Iron and montmorillonite content effects on the thermal stability of casting-grade bentonite

The performance of molding sand and casting quality are significantly influenced by bentonite's thermal stability. This study focuses on how the montmorillonite and ion content—particularly the calcium and iron content—influence the thermal stability of bentonite. Six different colors of bentonite from the same supplier are used in this investigation. The results indicate that when the montmorillonite content is similar, the bentonite with higher iron ion content exhibits significantly better thermal stability. At high temperatures, structural iron within montmorillonite hinders excessive dehydroxylation and structural collapse, effectively maintaining the layered framework integrity of montmorillonite. Due to its high iron content, the purified brown bentonite is the best option binder for casting applications.