9314349 LUTHER The concentration of trace metals in anoxic and sulfidic environments is controlled by the precipitation of metal sulfide phases as well as the complexation of the metals by sulfide and other sulfur species. Stability constants of a variety of metals of environmental significance with sulfide, thiosulfate and polysulfides will be determined. The constants will be obtained by voltammetric methods using the peaks of the sulfur species and/or the metal. The research also requires titrations of the complexes with acid and base to determine the number of protons attached to the sulfur species. This work will build on initial work in seawater which shows that iron (II) and sulfide form two complexes which are Fe(SH)+ (log B=5.5) and Fe2(SH)3+ (log B= 11.1). These constants are orders of magnitude higher than constants evaluated by linear free energy relationships. In fact, Fe2(SH)3+ was not predicted by this or any experimental approach which uses sulfide as a titrant. Thus, Fe(II) solubility at anoxic interfaces and in sulfidic environments can be enhanced over previous estimates.
