Ashes from combustion of sewage sludge were extd. with aq. H3PO4 and HNO3 for 60 min and then the extn. residues were washed with dild. HNO3 soln. and with water to recover the remaining PO43- ions from the filter cake. The expts. were carried out in 2 reactors (vol. 5 L and 50 L). The acidic washing resulted in a decrease in PO43- ion contents from 11% down to 3.4% by mass.