GB1403892A - Electrolytic metal producing process and apparatus - Google Patents

Abstract

1403892 Producing metals in fused electrolyte cells ALUMINUM CO OF AMERICA 22 Aug 1972 [8 Sept 1971(2) 9 Sept 1971(3)] 39033/72 Heading C7B Metal is produced from the metal chloride, e.g. Al from AlCl 3 or Mg from MgCl 2 , in a fused electrolyte cell including anode 14, at least one intermediate bi-polar electrode 15 and cathode 16 in superimposed spaced relationship defining inter-electrode spaces 19, by electrolyzing a bath comprising the metal chloride dissolved in molten solvent of higher decomposition potential than the metal chloride, such as alkali and/or alkaline earth metal halide, producing chlorine on each anode surface (41) and metal on each cathode surface (40), and establishing and maintaining a bath flow through each inter-electrode space to sweep out the metal produced and prevent its accumulation on the cathode surfaces, e.g. by using the chlorine produced as lifting gas to pump bath from the inter-electrode space upwardly while allowing molten metal swept therefrom to settle to a sump 4 below the cathode. The molten metal may be removed through a vacuum tapping tube inserted through port 10 in the cell roof 8 down through a bath supply passage 30 extending from an upper bath reservoir 7 into the sump. The bath reservoir may be fed periodically or continuously with the metal chloride through port 11 in the roof, and port 12 is for chlorine outlet above a bath return (gas lift) passage 35. As shown passages 30, 35 communicate with each space 19, being formed by holes (31, 36) and slots (32, 37) in the marginal edges of the superimposed electrodes, whereby the bath continuously circulates through spaces 19 and reservoir 7 by the chlorine flow. Each anode surface, preferably spaced less than ¥ inch from opposed cathode surface, has spaced channels therein for receiving and directing chlorine flow into the gas lift passage but not communicating with the bath supply passage. The cell refractory walls 3 lining the outer steel shell 1 may be nitride-based, e.g. a nitride of Si, B or Al (with or without oxide of Si, B or Al), or of Ti, Cr, Hf, Ga or Zr; silicon oxynitride (Si 2 ON 2 ) or Si 3 N 4 - bonded fused SiO 2 is preferred. A preferred bath comprises a molten solvent of 50-75% NaCl and 25-50% LiCl containing 1¢-10% AlCl 3 or 1¢-20% MgCl 2 . A mixture of AlCl 3 and alkali metal and/ or alkaline earth metal halide may be selectively condensed from the effluent gas and recycled to the bath. The chlorine recovered may be reacted with alumina to form AlCl 3 feed. Chlorine effluent (52), Fig.5 (not shown), containing alkali and alkaline earth metal and aluminium chloride may be cooled (53) to condense or sublime the chloride for recycling to the cell.