Electrode Technology for Aluminum Production: Spent Pot Lining (SPL) -Joint session with Aluminum Reduction Technology Symposium
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Duygu Kocaefe, University of Quebec at Chicoutimi
Tuesday 2:00 PM
February 25, 2020
Room: 3
Location: San Diego Convention Ctr
Session Chair: Pernelle Nunez, International Aluminium Institute
2:00 PM Introductory Comments
2:05 PM
Sustainable Spent Pot Lining Management Guidance: Pernelle Nunez1; 1International Aluminium Institute
Spent Potlining (SPL) is a solid waste generated during the primary aluminium electrolysis process. Approximately 20-30 kg of SPL is produced per tonne of primary aluminium and a significant amount of the SPL generated today is stored in secure facilities at or near aluminium smelters. SPL is classified as a hazardous waste, and there are various options for treating it before storage or transportation. There is also ongoing research on the use of SPL as a feedstock in other processes, and there have been a number of commercial partnerships in recent times. The International Aluminium Institute (IAI) has developed an industry guidance document that describes good practice for sustainable SPL management, subject to local constraints, risks and regulatory regimes. Case studies, data and other supporting information have been collated to provide a comprehensive overview to support sustainable management of SPL across the aluminium industry.
2:30 PM
Purification of Graphite by Thermal Vacuum Treatment of Spent Potlining: Kristin Sundby1; Ulf Sjöström2; Ellen Myrvold3; Morten Isaksen1; 1Hydro Aluminium; 2Swerim; 3Alcoa Mosjøen
The aluminium industry is striving towards a lower environmental footprint, and the management of spent potlining (SPL) is high on the agenda. The reuse and recycling alternatives of SPL are limited primarily due to its content of sodium, fluorides and cyanide. In this work, a thermal vacuum process for the purification of first cut SPL has been tested. The process consists of a vacuum furnace and an off-gas condensation system. Small scale trials using 1000 gram first cut SPL samples were carried out, with varying particle sizes and furnace temperatures. All tests demonstrated significant distillation of sodium fluoride and cryolite. The remaining residues contained up to 91 % graphite, with minor amounts of contaminants such as aluminium oxide and calcium fluoride. Conclusively, the vacuum treatment process shows great potential for reuse of the challenging material of first cut SPL.
2:55 PM
The LCL&L Process: A Sustainable Solution for the Treatment and Recycling of Spent Potlining: Laurent Birry1; Stephane Poirier1; 1Rio Tinto
Spent potlining (SPL) is a hazardous waste generated from the internal lining of Al electrolysis cells and consists of carbon and refractory bricks. It is classified as a hazardous waste because of its contamination with fluorides and cyanides and its hydroreactivity, generating explosive gases. Over the past number of years, the aluminum industry has made some progress by recognizing that SPL landfilling is no longer acceptable. In 2008, Rio Tinto inaugurated a new plant in Jonquière (Québec) for the treatment of SPL, based on the low-caustic leaching and liming process(LCL&L) developed in the early 1990s. This plant treats 80 kt of stored and fresh SPL annually. This treatment decontaminates SPL and produces inert by-products which can be used as raw materials in industries like cement industry. This paper describes LCL&L process characteristics, including valorization routes for its by-products and some recent improvements of the process to reduce treatment costs with better energy efficiency.
3:20 PM Break
3:40 PM
Environmental Benefits of Using Spent Pot Lining (SPL) in Cement Production: Mohammad Al Jawi1; Chun Man Chow2; Srinivasa Pujari2; Michael Pan2; Tanvi Kulkarni2; Mohamed Mahmoud1; Heba Akasha1; Salman Abdulla1; 1Emirates Global Aluminium; 2Massachusetts Institute of Technology
Spent pot lining (SPL) is a toxic waste material produced during the pot replacement process in the aluminium industry. This paper presents a comprehensive environmental assessment of a case study in the United Arab Emirates (UAE), where SPL from Emirates Global Aluminium (EGA) was used as a feedstock at a cement plant in Ras Al Khaimah, UAE. Three areas of environmental concern were studied: fuel savings and CO2 reductions, changes in NOx emissions, and raw material repurposing and toxic substance destruction. The use of SPL in cement production is shown to yield significant environmental benefits in terms of reducing emissions and coal consumption and destroying toxic substances. These changes are primarily attributed to the fluoride content in SPL creating fluoride fluxing effects that reduce the high temperature requirements of the cement kiln. This initiative bolsters the concept of a circular economy in which different industries collaborate to improve environmental sustainability.
4:05 PM Cancelled
Characteristic Analysis of Hazardous Waste from Aluminum Reduction Industry: Mingzhuang Xie1; Han Lv1; Tingting Lu1; Hongliang Zhao1; Rongbin Li1; Fengqin Liu1; 1University of Science and Technology Beijing
The carbon dust, aluminum dross and spent potlining from aluminum reduction cells are considered to be hazardous materials because they contain a large amount of soluble fluoride salts and trace amounts of toxic cyanides. Piling them outside or in landfill sites create environmental pollution and ecological problems. In this paper, the hazardous wastes were comprehensively investigated with scanning electron microscopy (SEM) and X-ray diffraction (XRD). It is found that the chemical compositions of these wastes are very complicated. A variety of fluoride salts and aluminum metal were embedded in pores and openings of lining materials such as carbon, silicon carbide and refractories. As a result, a variety of compounds have been formed. The disposal of hazardous waste is hampered by these complex components. This work provides some insight into dealing with such hazardous waste.
4:30 PM Panel Discussion