The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Drying process for waste zinc phosphate sludge

The removal of zinc phosphate have become a nightmare with rising costs, is there any one attempting to dry this waste off before it consigning out, if so I would interested to know what method would best be used, remembering Health and safety practices.
Many Thanks

Pauline Burley
Process Technician e-coat - UK
June 20, 2008

---

Look into filter presses. Phosphate precipitates are a slimy mess, so watch which filter "cloth" you use. Also consider using magnesium oxide for the initial portion of the neutralization. ( a less messy precipitate) It is barely soluble, but will react fairly well with acids, so it will work well to say a pH of 5. Polish the pH with lime or with caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] .
A small filter press should work for you. See if you can find a used one that is in good condition with a warranty on the pump. If you can get to Sur-Fin, you can get a great discount on their show units because they do not have to ship them home. OOPs, you are in the UK. There should be a major show in Europe somewhere this summer.

James Watts
- Navarre, Florida
June 21, 2008

---

The only thing I can add to Mr. Watts' excellent advice is to use a diatomaceous earth precoat on the filter press plates. This always improves the ease of cake release from the press plates, and can help with the clarity of the press return water.

Dave Wichern
Consultant - The Bronx, New York
June 24, 2008

---

---

I aid in the production of a large zinc phosphate spraying bath. We currently use a PFE for extracting sludge from the bath. We have had several issues with it over the years. Has anyone or does anyone use just a filter press? If so, how well does it work? Our tank has 6 cones in the bottom of it all with individual valves.

John Trapp
- Florence, Kentucky, USA
April 9, 2012