Aluminum Reduction Technology: Fundamental
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Jayson Tessier, Alcoa Corporation

Wednesday 8:30 AM
February 26, 2020
Room: 6D
Location: San Diego Convention Ctr

Session Chair: Gurdun Arnbjorg Saevarsdottir, Reykjavik University


8:30 AM Introductory Comments

8:35 AM  
Electrochemical Behavior of Cu-Al Oxygen-evolving Anodes in Low-temperature Fluoride Melts and Suspensions: Andrei Iasinskii1; Sai Krishna Padamata1; Peter Polyakov1; Aleksandr Samoilo1; Andrey Suzdaltsev2; Andrey Nikolaev2; 1Siberian Federal University; 2Institute of High-Temperature Electrochemistry, UB RAS
    Cu-based alloys have been considered as promising candidates (along with the Fe-Ni alloys) as the inert anodes material in aluminium reduction cells with low-temperature electrolytes. However, low purity of aluminium due to the contamination by anode corrosion products is a problem yet to be solved. Introduction of alumina suspension as an electrolyte has been presented recently as a possible solution for providing commercial purity aluminium produced with the metallic anode. An attempt to characterize the CuAl-based anodes electrochemical performance in KF-AlF3-Al2O3 melts and suspensions has been made and presented. The effects of the suspension (or melt) properties, the anode composition and the temperature on the electrochemical behaviour of the anode and the kinetics of the oxide layer formation during polarization are studied. The 90Cu-10Al anode in the KF-AlF3-Al2O3 suspension with the cryolite ratio 1.3 and the dispersed phase volume fraction not more than 0.12 is found to be the good option for further investigations.

8:55 AM  
Alumina Concentration Measurements in Cryolite Melts: Luis Carlos Bracamonte1; Espen Sandnes1; Christian Rosenkilde2; Karoline Nilsen1; 1Norwegian University of Science and Technology; 2Hydro Aluminium
     The alumina dissolution is one of the most important processes for advanced aluminium electrolysis. For a better understanding and improvements on the dissolution process, it is important to find an effective and reliable method to perform in situ measurements in the cryolite melt, obtaining in this way the variation in alumina concentration during the entire electrolysis process. Electromotive force (emf) measurements between a graphite sensor and the two different reference electrodes graphite and aluminium, were performed during the addition of alumina and throughout the entire dissolution process. Cell reactions between the graphite probe and the two reference electrodes were derived, and the theoretical cell voltages were calculated. Experimental measurements were analyzed and compared with the theoretical calculations, in order to determine the reliability of the electrochemical method for determination of alumina concentration in cryolite melts, and to obtain a characterization of the dissolution process.

9:15 AM  
The Influence of Polarization on the Wetting of Graphite in Cryolite-alumina Melts: Henrik Åsheim1; Ingrid Andersen Eidsvaag1; Asbjørn Solheim2; Henrik Gudbrandsen2; Geir Haarberg1; Espen Sandnes1; 1Norwegian University of Science and Technology, NTNU; 2SINTEF Industry, Metal Production and Processing
    The wetting properties of graphite were measured with the immersion/emersion technique in a high temperature lab scale alumina reduction cell. The wetting was measured for untreated, polarized and anode effect polarized samples. Most measurements were made in melts with 1 wt% alumina. Polarisation was found to improve wetting as long as anode effect was not induced, with stronger improvements reached at higher polarisation. Polarisation also decreased the hysteresis between advancing and receding contact angles compared to that of untreated graphite. Anodes polarized to anode effect exhibited consistently very poor wetting for both the advancing and receding direction as well as the smallest wetting hysteresis. The de-wetting process taking place during anode effect was very noticeably only after a few seconds on anode effect, the anode being fully de-wetted from about 60 seconds. Increased alumina content improved bubble detachment presumably from improvement in graphite/electrolyte wettability, notably from 6 wt% alumina.

9:35 AM  
Electrolysis of Low-temperature Suspensions: an Update: Andrey Yasinskiy1; Andrey Suzdaltsev2; Sai Krishna Padamata1; Petr Polyakov1; Yuriy Zaikov2; 1Siberian Federal University; 2Institute of High-Temperature Electrochemistry UB RAS
    Among different “novel” technologies for eco-friendly aluminium production with zero greenhouse gas emissions the electrolysis of alumina suspension (or slurry) based on halide melts deserves more attention than it got recently. The original idea of the slurry was first proposed by Theodor R. Beck and has been modified and developed basically by Russian researchers. This paper presents a comprehensive analysis of the current status of this technology, future opportunities, and the new experimental results, which have not been published yet. This overview covers the properties of high-temperature suspensions, including sedimentation behavior and apparent electrical conductivity; anodic process on oxygen-evolving electrodes, including the polarization characteristics and the bubble behavior at vertical anodes; cathodic process on wettable substrates; primary electrolysis results; and the general considerations touching upon the possible cell designs and the thermal balance. The future scope of the technology and possible applications are discussed.

9:55 AM Break

10:10 AM  
Adapting Modern Industrial Operation Parameters in a Standardized Laboratory Cell for Measuring Current Efficiency for Aluminium Deposition, Unexpected Challenges and Lessons Learned: Rauan Meirbekova1; Omar Awayssa2; Geir Haarberg2; Gudrun Saevarsdottir1; 1Reykjavik University; 2Norwegian University of Science and Technology
    “Current efficiency” is an important cell parameter which shows how efficiently current is used to produce aluminium. Operational parameters that affect current efficiency have been widely studied in the aluminium industry, and factors like electrolyte composition and superheat have been changed to improve the current efficiency. However, the industrial cell is a complex system where all parameters are closely interrelated, which makes it difficult to change any parameter independently. Sterten and Solli developed a laboratory cell specifically designed to study current efficiency. Many studies have been made using the cell to study the effect of various operational parameters on current efficiency. As a result of improved understanding, the operational parameters presently used by the industry have changed, which is reflected by new operating condition standards for the laboratory cell. This study focuses on the challenges faced when implementing new standards in the current efficiency laboratory cell; these standards (11.5% AlF3, 5% CaF2, 4% Al2O3, cryolite ratio 2.2, temperature 965°C) are comparable to typical parameters in the aluminium industry today

10:30 AM  Cancelled
Oxidation Study of Zinc sulfite on the Removal of Sulfur Dioxide from Aluminum Electrolysis Flue Gas by Zinc Oxide: Xuejiao Cao1; Ting-an Zhang1; Yan Liu1; Weiguang Zhang1; Simin Li1; 1Northeastern University
    As the high sulfur petroleum coke consumption gradually increase in the production of pre-baked anode, SO2 is produced higher than the new environmental protection standard at the process of aluminum electrolysis. Aiming at this problem, zinc oxide desulfurization process is put forward to remove low concentration SO2 and zinc sulfate heptahydrate is obtained as the final desulfurization product in this paper. The effects of the concentration of zinc sulfite, initial pH value, temperature, stirring speed and gas flow rate on the oxidation rate of zinc sulfite oxidation were investigated by orthogonal experiment. The results showed that the stirring speed was the greatest effect on the oxidation rate of zinc sulfite, followed by the initial pH value, the gas flow rate, the temperature and the initial concentration of zinc sulfite. The optimal experimental conditions were 1% of zinc sulfite, initial pH 3, temperature 30°C, oxygen flow rate 0.5L/min, and stirring speed 360r/min.