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The condensation behavior of magnesium vapor produced by metal Mg or pellets for magnesium production is investigated at heat source temperatures of 1173–1473 K under vacuum. The possibility of reduction of magnesite in vacuum was analyzed by means of thermodynamics. The results indicate that the thermal motion of magnesium is violent, and the volatilization rate increased with high heat source temperature, the results accord with Maxwell's velocity distribution law. Magnesium vapor condensation products were obtained with flake and powder macromorphologies, where the flake products accounted for more than 80% (in mass). Scanning electron microscopic analysis revealed that the main factor affecting the magnesium vapor condensed particles was the vapor pressure, which was determined by temperature and reaction. The end condensation temperature was between 528.1 and 637.1 K when the heat source temperature was 1173–1473 K. Increasing the temperature gradient decreases the condensation temperature range. X-ray diffraction results showed that the magnesium condensation products were more crystalline at lower vapor pressure and a small temperature gradient. The presence of Ca 2 SiO 4 in the reduction slag indicated the occurrence of the reduction reaction. The experimental results from pellets for magnesium production were consistent with those involving Mg metal. • The condensation of Mg vapor was studied by using magnesite in vacuum. • The vapor condensation behavior of Mg and pellets for magnesium production were compared. • The effects of temperature and temperature gradient on condensation behavior was analyzed. • Using Mg instead of pellets can provide theoretical support for magnesium production with magnesite. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photocatalyzed oxidative S 2 O 3 2− removal from sodium aluminate solutions. • Co doping enhanced the light utilization efficiency of photocatalyst. • Excellent catalytic performance was achieved under high-salt and -alkali conditions. • S 2 O 3 2− degradation was mediated by photogenerated holes and hydroxyl radicals. The strongly alkaline sodium aluminate solution generated from high-sulfur bauxites during their refinement through the Bayer process contains sulfur, mainly in the form of thiosulfate (S 2 O 3 2−) ions, which affects the quality of the target product (alumina). Consequently, the large-scale use of high-sulfur bauxites is severely limited, and methods of desulfurizing sodium aluminate solutions are urgently needed. To address this need, we herein prepared metal–organic framework (ZIF-8)-supported Co-doped TiO 2 (Co-TiO 2 @ZIF-8) using a sol–gel method and low-temperature calcination under N 2 and examined the ability of this composite to photocatalyze the oxidative degradation of thiosulfate ions in sodium aluminate solutions. Co-TiO 2 @ZIF-8 retained the large specific surface area and rich porosity of ZIF-8, which reduced the agglomeration of TiO 2 particles on the surface. The loading of Co-TiO 2 endowed Co-TiO 2 @ZIF-8 with a mesoporous structure and thus increased its adsorption capacity. Compared with ZIF-8, Co-TiO 2 @ZIF-8 featured new functional groups, and the formation of Zn–C and N–Ti–O bonds confirmed the successful integration of Co-TiO 2 with the ZIF-8 carrier. Consequently, the thiosulfate removal rates by Co-TiO 2 @ZIF-8 were 42 % and 26 % higher than those observed for the blank sample and pure TiO 2 (light source = xenon arc lamp, oxidant = O 3 , reaction time = 60 min), respectively. This high performance is primarily due to Co doping, which enhanced the efficiency of visible light utilization, and the photogenerated electron–hole pairs on the photocatalyst surface and hydroxyl radicals formed by the interaction of holes with the solution-phase OH− ions. [ABSTRACT FROM AUTHOR]

High-alumina fly ash is an alumina-rich mineral resource that can potentially replace low-grade bauxite. While a wide range of different traditional processes are available for extracting alumina from high-alumina fly ash, these processes have many disadvantages. Northeastern University has recently proposed a new electrotransformation processing technique for transforming AlCl 3 into Al 2 O 3 in the process of extracting Al 2 O 3 from high-alumina fly ash by the hydrochloric acid method. The feasibility of this new electrotransformation method was studied in this paper. The effects of the current intensity, electrotransformation time, initial electrotransformation temperature and initial HCl concentration on the electrotransformation process and roasting products were investigated. The results show that the pH of the electrolyte increases with increasing current strength, electrolytic time, initial electrotransformation temperature and HCl initial concentration, and its value tends to be 3.2. Under these conditions, XRD and SEM examinations confirm that the roasting products are Al 2 O 3 sheets with a cubic crystal system. An examination of the grain size shows that the grain sizes are uniform. Elemental content examinations show that the Cl contents of the obtained products are <0.08%. These results confirm that the new electrotransformation method is feasible for industrial use. We propose a new method of electrotransformation to extract alumina from high-alumina fly ash. CO 2 gas was injected into the cathode side of the electrolytic cell, and, at the same time, the power supply was connected. Then, the electrical transformation process proceeds. In the anode chamber, chlorine ions were oxidized to form chlorine gas. In the cathode chamber, the aluminum ions react with CO 2 and hydrogen ions to form hydrogen and electrically transformed products (carbon-containing aluminum salt). After electrotransformation, the carbon-containing aluminum salt in the cathode side was poured out, filtered and dried. Finally, after the roasting process, Al 2 O 3 products were obtained. We studied the feasibility of the electrotransformation technology in the present work. At the same time, we investigated the effects of electrotransformation parameters such as the current intensity, electrotransformation time, initial electrotransformation temperature and initial HCl concentration on the electrotransformation process and on the phase, morphology, particle size and chlorine contents of the roasting products. Unlabelled Image • A new method was proposed in this paper for preparing alumina from aluminum chloride aqueous solution. • The feasibility of electrotransformation is studied. • The change in pH value of solution was investigated during electrical transformation process. • The effects of different electrolytic parameters were investigated on the roasting products. [ABSTRACT FROM AUTHOR]

Due to the instability of thiosulfate ions (S 2 O 3 2−), the recovery of metals from thiosulfate solution using direct electrodeposition has not been widely adopted yet. In the current work, the cationic membrane electrolysis (CME) equipped with cationic membrane was employed for the copper recovery from thiosulfate solution. The effect of operational parameters such as pH and ionic strength of anodic compartment, electrode distance, cell voltage and electrolysis temperature on the copper stripping were investigated systematically, and the duration of cationic membrane was considered subsequently. The result indicated that the pH of anodic compartment played a decisive role in the electrolysis process, i. e. high pH value (>14.0) promoted OH− ions penetration, while low pH (<13.0) easily generated H+ and passed through cationic membrane leading to the dissociation of S 2 O 3 2−. At optimal experimental conditions, the recovery efficiency of copper reached more than 99%, with energy consumption of 1.58 W h/g Cu, while less than 0.3% of S 2 O 3 2− was decomposed which was consistent with IR analysis of electrolytic solution. Besides, the cationic membrane used in electrolysis process reached 10 times and easily regenerated. This work provided an effective green and economic approach to recover copper from thiosulfate solution, and then avoid the decomposition of S 2 O 3 2− using electrolysis process. [Display omitted] • CME technique is a promising alternative for Cu recovery from thiosulfate system. • The pH of anode compartment plays a key role in the CME prosess. • Current efficiency of Cu reaches 99% with 1.58 W h/g Cu energy consumption. • Decomposition of S 2 O 3 2− is significantly inhibited during CME process. [ABSTRACT FROM AUTHOR]