Christine Wenzl

Refractory Challenges in Lead Recycling Furnaces

The refractory linings in lead furnaces are exposed to several stresses rather complex in their interaction. In the present study the magnesia-chromite brick out of a lead recycling furnace suffered from a high chemical attack by the process slag. The high CaO, BaO and sulfur bearing silicate slag, as well as a high Na2O supply from soda resulted both in a deep-reaching infiltration of the brick microstructure and a severe corrosion of the brick components. Both the sintered magnesia and chromite were attacked chemically. The FactSage calculations showed the formation of high amounts of liquid phase in the infiltrated microstructure. Further phenomena affecting the refractory performance such as iron oxide attack, redox effects, and boron attack are also discussed in the paper. The obtained information and insights serve as a basis for improving refractory materials (i.e., choice of refractories for individual process and new developments) and consequently furnace operations.

Evaluation of High Temperature Refractory Corrosion by Liquid Al2O3–Fe2O3–MgO–SiO2

Corrosion mechanisms have been investigated between MgO refractory substrates and synthetic FeNi slags. The materials taken into consideration comprised a simple synthetically mixed slag with specific oxides of slags from a ferroalloy producer. The MgO refractory substrates with the slag specimens on it were heated in a hot stage microscope to two different characteristic temperatures, 1350 and 1650 °C. The experiments proceeded under a controlled gas atmosphere that simulates the relevant process conditions. The corrosion mechanisms of each system were determined by SEM analyses. The obtained results showed that slag corrosion is dominating with a pronounced partial dissolution of refractory. It was also observed that iron oxide present in the slag diffused into the coarse refractory grains forming the relative low melting magnesia wuestite. Finally, the comparison of these findings with those predicted by thermodynamic calculation (FactSage) indicated the corrosion mechanisms and draw implications for improving the refractory performance and lifetime.

Zinc and Refractories ‒ A Nasty Relation

Zinc is a component of many input materials used in various pyrometallurgical processes, for example primary lead and zinc production from Pb/Zn ores and recycling processes dealing with zinc-containing residues (e.g., copper recycling, WAELZ process). Hence, zinc and its compounds are present in the respective metallurgical vessels and interact with the refractory lining. In the present work the zinc attack on the refractories out of various primary and secondary furnaces is briefly introduced and discussed. At the prevailing processing temperatures in the metallurgical vessels, zinc oxide is highly corrosive for the brick components. The knowledge of the wear behavior is based not only on a detailed chemical and mineralogical characterization carried out on provided post mortem samples, but also on FactSage calculations. This together with results obtained by practical testing in the RHI pilot plant represents an important prerequisite for product development and brick selection for the individual customer application.

High temperature corrosion mechanisms of refractories and ferro-alloy slags

Refractory linings in pyrometallurgical furnaces are attacked by various process phases (e.g. metal, slag, gas). However, refractories are the barrier between these phases and the environment: refractory damages and consequent furnace failure can cause severe damages including potential danger for workers/operators. Hence, refractory corrosion and attack of molten phases require attention to study the mechanisms and effects on refractory performance and lifetime. This is of special importance in ferroalloys production, where temperatures are generally even higher than in base metal processes and the corrosion effects therefore more pronounced.