On August 19, 2022, He Niu (Fibre and Particle Engineering research unit, University of Oulu and Early Stage Researcher in the MSCA-ETN SULTAN project) obtained his PhD degree in Processing Engineering. He successfully defend his PhD thesis titled “Valorization of mining waste in alkali-activated materials”.
He Niu performed his doctoral research at Fibre and Particle Engineering research unit in University of Oulu under the supervision of Prof. Mirja Illikainen and Associate Professor Päivö Kinnunen. The PhD research is part of H2020-MSCA-ETN SULTAN project, the EU Training Network targeting the remediation and reprocessing of sulphidic mining wastes.
The mining industry can generate wastes from excavation and mineral processing, namely waste rock, and mine tailings, which poses potential environmental ricks worldwide. The European Union mining industries have discarded their waste residues for more than 100 years. It is estimated that almost 65% of the waste produced in the EU is mineral waste. Large amounts of waste rock and tailings are stored in stockpiles and tailing impoundments without further exploration. Small portions of these wastes are utilized as fillers or backfills with cement pastes. The challenge lies in how to valorize those underutilized side streams, turning mining waste issues into a secondary raw materials opportunity. Alkali-activated materials are alternative cementitious materials with a lower carbon footprint than traditional Portland cement. The typical raw precursor, calcined kaolin (metakaolin), is rich in aluminosilicates, generating a three-dimensional framework under alkali conditions. Mining wastes, that contain aluminosilicate minerals are potential precursors for alkali activation. In contrast to calcined kaolin, mining wastes containing aluminosilicate-bearing minerals can be chemically inert and cannot be directly used as precursors. This requires enhanced chemical reactivity or mixing with other reactive raw materials.
The aim of this work was to investigate the potential of using mining wastes as secondary raw materials for alkali activation and valorizing waste rock and mine tailings in alkali-activated materials. It focuses on enhancing the chemical reactivity of mining wastes via a potentially greener approach (mechanochemical activation) compared to the calcination. Mechanochemical activation was implemented on both mine tailings and waste rock. Further, mine tailings are incorporated with metakaolin and blast furnace slag to produce alkali-activated tailing co-binders. The role of tailings in final alkali-activated materials was also investigated using diverse characterization methods.
The phlogopite and carbonate-bear phosphate mine tailings and muscovite-bearing sulfidic waste rock were subjected to mechanochemical activation, and they generated amorphous phases, which yielded a higher alkaline dissolution. The sole mine tailings or waste rock-based alkali-activated materials were successfully synthesized. Incorporation of mine tailings in alkali-activated co-binders, such as metakaolin and blast furnace slag, can significantly affect the hydration process, alkali activation, and physical performance. The role of tailings in alkali-activated materials is complicated, especially after mechanochemical activation. The amorphous part of phosphate mine tailings participates in alkali activation, forming C-(N)-A-S-H and other zeolites. Although sulfidic mine tailings contain only crystalline substances, they considerably alter the hydration and porosity of the final products.
List of peer-reviewed publications in scientific journals:
- Niu, H., Abdulkareem, M., Sreenivasan, H., Kantola, A.M., Havukainen, J., Horttanainen, M., Telkki, V.-V., Kinnunen, P., Illikainen, M., 2020a. Recycling mica and carbonate-rich mine tailings in alkali-activated composites: A synergy with metakaolin. Minerals Engineering 157, 106535. https://doi.org/10.1016/j.mineng.2020.106535
- Niu, H., Adrianto, L.R., Escobar, A.G., Zhukov, V., Perumal, P., Kauppi, J., Kinnunen, P., Illikainen, M., 2021a. Potential of Mechanochemically Activated Sulfidic Mining Waste Rock for Alkali Activation. Journal of Sustainable Metallurgy.https://doi.org/10.1007/s40831-021-00466-9
- Niu, H., Helser, J., Corfe, I.J., Kuva, J., Butcher, A.R., Cappuyns, V., Kinnunen, P., Illikainen, M., 2022. Incorporation of bioleached sulfidic mine tailings in one-part alkali-activated blast furnace slag mortar. Construction and Building Materials 333, 127195. https://doi.org/10.1016/j.conbuildmat.2022.127195
- Niu, H., Kinnunen, P., Sreenivasan, H., Adesanya, E., Illikainen, M., 2020b. Structural collapse in phlogopite mica-rich mine tailings induced by mechanochemical treatment and implications to alkali activation potential. Minerals Engineering 151, 106331. https://doi.org/10.1016/j.mineng.2020.106331
- Niu, H., Zhang, K., Myllymäki, S., Ismail, M.Y., Kinnunen, P., Illikainen, M., Liimatainen, H., 2021b. Nanostructured and Advanced Designs from Biomass and Mineral Residues: Multifunctional Biopolymer Hydrogels and Hybrid Films Reinforced with Exfoliated Mica Nanosheets. ACS Appl. Mater. Interfaces 13, 57841–57850. https://doi.org/10.1021/acsami.1c18911
- Perumal, P., Niu, H., Kiventerä, J., Kinnunen, P., Illikainen, M., 2020. Upcycling of mechanically treated silicate mine tailings as alkali activated binders. Minerals Engineering 158, 106587. https://doi.org/10.1016/j.mineng.2020.106587
- Martins, N.P., Srivastava, S., Simão, F.V., Niu, H., Perumal, P., Snellings, R., Illikainen, M., Chambart, H., Habert, G., 2021. Exploring the Potential for Utilization of Medium and Highly Sulfidic Mine Tailings in Construction Materials: A Review. Sustainability 13. https://doi.org/10.3390/su132112150