Influence of Al content on the microstructure, phases, hardness, tensile and impact properties of quenched and tempered 4Cr5MoVSi die steel was studied by using optical microscopy, transmission electron microscopy (TEM), tensile testing machine among other instruments. It is found martensite is formed in the quenched and tempered 4Cr5MoVSi die steel with Al content of 0-0.6% (mass fraction, the same below), while martensite plus δ ferrite are formed in the quenched and tempered 4Cr5MoVSi die steel with Al content of 1.2%-1.8%. Without adding Al or with an addition of 0.3%-1.8% Al, 4Cr5MoVSi die steel after quench and tempering has α-Fe and M₇C₃ formed as its main phases. The 4Cr5MoVSi die steel with an Al content of 0.3%-1.2% has its relatively small variation in its hardness after quenching and tempering; however, with Al content up to 1.8%, the quenched and tempered die steel has its hardness significantly reduced. It is concluded that an appropriate addition of Al is beneficial to improvement in the room-temperature tensile strength, elongation at break, and impact toughness of quenched and tempered 4Cr5MoVSi die steel; with an addition of 1.2% Al, the quenched and tempered 4Cr5MoVSi die steel can have higher hardness, strength, and impact toughness.

The effect of ultrasonic melt processing time on the microstructures and hardness of as-cast and homogenized Al-Cu-Mg-Ag-Fe-Ni alloys was studied. The results show that ultrasonic melt processing leads to more uniform distribution of Fe/Ni-rich phases. Two-minute ultrasonic processing can result in grain refinement of the alloy. However, ultrasonic processing, if extended to 6 minutes, will result in grain coarsening. It is found that ultrasonic processing promotes the dissolution of Al₂Cu phase and enhances the solid-solution strengthening effect, resulting in improvement in hardness of the as-cast alloy. After homogenization, Fe/Ni-rich phase is detected as the residual secondary phase in the structure, which exhibits discontinuous distribution along the grain boundaries after ultrasonic processing.

There are well-developed faults in an open-pit molybdenum mine, which may lead to slope instability during open-pit mining. Three typical faults running through the ultimate boundary were selected to investigate progressive instability mechanism of the slopes in the open-pit mine under coupling effect of multiple faults by integrating Rhino+Griddle 3D geological modeling and FLAC^3D multi-field coupling simulation. Furthermore, the safety factors of slopes under different working conditions were calculated, and relatively unstable slopes were also identified for addressing the subsequent safety of the ultimate boundary. The simulation results show that, plastic failure and tensile stress concentration will occur in the slope at the junction of Zone C and Zone D, while local plastic failure will occur in the faults, which, however, won't induce instability failure in the surrounding slopes; there won't be much displacement in the slope at the ultimate boundary, with the maximum displacement (2.44 cm) at the toe of slope; the safety factors of the ultimate boundary of open pit under natural working conditions and rainfall are 2.48 and 2.36 respectively, indicating that the slope is stable. However, slope at Zone E with F1 fault is considered to be with a relatively instability, for which comprehensive measures including real-time monitoring, prevention and reinforcement can be taken to ensure the safety.

For phosphorus-iron waste left after lithium extraction from cathode powder of spent lithium iron phosphate (LFP) batteries, a selective leaching with sulfuric acid was adopted to remove impurities therein. The results indicate that after a 4-stage leaching at 80 ℃ for 2 h, with a sulfuric acid at a concentration of 0.32 mol/L and a liquid-to-solid ratio of 5 mL/g, the total leaching rates of elemental impurities, including Cu, Mn, Al, Ca, Na and Mg reach 70.81%, 68.33%, 65.57%, 68.03%, 67.85% and 64.28%, respectively, and the total leaching rates of P and Fe are only 2.52% and 2.24%, respectively. It is concluded that the main elemental impurities can be effectively leached out from such phosphorus-iron waste, with elements of P and Fe left for subsequent resource utilization.

To analyze the damage effect of drilling and blasting in construction on the surrounding rock of roadway, a Hopkinson pressure bar (SHPB) test and numerical simulation were carried out to investigate the dynamic response characteristics of saturated mudstone under one-dimensional impact load. Under impact with different strain rate, rock samples undergo four deformation stages, including compaction, quasi-elasticity, yielding and unloading. The saturated mudstone has its dynamic elastic modulus in a linear relationship with the strain rate. As the strain rate increases, dynamic fragmentation of the rock samples is significantly enhanced, and the energy dissipation of saturated mudstone also correspondingly increases. The mean error between the peak stress obtained from the numerical simulation and the experiment is 7.9%, which accurately reflects the dynamic characteristics, such as morphology of mudstone fragmentation and dynamic stress-strain relationship, under impact with different strain rates. The strain rate effect of mudstone indicates that blasting disturbance will continuously change its energy state, so dynamic monitoring should be strengthened for the deformation of surrounding rock during tunneling.

