Rheological Properties of Cemented Paste Backfill with Iron Oxide and Aluminum Oxide Nanoparticles

Abstract

Among the various options for managing mining waste, cemented paste backfills (CPB) have become important in mining operations worldwide due to their technical, economic, and environmental advantages. CPBs are cementitious materials produced by mixing residues with a solid percentage ranging from 70 to 85%, fresh water or water from mineral processing, and a hydraulic binder, typically representing 3 to 7% of the weight. Typically, these elements are blended and mixed on the surface before being moved (either by gravity or by pumping) to underground mining voids, or cavities, where CPBs can be utilized for waste residue management, maximizing mineral recovery, and supporting underground mines. The key properties of CPBs include mechanical stability (usually assessed through strength), cost (dependent on binder consumption), transportability (dependent on rheological properties), durability, and environmental performance (usually measured by leachability, permeability, and reactivity). The most commonly used binder in CPB preparation is Portland cement (PC). PC is not only an expensive binder, but its production also consumes a significant amount of energy, thus generating a substantial amount of CO2. Cement consumption can account for up to 80% of the CPB cost. The aforementioned factors have compelled mining companies to seek alternatives to cement that enhance CPB strength, reduce cement content, and decrease the carbon footprint of the mining industry. Iron oxide (Fe2O3) and aluminum oxide (Al2O3) nanoparticles represent the latest additive suggested to reduce the binder content of cemented backfills, increase their strength and improve their environmental footprint. However, the rheological properties of CPBs containing Fe2O3 and Al2O3 nanoparticles are not well understood. It is necessary to address this knowledge gap. Therefore, the primary objective of this research is to study the evolution of rheological properties (yield stress, viscosity) of CPBs containing Fe2O3 and Al2O3 nanoparticles. The investigation also involves measuring the materials' pH and Zeta potential, microstructural studies (TG/DTG and XRD), and electrical conductivity (EC). The findings show that adding Iron oxide (Fe2O3) and aluminum oxide (Al2O3) nanoparticles to CPB significantly changes its rheological properties, which in turn affects flowability. The yield stress and viscosity of CPB samples are greatly increased by the incorporation of nanoparticles, with the degree of influence varying based on variables including water content, curing duration, and type of binder. Because of the nanoparticles-induced microstructural changes in the CPB material, the interaction of Iron oxide (Fe2O3) and aluminum oxide (Al2O3) nanoparticles and a larger fraction of nanoparticles, along with an increase in curing time, raises rheological characteristics and decreases paste flowability. The results of EC, DTG, and XRD, which show that binder hydration rises with nanoparticles dosage, corroborate this. Furthermore, as nanoparticles increases, the zeta potential decreases in magnitude, which lowers flowability and repulsion force. However, EC, XRD, and DTG experiments indicate that the addition of 0.125% superplasticizer is identified as a compensator for the lower flowability caused by nanoparticles. These tests also suggest that the superplasticizer causes a drop-in cement hydration rate at very high ages. Additionally, it has been found that increasing the slag percentage from 0% to 50% and 75% of the binder content effectively increases yield stress while only marginally decreasing viscosity. The results of this research could significantly benefit the mining industry and enable a more environmentally friendly design of CPBs and improved residue management practices.