Electrochemical Cr(VI) reduction using a sacrificial Fe anode: Impacts of solution chemistry and stoichiometry

Chuang, Sheng-Ming; Ya, Vinh; Feng, Chiao-Lin; Lee, Shou-Jen; Choo, Kwang‐Ho; Li, Chi-Wang

doi:10.1016/j.seppur.2017.09.028

Cited by 33 publications

(4 citation statements)

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“…The Ministry of Ecology and Environment of the People's Republic of China and World Health Organization (WHO) have regulated the maximum concentration authorized in drinking water as being below 0.05 mg/L (Sanitary Standard for Drinking Water Quality (2001)) [3,4]. However, the inevitable drawbacks of high cost or secondary contamination still exist among conventional methods to remove heavy metals from aqueous solutions, such as chemical reduction [5,6], membrane separation [7], electrolytic [8], ferrite method [9,10], precipitation [11], adsorption [12,13], ion exchange [14] and biological method [15]. Hence, it is important to explore a cost-efficient method for Cr(VI) removal.…”

Section: Introductionmentioning

confidence: 99%

An Efficient Photocatalyst for Fast Reduction of Cr(VI) by Ultra-Trace Silver Enhanced Titania in Aqueous Solution

Hou

Chen

et al. 2018

Catalysts

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For the purpose of establishing a simple route to prepare a metal-semiconductor hybrid catalyst efficiently and reduce its cost through precise doping noble metals. In this study, ultra-trace silver doped TiO 2 photocatalysts were fabricated via a "green" ultrasonic impregnation-assisted photoreduction strategy in an ethanol system, and its photocatalytic performance was systematically investigated by utilizing Cr(VI) as the model contaminant. A schottky energy barrier was constructed in Ag@TiO 2 , which served as a recombination center and possessed superior photocatalytic activity for Cr(VI) reduction. The obtained catalysts exhibited a significant e − /h + separation efficiency which directly led to an obvious photocatalytic property enhancement. Then, the resultant Ag@TiO 2 (0.06 wt %, 30 min irradiation) showed about 2.5 times the activity as that of commercial P25 NPs for Cr(VI) degradation. Moreover, after five cycles, it still maintained considerably high catalytic ability (62%). This work provides a deep insight into preparation techniques of metal-semiconductor photocatalyst and broadens their application prospect.

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Section: Introductionmentioning

confidence: 99%

An Efficient Photocatalyst for Fast Reduction of Cr(VI) by Ultra-Trace Silver Enhanced Titania in Aqueous Solution

Hou

Chen

et al. 2018

Catalysts

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“…Hexavalent chromium is much more poisonous, soluble, and mobile than Cr(III), which has led the World Health Organization (WHO) to set the upper limit of Cr(VI) in drinking water at 0.05 mg/L . In addition, hexavalent chromium has been classed as a Group I human carcinogenic substance by the International Agency for Research Cancer . Therefore, there is an urgent demand for developing highly effective, reliable, and economical techniques to remove Cr(VI) from contaminated water or reduce Cr(VI) to Cr(III) to decrease its toxicity.…”

Section: Introductionmentioning

confidence: 99%

“…2 In addition, hexavalent chromium has been classed as a Group I human carcinogenic substance by the International Agency for Research Cancer. 3 Therefore, there is an urgent demand for developing highly effective, reliable, and economical techni-ques to remove Cr(VI) from contaminated water or reduce Cr(VI) to Cr(III) to decrease its toxicity.…”

Section: Introductionmentioning

confidence: 99%

Adsorption and Reduction Transformation Behaviors of Cr(VI) on Mesoporous Polydopamine/Titanium Dioxide Composite Nanospheres

Gao

et al. 2019

J. Chem. Eng. Data

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Mesoporous polydopamine/titanium dioxide (PDA/TiO2) composite nanospheres with different polydopamine content were successfully synthesized by a facile organic–inorganic self-assembly method. The synthesized composite materials were characterized by N2 adsorption–desorption isotherm, X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy (TEM), energy dispersive spectrometry, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, ζ--potential, and cyclic voltammetry. The results showed that the composite material with the most exposure active site exhibits a spherical morphology. The composite material could also be used as a reducing agent, and spheres of the composite material were used as adsorbents for removing hexavalent chromium from aqueous solutions by reducing Cr(VI) to Cr(III). The influence of factors, including the initial solution pH, contact time, initial ion concentration, temperature, coexisting ions, and dose of adsorbent, was also studied. The hexavalent chromium adsorption data fit well to a Langmuir isotherm model, and the maximum adsorption capacity was shown to be 244.5 mg/g. The kinetics data follow a pseudo-second-order kinetic model. The study of thermodynamics indicated that the adsorption on the composite nanospheres was a spontaneous and endothermic process. Moreover, a mechanism of adsorption and reduction on the composite spheres was proposed.

