Short course: Metallurgical thermodynamics applied to lead recycling
This short course discusses the basic tools of metallurgical thermodynamics and their application, with a special focus on lead recycling.
The starting point for the understanding of any metallurgical system is often the phase diagram. We discuss how to interpret a phase diagram, which type of information can be retrieved from it, as well as its link to the Gibbs energy description in thermodynamic software. Further it is shown how these software tools allow to make calculations for multicomponent processes.
Next, we discuss the thermodynamics of lead production and how recycling processes make clever use of these principles. The thermodynamics of lead production from primary resources have long been established, but secondary smelters are facing different challenges. Classical roasting-blast furnace, as well as more recent direct smelting processes, deal with sulfur in concentrates (PbS) by forming SO2 and capturing it in sulfuric acid plants.
Secondary production typically starts from battery fractions containing Pb, PbSO4, and PbO2. The strategy for sulfur is rather different: S is captured in a separate phase prior or during smelting. Secondary lead smelting has its own multicomponent slag system, which is very robust, but because of its robustness, not always fully understood nor optimally applied. As Fe and Na2CO3 are added to generate sulfides and sulfates, this requires the understanding of more than the Pb-O-S system. Moreover, the different phases (slag, matte, lead) are not strictly oxidic, sulfidic, or metallic. A number of relevant phase diagrams will be discussed, as well as the Ellingham stability diagrams of oxides and sulfides.
Sander Arnout is the founder of InsPyro, a consultancy company that focuses on high-temperature metallurgical processes. His company has been advising several leading smelters and recyclers via the use of advanced thermodynamics and flowsheet modelling, computational fluid dynamics and materials characterization tools. Sander holds a PhD from the University of Leuven, Belgium.