Sewage sludge (CH, fermentation) dried and incinerated at 600degreesC, was divided into 3 portions to be calcined 3 h at 850, 930 or 950degreesC, contg. PO43- 21.4-23.9 and Fe3+ 16.9-1&4% Each calcinate was leached 28 h with similar to20% HNO3, 1:2 w/w. At the higher calcination temperatures, Fe passed into the hematite phase insol. in HNO3, The P yield and the residual PO43- content in the ash were related to the calcining temperature, viz., 70 and 6.3% at 600degreesC, and 96 and 1.0% at 950degreesC (optimum).