Journal of Central South University最新文献

In the mining industry, precise forecasting of rock fragmentation is critical for optimising blasting processes. In this study, we address the challenge of enhancing rock fragmentation assessment by developing a novel hybrid predictive model named GWO-RF. This model combines the Grey Wolf Optimization (GWO) algorithm with the Random Forest (RF) technique to predict the D₈₀ value, a critical parameter in evaluating rock fragmentation quality. The study is conducted using a dataset from Sarcheshmeh copper mine, employing six different swarm sizes for the GWO-RF hybrid model construction. The GWO-RF model’s hyperparameters are systematically optimized within established bounds, and its performance is rigorously evaluated using multiple evaluation metrics. The results show that the GWO-RF hybrid model has higher predictive skills, exceeding traditional models in terms of accuracy. Furthermore, the interpretability of the GWO-RF model is enhanced through the utilization of SHapley Additive exPlanations (SHAP) values. The insights gained from this research contribute to optimizing blasting operations and rock fragmentation outcomes in the mining industry.

Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse, posing significant safety risks. However, previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress, especially that of the intermediate principal stress. The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation, and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load. Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress, intermediate principal stress, and detonation pressure, whereas negatively correlated with Poisson ratio and decoupling coefficient. The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior. The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress. As the in-situ stress increased from 0 to 70 MPa, the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.

The vibration pretreatment-microwave curing process is an efficient, low energy consumption, and high-quality out-of-autoclave curing process for carbon fiber resin matrix composites. This study aims to investigate the impact of vibration pretreatment temperature on the fiber weight content, microscopic morphology and mechanical properties of the composite laminates by using optical digital microscopy, universal tensile testing machine and thermogravimetric analyzer. Additionally, the combined mode of Bragg fiber grating sensor and temperature measurement fiber was employed to explore the effect of vibration pretreatment on the strain process during microwave curing. The study results revealed that the change in vibration pretreatment temperature had a slight impact on the fiber weight content when the vibration acceleration remained constant. The metallographic and interlaminar strength of the specimen formed at a vibration pretreatment temperature of 80 °C demonstrated a porosity of 0.414% and a 10.69% decrease in interlaminar shear strength compared to autoclave curing. Moreover, the introduction of the vibration energy field during the microwave curing process led to a significant reduction in residual strain in both the 0° and 90° fiber directions, when the laminate was cooled to 60 °.

Delayed rockburst experiments with different numbers of unloading surfaces (DNUS) were performed using an independently developed true triaxial multisurface unloading rockburst experimental system. Based on the rockburst excess energy theory, the energy storage characteristics, excess energy, excess energy release rate (EERR), and crack evolution characteristics of rockbursts with DNUS were studied, and the following main conclusions were obtained. The occurrence of rockbursts is mainly due to the generation of an excess energy ΔE. ΔE depends on the elastic strain energy stored in the rock before the rockburst, the energy input by the equipment after the peak, and the residual elastic strain energy. As the DNUS increases, ΔE gradually decreases, but the EERR value increases, and the rockburst becomes increasingly severe; Rapid unloading of the specimen under true triaxial high-pressure loading will produce an unloading platform in the stress–strain curve, causing unloading damage. The damage is mainly concentrated near the free surface in the form of tension failure, and the unloading damage gradually increases with increasing DNUS; Tensile cracks play a dominant role in the damage and destruction of sandstone. In the final rockburst stage, the slope of the shear crack curve was greater than that of the tensile cracks, indicating that shear cracks were a critical factor affecting the instability and failure of the specimen.

The dissolution behaviors of Cu and Fe from copper slags were investigated with photochemical reactions. Experiments were run intermittently with a quartz glass jacket in a glass reactor, by submerging ultraviolet (UV) lamps and using glass tube as an air supply distributed under the reactor. The behaviors of UVA (365 nm), UVB (311 nm), UVC (254 nm), and vacuum-UV (VUV) (185 nm) light at different wavelengths in a leaching solution were examined. All experiments were conducted comparatively in the presence and absence of UV lamps under identical conditions. The adaptation of the radical formation mechanism to the leaching environment and its usability in leaching by creating an oxidative solution medium were investigated. In the experiments in the UV light (185 nm) and non-UV light environments under optimum conditions, the copper extraction rates were obtained as 85.1% and 70.7%, respectively. In conclusion, the metal dissolution (Cu) behaviors at optimum conditions during leaching from copper slags in the photoreactor systems with UV (185 nm) light were more efficient than those without UV light. Moreover, photochemical reactor is a new approach to adapt them to hydrometallurgy applications and examine the process.

In this paper, sinter samples of limonitic nickel laterite were adopted for Fe-Cr-Ni alloy preparation at lower costs. Based on the thermodynamics analysis, smelting characteristics of sinter samples of S1 (4.84 wt% Cr₂O₃) and S3 (7.72 wt% Cr₂O₃) were revealed by the optimization of smelting process parameters. When smelting durations were kept at 60 min and 90 min for S1 and S3 and smelting temperature, coke dosage and slag basicity were maintained at 1600 °C, 20 wt% and 1.0, respectively, the qualified Fe-Cr-Ni alloys containing 84%–88 wt% Fe, 5.6%–9.3 wt% Cr and 1.55%–1.70 wt% Ni were prepared with the recovery rates of Fe, Cr and Ni of over 96%, 90% and 98%, respectively. Higher Cr₂O₃ content of sinter leads to the prolongation of smelting duration, which is adverse to the reduction of coke ratio and the increase of stainless steel output. The comprehensive furnace burdens including Ni-bearing sinter and Cr-bearing pellets will be developed in the follow-up study for the more efficient preparation of high-Cr ferronickel.

