The importance of the mining/milling industry in increasing the growth level and welfare of countries is quite high. However, at the end of mining/milling processes, huge amounts of waste (often ...known as tails) are inevitably produced that have no economic value and can even be considered dangerous due to some heavy metals they contain. These tails are highly problematic due to both their volume (difficult to manage environmentally) and toxicity (potential to cause acid/leach waters) and need to be handled outside of existing disposal methods. This article presents the effective and sustainable handling and application of tails resulting from the enrichment of copper–zinc ores, which are actively engaged in metallic mining activities in the northeast of Türkiye, with the submarine tails disposal (STD) method. In the mining operation under study, some (~55–60 wt.%) of the tails are employed as underground fill, even though the residual part is disposed of by the STD method. The characterization of ore beneficiation tails, their transportation to the subsea via a pipeline system, and discharge monitoring results are detailed in the present investigation. According to the limitations which are indicated by the Turkish Control of Water Contamination regulation, the concentration of Pb-Cu found in the results was under the allowable limit of 0.05 mg/L. The allowed 2 mg/L limit for Zn was not surpassed mainly by the concentration found in the collected samples. pH values were almost above the allowable limit of pH > 5. The results reveal that the STD technique works quite well as an integrated mine tails method in the mine under study.
•Effect of fiber reinforcement on mechanical behavior of cemented tailings backfill (CTB) was investigated.•Polypropylene fiber exhibited the strongest reinforcing effect, followed by ...polyacrylonitrile and glass fiber.•The peak strain and the post-peak ductility properties are positively correlated with fiber content.•Fiber-reinforced CTB samples have a dense microstructure and good adhesion, suppressed crack propagation.•Ampirical equation was developed to forecast the peak strength and elastic modulus of CTB samples.
Fibers are accountable for an increase of compressive and shear strengths, particularly at the post-peak and post-cracking stages. The level of the strength improvement is primarily based on several factors: fiber type and content; fiber geometry, fiber distribution within the matrix; and the fiber-matrix interaction. An experimental campaign consisting of uniaxial compression and scanning electron microscopy tests were carried out to realize the effect of fiber reinforcement on mechanical behavior and microstructural properties of cemented tailings backfill (CTB) prepared with different fiber types (e.g., polypropylene, polyacrylonitrile and glass fibers) and contents (0%-control sample, 0.3, 0.6%, and 0.9%). Experimental results exhibit that polypropylene fiber exhibited the strongest reinforcing effect, followed by polyacrylonitrile and glass fiber. The rate of strength increase of the three fiber-reinforced fills after curing of 28 days reached 39.6%, 34.8% and 23.1%, respectively. A fiber content of 0.6% in the mixture is considered as a critical point, and the compressive strength of fiber-reinforced CTB samples first increases and then decreases, the peak strain and the post-peak ductility properties are positively correlated with fiber content. The failure process of fiber-reinforced CTB samples is mainly divided into four stages: pore compaction, linear elasticity, strain softening and crack propagation. It has the feature of ‘cracking without breaking’. Besides, fiber-reinforced CTB samples have a dense microstructure and good adhesion, improved interface between the fiber and the CTB matrix, and suppressed crack propagation. Lastly, an empirical equation was developed to forecast the peak strength and elastic modulus of CTB samples with different curing times.
The ordinary cemented tailings backfill (CTB) is a cement-based composite prepared from tailings, cementitious materials, and water. In this study, a series of laboratory tests, including uniaxial ...compression, digital image correlation measurement, and scanning electron microscope characteristics of fiber-reinforced CTB (FRCTB), was conducted to obtain the uniaxial compressive strength (UCS), failure evolution, and microstructural characteristics of FRCTB specimens. The results show that adding fibers could increase the UCS values of the CTB by 6.90% to 32.76%. The UCS value of the FRCTB increased with the increase in the polypropylene (PP) fiber content. Moreover, the reinforcement effect of PP fiber on the CTB was better than that of glass fiber. The addition of fiber could increase the peak strain of the FRCTB by 0.39% to 1.45%. The peak strain of the FRCTB increased with the increase in glass fiber content. The failure pattern of the FRCTB was coupled with tensile and shear failure. The addition of fiber effectively inhibited the propagation of cracks, and the bridging effect of cracks by the fiber effectively improved the mechanical properties of the FRCTB. The findings in this study can provide a basis for the backfilling design and optimization of mine backfilling methods.
