The alloy structural steel for gear shafts was treated by adopting a quenching and partitioning process, and effects of temperature and time of partitioning on the tensile properties, physical phase composition, microstructure and fracture morphology of structural steel were all explored. The results show that when the end temperature of fixed quenching and temperature of partitioning remain unchanged, extension of partitioning time can lead to gradual decrease in the tensile strength of the steel for gear shafts, and an increase followed by decrease in the fracture strain; with partitioning temperature at 225 ℃ and 275 ℃ respectively, the highest fracture strain is obtained at partitioning time of 120 s and 90 s, respectively; extension of partitioning time can lead to an increase followed by decrease in the strength-elongation product of the steel for gear shafts; the highest strength-elongation product can be obtained when the partitioning time is 90 s, and the strength-elongation product of the sample after quenching and partitioning treatment is obviously higher compared to the sample just treated by quenching. There is almost no residual austenite in the directly quenched sample, while the residual austenite in the sample by quenching and partitioning treatment is in a volume fraction of 3.0%-6.4%. It is found that at the same partitioning temperature, extension of partitioning time can result in martensitic tempering transformation, and carbide precipitation and growth in the steel for gear shafts.

To investigate directional independence of multistage stress memory during progressive cyclic loading of granite under compression with a series of deflection angle, experiments were conducted on cyclic loading and unloading of granite with different deflection angles by using a self-made deflection device. The Kaiser effect (KE) and the incomplete erasion phenomenon (IEP) of the maximum stress in previous multistage cycles after progressive cyclic loading with deflection angles were explored in the experiments. Results show that both KE and IEP in granite exhibit directional independence. The directional independence of KE has a critical angle of 10° and the directional independence of IEP has a critical angle of 12°. With a deflection angle of 12°, the IEP will interfere with the memory of historical maximum stress by KE.

In order to know the status quo of technologies for deep-sea mineral resources development, the related patents were briefly analyzed. A total of 3 236 patents regarding deep-sea mineral resources development technologies published worldwide from 2000 to 2023 were taken from the incopat global patent database, and analyzed in terms of number of patent applications, geological distribution, subdivision of technologies, time of Chinese patents applications, as well as nationalities of Chinese patent applicants among others. It is found that the patents regarding deep-sea mineral resources development are mainly from China, United States, Korea, Russia and Japan, focusing on technologies including detection system, mining system and transportation system. In recent years, Chinese patent applicants have gradually predominated in the related patent application worldwide, reflecting China's great potential in R & D and market expansion of deep-sea mineral resources development technologies.

In order to effectively predict blast-induced rock fragmentation, a distribution of normalized rock fragmentation under different conditions was obtained by performing a designed experiment on drilling and blasting of a concrete specimen, and then the rock fragmentation exceeding 40 mm was selected for study. The correlation among variables under different testing conditions was analyzed by using Spearman correlation statistics, and the initial weights and thresholds of the BP neural network were optimized by using the ant colony optimization (ACO) to construct an ACO-BP model. The model was then trained with rock fragmentation by on-site blasting, and tested. Based on the comparison of such prediction mode with BP neural network model, random forest (RF) model and extreme gradient boosting (XGboost) model, it is found that the ACO-BP model is highly reliable in predicting blast-induced rock fragmentation, presenting a root mean square error of 0.13, an average absolute error of 0.11, and a coefficient of determination of 0.92. It is concluded that this model, with higher accuracy in prediction and applicability, can accurately predict blast-induced rock fragmentation.

The stability of goafs in a mine was analyzed. Firstly, the current situation of the goafs was investigated in detail to clarify the distribution and volume of goafs. Secondly, the stability variation of goafs before and after backfill was evaluated based on the FLAC^3D simulation results. It is found that there are five main goafs in the mine, which are distributed in the middle section of 700-860 m, with total volume of around 404 500 m³. Currently, the roof of goaf is unstable, posing a greater potential risk of collapse. The rock mass that is not connected together from 1^# to 4^# goaf has concentrated force on it and a plastic zone penetrates through, possibly causing large-scale instability. After the goafs in the middle section of 700-820 m are gradually backfilled, the risk of goaf instability can be gradually eliminated, and production activities in the middle section below 700 m won't be affected. It is recommended that 1^#-4^# goafs should be preferably backfilled to reduce the risk of roof collapse and penetration.

