BAYER PROCESS WASTE STREAM AS POTENTIAL FEEDSTOCK MATERIAL FOR GEOPOLYMER BINDER SYSTEMS

Recent developments in Mineral Polymer i.e. Geopolymer, binder technology points to a wide range of potential engineering applications within the mineral processing and mining sectors. Most notably, the principal raw feedstock materials required for this class of binders may be derived from both extractive and processing mineral waste materials such as clays, fly ash or red mud. It is the reaction of such solid mineral alumino-silicates with alkali silicate solutions that produces the chemical network structures characteristic of Geopolymer binders. The resulting high performance binder product can be mixed, placed and formed in the same manner as Portland cement mixtures with diverse applications in mineral waste processing, civil and geotechnical applications such as road pavement and embankments and in waste stabilization technologies and backfill mining cementing operations. Similar opportunities also exist in re-use options for Bayer process waste streams and in bauxite residue management.

This Paper presents fundamental synthesis parameters of Geopolymer binders with specific reference to oxide compositional limits of feedstock materials. In particular, experimental results disclosing the role of silica and alkali species present in feedstock materials and their impact on engineering properties such as strength development are presented. Geopolymer systems with high alkali contents (Na₂O/Al₂O₃ = 1.2) are shown to be characterised by high strength, low porosity and a dense, fine grained microstructure. Such properties may be equivalently achieved with high silica and low alumina contents (SiO₂/Al₂O₃ = 3.5–3.8). The observed synthesis parameters suggest potential beneficial and novel applications for red-mud as raw feedstock material in a variety of building product and civil construction applications.