METHOD FOR THE ELECTROCHEMICAL OXIDATION OF SULPHURIC ACID CHROMIUM III SOLUTIONS INTO CHROMIUM VI SOLUTIONS

摘要

PCT No. PCT/AT86/00016 Sec. 371 Date Jul. 24, 1987 Sec. 102(e) Date Jul. 24, 1987 PCT Filed Feb. 27, 1986 PCT Pub. No. WO86/05215 PCT Pub. Date Sep. 12, 1986.The processing of nitric acid-containing, sulphuric acid chromium-III-solutions as obtained during oxidative purification of flue gases meets with great difficulties as well as enormous costs. It is the object of the invention to provide a process having low current costs for the electrolysis. The inventive process for electrochemically oxidizing sulphuric acid chromium-III-solutions to chromium-VI-solutions essentially comprises an electrolyte which contains nitric acid, sulphuric acid and chromium. In such electrolyte the nitric acid is utilized as a redox carrier for the oxygen electrode which serves as the cathode, and the nitric acid is regenerated using the oxygen. Carbon or graphite is used as the cathode material. As the anode material there are used electrodes having high oxygen overvoltage such as, for example, lead dioxide. The cell voltages which can be attained under these conditions, lie in the range of 0.9 to 2 volt. This means that the current costs for the electrolysis are reduced to about one third.