The mechanical properties and energy evolution law of dolomite under a combined action of dry-wet cycle and cyclic loading and unloading were explored. The results show that the structural damage caused by dry-wet cycles leads to the transformation of dolomite from brittle fracture to ductile fracture, which is manifested by an increase in the area of hysteresis loops and a decrease in peak strength. At the early stage of cyclic loading and unloading, a strengthening effect is observed, and then the dolomite develops into the strain-softening and damage stages. An energy analysis indicates that the total input energy is mainly stored in the form of elastic strain energy, and the proportion of dissipated energy increases slowly with the accumulation of damage. Additionally, based on the variation of the damage variable defined by dissipated energy, the damage evolution tends to be stable after a progressive and accelerated process.

To improve the surface quality of high-end plates by descaling and cleaning process, an experimental study was carried out with different process routes that are determined based on the combination of Steel Eco Descaling (SED) technology and other surface pretreatment processes. Based on the analysis of surface appearance, surface roughness, surface micromorphology and surface energy spectrum of the plates treated by different processes, an optimal descaling process is finally determined, consisting of SED, soaking with roller brush cleaner, polishing with scouring pad buffering wheel, and high-pressure flushing. After cleaning treatment with this process, the plate sample is overall in a uniform metallic color, with significantly reduced surface roughness and oxygen content. It is concluded that after treatment with this combined process, surface quality of the third-generation advanced high-strength steel (AHSS) plates for automotive can be effectively improved.

Martensitic steel with different ferrite content and distribution was firstly fabricated by heat treatment. Then, the effects of ferrite content and distribution on the microstructure and properties of such ultra-high strength martensitic steel with yield strength more than 1 100 MPa was explored based on microstructure characterization and mechanical property tests. The microstructure evolution and strengthening and toughening mechanism were also analyzed. The results show that with a small amount of ferrite uniformly distributed in the martensite matrix, the steel sample in the experiment can exhibit not only ultra-high yield strength (1 245.44 MPa) and tensile strength (1 411.96 MPa), but also higher impact energy (80 J) at low temperature, presenting the optimal comprehensive mechanical properties. A small amount of ferrite in the local area continuously distributed along the rolling direction can slightly improve the tensile strength, but the unevenly distributed ferrite can improve the stress concentration and reduce the toughness. An increase in the content of continuously distributed ferrite can improve the tensile strength, but the formation of banded martensite and improved stress concentration make the toughness of the steel sample in the experiment substantially reduced.

A new short-process preparation technique for battery-grade iron phosphate was explored with iron powder and phosphoric acid as main raw materials. The effects of iron powder dissolution mechanism, iron phosphate reaction conditions, and mother liquor recycle on product indicators were investigated. The results show that the dissolution rate of iron powder can reach 97.92% at a temperature of 70 ℃, with phosphoric acid at a concentration of 20%, iron and phosphorus at a ratio of 1/3, and iron powder at a size of 150 μm；after 1 h precipitation at 100 ℃, with an addition of hydrogen peroxide at 110% of the theoretical amount, an iron phosphate with D₅₀ of 2 μm was prepared with the precipitation rate of 98.86%. The obtained iron phosphate has stable crystal form with uniform crystal grains, and the contents of elemental impurities are significantly lower than the requirements specified in the HG/T 4701—2021 standard. The precipitated mother liquor in the process can be recycled, leading to actualization of low-carbon and green production.

With tartaric acid as a leaching agent, an experiment was conducted to investigate the effects of different leaching conditions on the leaching rates of sodium and titanium from red mud. The process parameters were optimized by orthogonal experiments, and the leaching mechanism was then analyzed in combination with the study of leaching kinetics and the properties of leaching residues. It can be seen from the leaching test and orthogonal experiment that with tartaric acid at a concentration of 1.00 mol/L, leaching temperature of 90 ℃, liquid-solid ratio of 8 mL/g, and leaching time of 60 min, the leaching rates of sodium and titanium from red mud can reach 93.50% and 76.66%, respectively. XRD analysis of red mud before and after tartaric acid leaching shows that the sodium in the leaching solution mainly comes from cancrinite and sodium hydroxide in the Bayer process, while the titanium mainly comes from perovskite and secondary titanium that dissolves and re-precipitates on the surface of red mud during the Bayer process. The leaching kinetics analysis shows that both alkali removal and titanium leaching from red mud conform to an unreacted shrinking core model, and the processes of alkali removal and titanium leaching are mainly controlled by interfacial chemical reactions.

