Guizhou Jinfeng Gold Mine was taken as an engineering example for investigating effect of geometric features of rock surface on the performance of shotcrete support in the roadway constructed by drilling and blasting. The rock surface of the roadway was scanned by using a 3D laser scanner, and a 3D geometric model was established for the roadway. The actual shape of cross-sections was created by slicing the geometric model with a 3D software for analyzing the geometric features. With numerical models respectively established for the designed and actual sections, the variation in internal forces of the shotcrete and its supporting effect for the surrounding rock were analyzed. The results show that uneven rock surface of a roadway can lead to significant increase in the shear force and bending moment of shotcrete, but relatively small effect on the axial force. It is found that concave part of surrounding rock in a roadway is subjected to maximum negative bending moment, while convex part is mostly subjected to maximum positive bending moment. Under the interaction of axial force and bending moment, the shotcrete on convex part has an obvious lower safety factor, leading to weakened support to the surrounding rock, thus tensile failure is prone to occur.

A 5 mm thick DL510 ultra-high strength steel (1 500 MPa) was welded by using metal active gas (MAG) arc welding. The influence of heat input on the microstructure and mechanical properties of weld joint was investigated, and the residual weld stress of the joint was eliminated by hammering while welding. The results show that with heat input within the range of 43-70 kJ/cm, the obtained weld joints can have a good shape. If hammering time is less than 20 min, the tensile strength of weld joint increases as hammering time prolongs; however, after hammering time exceeds 20 min, there is little variation in the tensile strength. With the increasing of heat input, the grain size of weld joints grows obviously, and a small amount of fine granular bainite structure appears in the coarse-grained area with the heat input of 70 kJ/cm, leading to improvement in the toughness of weld joints.

Response surface methodology (RSM) was used to optimize the flocculation settlement parameters of fine iron tailings slurry. According to the Box-Behnken test method in Design-Expert 8.0 software, a three-factor and three-level test was designed to obtain a regression equation of turbidity model for flocculation settlement of fine-grained iron tailings slurry. The results show that with the following favorable flocculation settlement parameters, including addition of inorganic flocculant FeCl₃ at an amount of 113.44 mg/L, organic flocculant PAM at an amount of 0.61 mg/L and stirring speed of 440.57 r/min, the slurry turbidity is predicted to be 11.45NTU, while the measured value is 12.38NTU, indicating that the model has a good accuracy with a small error. Based on the model variance analysis, reliability analysis and factor interaction analysis, it can be verified that RSM is reasonable and feasible to be used for optimizing the flocculation settlement parameters of fine iron tailings slurry, which can provide theoretical basis for its efficient treatment.

Microseismic signals collected during roadway construction in Jinfeng Gold Mine in the southwest Guizhou Province are non-stationary and also contaminated with background noise. For solving this problem, a noise reduction method based on the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) combined with blind source separation (BSS) was proposed. With this method, a microseismic signal can be preliminarily decomposed by ICEEMDAN algorithm, and then correlation coefficient and marginal spectrum of signal can be calculated with MATLAB. Components of noise-containing mode and main frequency of signal can be filtered, and FastICA algorithm is finally used for BSS to achieve noise reduction. The practical application in mine shows that compared to empirical mode decomposition (EMD) and traditional wavelet packet threshold method, the proposed method, with higher signal-to-noise ratio (24.142 5 dB), can bring better noise reduction effect with smaller standard error (0.012 18).

A flowsheet consisting of pre-reduction magnetic roasting and magnetic separation was introduced to process a refractory weakly-magnetic iron ore from Jiangsu Province. The results show that after 60 min roasting at 750 ℃ by adding coal as a reducing agent at an amount of 3%, the pre-reduced iron ore was ground to a fineness of 75% -0.074 mm and then subjected to low intensity magnetic separation consisting of one roughing, one cleaning and one scavenging, resulting in a high quality iron concentrate grading 65.05% Fe at 96.19% recovery. The research results can provide technical reference for the mineral processing of refractory weakly-magnetic iron ore.

