Search Results (24)

Red mud (RM) is a strongly alkaline waste residue produced during alumina production, and its high alkali and fine particle characteristics are prone to cause soil, water, and air pollution. Phosphogypsum (PG), as a by-product of the wet process phosphoric acid industry, poses a significant risk of fluorine leaching and threatens the ecological environment and human health due to its high fluorine content and strong acidic properties. In this study, RM-based cemented paste backfill (RCPB) based on the synergistic curing of PG and ordinary Portland cement (OPC) was proposed, aiming to achieve a synergistic enhancement of the material’s mechanical properties and fluorine fixation efficacy by optimizing the slurry concentration (63–69%). Experimental results demonstrated that increasing slurry concentration significantly improved unconfined compressive strength (UCS). The 67% concentration group achieved a UCS of 3.60 MPa after 28 days, while the 63%, 65%, and 69% groups reached 2.50 MPa, 3.20 MPa, and 3.40 MPa, respectively. Fluoride leaching concentrations for all groups were below the Class I groundwater standard (≤1.0 mg/L), with the 67% concentration exhibiting the lowest leaching value (0.6076 mg/L). The dual immobilization mechanism of fluoride ions was revealed by XRD, TGA, and SEM-EDS characterization: (1) Ca²⁺ and F⁻ to generate CaF₂ precipitation; (2) hydration products (C-S-H gel and calixarenes) immobilized F⁻ by physical adsorption and chemical bonding, where the alkaline component of the RM (Na₂O) further promotes the formation of sodium hexafluoroaluminate (Na₃AlF₆) precipitation. The system pH stabilized at 9.0 ± 0.3 after 28 days, mitigating alkalinity risks. High slurry concentrations (67–69%) reduced material porosity by 40–60%, enhancing mechanical performance. It was confirmed that the synergistic effect of RM and PG in the RCPB system could effectively neutralize the alkaline environment and optimize the hydration environment, and, at the same time, form CaF₂ as well as complexes encapsulating and adsorbing fluoride ions, thus significantly reducing the risk of fluorine migration. The aim is to improve the mechanical properties of materials and the fluorine-fixing efficiency by optimizing the slurry concentration (63–69%). The results provide a theoretical basis for the efficient resource utilization of PG and RM and open up a new way for the development of environmentally friendly building materials. Full article

With the advancement of backfill mining technology, cemented high-concentration backfill (CHB), composed of solid particles, such as high-concentration tailings or waste rock mixed with a small amount of binder, has gained widespread applications due to its superior filling performance. Given the complexity of the backfill pipeline network, studying the characteristics of pipe transportation is crucial. The local resistance in bending pipes represents an important parameter for CHB pipeline transportation. However, existing research on the local resistance characteristics of bending pipes lacks comprehensiveness and depth. This study proposes a novel definition of the local resistance coefficient as the ratio of pressure loss per unit length of a bend pipe compared to that of a straight pipe. Utilizing the computational fluid dynamics (CFD) method the impact of six different factors on the local resistance coefficient of the bending pipe is investigated: flow velocity, pipe diameter, slurry concentration, binder content, turning radius, and bending angle. The results indicate that the local resistance coefficient positively correlates with the flow velocity and pipe diameter but negatively correlates with the slurry concentration, turning radius, and bending angle. Among these factors, the slurry concentration exerts the most significant influence on the local resistance coefficient. The recommended approach to control the local resistance coefficient in the mine is to use CHB with a 76% solid fraction at a 1.5 m/s flow velocity, along with pipe parameters of a 0.15 m diameter, a 2.5 m turning radius, and bending angles between 90° and 150°. The findings provide a valuable reference for determining the optimal parameters for bend pipes and CHB and facilitate the theoretical calculation of resistance in complex filling pipeline networks. Full article

