Aluminium industry sustainability study: composite anode improvement technologies

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Embargoed until 2015-03-17
Copyright: Clinch, Samantha Bernadette
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Abstract
The significantly high energy consumption and greenhouse (GHG) emissions associated with the production of primary aluminium has become of paramount concern to the aluminium industry. The production of one tonne semi-fabricated aluminium, from bauxite mining to semi-fabrication, produces 9.7 tonnes of CO2-equivalents (CO2e).As a primary CO2e contributor, and a component within the control of the anode producer/smelter, consumable carbon anodes have been spotlighted as the key to increasing energy efficiency and minimising GHG emissions. Presently there exist four major fields of research concerning anode improvement technologies: oxidation resistant treatments, pitch-free carbon composites, incorporation of alternative raw materials and inert anodes. The present study seeks to develop the foundations for the complete or partial replacement of either petroleum coke or coal tar pitch with waste polymeric material. Pilot scale laboratory anodes were produced according to a standard commercial recipe that was modified in order to assess the effect of polymer replacement on bulk anode properties and in-service performance. Five standard recipe anodes were produced in order to serve as the benchmark for property assessment. Polymer modified anodes were produced with 10, 20 and 30 % replacement of either carbon aggregate or coal tar pitch. Polymers investigated were Bakelite, high density polyethylene (HDPE), polyethylene terephthalate (PET) and a standard polymeric waste blend. Anodes were assessed in three stages. The first stage comprised the assessment of basic microstructural, mineralogical and thermal degradation characteristics of anodes. The second evaluated bulk anode properties utilising the same methods that are used for commercial quality control. The final stage was an assessment of in-service anode behaviour. The study determined that the overall impact of polymer replacement on the properties and in-service behaviour of anodes was negative. The replacement of carbon aggregate with Bakelite yielded anodes with low bulk density and high porosity. Bakelite anodes had poor bulk properties and experienced excessive carbon consumption during electrolysis. Replacement of coal tar pitch with HDPE, PET or the waste blend yielded similar outcomes. Thermoplastics were observed to increase the graphitisation of anodes; however at a bulk level porosity negated any positive effects that increased graphitisation would have on properties.
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Author(s)
Clinch, Samantha Bernadette
Supervisor(s)
Sorrell, Charles
Skyllas-Kazacos, Maria
Crosky, Alan
Burford, Robert
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Publication Year
2012
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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