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

by Mike McGinness, EcoShield Environmental Systems, Inc.
September, 2012

One Step Clean and Phosphate System

Q. We are presently setting up a Powder coating plant for aluminum extrusions. My search for a pre treatment solution led me to a one step clean and phosphate system by T. George Podell (CPR). Are you aware of this process ?

Initially I had planned to assemble some sort of filters and storage tanks to achieve reclaiming and reusing of chemicals much like this CPR system. It seems that there is more to this than meets the eye.

I am not a chemist, just a hands on metal fabricator/machinist. Do I build something that may not work or buy something that is proven to work?

Any thoughts or recommendation would be much appreciated.

A. I have serious reservations about these types of systems. For one, an iron phosphate coating is not possible with aluminum, it is for regular steel only. The so called dual metal products for steel and aluminum, only clean the aluminum, they do not leave or produce an iron phosphate or phosphate coating on the aluminum, and the aluminum cleaned using an iron phosphating dual purpose cleaner bath should be rinsed and then treated with a separate adhesion sealer in a final step. Second their adhesion tests on their web site were all on steel, none were on aluminum.

Due to the high variability of local water supplies and part soils on parts, I have reservations about recycling processes like this one. Not all soils and contaminates can be removed as easily as others, or with the same equipment. It is also a generally accepted practice to rinse phosphated and / or cleaned parts for good reason, namely to remove the excess un-reacted acid, and surfactants that might promote poor adhesion or corrosion resistance of the top coat. A system such as theirs may only work with certain coating top coats.

I also have serious reservations about the maintenance requirements and service life of various components in such a system. The Coil in the heater will be subject to rapid scaling, acidic corrosion and coil failure and I have not seen high pressure pumps in those style units that could handle recycling a hot, acidic, scale forming phosphate solution with out frequent valve and seal failures. Expect problems with the unloader valve as well. You might want to inquire as to the maintenance frequency and costs of the recycling equipment, pump and coil. Ask them to get you in direct contact with a customer you can visit that is using their system for aluminum parts like yours, and has been using it for at least 2-3 years, using the same top coat system you have chosen if possible. It is the entire cleaning and coating system you need to sure of.

Also ask for details on the actual waste streams produced by their system during any maintenance, the frequency and volume of the waste produced, and cost of disposal, and get it in writing (if you can). And yes, there is more to this than meets the eye! Also consider the labor and safety costs of a manned, manual wash operation.

That said, recycling a mildly acidic phosphate cleaner bath used for aluminum, is the norm. Recycling the rinse water is possible, but not usually economical, as most POTWs have little trouble handing the dilute rinse water from these systems. It is the bath dumps, cleaner and sealer dumps that are usually the real disposal and expense problem, and I dont see these systems avoiding that problem, they just replace that problem with other problems and wastes, and sooner or later that bath needs to be dumped and replaced anyway. The aluminum cleaner bath dumps have very high BOD, COD and oil and grease levels as well as high phosphate contents.

Feel free to contact me with any more questions on this topic as you progress!

Best Regards,

Mike McGinness