Rare earth metal salts as potential alternatives to Cr(VI) in the chlorate process

Gustavsson, John; Nylén, Linda; Cornell, Ann

doi:10.1007/s10800-010-0136-4

Cited by 21 publications

(14 citation statements)

References 19 publications

(35 reference statements)

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“…However, the use of Cr(VI) was banned within the European Union due to its high toxicity and is only allowed to be used under authorization . The lack of alternative substances that provide comparable selectivity to that of dichromate is the main reason why Cr(VI) has not yet been removed from the electrolyte. For the long term sustainability of the chlorate process, it is necessary to keep the energy consumption on a reasonable level, and to minimise the use of hazardous chemicals with negative effects on human health and the environment.…”

Section: Introductionmentioning

confidence: 99%

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Gomes

Busch²,

Wildlock

et al. 2018

ChemistrySelect

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Chlorate production is a highly energy demanding industrial process, where chlorate formation is accompanied with hydrogen formation on the cathode. To ensure a high cathodic current efficiency, sodium dichromate is added to the chlorate electrolyte to avoid reduction of hypochlorite formed as a reaction intermediate in the process. However, chromate is highly toxic to humans and environment, and therefore a replacement is desired. A model system with ex situ formed chromium oxide/hydroxide films were used to study hypochlorite reduction and hydrogen evolution. The experimental results demonstrate that the hypochlorite reduction is fully blocked while hydrogen evolution readily occurs. However, in the presence of hypochlorite the hydrogen evolution reaction is inhibited. By combining experimental findings with density functional theory (DFT) calculations, the mechanism of hypochlorite reduction was revealed and the reason for inhibition by the deposited chromium(III) film was demonstrated. Based on these results possible replacements for chromate are suggested.

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Section: Introductionmentioning

confidence: 99%

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Gomes

Busch²,

Wildlock

et al. 2018

ChemistrySelect

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“…Rare earth metal salts presented promising results in bench-scale experiments [24][25][26], but their solubility in a chlorate electrolyte [24] and/or low efficiency in long-term experiments [26] limit their application in real processes. Another option is the use of molybdate in the electrolyte.…”

Section: Introductionmentioning

confidence: 99%

Electrochemical Investigation of the Hydrogen Evolution Reaction on Electrodeposited Films of Cr(OH)3 and Cr2O3 in Mild Alkaline Solutions

et al. 2017

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The hydrogen evolution reaction (HER) from water reduction is the main cathodic reaction in the sodium chlorate process. The reaction typically takes place on electrodes covered with a Cr(III) oxide-like film formed in situ by reduction of sodium dichromate in order to avoid reduction of hypochlorite and thereby increase the selectivity for the HER. However, the chemical structure of the Cr(III) oxide-like film is still under debate. In the present work, the kinetics of the HER were studied using titanium electrodes covered with electrodeposited Cr(OH) 3 or Cr 2 O 3 , which were characterized by means of scanning electron microscopy (SEM), energydispersive x-ray spectroscopy (EDX), x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. A clear difference in the morphology of the deposited surfaces was obtained, and the structure could be revealed with Raman spectroscopy. The kinetics for the HER were investigated using potentiodynamic and potentiostatic techniques. The results show that the first electron transfer is rate limiting and that the activity decreases in the order Cr 2 O 3 @Ti > bare Ti > Cr(OH) 3 @Ti. The low activity obtained for Cr(OH) 3 @Ti is discussed in terms of the involvement of structural water in the HER and the slow ligand exchange rate for water in Cr(III) complexes, while the high activity obtained for Cr 2 O 3 @Ti is rationalized by a surface area effect in combination with reduction of surface water and water in solution.

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“…Elimination of Cl-containing interferences can also be accomplished via their preferential removal from a sample by reaction with N 2 H 5 + /OsO 4 [39], BH 4  [40], or Fe(II) [6] and/or careful adjustment of the reaction conditions [41,42] prior to initiating the electrochemical analysis of chlorate. Finally, recent work indicates that selective surface modification of the electrode with rare earth coatings [43,44] can hinder the reduction of certain Cl-containing species, such as hypochlorite, in the presence of chlorate.…”

Section: Introductionmentioning

confidence: 99%

Statistical evaluation of an electrochemical probe for the detection of chlorate

Trammell

Shriver‐Lake

Dressick

2017

Sensors and Actuators B: Chemical

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We describe the use and characterization of a multilayer film, prepared via layer-by-layer deposition of cationic para-rosaniline acetate dye (i.e., PR) and the vanadium-containing Keggintype polyoxometalate anion, [PMo 11 VO 40 ] 5 (i.e., PVMo 11 ), on indium tin oxide (ITO) as an electrode for determination of chlorate. A linear cyclic voltammetry (CV) current response was observed for the 0 M  [ClO 3  ]  1000 M range with a detection limit of ~220 M ClO 3  (S/N > 3) in a pH = 2.5 solution of 100 mM sodium acetate. Electrode response was insensitive to interference by oxygen and nitrogen-based explosives like TNT, a prerequisite for use in the field. A Taguchi L16 array was used to investigate the performance of the electrode as functions of number of PVMo 11 /PR bilayers (L; 3-6 bilayers), solution pH (H; pH ~1.32 -2.85), solution [ClO 3  ] (C; 250 -1000 M), CV scan rate (S; 50-200 mVs 1 ), and film age (A; 1-8 weeks). Maximum current response was obtained for a 1 week old 5 bilayer film immersed in a pH 2.85 0.10 M NaCl (aq) solution containing 1000 M ClO 3  . However, current response fell as films aged, requiring aging of films for approximately 8 weeks prior to use to obtain reproducible analyses. A two-level full factorial design using films aged 8 weeks identified the variables S, L, H, and C and variable interactions LS and HS as statistically significant contributors to the film current response and provided a model describing film performance.

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Rare earth metal salts as potential alternatives to Cr(VI) in the chlorate process

Cited by 21 publications

References 19 publications

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Understanding Selectivity in the Chlorate Process: A Step towards Efficient Hydrogen Production

Electrochemical Investigation of the Hydrogen Evolution Reaction on Electrodeposited Films of Cr(OH)3 and Cr2O3 in Mild Alkaline Solutions

Statistical evaluation of an electrochemical probe for the detection of chlorate

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