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How to remove excess sulphate in chromate conversion

(-----) January 14, 2008

I having a contamination of sulphate in the Alodine solution which unable to work with the solution. The thing is I've mis read the instruction of adding the sulphuric acid instead on Nitric acid. How can I remove the extra sulphate in the solution.

Riexal Ars
plating chemist - Shah alam, Selangor, Malaysia

simultaneous January 16, 2008

Some other brand names of chromate conversion process include a barium compound that lays on the bottom of the tank and takes out small amounts of sulfate that are dragged in from the deoxidizer. However, if you have overloaded with sulfate, you might just as well dump, waste treat, and start over.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina

January 17, 2008

Quite honestly your best bet is to throw out that solution and start over again. Depending on the size of your tanks you may have to remove a huge amount of sulphate.

If you want, you may try precipitation with something like barium carbonate, precipitating out insoluble barium sulphate, filtering the solution to remove the sulphate and then replenishing the nitric acid. You will need to check with the manufacturers whether this is possible or if you are on to a total loser. You may find that whatever you use for the precipitation will detrimentally affect the solution.

Brian Terry
Aerospace - Yeovil, Somerset, UK

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