On-line process monitoring in electrolytic manufacturing of chromic acid

Abstract

dichromate content in concentrated liquors from the electrolytic production of chromic acid were investigated. Experimental results showed that Artificial Neural Network technology applied to highly diluted hexavalent chromium solutions, which are known to have been prepared from chromic acid and sodium dichromate, do not yield useable results for quantification purposes. Combining ion selective electrode measurements and ultra-violet – visible spectrophotometric techniques to highly diluted hexavalent chromium solutions, prepared from chromic acid and sodium dichromate, yields errors of about 2.3 % for hexavalent chromium and about 2.8 % for sodium determinations versus a standard titrimetric method. Tests to prove the suitability of the standard titrimetric acid –base titration technique confirmed an accuracy of 0.6 % for a known chromic acid content and 0.7 % for titrations based on a known sodium dichromate content for liquors highly concentrated in hexavalent chromium. A simple on-line analytical instrument was developed based on the titrimetric acid –base titration technique. The on-line instrument evidenced average errors of about 1.9 % for the chromic acid content and about 2.6 % for the sodium dichromate content.