With the escalating demand for advanced and eco-friendly processing technologies in mining engineering, the potential applications of microwave heating technology in the treatment of cement tailings backfill (CTB) are expanding significantly. This research comprehensively investigates the mechanisms through which microwave irradiation duration and power influence the mechanical properties of CTB with varying concentrations and cement-to-sand ratios. The aim is to reveal the influencing patterns through experimental methods, providing scientific evidence for optimizing CTB treatment processes. This paper conducted microwave heating tests, uniaxial compression tests, and SEM-EDS tests on CTB. The research results indicate that heating time and power significantly enhance the early strength of CTB, with a more pronounced effect on CTB with higher concentrations and higher cement–sand ratios. When the heating time is 7 min and the heating power is 340 W, the cement hydration reaction is maximally promoted, thereby increasing the density and strength growth rate of CTB. However, excessively long heating time or overly high heating power may cause microcracks or thermal stress concentration within the CTB, adversely affecting the strength growth rate of CTB. Optimal thermal exposure duration and microwave power settings facilitate the activation of cementitious materials and the nucleation of calcium-silicate-hydrate (C-S-H) phases, thereby accelerating the compressive strength evolution of cemented tailings backfill (CTB). The outcomes of this research offer valuable insights into the deployment of microwave heating methodologies in underground mine backfilling, which are pivotal for augmenting the economic viability and environmental sustainability of mining operations. Full article

The high consumption and high cost of cement are the bottleneck problems that limit the development of cemented tailings backfilling technology. The low-consumption cement backfill is immersed in a weak acid/alkaline groundwater environment for a long time. Reducing the consumption of cement can easily lead to problems such as a sudden decrease in strength and the leakage of heavy metals. Through the monolithic leaching test in static and uniaxial compressive tests, the heavy metals’ leaching concentration and the compressive strength of low-consumption cement backfills in different pH soaking solutions were measured at different soaking times. Results show that a lower cement concentration will result in a lower CTB compressive strength and a higher rate of heavy metal leaching. Long-term exposure to an acidic/alkaline environment will lead to the instability and destruction of the CTB structure. A microscopic examination reveals that the creation of hydration products can improve the structure’s compactness while also lowering the internal porosity of CTB but can also solidify heavy metal ions in various ways. A first-order reaction/diffusion model (FRDM) can better evaluate the leaching behavior of CTB. This study helps to improve backfilling technology, thereby contributing to the creation of sustainable mining geotechnologies. Full article

The flowability and mechanical properties are increasingly crucial in the filling process of deep metal mines with mining depths exceeding 1000 m. The rheological properties of filling slurry in the pipeline were analyzed through rheological tests, L-tube self-flow tests, and semi-industrial loop tests. The results revealed that with an increase in the cement-to-tailings mass ratio (c/t ratio) and mass concentration, the slurry exhibited a higher flow resistance and decreased stowing gradient. During slurry transportation, the pressure loss in the straight pipe was positively correlated with the slurry flow rate, c/t ratio, and mass concentration. A uniaxial compressive strength (UCS) test was conducted to analyze the mechanical properties of the cemented paste backfill containing BMC (CCPB) in both standard and deep-underground curing environments. The UCS of the CCPB showed an increasing trend with the rise in curing age, mass concentration, and the c/t ratio. The comprehensive analysis concluded that when the c/t ratio is 1:4, and the mass concentration is approximately 74%, and parameters such as the slump, bleeding rate, and flowability of the filling slurry meet the criteria for conveying and goaf filling, resulting in a high-strength filling body. Full article

In underground filling mining, freshly prepared cemented gangue-fly ash backfill (CGFB) slurries are typically piped into the gobs. The rheological properties of backfill slurry during pipeline transportation have a direct impact on the transportation characteristics, which in turn affect pipeline blockage and wear. In this paper, the rheological behavior and viscoelastic-plastic properties of CGFB during pipeline transportation are investigated. The effects of different solid content and cement content on resistivity were tested experimentally, and their viscoelasticity and plasticity were analyzed. The results show that with the increase in solid phase content and cement content, the viscosity, yield stress, and energy storage modulus of the materials showed an increasing trend. The viscosity and yield stress of the material both increased, reaching 32.77% and 51.22%, respectively. It was found by the dynamic shear test that in the low-strain region, the material showed a more significant elastic nature of the solid, while in the high-strain region, the viscosity of the material gradually increased. Cement has a substantially lower resistivity than fly ash and gangue, and with the increase in solid concentration, the resistivity of the material shows an increasing trend. With the increase in cement content, the resistivity generally shows a decreasing trend, but it should be noted that the resistivity change trend may tend to stabilize after the cement content exceeds 12%. The study’s findings can aid in understanding the rheological properties of CGFB and its viscoelastic-plastic behavior during the underground filling and conveying process, which can provide a reference basis for research and application in related fields. Full article

