Sequential extraction of iron-phosphate and calcium-phosphate from sediments by chelating agents

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.