REACTIVITY OF AG+ ION WITH THIOL LIGANDS IN THE PRESENCE OF IRON SULFIDE

Dissolved silver (Ag) in the presence of amorphous iron sulfide (FeS) rapidly equilibrates to ultra-trace levels (similar to 5 ng/L), which agrees with equilibrium calculations based on Ag2S solubility. This fi nding, along with the authors' discovery that crystalline Ag2S (acanth ite) precipitates rapidly under supersaturated conditions, suggests th at a discrete Ag-S phase is formed. Furthermore, potential interferenc es (Cl-, Cu2+, and dissolved organic carbon) show no effect on the Ag- FeS system. Only the presence of organosulfur (thiol) ligands at 10(-3 ) to 10(-4) M result in increased dissolved silver. Agreement between calculations and measured values were good for 1.8 x 10(-4) M 3-mercap topropanoic acid; however, calculations predicted higher dissolved sil ver than measured values for higher thiol levels, possibly due to Ag-t hiol binding to FeS.