Utilization of alkaline additives for backfilling performance improvement of sulphide-rich tailings

High-sulfur tailings, characterized by their elevated sulphide content, represent a unique hazard exceeding conventional tailings. The peculiar mineralogical composition of these tailings, which often fails to meet strength requirements, poses a significant challenge to their effective underground disposal. This study addresses the suboptimal backfilling performance of sulphide-rich tailings by employing a suite of experimental techniques, including rheological tests, mechanical tests, microscopic analyses, leaching assays, and cost-benefit assessments, specifically focusing on the influence of additives. While incorporating fly ash (FA) mitigates cracking in the sulphide-rich cemented paste backfill (SCPB), it does not fully satisfy strength criteria. 30 wt% CaO addition increased UCS to 1.82 MPa at 28 days (vs. 0.48 MPa control)-280 % improvement - meeting mining safety thresholds (>1 MPa). The degradation in SCPB strength is primarily attributed to the unfavourable pH conditions during hydration, which hinders the formation of essential hydration products like calcium Silicate Hydrate (C-S-H), and the concurrent production of significant gypsum amounts leading to pervasive cracking. CaO reduced harmful pores (>200 nm) by 78 %, promoting the abundant generation of hydration products such as calcium hydroxide (CH) and C-S-H. CaO-CPB achieved 98.6 % Zn²⁺ immobilization, outperforming Pb²⁺ (93.2 %), Cu²⁺ (89.1 %), and Fe³⁺ (85.4 %) through synergistic hydroxide precipitation and C-S-H substitution. Lastly, an economic evaluation of cementitious materials confirms that CaO is well-suited for modulating the backfilling performance of sulphide-rich tailings. This research offers critical insights into addressing the strength degradation issues associated with using sulphide-rich tailings as backfilling material, thereby contributing significantly to safe, environmentally friendly, and efficient underground disposal.