Thermodynamics of Palladium (Pd) and Tantalum (Ta) Relevant to Secondary Copper Smelting

The slag-to-metal distribution ratios of palladium (Pd), \( L_{\text{Pd}}^{s/m} \), in the range of oxygen partial pressure (pO₂) from 10⁻¹⁰ to 10⁻⁷ atm at 1473 K to 1623 K (1200 °C to 1350 °C); distribution ratios of tantalum (Ta), \( L_{\text{Ta}}^{s/m} \), in the range of pO₂ from 10⁻¹⁶ to 10⁻¹² atm at 1673 K and 1873 K (1400 °C and 1600 °C), have been determined in this study. The \( L_{\text{Pd}}^{s/m} \) in FeO _x -CaO-SiO₂-MgO and copper at 1573 K (1300 °C) and pO₂ = 10⁻⁸ atm is dependant strongly on basicity of slag, i.e. (CaO + MgO)/SiO₂ or optical basicity. The current results suggest that Pd presents in the FeO _x -CaO-SiO₂-MgO slag predominantly as Pd²⁺. The activity coefficient of PdO in the slag at 1573 K (1300 °C) and pO₂ = 10⁻⁸ atm was calculated to be in the range of 3.89 × 10⁻³ to 2.63 × 10⁻². The \( L_{\text{Pd}}^{s/m} \) was also found to increase with increasing of pO₂ and with decreasing of temperature. It was observed that Ta mostly partition to slag phase and very small amount of Ta was found in liquid copper at the high temperature and reduced condition studied. It can be suggested that to promote recovery of palladium from Pd-containing e-waste, a slag with lower silica content and basic flux based, high temperature with reducing atmosphere, is highly desired particularly in secondary copper smelting.