Development of lead smelting slag-based ecological mine backfill material: Performance control and heavy metals solidification

Abstract

As the heavy metals (Cr, Ni, Cu, Zn, As, and Pb) contained in the hazardous waste lead smelting slag (LSS) can cause irreversible harm to natural ecosystems, the resourceful utilization of LSS is an urgent requirement for promoting ecologically sustainable development. In this study, multi-solid waste-excited LSS was used to prepare eco-mine cemented backfill materials (MCBM). The results show that the optimal ratio of binder composition by mass is 46% for LSS, 20% for lime ash slag (LAS), 13% for slag powder (SP), 17% for cement clinker (CC), and 4% for bischofite (BF), at which time the compressive strengths of specimens at 3, 7, and 28 days are 11.1 MPa, 16.9 MPa, and 24.2 MPa, respectively. Clearly, increasing the ratio of binder-sand will increase the compressive strength of the MCBM. The backfill slurry with a binder-sand ratio of 1:2 and a solid content of 74% has a fluidity of 259 mm and a 28-day compressive strength of 5.48 MPa, which meets the requirements for high-strength grade MCBM for self-weight backfill. The results of XRD, MIP, and SEM indicate that the hydration products are predominantly composed of CSH gels, Friedel’s salts, and other mineral phases that contribute to the strength. As the ratio of binder-sand increases, the relative proportion of harmless pores increases, the mechanical properties of the MCBM improve, the hydration products become denser, and the unclassified tailings sand (UTS) is encapsulated more effectively. According to the results of the TCLP, the solidification ratio of the MCBM for each heavy metal exceeds 70%, and the leaching of heavy metals conforms to the Chinese Class IV groundwater standard. The process is more environmentally friendly, with lower energy consumption and CO2 emissions, in line with the local government’s environmental legislation.