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| Extending the life of Chromic Acid Process Baths
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The Separated Cell
Anodic oxidation can be used to continually regenerate chromic acid anodising solutions and regenerate batch volumes of chrome/sulphuric pickles. The trivalent chrome contamination is oxidised back to hexavalent chrome and trace chlorides are converted to chlorine at the anode for subsequent fume extraction. The separated cell system is sized upon the regeneration rate required which is a function of the mass of chrome reduced over a known period of time. Both chromic acid anodising and chrome/sulphuric solutions will operate with a background concentration of 15-20g/l of trivalent chrome.
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Commercialised Technology
The plant has been in operation for 18 months with the following run profile having been established. Chromic acid additions to the process bath reduced by in excess of 90%. Makeup is now considered to be for dragout losses only. The chloride content has been reduced from 120mg/l to less than 10mg/l. The bath was requiring a 50% dumping every 3 months and a full dump every 6 months (90, 000 litres/annum). The same bath has been in operation for 23 months as it was due for dumping when the plant commissioning was undertaken. The catholyte circuit, has been dumped once during this period giving a disposal reduction equivalent to 99%. The system allows for more stable specification of free chrome content, which has improved product consistency. Down time for the plant has been recorded as 2 hours in every thousand hours run. Pay back in less than 2 years |
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This page was last reviewed 06.06.08 | |||||||||||||||