Currently, in some domestic and foreign mines, the backfill drilling pipeline experiences a rupture phenomenon even when the wear degree is low. This results in a delay in production due to the filling becoming ‘sick’. This paper presents, for the first time, the damage mechanism from a mechanical perspective and re-derives the anti-extrusion strength model of the backfill drilling pipeline. We investigate the influence of the law on the anti-extrusion strength of pipelines from the perspective of strata and cement rings. We then verify the theoretical and simulation results through engineering examples. The results demonstrate that the Mises stress criterion is a suitable modification principle for the anti-extrusion strength model of the backfill drilling pipeline. The anti-extrusion strength of the pipeline is related to the elastic modulus and Poisson’s ratio of the stratum, and the thickness of the cement ring. It is negatively affected by the depth of the stratum. For hard strata, a cement ring with a smaller elastic modulus is suitable, while for soft stratum, a cement ring with a larger elastic modulus is recommended. When the missing angle of the cement ring is less than 60°, the stress concentration factor increases up to 2.2. The stress unloading capacity of the cement ring ranges from 32.7% to 37.8%, and optimal performance of the cement ring is achieved when it has high strength and low rigidity. The backfill filling pipeline of a copper mine abroad was destroyed due to external extrusion force exceeding its anti-extrusion strength value. The modified pipeline anti-extrusion strength model is 18.2% higher than the pipeline API strength value. This finding can inform the design of the backfill filling pipeline for China’s kilometer-deep wells in the future. Full article

Cement paste backfill (CPB) suffers serious damage and deterioration under the dual erosion conditions of the dry–wet cycle caused by the high chloride salt concentration in mine water and the fluctuation of mine water level. In order to discuss the mechanical properties and permeability characteristics of CPB under erosion, this study designs an immersion experiment for CPB under chloride salt and dry–wet cycle conditions. Through a uniaxial compressive strength (UCS) test, the change law for the mechanical parameters of the CPB was investigated, the strength constitutive equation of the CPB was constructed and the deterioration process of the CPB was analyzed. The penetration test was used to investigate the diffusion characteristics of the packing under chloride salt and dry–wet cycle conditions. The results showed that the strength and Young’s modulus of the CPB initially increased and then rapidly decreased, with maximum decrease rates of 32.2% and 38.2%, respectively. The CPB structure exhibits an initial undamaged stage, an initial damaged stage, a damaged development stage, a damaged destruction stage and a residual damaged stage. The chloride ion penetration depth gradually increased with the number of dry–wet cycles, with a maximum diffusion depth of 20.5 mm. The maximum apparent diffusion coefficient of chloride ion was 18.99 × 10⁻¹⁰ m²/s, and the maximum concentration was 0.303 mol/L. Under the double erosion conditions of chloride salt and dry–wet cycle, the CPB structure was severely damaged. Full article

To study the influences of different mix proportions of materials on the ultrasonic p-wave velocity of coal slime based backfill materials, influences of four factors on the p-wave velocity of specimens were investigated by designing orthogonal tests and taking coal slime as the principal raw material. The four factors included the following: (A) the mass concentration of coal slime, (B) the content of high-water-content material, (C) cement content, (D) and content of fly ash. Test results revealed the following: (1) the ultrasonic p-wave velocity is in the range of 3.916 to 8.319 km/s and various factors are listed in a descending order as A, D, B, and C according to their influences on the ultrasonic p-wave velocity; (2) the ultrasonic p-wave velocity is positively correlated with the compressive strength and shear strength, with correlation coefficients separately of 0.87 and 0.65; (3) the equations for variations in the ultrasonic p-wave velocity under influences of different factors are fitted. The ultrasonic p-wave velocity has a quadratic polynomial relationship with factor A, while following exponential relationships with factors B, C, and D. A predictive model for characteristic parameters of the ultrasonic p-wave velocity of coal slime based backfill materials jointly influenced by the four factors was established based on the fitting equation for variations of single factors and ultrasonic p-wave velocity. The predictive model was then verified. Full article

