Qiu Zhu-xian

Formation of metal fog during molten salt electrolysis observed in a see-through cell

Visual observations of several molten salt electrolysis processes were made in a two-compartment, see-through quartz cell. The electrolyses of aluminium, magnesium, lead, zinc, sodium and potassium were studied. The colour of the melt in the anode compartment was pale yellow for fluoride-chloride melts and red for chloride melts, caused by the presence of dispersed anode gases during electrolysis. In the cathode compartment, streamers of metal fog were formed. The colours of the metal fog were purple for aluminium, grey for magnesium, lead and zinc, blue for sodium and green for potassium.The metal fog tended to sink to the bottom of the cell, which indicated that it had a higher density than that of the melt. The metal fog also penetrated into the anode compartment, probable due to convection and diffusion in the melt. The most probable explanation of the nature of the metal fog is that it consisted ofdispersed metal particles. This chemically unstable phase dissolved easily in the melt and was oxidized quickly by the anode gases.

Key improvements to Hall-Héroult since the end of World War II

During the last 50 years, some of the most important developments in the Hall-Héroult process include improvements to bath chemistry, alumina feeding, anode and cathode quality, and process control. In addition, progress has been made in cell size and design, production capacity, energy consumption, and magnetic field modeling.

Continuous bath temperature measurements in Al electrolysis cells

This article describes the importance of temperature monitoring in aluminum electrolysis cells. The challenge of getting long-term performance from thermocouples is discussed, and appropriate examples are given of information of value to cell operations derived from bath temperature measurements.

Electrical conductivity and corrosion resistance of ZnFe2O4-based materials used as intert anode for aluminum electrolysis

ZnFe2O4 and ZnFe2O4-based materials were tested to obtain the electrical conductivity and corrosion resistance in melting bath for aluminum electrolysis. The results proved that adequate additives, such as Ni2O3 CuO, Cu, ZnO and CeO2 would increase the electrical conductivity, and the ZnFe2O4-based anodes with these additives were of good corrosion resistance. The current density on anode, the mole ratio of NaF/AlF3 (MR) and the content of alumina in the bath effect the anode corrosion rate in different way.

Studies on Anode Effect in Aluminium Electrolysis

Anode effect is a characteristic phenomenon in molten salts electrolysis, especially in aluminium electrolysis. When it occurs, many small electric sparks appear on the anode, and the cell voltage increases suddenly. In this paper the anode effect was studied by means of cathode-ray oscillography. The back electromotive force of the aluminium electrolysis cell with various kinds of anode materials (carbon, graphite, platinum and other inert materials) was measured. It was clearly observed that a series of electrochemical decomposition processes took place when the anode effect occured on carbon anodes. The values of back EMF of these processes were in the range of 1.0 – 5.5 V. These were checked with thermodynamics calculations. A direct short-circuit of current from anode to cathode was also observed during the whole process of anode effect. These phenomena were compared with those observed on microelectrolysis cells, and the mechanism of anode effect was suggested.

Thermodynamic calculation of systems of magnesium fluoride with lithium, sodium and potassium fluoride

Abstract The Discrete Complex Anion Model was introduced to the molten salt systems of LiF-MgF2, NaF-MgF2,and KF-MgF2,based upon the assumption of existence of the MgF−3 complex ions contained in the melts. A set of parameters were evaluated from the experimental data representing the enthalpies of mixing and the phase diagrams of all these three systems. The thermodynamic properties and phase diagrams of the melts were calculated by using the model. The results obtained were in good agreement with the experimental data.

Recovery of cryolite from spent potlining of Al reduction cells by flotation method

The possibility of cryolite recovery from spent potlining by flotation method has heen investigated in the laboratory. The results of experiment showed that the acidity and concentration of liquid and particle size of material affected the recovery rate of flotation. Suitable collecting agents, modifiers and flothing agents were examined in experiments. In suitable conditions, the recovery of cryolite reached over 90%. The treatment of fluoride—containing waste water was examined and the results were satisfactory.