Proof of concept to investigate a cost effective, environmentally safe closed loop system, to recover metals from spent pot liners / crucibles used in the melting of all types of metals, either during the initial smelting stage or metal purification stage

Spent pot linings (SPL’s) are the waste material generated in the de-lining of crucibles/pots
following the aluminium (and other metal) smelting electrolysis process. The SPL is
composed of carbon & various inert elements but also fluoride and cyanide and is thus
hazardous waste. It is regarded as a difficult and expensive waste stream to deal with because:
• It has a propensity to combine with water and generate explosive gases.
• The presence of cyanide at toxic levels potentially lethal for humans and other living
organisms.
SPL's are highly regulated as a hazardous waste in most parts of the world & are subject to:
• The Basel Convention on the Control of Trans-boundary Movements of Hazardous
Wastes and their Disposal.
• Increasingly onerous regulatory requirements when shipped beyond the smelter.
• Bans on landfill in an increasing number of countries
Effective disposal of SPL’s from aluminium reduction cell cathodes is a significant
environmental challenge for the aluminium industry but is also a commercial opportunity
because of the residual metal & the potential to reuse the inert residual material for making
new pot liners or as input for other manufacturing e.g. aggregates. Such reuse has been
unattractive previously due to the toxicity of the material.
Our idea is to conduct further research with some of the novel methods we are developing for
materials separation and applying these to SPL’s. We have carried out simple tests which
showed a degree of preferential reduction & separation of the metals. Further research &
experimentation will enable us to explore these novel processes more fully for SPL’s. We
propose that the residual, de metalled material can be treated on a Wilfley table (or similar)
and with the addition of calcium hypochlorite to render the trace amount of cyanides into inert
cyanites at the same time converting the fluoride to inert calcium fluoride.
The inert material can then be safely re used in manufacturing.