Trace element distributions in black copper smelting

Black copper smelting is a flexible method for collecting several trace elements from e.g. WEEE fractions to the metal to be refined. Examples are precious and most platinum group metals which dissolve effectively in the molten copper phase of black-copper smelting. This is not the case with metals with small solubility in molten copper or in cases the element and its oxides are volatile. This paper presents experimental observations about iridium, rhenium and molybdenum and their distributions between molten copper and iron silicate slags rich in alumina. The experimental technique included laser ablation-inductive-ly coupled plasma-mass spectrometry as a very sensitive analytical tool for measuring trace elements in metallurgical slags at concentrations down to ≈1 ppbw (parts per billion by weight). Some limitations and sources of error of the analytical technique in this novel application will be discussed. The results indicate that copper is not the optimum medium for collecting molybdenum and rhenium from secondary raw materials, due to thermodynamic reasons, low solubility and high volatility, respectively. For iridium, very high distribution coefficients between copper and slag of L^Cu/s(Ir) = 10⁶ were measured in reducing conditions, below P(O₂) = 10^-6 atm.Grant: CLIC Innovation Oy and Tekes supported this research trough ARVI programme. The authors are indebted to services of Geological Survey of Finland for the EPMA (Mr Lassi Pakkanen) and LA-ICP-MS (Dr Hugh O'Brien) measurements.