Based on the causes of historical dam failure accidents in tailings ponds, a safety grade evaluation index system was built for tailings ponds. The correlation between safety evaluation indexes was demonstrated with Pearson correlation analysis method. An in-depth analysis was conducted for the distribution of sample data to confirm that the sample data met the requirements of the Kriging method for data distribution. Then, the weight of each safety evaluation index was calculated with entropy weight method. The two safety evaluation indexes with higher sensitivity were selected as the X-axis and Y-axis of the Kriging geostatistical model. A geostatistical model was established by using the Kriging method and was verified with empirical case data. The results show that the predicted safety grades of 12 groups of tailings pond data with known safety grades in the geostatistical model are completely consistent with the actual safety grades, which verifies the feasibility and high accuracy of this method.

To investigate the rheological properties of heat-treatment-free AlSi9MnMg alloy specifically for high-pressure die casting (HPDC) process, influence of temperature and shear rate on the viscosity of molten alloy was studied by using a rotational rheometer based on the Searle principle, and the microstructure of the samples in rheological testing was analyzed. The results indicate that the viscosity of molten alloy decreases as the temperature rises in the test. At a given temperature, the viscosity decreases as the shear rate increases. With the shear rate exceeding 800 s^-1, the viscosity remains unchanged with shear time at the same shear rate. Under the action of shear force, the dendritic grains in the melt undergo fragmentation, agglomeration and spheroidization. Moreover, as the temperature rises in the test, the particle agglomerates become smaller in size.

In order to explore the stability and durable service of a blend of construction waste and red clay under load, a California Bearing Ratio (CBR) test, rebound modulus test and failure strength test were performed to determine the appropriate content of red clay in the blend. The influence of compaction degree, confining pressure, stress ratio and loading times on the macroscopic permanent deformation of the blend was comprehensively analyzed by triaxial tests, and the evolution of internal structure during the deformation process of the blend was simulated by discrete element method. The results show that with red clay at an appropriate content of 65%, the blend of construction waste and red clay can have its permanent deformation increase gradually as the stress level becomes higher, and decrease gradually with the increase of confining pressure and compaction degree. During the deformation process, the internal shear stress, coordination number and slip rate of the blend all increase gradually as the stress level becomes higher. Based on the test results and in consideration of stress state, including confining pressure, failure strength and loading stress, physical state, such as compaction degree, and loading times, a permanent deformation prediction model was proposed and validated. With a correlation coefficient of 0.89, the model is considered to have a “relatively good fit”.

Extraction of rhenium from low-grade molybdenum concentrate by adopting a process of oxidative volatilization followed by ion exchange was explored in experiments. Firstly, a two-stage high-temperature oxidative roasting was adopted to oxidize rhenium into Re₂O₇. Rhenium and molybdenum were effectively separated due to rhenium volatilizing into the flue gas. The volatilization rate of rhenium reached 85.42% after roasting process at 675 ℃. Then, the rhenium-containing flue gas was eluted to get rhenium-containing solution, in which rhenium was selectively extracted with D201×7 ion exchange resin. With the solution pH of 9, liquid/solid ratio of 50 mL/g, a 20 min adsorption at temperature of 35 ℃ brought the adsorption rate of Re up to 97.52% and the adsorption rate of Mo less than 20%. Finally, a product of ammonium rhenate was prepared by stepwise desorption followed by concentration and crystallization. By this process, the total recovery of Re can reach 70.68%.

Vanadium slag and sodium carbonate, as raw materials, were mixed and grounded for pretreatment. The obtained mixture was then taken in a roasting experiment for investigating effects of factors, such as holding time, temperature and feeding materials for roasting process with different alkali ratios (a mass ratio of sodium carbonate to the converted content of V₂O₅ in vanadium slag) on transformation and leaching rate of vanadium from clinker, and also exploring phase transformation of vanadium slag during the roasting with a low alkali ratio. The results show that if roasting process at higher temperatures is held for 90 minutes, the alkali ratio in the roasting process can be reduced by properly increasing the temperature. After roasting at a temperature of 880 ℃ with an alkali ratio of 1.0, water leaching can result in the total vanadium (TV) content in the residue falling down to 0.49% and the leaching rate of vanadium up to 94.70%. This method is suitable for sodium roasting in a rotary kiln. Under the existing process conditions for sodium roasting of vanadium slag in a multiple hearth furnace, an addition of some clinker into the material for roasting is beneficial to reducing the alkali ratio. It is shown that after roasting is held for 45 minutes at 780 ℃ with an alkali ratio of 1.2, the TV content in the final leaching residue can fall to 0.96% and the leaching rate can reach 89.19%. The microscopic analysis of the clinker after roasting with a low alkali ratio show that there is a high aggregation of sodium vanadate phase, which is in good consistency with NaVO₃ in the elemental composition.