Valorization of Treated Aluminum SPL as Cementitious Materials

Approximately 22 kg of used material (SPL) is generated per ton of aluminum produced. Untreated SPL is classified as hazardous industrial waste due to its hydroreactive nature and the presence of leachable cyanides and fluorides. After treatment with the Low Caustic Leaching and Liming (LCL&L) industrial process, the refractory portion of the SPL is transformed into an inert material called LCLL Ash. This project analyzed the potential use of LCLL Ash as a cement binder. The reactivity of LCLL Ash was evaluated by compressive strength activity index, Frattini and Rilem R3 tests, and X-ray diffraction (XRD) analysis. Inert materials (limestone filler, quartz powder) and conventional cement additives (fly ash, slag) were used as references. According to XRD results, LCLL Ash is composed of stable crystalline phases such as corundum, albite, nepheline, and contains graphite. In cement, LCLL Ash has inert properties, similar to quartz powder, with a retarding effect at early ages due to the presence of alkalis. Calcinating and addition of synthetic fluorite to LCLL Ash were explored as means to improve its reactivity. These methods significantly improved the reactivity by generating larger amounts of reactive amorphous phases with high silica and alumina content. The reactivity of calcined LCLL Ash was then similar to fly ash, without retarding effect, and showed compressive strength similar to cement at 28 and 112 days. A greater reactivity in cement pastes containing calcined LCLL Ash was also confirmed in XRD analysis by showing lower portlandite content and the formation of a new phase, rich in carboaluminate. These results demonstrate the potential for LCLL Ash valorization in cement, either as a filler or as a reactive cement additive after calcination.