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“…Por ejemplo, el reactor de electrocoagulación de columna optimizado con técnicas estadísticas propuesto por Khan y colaboradores[76] consume 12.9 kW-h‧kg-Cr(VI) −1 , lo que es 2.8 veces el consumo del EAR. Otro ejemplo son los trabajos en la reducción de Cr(VI) reportados por el grupo de investigación de Chi-Wang Li utilizando celdas electroquímicas de electrocoagulación, donde el consumo energético reportado varía de entre 38 a 93 kW-h‧kg-Cr(VI) −1[77,78], los cuales están más de diez veces por encima de los reportados en la Tabla 3.Parámetros de eficiencia hidráulica de los sistemas de agitación.…”

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Intensificación del proceso electroquímico para la remoción de cromo en residuos líquidos

Varela¹

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Chromium is a metal commonly used in the electroplating industry, which generates rinsing water containing hexavalent chromium concentrations above those allowed by environmental regulations. Several treatment alternatives have been proposed to attack this problem, among which electrochemical methods stand out. Among the latter, an attractive process is the one that uses iron electrodes, which are the source for the in situ electrochemical generation of the reducing agent, which chemically reduces the chromium in the liquid from its hexavalent to its trivalent state. The effluent is passed to a mixing tank to promote the precipitation of the metals into metal hydroxides by increasing the pH of the medium in order to separate them from the treated water. In this work, different strategies are presented to intensify this treatment process in order to improve the hydrodynamic performance of the electrochemical reactor and the precipitation stage. To assess the processes performance, in both systems, the electrochemical reactor and in the precipitation reactor, experimental tests were carried out in stirred tank reactors and jars test, which were complemented with studies using computational fluid dynamics to integrate the information on the performance of the processes under the different scenarios tested. Chapter two details the study carried out using computational fluid dynamics tools on the rotating rings electrochemical reactor, which has shown high removal efficiencies of hexavalent chromium in pollulet water. This part of the project shows the most appropriate modeling approach to simulate the hydrodynamics inside the reactor. Comparison of the results predicted by three variants of the κ-ε turbulence model (stadard, RNG and realizable) coupled to the multi-reference frame model to simulate the electrode rotation is performed. The effect of position of the rotational reference frame boundaries relative to the stationary reference frame boundaries is also evaluated. It is shown that the prediction with the κ-ε realizable model in conjunction with the position at 0° generates the results with the closest approach to the experimental mixing time measurements obtaining a 6% error. Chapter three shows the results of the incorporation of a novelty, which consists of a reactor equipped with the static electrode of electro-baffles agitated by two inclined vane impellers, known as PBT. The results of this modification are compared with those obtained with the performance of the electrochemical reactor equipped with the dynamic rotating ring electrode. The comparison is made theoretically to evaluate their differences in terms of hydrodynamic performance, and experimentally to know their efficiency against the reduction of hexavalent chromium. For the comparison, the reactors were operated at the same stirring speed and Reynolds number. The results of the hydrodynamic analysis show that the arrangement of static electro-baffles together with the pair of impellers improves the mixing time by 36%, increasing the hydraulic efficiency by 85% when the reactor is operated at the same Reynolds number. It is evident that the circulation capacity of the reactor directly affects the reduction rate of hexavalent chromium, since the treatment times have a similar trend to the axial circulation times. It is also shown that there is a reduction in energy consumption of at least 21% when the reactor is equipped with the electro-baffles and the two-impeller agitation system. In chapter four, the operating conditions of the electrochemical reactor are evaluated, such as: geometric configuration of the electrode, stirring speed and current intensity. To evaluate the change in the electrode configuration, the static ring electrode and electro-baffles are used. When operating the electrode with static rings, the need to incorporate conventional baffles is also evaluated. The reactor agitation systems are composed of two PBT impellers, of which the separation between them is also evaluated. In performing the simulations, the interaction of the liquid-gas interface was considered. The results reveal that due to the position of the impellers it is necessary to take into account the liquid-air interaction in the model to obtain a more realistic prediction of the flow pattern in the electro-baffles configuration. As a result of the studies, it was found that the configuration with the lowest energy consumption was the electro-baffles with a separation between impellers equal to their diameter, since its geometrical and hydrodynamic characteristics allow it to be more efficient. The effect of agitation speed and current intensity was explored in this system. The agitation speed increases the reduction rate of hexavalent chromium, finding its limit at 300 rpm. At this agitation speed, the effect of the current intensity was explored, from which a linear dependence of the reactor energy consumption on this variable was found in the range evaluated. In chapter five, the precipitation stage is studied. The studies are carried out in an agitated jar system with two types of impellers, one radial and the other axial. The evaluation of the effect of the pH at which the effluent is adjusted to perform precipitation at values of 4, 6, 7 and 9 is carried out. The results show that after precipitating the treated water at pH = 9.0, a clarified product with neutral pH is obtained and all species are precipitated. The hydrodynamic environment of the jars is also evaluated experimentally and numerically, determining that the radial impeller dissipates more turbulent energy than the axial impeller. Therefore, the axial impeller provides a favorable hydrodynamic environment for the development of flocs, which results in higher sedimentation velocities than those achieved when the jar is operated with the radial impeller. In addition, the axial impeller consumes only 50% of the energy consumed by the radial impeller.

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Electrochemical Cr(VI) reduction using a sacrificial Fe anode: Impacts of solution chemistry and stoichiometry

Cited by 33 publications

References 21 publications

An Efficient Photocatalyst for Fast Reduction of Cr(VI) by Ultra-Trace Silver Enhanced Titania in Aqueous Solution

An Efficient Photocatalyst for Fast Reduction of Cr(VI) by Ultra-Trace Silver Enhanced Titania in Aqueous Solution

Adsorption and Reduction Transformation Behaviors of Cr(VI) on Mesoporous Polydopamine/Titanium Dioxide Composite Nanospheres

Intensificación del proceso electroquímico para la remoción de cromo en residuos líquidos

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