Synthesis and Characterization of a Red Mud and Rice Husk Based Geopolymer for Engineering Applications

Summary Red mud (RM) is the major waste material of the alkaline extraction of alumina from bauxite. It occupies precious land and threatens the environment. Rice is composed by approximately 20% of rice husk (RH) creating disposal and pollution problems. After burning RH, the resulting rice husk ash RHA contains about 90% silica. Synthesis of geopolymers is an emerging technology for the utilization of industrial by‐products. For the synthesis of a RM/RHA based geopolymer, we used RM from a local Alumina Plant, RH from a local mill in Guinea and NaOH solutions. The synthesis consisted of mixing the RHA to RM powders at a pre‐designed weight ratio. The NaOH solution was added with a given concentration. The effect of mix ratio, alkalinity and curing age on the geopolymer specimen were investigated. X‐ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and compression test were used to study the microstructure of RM, RHA and RHA/RM. The analyses showed that the final product is mainly composed of amorphous geopolymer binder and that the compressive strength ranges from 3 to 20 MPa.