Technetium Electrodeposition from Aqueous Formate Solutions at Graphite Electrode: Electrochemical Study

Maslennikov, A. G.; Masson, M.; Peretroukhine, Vladimir F.; Lecomte, M.

doi:10.1524/ract.1999.84.1.53

Cited by 5 publications

(6 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Theoretically, electrochemical Se(VI) reduction should be thermodynamically favorable, as indicated by the high redox potential of the Se(VI)/Se(IV) couple (eq ). However, the reduction of the Se(VI) oxyanion to its Se(IV) counterpart is extremely slow due to the necessity of anion structure change and the high activation energy required to break the SeO double bond . While it is possible to facilitate the conversion of Se(VI) to Se(IV) using solution-phase biological or metallic catalysts, doing so is not the focus of the present work. …”

Section: Resultsmentioning

confidence: 99%

Direct Electrochemical Pathways for Selenium Reduction in Aqueous Solutions

Zou

Mauter

2021

ACS Sustainable Chem. Eng.

View full text Add to dashboard Cite

Direct electrochemical reduction provides a novel strategy for selenium removal from complex wastewaters. While electrochemical Se(IV) reduction is thermodynamically favorable, anion structure reorganization hinders process kinetics and the phase of reduced Se(0) determines process performance. This study evaluates the thermodynamic and kinetic performance of Se(IV) removal via direct electrochemical reduction (SeDER) and proposes moderate heating to promote efficient and continuous process operation. We find that SeDER is a robust process that can handle 0.001–10 mM Se(IV) in a weakly acidic solution (pH 4–7). Se(IV) can be electrochemically removed from the aqueous phase through either a four- or six-electron pathway, with the former generating Se(0) directly attached to the electrode surface and the latter producing Se(-II) that is subsequently converted to Se(0). The four-electron pathway is a surface-limited process below 70 °C and terminates when the cathode is fully covered with the insulative amorphous Se(0). We demonstrate that raising the solution temperature to 80 °C deposits Se(0) in a conductive crystalline form and enables continuous reduction on the electrode surface. In a simple batch process design, we observe Se(IV) removal rates of up to 89 mg h–1 m–2 of electrode surface area, up to 10% Faradaic efficiency, and up to 95% removal, although we observe moderate trade-offs between these metrics depending on the electron pathway and the initial concentration of Se(IV). Our results suggest value in future work to enhance Faradaic efficiency via better reactor and electrode design, investigate parasitic reactions among competing ions, and select cost-effective electrodes for an economically competitive SeDER process.

show abstract

Section: Resultsmentioning

confidence: 99%

Direct Electrochemical Pathways for Selenium Reduction in Aqueous Solutions

Zou

Mauter

2021

ACS Sustainable Chem. Eng.

View full text Add to dashboard Cite

show abstract

“…Attempts to electrodeposit Tc metal are often hindered due to the formation of oxides. 13,14 Habitually, results are misleading or repeated experiments do not mimic results reported in literature. Because of this ambiguity, and because deposition products are not well structurally characterized, we have investigated the most simple system of TcO 4 − in H 2 SO 4 , electrodeposited onto gold.…”

mentioning

confidence: 93%

Characterization of Electrodeposited Technetium on Gold Foil

Mausolf

Poineau

Hartmann

et al. 2011

J. Electrochem. Soc.

View full text Add to dashboard Cite

The reduction and electrodeposition of TcO 4 − on a smooth gold foil electrode with an exposed area of 0.25 cm 2 was performed in 1 M H 2 SO 4 supporting electrolyte using bulk electrolysis with a constant current density of 1.0 A/cm 2 at a potential of −2.0 V. Significant hydrogen evolution accompanied the formation of Tc deposits. Tc concentrations consisted of 0.01 M and 2 ϫ 10 −3 M and were electrodeposited over various times. Deposited fractions of Tc were characterized by powder x-ray diffraction, x-ray absorption fine structure spectroscopy, and scanning electron microscopy with the capability to measure semiquantitative elemental compositions by energy-dispersive x-ray emission spectroscopy. Results indicate the presence of Tc metal on all samples as the primary electrodeposited constituent for all deposition times and Tc concentrations. Thin films of Tc have been observed followed by the formation of beads that are removable by scratching. After 2000, the quantity of Tc removed from solution and deposited was 0.64 mg Tc per cm 2 . The solution, after electrodeposition, showed characteristic absorbances near 500 nm corresponding to hydrolyzed Tc͑IV͒ produced during deposition of Tc metal. No detectable Tc͑IV͒ was deposited to the cathode.Technetium, element 43, has 34 radioactive isotopes that are known, with none being stable, from mass 85-118. The most common isotope, 99 Tc ͑t 1/2 = 2.14 ϫ 10 5 y͒, is present in large quantities in spent nuclear fuel, where it constitutes approximately 6% of the fission yield. 1 With regard to nuclear waste management, Tc presents a threat to the biosphere because it is very stable and mobile as the anion pertechnetate. Two methods to reduce the potential long-term environmental hazards of Tc have been considered: transmutation of Tc metal targets by neutron capture in a reactor to produce stable isotopes of ruthenium or the incorporation of Tc into stable forms for long-term geological disposal ͑i.e., Tc alloys or oxide materials͒. 2,3 For this reason, the production of Tc metal for eventual use in a target or waste form represents a challenge for the management of nuclear wastes. Different methods to produce Tc metal have been reported. 4-8 A common route of reduction is to use H 2 gas or an Ar/H 2 mixture at 400-1100°C from NH 4 TcO 4 4 and TcO 2 6 . Secondary techniques such as the electrodeposition of Tc from aqueous solutions have also been previously explored as an option for the recovery of Tc as the metal. With regard to Tc electrodeposition, technetium is unique. It is a very complex element to study electrochemically because of its large variety of chemical forms, oxidation states, and known disproportion reactions available to it in various aqueous systems that have the ability to hinder production of Tc metal on a cathode substrate. 9-12 The potential uses of the electrodeposition of TcO 4 − for the recovery of Tc metal from aqueous solutions has gained notoriety as a possible method for the isolation of this fission product prior to being introduced into a...

show abstract

“…(l max = 530 nm 27 ). The low water content in the mixture prevents generation of technetium dioxide.…”

Section: àmentioning

confidence: 99%

“…In turn, Rajec and Maca ´s ˇek 23 reported the formation of hexachlorotechnetates(IV) as a result of electrochemical reduction of TcOCl ) are observed. 24 Dimeric Tc species are reported to be generated in concentrated aqueous formate [25][26][27] or acetate 28 solutions.…”

Section: A Introductionmentioning

confidence: 99%