Vanadium slag and sodium carbonate, as raw materials, were mixed and grounded for pretreatment. The obtained mixture was then taken in a roasting experiment for investigating effects of factors, such as holding time, temperature and feeding materials for roasting process with different alkali ratios (a mass ratio of sodium carbonate to the converted content of V₂O₅ in vanadium slag) on transformation and leaching rate of vanadium from clinker, and also exploring phase transformation of vanadium slag during the roasting with a low alkali ratio. The results show that if roasting process at higher temperatures is held for 90 minutes, the alkali ratio in the roasting process can be reduced by properly increasing the temperature. After roasting at a temperature of 880 ℃ with an alkali ratio of 1.0, water leaching can result in the total vanadium (TV) content in the residue falling down to 0.49% and the leaching rate of vanadium up to 94.70%. This method is suitable for sodium roasting in a rotary kiln. Under the existing process conditions for sodium roasting of vanadium slag in a multiple hearth furnace, an addition of some clinker into the material for roasting is beneficial to reducing the alkali ratio. It is shown that after roasting is held for 45 minutes at 780 ℃ with an alkali ratio of 1.2, the TV content in the final leaching residue can fall to 0.96% and the leaching rate can reach 89.19%. The microscopic analysis of the clinker after roasting with a low alkali ratio show that there is a high aggregation of sodium vanadate phase, which is in good consistency with NaVO₃ in the elemental composition.

After an introduction of the current status of gallium resources and analysis of the occurrence state of gallium in sodium aluminate solution, zinc smelting slag, tailings from vanadium extraction and coal-based solid waste, progress in the research of gallium extraction processes is elaborated and the adaptability, advantages and disadvantages of each technique are also summarized. Finally, based on the discussion of problems faced by the gallium industry and the development direction in the future, it is suggested that iteration and upgrading of gallium extraction processes should be vigorously promoted based on China's scale advantage in alumina industry.

An extraction system composed of P507 as the extractant and sulfonated kerosene as the diluent was used to separate zinc from a sulfuric acid leachate containing cobalt, manganese and zinc. The effects of key parameters on zinc separation efficiency were investigated, including the volume fraction of P507 in organic phase, saponification degree, pH value of feed, O/W ratio, reaction time, and reaction temperature. The results show that under the following optimal process conditions, including P507 at 20% by volume, saponification degree of 80%, feed pH of 5, O/W ratio of 1∶1, reaction time of 10 min and reaction temperature of 25 ℃, the extraction rate of Zn reaches 99.92%, while the extraction rates of Mn and Co are just 17.41% and 3.69%, respectively, presenting an excellent separation effect.

Heavy metal pollution in Dalong River was assessed by field sampling and detection analysis. Hg(II) and Pb(II) in the water and sediment were adsorbed with sludge-derived biochar for ecosystem restoration in Dalong River, and the restoration effect was then compared with that by using activated carbon. The results indicate that heavy metal pollution in Dalong River is relatively slight, and the contents of heavy metals in the surface water at all sampling points are within a safe range, only the sediment at some sampling points has the heavy metal pollution at a light pollution level. It is shown that sludge-derived biochar has a good adsorption for Hg(II) and Pb(II), with the adsorption process conforming to the Langmuir isotherm (with R² of 0.932 2 and 0.998 9). Compared with activated carbon, the sludge-derived biochar can bring better restoration effect, and its desorption of Hg(II) and Pb(II) also shows that it can have a significantly better fixation effect of heavy metals.

To extract rare earth elements (REE) of yttrium (Y) and cerium (Ce) from yttrium aluminium garnet (YAG) fluorescent powder, experiments were performed for YAG by adopting direct acid leaching and roasting-acid leaching process, respectively. The effects of various factors on the leaching rates of Y and Ce were investigated, including roasting agent types and dosage, roasting temperature, roasting time, as well as leaching temperature and leaching time. It is shown that YAG fluorescent powder is stable in structure, while Y and Ce elements therein, not in the form of simple oxides, cannot be effectively extracted by direct acid leaching; a roasting pretreatment can effectively destroy the structure of YAG fluorescent powder, and convert the rare earth elements into oxides, which is beneficial to the following acid leaching process. After 2 h roasting at 900 ℃ with YAG and Na₂CO₃ in a mass ratio of 1∶0.5, and then 1 h leaching at 60 ℃ with HCl at a concentration of 3 mol/L, a liquid-solid ratio of 20 mL/g, and 1.2 mL/g of hydrogen peroxide, the leaching rates of Y and Ce can reach 97.23% and 84.91%, respectively.

