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I.

INTRODUCTION

THE present study of the CaO-ZnO-SiO2 system is a part of a wider research program aimed at characterization of phase equilibria and thermodynamic properties of the seven-component PbO-ZnO-FeO-Fe2O3-Cu2 O-CaO-SiO2 gas–slag–solid–metal system for the zinc/ lead/copper smelting industry using an integrated experimental investigations and thermodynamic modeling approach. This overall research program has already been described in previous publications of the present authors.[1] II.

LITERATURE REVIEW

[2]

Segnit conducted a study of the CaO-ZnO-SiO2 system using quenching of equilibrated slags with subsequent optical microscopy; no data on phase compositions were reported, except the bulk composition of the initial sample mixture. There was also no information on whether the solid compounds are stoichiometric or form solid solutions. Recently, Hansson[3] and Bonner[4] studied selected parts of the tridymite and dicalcium silicate (C2S) liquidus and

M. SHEVCHENKO and E. JAK are with the Pyrometallurgy Innovation Centre (PYROSEARCH), The University of Queensland, Brisbane, QLD 4072, Australia. Contact e-mail: m.shevchenko@ uq.edu.au Manuscript submitted June 18, 2019.

METALLURGICAL AND MATERIALS TRANSACTIONS B

detected solubility of about 5 mol pct Zn/(Zn + Ca + Si) in C2S = (Ca, Zn)2SiO4. Those data had significant scatter and some inconsistencies. From Reference 2 and the public FactSage database, the low-SiO2 range of the system was estimated to melt at temperatures > 1800 C, and therefore experimental study was not previously attempted. Recently, however, a eutectic between lime and zincite at 1535 C in the CaO-ZnO binary system was identified by Xia et al.[5]; addition of small amounts of SiO2 to this composition will lower the liquidus even further. Liquidus in the ZnO-SiO2 system has been determined by Bunting.[6] Several recent independent studies (Jak,[7] Zhao,[8] Hansson et al.[9] and Xia et al.[10]) determined zincite and tridymite liquidi ~ 100 C higher than the earlier work by Bunting.[6] Uncertainty still exists regarding the compositions of phases (cristobalite and two immiscible liquids) at the monotectic point (~ 1690 C). Liquidi in the CaO-SiO2 system have been studied by Rankin and Wright[11] and Osborn.[12] The lower temperature limit of the Ca3SiO5 stability was reported as 1250 C by Rankin and Wright,[11] 1300 C by Meyers[13] and Carlson,[14] ~ 1200 C by Zawadski and Gotlied[15] and 1300 C by Tromel et al.[16] There are contradicting reports on the upper temperature limit of stability of the Ca3SiO5 phase (1900 C by Rankin and Wright,[11] 2000 C by Zawadski and Gotlied,[15] 2070 C by Welch and Gutt,[17] 1800 C by Tromel et al.[16]), on the excess solubility of CaO in Ca2SiO4 and on liquidus < 40 mol pct SiO2. In particular, the reported melting temperatures of CaO are characterized by large discrepancy: 2572 C, Kanolt[18]; 2576 C,

Schumacher[19]; 2625 C, Doman et al.[20]; 2550 C to 2650 C, Schenck, extrapolated from CaO-MnO[21]; 2585 C, Noguchi et al.[22]; 29