Letter 41069

Phosphating sludge treatment and disposal  

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We have a powder coating unit. We do hot phosphating (zinc phosphating). I want to dispose of the large amount of phosphating sludge collected. I was told that there is Nitric acid process to treat the phosphating sludge. I would like to know various options available and the costs involved.

BHANUPRAKASH
- BANGALORE, KARNATAKA, INDIA

Some possible options for handling phosphating sludge:

United States Patent 5273667 (1993) describes a process which involves collecting the phosphate sludge, dewatering using a filtering process, drying the dewatered sludge at an elevated temperature to a moisture content of less than 10 wt.% and reducing the particle size of the dried sludge to less than about 20 mesh. The dried and ground phosphate sludge has been found to be an excellent lubricant additive, which is suitable for use in lubricant formulations designed for the metal treatment, metal forming and industrial lubrication.

The use of phosphating sludge in the process of clinker production is suggested as one of the possible mode of reclamation of such waste by Caponero and Tenorio (Resources, Conservation and Recycling 29 (2000) 169). Their study proves that an addition of up to 7.0% of phosphating sludge to the raw cement meal of Portland cement did not cause any damage to the clinkerization process. Additions of the phosphating sludge up to 5.0% significantly modify only the zinc content of the clinker that was produced. The major element of the sludge, zinc, shows an average of incorporation of 75%.

T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India

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