Advanced Materials Research Vol. 402

Abstract: The present work is concerned with the kinetic study of pressure leaching of zinc silicate ore in sulfuric acid solutions. The effects of leaching temperature, particle size, sulfuric acid concentration and agitation speed on the zinc extraction were evaluated. The results obtained show that the zinc extraction increases with increasing sulfuric acid concentration and leaching temperature. The leaching kinetics was analyzed by using a shrinking core model with diffusion control given by: 1-2/3x-(1-x)^2/3=Kt, which represented well the experimental data. The apparent activation energy was determined to be 44.56kJ/mol at temperatures ranging between 80 and 140°C.

Abstract: In this work the cooling slope (CS) method was employed to produce the A356 feedstock in semisolid processing. The dendritic primary phase in the conventionally cast A356 alloy has transformed into a non-dendritic one in ingots cast over a cooling plate with (625°C, 650°C and 680°C) superheat. After pouring, the melt which became semisolid at the end of the plate was consequently poured into cylindrical steel mold with the various mold temperatures of (25°C, 200°C, 400°C). In this study, the cooling slope was adjusted at 50o with respect to the horizontal plane and 500mm length. It was found that the pouring and mold temperature affect the size and morphology of α-Al phase.

Abstract: According to the reaction shaft operation characteristics during the flash smelting process, 15 groups of slag samples containing high Fe₃O₄ were prepared by some chemical reagents, and the slag melting temperatures were measured using a ZDHR-200 type intelligent test instrument for ash melting point by means of hemisphere point. Then, the mathematical formula between the melting temperature and the chemical composition of freeze slag were acquired by means of nonlinear regression analysis. The effects of the Fe/SiO₂ ratio (m_Fe/m_SiO2), CaO/SiO₂ ratio (m_CaO/m_SiO2), Fe₃O₄ content (ω_Fe3O4), Cu₂O content (ω_Cu2O) and MgO content (ω_MgO) on the slag melting temperature were also studied. Results show that the melting temperatures calculated by the regression formula reproduce the experimental data in molten freeze slag with high precision. The slag melting temperature ascends rapidly with increasing ω_Fe3O4 when ω_Fe3O4>18%, and descends quickly when ω_Cu2O raises from 3 % to 7 %, but descends slowly with increasing ω_MgO. The melting temperature tend to go down first and then rise up with the increase of m_Fe/m_SiO2 and m_CaO/m_SiO2, arriving at the minimum when m_Fe/m_SiO2=1.3 and m_CaO/m_SiO2=0.8, respectively.

Abstract: Biological desilication by Bacillus mucilaginosus was investigated using 10 g/L of the cell suspension, fermented liquid and 100 μg/mL of polysaccharide solution. Results showed that the ratio (A/S) of Al and Si in bauxite increased from 2.84 to 3.32, 3.74, 4.19, respectively; and the effects of desilication were all significant by T test. The infrared spectra both of the cell and polysaccharides before and after leaching had significant changes at the wave number of 1070 cm-1 and there were two peaks broadened absorption after leaching, so these appear that the silicon complexes were formed by Si-O-R form. Before and after leaching of bauxite, it was observed by the scanning electron microscope, many holes were formed and the bacteria in the leaching process had significantly erosion on the bauxite surface. Otherwise XREDS analysis further proved that Bacillus mucilaginosus GSY had significant desilication effect.

Abstract: For the low m(Al₂O₃)/m(SiO₂) (mass ratio, for short A/S) calcium aluminate slag obtained from smelting reduction Pingguo red mud, the impact of different n(CaO)/n(Al₂O₃))(molar ratio, for short C/A) and A/S on the separateing out phase of slag in cooling and solidification process was studied by FactSage thermodynamic calculation software, and the material ratio of the slag was optimized. The physical-chemical properties of slag prepared in the experiment were analyzed by means of XRD, EMS, EDS, Particle size analysis and Chemical analysis. The thermodynamic calculation results indicate that the effect of C/A on the phase composition of the slag is great, but the influnce of A/S from 0.5 to 1.0 is small, the material ratio optimized is C/S=2, A/S=0.5～1.0, C/A=1.61～1.81, under the conditions, the phase composition is mainly Ca₂SiO₄, Ca₁₂Al₁₄O₃₃ and even a small amount of less than 5% of CaAl₂O₄ or Ca₃Al₂O₆. The phase composition of experimental slag is consistant with that of thermodynamic calculation. In the material proportion optimized scope, the calcium aluminate slag has better the self-disintegrating and the alumina leaching performance, and satisfies completely the technological requirements of extracting alumina. The results provide the scientific basis for using the low A/S calcium aluminate slag obtained from smelting reduction Pingguo red mud producting alumina.

