Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
February, 2002

DI and RO Systems for Decorative Nickel Chrome Line

Q. We are looking to install a decorative nickel chrome line for aluminum. Process would cover citric clean, caustic etch, deox, zincate, strip, zincate, watts ni, semi ni, bright ni and chrome. I am leaning towards DI for recyling the rinse water. Which rinse tanks would best to hook up to this system and prevent problems in the future. Could one DI uniot handle the entire line or would it better to have two or three smaller units more targeted to the removal content?

A. Thanks for the question. DI water is always a good idea. I would purchase an RO (Reverse Osmosis)system first that could produce near-DI water and then use a single DI column (you can rent the DI column) to cleanup the final 5 to 10 ppm not removed by the RO unit. This way the DI column will last 20 times (20 months versus 1 month) longer. Then I would run the RO reject water through a water softener to produce rinse water and bath make up water for the citric clean and caustic etch only. Devote those rinses and cleaners to cleaning parts only (i.e. keep the nickels, chrome, and zincate out of them).

You will need storage tanks to hold the DI and Soft water in reserve in order to keep the RO and water softener capital costs down. It is best to run a small unit all day & night filling up a storage buffer tank overnight for peak demand during the day and to keep the capital costs down.

I would need to know more about the deox and strip chemistry before making a recommendation on them as to whether DI or softwater would be best. For the rest of the processes (nickel, chrome and zincate I would recommend separate 1st rinse tanks). A common rinse could be used for the second rinses of the nickels with a DI + carbon filter + pump operated on the second nickel rinse. I would use a separate first ad second rinse for the chrome dedicated to chrome only. I would not use a DI on the Chrome. I would need to know more about the zincate formula (chemistry) to advise on the first and second rinses for it.

General rule is the more dedicated rinse tanks the better and always keep the (1) chrome (Hex), (2) other metals, and (3) cleaners and their rinses totally separate from each other in order to minimize any final waste treatment costs and to maximize in house recycling potential.

Hope this helps some.

If you are looking for a consultant who can look at the actual bath formulas you are planning to use, tank layouts, part racks, etc., and advise you further on how to set up for recovery and recycling (RO, DI, process control of rinse water and bath additives, Waste water treatment, pollution prevention, etc.) before you commit any dollars please consider giving me a call.