Packed Bed Electrochemical Reactor Research Articles

Treatment of Se-Impacted Wastewater Using a Three-Dimensional Packed Bed Electrochemical Reactor

Selenium is an essential element for flora and fauna in trace amounts. It plays a crucial role in bolstering photosynthesis and facilitating thyroid hormone metabolism. However, excessive consumption of selenium can result in health concerns such as reproductive complications and cancer. Selenium usually coexists with minerals such as copper and coal in the natural environment. The associated activities, such as copper mining and coal combustion, have greatly accelerated the mobilization of selenium. The selenium released through coal combustion is mostly captured in the flue gas desulfurization (FGD) wastewater as inorganic selenite and selenate.Our lab previously validated the viability of direct electrochemical reduction (SeDER) to remove dissolved selenite from a simplified FGD water matrix using planar gold and graphite cathodes, where more than 94% of the aqueous selenite can be converted to elemental Se(0) deposited on the cathode surface. Graphite is eventually selected for its low material cost, decent removal performance, and minimum secondary pollution as compared to gold and other non-noble metal cathodes. This direct electrochemical deposition process provides many benefits that existing biological and indirect electrochemical methods lack, such as zero chemical addition and low to zero solid generation. However, this method is only suitable for wastewater with elevated temperatures necessary to generate conductive Se(0) for continuous reduction. The inclusion of a heating process adds complexity to the design, impeding the scalability of the SeDER system. Furthermore, the application of SeDER is constrained to Se-impacted wastewater with an elevated temperature.In this study, we propose a novel reactor design utilizing electrochemical reduction to treat Se-impacted wastewater at ambient temperature. The electrodes we used are made of graphite for the reasoning stated above. The reactor consists of a pair of planar graphite anode and cathode, and the inner chamber is filled with cylindrical graphite particle electrodes (PEs) separated by a nylon spacer to create an anodic chamber and a cathodic chamber. The PEs act as an extension of the planar electrodes, which offers numerous reaction sites and minimizes the travel distance for selenite ions to reach the electrode surface. In our 120-mL batch test with 0.1-mM selenite in 100-mM phosphate buffer, the exact system without filler removed 0% selenite at room temperature, while the filled 3D system removed on average 50% of the selenite in 3 hours. Using the same 3D system, we then investigated performance enhancement with a recirculating operation. The total working volume is fixed at 200 mL, while the flow rate and the applied voltage vary. The flow rate is set at the values with hydraulic retention time (HRT) fixed at 15 min, 30 min, and 60 min. The system-applied voltage is set at -1.9V (just enough for selenite reduction), -2.1V, and -2.3V. We found that the shortest HRT combined with -2.1V system applied voltage yielded the highest selenite removal performance in all tests, with an average of 47% removal in 3 hours. We hypothesized that the shorter HRT provides a faster flow rate that refreshes the PE’s surface from insulative Se(0) deposition, which provides sustainable reaction sites for the incoming selenite. At -2.1V, the potential is negative enough to allow selenite reduction while fewer parasitic reactions (e.g., hydrogen evolution reaction) occur compared to that under -2.3V.With the selected system voltage and flow rate, we eventually explored competing ion behavior and switched from a simplified water matrix to simulated Se-impacted wastewater. We found that of all the commonly found competing ions (i.e., sulfate, nitrate, and chloride), chloride significantly impacts selenite removal, with performance dropping to 10% removal in 3 hours. Nitrate slightly decreased the selenite removal, with an average Se removal performance of 23%. Sulfate, on the other hand, resulted in an increase in selenite removal after addition. We hypothesize that a high sulfate concentration in simulated wastewater could help alleviate the repulsing force from the cathode surface for the selenite ions. The double layer of the PEs could also be compressed by the high ionic strength, which decreases the capacitance and promotes selenite reduction. To confirm this hypothesis, we conducted an electrochemical impedance study to analyze the effect of competing ions on reaction kinetics and capacitance. We also performed surface analysis for the wasted planar electrodes and PEs to investigate the change in morphology and observed possible chemical residue. These characterizations will help us develop a regeneration protocol in long-term operation and help us scale up our prototype to manage actual Se-impacted wastewater.

