In view of problems such as low grade of iron concentrate and low metal recovery for 0-15 mm fine ore in JISCO by adopting high-intensity magnetic separation process, experimental researches were conducted, including pre-concentration for tailings discarding, optimization of grinding-separation process and enhancing recovery of tailings by selective flocculation and magnetic seed magnetization. The results show that, the pre-concentration can effectively discard the surrounding rock and gangues that affect the separation indices, thus improving the grade of feed to grinding and separation. Tower grinding of rough concentrate can avoid overgrinding, and the recovery of magnetic concentrate can be increased by 5.32%, while concentrates have similar grade. Selective flocculation and magnetic seed magnetization can further improve metal recovery and reduce iron grade of tailings. An iron concentrate with TFe grade of 48.29% and recovery of 82.90% can be collected over the whole process. The scanning electron microscopy and infrared spectroscopy analyses show that caustic starch can establish bridges between target minerals and magnetic seeds, and it can be adsorbed onto target minerals mainly in the forms of chemisorption and hydrogen bonding, which can reduce the inclusion of gangue minerals in magnetic flocs and improve significantly the iron recovery while ensuring the iron grade of concentrate.

A basic polishing solution consisting of perchloric acid and methanol was optimized by adding citric acid and glycerol, and different kind of polishing solution was used for electropolishing of titanium nickel alloy wires. The surface morphology, corrosion resistance, and blood compatibility of untreated and polished wires were compared and studied. The results show that addition of citric acid and glycerol has a significant effect in corrosion inhibition and increases the controllability of the polishing process. With the optimized polishing solution, the surface of electropolished titanium nickel wire becomes flatter, with average roughness declined from 161.3 nm to 15.6 nm. The self-corrosion potential increases from -0.167 V to 0.045 V. The dissolved nickel content of phosphate buffer solution becomes lower, indicating the higher corrosion resistance. The hemolysis rate declines from 2.333% to 0.333%, and the number of adhesive platelet significantly decreases, thus the blood compatibility is enhanced.

With Pr₆O₁₁ and CeO₂ as additives, B₄C matrix composite materials were prepared at 2 200 ℃, 1 900 ℃, and 1 700 ℃ by adopting techniques of pressureless sintering, hot pressing sintering, and spark plasma sintering, respectively. The relative microstructure and mechanical properties were also studied. It is found that PrB₆ and CeB₆ formed in situ can fill the pores between B₄C grains, and improve the density of the composites. Compared with pressureless sintering and hot pressing sintering, the technique of spark plasma sintering can bring the prepared composites with higher density. The fracture toughness of B₄C-CeB₆ composites can be improved due to its high relative density, as well as the deflection, branching and bridging of cracks occuring along CeB₆, which extends the expansion path of cracks and reduces stress concentration. The B₄C-CeB₆ composite prepared by spark plasma sintering has good comprehensive mechanical properties, with the relative density, vickers hardness, bending strength and fracture toughness reaching 99.3%, 34.7 GPa, 451 MPa and 4.38 MPa·m^1/2, respectively.

Tailings slurry with different mass concentration and cement to sand ratio was prepared with a certain kind of tailings, which was taken to study for its rheological properties by adopting Brookfield R/S+ rheometer. It is found that at room temperature, the mass concentration of paste slurry has a stronger effect on the rheological properties of paste than the cement to sand ratio of slurry. When the concentration is lower than 64%, the cement to sand ratio has little effect on the rheological properties. As the slurry concentration increases, its yield stress and viscosity present exponential growth, which increase at the fastest rate when the slurry concentration is 68%. As the cement to sand ratio of slurry increases, its yield stress and viscosity increase approximately linearly. The influences of slurry concentration, cement to sand ratio, gradation and temperature on rheological properties of slurry were studied by experiments, and then the rheological parameters were predicted by using XGBoost based on the obtained experimental data. It is shown that the relative errors and variances between the predicted results and the actual values are within a reasonable range, which has proven the accuracy of the prediction model.

In view of the resource characteristics and production status of Ekou Iron Mine of Taiyuan Iron & Steel (Group) Co Ltd, an experimental research was conducted to upgrade iron grade of the concentrate from the second-stage magnetic separation while reducing impurities therein. An optimized flowsheet consisting sequentially of grinding, low-intensity magnetic separation and reverse flotation was adopted in the experiment, resulting in a high-quality iron concentrate grading 69.93% TFe at a recovery of 93.08%, with a yield of 76.33%, while the SiO₂ content was reduced to 1.63%.

