Papers by Keyword: Cryolite

Abstract: The possibility of using modern high-tech flotation equipment at RUSAL Bratsk PJSCis considered, which allows to significantly reduce discharges of extremely hazardous waste of fluorine, sodium, and aluminum to the sludge fields, and to initiate recycling of waste from the sludge fields. The results of operation are presented for a coal foam column flotation system at PJSC RUSAL Bratsk. An innovative technique has been developed allowing to recycle lining waste from aluminum electrolysis pots. The recycling of the waste lining coming from aluminum electrolysis pots is a completely closed waste-free cycle, which provides alumina and cryolite — products that can be used in the aluminum electrolysis, as well as allows using all the secondary solid waste in the satellite cement production.

Abstract: Structure properties of Al-Ti-C mother alloy which was prepared by TiH₂ and graphite method were studied by various characterization methods.Results demonstrated that the synthesis process of Al-Ti-C alloy contained three stages.Firstly,TiH₂ and graphite was respectively used as titanium and carbon sources.Secondly,titanium reacted with aluminum and graphite,producing Ti-Al,C-Al,Ti-C compounds.Finally,these compounds formed Al-Ti-C alloy.It was equiaxed or dendrite structure with grain size of 20～40μm.There were needle-like and elongated phases in alloy matrix.There are petal primary crystals containing Ti,C,Fe and Si on grain boundaries.Ti and C distribute evenly along grain boundaries and grains.Ti and C enrichment and segregation occurred close to the primary phase.Cryolites were conducive to wetting of carbon and aluminum, the second phase generated more fully in the grain.

Abstract: The liquidus temperature in the [NaF-AlF₃(30 mol.%)]-Sc₂O₃ molten system with the Sc₂O₃ additions up to 12 wt% was measured by the thermo analysis. The effect of the cathode current density (0, 0.25, 0.50, and 1.0 A∙cm^-2), the Sc₂O₃ content (1, 2, 4, and 8 wt%) in the NaF-AlF₃(30 mol.%)-Al₂O₃-Sc₂O₃ electrolyte, the rate of the molten aluminum agitation (0, 100 rotates/min), the synthesis duration (30-210 min) on the Sc content in the aluminum alloy at 980 °С was studied. The Al-Sc alloys with the scandium content of 0.15-1.30 wt%, depending on the synthesis conditions, and with the uniform Sc distribution throughout the aluminum matrix were produced.

Abstract: A novel technology of preparing cryolite free of wastewater containing ammonia was studied by using industrial grade sodium fluorosilicate from phosphate fertilizer production. Effects of reaction temperature and pH were studied for the decomposition of sodium fluorosilicate, and the suitable reaction conditions were decomposition temperature above 54 °C and pH 8.4. Effects of Na/Al (molar ratio of Na to Al in the raw materials), reaction temperature and pH on the quality of cryolite were investigated for the synthesis of cryolite. The results indicate that the obtained cryolite can meet the national first-grade quality standard of China at the conditions of pH from 3.0 to 5.0, Na/Al from 2.8 to 3.0 and temperature above 70 °C.

Abstract: Thanks to their good electronic conductivity and their low solubility in cryolite melts, nickel ferrites are considered to be among the most suitable ceramic materials that could be used as inert anodes in the electrowinning of aluminium. In this work, electrodes composed of single phased and stoichiometric nickel ferrite NixFe3-xO4 (0≤x<1) have been studied by electrochemical techniques (linear voltammetry and potentiostatic electrolysis) in a molten cryolite mixture at 960°C. The aim was to understand the oxidation reactions susceptible to take place inside the material under anodic polarization and oxygen evolution. Ex situ characterization of the electrodes by SEM-EDX and microprobe analysis allows proposing a degradation mechanism of the pure nickel ferrites: the formation of haematite Fe2O3 at the grain boundaries was evidenced and it resulted in a slow degradation. The influence of the Ni content in the ceramic phase was investigated, and it was shown that rich-Ni compositions exhibit a better resistance to corrosion.

Abstract: A ceramic thermocouple (CTC) was assembled using SiC as the cathode and MoSi2 as the anode for the temperature test of the aluminum electrolysis. The NiFe2O4 was sprayed on the surface of SiC cathode for increasing the corrosion resistance ability in the cryolite. The corrosion behavior of NiFe2O4 in the cryolite was investigated. The results of the corrosion tests show that the NiFe2O4 has a very low corrosion rate in the cryolite, and a corrosion layer was formed during the corrosion test. The mechanisms of the NiFe2O4 corrosion are reactive corrosion and particles flaking. The thermo emf of SiC-MoSi2 CTC was tested from 25 °C to 1300 °C in air. The results show that thermo emf has a linear relationship with the temperature dependence, and reached 350 mV at 1300 °C. The CTC which consists of SiC-MoSi2 prepared in the same batch has a preferable interchangeability. By holding temperature at 1300 °C, the deviation of thermo emf is 0.5 %, which is better than the criterion of industry thermocouple, 0.75 %. The CTC response time was also analyzed.