Conversion of ferric oxide to magnetite by hydrothermal reduction in Bayer digestion process

Digesting aluminum-bearing minerals and converting ferric oxide to magnetite simultaneously in Bayer digestion process is crucially important to deal with high-iron diasporic bauxite economically for alumina production.The reaction behaviors of hydrothermal reduction of ferric oxide in alkali solution were studied by both thermodynamic calculation and experimental investigation.The thermodynamic calculation indicates that Fe3O4 can be formed by the conversion of Fe2O3 at proper redox potentials in alkaline solution.The experimental results show that the formation ratio of Fe3O4 either through the reaction of Fe and Fe2O3 or through the reaction of Fe and H2O in alkaline aqueous solution increases remarkably with raising the temperature and alkali concentration,suggesting that Fe（OH）3- and Fe（OH）4- form by dissolving Fe and Fe2O3,respectively,in alkaline aqueous solution and further react to form Fe3O4.Moreover,aluminate ions have little influence on the hydrothermal reduction of Fe2O3 in alkaline aqueous solution,and converting iron minerals to magnetite can be realized in the Bayer digestion process of diasporic bauxite.

A clean process of lead recovery from spent lead paste based on hydrothermal reduction

An innovative process was proposed for recovering lead from spent lead paste, and it produced less pollution and used lessenergy than the traditional process. First, lead dioxide in lead paste was reduced by glucose under hydrothermal conditions. Theeffects of the reaction time, glucose excess coefficient, temperature and pH on the hydrothermal reduction were systematicallyinvestigated. Under the optimized reduction conditions （i.e., temperature of 175 ℃, time of 120 min, glucose excess coefficient of3.0 and pH of 5.5）, 99.9% reduction ratio of lead dioxide is achieved, and only the PbO·PbSO4 and PbSO4 phases are observed in thereducing residue. Subsequently, the reducing residue is desulfurized in a NaOH solution, and approximately 99.40% of the sulfur isremoved. The main lead phase in the desulfurization residue is 3PbO·H2O.

Preparation of Cr_2O_3 precursors by hydrothermal reduction in the abundant Na_2CO_3 and Na_2CrO_4 solution

Precursors of chromium oxide （p-Cr203） were prepared by reducing hexavalent chromium in the presence of sodium carbonate solution under hydrothermal conditions. Methanal was used as the reductant, and carbon dioxide was the acidulating agent. The influences of reaction temperature, initial pressure of carbon dioxide, isothermal time and methanal coefficient on Cr（VI） reduction were investigated. Ex- perimental results showed that Cr（VI） was reduced to Cr（III） with a yield of 99%. Chemical titration, thermogravimetry （TG）, X-ray diffrac- tion （XRD） analysis, and scanning electron microscopy （SEM） were used to characterize the p-Cr203 and Cr203. The series of p-Cr203 were found to be multiphase even if they presented different colors, from gray green to lavender. After these p-Cr203 samples were calcined, the product of rhombohedral Cr203 with a purity of 99.5wt% was obtained.

Hydrothermally Synthesizing Nanospheres of Pd Loaded TiO_2 for Photocatalytically Reducing CO_2 in Isopropanol to Isopropyl Formate

Photocatalytic reduction of CO2 was carried out on villiform spherical catalysts of Pd-TiO2 in isopropanol solution.The catalysts were synthesized by hydrothermal method,their structures,morphologies and optical absorption properties were characterized by X-ray diffraction（XRD）,energy dispersive X-ray spectroscopy（EDS）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,highresolution transmission electron microscopy（HRTEM）and UV-vis absorption spectroscopy（UV-vis）.The photocatalytic activities with different loading amounts and morphologies were evaluated for determining the dominant effect and optimizing the catalyst preparation.Based on a villiform spherical TiO2 with the largest specific surface area in our experiments,we prepared a set of catalysts with various loading amounts of palladium and tested them by bubbling CO2 through the slurry of catalyst and isopropanol.The highest formation rate of isopropyl formate was 276.6μmol/g？cat/h.Eventually we proposed the reaction mechanism.

Effect of Doped Vanadium Dioxide on Oxidative Desulfurization Reaction

VO2(M) doped with different metals(Ti, Ce, Nb, Zr, W, and Mo) was successfully synthesized by the hydrothermal reduction process using oxalic acid as the reductant. The results showed that doping metals in the VO2(M) lattice could enhance the oxidative desulfurization(ODS) activity. The DSC and Raman spectra revealed that VO2(M) retained its monoclinic structure after doping. Mechanism for the improvement of ODS activity by doping was investigated. Electron transfer to V(V) atom occurs upon doping, and then V(V) changes into V(IV), which can promote the ODS reaction. This explanation can be confirmed by the fact that doping can promote the proportion of V(Ⅳ) after doping as revealed by the XPS analysis.