Understanding the flow process of cemented tailings backfill (CTB) is important for successful pumping into underground stopes. This study examines the effects of solid content (SC), cement/tailings ...(c/t) ratio, and curing time (CT) on rheological and mechanical properties of CTB mixes. The slurry concentration of the mixes was 65, 67, and 69 wt. %, with c/t ratios ranging from 1:4 to 1:20. Unconfined compressive strength (UCS) tests were performed on hardened CTB mixes after curing 3, 7, and 28 days. The rheological properties of CTB slurries are mainly related to SC. The yield stress and viscosity of fresh mixes increase with increasing SC, but the pipeline resistance loss (PRL) also increases with increasing SC. According to the analysis of variance, the SC and flow rate are the most significant parameters which greatly affect the PRL performance. The c/t and CT parameters are the most significant parameters for affecting the shrinkage rate. The findings offer a reference for theoretical optimization for mine filling systems of similar type.
Polypropylene (PP) fiber-reinforced cement-based tailings backfill (FRCTB) is a green compound material with superior crack resistance and has good prospects for application in underground mining. ...However, FRCTB exhibits susceptibility to dynamic events, such as impact ground pressure and blast vibrations. This paper investigates the energy and crack distribution behavior of FRCTB under dynamic impact, considering the height/diameter (H/D) effect. Split Hopkinson pressure bar, industrial computed tomography scan, and scanning electron microscopy (SEM) experiments were carried out on six types of FRCTB. Laboratory outcomes confirmed fiber aggregation at the bottom of specimens. When H/D was less than 0.8, the proportion of PP fibers distributed along the
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angle direction of 80°–90° increased. For the total energy, all samples presented similar energy absorption, reflectance, and transmittance. However, a rise in H/D may cause a rise in the energy absorption rate of FRCTB during the peak phase. A positive correlation existed between the average strain rate and absorbed energy per unit volume. The increase in H/D resulted in a decreased crack volume fraction of FRCTB. When the H/D was greater than or equal to 0.7, the maximum crack volume fraction of FRCTB was observed close to the incidence plane. Radial cracks were present only in the FRCTB with an H/D ratio of 0.5. Samples with H/D ratios of 0.5 and 0.6 showed similar distributions of weakly and heavily damaged areas. PP fibers can limit the emergence and expansion of cracks by influencing their path. SEM observations revealed considerable differences in the bonding strengths between fibers and the FRCTB. Fibers that adhered particularly well to the substrate were attracted together with the hydration products adhering to surfaces. These results show that FRCTB is promising as a sustainable and green backfill for determining the design properties of mining with backfill.
The utilization of solid wastes (SWs) as a potential resource for backfilling is not only conducive to environmental protection but also reduces the surface storage of waste. Two types of SWs, ...including fly ash (FA) and desulfurized gypsum (DG), were used to prepare cementitious backfilling materials for underground mined-out areas. Ordinary Portland cement (OPC) was used as cement in mine backfill. To better investigate the feasibility of preparing backfill materials, some laboratory tests, such as uniaxial compressive strength (UCS), scanning electron microscopy (SEM), and energy dissipation theory, were conducted to explore both strength and microstructural properties of backfilling. Results have demonstrated that the main components of FA and DG in this study are oxides, with few toxic and heavy metal components. The ideal ratio of OPC:FA:DG is 1:6:2 and the corresponding UCS values are 2.5 and 4.2 MPa when the curing time are 7 days and 14 days, respectively. Moreover, the average UCS value of backfilling samples gradually decreased when the proportion of DG in the mixture increased. The main failure modes of various backfilling materials are tensile and shearing cracks. In addition, the corresponding relations among total input energy, dissipated energy and strain energy, and stress–strain curve were investigated. The spatial distribution of oxygen, aluminum, silicon, calcium, iron and magnesium elements, and hydration product are explored from the microstructure’s perspective. The findings of this study provide both invaluable information and industrial applications for the efficient management of solid waste, based on sustainable development and circular economy.
