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MEASURING METAL SULFIDE COMPLEXES IN OXIC RIVER WATERS WITH SQUARE WAVE VOLTAMMETRY. (R825395)
Citation:
Rozan, T. F., G. Benoit, AND I. I. Luther. MEASURING METAL SULFIDE COMPLEXES IN OXIC RIVER WATERS WITH SQUARE WAVE VOLTAMMETRY. (R825395). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 33:3021-3026, (1999).
Description:
A sulfide identification protocol was developed to quantify specific metal
sulfides that could exist in river water. Using a series of acid additions,
nitrogen purges, and voltammetric analyses, metal sulfides were identified and
semiquantified in three specific groups: (a) Co, Fe, Mn, and Ni (bi)sulfides,
(b) Fe, Zn, and Pb sulfides, and (c) Cu sulfides. All metal sulfide complexes
were measured in low nanomolar concentrations in the oxic waters of four
Connecticut rivers, using a thin mercury film rotating disk glassy carbon
electrode (TMF-RDGCE). The short residence times associated with a RDE prevents
certain strong metal sulfide complexes (Cu, Zn, and Pb) from dissociating at pH
> 7.0 during depositions, which allows for identification in certain pH
zones. The concentrations of the specific metal sulfide complexes were linked to
the extent of watershed development and proximity to source areas. At sampling
sites impacted by treated sewage effluent, the concentrations of Cu and Zn
sulfide complexes accounted for over 30% of the total metals passing through a
0.45-
m filter. Ultrafiltration revealed
that between 30% and 60% of these Cu and Zn sulfide complexes were >3000 MW
and probably associated with organic matter. A kinetic loss experiment showed
that the Cu and Zn sulfide complexes had half-lives > 15 days, demonstrating
the importance of these complexes as metal carrier in small- and medium-sized
river systems.