Spent Potlining (SPL) is a waste material generated in the primary aluminium smelting industry. Spent Potlining is also known as Spent Potliner and Spent Cell Liner.
Primary aluminium smelting is the process of extracting aluminium metal from aluminium oxide (also known as alumina). The process takes place in electrolytic cells that are known as pots. The pots are made up of steel shells with two linings, an outer insulating or refractory lining and an inner carbon lining that acts as the cathode of the electrolytic cell. During the operation of the cell, substances, including aluminium and fluorides, are absorbed into the cell lining. After some years of operation, the pot lining fails and is removed. The removed material is spent potlining (SPL).
The toxic, corrosive and reactive nature of SPL means that particular care must be taken in its handling, transportation and storage.SPL from aluminium reduction cell cathodes is becoming one of the aluminium industry's major environmental concerns. On the other hand, it also represents a major recovery potential because of its fluoride and energy content.
Most SPL is currently stored at the aluminium smelter sites or placed in landfills.
Past practices for dealing with Spent Potlining (SPL) include dumping it in rivers or in the sea or storing it in open dumps or landfilling. These methods are not environmentally acceptable because of the leachability of cyanides and fluorides.
SPL is classified as hazardous and dangerous due to:
Toxicity from fluoride and cyanide compounds that are leachable in water
Reactive with water in a way that produces inflammable, toxic and explosive gases
International shipment of SPL is subject to the protocols of the Basel Convention on the Transboundary Movement of Hazardous Wastes and Their Disposal. As the environmental regulation agencies in an increasing number of countries define SPL as a hazardous material, the disposal costs can easily run to more than $1000 per tonne SPL.
WESTON TREATMENT Solution:
Weston Aluminium has developed a proprietary process in which it converts SPL to a non hazardous and non dangerous material. This manufactured product named Nepheflux, is ideal as a flux and mineraliser for the brick and cement industry.
Weston has demonstrated that bricks made with as little as 3% Nepheflux not only fire at a reduced temperature and subsequently save on fuel and green house gases but also produce a brick which is harder and less water absorbent. Its main benefits are;
Lower energy consumption or increased throughput
Increased strength of resultant bricks
Reduction in water absorption of resultant bricks, producing a significantly superior brick
Reduced NOx generation
Ideal mineral substitution with little to no water content
The alumina, sodium and fluoride compounds decrease the melting point of the liquid phase. The benefits of this are:
Lower energy consumption
An increase in the temperature difference between the flame (~1900oC) and the clinker increases the rate of heat exchange in the burning zone, and therefore increases output
Reduced NOx generation by reducing kiln temperature
Reduced impact by fuels with higher sulfur content at the lower temperatures – promotes incorporation of sulfur in the clinker vs. oxidation