Naslov
Electrochemical and Colorimetric Measurements Show the Dominant Role of FeS in a Permanently Anoxic Lake

Autori
Bura-Nakić, Elvira ; Viollier, Eric ; Ciglenečki, Irena

Izvornik
Environmental science & technology (0013-936X) 47 (2013); 741-749

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
iron; sulfide; FeS(aq); mackinawite; nanoparticles; voltammetry; anoxia; Lake Pavin

Sažetak
Recent publications have shown that the anodic reaction between FeS and Hg can be used for electrochemical detection of colloidal and particulate FeS in natural waters. Anodic waves that were recorded around -0.45 V (vs. Ag/AgCl) in model solutions correspond to the electrochemical transformation of nanoparticulate FeS to HgS. Here, as a further step, the proposed approach is tested on anoxic, sulfidic and iron-rich samples of a meromictic freshwater lake (Lake Pavin, France). Based on new and more comprehensive work on FeS electrochemistry in model and anoxic Lake Pavin samples, a new interpretation is given for previously recorded voltammetric signals in sulfide and iron rich environment, usually designated FeS(aq), and its role in controlling solubility of different FeS phases. A comparison of the depth profiles of S(-II) measured by voltammetry and the methylene blue method showed that the majority of S(-II) is in the form of FeS. In the monimolimnion layer, thermodynamic calculations based on total Fe(II) and S(-II) concentration, measured by ferrozine and the methylene blue method, predict precipitation of FeS with log Ks values between -3.6 and -3.8, very close to mackinawite’s Ks value. In the upper part of the same layer, precipitation of greigite is predicted. It is shown that modification of a Hg electrode by surface-formed FeS has a significant influence on voltammetric Fe(II) determination, since reduction of Fe(II) under such conditions occurs both on bare (-1.4 V) and on FeS modified Hg surfaces (-1.1 V) ; Fe(II) may be underdetermined when only the -1.4 V peak is measured.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

POVEZANOST RADA