To study the flow and strength characteristics of loess-based backfill materials, orthogonal tests were used to design a cemented backfill material combining loess, high-water content materials, cement, and fly ash. By using the range, analysis of variance, and multi-variate regression analysis, influences of four key factors on the initial setting time, diffusivity, compressive strength, and shear strength of the backfill material were investigated. These four factors included the mass concentration of loess water (A), the content of high-water content materials (B), cement content (C), and content of fly ash (D). The results showed that the initial setting time, diffusivity, compressive strength, and shear strength of the backfill material were 13~33 min, 400~580 mm, 0.917–3.605 MPa, and 0.360–0.722 MPa, respectively, all distributed in wide ranges. For the initial setting time, the four factors were listed in descending order as A > D > B > C according to their influences; for diffusivity, the four factors were listed as A > B > C > D; for the compressive strength, the four factors were ranked as A > C > D > B; for the shear strength, the four factors were ranked such that A > C > D > B. With regard to the comprehensive index, the four factors were such that A > B > D > C. That is, the factors were listed in descending order as the mass concentration of loess water, cement content, the content of fly ash, and content of high-water content materials according to their significance in influencing characteristics of the loess-based backfill material. Comprehensive analysis indicated that the fluidity of the material was mainly influenced by the mass concentration of loess water, and the two were negatively correlated. The hydro-consolidation effect of materials with high-water contents accelerated material solidification. The strength of the backfill material was mainly influenced by the cement content while only slightly affected by contents of other materials. In this way, a prediction model for characteristic parameters, namely, fluidity and strength, of the loess-based backfill material under the action of various factors was established. Full article

Compared with the post-treatment of pollutants, such as the removal of phosphate from wastewater, it is more important to develop effective emission control strategies to reduce phosphate pollution. Phosphogypsum (PG) is a typical solid waste byproduct of phosphate production and contains high amounts of residual phosphate. In order to control the phosphate emissions during the recycling of PG aggregates for cemented backfill, another solid waste product—iron tailings (ITs)—was added during the preparation of backfill slurry. The results showed that the ITs effectively accelerated the phosphate removal in cemented PG backfill, enabling the quick reduction in the phosphate concentration to the discharge standard (<0.5 mg/L) within 15 min. This means that the emissions of phosphate to bleeding water were effectively controlled. The adsorption experiment showed that phosphate was adsorbed by the ITs, and the adsorption data fitted well with the Langmuir adsorption model (R² = 0.98) and pseudo-second-order kinetic model (R² = 0.99), indicating that the phosphate adsorption of ITs was a monolayer chemical adsorption. Furthermore, an unconfined compressive strength (UCS) test was performed on the backfill with the addition of ITs. Compared to the control group (without ITs), the UCS of backfill with 20% ITs increased from 1.08 MPa to 1.33 MPa, indicating that the addition of solid waste could be beneficial to the strength development of the backfill by mitigating the interference of phosphate with the hydration process. The backfill cured for 28 d was selected for the toxic leaching test, and the phosphate concentration in the leachates was always below 0.02 mg/L, indicating that ITs can effectively immobilize phosphate in backfill for a long time. Full article

SMW (soil mixing wall) piles have been widely used in soft soil areas such as Jiangsu, Shanghai, Tianjin and so on, and they have many advantages, such as retaining the structures of foundation pits. In order to promote the application of SMW piles in sandy soil areas such as Henan province, SMW piles were used in a deep foundation pit project of a high-rise building in Zhengzhou. Three SMW piles in the middle area of the foundation pit were selected for site measurement to determine the mechanical properties of SMW piles in sandy soil areas. Several typical test sections were determined along the height of the pile. The vibrating string type of the reinforcement dynamometers were set on the H-shaped steel of each test section, and the stress distribution of the H-shaped steel along the depth of the pit was obtained via testing. The axial force, bending moment and shearing force of the H-shaped steel were further calculated, and the affecting factors and development laws of the internal force distribution of the H-shaped steel were analyzed in detail. The research shows that, at the stage of foundation pit excavation, the overall stress of H-shaped steel increases gradually. The axial force of H-shaped steel in an SMW pile is mainly affected by such factors as the weight of the H-shaped steel, the weight of the crown beam and the first support system, the weight of the breast beam and the second support system, and the frictional resistance of the cemented soil. The bending moment and shearing force of H-shaped steel are mainly affected by such factors as the lateral soil pressure and the concentrated forces of the two support systems. When the foundation pit was excavated to the base, the development of and changes in the law of internal force with regard to the H-shaped steel was analyzed. When the overall internal force of the H-shaped steel is at its maximum, the maximum absolute values in terms of the axial force, bending moment and shearing force are −481 KN, 371 KN·m and 123 KN. In the process of foundation pit excavation and backfilling, the point of contraflexure of the H-shaped steel moves down gradually, and the fixed end of corresponding SMW pile also moves down and stabilizes below the base. These results may provide a reference for the design and construction of SMW piles of building structures in sandy soil areas. Full article

