The study of electrode processes of Fe(II)-thiosulphate complexes on mercury electrodes

FeS-biochar and Zn(0)-biochar for remediation of redox-reactive contaminants

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis. These biochars significantly promoted the removal of 2,4-dichlorophenol (DCP) by means of sorption and reduction. Compared to direct reduction with FeS and Zn(0), the formation of reduction intermediates and product was enhanced from 21% and 22% of initial DCP concentration to 41% and 52%, respectively. 2,4-Dinitrotoluene (DNT), chromate (CrO₄²⁻) and selenate (SeO₄²⁻) were also reductively transformed to reduction products (e.g., 2,4-diaminotoluene [DAT], Cr³⁺, and selenite [SeO₃²⁻]) after they sorbed onto the biochars including FeS and Zn(0). Mass recovery as DAT, Cr³⁺ and selenite was 4–20%, 1–3%, and 10–30% under the given conditions. Electrochemical and X-ray analyses confirmed the reduction capability of the biochars including FeS and Zn(0). Fe and S in the FeS–biochar did not effectively promote the reductive transformation of the contaminants. Contrastingly, the stronger reducer Zn(0) yielded faster reductive transformation of contaminants over the Zn(0)-containing biochar, while not releasing high concentrations of Zn²⁺ into the aqueous phase. Our results suggest that biochars including Zn(0) may be suitable as dual sorbents/reductants to remediate redox-reactive contaminants in natural environments.

To enhance the removal of redox-reactive contaminants, biochars including FeS and Zn(0) were developed via pyrolysis.

Electrochemical and colorimetric measurements show the dominant role of FeS in a permanently anoxic lake

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 K(s) values between -3.6 and -3.8, very close to mackinawite's K(s) 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.