FAILURE MECHANISMS OF REFRACTORY LININGS FOR NONFERROUS FLASH SMELTING FURNACES

Although the flash smelting technologies use different furnace designs, the refractory linings are exposed to very similar aggressive environments and, as a result, the corrosion analysis results on one type of furnace could be generally applied to other furnaces of similar high temperature processes. Particularities regarding the different chemistries of the pyrometallurgical process and operating parameters of these furnaces could also bring particular aspects to be considered when analyzing the refractory ware and final failure in use. This paper presents a review of the existent experimental. data of corrosion analyses on refractory linings used in two particular flash furnaces for zinc-lead and respectively nickel-copper smelting. Although various modern water cooling systems are generally used to protect the refractory wall linings against corrosion by molten slag and matte, the performance of the refractory roof lining, usually used without water cooling, represents a permanent concern and the object of research studies to extend their life in service. The failure mechanisms analysed in this study are based on postmortem analyses and laboratory corrosion experiments with magnesite-chrome bricks of different chemical and mineralogical compositions. The gaseous atmosphere, usually rich in SO2 and/or CO and various metal fumes, produces irreversible microstructural changes which could shorten the life in service of the refractory lining. The experimental data proved that thermal cycling in SO2/SO3 atmospheres could bring more damage than a continuous use at relatively constant temperature, due to the magnesium and calcium sulphate formation. The laboratory experiments and postmortem analyses showed that that metal fumes at various partial pressure of oxygen would condense as oxides and react inside the pores and at the grain boundaries, contributing to the continuous deterioration of the ceramic matrix of the refractory brick lining. The mechanisms of corrosion, discussed based on laboratory experiments, were confirmed by the postmortem analyses on brick samples used in the industrial flash smelting furnaces.