Electrochemical Treatment of Wastewater Containing Cyanide and Zinc (Dept.p)

A study was carried out to investigate the feasibility of using a packed bed electrochemical reactor with low-through porous graphite electrodes to remove either cyanide and/or zinc ions simultaneously from wastewater. The effects of cell current density, flow rate, pH and inlet concentration on removal efficiency and current efficiency of either cyanide ion or zinc ion and combination of both ions removal were studied. It was found that the removal efficiency of cyanide ions increases with cell current density, pH and feed flow rate. Several cell arrangements were investigated. It was found that the vertical arrangement of cells is better than the horizontal arrangement. For zinc removal it was found that removal efficiency of zinc ions increases with cell current density. For a combination of both ions it was found that removal efficiencies of zinc and cyanide increase with flow rate, current density and inter concentration. Current efficiency of zinc removal increases with current, flow rate and zinc ion concentration but remains constant with pH change.

In-situ preparation of biochar-loaded particle electrode and its application in the electrochemical degradation of 4-chlorophenol in wastewater

In order to effectively degrade 4-chlorophenol in wastewater, a biochar-loaded particle electrode was prepared using an in-situ method. The method employed bagasse as the raw material, KOH as the activator, SnCl4·5H2O, MnCl2·4H2O and SbCl3 as the modifiers. Furthermore, X-ray diffraction, scanning electron microscopy and energy dispersive spectrometer were used to characterize the crystal composition, morphology and elemental compositions of the proposed particle electrode. The electrochemical performance of the proposed particle electrode was analyzed using an electrochemical workstation. A three-dimensional packed-bed electrochemical reactor was constructed using the loaded biomass carbon particle electrodes. The effects of different loaded biomass carbon particle electrodes on the electrochemical degradation of 4-chlorophenol were studied, and the mechanism of electrochemical degradation of 4-chlorophenol was discussed. The results showed that the effect of the supported biomass carbon particle electrode on the degradation of 4-chlorophenol was significantly higher than that of the unsupported biomass carbon particle electrode. Additionally, the electrochemical degradation of 4-chlorophenol was greatly influenced by the biomass carbon particle electrode with different loading and concentration. The removal efficiencies of 4-chlorophenol using the electrochemical treatment under the studied experimental conditions were found in the following descending order: Mn/AC > Sn/AC > Sb/AC. Among them, the biomass carbon particle electrode prepared using 150 g L−1 MnCl2·4H2O showed the best treatment effect for 4-chlorophenol. After electrochemical treatment of 500 mg L−1 of 4-chlorophenol-simulated wastewater for 1 h, the removal efficiency of 4-chlorophenol reached 99.93%.

Removal of Cadmium from Simulated Wastewater using Rotating Tubular Packed Bed Electrochemical Reactor: Optimization through Response Surface Methodology

A rotating tubular packed bed electrochemical reactor was used for the electrochemical removal of cadmium (Cd) from simulated wastewater. Impacts of electrolysis operating parameters: current (0.56–2.8 A), rotation speed (100–500 rpm), initial cadmium concentration (20–100 ppm), and pH (3-9) were investigated. Response surface methodology and Box-Behnken design were used for optimizing the process parameters where cadmium Removal Efficiency (RE %) was selected as a response function. Findings of the present work suggested that currently has a main impact on the removal efficiency of cadmium followed by rotation speed, then concentration and pH. The results of the regression analysis showed that experimental data could be fitted to a second-degree polynomial model with value of the determination coefficient (R2) equal to 91.8 %. Optimal conditions for process parameters based on the RSM model were initial Cd concentration of 32.0 ppm, current of 2.8 A, rotation speed of 371 rpm and pH = 3, where a final cadmium concentration less than 0.3 ppm was obtained after 30 min of electrolysis process (RE= 99.28% ).

