Wise Process Routes for Varying Feedstock in Base Metal Extraction Modelling of a Peirce-Smith Converter and Investigation of Buildup Formation in an Electric Smelting Furnace

Sammanfattning: Copper, like silver and gold, is one of the metals that are known to have been worked by some of the oldest civilisations on record. It is used for its unique properties such as corrosion resistance, good workability, high thermal conductivity and attractive appearance. New mines are opened to maintain a supply of primary feedstock for copper smelters. These new deposits are in many instances found to have a more complex mineralogy with several minor elements. Besides treating primary material, copper smelters are also showing an increasing interest in treating secondary materials, such as copper containing scrap from waste electrical and electronic equipment, which also have a complex composition. This increased complexity of the raw material can potentially lead to smelter plants having to deal with a feedstock containing several minor elements, including antimony, arsenic, bismuth, gold, silver, etc., at levels that can influence the ability to, in a cost effective way, maintain the final grade of the copper cathode. Process simulations can be an important tool for understanding the impact of process parameters on product quality and for the purpose of process optimisation. In the present work a dynamic, non-equilibrium model based on thermodynamics over the Peirce-Smith converter has been developed. The model was found to predict the composition of the main condensed phases well. Thermodynamic calculations in combination with characterisation have also been used to understand the buildup in an electric smelting furnace. Results from the characterisation and the modelling showed that the buildup consists mainly of different phases such as spinel, matte, olivine and metalloids and has a complex and varying mineralogy, which indicates that the buildup is not formed under equilibrium conditions. During the modelling the impact of parameters such as Fe/SiO2 ratio, partial pressure of oxygen and the content of the oxides ZnO, Al2O3 and Cr2O3 in the slag were investigated with respect to the liquidus temperature of the slag. The modelling showed that the chromium content in the slag has the greatest impact on the liquidus temperature and on the formation of solid particles. The thermodynamic modelling supports the result from the characterisation. The combination of characterisation, thermodynamic-based modelling and process knowledge gives further understanding of element distribution. This enhances the potential to adjust for variations in raw material feed and flexible process routes.