Patent GB-569444-A (GB)
Title: Improvements relating to the electrolytic purification of nickel
IPC: C25C1/08
Filed: 1943-10-01
Abstract: 569,444. Electrolytic refining. MOND NICKEL CO., Ltd. Oct. 1, 1943, No. 16148. Convention date, Nov. 5, 1942. [Class 41] [Also in Group III] In a process for the electrolytic purification of nickel by the anodic dissolution of impure nickel, the impure electrolytes being then purified, and pure nickel deposited therefrom cathodically, part of the usual all-sulphate anolyte is replaced by chloride ions, the composition being preferably 71 to 120 grams of sulphate ions, and 27 to 30 grams of chloride ions, per litre. The complete process is shown by the flow-sheet, Fig. 2, in which three Hybinette cells have soluble-anode compartments 1 and two have insoluble-anode compartments 2, the catholyte from each compartment 31 being returned to the anode compartments, and the compartments being separated from one another by the usual diaphragms. The impure nickel in cast form is inserted in compartments 1 containing, in addition to the sulphate and chloride, 40 to'60 grams of nickel, 20 to 30 of sodium, and 15 to 25 boric acid, per litre, the ratio of nickel to sodium being not less than 1.5: 1. The impure anolyte is continuously withdrawn and purified by the removal of iron, lead, and arsenic, and copper and cobalt, the former by oxidation and precipitation as oxide or hydroxide or arsenides, in tanks 6 ... 9 in which air is blown, nickel carbonate or hydroxide added, and chlorine from compartments 2 introduced. The resulting slimes are separated in a filter press 12, and the electrolyte containing copper and cobalt (of which some may have been removed in the slimes) cleared of copper in a series of tanks 13 ... 22 by the addition of nickel powder which precipitates the copper as cement, and by the return of solids from a later stage of the cementation process. The electrolyte from the filter press 22 may, if sufficiently pure, be returned at 32 direct to the cathode compartments 31, but if excess cobalt remains, the electrolyte is treated in tank 28 with chlorine and nickel carbonate before being returned, the cobalt being precipitated as hydroxide. The slimes from filter press 12 contain in addition to the iron, arsenic, and lead, traces of nickel and cobalt which are recovered, the former for return to tank 8. The treatment depends on the amount of cobalt present and, if there is over 5-6 per cent, the slimes are washed and treated in tank 33 with SO2 and dissolved in H2SO4. More slimes are added in tank 35 and iron precipitated. Reduced nickel powder removes copper and NaClO removes cobalt, the nickel solution being then treated with sodium carbonate to produce the nickel carbonate for the initial copper cementation at tank 8. The alternative slimes treatment, for low-cobalt content, is to add chlorine from compartments 2 and a filter press 79 to a tank 60, iron being removed from a filter press 64 and the residual solution being returned to tank 3. Gold, silver and metals of the platinum group which form anode slimes in compartments 1, are washed from the spent anodes 66 by means of anolyte from compartments 1 and filtered at 74, the solids being further washed and filtered at 79 to reduce the chlorine content. The sulphur is reduced by roasting in a calciner 80 and the resulting oxidized metal introduced, with coke, into an anode electric furnace 82 and cast into moulds 83 to form anodes. Details of temperature and pH values at the various stages of the process are given.