Session Sheet - Bauxite Residue Valorization and Best Practices: Technologies for Valorization as Binder, Cement and Geopolymers

Bauxite Residue Valorization and Best Practices: Technologies for Valorization as Binder, Cement and Geopolymers
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Tobias Hertel, Ku Leuven; Christina Meskers, SINTEF; Efthymios Balomenos, Metlen Energy and Metals; Casper Van Der Eijk, SINTEF; Brajendra Mishra, Worcester Polytechnic Institute; Yiannis Pontikes, Ku Leuven R&D

Tuesday 2:30 PM
March 25, 2025
Room: 111
Location: MGM Grand

Session Chair: Casper Van Der Eijk, SINTEF

2:30 PM
Processing Routes of Bauxite Residue And Its Valorisation Potential: Various Case Studies Demonstrated at Pilot Scale: Glenn Beersaerts¹; Ganesh Pilla¹; Michiel Giels¹; Tobias Hertel¹; Yiannis Pontikes¹; ¹KU Leuven
    Bauxite residue (BR) is a by-product from the alumina industry and could be an interesting raw material for metal recovery and the construction industry. Despite its potential, only 1-3% of BR is used as a minor constituent for clinkering. In order to upcycle BR, a hydrothermal (200°C) or high-temperature process (>600°C) is required. The former comprises autoclaving of pressed monoliths, while the latter comprises roasting through hydrogen reduction for metal recovery and vitrification to obtain a supplementary cementitious material. These processes were developed at lab scale, but not yet validated at pilot scale. However, it is essential to demonstrate that these processes are scalable and consistent. Several processing lines for BR treatment were developed such as homogenization, pelletization, pressing, heat treatment, granulation and milling. Several experimental campaigns are presented for each processing route and the suitability to recover metaloxides and to obtain construction products is tested.

2:50 PM Question and Answer Period

2:55 PM
Towards Scalable Autoclaved Masonry Units: How Bauxite Residue Feedstock Characteristics Impact Performance: Tobias Hertel¹; Yakinthi Avtzi¹; Nikolaos Athanasakis¹; Fábio Oliveira¹; Glenn Beersaerts¹; Yiannis Pontikes¹; ¹KU Leuven
    One barrier for the valorisation of bauxite residue (BR) in the construction sector is the limited benefit to the performance. Various processing routes to enhance the reactivity are discussed in the literature; however, they are often limited to lab-scale testing, with economic feasibility and sustainability often not considered. In this study, we propose an alternative process for transforming a BR-rich blend into autoclaved masonry units and investigate the impact of different BR feedstocks on their performance. To minimise environmental and economic risks of a potential implementation, off-the-shelf-equipment with industrial process parameters were used (200°C-16 bar steam pressure). Results demonstrated a dependence of performance on the BR-feedstock characteristics, notably phase assemblage and pore solution chemistry. The mechanical properties varied, ranging from 10-25 MPa. Selected blends were successfully scaled up to tiles using pilot-scale equipment, indicating the technical feasibility to upscale and implement the process for a wide range of BRs.

3:15 PM Question and Answer Period

3:20 PM
Assessment of High Temperature Valorisation Routes for Bauxite Residue towards Cementitious Binders: A Case Study on Vitrification: Michiel Giels¹; Tobias Hertel¹; Glenn Beersaerts¹; Yiannis Pontikes¹; ¹KU Leuven Materials Engineering
    Bauxite residue (BR) holds significant potential for use in the construction industry due to its widespread availability. However, BR derived from the Bayer process often lacks the reactivity necessary for cementitious applications, such as hydraulic/pozzolanic activity. To enhance its reactivity, BR can undergo heat treatment processes including calcination (<1000°C), partial vitrification (1100–1300°C), or smelting combined with iron extraction (1500–1700°C). Recent research has demonstrated the feasibility of vitrification of BR at laboratory and pilot scales, but questions persist regarding its sustainability at an industrial scale. This study comprehensively reviews the entire process chain, starting from BR pre-processing to vitrified BR, and examines its utilization as supplementary cementitious material (SCM) in blended cement. Key bottlenecks in the processes are identified and evaluated critically. Finally, pathways are put forward for developing sustainable heating and binder technologies applicable to all processes requiring heat treatment for BR valorization.

