plating, anodizing, & finishing Q&As since 1989
Chromate rinse filtration
We are currently using a chromate conversion process to pretreat our aluminum parts before powdercoating or painting. As our throughput increases so does our wastewater from our rinse tanks. We currently generate about 5000 gal / week and have it hauled away. We are looking into the possibility of filtering the wastewater and reusing it. What is the best way to filter and reuse the wastewater. Evaporation , reverse osmosis, ultra filtration, deionization seem to all have uses in the plating industry but one must be more suitable for the chromate rinsewater.
Any suggestions about what process we should investigate would be greatly appreciated.Chris Babek
- New Gretna, NJ
Ion exchange is almost surely the way to go with this one. Removing chrome from chromate rinse water this way has been done in hundreds of shops for decades. Spare chambers are kept on hand and a service company picks up the exhausted chamber for off-site regeneration and leaves behind a fresh one. It's much more practical to transport an ion exchange cylinder than 5000 gallons of dilute wastewater.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
You will need separate cation and anion columns. Filter first, then cation first, then anion.
The cation will remove aluminum, reduced (trivalent) chrome, and any other metals in solution, such as sodium.
The anion gets the chromate and other anions like nitrate and chloride.
I think mixed beds are not recommended because they will probably plug with aluminum hydroxide.
Be sure the service company that removes the spent columns is a licensed hazardous waste hauler and manifests them properly, unless you can get the EPA to provide a letter exempting the spent columns from regulation (unlikely).
microwave & cable assemblies - Mesa (what a place-a), Arizona
A DI recycling system as described in a previous response is the best way to recycle the dilute rinsewater. It is being done successfully in dozens of locations in the US.
Hexavalent chromium is too strong an oxidizer to use RO as a rinse recycling technology. It will destroy the membranes.Lyle Kirman
consultant - Cleveland Heights, Ohio
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