Thermochemistry Study for BHP Olympic Dam Copper Electric Slag Cleaning Furnace Optimization

Characterisation of thermochemistry of iron in blister and copper in slag in the copper electric slag cleaning furnace is important to improve copper slag processing in BHP Olympic Dam direct-to-blister process. Phase equilibria investigation in the “CuO_0.5”–“FeO”–MgO–SiO₂ system in equilibrium with copper metal was undertaken using a high-temperature equilibration, quenching, and electron probe microanalysis (EPMA) technique integrated with thermodynamic modelling using FactSage computer package. Experiments were conducted at conditions relevant to the industrial electric furnace operation, at 1300 °C and log (pO₂) = −5, −6, −7, −8, −9, −10, and in equilibrium with iron metal. The experimental results are used for optimization of the thermodynamic database of the system. Furthermore, an industrial electric furnace slag sample was collected and analysed systematically, including analysis of macro and micro-features, phase identification and measurement, and FactSage prediction. The microanalysis of the electric furnace slag samples was compared to the currently available thermodynamic database. Phase equilibria findings showed that copper concentration in slag and iron partitioning in blister are greatly influenced by oxygen partial pressure, and the thermodynamic model agrees reasonably with the experimental results. Microanalysis of the industrial electric furnace slag sample suggested differences between the industrial slag phases and chemical partitioning compared to the currently available thermodynamic database. Differences are analysed, and possible causes are found to be non-equilibrium condition in furnace related to kinetic factors and analytical uncertainties in EPMA.