Zhancheng Guo

Low-temperature purification process of metallurgical silicon

The removal of B and P consumes most of heat energy in Si metallurgical purification process for solar-grade Si. Metal-liquating purification of metallurgical grade silicon (MG-Si), also called Si-recrystallization from metal liquid, was a potential energy-saving method for the removal of B and P efficiently, since Si could be melted at lower temperature by alloying with metal. The selection criteria of metal-liquating system was elaborated, and Al, Sn and In were selected out as the optimum metallic mediums. For Sn-Si system, the segregation coefficient of B decreased to 0.038 at 1 500 K, which was much less than 0.8 at the melting point of Si. The mass fraction of B was diminished from 15x10(-6) to 0.1x10(-6) as MG-Si was purified by twice, while that of most metallic elements could be decreased to 0.1x10(-6) by purifying just once. During the metal-liquating process, the formation of compounds between impurity elements and Si was also an important route of impurity removal. Finally, one low-temperature metallurgical process based on metal-liquating method was proposed.

Reduction mechanism of natural ilmenite with graphite

Abstract Reduction of Bama ilmenite concentrate containing 49.78% TiO2 and 27.96% total Fe by graphite was studied using thermogravimetric analysis system under argon gas ambient from 850 to 1 400 °C. The reduction degree of Bama ilmenite is enhanced with increasing temperature and the molar ratio of carbon to oxygen, and the reaction rate varies with temperature and reduction time simultaneously. The phase transformation, chemical composition, microstructure and morphology of reduced samples were investigated by using X-ray diffractometry, scanning electron microscopy, and energy disperse spectroscopy, respectively. The high content of impurities in Bama ilmenite evidently bates the reduction of ilmenite. Forming the enrichment zone of manganese prevents complete reduction of Fe2+. The reduction products are mostly reduced iron, rutile, reduced rutiles, Ti3O5 and pseudobrookite solid solution. The reduction kinetics was also discussed. The results show that the reduction temperature is a key factor to control reaction rate.

Adjustment on gibbsite and boehmite co-precipitation from supersaturated sodium aluminate solutions

Gibbsite is the usual precipitation product from alumina refineries with either Bayer or sintering process. However, the advantage of boehmite precipitation over gibbsite precipitation is the significant energy saving in the subsequent calcination step. The current investigation takes a pragmatic approach to measure precipitation ratios, determine product phase, morphology and particle size distribution, and assess the impacts and adjustment capability of main parameters such as seed, temperature, ethanol medium, and supersaturation on the precipitation kinetics and alumina hydrate type during co-precipitation process. The results clarify that gibbsite and boehmite both can be precipitated from supersaturated sodium aluminate solutions simultaneously, and the competitive formation between Al(OH)3 and γ-AlOOH determines the main precipitate phases from pregnant liquor. Boehmite seeds, high temperature and ethanol addition can promote the boehmite precipitation and improve the mass fraction of boehmite in products. Co-precipitation changes the multimodal distribution of seeds to a normal and well distribution of products, and the particle size is more than several times that of seeds.

Kinetics of Boehmite Precipitation from Supersaturated Sodium Aluminate Solutions with Ethanol-Water Solvent

Boehmite was prepared from supersaturated sodium aluminates solutions with ethanol-water solvent. The results of thermo-gravimetric analyzer and XRD showed that the product was mixture of boehmite and gibbsite, and the mass ratio of gibbiste and boehmite varied greatly with different process conditions. This work presents the effects of mass ratio of ethanol and temperature on the precipitation rate and phase compositions of alumina hydrate. The ratio of AlOOH in the product increased significantly with the increase of mass ratio of ethanol because the precipitation of gibbsite was restrained. When the solvent was pure ethanol, the ratio of AlOOH in the product reaches the peak of 90%. Ethanol reduces the free caustic concentration and increases initial supersaturation coefficient significantly. The boehmite activation energy of precipitation in ethanol solvent was 13.7 kJ/mol, indicated that ethanol reduces effectively energy barrier of boehmite from sodium aluminate solutions and it was controlled by diffusion process.

Growth and Agglomeration of Boehmite in Sodium Aluminate Solutions

Boehmite precipitation is a new alternative way from sodium aluminate solutions to alumina, however, the too small particle size becomes one bottleneck for this methods replacing the current production route. Growth and agglomeration of crystals are the main factors influencing product size. The results show that the growth rate of boehmite is in a low range from 0.08 to 2.4 μm/h. Thus, agglomeration of boehmite is a major means to enlarge the particle size of precipitation products from sodium aluminate solutions. By means of laser particle size analyzer and powder attrition index analyzer, the agglomeration efficiency was represented by combining agglomeration degree and attrition index. The influences of seed ratio, temperature, the molar ratio of Na2O to Al2O3 and organic additives on agglomeration were investigated. The alcohol type additives PPG increases precipitation ratio and agglomeration degree, but reduces the strength of products and makes attrition index increase.