3:40 PM Question and Answer Period

3:45 PM
Impact of Chemical Admixtures on the Setting Time and Freeze-Thaw Resistance of Bauxite Residue-Based Geopolymer: Andrie Harmaji¹; Reza Jafari¹; Guy Simard¹; ¹Université du Québec à Chicoutimi
    Saguenay is one of the regions that produce aluminium in Canada which simultaneously generated bauxite residue that rich in SiO₂ and Al₂O₃. Both oxides are essential for Geopolymer raw material. However, it cannot be used as standalone raw material since bauxite residue are lack of reactive SiO₂. Moreover, implementing geopolymer in Canada is challenging, because previous research reported that geopolymer has lower freeze-thaw durability than Portland cement-based concrete. To address both problems, silica reactive material and chemical admixtures can be added. Therefore, this study aims to analyse the effect of fly ash, glass powder, calcium chloride, and borax addition to strength of geopolymer and morphological assessment after freeze-thaw cycle. The result shown that the materials influenced the compressive strength of the geopolymer. The SEM and FTIR characterization revealed that freeze-thaw cycle alters the bonding formation and fracture pattern of geopolymer.

4:05 PM Question and Answer Period

4:10 PM Break

4:25 PM
Assessing the Carbonation Potential of De-alkalized Bauxite Residue Using Different Carbonation Methods: Fabio Cabral De Oliveira¹; Tobias Hertel¹; Yiannis Pontikes¹; ¹KU Leuven
    This study investigates the carbonation potential of de-alkalized bauxite residue (DABR) under various methods. DABR was carbonated in slurry, dry powder, and wet powder states using three techniques: exposure to air; exposure to CO2 in a chamber at 50 °C; and exposure to CO2 pressure in an autoclave at 50 and 100 °C. After carbonation, CO2 uptake was measured via thermogravimetric analysis (TGA), mineral composition was determined by x-ray diffraction (XRD), and reactivity was assessed using the rapid, relevant, and reliable (R3) test. The results indicated that hydrogarnet is the only phase in DABR susceptible to carbonation, forming CaCO3 and an amorphous phase. Nearly all carbonation in the CO2 chamber occurred within one day, achieving a CO2 uptake of about 9%, which significantly offsets CO2 emissions attributed to the lime added during the de-alkalization process. The R3 tests showed low cumulative heat, indicating low reactivity of the carbonated DABR.

4:45 PM Question and Answer Period

4:50 PM
Mineralogy Prediction for Iron-Rich Sulfo-Aluminate Cements Made from Elevated Contents of Bauxite Residue: Rahul Roy¹; Debadri Som¹; Tobias Hertel¹; Yiannis Pontikes¹; ¹KU Leuven
    Bogue equations is a system of simultaneous mathematical linear equations widely used by the industry to determine the mineralogy of the Portland cement clinker. In this study, a novel approach has been undertaken to formulate a new set of modified Bogue equations for raw-meal compositions constituting > 15% Fe2O3 and > 2% TiO2. The approach incorporates the use of electron probe micro-analysis (EPMA) and X-ray fluorescence spectroscopy (XRF) to determine the crystalline and chemical composition of the synthesized clinkers, which provides the basis for a matrix inverse method to solve new linear equations. This method improves the accuracy of predicting the mineralogy of Fe-rich clinkers, enabling users to incorporate resources such as bauxite residue and synthesize iron-rich sulfo-aluminate cements. The obtained mathematical linear equations are integrated in the beta SREbind version, and their use is demonstrated along with the SREmix.

5:10 PM Question and Answer Period

5:15 PM
A Linear Programming-Based Approach for Creating Cements from Bauxite Residue: Debadri Som¹; Rahul Roy¹; Tobias Hertel¹; Panagiotis Patrinos¹; Yiannis Pontikes¹; ¹KU Leuven
    In this study, we present a framework for producing classical Portland cements and low energy calcium sulfoaluminate clinkers from bauxite residue in the raw meal. Using a user-defined multi-objective linear programming approach and modified Bogue’s equations, we show the optimal chemistry necessary to maximize the cement phases. Additionally we present the ideal combination of materials in the raw meal (including bauxite residue) to generate the optimal chemistry with minimized cost and equivalent CO2. This framework is based on the database (https://www.sreway.info/sredat/) created to facilitate the optimization of cement clinkers and concrete mix design where users can select raw materials and make clinkers from the formulations suggested. This model can be beneficial to both the alumina and the cement industries where the former has access to quantified valorization through mathematical modelling and the latter has the possibility to reduce the cost and CO2 equivalent of cement production.

5:35 PM Question and Answer Period

5:40 PM Concluding Comments