Voltammetric Evidence Suggesting Ag Speciation Is Dominated by Sulfide Complexation in River Water

Using voltammetric methods, free HS-/H2S, acid volatile sulfide (AVS), and only Cr(II) reducible sulfide (OCRS) fractions were measured in seven rivers spanning the mid-Atlantic region of the United States to determine the effect of sulfide complexation on dissolved Ag (Agdiss) speciation in freshwaters. In all waters, the AVS: Agdiss ratio was observed to be greater than 600. This increased to a range of 1000 - 5000 for rivers that received sewage treatment plant (STP) effluent. In laboratory experiments, Ag was observed to quickly (< 1 min.) replace both Cu and Zn in metal sulfide solutions, indicating that the measured AVS concentrations in natural waters provide an excess pool of available sulfide for complete Ag complexation.