Metal finishing Q&As since 1989

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Options for Regenerating Phosphating Operation Chemicals

We operate a phosphating dip operation used to phosphate equipment prior to painting. The operation consists of the following 7 vats (~3500 gallons each): Sodium Hydroxide cleaner; rinse; Phosphoric Acid Cleaner; rinse; Dip Phosphate Coating (consists of phosphoric and nitric acids, zinc salts, nickel nitrate solution, and manganese salts); rinse; rust protection oil.

Couple of questions:

1) Is this considered a Zinc or Manganese Phosphating operation?

2) Are there methods for regenerating the caustic and acid cleaners and the phosphating chemicals used? We are preparing to clean out the vats and remove sludge, descale the burners, etc. and would like to know if filtering the solutions is an option or if other regeneration methods are available. In the past, we have just used elementary neutralization to deal with old solutions and disposed of this as non-hazardous then we recharged with new chemicals. Obviously this is very expensive and we are looking for other options.

Any help with options for regenerating the cleaners and phosphating chemicals is appreciated.

Dustin Campbell
HSE Coordinator - Houston, Texas
2004

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2004

Hi Dustin,

The answer to (1) can easily be given by the manufacturer of the phosphating chemicals. Sounds to me like you've got a zinc phosphate bath because you describe your operation as pre-paint. But the supplier will always be the best source of information.

In (2), I don't know what you mean by regeneration. The strength of your pretreatment baths can be determined by titration. If a particular bath is low on concentration, more product concentrate can be added to get back to the target level. Your question implies that you believe that one or more of the baths are "dead" but I don't how you can determine that conclusively. If I've got it wrong, please re-state your question.

George Gorecki
- Naperville, Illinois

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Regeneration of phosphating bath is possible by following steps
1.Removal of sludge by filtration
2.Removal of extra Iron contents by sludge removal for that you can treat your bath solution with a 5% alkali solution and .5-1% toner and give vigorous agitation to generate sludge and allow the bath to settle down followed by removal of sludge.
3. maintain the bath conc. by simple titration method.
that is how you can regenerate your phosphate bath.

Navin Maheshwari
- New Delhi, India
2004