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

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

Phosphating, Parts Cleaning Definitions With Repect to 40 CFR 433

Q. With respect to 40 CFR 433, what is the difference between phosphating and "4-stage parts cleaning where the process is a spray with a monosodium phosphate solution, followed by a water rinse, another monosodium phosphate solution spray and a final water rinse". Is the parts cleaning process considered one of the SIX major metal finishing operations -- ie, Coating (phosphating)?

A. Excellent Question!!!!

That would definitely be one of those gray areas for sure. Assuming a facility is not otherwise already a metal finishing facility (i.e. if they are already doing some obvious electroplating, electroless plating, etc., work they are already a metal finisher or plater and therefore your question would not be important), then I would suggest the following expansion of your question. Keep in mind that as soon as any one process in a facility is identified as a coating process under electroplating then every metal finishing process in that facility also becomes covered as metal finishing under 40 CFR Part 433, thus eliminating the need to answer your question. Therefore I am assuming that your question applies to a situation where the only process that could possibly be considered metal finishing (coating under electroplating category) is the sodium mono-phosphate cleaner bath.

First let us assume that the phosphate formula does not contain any coating additives in the cleaning formula such as molybdates, chromates, zinc, copper, etc., or similar coating additives other than sodium mono-phosphate. Furthermore, assume it is an aluminum parts only process as you described below. In this case since sodium mono-phosphate phosphate coating cleaners do not leave a phosphate coating on aluminum parts (they only etch and clean the aluminum parts) it would technically not be a coating process step and therefore not regulated by 40 CFR part 433. However, if the final rinse is a chromated rinse (sealer-coating step) I think it would be considered (due to the final chromate conversion coating step - rinse) a metal finishing (or aluminum anodizing which has its own category) operation or step.

If it were a non metallic (plastic or ceramic) part the answer would be: No it is not considered a metal finishing process.

Now for the tough ones. I see two possibilities. If it is a nonferrous metal part and it is strictly a cleaning and mild etching process with no coating being placed on the part (perhaps some stainless steels would fit this description) while it is in the sodium mono-phosphate cleaning bath, then I would say it is also not a metal finishing process as defined by 40 CFR Part 433.

If it is a steel part and the bath actually leaves a coating (iron phosphate) on the part then one could make a case for it being a metal finishing process (although I do not personally believe that was the intention when the rules were written). If the sodium mono-phosphate cleaning bath also has zinc, or nickel, or chrome, or copper, in the formula, or any other metal finishing regulated metals, and it leaves a coating on the parts then I am sure it is a metal finishing process and is therefore regulated by 40 CFR Part 433.

If it is strictly an iron phosphate coating being applied during the cleaning process on a steel part and iron is the only metal going into solution, then I think it could be argued that the metal finishing category (40 CFR Part 433) was not intended to apply to this situation. My reasoning for this is that (1) iron is not a regulated metal finishing category waste water metal. Also, many companies clean steel parts (engine & valve rebuilders for example) prior to painting these parts (with sodium mono-phosphate cleaners) or prior to repairing and rebuilding them and to my knowledge non of them are being regulated as metal finishers (unless they are an integrated facility with plating operations).

You may want to check into the new MP&M rule that will apply once it is finalized late this year. But note that even the MP&M rule will not regulate iron. It will regulate organics and TSS from cleaning of all metals.

Thanks for the great question. Hope this answers your question. If you need more help with this topic please give me a call.