Extraction of rhenium from low-grade molybdenum concentrate by adopting a process of oxidative volatilization followed by ion exchange was explored in experiments. Firstly, a two-stage high-temperature oxidative roasting was adopted to oxidize rhenium into Re₂O₇. Rhenium and molybdenum were effectively separated due to rhenium volatilizing into the flue gas. The volatilization rate of rhenium reached 85.42% after roasting process at 675 ℃. Then, the rhenium-containing flue gas was eluted to get rhenium-containing solution, in which rhenium was selectively extracted with D201×7 ion exchange resin. With the solution pH of 9, liquid/solid ratio of 50 mL/g, a 20 min adsorption at temperature of 35 ℃ brought the adsorption rate of Re up to 97.52% and the adsorption rate of Mo less than 20%. Finally, a product of ammonium rhenate was prepared by stepwise desorption followed by concentration and crystallization. By this process, the total recovery of Re can reach 70.68%.

With nickel laterite ore from Morowali of Indonesia as the raw material, effects of various factors, including reaction time and temperature, stirring speed, acid-to-ore ratio, and slurry concentration, on the leaching rate were systematically investigated. Additionally, the leaching mechanism was explored by using the PHREEQC, a thermodynamic calculation software. The results show that after one hour reaction at 250 ℃, with acid-to-ore ratio of 300 kg/t and slurry concentration of 25%, the leaching rates of Ni and Co can reach 98.40% and 99.90%, respectively, while the leaching rates of Fe and Al are just 3.84% and 40.25%, respectively. The high selectivity of high pressure acid leaching (HPAL) is attributed by the factor that at high temperatures, not only the hydrolysis reaction of Fe and Al can be promoted, but also the pOH can be decreased from 14 to 10, which thereby inhibits leaching of Fe and Al. As the temperature rises to above 200 ℃, the number of H⁺ increases, which can ensure a sufficient amount of H⁺ for leaching of nickel and cobalt metals.

Based on an overview of progress in the research on iron recovery from high-iron red mud by alkaline electrolysis, the research findings at home and abroad are introduced in terms of principle and advantages of electrolysis, influencing factors for the process, and the obtained iron products. The advantages of red mud in the process for preparing metallic iron by electrolytic reduction of red mud in alkaline media at low temperatures are elaborated, and some problems to be solved in the future are proposed, which can provide references for innovation and development of this process.

In combination with experiments and multi-step finite element simulation, the residual stress distribution in components manufactured by laser powder bed fusion (LPBF) and the influence of the initial residual stress field on the laser shock peening (LSP)-induced compressive residual stress field. The validity of the simulation results was verified by the residual stress values measured with X-ray diffraction. The results show that the thermal stress of the lower and middle layer materials in the component fabricated by LPBF undergoes a transition from zero stress, compressive stress, tensile stress to compressive stress, while the top layer material shows a transition from zero stress, compressive stress to tensile stress, thus leading to tensile residual stress occurred on the surface layer of LPBF fabricated component, while compressive residual stress in the lower part. The action of initial residual stress field results in the reduced peak value but increased depth of LSP-induced compressive residual stress. The initial residual tensile stress field of LPBF components can exert a suppressive and dragging effect on the reverse plastic deformation caused by surface waves, leading to reduced intensity and changed position of the “residual stress hole”, which can improve the uniformity of LSP-induced residual stress distribution.

Manganese-containing master alloy was prepared by vacuum induction melting. Effects of factors, such as manganese source, Mn/Al mass ratio, preheating time, and refining time on the composition of the manganese-containing master alloy were studied, and the influence of manganese-containing master alloys replacing the traditional “Mn + Al” feed on the prepared manganese-containing AB₅-type rare-earth-based hydrogen storage alloy was also discussed. The experimental results show that compared to manganese powder, manganese flakes as manganese source can bring higher melting yield. Manganese-containing master alloys can be formed with different Mn/Al mass ratios. As the preheating time is prolonged, the melting yield firstly increases and then decreases, and the optimal condition for preheating is 10 minutes at a power of 4 kW. As the refining time increases, the melting yield decreases slightly, and the optimal condition for refining is 1 minute at a power of 15 kW. The average melting yields of rare-earth-based hydrogen storage alloy prepared with MnAlNi alloy and MnAl alloy are increased by 0.37% and 0.78% respectively than that with “Mn + Al” as raw material. The preparation of AB₅-type rare-earth-based hydrogen storage alloy with manganese-containing master alloy can optimize the yield, with the hydrogen storage performance not influenced. The application of this method in practical industrial production brings good effect.