A systematic review of hydrometallurgical processes for lithium extraction from hard rock minerals, with a focus on enhanced utilisation of Delithiated Residues

Due to surging global demand for batteries and renewable energy technologies, lithium extraction from hard-rock lithium deposits has become a critical challenge. Conventional extraction processing involves high-temperature roasting, which is energy-intensive and generates large volumes of solid residues and heavy metal mobilisation, indicating the need for alternative efficient techniques. This systematic review paper, using the PRISMA guidelines, covers recent advances in hydrometallurgical lithium extraction processing from common hard-rock lithium ores such as spodumene, lepidolite, petalite, amblygonite, and zinnwaldite. The study investigates a range of processes, including acid and alkaline roasting, sulfation, chlorination, carbonation, fluorination, and emerging solvent leaching techniques, highlighting optimal reaction conditions to achieve higher lithium extraction efficiency. In addition, this work addresses valorisation of valuable by-products as supplementary cementitious materials (SCMs) in concrete, geopolymers, zeolites, ceramics, and road construction. By linking optimised extraction routes with efficient waste utilisation, this comprehensive review addresses key knowledge gaps and offers a coherent perspective on integrating lithium extraction with circular economy practices. Characterisation of leaching residues is also investigated for a better understanding of viable process adjustments to minimise environmental impacts. This review paper sheds insight into future research directions and supports the development of more sustainable industrial lithium extraction processes.