Long-term ageing characteristics of cemented paste backfill: Usability of sand as a partial substitute of hazardous tailings

Abstract

Considering environmental problems caused by sulfidic tailings as a result of long-term ageing as well as inadequacies in their gradations in ensuring the strength needed for cemented paste backfill (CPB), there is a need for viable and inexpensive solutions to eradicate these negativities caused by tailings. This study aims to boost long-term filling performance and lessen cement-related costs and environmental risks by using diverse proportions of sand as a partial substitute of tailings in CPB. For this purpose, rheological (mini slump), mechanical (e.g., UCS), microstructural (e.g., XRD, FTIR, SEM, and TG/DTG), and costs analyses of sand-based fills were investigated experimentally. Samples were prepared with a fixed solid content (70 wt%), five diverse replacement ratios (tailings/sand: 100/0, 90/10, 80/20, 70/30, and 60/40), and three diverse cement contents (3, 5, and 7 wt%), and then cured up to 180 days. Results showed that using sand as tailings substitution in CPB ameliorated its strength up to 3.22 MPa. This could be clarified by the fact that sand usage mends tailings gradation by improving its skeleton structure and forming a more compact material. Besides, owing to its high CaO content (similar to 54 wt%), sand contributes positively to hydration reactions of cement and prevents acid/leach formations that may occur in the long-term ageing. Lastly, it was concluded that sand increases CPB's performance and subsidizes sustainable mining/filling operations by falling the environmental impacts of hazardous tailings subjected to diverse disposal/curing conditions.