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Trivalent as a contaminant

How do you remove trivalent chrome from a hard chrome bath?

Ramona C. Fletcher
captive plater - Camden, South Carolina
 

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You need to have a very high anode to cathode ratio, 15:1. Also a high current density as you can safely put on the cathode. Also as you plate on the cathode you will form dendrite which will increase the surface area of the cathode. Thereby decreasing the anode to cathode ratio. You must clean the cathode of the dendrites so you maintain the high anode to cathode ratio.

George Shahin
Atotech - Rock Hill, South Carolina
 

There are a couple of methods that may be employed. The first method is to dummy plate the solution at high current density with a high anode to cathode ratio. Another technology is the porous pot. Hard Chrome Plating Consultants are one supplier of this technology. Finally, there are acid purification systems that use selective ion exchange to remove trivalent chrome and other metallic contaminants. Eco-tec is one manufacturer of such technology.

Ira Donovan, M.S.F.
Kansas City, Missouri

You oxidize it back to hexavalent. Porous pots work very well for this and they also remove a good bit of tramp metal ions. Cheapest effective unit used to be sold by Hard Chrome Consultants in Cleveland, OH. Tiny company.

James Watts
- Navarre, Florida

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Electrolyze with a high anode area and low cathode area. Find out why it is building in the first place.

  
Tom Pullizzi
Falls Township, Pennsylvania
 

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Typically, you don't have to. Cr III will get oxidized to Cr VI at the anode. This Rxn will also occur in a porous pot.

James Totter, CEF
- Tallahassee, Florida
 

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You can use a strong acid cation resin. However, run the solution through and then rinse the column, as the strong oxidizers will destroy the resin if in touch for extended periods. You should try to use highly crosslinked cation resin (X-10) or macroreticular resins. A pre rinse with dilute chromic will avoid dilution of the bath, as the resin is typically >40% void.

Hope this helps.

Juzer Jangbarwala
waste water treatment supplier - Santa Fe Springs, California, USA