Application of Response Surface Methodology for Optimization of Phenol Removal from Simulated Wastewater using Rotating Tubular Packed bed Electrochemical Reactor

Phenol removal from simulated wastewater by indirect electrochemical oxidation was investigated using a rotating tubular packed bed electrochemical reactor. Effects of operating parameters like current density (3-15mA/cm2), rotation speed (100–500 rpm), initial phenol concentration (20–100ppm), and pH (3-9) were investigated. Optimization of the process parameters was carried out by adopting response surface methodology (RSM) combined with Box–Behnken Design (BBD) where COD removal efficiency (RE %) was selected as a response function. The results indicated that initial phenol concentration has the main effect on the COD removal efficiency followed by current density then pH and rotation speed. The results of regression analysis revealed that the experimental data could be fitted to a second-order polynomial model with a value of determination coefficient (R2) equal to 98.38% .The optimum conditions of the process parameters based on RSM method were an initial phenol concentration of 41 ppm, current density of (9.3 mA/cm2 ), rotation speed of 367 rpm and pH = 3 where COD removal efficiency of ( 99.83%) was accomplished after 60 min of electrochemical oxidation process in which current efficiency of (9.87%) was observed and energy consumption of (179.86 KWh/Kg COD) was required.

Galvanic interaction of pyrite with Cu activated sphalerite and its effect on xanthate adsorption

In the presence of Cu ions, a packed bed electrochemical reactor (PBER) was employed to deliberately avoid or induce galvanic coupling between pyrite and Cu‐activated sphalerite. The effect of galvanic interaction on Cu ions uptake and xanthate adsorption were investigated. Solution chemistry and surface chemistry studies (ethylenediaminetetraacetic acid extraction and time of flight secondary ion mass spectrometry) have observed that when sphalerite and pyrite were galvanically coupled, Cu ions migrated from the pyrite surface to the surface of the sphalerite. Along with the marked decrease in the adsorption of Cu ions on pyrite, xanthate adsorption on the minerals also dramatically dropped. The pseudo‐adsorption rate constant for the minerals in the mixed mode is only 0.0583 s‒1, much less than that in the decoupled mode, which is 0.1368 s ‒1. This testing program shows that the galvanic coupling of minerals contributes to more copper transfer and Cu ions preferentially adsorbed by sphalerite rather than pyrite. This affects the pyrite surface and causes it to become xanthate unflavoured.

The role of electrolyte acid concentration in the electrochemical exfoliation of graphite: Mechanism and synthesis of electrochemical graphene oxide

Electrochemistry has emerged as a major route for graphene and graphene oxide synthesis from graphite. Anodic graphite oxidation is commonly used with dilute mineral acid or aqueous salt electrolytes. In this system, the electrolyte acid concentration appears to be a critical parameter. However, the effect of the acid concentration, particularly at low concentrations, is still not fully understood. To address this issue, we used a packed bed electrochemical reactor to synthesize seven different electrochemical graphite oxide (EGO) products in 2–16 M sulfuric acid. Detailed XRD, XPS, Raman, conductivity and optical microscopy analysis of the products was carried out. We found dilute acid (<10 M) graphite oxides were less crystalline and less oxidized than those produced in stronger acids. The oxygen evolution reaction at the graphite surface appears to affect the structural changes, oxidation mechanism, and electrochemical corrosion of the anode. EGO conductivity is also strongly affected by the electrolyte’s acidity. We show that well oxidized, yet reasonably conductive, single layer graphene oxide can be produced from 7.1 M acid. These results broaden our understanding of graphite electrochemistry and will serve to inform future electrochemical graphene synthesis efforts.

Modeling Residence Time Distribution (RTD) Behavior in a Packed-Bed Electrochemical Reactor (PBER)

This paper focuses on understanding the electrolyte flow characteristics in a typical packed-bed electrochemical reactor using Residence Time Distribution (RTD) studies. RTD behavior was critically analyzed using tracer studies at various flow rates, initially under nonelectrolyzing conditions. Validation of these results using available theoretical models was carried out. Significant disparity in RTD curves under electrolyzing conditions was examined and details are recorded. Finally, a suitable mathematical model (Modified Dispersed Plug Flow Model (MDPFM)) was developed for validating these results under electrolyzing conditions.

