Calcined nickel laterite leaching residue as a supplementary cementitious material

This research investigates the valorisation of a silica-rich leaching residue (LR) as a supplementary cementitious material. The LR originates from a novel hydrochloric acid-based processing route applied to laterite ores for the recovery of nickel (Ni) and cobalt (Co), metals whose demand is expected to increase significantly due to the ongoing global transition toward electrified energy systems. In this study, different batches of the LR are characterised, and the R3 test is used to determine the evolution of reactivity at different calcination temperatures. The changes caused by calcination are thoroughly evaluated by laser diffraction, nitrogen-Brunauer–Emmett–Teller method, X-ray diffraction analysis, thermogravimetric analysis and scanning electron microscopy-energy-dispersive spectroscopy. Next, selected calcined samples are used as a 30 wt% cement replacement in hydration studies and mortar production. The calcined LR shows optimum reactivity, that is > 300 J/g, and delivers the best mortar properties (i.e. lower superplasticiser requirement and 7-day and 28-day strength activity index >90%) and lower Cr leaching when calcined at 800°C. The early age pozzolanic reactivity of the calcined LR is caused by the structural disorder induced by thermal removal of bound water from the acid-leached silicate structures of the original smectite.