HOME FAQs BOOKS JOBS: Help Wanted Suggestions you are here: Hotline/Forum => Letter 31013
How to determine phosphate sludge for proper waste disposal
++++
We are cleaning and zinc phosphating (250 mg/sq.ft) prior to e-coating on large and small parts in a conveyorized system. The resulting phosphating sludge is put through a continuous filter bed and the phos sludge cake is hauled away at a cost per metric ton. I am told that there are phosphates in the marketplace that produce sludges that are considered non-hazardous (containing less than 1000 ppm nitrates/nitrites consistently). Why would values in nitrates/nitrites change on the sludge? Is there a simple way to reduce the nitrates/nitrites if they have been detected in sludge. Or does everyone that has phos sludge haul it away as "hazardous". I don't understand why nitrites or nitrates would be considered hazardous in our environment to begin with. Are they not similar chemicals in our food processing industries?
Hellen Senczae-coatings applicator - Cambridge, Ontario, Canada
++++
Zinc Phosphate processes that don't use nitrate or nitrites as accelerators will not have any of those components in the sludge. Several other accelerators exist such as chlorate, peroxide, and a few organic ones, all of which have advantages and disadvantages. I'm not up on the Canadian regs, but I know several shops down here that dispose of treated zinc phosphate sludge as a non-hazardous industrial waste.
|
Jeff Watson - Pearland, Texas |