66th Annual Technical Meeting of the Indian Institute of Metals

Applying Industrial Ecology to Address Environmental Concerns Associated with Aluminum Smelter Spent Potlining

Paper presented at the 66th Annual Technical Meeting of the Indian Institute of Metals, Jamshedpur, Jharkhand, India 2012

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Abstract: 

Production of primary aluminium metal with the Hall-Heroult process involves electrolytic reduction of alumina in cells or pots. The electrolyte is made up of molten sodium aluminium fluoride (cryolite) and other additives and is contained in a carbon and refractory lining in a steel potshell. Over time, the effectiveness of the lining deteriorates and the lining of the pot is removed and replaced with a new lining. The lining material that is removed from the pots is known as spent potlining (SPL). 

When SPL is first recovered from the pot it contains substances that are toxic and that present environmental hazards. With changing environmental regulatory requirements, primary aluminium smelters are faced with increasing expectations that they will find alternatives to landfilling and/or long-term storage of SPL. SPL has become a major environmental concern. 

Separately, manufacturers of energy intensive products such as cement and clay bricks are faced with increasing energy costs and societal expectation of reduction in carbon dioxide emissions. SPL is rich in substances that have beneficial energy saving and carbon dioxide emission reduction properties when used in cement and clay brick manufacture. However, the hazards associated with SPL and its highly variable nature have prevented realisation of the potential energy savings and CO2 emission reduction. A new level of industrial sustainability emerges when: 

1. The hazards in SPL are addressed, and 

2. The SPL materials are reprocessed into forms that enable predictable and reliable beneficial effects in the complex chemical processes at the heart of cement and clay brick making. 

This paper sets out a solution to the problems associated with SPL developed using the principles of industrial ecology. Industrial ecology uses the natural environment as a model for solving environmental problems. In the natural environment, the waste from one species is food for other species. Industrial ecosystems are based on reconceptualising waste as products. Industrial ecology fosters broad stakeholder engagement with a synthesis of environmental imperatives, technological innovation and business economics. 

This SPL solution has been proven over ten years with more then 90,000 tonnes of SPL reprocessed from four aluminium smelters in Australia. All of the SPL is incorporated into products with genuine value in energy intensive cement and clay brick manufacture such that there is economic gain, reduced energy usage and CO2 emission reduction. Regulatory acceptance has been gained with recognition that the SPL is being managed as a byproduct of aluminium smelting rather than a waste with all of the SPL transformed into manufactured products with genuine downstream industrial use and with no residual waste material. 

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