Current efficiency in the chlorate cell process

Spasojevic, Danijel; Ribic-Zelenovic, J Lenka; Spasojević, M.; Nikolic, Zoran

doi:10.2298/jsc131023004s

Cited by 5 publications

(15 citation statements)

References 16 publications

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“…In the history of the chlorate process, different explanations for the role of chromate have been suggested, such as buffering ability in solution, formation of a thin layer on the cathode that prevents hypochlorite reduction and as corrosion inhibitor for the mild steel cathodes [4,[7][8][9][10][11][12][13][14][15][16][17]. The nature of the film formed by reduction of Cr(VI) is still not completely known, even though in situ characterization have suggested Cr(OH) 3 · xH 2 O on Pt [6] and both Cr(OH) 3 [6,11] and Cr 2 O 3 [41] on gold.…”

Section: Discussionmentioning

confidence: 99%

“…The film consists of Cr(III) hydrous oxide or hydroxide, which is oxidized back to chromate when the current is switched off [5,6]. Other benefits from chromate addition are pH buffering and corrosion inhibition on the steel cathodes used [4,[7][8][9][10][11][12][13][14][15][16][17]. However, sodium dichromate is listed in the Annex XIV under REACH [18], which means that without authorization it is forbidden to use after the sunset date in late 2017.…”

Section: Introductionmentioning

confidence: 99%

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Study of Hypochlorite Reduction Related to the Sodium Chlorate Process

et al. 2016

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Reduction of hypochlorite is the most important side reaction in the sodium chlorate reactor leading to high energy losses. Today chromate is added to the reactor solution to minimize the hypochlorite reduction but a replacement is necessary due to health and environmental risks with chromate. In order to understand the effect of different substrates on the hypochlorite reduction, α-FeOOH, γ-FeOOH, Cr 2 O 3 and CrOH 3 were electrodeposited on titanium and subjected to electrochemical investigations. These substances are commonly found on cathodes in the chlorate process and can serve as model substances for the experimental investigation. The mechanism of hypochlorite reduction was also studied using DFT calculations in which the reaction at Fe(III) and Cr(III) surface sites were considered in order to single out the electrocatalytic properties. The experimental results clearly demonstrated that the chromium films completely block the reduction of hypochlorite, while for the iron oxyhydroxides the process can readily occur. Since the electrocatalytic properties per se were shown by the DFT calculations to be very similar for Fe(III) and Cr(III) sites in the oxide matrix, other explanations for the blocking ability of chromium films are addressed and discussed in the context of surface charging, reduction of anions and conduction in the deposited films. The main conclusion is that the combined effect of electronic properties and reduction of negatively charged ions can explain the reduction kinetics of hypochlorite and the effect of chromate in the chlorate process.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Study of Hypochlorite Reduction Related to the Sodium Chlorate Process

et al. 2016

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“…It is formed in several reactions in the electrolyte bulk as well as on the anode (for descriptions of the reactions see the review by Karlsson et al in ref [21]). At the anode oxygen has been suggested to be formed mainly from anodic reactions involving hypochlorite [69][70][71], or from the oxidation of water [40]. Fig.…”

Section: Effect Of Chromium(vi) On the Selectivity Of The Anode Towarmentioning

confidence: 99%

“…Anodic current efficiency for active chlorine evolution as a function of the hypochlorite concentration in the solution (DSA anode, 300 g dm À3 NaCl, 2 g dm À3 Na 2 Cr 2 O 7 , T = 80 C)[71].…”

mentioning

confidence: 99%

A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

Endrődi

Simic

Wildlock

et al. 2017

Electrochimica Acta

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Sodium chlorate is industrially produced by electrolysis of an aqueous salt solution, in which chromium (VI) constitutes an important excipient component. It is added to a concentration of a few grams Na 2 Cr 2 O 7 /liter to the electrolyte and has several functions in the process, the most important being to increase the Faradaic efficiency for hydrogen evolution in the undivided electrochemical cells. A thin film of Cr(OH) 3 Â nH 2 O formed by reductive deposition on the cathodes decreases the rate of unwanted side reactions, while still enabling hydrogen evolution to occur. In addition chromium(VI) buffers the electrolyte at the optimum pH for operation and promotes the desired homogeneous reactions in the electrolyte bulk. Chromium species also affect the rates of hydrogen and oxygen evolution at the electrodes and are said to protect the steel cathodes from corrosion. Although chromium(VI) stays in a closed loop during chlorate production, chromate is a highly toxic compound and new REACH legislation therefore intends to phase out its use in Europe from 2017. A production without chromium(VI), with no other process modifications is not possible, and today there are no commercially available alternatives to its addition. Thus, there is an urgent need for European chlorate producers to find solutions to this problem. It is expected that chromium-free production will be a requirement also in other parts of the world, following the European example. As the chromium(VI) addition affects the chlorate process in many ways its replacement might require a combination of solutions targeting each function separately. The aim of this paper is to explain the role and importance of chromium(VI) in the chlorate manufacturing process. Previous achievements in its replacement are summarized and critically evaluated to expose the current state of the field, and to highlight the most promising avenues to be followed. An attempt is also made to reveal connections with other research fields (e.g. photochemical water splitting, corrosion science) facing similar problems. Allied effort of these different communities is expected to open up research avenues to the mutual benefit of these fields.

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“…Облик ћелије, димензије електрода и међуелектродно растојање утичу на искоришћење струје и енергије. Анализом времена задржавања елемената запремине електролита у ћелији установљен је њен оптималан облик [1,2,[13][14][15][16][17]27,28]. Димензије електрода зависе од капацитета електролизера.…”

Section: резултати и дискусијаunclassified

Development of RuO2/TiO2 titanium anodes and a device for in situ active chlorine generation

Spasojević¹,

Trišović

Ribić-Zelenović³

et al. 2013

Hem Ind

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Chlorine is used worldwide for water disinfection purposes. However, due to its toxicity the EU has imposed a set of standards that must be applied when transporting and storing chlorine. In Serbia, numerous studies have been conducted attempting to develop the technology for the generation of active chlorine disinfectant but with a non-toxic aqueous solution of sodium chloride as the raw material. This study provides an overview of the titanium anodes activated by thermally obtained solid solution of ruthenium and titanium oxide development. It also presents new findings on the effect of the temperature of thermal treatment, the composition, the thickness of an active coating on its microstructural properties, and consequently on the catalytic activity, ion selectivity, and corrosion stability during active chlorine generation through the electrolysis of dilute sodium chloride solutions at room temperature. The study also evaluates the effect of the kinetic and operational parameters of the electrochemical process of active chlorine generation on both current and energy efficiencies. The results obtained were used to determine optimal values of technological parameters of the production process. This comprehensive research resulted in the construction of different types of remote-controlled and fully automated active chlorine generating plants

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Current efficiency in the chlorate cell process

Cited by 5 publications

References 16 publications

Study of Hypochlorite Reduction Related to the Sodium Chlorate Process

Study of Hypochlorite Reduction Related to the Sodium Chlorate Process

A review of chromium(VI) use in chlorate electrolysis: Functions, challenges and suggested alternatives

Development of RuO2/TiO2 titanium anodes and a device for in situ active chlorine generation

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