Voltammetric characterization of iron(II) sulfide complexes in laboratory solutions and in marine waters and porewaters

Abstract

We report on metal sulfide complexes in marine waters and porewaters using voltammetric methods and compare field data with standard solutions containing Fe(II) and sulfide. Field data indicate that sulfide is complexed and not free at the sulfidic/nonsulfidic interface when the Fe(II) content≥0.1 of the sulfide content of the sample. Acid-base titration data for field samples indicate that the forms of the sulfide complex are FeSH + and [Fe 2 -(SH)] 3+ at seawater pH. From pH 7-10, the complexes FeS and Fe(H 2 S) 2+ are not consistent with the data. Salt marsh creek waters obtained at low tide and Chesapeake Bay sulfidic waters contain strong Fe(II) sulfide complexes [log K f near 6.95 for Fe(SH) + ].