After 6061-T4 aluminum alloy sheet for automobile was welded by laser welding, the microstructure, microhardness, strength and plasticity of welded joint, as well as fracture surface morphology of tensile specimen were studied by using metallographic microscope, transmission electron microscope, scanning electron microscope, Vickers hardness test and tensile test. The results show that the laser welded joint of 6061-T4 aluminum alloy has a coarse strip of grain structure in its base metal area, the weld seam has a structure of very fine as-cast dendrite in the center, acicular β″ precipitates segregate at grain boundary, and dislocation density decreases. It is found that both the strength (hardness) and plasticity of laser welded joint are lower than those of base metal.

In order to protect ecological environment during exploitation of coal resources in lake, a mining mode with distributed ecosystem was developed for lake mining area, and the function mechanism of such system was explored. In such mode of lake mining, an ecosystem is composed of six subsystems, including biological function system, ecological water treatment and utilization system, ecosystem development and utilization system for land resources, organic fertilizer processing system, integrated energy utilization system, and ecosystem utilization system for solid waste resources. These subsystems can not only function alone but also interact with each other, thus forming mechanisms for life cycle, metabolism, balance, combination, sharing and cooperation. With these mechanisms as the theoretical basis for the distributed ecosystems in lake mining area, effective exploitation of lake resources, sustainable development of ecological environment, as well as promotion of economic benefit from lake resources mining can be actualized by recycling the resources among those six distributed subsystems. This study can provide reference for underwater coal resources mining while ensuring ecological conservation.

Qingdao Metro Line 8 was taken as an example for studying the surrounding rock stability of underground tunnel in mud-containing sandstone stratum with pore water. Based on the analysis of deformation and stress evolution law of surrounding rock by simulating three different pore water conditions, the maximum values of vertical displacement (roof subsidence), horizontal displacement (side walls moving closer), vertical stress, horizontal stress and shear stress of the tunnel were finally obtained. The numerical simulation results of tunnel with three kinds of pore water content were applied to the tunnel construction for Qingdao Metro Line 8, and the on-site monitoring results show the deformation of surrounding rock of tunnel roof and side wall is all controlled within the safety range. It is shown that such numerical simulation results provide good reference for the construction of Qingdao Metro Line 8.

As for pipes with different lengths, with heave compensation device replaced by elastic constraint, a vibration equation was established by using energy integration approach, and the dynamic response of lifting pump installed at different positions of pipes was analyzed by finite element method. Results show that the harmonic response of stress excited by the following single loads was in an ascending order: torque, wave in longitudinal direction, and a combination of wave and current in horizontal direction. Under excitation by all these three loads with the same phase, the harmonic response of the system increased significantly. When the installed lifting pump was changed from a high position to a low position, the maximum equivalent stress of pipeline increased after an initial falling down. The installation position of lifting pump on the pipe corresponding to the minimum of the maximum equivalent stress was the suboptimal installation position. Based on the suboptimal installation position for the lifting pump on the pipeline with specific length, an empirical formula was established for the suboptimal installation position, which can provide reference for the quantitative design of lifting system.

A study on the separation of a copper-lead-zinc sulfide ore from Yunnan was presented by adopting a Cu-Pb-Zn full selective flotation process. The mineral liberation degree was enhanced by adopting fine grinding of raw ore and selective regrinding of lead roughing concentrate. A combined usage of depressants sodium sulfite and zinc sulfate benefited the synergistic effect and selectivity in depressing, and collectors Z-200, ethionitrogen and BK906 exhibited high selectivity. Under optimized parameters, a copper concentrate with Cu grade of 22.78%, Cu recovery of 83.28%, Pb content of 3.01% and Zn content of 4.23%, a lead concentrate with Pb grade of 75.86%, Pb recovery of 82.75%, Cu content of 0.17% and Zn content of 1.64%, and a zinc concentrate with Zn grade of 51.87%, Zn recovery of 93.16%, Cu content of 0.24% and Pb content of 0.31%, were obtained.

