GB774896A - Improvements in and relating to processes and apparatus for the electrolysis of "iron metal" salt solutions particularly of pickle liquors - Google Patents

Abstract

774,896. Electrolytic regeneration of pickle liquors and other solutions of salts of " iron metals." SIEMENS AND HALSKE GES. Oct. 23, 1953 [Oct. 24, 1952], No. 29362/53. Class 41. " Iron metals," i.e. iron, cobalt, nickel, chromium, manganese or a mixture of one or more of these metals, is electrolytically produced from aqueous solutions of salts of these metals and sulphuric or phosphoric acid, particularly spent pickle liquors, and deposited on mercury cathodes by employing a current density of at least 5 amps/sq. dm., preferably of 15 amps/sq. dm. or more and in conjunction with a concentration of the metal to be deposited of at least 0.2 mol. per litre of electrolyte, the cathode space being separated from the anode space by a diaphragm. Preferably an insoluble anode is used and the process is carried out in a multiple weir cathode cell having a progressively greater fall so that the mercury always presents a fresh surface, and the anode and separating diaphragm of acidresistant plastic or thin ceramic may be similarly stepped so as to provide uniform electrode spacing throughout. For ferromagnetic metals the amalgam formed is removed continuously by a stationary or moving magnetic field whether the mercury cathode is moved through the cell or not. The metal is removed as'a a powder which is later compacted from the amalgam by evaporation in an external chamber having a non-oxidizing atmosphere, e.g. vacuum, which is sealed from the outer air by the amalgam and the re-condensed mercury. Typically for iron from ferrous sulphate solution the electrolyte is fed into the cathode compartment from which the iron-free acid-enriched liquor is withdrawn, the anolyte comprising initially metal free dilute acid and being kept largely free of metal salt. If the diaphragm is very permeable a slow flow of anolyte into the catholyte may be effected by adding water sulphuric acid to the anolyte to oppose diffusion of metal ions into it. To prevent hydrogen bubbles insulating the cathode the electrolyte may be moved relatively to it. The pickling and regenerating processes may be combined as a continuous cycle or FeSO 4 .7H 2 O may be separated from the spent pickle liquor by day and electrolysed at night. Specification 667,528 is referred to.