New glass-based binders from engineered mixtures of inorganic waste

Aluminum is one of the most important strategic resources, but the Bayer process, typically applied for the purification of ores, leads to vast amounts of alkaline slurry waste, known as red mud. Though interesting for potential reprocessing, red mud is still predominantly stored in big slurry pools, due to high levels of toxic metals. Toxic ions can be easily immobilized by vitrification, but the high costs of this solution need to be balanced by the reuse of the obtained glass. The present paper is dedicated to the transformation of waste-derived glass into new binders for the construction industry, according to both “conventional melting” and “smelting” approaches. In the first case, red mud was included in a mixture of waste, designed to yield a reactive glass (CMG), that is, forming stable gels after activation in an alkaline aqueous solution. In the second approach, red mud was subjected to a thermal treatment in a reductive atmosphere, implying the separation of molten iron alloy. The remaining glassy slag, according to its chemical composition (CaO and Al2O3-rich) underwent gelation by simple interaction with pure water, without any alkaline activator, thus configuring a new “glass cement”.