Experiments were performed in a tube furnace for reduction roasting of high-iron manganese oxide ore, respectively with gas-based (CO) and pulverized coal as reducing agents. The effects of roasting temperature and roasting time on the simultaneous reduction of manganese and iron oxides therein were investigated. The results show that during the gas-based reduction roasting, the reduction process of Mn₂O₃ is controlled by chemical reaction, with apparent activation energy of 42.64 kJ/mol. However, the magnetization process of Fe₂O₃ is controlled by internal diffusion, with apparent activation energy of 21.30 kJ/mol. Compared to coal-based roasting process, Mn₂O₃ and Fe₂O₃ are easier to be reduced during the process of gas-based reduction roasting, and the manganese oxides can be directly reduced from Mn₂O₃ to MnO without the step of being reduced to intermediate product Mn₃O₄.

The influence of roasting on mineral decomposition under stable magnetic field was investigated. A direct reduction roasting experiment without carbon presence was performed for Bayan Obo lean iron, with roasting temperature of 950 ℃ and magnetic induction density of 1.02 T. Based on the analysis of the loss rate of mineral weight, mineral phase transformation and micro-morphology change by means of TG-DSC, XRD and SEM-EDS, the phase evolution law for rare earth minerals, gangue minerals and iron minerals under magnetic field was revealed. The results show that the decomposition time of bastnaesite is shortened by about 20 min after applying a stable magnetic field, and even the monazite with extremely low decomposition rate is almost completely decomposed after 60 min-roasting process. It is found that magnetic field can promote the decomposition and transformation of gangue minerals that cannot be decomposed without application of magnetism, and also accelerate the migration of alkali metal ions and the replacement of Fe²⁺ with fayalite.

The phase composition and morphology of a molten mixture of steel slag and furnace slag prepared at a high temperature was analyzed by X-ray diffraction and SEM-EDS scanning electron microscope to investigate the effect of MgO doping. The results show that MgO doping can effectively inhibit the formation of MgFe₂O₄ phase and non-gel Ca₂Al₂SiO₇ phase, and promote the formation of MgFeAlO₄ phase, thus increasing the melting point of the mixed slag. It is found that the mixed slag after doping 2% MgO presents a layered structure on its cross section. The inner layer has an increased proportion of MgFeAlO₄ phase, with uniform and fine pores; and the MgFeAlO₄ phase is wrapped by MgFe₂O₄ spinel with layered structure in the middle part; and the outer layer has Ca₂Al₂SiO₇ phase with uniform pores and moderate density. The mixed slag with such kind of structure is suitable to be used as the filter material for removing heavy metal ions.

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.

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.

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.

A technique of nanofiltration combined with ammonium sulfide precipitation was verified for its feasibility of separating and recovering ammonium nitrate and nickel nitrate from nickel-containing feed solution. Based on investigating the effects of pressure on the side of concentrate stream in nanofiltration, stages of nanofiltration and pH value of ammonium sulfide precipitate, an appropriate route was determined, including two-stage nanofiltration, KLNi-01 ion exchange to remove nickel, nickel precipitation with ammonium sulfide, and dissolution with nitric acid to recover nickel nitrate. The feed stream with pH of 6 was subjected to a two-stage nanofiltration, with pressure of 0.8 MPa on the side of concentrate stream. The obtained permeate stream with nickel content decreased to 0.181 g/L was adsorbed with KLNi-01 resin, leading to the nickel content therein further reduced to 0.002 mg/L. Then, 36 mL/L ammonium sulfide solution was added into the concentrate stream with an initial pH of 6 for nickel precipitation. The generated solution had nickel content of 4.7 mg/L, and no sulfide was detected, while the obtained precipitate of nickel sulfide was then dissolved with nitric acid, and the nickel nitrate solution was obtained with concentration of 258.40 g/L. The material balance calculation shows that treatment of 1 m³ of nickel-containing feed stream can generate 0.3 m³ permeate, and 192.93 L of nickel nitrate solution with concentration of 258.40 g/L can be generated with the consumption of 25.20 L of ammonium sulfide solution with concentration of 20%-26%, 37.22 L of concentrated nitric acid and 109.05 L of water.

A technique combining mechanical force and heating effect was adopted to selectively disassociate cathode material from spent lithium-ion batteries and roll the aluminum foil by adjusting processing parameters. The results show that a better disassociation effect can be obtained with the frequency of electric motor, air circulation fan and dissociation device at 40 Hz, 40 Hz and 50 Hz, respectively. The aluminum foil with particle size of -1.7+0.075 mm is rolled to be spherical, and the cathode materials with particle size of -0.075+0.048 mm and -0.048 mm are rough on the surface and wrapped by organic binder. The final dissociation rate of cathode sheet can be up to 96.35%, and the cathode material can be recovered at a rate of 94.95% by single operation, with the content of Al impurity less than 0.15%. It is shown that this selective dissociation technique based on a combination of mechanic force and heating effect can actualize an efficient separation and sorting of cathode sheet, not only shortening the battery disposal process flow but also achieving efficient metal enrichment.

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.