Aluminum Reduction Technology: Joint Session on Cell Lining Materials
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Mark Dorreen, Light Metals Research Centre, The University of Auckland
Tuesday 8:30 AM
February 28, 2017
Location: San Diego Convention Ctr
Session Chair: Stephan Broek, Hatch
8:30 AM Introductory Comments
Chemical Stability of Thermal Insulating Materials in Sodium Vapour Environment: Raymond Luneng1; Søren N. Bertel2; Jørgen Mikkelsen2; Arne P. Ratvik3; Tor Grande1; 1NTNU; 2Skamol A/S; 3SINTEF Materials and Chemistry
The most typical thermal insulating materials used in the cathode lining in aluminium electrolysis cells are moler, calcium silicate or vermiculite based materials. The thermal insulation is important for the overall thermal and dimensional stability of the cell. A refractory layer protects the thermal insulation layer, but recently it has become important to investigate the chemical stability of these thermal insulating materials. Here we report on the chemical degradation, caused by sodium vapour, of thermal insulating materials in a laboratory test resembling the environments in the cathode lining. The exposed materials were investigated with respect to changes in the microstructure, chemical and mineralogical composition by a combination of optical and electronic microscopy and powder X-ray diffraction. These investigations revealed different reaction patterns for the three materials and the formation of new mineralogical phases were identified. Finally, these findings were compared with chemical reactions with sodium based on computational thermodynamics.
Aging of Insulating Linings in Aluminium Electrolysis Cells: Ove Paulsen1; Christian Schøning1; Ove Darell1; Arne Ratvik1; 1SINTEF
Dimensional stability of materials used in aluminium electrolysis cells are important for design and long term stable cell operation. The observed compression of insulating linings from autopsies of industrial cells are in many cases much higher than would be expected from the laboratory creep tests of the corresponding materials. Creep in compression of four commercial insulating materials (moler, calcium silicate, and two perlite) for use in aluminium electrolysis cells has been studied. The creep rates were measured versus temperature and load on as received materials, materials after additional heat treatment, and materials contaminated with KF and NaF. Firing the as received materials resulted in a substantial decrease in the creep rate. The contaminated materials showed a modest increase in the creep rate compared to the virgin materials.
Cathode Wear Based on Autopsy of a Shut down Aluminium Electrolysis Cell: Samuel Senanu1; Tor Grande1; Arne Petter Ratvik2; Zhaohui Wang2; Stein Rørvik2; Christian Schøning2; 1Norwegian University of Science and Technology; 2SINTEF Materials and Chemistry
To investigate cathode wear, an autopsy of a shut down aluminium electrolysis cell was conducted. The original lining consisted of a fully impregnated and graphitized carbon block and the cell was shut down after 2461 days operation. The cell was cleaned down to the surface of the carbon cathode, revealing the profile of the cathode wear. Generally, the cathode wear was uneven across the cell with typical potholes. At a finer length scale, the wear was characterized by small “pitholes” resembling wide shallow pitting corrosion. Samples of the cell lining were obtained by drilling cylindrical samples at different locations in the cell. These samples were analysed with respect to phase composition and microstructure by a combination of X-ray computed tomography, optical and electron microscopy. These findings are discussed in relation to the current understanding of the underlying mechanism(s) for cathode wear.
9:50 AM Break
SPL Recycling and Re-Processing: Victor Mann1; Vitalii Pingin2; Aleksey Zherdev2; Aleksandr Proshkin2; Sergey Pavlov2; Yurii Bogdanov2; Vladimir Somov2; 1RUSAL Global Management B.V.; 2RUSAL ETC LLC
Aluminum smelters generate a considerable amount of SPL, which results from the chemical and mechanical degradation of carbon, refractory and insulating materials, which are used to isolate a high-temperature and chemically aggressive process of electrolysis. The specific amount of generated SPL is 25-40 kg/t Al, and it depends on the life of the cell, which varies from 5 to 7+ years. Besides considerable expenses for cell relining, SPL has a negative impact on the environment due to fluorine compounds and cyanides, which SPL contains. There are two most evident ways of minimizing the above negative impact from SPL: a decrease in the amount of SPL, and SPL re-processing, including SPL neutralization and the production of sub-products, such as fluorine, carbon and aluminosilicates, which can either be used in-house or sold to third parties. This paper covers RUSAL’s efforts aimed at developing and implementing a technology to recycle and re-process SPL.
Alternative Applications of SPL: Testing Ideas through Experiments and Mathematical Modeling: Dawei Yu1; Vishnuvardhan Mambakkam2; Lei Gao3; Donghui Li2; Kinnor Chattopadhyay2; 1Canmet MINING, Natural Resources Canada; 2University of Toronto; 3Kunming University of Science and Technology
Spent pot lining (SPL) is a well-known waste product from the aluminium electrolytic cell. The SPL generation rate is approximately 1 to 1.5 million tons per annum, and this is a significant environmental burden to the aluminium industry. Previous reports indicated that more than half of the total amount of SPL generated is stored in lined/ unlined sites/buildings, waiting for further treatment. At the University of Toronto, the Process Metallurgy and Modelling Group (PM2G) is working extensively to understand the chemistry of SPL and find alternate applications of SPL. Some of the potential applications of SPL conceptualized at the University of Toronto, are: (a) as a flux in the non ferrous industry, (b) as an alternate to coal in ironmaking blast furnaces (c) as a raw material for producing SiC bricks. Experimental and mathematical modeling techniques have been used to test these ideas, and the results are discussed in details.