Mohammed A. Hefni

Mine backfilling technologies have evolved, making the mining industry more sustainable. Further gains could be made by exploring additives that enhance the mechanical, rheological, and thermal properties of backfill. In this study, a sustainable additive, basalt fiber (BF), was added to cemented paste backfill (CPB) samples at two BF lengths (12 and 18 mm) and three BF dosages (0.50, 0.75, and 1.0%). BF length and dosage influenced the properties of BF-reinforced CPB. Addition of 18 mm BF to the CPB at a dosage of 1% decreased the slump value by up to 74% compared with the control. Consequently, the calculated yield stress doubled from 191.8 Pa to 398.8 Pa. Incorporating 12-mm BF at a dosage of 1% improved the uniaxial compressive strength of the CPB by up to 35% after 7 days of curing. The thermal conductivity of CPB reinforced with 12 mm BFs at a dosage of 0.50% decreased by nearly 36%. Whereas most studies focus on the effects of BF on concrete and other construction materials, these findings show that BF has the potential to improve CPB properties for mining applications, which could help reduce binder content, contributing to improved project economics and sustainable mining practices.

Cement production may involve excessive use of natural resources and have negative environmental impacts, as energy consumption and CO² emissions can cause air pollution and climate change. Cement kiln dust (CKD), a by-product waste material, is also a primary issue associated with cement production. Utilizing CKD in mining applications is a pathway to eco-sustainable solutions. Cemented paste backfill (CPB) made with mine tailings is an efficient method for void backfilling in underground mines. Therefore, this study investigated the eco-sustainable utilization of CKD as a co-binder material that can partially replace cement in CPB prepared with copper tailings. At 7, 14, 28, 56, and 90-day curing times, the experimental campaign measured the physical and mechanical parameters of the cured CPB samples, including density, UCS, and elastic modulus (stiffness). Additionally, the CPB-cured mixes were analyzed using XRF, X-ray XRD, SEM, and EDX techniques to link the mineral phases and microstructure to mechanical performance. Four proportions (5, 10, 15, and 20%) of CKD represented in 75 samples were prepared to replace ordinary Portland cement (OPC) in the CPB mixtures, in addition to the reference mix (control) with 0% CKD. As all combinations exceed the compressive strength of CPB required for achieving stability in underground mines, the results showed that CKD could be utilized advantageously as a partial substitute for OPC with a proportion of up to 20% in the CPB mixture. When tested after 90 days, the combination modified with 5% CKD exhibited comparatively higher compressive strength than the control mixture.

In underground mining, the application of mine backfill has evolved into a standard practice. Mine backfill typically consists of tailings, water, and hydraulic binders. However, the high cost of binders has prompted scholars to research alternatives to reduce this cost while maintaining or even improving the properties of the backfill. One potential alternative is leveraging microwave irradiation. In this study, an innovative approach was developed to increase the unconfined compressive strength (UCS) of early age cemented paste backfill (CPB). Microwave treatment was applied to CPB samples at various curing ages for varying durations. The UCS and ultrasonic pulse velocities were measured and analyzed in an experiment with a full factorial design. Moreover, the microstructural properties of the CPB were investigated using mercury intrusion porosimetry. The results indicate a significant potential to increase the UCS of CPB by up to 25% when microwave-treating samples for 8 min after 7 days of curing. This approach could shorten mining cycle times and improve productivity, presenting a promising method to enhance CPB strength.

This study investigates the effect of the partial replacement of ordinary Portland cement (OPC) with cement kiln dust (CKD) on the engineering properties of pozzolanic concrete for use in block manufacturing. Ultimately, this could potentially reduce cement consumption and CO₂ emissions. The study was carried out on cylindrical concrete samples prepared from five mixtures comprising 71.13% pozzolan and 14.16% water, with 0, 5, 10, 15, or 20% of the OPC fraction (14.71 wt.%) replaced by CKD. The samples were tested for density and compressive strength (UCS) at curing ages of 7, 14, 28, 56, and 91 days; and for voids and water absorption after 28 curing days. Results show that increasing CKD content lowered the voids and increased the water absorption. The 15% CKD sample had the highest UCS, regardless of the curing age. X-ray diffraction analysis confirmed that the phase responsible for hydration, calcium silicate hydrate, was higher in the 15% CKD sample than the control.

Cement global demand shows continued growth and a significant increase in the production volume, which may negatively impact the non-renewable natural resources and the environment, which is incompatible with sustainability goals. Cement kiln dust (CKD) is a primary concern associated with clinker manufacturing as a waste byproduct. Similarly, the mining industry produces copper tailing as unwanted material while beneficiating the ore, creating environmental problems due to difficulty in managing worldwide generated quantities that reach billions of metric tons. This study investigated the beneficial utilization of cement kiln dust and copper tailing as undesirable wastes in industrial applications through underground mines’ cemented paste backfill (CPB). Sixty different mixtures were prepared with three types of CKD collected from various cement manufacturers and were accordingly used with a proportion of 5, 10, and 15% to partially replace ordinary Portland cement (OPC) and pozzolan Portland cement (PPC) binders, represented in hundreds of CPB samples. The hardened specimens were subjected to density, uniaxial compressive strength (UCS), and axial deformation measurements to evaluate the physical and mechanical properties at curing up to 90 days. Meanwhile, X-ray powder diffraction (XRD) was extensively applied to chemically investigate the hydration products of CPB-hardened mixtures. Moreover, we developed a UCS predictive model applying two techniques: multiple variables regression analysis and artificial neural network (ANN). The results showed that the tricalcium silicate (Alite) and dicalcium silicate (Belite) phases form C-S-H upon hydrations and provide high strength in the binary mixtures. Meanwhile, the CKD’s lime saturation factor (LSF) governed the strength value in the ternary mixtures that utilized copper tailings. That makes CKD practical in the CPB mixture when partially replacing the OPC and PPC binders, with a proportion of up to 15%. In addition, the ANN technique’s predictive model exhibited a significant positive correlation with excellent statistical parameters that achieved 0.995, 0.065, and 0.911 for R2, RMSE, and MAE, respectively.

Mining still plays a vital role in providing various sectors with essential materials since many industries depend heavily on mined minerals. Moreover, the mining industry is the primary driver for many economies worldwide. On the other hand, new mining projects face many challenges, the most important of which are risks related to the economic aspects, e.g., the significant uncertainty about mineral resources compared to other engineering projects. Therefore, many jurisdictions worldwide depend on detailed engineering studies conducted according to internationally recognized standards to assess the new mining projects from an economic and technical perspective. In the same context and due to the significant lack of published research in this field, as the literature review revealed, this article reviewed and discussed the different main stages of engineering studies to evaluate new potential mining projects, including scoping, pre-feasibility, and feasibility studies, to ensure that the engineering study report complies with all the recognized main requirements. Results indicated the necessity of adhering to the needs of the engineering tasks while preparing reports of evaluation studies for new mining projects to reduce potential uncertainty risks and thus raise the level of confidence in these types of projects. Furthermore, they showed direct progress between the investigation details conducted in the evaluation studies and the value of the new mining project.