Comparison of deep desulfurization methods in alumina production process

Several methods of deep desulfurization in alumina production process were studied, and the costs of these methods were compared. It is found that most of the S2- in sodium aluminate solution can be removed by adding sodium nitrate or hydrogen peroxide in digestion process, and in this way the effect of S2- on alumina product quality is eliminated. However, the removal efficiency of 2?32OS in sodium aluminate solution is very low by this method. Both S2- and 2?32OS in sodium aluminate solution can be removed completely by wet oxidation method in digestion process. The cost of desulfurization by wet oxidation is lower than by adding sodium nitrate or hydrogen peroxide. The results of this research reveal that wet oxidation is an economical and feasible method for the removal of sulfur in alumina production process to improve alumina quality, and provide valuable guidelines for alumina production by high-sulfur bauxite.

A Device for Measuring the Density and Liquidus Temperature of Molten Fluorides for Heat Transfer and Storage

An experimental device is constructed for measuring the density and liquidus temperature of molten fluorides by using the Archimedean and cooling curve methods respectively.Its operation is tested by measuring the density and liquidus temperature of NaCl salt.The accuracy of the liquidus temperature measurement is about±1 K.The density of NaCl measured is in good agreement with the widely recognized data and the deviation is less than 0.2%.The liquidus temperature and density of a typical heat transfer fluoride LiF-NaF-KF(46.5-11.5-42mol%)are investigated.

Leaching Kinetics of Calcium Vanadate by Na_2CO_3 Solution

Leaching kinetics of calcium vanadate by Na2CO3 solution was studied. Kinetic equation was established according to the variation of VO3-concentration with time during the leaching process. The influences of initial pH value and stirring speed on reaction rate constant were examined and the corresponding apparent activation energy was calculated. The results indicate that the leaching process is a 0.68 order reaction, and the reaction rate constant 8.64×10-6 mol/(L-s). It increases with the increase of pH value and stirring speed. And the dissolution rate of calcium vanadate also increases. The apparent activation energy is 38.98 kJ/mol, and temperature has great influence on the leaching rate of calcium vanadate.

Effect of Heat Treatment on Microstructures And Properties of Mg-9Gd-3Y-0.3Zr Cast Alloy

Microstructures, aging hardness and mechanical properties of as-cast Mg-9Gd-3Y-0.3Zr alloy were investigated. The microstructure is a typical dendritic structure of as-cast sample. The aging test was carried at 250 ℃ and at a different aging time. The aging peak hardness is about 110HV of as-cast T6 alloy and higher than that of as-cast T5 alloy, tensile test result showed that tensile strength of as-cast T6 is higher than as-cast T5 but the elongation of as-cast T5 is higher than as-cast T6. The fracture mode of as-cast T6 is intergranular and transgranular cleavage fracture, but as-cast T5 is mainly microvoid coalescence fracture combination the brittle cleavage fracture.

Aging characteristics and high temperature properties of Mg-9Gd-3Y-0.3Zr

The microstructures and tensile properties of Mg-9Gd-3Y-0.3Zr alloys were investigated by OM,SEM and mechanical property tester. The results show that the microstructure of as-cast sample is a typical dendritic structure,the grain size of extruded sample is finer than that of the as-cast because of recrystallization. The aging response of extruded specimens is quick and marked when the samples are aged at 200 to 250 ℃ for different time,and the peak aging hardness is about HV120. The tensile strengths at 25,200,250 and 300 ℃ are 375,364,329 and 286 MPa,respectively. The maximum elongation is higher than 18% at 300 ℃. The fracture mode is mainly microvoid coalescence fracture combining with brittle cleavage fracture at room temperature,and microvoid coalescence fracture at 250-300 ℃.

Ferrous ion oxidation by Thiobacillus ferrooxidans immobilized on activated carbon

The immobilization of Thiobacillus ferrooxidans on the activated carbon particles as support matrix was investigated. Cycling batch operation results in the complete oxidation of ferrous iron in 8 d when the modified 9 K medium is set to flow through the mini-bioreactor at a rate of 0.104 L/h at 25 ℃ . The oxidation rate of ferrous iron with immobilized T. ferrooxidans is 9.38 g/(L·h). The results show that the immobilization of T. ferrooxidans on activated carbon can improve the rate of oxidation of ferrous iron. The SEM images show that a build-up of cells of T. ferrooxidans and iron precipitates is formed on the surface of activated carbon particles.

A Novel Processing Route for Ni-doped Alumina Composites

Alumina-based composites containing 0-15wt% Ni metallic phase were produced by hot press-sintering Ni-coated alumina powders. The Ni-coated alumina powders were prepared by the aqueous heterogeneous precipitation of alumina micro-powders and nickel sulfate salt followed by reduction process. The microstructural features and dispersion of Ni phase in Ni-coated alumina powders and the subsequent alumina-Ni cermets were investigated using scanning electron microscope （SEM）, X-ray diffractometer （XRD）, and transmission electron microscope （TEM）. The relative density of the hot press-sintered composites was measured with the Archimedes＇ method while the fracture strength and the fracture toughness were defined with the three-point bending method and the micro-indentation fracture method. In the formation of alumina-Ni cermets from sintered Ni-coated alumina powders, Ni phase to some extent limits the densification rate and stifles the coarsening and growing process of alumina grains. The Ni phase is found to be located at the interfaces and the triple-joint junctions of alumina grains which results into alteration of the fracture mode of alumina and its increased fracture strength and fracture toughness if compared with monolithic alumina.

Fabrication of magnetic nanosized γ-FeNi-coated ceramic core-shell microspheres by heterogeneous precipitation and thermal reduction

Precursors with NiCO3-2Ni（OH）2.2H2O- and Fe203.nH20-coated alumina, graphite and cenosphere were synthesized by precipitation using ferrous sulfate, nickel sulfate, ammonium bicarbonate, alumina, graphite and cenosphere as the main starting materials. Magnetic γ-FeNi-coated alumina, graphite and cenosphere core-shell structural microspheres were subsequently prepared by thermal reduction of the as-prepared precursors at 600℃ for 2 h. Precipitation parameters, e.g. concentration of ceramic micropowders （lOg/L）, sulfate solution （0.2mol/L）, rate of adding reactants （3 mL/min） and pH value were optimized by a trial-and-error method. Powders of the precursors and the resulting coating of γ-FeNi with grain size below 40 nm on alumina, graphite and cenosphere microspheres were characterized by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） and X-ray diffraction （XRD）. The magnetic properties of the nanosize γ-FeNi-coated alumina, graphite and cenosphere microspheres were measured by vibrating sample magnetometer （VSM）. The results show that the core-shell structural γ-FeNi-coated ceramic microspheres exhibited higher coercivity than pure γ-FeNi powders, indicating that these materials can be used for high-Derformance functional materials and devices.