GB1084196A - Electrolytic regeneration of alkali liquors - Google Patents

Abstract

<PICT:1084196/C6-C7/1> A process for removing undesired components, for example alkali metal thiosulphates, thiocyanates and/or ferrocyanides from an alkaline liquor containing an organic additive such as glycine comprises electrolyzing the liquor in an electrolytic cell 10 which is divided into three chambers, namely an anolyte chamber 15, a central chamber 16 and a catholyte chamber 17 by means of an anion exchange membrane 18 and either a cation exchange membrane or simple porous membrane 19, the pH of anolyte being maintained below 7, e.g. 2.5-7, and the pH of the catholyte being maintained above 7, preferably above 12. Initially the catholyte chamber is filled with potassium hydroxide solution and the anolyte chamber with potassium sulphate. A source of free iron, e.g. in the form of scrap iron, may be provided in the anolyte chamber. Small quantities of the liquor to be treated may be passed into the anolyte and catholyte chambers during electrolysis and pH control in the anolyte and catholyte chambers may be effected by controlling the relative flow rates of liquor into the three chambers. The cell is provided with double walls 11, 12, the gap there-between being filled with water into which the sides of the lid 13 dip to provide a gas-tight seal. A gas inlet 51 and outlet 52 are provided so that an inert gas such as nitrogen may be passed over the liquor in the cell to remove gaseous products of the electrolysis. The anolyte may be constantly circulated through pipe 35, filter 45, pump 46 and pipe 47 and then returned to the cell, precipitated sulphur and Prussian blue in the anolyte being maintained in suspension thereby, and are removed by the filter 45. Electrolyte is supplied to the three chambers of the cell via pipe 25 and pipes 26, 27, 28 respectively, and may be removed therefrom via the pipes 32, 35, 36 respectively and via the outlet pipe 33. Valves are positioned as required throughout the external circuitry. The anode and cathode may be formed of carbon or stainless steel. The process may be used to remove undesired components from used Alkazid lye, which primarily consists of an aqueous solution of potassium dimethyl glycine.