With laser high-energy beam as heat source to initiate exothermic reaction, Cu-Al powder was compacted and sintered into Cu-Al alloy containing in-situ formed hard reinforcing phase Al₂O₃ by laser-induced self-propagating synthesis. The effect of Cu-Al ratio in the composition on the microstructure and properties of alloy system was explored. The results show that the microstructure of Cu-Al alloy is a multiphase structure composed of hard reinforcing phase Al₂O₃ and matrix of CuAl₂, AlCu₄, Al₄Cu₉ and other intermetallic compounds. The alloy has rich dendritic crystals in microstructure, and becomes more uniform and fine-grained with the increase of aluminum content. Increasing the content of aluminum to a certain range is helpful to improve the compactness of sintered products. With copper and aluminum in a mass ratio of 33.2∶66.8, the sintered product has the lowest porosity (10.57% ), the highest microhardness (373HV) and the best wear resistance (with wear rate of 0.137 g/mm²).

The interaction mechanism of kyanite group minerals and quartz in cationic flotation system was studied by using an extended DLVO (EDLVO) theory combined with microscopy analysis. The results show that, under conditions including pH value of 8, FeCl₃·6H₂O dosage of 30 mg/L and dodecylamine dosage of 80 mg/L, there is interaction between quartz and kyanite group minerals in various size fraction, and the adhesive coating among particles is one of the main reasons for the interaction between kyanite group minerals and quartz amidst flotation process. Besides, the adsorption force between kyanite group minerals and quartz is in the following descending order：andalusite/quartz ≥kyanite/quartz ≥ sillimanite/quartz, indicating that it is relatively difficult for andalusite to be separated from quartz by flotation.

The effects of different cooling rates in retrogression and re-aging on the microstructure and properties of Al-Zn-Mg-Cu alloy profiles were investigated by performing tests on hardness, electrical conductivity, room temperature tensile, local corrosion and stress corrosion, combined with microstructure characterization by using metallographic microscopy and transmission electron microscopy. The results show that retrogression with cooling rates of 660.0, 12.7 and 0.5 ℃/min, the alloy has a tensile strength of 663.1, 653.4 and 636.9 MPa, an electrical conductivity of 35.1% IACS、35.2% IACS and 36.8% IACS, an exfoliation corrosion in the form of EC, EB-and EB, and a stress corrosion sensitivity of 4.7%, 4.0% and 3.2%, respectively. The precipitates at grain boundaries along the direction of length, with an average size of 48.7, 54.7 and 68.7 nm, are distributed with a spacing of 28.9, 33.6 and 40.3 nm, respectively. The variation in size and distribution is the main reason for variation of the above-mentioned properties. With both mechanical properties and corrosion resistance taken into consideration, it is appropriate to select cooling rates ranging from 0.5 ℃/min to 12.7 ℃/min for retrogression.

In order to find a more accurate and efficient way to measure volume of explosion-produced craters, the traditional method by using a reference plane with a vertical section was improved. Taking the crater produced by single-hole blasting of the deep orebody in Gaofeng Mine as an example, the measurement result by using 3D laser scanning was compared to that by using a reference plane with a vertical section. It is found that 3D laser scanning measurement is superior in terms of accuracy, efficiency and measuring operability. This research can provide a new idea for accurately measuring the volume of explosion-produced craters.

In order to explore disturbance of seabed sediment during mining of polymetallic nodules, a pool experiment was carried out to scour sediment by a waterjet from polymetallic nodules collector. Variation of gully depth, and migration and diffusion regulation of sediments were investigated in the experiment by setting the waterjet at different speed, with nozzle at different height from sediment, and collector at different traveling speed. The results show that the collecting process of polymetallic nodules brings scour to both particles and blocks of sediment, leading to uneven surface of the gully. Then, disturbed sediment migrates and diffuses through upper plume flow and bottom gravity flow.