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

Bura-Nakić, Elvira; Viollier, Eric; Ciglenečki-Jušić, Irena (2013) Electrochemical and Colorimetric Measurements Show the Dominant Role of FeS in a Permanently Anoxic Lake. Environmental Science and Technology, 47 (2). pp. 741-749. ISSN 0013-936X

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Abstract

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.

Item Type:	Article
Uncontrolled Keywords:	iron, sulfide; FeS(aq); mackinawite; nanoparticles; voltammetry; anoxia; Lake Pavin
Subjects:	NATURAL SCIENCES > Geology
Divisions:	Division for Marine and Enviromental Research
Projects:	Project title Project leader Project code Project type Nature of organic matter, interaction with traces and surfaces in environment (Priroda organske tvari, interakcije s mikrokonstituentima i površinama u okolišu)- Irena Ciglenečki-Jušić 098-0982934-2717 MZOS
Depositing User:	Elvira Bura Nakić
Date Deposited:	01 Feb 2016 17:19
URI:	http://fulir.irb.hr/id/eprint/2448
DOI:	10.1021/es303603j

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