The Aluminium Industry in Scotland

Abstract

The production of aluminium is divided into five sections: mining, alumina manufacture, carbon electrode works, aluminium reduction works, and rolling mills; and the reasons determining the location of factories are set forth. The aluminium industry in Scotland includes the manufacture of alumina and carbon electrodes, and the electrolytic production of the metal. The latter is absolutely dependent on cheap regular supplies of electrical power, as approximately 26,000 kilowatt-hours are required for the manufacture of one ton of aluminium from alumina. The Burntisland Alumina Works of the British Aluminium Company are described. The process is a chemical one: the ore is ground and mixed in caustic soda liquor and digested under pressure and heat. Separation of solid impurities takes place, leaving a sodium aluminate liquor from which alumina hydrate settles out and is subsequently calcined. The plant includes grinding machines, digesters, decomposition tanks, rotary calciners, and accessory plant such as pumps and conveyers. A large supply of steam is necessary for the process. The Carbon Works at Kinlochleven supply the electrodes necessary for three factories in the north of Scotland, and a description is given of the various raw materials used and their conversion into baked electrodes by grinding, mixing whilst hot with a binder of tar and pitch, pressing under 2,000 tons pressure, and baking in producer-gas-fired furnaces. The electrolytic furnaces used to produce aluminium from alumina are similar in principle at the Foyers, Kinlochleven, and Lochaber factories, and as the latter is the latest factory erected in the north, a short description of the power system is given. Ultimately the power house will contain some 120,000 h.p. of generating plant. At present 33,000 kW. are installed. Each of the furnaces takes 40,000 amperes and is built of steel plate with a carbon lining forming a bath and serving as a cathode. The molten aluminium is deposited as a layer under the electrolyte, which is cryolite, and the carbon anode electrodes are consumed as the alumina is decomposed. The cost of the complete development at Lochaber will be in the neighbourhood of £4,500,000.