The role of mass transfer in the electrolytic reduction of hexavalent chromium at gas evolving rotating cylinder electrodes

Radwan, Amr; El-Kiar, A.; Farag, H.A.; Sedahmed, G.H.

doi:10.1007/bf01297418

Cited by 24 publications

(13 citation statements)

References 16 publications

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“…14,15 Therefore, mass transfer is considered to play a critical role in the electroreduction of Cr(VI). 16,17 Unfortunately, the classical parallel-plate electrodes often show poor mass transfer. 13 In such cases, the detoxification of aqueous Cr(VI), particularly when Cr(VI) is present at low concentration, often shows low current efficiency and results in high energy demand.…”

Section: ■ Introductionmentioning

confidence: 99%

“…13 In such cases, the detoxification of aqueous Cr(VI), particularly when Cr(VI) is present at low concentration, often shows low current efficiency and results in high energy demand. 17 Flow-through porous electrodes demonstrate high current efficiency, enhanced mass transfer, and high volumetric rates of reaction and have been used in fuel cells, 18 electrooxidation, 19 desalination, 20 and adsorption. 21 This flow-through architecture enables optimal utilization of the active sites inside the porous electrodes and provides enhanced rates of mass transport, which could be especially useful for treatment of dilute solutions.…”

Section: ■ Introductionmentioning

confidence: 99%

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Microfluidic Flow through Polyaniline Supported by Lamellar-Structured Graphene for Mass-Transfer-Enhanced Electrocatalytic Reduction of Hexavalent Chromium

Zhang

et al. 2015

Environ. Sci. Technol.

104

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Owing to its high efficiency and environmental compatibility, electroreduction holds great promise for the detoxification of aqueous Cr(VI). However, the typical electroreduction system often shows poor mass transfer, which results in slow reduction kinetics and hence higher energy consumption. Here, we demonstrate a flow-through electrode of polyaniline supported on lamellar-structured graphene (LGS−PANI) for electrocatalytic reduction of Cr(VI). The reaction kinetics of the LGS− PANI flow-through electrodes are 6.4 times (at acidic condition) and 17.3 times (at neutral condition) faster than traditional immersed parallel-plate electrodes. Computational fluid dynamics simulation suggests that the flowthrough mode greatly enhances the mass transfer and that the nanoscale convection induced by the PANI nanodots increases the nanoscale mass transport in the interfacial region of the electrode/ solution. In situ Raman spectroscopy shows that the PANI−Cr(VI) redox reactions are dominated by the leucoemeraldine/ emeraldine transition at 1.5 V cell voltage, which also remarkably contributes to the fast reaction kinetics. Using single-pass flowthrough mode, the LGS−PANI electrode reaches an average reduction efficiency of 99.

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Section: ■ Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

Microfluidic Flow through Polyaniline Supported by Lamellar-Structured Graphene for Mass-Transfer-Enhanced Electrocatalytic Reduction of Hexavalent Chromium

Zhang

et al. 2015

Environ. Sci. Technol.

104

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“…The overpotential of chromium deposition apparently is decreased, which facilitates chromium electrodeposition. The rate of reaction follows a first-order rate equation [42]. In case of a rotating cylinder, the specific reaction rate constant was found to increase with increasing rotation speed up to a limiting value which is reached with further increase in the rotation speed.…”

Section: Polychromatesmentioning

confidence: 99%

Electrodeposition of Chromium

Mandich¹,

Snyder²

2010

Modern Electroplating

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Electroplated chromium deposits rank among the most important plated metals and are used almost exclusively as the final deposit on parts. Without the physical properties offered by electroplated chromium deposits, the service life of most parts would be much shorter due to wear, corrosion, and the like. Parts would have to be replaced or repaired more frequently, or they would have to be made from more expensive materials, thus wasting valuable resources.The thickness of electroplated chromium deposits falls into two classifications: decorative and functional. Decorative deposits are usually under 0.80 mm in thickness. They offer a pleasing, reflective appearance while also providing corrosion resistance, lubricity, and durability. Decorative chromium deposits are typically plated over nickel but are occasionally plated directly over the substrate of the part.Functional ''hard chrome'' deposits have a thickness customarily greater than 0.80 mm and are used for industrial, not decorative, applications. In contrast to decorative deposits, functional chromium is usually plated directly on the substrate and only occasionally over other electrodeposits, such as nickel. Industrial coatings take advantage of the special properties of chromium, including resistance to heat, hardness, wear, corrosion, and erosion, and a low coefficient of friction. Even though it has nothing to do with performance, many users want their functional chromium deposits also to be decorative in appearance. Functional deposits are also used on parts such as cutting tools and strip steel and are even thinner than decorative deposits.The most common and oldest commercial type of chromium process utilizes hexavalent chromium (Cr 6 þ ) in an aqueous solution containing one or more catalysts. The

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“…Bioremediation by strains of bacteria can effectively degrade Cr(VI) and is economically favorable [16][17][18], but the presence of bacterial toxicants at many waste sites would limit their growth and effectiveness. Electrochemical techniques [19][20][21][22] and electro-coagulation process [23][24][25] have been used for Cr (VI) reduction. Chemical reduction of Cr(VI) to Cr(III) followed by precipitation of reduced chromium with alkali is the most commonly used method [26,27].…”

Section: Introductionmentioning

confidence: 99%

Reduction of hexavalent chromium using zerovalent iron spheres packed in a rotating basket reactor: kinetic and mass transfer study

Amin

2013

Desalination and Water Treatment

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A B S T R A C TKinetics of hexavalent chromium reduction to trivalent chromium onto iron spheres, packed in a rotating basket reactor was investigated under different conditions, such as H 2 SO 4 acid concentration, basket rotational speed, sphere diameter, and solution temperature. The rate of Cr(VI) reduction was found to increase with increasing basket rotational speed, H + ions concentration, and temperature. On the other hand the rate decreases with increasing the diameter of iron spheres. The activation energy was found to be 4.9 kcal/mol which confirm the diffusion controlled nature of the reaction. The thermodynamic parameters for the present study were calculated at 25˚C and was found to be 17.99 kJ mol À1 , 278.98 J mol À1 K À1 , and 103.6 kJ mol À1 for DH, ÀDS, and DG, respectively. Rate of Cr(VI) reduction expressed in terms of the rate of mass transfer was correlated to the controlling parameters by the dimensionless equation Sh ¼ 0:3463 Re 0:55 Sc 0:33The present mass transfer data was found to agree with the surface renewal theory.

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The role of mass transfer in the electrolytic reduction of hexavalent chromium at gas evolving rotating cylinder electrodes

Cited by 24 publications

References 16 publications

Microfluidic Flow through Polyaniline Supported by Lamellar-Structured Graphene for Mass-Transfer-Enhanced Electrocatalytic Reduction of Hexavalent Chromium

Microfluidic Flow through Polyaniline Supported by Lamellar-Structured Graphene for Mass-Transfer-Enhanced Electrocatalytic Reduction of Hexavalent Chromium

Electrodeposition of Chromium

Reduction of hexavalent chromium using zerovalent iron spheres packed in a rotating basket reactor: kinetic and mass transfer study

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