To effectively recover titanium resources in the tailings from a titanium processing plant and improve the relative utilization rate of raw ore, beneficiation of the tailings with a TiO₂ grade of 5.81% from the tailings pond was studied. A gravity and magnetic separation process were proposed and the influences of magnetic field intensity, rising water flow rate, feeding rate and feeding concentration on ilmenite separation indices were studied. The results show that after a gravity separation of +38 μm range, a gravity separation of underflow from -38 μm classification and magnetic separation of overflow from -38 μm classification, a rough concentrate with TiO₂ grade of 16.08% was obtained at recovery of 62.63%, while tailings with a yield of 77.41% and TiO₂ grade of 2.39% was cast off. Consequently, the feeding amount of succeeding flotation can be greatly reduced.

The effects of low temperature tempering on the microstructure and mechanical properties of Q1100 ultra-high strength steel after pretreatment of normalizing and quenching were studied. The results show that tempered martensite were obtained after normalizing (890 ℃ × 40 min) + quenching (890 ℃ × 30 min) + tempering (185-320 ℃ × 90 min) processes. After tempering at different temperatures, all tested steels have their tensile strength higher than 1 360 MPa, yield strength higher than 1 200 MPa, hardness higher than 400HV3, elongation higher than 13%, and impact energy at -40 ℃ higher than 35.2 J. With the rising of tempering temperature, the tensile strength and hardness gradually decrease, the yield strength first increases and then decreases, the elongation after fracturing increases after an initial slight decrease, and the impact energy at -40 ℃ decreases followed by increase. At a tempering temperature of 230 ℃, the steel in the test has tensile strength of 1 445 MPa, yield strength of 1 238 MPa, hardness of 429HV3, plasticity of 13.8%, and toughness of 47.5 J, which all largely exceed the service standard of Q1100 ultra-high strength steel for construction machinery.

The pollution of heavy metals in the soil of a zinc smelting site was analyzed, and the influence mechanism of goethite on cadmium migration in the soil was discussed by performing simulation experiments. The results show that the geometric mean values of As, Cd, Cu, Hg and Pb in zinc smelting site soil are 15.9 mg/kg, 1.52 mg/kg, 62.1 mg/kg, 0.108 mg/kg and 167 mg/kg respectively. The average content of Cd is 11.7 times the general value of soil in Hunan Province. It is shown that Cd in the soil has strong migration, and can be infiltrated down to the depth of 6 m or more of the soil. The results of stochastic forest model analysis show that Cd migration in the soil is mainly affected by goethite and silt. Cd in the soil can be adsorbed by goethite and then migrated. The pH value and ionic strength of leachate obviously affect the migration of Cd by goethite in the soil. When the pH of leachate is 6 and the ionic strength is 1 mmol/L, 37.6% of Cd in the soil can be migrated by goethite. Adjusting the pH value and salt ions concentration of soil can change the migration of Cd by goethite in the soil. As a result, the risk of pollution by heavy metals such as Cd in the soil of zinc smelting site can be controlled.

The microstructure and mechanical properties of A356 aluminum alloy joints were studied after they were processed with technique of T6 heat treatment followed by friction stir welding (T6-FSW) and technique of friction stir welding followed by T6 heat treatment (FSW-T6) respectively. It is found that the nugget zone of T6-FSW joint is composed of dynamically recrystallized fine-grains, but the precipitates are dissolved or coarsened. The transverse tensile strength and elongation of T6-FSW joint are 214 MPa and 5.3% respectively, and an average hardness is 76HV_0.5. The tensile strength and elongation of the nugget zone are 236 MPa and 12.5% respectively, and the impact toughness of the joint is 12.10 J. Abnormal grain growth occurs in the nugget zone of FSW-T6 joint, where fine precipitates with high density are formed. The transverse tensile strength and elongation of FSW-T6 joint are 254 MPa and 8.5% respectively, and an average hardness is 96HV_0.5. The tensile strength and elongation of the nugget zone are 297 MPa and 7.0% respectively, and the impact toughness of the joint is 8.23 J.

An interactive orthogonal experiment was carried out. With the metallization rate of the products of fluidized reduction of iron ore powder as dependent variables, reduction temperature, reduction time, gas linear velocity and pressure of reduction as independent variables, the effects of various operating parameters and their interactions on the fluidized reduction of iron ore powder were investigated by means of range analysis and variance analysis. Results show that effects of four factors and their interaction on the metallization rate of fluidized reduction of iron ore powder are in the following descending order: reduction temperature > gas linear velocity > reduction time > pressure of reduction > interaction between reduction temperature and gas linear velocity > interaction between reduction temperature and pressure of reduction > interaction between reduction time and gas linear velocity > interaction between pressure of reduction and gas linear velocity > interaction between reduction temperature and reduction time > interaction between pressure of reduction and reduction time. It is shown that higher reduction temperature is helpful to the combination of iron whiskers, forming a compact structure. A higher gas linear velocity can improve the kinetic conditions of fluidized reduction, which is beneficial to fluidized reduction of iron ore powder.