A hydrochloric acid leaching process was adopted to recover rare earth from rare earth polishing powder waste. The effects of hydrochloric acid concentration, leaching temperature, leaching time and liquid-solid ratio on the leaching rates of rare earth and main impurity Al₂O₃ were investigated, and the leaching mechanism was also discussed. It is found that the optimal conditions for single-stage leaching with HCl system are as follows: HCl concentration of 8 mol/L, leaching temperature of 80 ℃, leaching time of 3 h, and liquid-solid ratio of 4∶1. Under such conditions, the leaching rates of rare earth and Al₂O₃ are 90.81% and 43.68%, respectively．Based on the comparison of results from single-stage leaching, two-stage leaching and three-stage countercurrent leaching, it is shown that the leaching rate of rare earth by three-stage countercurrent leaching can be up to 98.38%. An increased amount of rare earth in the leaching solution is beneficial to the extraction and recovery of rare earth elements in the next step, thus greatly cutting recovery cost.

In order to investigate the influence of additive on iron recovery from red mud by using a process consisting of magnetizing roasting and low intensity magnetic separation, a kind of red mud containing high content of iron and aluminum was taken for experiments. It is found that addition of dolomite and phosphogypsum won't bring any effect to iron recovery, but sodium sulfate can bring an obvious activation effect. In the experiment, the roasting process ran at 650 ℃ for 90 min, with the addition of sodium sulfate at an amount of 10%, with total gas flow at a rate of 500 mL/min and CO at a volume fraction of 30%. And then, the obtained calcine, after being ground to a fineness of -0.045 mm 65%, was subjected to a magnetic separation with magnetic intensity of 68.8 kA/m, yielding an iron concentrate with 60.65% TFe grade at 94.01% recovery. The subsequent thermodynamic analysis showed that at the temperature within the tested range, both dolomite and phosphogypsum were conducive to the decomposition of iron olivine rather than iron spinel, while sodium sulfate could work for both.

With Bayan Obo niobium concentrate and semi-coke powder as raw materials, effect of basicity on melting process of the reduction product of carbon-containing pellets was observed in situ by using a high temperature heat table. The samples with optimum basicity were quenched and prepared at different melting conditions. The migration rule of elements during the melting process was analyzed by SEM-EDS, and the reaction rates of Nb and Si in the melting process were quantitatively analyzed by XRD, TG-DSC and ICP. Results show that with the binary basicity of 1.0, the spattering of molten slag can be effectively suppressed and the melting efficiency can be improved. With the basicity of 1.0 and temperature of 1 350 ℃, the SiO₂ in the slag is reduced at slag-gold interface and pulled into iron phase. After the molten slag is held at 1 400 ℃ for 2 min, the C in molten iron at slag-gold interface is preferentially reacted with the niobium oxide in the slag and reduced to NbC. A small amount of NbC is dissolved into the iron phase, and most of the remaining NbC is wrapped around the granular iron, forming a retention zone, which hinders the mass transfer at the slag-gold interface and reduces the reduction rate. After hot-holding at 1 400 ℃ for 10 min, the reaction rates of Nb and Si are 36% and 1.7% respectively. Titanium and rare earth are not involved in the reaction during the whole melting separation process.

The impact of blasting vibration on the open-pit slope in a limestone mine was explored. The characteristics and law of blasting vibration was investigated by performing field blasting vibration tests based on the consideration of geological conditions on site. Based on fitting with Sadowski formula, an obvious attenuation trend was found for the velocity of particle vibration in the data about two field blasting vibration. With Sadowski formula modified based on elevation effect, the correlation coefficient was up to 0.94, better than the fitting effect by the traditional Sadowski formula. The maximum vibration velocity on each bench of limestone slope was predicted by using the modified fitting formula in this paper, and considering the designed detonate charge for steep end-slope, showing that the impact of vibration source on the adjacent bench should be taken into consideration in blast design.

An introduction of preparation method of Fe/Al₂O₃ ceramet composites is presented. The combination mechanism of Fe-base and ceramic phase in the preparation process of Fe/Al₂O₃ cermet composites, as well as the optimization of preparation technique and material properties are all expounded based on the principle of powder metallurgy. Finally, the future direction for Fe/Al₂O₃ cermet composites research is also predicted.

