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Sludge removal in zinc phosphating bath

(-----) 2007

We run a powdercoating jobshop.We are filtering the hot phosphating bath continuously using an online filtration system and also de-sludge the bath weekly. Is there any better method to get the sludge out of the system on a continuous basis.

Jothi Ramalingam
job shop employee - Chennai, India


A a better filtering system. This would start with one that picks up off of the absolute bottom and possibly at more than one point. Next is use a higher filtration rate. You might achieve this with a larger filter, with a larger pore size, and frequent changes. It may require a larger pump.

James Watts
- Navarre, Florida


Try a filter press. Run it all the time. This decreases the frequency of de-canting.

Adam Adkisson
- S. Texas

2007 -- appended to this thread by editor

We are currently involved in solving a sludge build up problem in the phosphatizing bath. We will be installing conductivity control and installing counter current flow of overflow and make up water. My question is what is the best type of filtration to use. The bath is about 6 cubic meters in volume. We were considering bag filtration but are concerned about the amount of sludge develop and the cost of bags. Are there other types of filtration and what are they? I have read that cycloning has been used and filter presses.
Is the formation of precipitation on a 1:1 ratio for the amount of Phosphoric acid that is added (approx. 25kg of product added per day would = 25kg of sludge precipitated). It is estimated that a bag filter would be able to hold up to 500grams before being needed to be replaced. This would mean that you would need 50 bags per day.

Your help in this matter would be greatly appreciated.

Kind regards,

Gavin Bigham
Industrial Water Treatment - Johannesburg, South Africa

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