During iron ore pellet production the ore is first ground to a powder and then sintered in a kiln at ~1250ºC. The company LKAB uses a kiln that is ~ 40 m long and ~ 6.5 m in diameter, insulated with Al2O3- and SiO2- containing bricks. The bricks wear and after some time need to be replaced, which is costly and time consuming. This ongoing project aims at understanding the wear mechanisms of these bricks. The technological problem is rather complex; both oxidizing and reducing atmospheres are locally present, as are various alkali species, the thermomechanical load varies, and slag degrades the bricks. The slag consists of ~95% hematite from pellets that have disintegrated and stick to the bricks. Slag/brick compatibility tests were performed in a laboratory furnace at various temperatures, holding times and atmospheres. Slag collected from a production kiln and three commercial bricks, in powder or solid form, were used. Deliberate additions of alkali species in the form of CaO, K2CO3 and Na2CO3 were included in some of the tests. DSC, TG and in-situ mass spectrometry showed an endothermic reaction, together with mass loss and release of oxygen. Analysis and characterization by microscopy and XRD revealed microstructural changes. It is clear from these observations that the slag degrades the refractories by a combination of capillary infiltration and diffusion/chemical reaction. The depth of slag penetration is more affected by increased temperature than increased time. Moreover, the bricks with higher Al2O3 content are more resistant in the presence of alkali species.