This experimental study investigates the influence of silanized micro-size silicate-based minerals on mechanical, thermal, and rheological properties of wood (maple) polymer (high-density ...polyethylene) composites. The silicate-based minerals used in the experiments are prepared from mine tailings through the inertization process (acid leaching). Two different types of organo-functional silanes including vinyl-trimethoxy and amino-ethyl amino-propyl trimethoxy silanes (3%) are used to modify the mineral fillers. The different amounts of mineral fillers (1–5%) are added to the composites as wood filler replacement and while the composite properties are evaluated. The obtained results implicated that the addition of 1% silane modified minerals decreases the rigidity and increases the ductility (up to 25%) of wood polymer composite. Mineral fillers modified with vinyl-silane were more effective to improve both tensile and flexural strengths and less advantageous on rheological behaviour. Amine-modified minerals had no negative influence on rheological performance even if they significantly decreased the rigidity of composites. Both surface modified minerals improved the thermal stability of wood plastic composites.
For mines with poor ore bodies and surrounding rocks, the general mining method does not allow the ore to be extracted from underground safely and efficiently. For these mines, the downward layered ...filling mining technique is undoubtedly the most suitable mining method. The downward filling mining technique may eliminate the troubles relating to poor ore deposit conditions, such as production safety, ore loss rate, and depletion rate. However, in this technique, the safety of the artificial roof of the next stratum is of paramount importance. Cementitious tailings backfilling (CTB) that is not sufficiently cemented and causes collapses could threaten ore production. This paper explores a diamond-shaped composite structure to mimic the stability of a glued false roof in an actual infill mine based on the recently emerged three-dimensional (3D) printing technology. Experimental means such as three-point bending and digital image correlation (DIC) techniques were used to explore the flexural characteristics of 3D construction specimens and CTB combinations with different cement/tailings weight ratios at diverse layer heights. The results show that the 3D structure with a 14-mm ply height and CTB has strong flexural characteristics, with a maximum deflection value of 30.1 mm, while the 3D-printed rhomboid polymer (3D-PRP) structure with a 26-mm ply height is slightly worse in terms of flexural strength characteristics, but it has a higher maximum flexural strength of 2.83 MPa. A combination of 3D structure and CTB has more unique mechanical properties than CTB itself. This research work offers practical knowledge on the artificial roof performance of the downward layered filling mining technique and builds a scientific knowledge base regarding the successful application of CTB material in mines.
Mining methods use cemented tailings backfill (CTB) for filling mined-out voids and make operations safer since employees are working under it. Hence, the durability behavior of CTB is of great ...importance in applications, for example, in the assessment of slope stability when extracting ore left in neighboring stopes. Addition of cement content would increase the strength of CTB but creates extra costs to mines. To cut cement-related costs as well as improve durability, different types of fibers are added to CTB samples. This paper aims to analyze flexural behavior of fiber reinforced CTB samples under three-point bending loading. To do so, a comprehensive laboratory work was undertaken to explore the effect of fiber reinforcement on bending resistance of CTB samples, based on orthogonal experimental design. The effect of fiber type (FT), fiber content (FC), solid content (SC) and cement-to-tailings ratio (c/t) on bending characteristics was investigated. Results indicate that the addition of fiber enhances the bending strength of fiber reinforced CTB samples and the bearing capacity after the peak in the load-deflection curve. Fibers help correct the faintness of CTB samples by mobilizing tensile strength along the failure planes. The crack resistance of fiber is reflected in the crack propagation stage. Secondly, the order of the sensitivity of four factors on bending strength of fiber reinforced CTB samples is as follows: c/t > SC > FT > FC. Lastly, the main findings of this study can provide a major reference for CTB's last design in underground mining.
Using solid wastes (SWs) as backfilling material to fill underground mined-out areas (UMOAs) solved the environmental problems caused by SWs and reduced the backfilling cost. In this study, fly ash ...(FA), gypsum and steel slag (SS) were used to prepare cement-based composites (CBC). The uniaxial compression, computed tomography (CT) and scanning electron microscope (SEM) laboratory experiments were conducted to explore the macro and micromechanical properties of CBC. The findings showed that the uniaxial compressive strength (UCS) of CBC with a curing time of 7 d could reach 6.54 MPa. The increase of SS content reduced the UCS of CBC, while the gypsum and FA content could increase the UCS of CBC. Microscopic studies have shown that the SS particles in CBC have noticeable sedimentation, and the increase of SS content causes the failure mode of CBC from tensile to tensile-shear. These research results can provide a scientific reference for the preparation of backfilling materials.
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