Q. What is the composition of phosphate sludge from a zinc-phosphate process bath? What are the precipitates that are formed?—K.P.
A. The composition of the sludges generated in a phosphate bath varies with the type of bath in which they are produced. The composition of the sludge found in a zinc-phosphate bath is as follows:
| Component | Amount |
|---|---|
| Iron | 20% |
| Zinc | 8% |
| Phosphate as PO4 | 45% |
| Water | 27% |
These percentages can vary depending on the operating temperature of the bath.
The precipitates are primarily metal phosphates. Search pfonline.com to find a number of excellent articles on phosphating.
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