Iron Phosphate Start-Up


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Q. I read an article you wrote on PFONLINE. I was hoping you could give me the short answer or a reference for what the wastewater issues may be with iron phosphating. I understand it is safe, but can’t find specific information about it and would like an expert’s point of view.

What do you think about iron phosphatizing and wastewater issues? Any information you can offer would be greatly appreciated. R.D.


A. If you are discharging any waste from your facility (and eventually you will be), you will need to have the appropriate permits from federal, state and local authorities in order to be able to operate. Because of the iron phosphating process, it is possible that you will be categorized under the “Metal Finishing” guidelines which can lead to fairly stringent wastewater discharge allowances.

Where you discharge will also make a difference. Discharging to a Publicly Owned Treatment Works (POTW) may provide more latitude than if you request permission to be a direct discharger to surface waters. Obviously, this will depend on the location of your business and access to local utilities. You can explore both if available; however, discharge to a POTW would likely be preferred.

Of the two primary types of phosphating (zinc and iron), your selection of iron phosphating will be the easier of the two to permit due to the chemistry of the bath.

The iron phosphate will present fewer disposal and treatment problems than the zinc phosphate for several reasons. First, the mixture is less acidic in the as-used form (pH in the range of 5 compared, to about 3 for zinc phosphate).

Iron phosphate also contains fewer or no heavy metals. In addition to zinc, the zinc phosphate may have nickel and/or manganese to modify crystal structure of the deposit.

All phosphating processes require an oxidant to accelerate the process. The iron phosphate will have less aggressive accelerators.

Very little sludge is associated with the iron phosphate process. What sludge is generated may be categorized as non-hazardous, while the zinc phosphate can generate a significant amount of sludge.

The primary metals regulated under the federal Metal Finishing requirements are cadmium, chromium, copper, cyanide, lead, nickel, silver and zinc. State or local requirements could make these regulations even more severe. The only thing state and local authorities cannot do is make their requirements less stringent than the federal ones.

Given that, I would suggest starting this discussion with your local wastewater authorities. Explain your process, intended discharge location and expected discharge parameters including gallons per day, expected pollutants, and approximate concentrations.

The phosphating process will also require a separate cleaning step unless this is formulated to be done in parallel in the phosphating bath. Regardless, cleaning will generate an oil and grease waste stream that will be governed by the local authorities as well. 

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