 20 wt%, spinel and/or zincite will be present in the slag system. As an application of the phase diagram, the liquid phase compositions below the liquidus surface were estimated, then their viscosities were calculated using FACTSage software.
Highlights
Metallurgical slags have a relevant role to play in the extraction and refining of metals
Efficient fluxing requires the knowledge of phase relationships in the slag, and these may be represented graphically on phase diagrams
About 20 g of each slag sample were homogenized and equilibrated in platinum crucible (25 mm inner diameter and 35 height) in air in two steps, the first involving the melting of the sample at 1300oC over 6 h, and the second equilibration at the predetermined temperatures of 1300, 1200 and 1100oC over 4 h
Summary
Metallurgical slags have a relevant role to play in the extraction and refining of metals. They are formed by fluxes, added to or included in the charge, which produce a slag with a low melting point. Efficient fluxing requires the knowledge of phase relationships in the slag, and these may be represented graphically on phase diagrams. Zhao[1] has explained that among the various methods for phase diagram determination, the equilibrium-quenching-analysis method is helpful to constructing isothermal sections. This method is based on keeping the high-temperature phase equilibria at room temperature by quenching. The method is appropriate for investigating systems in which the phase transitions are sluggish, and long-term homogenization is needed, such as with silica based slags
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