Summary
A method has been developed to extract iron-bound and calcium-bound phosphates from calcareous sediments at pH values near those of the sediment itself. In about 30 minutes Fe-bound P is extracted with 0.02 MCa-NTA with dithionite in 0.1 M TRIS-buffer at the same pH as the sediment. Subsequently Ca-bound P can be extracted with Na-EDTA, still at the same pH, in about one hour.
Phosphates adsorbed onto Fe (OH)3 or onto freshly precipitated CaCO3 are dissolved with the first extractant for 100% and 1–2% rsp., and with the second for 10 and 100% respectively.
Extracts from a calcareous sediment (Camargue) did not contain organic phosphate.
Iron-bound phosphate can be extracted from acid sediments with 0.02MCa-NTA with ascorbic acid or NH2OH as reducing agents.