In order to improve surface hardness and corrosion resistance of 304 stainless steel, a medium-entropy alloy (CoCrNi) coating was prepared on the surface of 304 stainless steel by laser cladding, and phase composition, element distribution and corrosion resistance of the cladded coating were studied. The results show that the treatment has achieved good metallurgical bonding between the cladded CoCrNi coating and the substrate, with no cracks, pores and other defects. The cladded coating is composed of single FCC phase, and exhibits dendrite and inter-dendrite structure. The elements are uniformly distributed on the cladded coating without obvious segregation. The uniform distribution of Cr element plays a positive role in improving corrosion resistance of the coating. The CoCrNi coating has its polarization resistance (101.65 kΩ) higher than that of 304 substrate (90.56 kΩ), and also significantly higher corrosion resistance.

The effect of laser remelting (LR) on the microstructure property and thermal stability of Ti-6Al-4V alloy prepared by laser powder bed fusion (LPBF) was investigated. The results show that after LR treatment, the thermal stability of the α′ phase within the LRed-Ti-6Al-4V titanium alloy samples is significantly improved, and the temperature at which β-Ti phase appears is up from 500 ℃ to 700 ℃. After heat treatment, the grains in LPBF-Ti-6Al-4V titanium alloy grow continuously, and obviously appear to be “short bar-like” and “coarse lamellar” at the temperature above 700 ℃; while the grains in the melting zone of the surface layer of the LRed-Ti-6Al-4V sample are still maintain equiaxial, and the relatively uniform and fine needle-like microstructure are observed in the melting zone and heat affected zone above 700 ℃. The surface microhardness of those two groups of samples decreases with the increased temperature, especially significant at 700 ℃ and 850 ℃ respectively. It is found that the rapid coarsening of β-Ti grains is the main reason for the falling down of hardness.

Based on the properties of Shizhuyuan molybdenum-bismuth sulfide ore, a new eco-friendly collector CYB-06 was developed. The results of industrial experiment show that, when using collectors CYB-06 and ethyl thiocarbamate coordinately, the recovery of molybdenum, bismuth and sulfur in the bulk sulfide concentrate attains respectively to 84.12%, 67.90% and 83.28%, up by 2.32 percentage points, 2.82 percentage points and 6.55 percentage points respectively, and the COD in the wastewater from processing plant is 117 mg/L, declined correspondingly by 41.21%, compared to the concentrate obtained with the combined collector of butyl xanthate and ethyl thiocarbamate. As CYB-06, without pungent odor, exhibits good selectivity index, and leads to low COD in the wastewater from processing plant, its application is of significance for improving product quality and operation efficiency, cleaning production and environmental protection of mining enterprises.

To study the effect of sand content on the rheological properties of lacustrine soft soil in northern Hunan, one-dimensional rheological consolidation tests under single-stage load were carried out with soft soil samples prepared with different sand content in the laboratory. The results show that the sand content has a significant effect on consolidation deformation of lacustrine soft soil in northern Hunan. The time of primary consolidation is almost unaffected by consolidation pressure, and decreases linearly with the sand/soil ratio. The higher the sand content in soil, the greater the consolidation pressure, and the smaller the secondary consolidation coefficient. The relationship between the secondary consolidation coefficient and the sand/soil ratio can be well represented by a power function. The higher the content of coarse particles in soft soil, the greater the fractal dimension. There is a linear relationship between the secondary consolidation coefficient and the fractal dimension.

The influence of hydraulic properties of geogrid on the stability of expansive soil slope was explored by conducting fluid-solid coupling analysis with Plaxis software. On this basis, the principle of flexible support for expansive soil slope under different rainfall conditions was analyzed. It is found that the axial forces on geogrid in each layer of the reinforced slope increase with the continuous infiltration of rainwater, presenting a “convex” shape variation. Without taking consideration of the hydraulic properties of geogrid, the axial forces on the geogrid will be underestimated and the stability of the slope will be overestimated. Flexible support structure can effectively control rainfall infiltration into slope and maintain the shear strength of expansive soil, meanwhile control the slope deformation and displacement growth. Thus, it is regarded as an effective way to support expansive soil slope.

