Development of a Combined Leaching and Ion-Exchange System for Valorisation of Spent Potlining Waste
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ORIGINAL PAPER
Development of a Combined Leaching and Ion‑Exchange System for Valorisation of Spent Potlining Waste Thomas J. Robshaw1 · Keith Bonser2 · Glyn Coxhill2 · Robert Dawson3 · Mark D. Ogden1 Received: 8 August 2019 / Accepted: 3 February 2020 © The Author(s) 2020
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, H 2O2 and H 2SO4, 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 Abstract
Keywords Spent potlining · Leaching · Ion-exchange · Fluoride · Aluminium · Resource recovery
Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12649-020-00954-1) contains supplementary material, which is available to authorized users. * Thomas J. Robshaw [email protected] Extended author information available on the last page of the article
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. There are two distinct fractions, these being “first-cut”, composed mainly of graphitic material from exhausted cathode blocks, and
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“second-cut”, formed mainly of cement and brick. Both cuts are heavily contaminated with fluoride-bearing compounds, with reported fluoride concentrations ≤ 20% [1]. Various other chemical species are also present, including ≤ 1% cyanides [2]. Estimates for the average mass of SPL generated per tonne of aluminium produced vary between 7 and 50 kg [3], but an average of ~ 25 kg is frequently given [4, 5]. The estimated global production of aluminium in 2018 was 64.3 MT, meaning ~ 1.61 MT of SPL was a
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