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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). SPL was listed by the United States Environmental Protection Agency in 1988 as a hazardous waste. Hazardous properties of SPL are: * Toxic fluoride and cyanide compounds that are leachable in water * Corrosive - exhibiting high pH due to alkali metals and oxides * Reactive with water - producing inflammable, toxic and explosive gases. 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. Dissolved fluorides and cyanides from SPL landfill leachate may have environmental impacts. It is not acceptable that leachate contaminated with these harmful compounds may escape from stockpiles. Other storage methods are secure landfills or permanent storage buildings. These are expensive solutions and may create future problems. == Background == Production of primary aluminium metal with the Hall–Héroult process involves the electrolytic reduction of alumina in cells or pots. The electrolyte is made up of molten cryolite and other additives. The electrolyte is contained in a carbon and refractory lining in a steel potshell. The pots typically have a life of 2 to 6 years. Eventually the cell fails and the potlining (SPL) is removed and replaced. The SPL generated is listed by various environmental bodies as hazardous waste. Due to the concentrations of fluorides and cyanides in spent potliner, and the tendency to leach in contact with water, the US Environmental Protection Agency (USEPA) listed the materials on 13 September 1988 (53 Fed. Reg. 35412) as a hazardous waste (K088) under 40 C.F.R., Part 261, Subpart D. 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. World production of primary aluminium is in the order of 40 million tonnes. The world’s smelters also produce about one million tonnes of toxic SPL waste. Past industry practice has been to landfill this waste. This must change if the aluminium industry wants to claim a reasonable degree of sustainability and environmentally tolerable emissions. Landfill of unreacted SPL is considered a practice of the past. The primary aluminium industry has systematically worked to minimize the amount of SPL produced, by extending the lifetime of the lining in the smelter pots. Since the 1970s, SPL has been recognised as a valuable resource for other industries, including as a feedstock in the cement, mineral wool and steel production processes. The International Aluminium Institute has defined the following ''“International Aluminium Institute SPL Voluntary Objective'' *''The Aluminium Industry recognises that spent pot‐lining has properties that makes it a valuable material for use in other processes and will therefore strive to convert all spent pot lining into feed stocks for other industries, which include cement, steel, mineral wool and construction aggregate companies or to re‐use and or process all SPL in its own facilities.'' *''Pending final deposition, the industry will endeavour to store all spent pot‐lining in secure, waterproof, ventilated buildings/containers that will maintain the spent pot‐lining in a dry state with no potential for the build up of noxious gases.”'' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Spent potlining」の詳細全文を読む スポンサード リンク
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