Xianwei Hu

Mechanism of Dissolution Behavior of the Secondary Alumina

The study on dissolution of alumina in aluminum electrolyte has never been suspended. The raw materials used in aluminum smelter are made up of primary alumina and secondary alumina. The latter is the by-product of a dry scrubbing system. The differences in dissolution behavior of these two kinds of alumina are studied in this article. A see-through cell was used for observing the dissolution behavior of alumina. It was found that the dissolution rate of the secondary alumina was significantly faster than that of the primary alumina. The effect of possible impurities in the secondary alumina on the dissolution behavior, including carbon dust, hydrogen fluoride (HF), and other fluorides (Na5Al3F14, Na3AlF6, AlF3), was investigated. The carbon dust played an important role in improving the dissolution behavior. However, fluorides and chemisorbed HF have little effect on the dissolution behavior of the secondary alumina.

Liquidus Temperatures of Na3AlF6-AlF3-CaF2-NaCl-Al2O3 Melts

Temperatures for the primary crystallization of Na 3 AlF 6 in multicomponent electrolyte systems of interest for the aluminum electrolysis process were determined by thermal analysis. The molar ratio of NaF/AlF 3 ranged from 2.0 to 3.0. The melts contained up to 9 % NaCl (by mass). An empirical equation describing liquidus temperatures for the primary crystallization of Na 3 AlF 6 was derived: t/°C = 978.142 - 4.078w(AlF 3 ) -13.341w(NaCl) + 0.619w(AlF 3 ) 2 + 1.210w(NaCl) 2 + 1.052w(AlF 3 )w(NaCl) - 0.034w(AlF 3 ) 3 - 0.050w(NaCl) 3 -0.040w(AlF 3 )w(NaCl) 2 - 0.070w(AlF 3 ) 2 w(NaCl), where w(AlF 3 ) denotes the mass fraction of excess aluminum fluoride with respect to cryolite and w(NaCl) denotes the mass fraction of sodium chloride.

Study on the thermal decomposition of aluminium chloride hexahydrate

ABSTRACT This paper presents a preliminary study on the thermal decomposition process of aluminium chloride hexahydrate (AlCl3·6H2O) crystal with non-isothermal thermal kinetic analysis and static calcination experiments. The ‘kinetic triplets’ including activation energy, pre-exponential factor and mechanism function for the decomposition reaction were determined through thermal analysis from Differential Scanning Calorimetry–Thermos Gravimetric Analysis results. It is found that the average activation energy and pre-exponential factor were 59.668 kJ mol−1 and 6.67 × 105 min−1, respectively, and the most suitable conversion function was . The emission rates of the gaseous products, water (H2O) and hydrogen chloride (HCl), were calculated from the chlorine content evolution obtained from the static calcination tests, respectively. The phase transformation and the change of particle morphology during the decomposition process were also investigated through X-ray diffraction and scanning electron microscope technologies.

Density of lithium fluoride—lithium carbonate-based molten salts

The density of the LiF-Li2CO3 melts system was measured using the Archimedean method. Using the quadratic regression orthogonal design with two factors, a regression equation for the density of LiF-Li2CO3 melts was obtained in which the concentration of LiF and temperature were considered. The results indicated that the density of the LiF-Li2CO3 melts decreased with either increasing the concentration of LiF or increasing temperature; a linear relation was observed between density and temperature. In addition, the influences of NaF, KF, NaCl, and KCl additives on the densities of the given systems were studied. The addition of NaF and KF increased the density of the melts, whereas NaCl and KCl resulted in an initial increase and subsequent decrease with an increasing additive concentration. The density attained a maximum at NaCl and KCl mass fraction of approximately 15%.

Thermo-electric field analysis on heat recovery aluminum reduction cell

The distribution of the electricity and the thermal field directly affects the stability, current efficiency and energy consumption of electrolysis cells. In this paper, by using finite element software ANSYS, the thermoelectric field of 2000 A heat recovery aluminum reduction cell model was built. Through the use of APDL, a parametric model was established and then the thermoelectric field was simulated. The results indicate that the model is accurate. On the basis of the established model, the thermoelectric field was further analyzed.

Phase composition and its impacts on bath ratio determination of aluminum electrolyte with additives of KF and NaCl

Phases of aluminum electrolytes with additives of NaCl and KF were investigated. The definition and determination of the cryolite ratio of bath were discussed based on the results of phase composition. The deduced cryolite ratio equation was justified by fluorideion selective electrode analysis (FISEA). Experimental results show that FISEA has good performance with high accuracy and reproducibility for an aluminum bath containing NaCl and KF.

Finite element analysis of thermo-electric coupled field in 400kA large-scale aluminum reduction cell

In order to apply non-grid-connected wind power to the aluminum electrolysis industry, it is necessary to describe and study characteristics of temperature field of present cell. In this paper, a thermo-electric mathematical model was built up by using ANSYS finite element analysis software, and the 3D coupled thermo-electric field of 400kA aluminum electrolysis cell was analyzed. It is concluded that if applying non-grid-connected wind power to the large-scale industrial aluminum reduction cell, some structural improvement should be made in order to make thermo field more stability against current change. The results obtained provide a basis for the further structural improvement of the cell.

Discussion on Alumina Dissolution and Diffusion in Commercial Aluminum Reduction Cell

Dissolution model for smelting grade alumina (SGA) in the commercial reduction cell should take into account both thermodynamic and kinetic factors because of the specific dissolution environment in the cell referring to bath chemistry condition and feeding strategy. Earlier dissolution model are mainly focused on the dissolution mechanism and laboratory kinetics, while few considerations on the effects of industrial dissolution kinetics. This paper presents measurements on the velocity (by adding traceable element—strontium ‘Sr’) of the bath were carried out on two 400 kA commercial cells, and the effects on the SGA dissolution rate are discussed to support an initial investigation for the establishment of an advanced dissolution model for alumina.

Impact of Anodic Large Bubble on Horizontal Current Distribution in Metal Pad of an Aluminum Reduction Cell

In this paper, the effects of anodic large bubble including bubble position and coverage on horizontal current (HC) in the metal pad in an aluminum reduction cell have been investigated using a three-dimensional electric model. Results show that the HC, the maximum HC, and inward HC flow are greatly influenced by the large bubble position and coverage. It is necessary to take the large bubble into account when we study the horizontal current in a cell.

Elimination of Lithium from Aluminium Electrolyte by Acid Leaching Method

This paper report on an acid leaching method to eliminate lithium from aluminium electrolyte system (CR=3). Both deionized water and HNO3 were used. Also, the effects of the influences of acid concentration, leaching time, liquid-to-solid (L/S) ratio and temperature on the leaching efficiency were investigated. The results show that the effect of HNO3 on leaching efficiency is much better than deionized water. The leaching efficiency increases with the increase of HNO3 concentration, leaching time, L/S ratio and temperature. The optimized conditions for removing lithium for aluminium bath are presented as following: the concentration of HNO3 is 14 mol/L; the leaching time is 120 min; the L/S ratio is 12.5 cm3g−1 and the leaching temperature is 80 °C, the leaching efficiency is up to 93.21 %. This new process generates Na3AlF6 and LiNO3 as products from aluminium electrolyte containing lithium salts.