As for the thickener designed for the new concentrator of a multi-metal mine in Hunan, aiming at the problems of covering a large area, high cost and long period of time for construction, efforts were made to increase the concentration of products from classification for reducing thickener area or even cancelling thickening operation, so as to actualize a simple, efficient and low energy-consuming pre-treatment of feed ore. For this purpose, experiments were carried out to determine parameters, such as hydrocyclone replenishment water, cone angle, cylinder height and apex diameter. It is found that by using a hydrocyclone consisting of a long cylinder and a short cone with cone angle of 90°, cylinder height of 800 mm and apex diameter of 50 mm, the overflow concentration can be increased from 34% to more than 44%, with the classification efficiency up by 0.77 percentage points, and the content of -74 μm size range is stabilized at more than 70%. Therewith, the content of easy-to-separate range increases by 2.19 percentage points and the WO₃ distribution increases by 9.87 percentage points. Furthermore, the grade and recovery of tungsten, molybdenum and bismuth all become stabilized in the follow-up flotation operations.

According to the existence of manganese, an experiment was carried out by adopting a processing technique consisting of reduction roasting and acid leaching to treat high-silicon manganese oxide ore. The effects of roasting temperature, roasting time, mass ratio of coal to ore, leaching temperature and time, initial sulfuric acid concentration, and liquid-solid ratio on the manganese leaching rate were all investigated. The results show that the leaching rate of manganese can reach 95.83% under the conditions including roasting temperature of 880 ℃, roasting time of 1.5 h, a mass ratio of 18% for coal to ore, leaching temperature of 55 ℃, leaching time of 2 h, initial sulfuric acid concentration of 1.80 mol/L, as well as liquid-solid ratio of 5 mL/g.

The iron-carbon (Fe-C) micro-electrolysis was adopted to treat arsenic-containing wastewater from copper smelting, and the effects of processing parameters, including pH of inlet water, air blowing rate, contacting time, vibration frequency, solid-liquid ratio (mass ratio of Fe-C micro-electrolysis material to inlet water per minute), on the arsenic removal efficiency were explored. Results show that during the treatment by Fe-C micro-electrolysis, the generated oxides such as FeAsO₄, Fe₂O₃, and Fe₃O₄ are deposited on the surface of the Fe-C micro-electrolysis material, making passivation of the Fe-C micro-electrolysis material ineffective, thus resulting in poor arsenic removal efficiency. The use of vibration can effectively solve such problem. It is shown that after 90 d continuous treatment under the conditions, including pH of inlet water at 2.0, air blowing rate at 5 L/min, contacting time of 2 min, solid-liquid ratio of 2.5∶1, vibration frequency rate at 2 min every 4 h, the arsenic removal rate can be up to 99.99% and the arsenic content in water falls down to 0.033-0.036 mg/L, presenting a good and stable removal effect. It is concluded that this arsenic removal approach by adopting Fe-C micro-electrolysis can provide a new idea for treatment of arsenic-containing wastewater from copper smelting.

Based on the process mineralogy study, an experimental study on grinding-separation technique was performed for JISCO's magnetite obtained from its suspension magnetization roasting process. In the experiment, a 110 mT low-intensity magnetic separator was firstly adopted for pre-concentration. The middlings were reground and processed by magnetic separation for enrichment and tailings discarding, and the obtained concentrate was subjected to reverse cationic flotation. Finally, the whole process produced the comprehensive concentrate grading 60.06% TFe and containing 5.17% SiO₂, with metal recovery of 84.27%. In comparison with the previous processing technique, the TFe grade of concentrate is improved by 1.96 percentage points and the metal recovery is increased by 1.38 percentage points, while the SiO₂ content falls by 1.06 percentage points.

A two-step acid leaching process was used to leach scandium and yttrium from red mud. Phosphoric acid was used in the first stage of leaching to achieve dealkalization, desilication and enrichment of rare earth elements (scandium and yttrium). Then, the leaching residue was leached with sulfuric acid in the second stage. The effects of sulfuric acid concentration, liquid-solid ratio, reaction temperature and reaction time on the leaching process of scandium and yttrium were investigated, and the leaching kinetics was also analyzed. It is found that leaching of red mud with phosphoric acid can bring better dealkalization and desilication effect, showing the leaching rates of K, Na and Si at 75.62%, 87.82% and 80.25%, respectively. Then, in the second stage of leaching process with sulfuric acid concentration of 2.5 mol/L and liquid-solid ratio of 7∶1, reaction runs at 70 ℃ for 45 min, leading to the average leaching rates of Sc and Y up to 74.49% and 80.02%, respectively. It is shown that the leaching processes of Sc and Y with sulfuric acid follow the liquid-solid reaction model, which is controlled by diffusion, and the apparent reaction activation energies are calculated to be 18.50 kJ/mol and 16.74 kJ/mol, respectively.