GB921366A - Process and apparatus for controlling counter-current electro-migration apparatus - Google Patents

Abstract

921,366. Fused-electrolyte processes; measurements in electrolytes. COMMISSARIAT A L'ENERGIE ATOMIQUE. March 8, 1960 [April 3, 1959], No. 8151/60. Classes 37 and 41. A method of electrolysing a fused salt, e.g. to separate Li isotopes, in which an electrolyte, e.g. Br, is continuously added to the bath to assist in the dissolution of the metal which tends to be deposited at the cathode, e.g. the unwanted slower isotopes of Li, comprising measuring periodically the instantaneous voltage between the cathode 12 and a reference electrode 13 adjacent thereto, and utilizing the measured voltage to operate a relay to control the supply of electrolysis current. The added Br produces a flow of electrolyte from the cathode 12 to the anode 13, the flow tending to prevent the slow isotopes from reaching the cathode. The apparatus operates as follows : electrolysis voltage is supplied across the cathode 12 and anode 15 of a cell 1, 2 from the mains 7 and transformer 8 so long as a switch 21 is closed, i.e. so long as mercury remains in a compartment 25 from which it dribbles at a known rate to a compartment 26. A galvanometer 14 measures the potential across the cathode 12 and the reference electrode 13 as soon as the electrolysis current is interrupted by the switch 21, and if this potential is zero (as when the electrodes 12, 13 are of the same material) or small, e.g. less than 0.2 volts (as when they are of different materials) the needle 17 touches a contact 19 to pass current through a solenoid 22 via a normally closed switch 33 (circuit PNM) and thus tilt the switch 21 and reset it for a further predetermined period, e.g. 45 minutes. If the potential across the electrodes 12, 13 exceeds zero or 0.2 volts, however, as the ease may be, the switch 17, 19 remains open and therefore so does the switch 21, to be re-set when the metal deposited on the cathode 12 is dissolved and the reference potential approaches zero. The switch 33 sets a time limit to this resetting, however, for after a predetermined period after the interruption of the electrolysis current and of the current through a solenoid 34 in series with the switch 21 (circuit PQRTSV) the switch 33 opens and cannot be re-set automatically, since closing of 17, 19 will not now send a current through the solenoid 22 to close the switch 21 and thus energize the solenoid 34. The electrolyte may comprise 70% LiBr and 30% KBr (parts by weight) the bromine from the anode 15 being recirculated to the cathode 12 to establish counter-current flow of electrolyte. A porous filling 4, e.g. of zirconia, separates the electrode compartments 1, 2, and the electrodes 12, 13, 15 may be of graphite. A current of 0.4 amps. is mentioned, and a temperature of 460‹ C., the control mechanism being adapted to stop and start an auxiliary heating system in synchronism with the electrolysis current, the heating being initiated when the current is interrupted and vice versa. The process is applicable to K and V cations, and the added material may be a salt, e.g. NH 4 NO 3 , if the anion is, e.g. a nitrate.