Understanding Copper Smelting through Computational Thermodynamics
Pyrometallurgy provides excellent case studies of thermodynamic principles. They are multi-phase, multi-component systems where each major phase is a solution and where, due to the high temperatures involved, processes closely approach chemical equilibrium. They could be used in the classroom to provide an industrial context to the teaching of thermodynamics to chemical engineering students but this rarely happens, probably because few academic staff are familiar with smelting operations and because they are perceived to be overly complex. Copper smelting is a good example of such a pyrometallurgical process. Copper iron sulphide concentrates are smelted to a molten sulphide phase called “matte” and a molten oxidic waste called “slag”. The matte is then oxidised to copper in converters. The law of mass action, and the associated concepts of activity, activity coefficient, species formalism etc. are need to understand the relationship between copper matte grade and copper recovery. They explain why smelting can produce a discardable slag but converting produces a slag which must be recycled to smelting. Phase equilibria shows why silica flux is needed to form a slag and how the oxidation state of iron in the slag is critical. All of the relationships can be integrated and made quantitative through the application of computational software such as HSC Chemistry for Windows. It will be demonstrated in this paper that this approach makes the understanding of such a complex system as copper smelting very manageable in the classroom.