GB730649A - Improvements in or relating to electrolytic cells - Google Patents

Abstract

730,649. Electrodeposition of silver. BAKER PLATINUM, Ltd. March 20, 1953 [March 28, 1952; Oct. 13, 1952], Nos. 8030/52 and 25634/52. Class 41. An electrode assembly for immersion in liquid to be electrolysed, such as photographic fixing solutions from which silver is to be recovered, including a cathode having a plurality of superposed portions each to face towards an anode surface which is dissimilar in shape and to be inclined with respect to the anode surface, and the cathode being also constructed and arranged so that when liquid in contact with one such portion rises, it tends wholly or partially to flow in such a way as to avoid contacting the corresponding portion above, the arrangement also being such that liquid from the main body of the solution may circulate freely to and from the cathode surfaces. According to one modification (Fig. 2), stainless steel cathode members 3 and carbon anode members 2 are secured between long rubber strips 1. Wires 4 and 5 connect the anode and cathode members respectively, the wires being held in the slit or aperture for each electrode member by the resilience of the rubber strips. In another modification (Fig. 4) the cathode 6 is a sheet of corrugated austenitic stainless steel and the anode member 7 is formed of two rectilinear, carbon strips. The anode members may have insulating stopping-off coatings 11 opposite the crests of the cathode corrugations. The electrodes are supported in insulated frame members 12. In a third modification (Fig. 6), the cathode 18 is formed by a steel sheet having a series of semi-circular recesses in which anodemembers 15 consisting of carbon rods are positioned. Several spaced apertures 21 are provided in the upper surface of each recess. In a fourth modification (Fig. 8), the cathode is formed of a series of stainless steel strips 24 and the anode is formed by two rectilinear carbon strips 23. As well as the materials mentioned above the cathode may be made of chromium coated copper, brass, nickel or steel or silver or silver coated copper, brass or steel. The anode may also be made of austenitic stainless steel. Examples are given of the use of the apparatus in the recovery of silver from spent photographic fixing solutions, notably from a solution containing silver bromide, sodium thiosulphate and sodium metasulphite and having a pH of 5.0 using a cathode current density of 0.9 amps per square foot at 0.5 volts for 21 hours. Specifications 377,051 and 476,985 are referred to.