For reducing energy consumption while ensuring weld joint quality, the welding process parameters for electron beam welding of TU2 oxygen-free copper were optimized with SYSWELD simulation software, and a finite element model with appropriate boundary conditions was established for a 30-mm-thick TU2 copper plate. A heat source model was determined based on the actual situation of electron beam welding, and simulation analysis was made by imputing varied energy consumption value in the welding process, with the obtained simulation results compared with actual welding results. It is shown that with a double-ellipsoidal heat source input of 1260 J/mm and a 3D Gaussian heat source input of 5 000 J/mm, a full penetration weld with the lowest energy consumption can be achieved. The simulation results show that the obtained morphology of molten pool is almost the same with that in the actual welding, proving that the welding parameters set in the simulation analysis are feasible for TU2 welding. It is concluded that this study can provide a reliable reference for optimizing the parameters in welding of TU2 oxygen-free copper.

To explore the impact of near-surface ore body mining on the stability of overburden and dangerous rock masses of slopes, a phosphate mine was taken as an engineering project in the study. The stability of the dangerous rock mass of the slopes was determined by on-site investigation, and the evolution of deformation, stress and plastic zone of overburden under different mining schemes were simulated with FLAC^3D software. The research results indicate that structural planes between layers of surrounding rock on the roof of stope are well-developed, probably causing falling debris in blocks or flakes. The strata are hard and brittle in lithology and have developed rock fractures. Under unloading effect of high and steep slopes, dangerous rocks are prone to be separated along the combination of fractures and strata plane, forming dangerous rock masses. The response law of the maximum stress in the overburden is similar to the law of the unbalanced force in numerical calculation. There is relatively small disturbance generated during mining process, which brings a little impact to the stability of adjacent stopes and surface. It is found that the ground surface is less affected by underground mining, with the deformation within the maximum limit value specified in the standard. If Ph2^# ore body is mined after Ph1^# ore body, the overburden can have relatively small displacement, and no connectivity in the plastic zones is occurred in the mining pillars, stopes and overlying strata.

Based on the characteristics of the exploration contracts approved by the International Seabed Authority (ISA), the global competition status and variation trend of the exploration contract areas are analyzed in terms of temporal changes, spatial distribution and mineral types. Based on the analysis results, strategies to cope with the variation in the situation of ISA exploration contract areas are proposed, including commercial companies acting as the main players, strengthening international cooperation with African countries and the Enterprise of ISA, giving priority to exploration of polymetallic nodules, cultivating advantageous contractors and safeguarding the rights and interests of contractors.

A beneficiation test was performed with a kind of fine-grained refractory fluorite ore in Hunan Province for rational development and utilization. In the test, a process consisting of coarse grinding, pre-concentration, regrinding and re-concentration of rough concentrate was adopted, with CYP-01 as a collector, sodium carbonate as a modifier, and water glass as a depressant. Depression in steps was performed in the cleaning stage. With the coarse grinding fineness of －0.045 mm 50%, regrinding fineness of－0.045 mm 85%, a kind of chemical-grade fluorite product with CaF₂ grade of 93.04% was obtained at 64.24% recovery after one stage of roughing and eight stages of cleaning. It is shown that such kind of fine-grained refractory fluorite ore can be effectively recovered and utilized.

In order to comprehensively recover titanium resources and iron resources from a low-grade ilmenite ore, an experimental study was performed for the ore by a process of low intensity magnetic separation (LIMS) followed by regrinding and re-concentration to recover Ti and Fe therein. The results show that LIMS with ore at a grinding fineness of－0.074 mm 84.78% can yield an iron concentrate grading 62.82% TFe and 3.62% TiO₂ with iron recovery of 51.32%, presenting a good recovery of magnetic iron; the obtained LIMS concentrate is subjected to high-intensity magnetic separation (HIMS) consisting of one roughing and one cleaning, followed by gravity separation with a shaking table, resulting in the obtained Ti concentrate grading 40.81% TiO₂ at 18.47% recovery. It is shown that both Fe and Ti therein can be comprehensively recovered.