A kind of similar rock material was prepared with gypsum and quartz sand, and influence of seven factors on the strength index of the material was analyzed by performing laboratory tests. The results show that curing temperature and material density are in positive correlation with material strength index, while curing humidity, sand-to-binder ratio, ash-to-paste ratio, fine-grained quartz sand content, as well as water content are in negative correlation with material strength index. Based on the calculation of the sensitivity indices of different influencing factors, it is found that material strength has a sensitivity of only 4.5% to curing temperature, a sensitivity of 104.9% to sand-binder ratio. Factors of curing temperature, water content, material density, curing humidity, ash-to-paste ratio, fine-grained quartz sand content and sand-to-binder ratio are in an ascending order in terms of their sensitivity to uniaxial compressive strength; while factors of sand-to-binder ratio, ash-to-paste ratio, material density, curing humidity, water content, fine-grained quartz sand content and curing temperature are in a descending order in terms of their sensitivity to tensile strength.

An experimental study was carried out for sulfur reduction and upgrading of a high-sulfur antimony-gold bulk concentrate from Russia with Sb grade of 24.58%, Au content of 76.92 g/t and S content of 14.46%. A closed-circuit flotation test was conducted using a new collector CJ-201 and a new depressant CJ-5S. The Sb and Au grades in the antimony concentrate attained respectively 42.26% and 92.36 g/t, with the corresponding recoveries of 88.04% and 62.18%. With this approach, a antimony-gold concentrate product with high content of antimony and low content of sulfur can be separated out from antimony-gold bulk concentrates collected in a Russian mine.

With sodium bicarbonate as a precipitant, praseodymium neodymium oxide was prepared by feeding step by step in a positive sequence. The effects of pH value at the end of precipitation and precipitation temperature on particle size and impurity content of the precursor and product of praseodymium neodymium oxide were all investigated. The results show that precipitation at 50 ℃ with pH value of 5.10 at the end can prepare a praseodymium neodymium oxide powder with a median particle size D₅₀ of 21.45 μm and narrow particle size distribution. It is sphere-like powder formed by flake crystallization agglomeration, with the content of Cl^-and Na₂O at 0.017% and 0.012%, respectively, indicating higher than the national standards.

Aiming at complicated flow field of Y-shaped pipe in pump piping system and risk of ore leakage in conveying test for deep sea mining, numerical simulation was performed by using CFD-DEM method for ore particles with different velocities, different volume concentration and different particle sizes. Based on that, the movement features of particle groups and flow field distribution pattern in Y-shaped pipe were all analyzed. It is found that the flow field distribution in Y-shaped pipe is influenced by the curvature of pipe elbow and the flow distribution in the inlet of Y-shaped pipe. The particle groups flow against the inner wall of elbow, and deflect upward under the influence of upward flow. If upward flow with lower velocity, particles with large grain size and high volume concentration will hit the bottom of pipe, leading to some losses. As the upward velocity decreases and both particle volume concentration and grain size increase, more and more particles will be continuously lost on the bottom of pipe. Due to the existence of particle flow, both intensity and scale of the low-pressure vortex region in Y-shaped pipe become weaken.

A Fe-based cladding layer was prepared on the surface of 27SiMn steel by using laser cladding technique, and effect of preheating on the microstructure and mechanical properties of the heat affected zone (HAZ) of 27SiMn steel was investigated. The results show that a large amount of martensite appears in the HAZ of 27SiMn steel after laser cladding process. The tensile fracture is composed of river-pattern cleavage plane, tear edge and dimple, representing a quasi-cleavage fracture; preheating treatment effectively reduces the amount of martensite and brings pearlite structure. When the preheating temperature is 100 ℃, the quenched layer has its hardness decreased by 25.4%, elongation increased by 11.5%, and tensile strength decreased by 14.3%. When the preheating temperature rises to 300 ℃, ductile fracture occurs in the material under tensile force. Appropriate preheating can effectively reduce the martensite in the HAZ of 27SiMn steel and alleviate the decline in the toughness of 27SiMn steel caused by quenching, thus improving the safety during the service of hydraulic cylinder made of laser cladded 27SiMn steel.