In order to analyze mechanical properties of conveying hose during deep-sea mining operation, a mechanical model was established with Abaqus software for the buffer, flexible hose, and mining vehicle under different working conditions to analyze effects of buoyant ball position, buoyant force, ocean current velocity and volume fraction of conveyed mineral ores on hose configuration, as well as effect of forces that flexible hose exerts on the mining vehicle. When buoyant balls are put on the position far away from a mining vehicle, the hose is prone to be dragged on the seafloor；while being closer to a mining vehicle, the hose is prone to be entangled. It is shown that the closer to a mining vehicle, the greater the buoyant force and the greater the forces that the hose exerts on the mining vehicle. Furthermore, slower current velocity is more likely to bring greater impact to the hose configuration. The velocity of ocean current will influence the direction, magnitude and variation of the forces exerted on the mining vehicle. It is suggested that with ocean current at a velocity of 0.2 m/s, buoyant balls should be put on the position 12 m away from the buffer, with buoyant force selected at 1 500 N. In this case, the maximum horizontal and vertical tensile forces of the hose on the mining vehicle are 941 N and 1 258 N, respectively.

In order to balance productivity against safety in the mining of high-level stope with gently-dipping and extrathick orebody, an iron mine adopting sublevel open stoping with backfill was taken as an example to optimize the mining sequence. Firstly, pillars was determined to at a reasonable spacing from 14.2 m to 47.2 m based on the theory of bearing capacity of pillars. Secondly, according to stope structure parameters, the pillars were designed to be 15 m, 30 m and 45 m in thickness, respectively. An orebody model was also established with FLAC^3D and then was used to analyze the roof subsidence and pillar stability based on comparison of each mining scheme. Finally, a judgment matrix of mining sequence was constructed based on analytic hierarchy process and fuzzy comprehensive evaluation method, with both factors of safety and productivity taken into consideration in the numerical simulation. The comprehensive membership degrees of those three schemes were calculated to be 0.86, 0.79 and 0.80, respectively, and pillars in the best scheme were determined to be in the thickness of 15 m. The results of an industrial experiment have proven that this scheme can ensure stope with relative stability while achieving the maximum production capacity.

In order to address the problem of slope stability for a valley dumpsite in one mountain area, numerical simulation was conducted with FLAC^3D for the stability of slope under three working conditions, including natural state, rainstorm case and earthquake occurrence. The stability and reliability of the dump under conditions of rainstorm plus seismic was evaluated with introduced Monte Carlo algorithm. Results show that the overall and part of dumpsite slope, under all three working conditions of natural state, rainstorm and earthquake, can be in a stable state, and the overall safety factors present a normal distribution and are mainly within the range of 2.0-2.1, consistent with the numerical simulation results (2.08); under conditions of rainstorm plus seismic, the probability for the overall dumpsite to be unstable is 0, while some parts of dumpsite have a 35.99% probability to be unstable. It is shown that the numerical simulation value and on-site monitoring result present a deviation from 9.8% to 15.4% based on the comparison.

An iron concentrate obtained from magnetic separation of red mud from Shandong was used in an experimental study on the effect of titanium removal by reverse flotation. In the experiment, with sodium oleate as collector, corn starch as hematite depressant, sulfuric acid as pH regulator, pulp pH of 9, and the addition of corn starch and sodium oleate at an amount of 500 g/t and 1 500 g/t, respectively, the iron concentrate was produced, with the TiO₂ grade fell down from 6.90% to 2.73%, and the TFe recovery reaching 41.80%. The results of collector adsorption and IR analysis show that sodium oleate exhibits selective adsorption characteristics, which has further confirmed the feasibility of sodium oleate used in removing titanium by reverse flotation of iron concentrate obtained from magnetic separation of red mud.

An experimental research was performed on pre-enrichment of a weathered low-grade vanadium-bearing stone coal ore to solve the problems of complex flow and high cost for the existing direct vanadium-extraction process. The process mineralogy study shows that the predominant vanadium minerals in the stone coal ore are vanadium-bearing limonite and vanadium-bearing mica, both being weakly magnetic, and a superconducting magnetic separation (SMS) plus sedimentation process is proposed for pre-enrichment of vanadium. With magnetic field strength of 4 T and slurry flow rate of 8.0 L/min, SMS produced a pre-enriched concentrate with V₂O₅ grade of 1.44% at a recovery of 55.08%. The SMS tailings were then subjected to sedimentation and classification to further recover vanadium, leading to the final concentrate with V₂O₅ grade of 1.03% and recovery of 79.48%, presenting that 59.02% tailings were discarded. With this pre-enrichment process, vanadium in the stone coal ore can be efficiently reclaimed, which meets the requirements for subsequent metallurgical vanadium extraction.