Abstract
This work aims to contribute to addressing the global challenge of recycling and valorising spent potlining; a hazardous solid waste product of the aluminium smelting industry. This has been achieved using a simple two-step chemical leaching treatment of the waste, using dilute lixiviants, namely NaOH, H2O2 and H2SO4, and at ambient temperature. The potlining and resulting leachate were characterised by spectroscopy and microscopy to determine the success of the treatment, as well as the morphology and mineralogy of the solid waste. This confirmed that the potlining samples were a mixture of contaminated graphite and refractory materials, with high variability of composition. A large quantity of fluoride was solublised by the leaching process, as well as numerous metals, some of them toxic. The acidic and caustic leachates were combined and the aluminium and fluoride components were selectively extracted, using a modified ion-exchange resin, in fixed-bed column experiments. The resin performed above expectations, based on previous studies, which used a simulant feed, extracting fluoride efficiently from leachates of significantly different compositions. Finally, the fluoride and aluminium were coeluted from the column, using NaOH as the eluent, creating an enriched aqueous stream, relatively free from contaminants, from which recovery of synthetic cryolite can be attempted. Overall, the study accomplished several steps in the development of a fully-realised spent potlining treatment system.Graphic
Highlights
Spent potlining (SPL) is a hazardous waste product of aluminium smelting operations, which is generated at the end of the lifespan of a smelter electrolysis cell
From the elemental composition of the leached samples, it is seen that the C % of the SPL increases for mixed-cut and mainly first-cut samples, following the acidic leach, as more contaminants are solublised
The H % decreases significantly for most samples between the leaching treatments, which may suggest the original material contained an organic hydrocarbon component, which dissolves during the treatment
Summary
Spent potlining (SPL) is a hazardous waste product of aluminium smelting operations, which is generated at the end of the lifespan of a smelter electrolysis cell. It has the potential to contribute towards efficient fluoride recycling, and add economic value to Al smelting operations It must be noted that the elution behaviour of our column system was not optimised and it is vital to prove that the ion-exchange system performs equivalently in treating actual SPL leachate, as opposed to a simplified simulant solution. We demonstrate the feasibility of the proposed ion-exchange circuit implementation via column loading and elution studies These show that resin uptake performance and the quality of the resulting fluoride/Al-rich liquor exceeds results achieved previously with a simulant feed and marks a clear step towards realisation of this system industrially. The % recovery of fluoride from the inlet leachate was estimated by calculating the area under the major fluoride elution peak and dividing this by the theoretical uptake capacity of the column, determined from dynamic model-fitting
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