A medium-low grade calcium-magnesium phosphate ore was ground to a fineness of 56.74% -0.075 mm and was used to study the liberation characteristics of particle size within varied ranges on its flotation behavior. The particles were classified into coarse ranges (+0.15 mm, -0.15+0.106 mm and -0.106+0.075 mm) and fine ranges (-0.075+0.038 mm and -0.038 mm). The content of different minerals in each size range was estimated by using X-ray fluorescence spectroscopy and X-ray powder diffraction analysis, while the intergrowth and monomer liberation was evaluated with the backscattering images obtained from scanning electron microscopy. It is found that the content of liberated minerals increases as the particle size decreases. Fluorapatite is primarily enriched in the coarser particles within the size range of +0.075 mm, whereas dolomite is concentrated mainly in fine particles of -0.075 mm. By improving the selective aggregation of valuable minerals and gangues in size range of -0.038 mm, the P₂O₅ loss can be reduced. Furthermore, by reducing the content of coarse particles within the size of +0.075 mm and increasing the content of particles within -0.075+0.038 mm range, both P₂O₅ grade and recovery of the concentrates can be effectively improved.

In order to comprehensively recover fluorite resources from the tailings left after hot flotation of scheelite, a beneficiation process consisting of regrinding, water displacement and concentration, and fluorite flotation was proposed. It is shown that with the feed ore with CaF₂ grade of 25.47%, a fluorite concentrate can be obtained with CaF₂ grade and recovery at 92.35% and 60.59% respectively.

Rhodococcus opacus (R opacus) was taken as a microbe collector in a flotation experiment to investigate the recoveries of cassiterite, calcite and quartz pure minerals. The results show that, with pulp pH as 4 and R opacus dosage as 1.24 g/L, the recoveries of these three minerals were correspondingly 82.07%, 45.42% and 13.66%. The interaction mechanism between R opacus and cassiterite was investigated by measuring zeta potential and surface tension. Finally, an open-circuit flotation experiment of tin ore was carried out with R opacus as the collector and sodium silicate as the depressant, showing that the grade of tin concentrate was improved from 3.98% to 23.83%.

In order to improve the efficiency of lithium extraction by brine adsorption, a process consisting of pre-concentration and adsorption was developed for lithium extraction. Based on the theory of phase diagram of Na⁺, K⁺//Cl^--H₂O ternary system at 50 ℃ and 100 ℃, variation of lithium concentration and lithium loss rate in brine at different temperatures with different evaporation rate was explored in the test, and the adsorption effects of adsorbents on brine before and after pre-concentration were compared. The results show that the concentration and loss rate of lithium in the solution are not affected by evaporation temperature. As the evaporation rate exceeded 40%, the loss rate of lithium in brine increased rapidly. The pre-concentrated brine with concentration of 55 mg/L lithium at an evaporation rate of 40% was adsorbed with manganese absorbent, showing that the lithium adsorption capacity reached 4.25 mg/g after 4 hours, higher than the adsorption capacity of 3.39 mg/g in the original brine without pre-concentration. It is proven that brine pre-concentration can enhance the adsorption effect of lithium brine extraction.

Research on redox leaching of intermediate of nickel hydroxide with synergetic effect of nickel sulfide was carried out, and optimum leaching conditions were obtained from tests, including intermediates of nickel sulfide and nickel hydroxide in a mass ratio of 1/10, initial acidity of 4 mol/L, temperature of 90 ℃, liquid and solid in a ratio of 2.0, and a reaction time of 5 h. Under such conditions, the leaching rate of manganese from nickel hydroxide can reach 99.88% and the utilization rate of nickel sulfide is also up to 79.50%. And the leaching residue can be returned as a reducing agent in the reduction and leaching of nickel hydroxide. By using this method, the consumption of both the reducing agent in leaching of nickel hydroxide and the oxidizing agent in leaching of nickel sulfide can be greatly reduced. In addition, the leaching of intermediate of nickel hydroxide can be achieved with synergetic effect of nickel sulfide, which is easy to operate and can be applied into industrial production.