GB299725A - - Google Patents

Abstract

299.725. Metallges. Akt.-Ges., (formerly Metallbank und Metallurgische Ges.). Oct. 27, 1927, [Convention date]. Copper, zinc, and other metals, depositing.- Smooth and dense deposits of metals are obtained by the addition to the bath of a hydrophilic inorganic colloid insoluble in the electrolyte in the absence of oxidizing agents akin to hydrogen peroxide care is taken that the colloidal material enters the cell in the required state of dispersion and that detrimental substances are not introduced with it. The colloidal material is not extracted from an ore in the formation of the electrolyte. The colloidal material should be added in very dilute form either continuously or in small amounts at short intervals. In electrolyzing solution obtained by leaching zinc oxide not containing silica with acid zinc sulphate solution the addition may consist of 0.25 gms. per litre of colloidal silicic acid obtained by mixing zinc silicate with a multiple of the amount of sulphuric acid required for decomposition. Smaller additions are necessary when the zinciferous material already contains silicic acid. The zinc silicate may be precipitated by the addition of water glass to neutral regenerated electrolyte, and the colloidal silicic acid obtained from the separated precipitate by addition of spent electrolyte. Alternatively an alkaline earth silicate may be employed as the source of silica. In the refining of copper, the colloidal addition may consist of hydrated tunstic acid obtained from copper tungstate by the addition of an equivalent amount of sulphuric acid. Metatitanic acid or zirconic acid may be employed as colloidal additions in the case of acid electrolytes, and ferric hydroxide or magnesium hydroxide in the case of alkaline electrolytes.