Ultra-fine cemented paste backfill (UCPB) is prepared using tailings, binder and water. The factors affecting the resistance of UCPB pipe transport are numerous and complex, and the factor interactions restrict the rational development of the filling pipe transport design, which is not conducive to reducing the resistance. This paper categorizes and integrates the factors of pipe transport resistance by theoretical analysis and uses response surface methodology (RSM) to study the influence of different types of factors on the UCPB pipe transport resistance. The results show that the pipe transport resistance factors are classified into endogenous and exogenous factors. According to the classification, the reduction rate of the optimized pipe transport resistance is as high as 25.31% and 15.81%. This shows that the categorization of factors affecting the pipe transport resistance is important for investigating UCPB pipe flow. The single-factor terms with the highest significance under the effect of endogenous and exogenous factors are mass concentration and pipe diameter, respectively. The two interaction terms with highest significance are mass concentration and slurry temperature, pipe diameter and flow velocity, respectively. The results provide new ideas to reduce the resistance of mine pipeline and improve the filling benefit and convenience of pipeline design. Full article

To explore the strength development characteristics and engineering performance of different coal-based solid waste filling materials cemented into filling body, coal gangue was used as coarse material, fly ash, desulfurization gypsum, gasification slag, and furnace bottom slag as fine material, and cement as a gelling agent. The uniaxial compressive strength (UCS) and bleeding rate of coal-based solid waste cemented backfill (CBSWCB) were tested by an orthogonal experiment, and the influencing factors of mechanical properties and strength development were analyzed. The multiple generalized linear model of strength and bleeding rate was established, and the optimal filling material ratio was determined. The engineering performance index of CBSWCB with the optimal ratio was tested. The results show the following points: (1) the concentration and content of desulfurization gypsum had a great influence on the early compressive strength of CBSWCB, while fly ash, gasification slag, and furnace bottom slag had little influence on the early compressive strength. (2) High concentration, high content of fly ash and furnace bottom slag, low content of desulfurization gypsum, and gasification slag can significantly improve the early strength. High concentration and high content of fly ash, low content of gasification slag, furnace bottom slag, and desulfurization gypsum are beneficial to the later strength increase. (3) Under the optimal ratio scheme, the bleeding rate of CBSWCB was 1.6%, the slump was 16.6 cm, the cohesion was general, the segregation resistance was good, the initial setting time was 5.42 h, the final setting time was 7 h, and the early strength after curing for 8 h reached 0.24 MPa. Full article

Over many decades, cement has been the primary component in construction projects and is considered one of the essential industries worldwide. At the same time, it overconsumes natural resources and can negatively impact the environment through a few byproducts, such as carbon dioxide (CO₂) and cement kiln dust (CKD). The generated quantity of CKD is estimated to be 15–20% of the produced cement, which means CKD can be induced in hundreds of millions of metric tons synchronously with annual global cement production. Unfortunately, not all materials of CKD are suitable for recycling in cement manufacturing since it contains high levels of alkalis, sulfate, and chloride, leading to excessive concentrations in the final product. Therefore, CKD industrial utilization has become highly recommended in recent research as a potential beneficial application from economic, environmental, and sustainability perspectives. This review paper highlights and discusses the recently conducted research articles that investigate the industrial applications of CKD. The obtained outcomes showed that CKD has physical and chemical properties that make it practical in many fields, such as soil stabilization, concrete mix, chemical treatment, ceramic and brick manufacturing, and mine backfill. They also indicate a lack of studies investigating CKD in mine backfill applications as a partial replacement material for cement due to the high cost of binders, optimization, and sustainability purposes. Full article