Seawater coral aggregate concrete (SCAC) has demonstrated advantages in reducing material cost and energy consumption of marine infrastructure on reefs and islands. However, SCAC exhibits increased brittleness and higher dependency on coral aggregate type as its strength increases. In this study, two types of coral aggregates are used to compare their influence on SCAC performance. Flexible fiber and rigid fiber are blended to improve the strength, toughness, and fracture properties of SCAC. The results show that the compressive strength of SCAC incorporating low-strength coral aggregate is reduced by 30.8% when comparing to that containing high-strength coral aggregate (from 55.6 to 38.5 MPa). Fiber incorporation could mitigate the strength reduction that originated from weaker coral aggregates. A novel constitutive model is proposed to describe the stress-deformation curves of SCAC. Good agreement between the model prediction and test data is observed. Relative to reference group, the fracture energies of SCAC adding 0.1%, 0.2%, and 0.3% polyvinyl alcohol fibers are increased by 10%, 49%, and 88% respectively. The fracture energies of hybrid fiber groups are 46% higher than that of mono fiber groups with the same fiber dosage.

The non-ammonia thiosulfate leaching system is considered to be an attractive and eco-friendly route for gold leaching without the usage of cyanide or ammonia. In this paper, the role of four organic carboxylic acids, named oxalic acid (Ox), malic acid (Mal), citric acid (Cit), and tartaric acid (Tart) in copper-thiosulfate system has been studied comparatively. Based on the available thermodynamic data, a series of E_h–pH and species distribution diagrams for copper-Ox/Mal/Cit/Tart-thiosulfate system under various conditions have been constructed from thermodynamic calculation. The results show that thiosulfate is the only effective complexing agent for aurous ions, while the organic carboxylic acids work as a copper ligand. The copper-Mal/Cit/Tart-thiosulfate system exhibits potential advantages over the traditional copper-ammonia-thiosulfate system, such as wider pH range and lower thiosulfate consumption. The calculation also indicates the redox potentials of Cu(II)/Cu(I) for the leaching systems are in the subsequence of E⁰[Cu(Ox)₂²⁻/Cu(S₂O₃)₃⁵⁻] >E⁰[Cu(NH₃)₄²⁺/Cu(S₂O₃)₃⁵⁻] >E⁰[Cu₂(Mal)₂H₋₂²⁻/Cu(S₂O₃)₃⁵⁻] ≈E⁰[Cu₂(Cit)₂H₋₂⁴⁻/Cu(S₂O₃)₃⁵⁻] > E⁰[Cu(Tart)₂H₋₄⁶⁻/Cu(S₂O₃)₃⁵⁻]. Increasing thiosulfate concentration leads to a sharp decline in the content of copper-Ox/Mal/Cit/Tart complex, and the stability of the formed cupric complex follows the descending order of tartaric acid>citric acid>malic acid>oxalic acid.

Cemented gangue backfill technology is an important backfill mining method. However, the acid mine water environment could seriously affect the strength of the cemented gangue backfill body (CGBB). In this study, CGBB specimens were placed in different environments (air, water, H₂SO₄ solution, and H₂SO₄ solution coupled with load) to test the strength, resistivity, and ultrasonic pulse velocity (UPV) of CGBB at different ages. The acoustic emission (AE) energy of the specimens during loading was monitored, and the microstructure was analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Test results showed that: 1) The strength of CGBB cured in air and water gradually slowed down with age. The strength of CGBB in the H₂SO₄ solution was greater than that of CGBB cured in air or water in the first 90 d. The strength of CGBB under the coupling of the H₂SO₄ solution and load decreased more slowly with age than that of the single H₂SO₄ solution; 2) The resistivity and UPV had a good corresponding relationship with the strength of the CGBB. The failure modes of the CGBB after erosion were various, and the CGBB showed different AE energy characteristics at different stages of loading. The surge of AE energy could be used as a precursor to the failure of CGBB; 3) Erosion products compacted CGBB in the early stages and improved its strength. In the later stage, the CGBB cracked under the action of expansion stress and the strength decreased. Applying a 40% stress-to-strength ratio would resist the erosion of the H₂SO₄ solution. The research could provide a reference for the design of the corrosion resistance of CGBB.

In paste backfill mining, cemented coal gangue-flyash backfills (CGFB) can effectively control surface subsidence. CGFBs are subjected to water pressure and chloride ion erosion in the gob. Therefore, an improved understanding of the influence of pressurized water and chloride salt erosion on the performance of CGFB is crucial for realizing effective green mining. In this study, CGFB samples were soaked in a NaCl solution at 0, 0.5, 1.5, or 3.0 MPa for 15 d. The mechanical properties of the samples and deterioration mechanisms were investigated using uniaxial compression tests, acoustic emission tests, digital speckle strain measurements, scanning electron microscopy, and X-ray diffraction. The results show that the uniaxial compressive strength (UCS) increased and then decreased with the increase of soaking pressure. When the soaking pressure increased from 0 to 1.5 MPa, the average UCS increased by 43.5%. Then, when the soaking pressure increased from 1.5 to 3.0 MPa, the average UCS decreased by 18.9%. Moreover, water pressure promotes chloride ions into the interior of CGFB and the production of Friedel’s salt. Higher water pressures-chloride salt erosion coupling increases the porosity of CGFB, with the 3.0 MPa sample showing an 8.2% increase in porosity compared to the 0 MPa sample. Thus, internal pore cracks developed and penetrated the samples, which degraded their mechanical properties and reduced their strength and compactness.