The Noranda continuous converter at Xstrata Copper, Rouyn-Noranda - optimization of slag chemistry
Xstrata Copper’s Horne smelter treats a wide range of copper concentrates and other copper-containing recyclable materials imported from many parts of the world. The recyclable materials include metallic alloys, spent slags, and catalysts, as well as used electronic components containing copper and/or precious metals. The plant feed material, totalling some 780 kt/y, is smelted in the Noranda process reactor where a 73% Cu matte is produced (215 kt/y), along with reactor slag.
The reactor matte, containing about 3% Fe and 21% S along with small amounts of impurity elements like Pb, Zn, etc., is tapped and conveniently transferred within the same building to the Noranda converter (NCV) for conversion to a blister copper. As well as handling liquid matte, the NCV, which was commissioned in 1997, was also designed to handle a certain amount of solid copper-containing materials, such as crushed matte, or other materials that may be beneficially treated in the NCV rather than in the Noranda process reactor.
The NCV blister copper is tapped periodically from the vessel and transferred to the pyro-refining vessels for desulphurization and impurity control. Finally, the copper is transferred to the anode furnaces for final deoxidation using natural gas injection prior to anode casting. The anodes produced at the Horne Smelter are shipped to Xstrata Copper’s refinery in Montreal, where high-grade cathode copper is produced by electro-refining, along with the recovery of precious metals.
Thorough knowledge of both the process control parameters and smelting physico-chemistry of the NCV has been beneficial to help meet the required matte capacity while maintaining plant flexibility. In this regard, some level of predictive knowledge related to slag chemistry, in particular the liquid and solid phases such as silica, spinels, or olivines, has been found to be beneficial.
Over the last decade or so, the availability of commercial thermodynamic modelling packages, such as FactSage™, have been utilized with the advantage of helping the plant optimize slag chemistry and minimize slag handling issues that can arise, such as those due to a process upset, for example, by undue feed variability. This paper illustrates the application of this software in examining a range of NCV operating parameters, such as the %Fe/SiO2 ratio in the slag, and the level of minor gangue components in the slag, including CaO, Al2O3, ZnO, MgO, and PbO. The conditions influencing the slag liquidus ranges of NCV slags are discussed with respect to the overall process chemistry.
Given that a sufficiently low %Fe/SiO2 ratio is used in NCV slag, most components such as CaO-ZnO-PbO-Al2O3-MgO, in small concentration, help in lowering the NCV slag liquidus. Considering the present level of these minor components, the NCV can operate consistently at 1200°C if the %Fe/SiO2 is between 0.6 and 0.8 in the slag. Using the type of phase diagrams presented in this paper, it is possible to develop different Noranda reactor/Noranda converter operating strategies adapted to the feedstocks available at Xstrata mines and plants or from other sources.