Behaviour of Critical Metals During Smelting of Copper Concentrates from Olympic Dam Plant, South Australia
Date
2025
Authors
Gezzaz, Hassan
Editors
Advisors
Ciobanu, Cristiana
Cook, Nigel
Ehrig, Kathy
Cook, Nigel
Ehrig, Kathy
Journal Title
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Thesis
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Abstract
This thesis provides a comprehensive characterisation of slags produced during direct-to-blister copper smelting at Olympic Dam, South Australia. It aims at measuring and interpreting the content and behaviour of selected critical elements in slags,: rare earths elements (REE), Co, Ni, Ti, Nb, and V. Whereas Co and Ni are inherently present as minor elements within Cu-(Fe)- sulphides, these minerals are intrinsically intergrown with REE-U-bearing minerals, as well as Fe-oxides containing minor/trace contents of Nb, V, and Ti, among other high field strength elements, in Olympic Dam ores. Two distinct solid slags are produced under oxidizing (flash furnace; FF) and reducing conditions – phases crystallized at the quartz-magnetite-fayalite buffer (electric furnace; EF). By employing micron- to nanoscale analytical techniques combined with modellingcomputational methodologies, this work addresses the composition of all solid phases, the crystal chemistry of crystallized compounds (magnetite, delafossite and monazite), as well as slag evolution in terms of phase assemblages and textures. Energy loss measurements of Fe-L3 edge shift between atom columns into specific cation sites within EF magnetite show this has one of the lowest inversion parameters (i=0.72), compatible with formation at 1300°C and rapid cooling (dendritic growth). Results allow calculation of interchange enthalpy and constraints on the site occupancy preferences of minor elements in EF magnetite. In FF slag, ubiquitous inclusions of delafossite grow epitaxially with the magnetite host. In EF slag, magnetite displays Si-rich defects (silician magnetite) along {110} twin sets. Microstructural evolution of the system Cu-Fe-O during cooling of FF slag is assessed from mineralogicalpetrological study of Cu-rich magnetite, delafossite and associated phases. Microanalyses of phases from both slags reveal the ubiquitous presence of monazite, REE-rich Si-Fe-glasses, and critical metals (Co, Ni, Ti, Nb, V) incorporated within main slag phases. Constraints on critical metal behaviour in Si-Fe-rich melts come from fitting parabolas obtained by applying the lattice strain model to experimental values of calculated partition coefficients. Significantly, REE concentrations in Si-Fe-rich glasses, up to 6.8-6.2 wt.% if contained monazite is added, exceed those found in natural silicate melts, underscoring the potentially significant role of Fe in concentrating REE in terrestrial melts. Predictions of REE immiscibility in Si-Fe-rich melt based on the presence of amorphous ‘monazite-like’ droplets within lanthanide-rich glasses is consistent with experiments showing that silicate and Fephosphate melt immiscibility promotes REE enrichment in Fe-rich silician melts. Analytical work is complemented by thermodynamic modelling of three binary subsystems in the Ce-Si-P-O system using the CALPHAD approach, using input from published experimental data. This leads to refinement/prediction of the Ce2O3-P2O5 phase diagram for which experimental data is scarce even if this chemical system is highly relevant for monazite precipitation from slag melts. Formation of monazite in equilibrium with CeP3O9 is predicted, coexisting with SiO2 polymorphs from a cerium-phosphorus oxide melt with a composition of 80 wt.% SiO2, 10 wt.% Ce2O3, and 10 wt.% P2O5. This overview of the qualitative and quantitative behaviour of critical metals during the cooling of copper smelter slag under two redox environments is significant for ore petrology and also provides a knowledge basis for future attempts at recovery of critical metals, notably REE, from slags.
School/Discipline
School of Chemical Engineering
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering, 2025
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