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Backtech Pty Ltd (ABN 76 663 206 237) is a company specialised in backfilling. Backfill concrete is used to fill voids or trenches after utility installation or construction projects, and its production contributes to carbon emissions in various ways. Western Australia is implementing strict regulations on carbon emissions and environmental impact because of cement usage. This company is looking for decarbonising backfill concrete by reducing the use of cement in their mixes.
The worldwide increasing demand for lithium-ion batteries, used in portable electronic devices and electric vehicles, initiated an unprecedented level of attention in lithium extraction. Australia, Chile, China, and Argentina as the four largest lithium producers hold 76% of the global lithium reserves, while Australia accounted for 43% of world’s lithium extraction in 2022. Australia’s lithium reserves are extracted through hard-rock mining and the ore processed into spodumene, which can then be refined into either lithium hydroxide or lithium carbonate [1].
Delithiated 𝛽−Spodumene (D𝛽S) is the leach residue produced after lithium refining. It denotes the largest material stream produced in the process; approximately 7-10 tonnes of D𝛽S are created per tonne of lithium hydroxide monohydrate produced [2]. Development in mining and lithium production industry implies that D𝛽S waste is expected to increase, which should be managed properly. The chemical formula of spodumene is Li2O⋅Al2O3⋅4SiO2, which reveals about 8% lithium oxide and 92% aluminosilicates by mass in ideal scenarios. Lithium ore is always associated with gangue and the actual grades are significantly lower than the ideal figure. Spodumene can be processed in various ways and in Australia, processing plants typically produce lithium hydroxide along with D𝛽S (essentially aluminosilicates and gypsum/limestone) and sodium sulphate [3].
Researchers have discovered that D𝛽S has relevant pozzolanic properties which can be suitable to apply in geopolymer [4]. Metakaolin, ground granulated blast furnace slag (GGBS), and fly ash (FA) are the commonly used binders to produce geopolymers [5]. D𝛽S shares many chemical properties with FA and has been identified as a potential geopolymer precursor.
Although there is not much studies on utilizing D𝛽S as a geopolymer precursor, the limited number studies were conducted to examine the mechanical properties of geopolymer containing D𝛽S. Karrech et al. [3] performed a study on using D𝛽S as a precursor for geopolymer paste. In the study, D𝛽S proved to be an acceptable geopolymer precursor. Flowability, penetration resistance, and shrinkage tests proved that the D𝛽S improves workability, increases initial setting time and decreases drying shrinkage of the geopolymer. The XRD analysis of D𝛽S also revealed that this aluminosilicate by-product comprised leached pyroxene (62%–63%), quartz (18%–20%), gypsum/bassanite (7%–8%), K-feldspar (3%–4%) and other minerals.
This project aims at finding appropriate D𝛽S ratio to produce highly efficient geopolymer with acceptable physical, mechanical and durability properties for backfill application. The main purpose is to develop a geopolymer by incorporating D𝛽S as a precursor and silica fume as a geopolymerisation activator instead of sodium silicate which is relatively expensive. The key steps of the project are summarised below:
• Physical, mechanical and chemical characterization of the D𝛽S to fully examine the behaviour of this material as a main geopolymer precursor.
• Utilization and developing silica fume as the effective activator in geopolymer instead of sodium silicate activator. Silica fume is the source of amorphous and reactive silica for activators raw material in geopolymer technology. This material has shown numerous applications as an amorphous supplementary cementing material (SCM).
• Preparing the geopolymer mixes and conducting mechanical, physical, chemical, durability and microstructural analyses on the prepared mixes based on Australian standards.
• Analysing life-cycle assessment of the produced material for CO2 emission and cost.
References
1. https://www.mckinsey.com/industries/metals-and-mining/our-insights/australias-potential-in-the-lithium-market.
2. Safari, A. and H. Lim. The benefit of delithiated beta spodumene to reduce the carbon footprint of cemented paste backfill. in Paste 2023: 25th International Conference on Paste, Thickened and Filtered Tailings. 2023. University of Alberta, Edmonton, and Australian Centre for Geomechanics, Perth.
3. Karrech, A., et al., Delithiated β− spodumene as a geopolymer precursor. Construction and Building Materials, 2021. 309: p. 124974.
4. Munn, B., I. Dumitru, and D. Maree, Assessment of the performance of new supplementary cementitious materials from lithium production residues. CIA Binnual Coference, 2019.
5. Davidovits, J., Geopolymers: Ceramic-like inorganic polymers. J. Ceram. Sci. Technol, 2017. 8(3): p. 335-350.
6. Lloyd, N. and V. Rangan. Geopolymer concrete with fly ash. in Proceedings of the Second International Conference on sustainable construction Materials and Technologies. 2010. UWM Center for By-Products Utilization.
7. Karrech, A., et al., Management and valorisation of delithiated β-spodumene and its processing stream. Case Studies in Construction Materials, 2021. 15: p. e00671.
8. Liu, H., et al., Morphology and composition of microspheres in fly ash from the Luohuang Power Plant, Chongqing, Southwestern China. Minerals, 2016. 6(2): p. 30.
9. Devarangadi, M., Use of ground granulated blast furnace slag blended with bentonite and cement mixtures as a liner in a landfill to retain diesel oil contaminants. Journal of Environmental Chemical Engineering, 2019. 7(5): p. 103360.
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