Abstract: In this study, the iron precipitation and associated nickel loss from synthetic ferric and nickel sulphate solutions were investigated. Two types of common neutralizing agents, magnesium oxide and calcium carbonate were applied in the investigation. The results indicated that pH and temperature had significant impacts on nickel loss during the iron precipitation process, whereas the type of neutralizing agents had little effect. It was found that increasing in pH and temperature resulted in more nickel loss in the pH range of 2 to 4 and temperature range of 25 to 85 °C. Mineralogical examination by XRD indicated that the iron precipitates were combinations of schwertmannite, ferrihydrite and goethite. In addition, more crystalline goethite was formed from the ferric solutions when no nickel was present, indicating that nickel might play a role in inhabiting the crystallization of goethite.

Abstract: This paper investigates the mechanism of removal of Sb and Bi from copper electrolyte under the function of arsenic. The precipitation reactions were carried out from a synthetic electrolyte containing 185g/L sulfuric acid and 45g/LCu²⁺ in the presence of As (III, V), Sb(III, V) and Bi(III) under the temperature 65°C and stirring rate of 300r/min. The structure, morphology and component of the precipitate were clarified by methods of chemical analysis, SEM, XRD, TEM, EDAX and IR spectroscopy. A kind of white precipitate has irregular shape and mainly consists of As, Sb, Bi and O elements forms in this electrolyte. The characteristic bands in the IR spectra of the precipitate are O-H, As-OH, As-O-Sb, Sb-OY (Y=As, Sb, Bi), and O-As-O. The precipitate is a mixture of microcrystalline of (Sb,As)₂O₃, BiSb₂O₇, SbAsO₄ and amorphous phases by XRD and electronic diffraction. The removal rate of Sb and Bi reaches 43% and 64%, respectively from copper electrolytes by a 4g/L arsenic solution owing to these precipitate.

Abstract: This paper summarizes the fundamental regularities and characteristics of vacuum distillation of aluminum alloy. It includes the vapor pressure values of aluminum alloy, the possibility and extent of distilling separation of the alloy, the proper temperature and time of distillation. With the temperature higher than 750°C，the distillation time longer than 30min，the content of zinc in the residue can be less than 0.3%．In this paper, the use of vacuum distillation resolved the difficulties of removing zinc from aluminum alloy, which is friendly to the environment and will not cause secondary pollution.. The theoretical analyses are in correspondence with the experimental data closely.

Abstract: The influences of alloying elements Mg, Zn and Cu and rare metals Ce, Er and mix rare metal (MRE) on the hydrogen content and inclusion in 1050 aluminum alloy were studied by optical microscope, scanning electronic microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that when adding 1wt.%Mg, 5wt.%Zn, 0.5wt.%Er and 0.5wt.%MRE into 1050 aluminum alloy, respectively, the decrements of density of the reduced pressure test (RPT) samples are 0.36g/cm³, 0.24g/cm³, 0.72g/cm³, and 0.24g/cm³, respectively. Mg and Er significantly increase the tendency of hydrogen adsorption in Al melt. The results of XRD analysis and microstructural observation indicate that the alloys adding Er contain more oxides and gas porosity.

Abstract: Upgrade silicon powder have been prepared by a two-stage technique consisting of a self-propagating high-temperature synthesis (SHS) process in a SiO₂+Mg system in an inert atmosphere and the hydrometallurgical treatment of the combustion product. It was found from DTA curve that the initial starting temperature(T_in) of the reaction was 615°C. The adiabatic temperature (T_ad) of system was calculated under the different molar ratios of Mg/SiO₂ and the results showed the reaction would happen and be kept by the self-propagating way only when the excess coefficient(x) of Mg was more than 0.9. The value of Tad would increase with the increasing of x. XRD Pattern indicated MgO₂ and element Si were main phases in combustion products except a little matter MgSi₂O₄. The purity of the combustion-synthesized Si samples was greater than 99.98% after the acid leaching treatment, and the experimental yield of the powder was approximately 78%.