New procedure for determining reactive Fe(III) and Fe(II) minerals in sediments

Sediments from the River Elbe estuary and incubated sediments were extracted with 1 N HCI for 24 h at room temperature. The extracted ferric and ferrous iron was determined with DC and AC polarography. Acid-volatile sulfide was determined from H2S trapped in aqueous zinc acetate solution. Analysis of sediment samples and extraction residues with Mossbauer spectroscopy demonstrated that the Fe oxidation state was conserved during extraction and polarographic determination, siderite and vivianite were completely dissolved, and Fe(II) in chlorite was partially extracted with HCl. Incubation experiments showed that extractable Fe was almost completely oxidized to Fe(III) at the oxic sediment surface and reduced to Fe(II) in deeper anoxic layers within a few weeks. Reactive Fe(III), i.e. that fraction of Fe which was reducible on the time scale of the incubation experiment, was completely extracted with HCl