Scalable Production of Graphene Oxide Using a 3D-Printed Packed-Bed Electrochemical Reactor with a Boron-Doped Diamond Electrode

Although graphene oxide (GO) has shown enduring popularity in the research community, its synthesis remains cost prohibitive for many of its demonstrated applications. While significant progress ha...

Bipolar Packed-bed Electrochemical Reactor for the Degradation of Diclofenac; a Bio-refractory Organic Compound

Pharmaceuticals have low biodegradability and can retain their chemical structure for long periods of time leading to an accumulation in the environment causing irreversible changes. Electrochemical oxidation has been proved to be an environmentally friendly and economically viable solution for bio-refractory of organic molecules as well as for the disinfection of wastewaters. This paper aims to evaluate the performance of specific energy consumption for a given reduction of toxic organic compound loads in a continuous flow bipolar packed-bed electrochemical reactor and compare this with a classical parallel plate reactor. The energy cost for both the parallel plate and bipolar electrochemical reactors are similar (around 1.6 kWh m-3) lower than other advanced oxidation process reported in literature. However, the bipolar configuration is particularly suitable for low conductivity waste water and/or for avoiding the formation of organochloride compounds in a chloride rich wastewater.

Design and Development of Packed Bed Electrochemical Reactors (PBER’s) Using Scrap Lead Dioxide as Novel Electrodes

The present work focuses on the effective utilization of discarded Lead dioxide particles as particulate electrodes in a carefully designed packed bed electrolyser. It is known that particulate electrodes provide a large electrode area in proportion to conventional flat electrode configuration. Consequently, this packed bed electrolyser, will be exceptionally useful when dealing with slow reactions. This design entirely avoids the necessity of expensive valve metals as substrates and associated noble metal oxide undercoating. In the present study, an optimized design of a packed bed electrochemical reactor setup using peeled off electro deposited Lead dioxide particles was carried out. The above electrolyser was used for studying its effectiveness in the electrochemical oxidation of Sodium Chlorate to Sodium Perchlorate, which is the starting raw material for the manufacture of rocket propellant oxidizers. Effect of certain parameters like electrolyte flow rates, current density and thickness in the desired current efficiencies for the formation of perchlorates were estimated. Results indicate that this electrolyser proves to be a potential method for improving the reaction rates of slow reactions like perchlorate formation, utilizing cheaper discarded Lead dioxide particles.

Electrochemical capacitance behavior of a packed bed electrochemical reactor toward phenol electro-oxidation

The electrochemical capacitance behavior of a packed bed electrochemical reactor (PBER) toward phenol electro-oxidation in aqueous solution was studied. In the absence of phenol, a decrease in the response current (i) coupled with an increase of the specific capacitance (C s ) was obtained for PBER compared with a flat-bed electrochemical reactor. However, following intercalation of phenol, simultaneous improvement of i, and reduction of C s were observed. The reasons for the former were ascribed to an increased resistance, an abundant pore structure for charge, and electrolyte transportation owing to the packing of the fixed granular active carbon (GAC) filler, whereas anode extension and formation of the polyoxyphenylene film on the anode and the GAC surface were responsible for the latter. Although significant attenuation (42.06 % after 300 cycles at current density 1.90 mA cm−2) of C s was observed for PBER in the long cycle test, the non-negligible C s value (30.86 mF cm−2) holds great promise for pulsating power supplies. An equivalent circuit associated with electrochemical capacitance and resistance distribution was proposed, which gives an exhaustive explanation of the electrical characteristics during the phenol electro-oxidation process.

Numerical Simulation of the Primary, Secondary and Tertiary Potential Distribution on Porous Cathode in a Flow-through Packed Bed Reactor. Influence of Thickness, Concentration and Hydrodynamics in Porous Media

Packed bed electrodes can be used for electrochemical recovery of heavy metals from a variety of industrial and laboratory model solutions. The packed bed electrode forms a porous flow-through (Figure 1) configuration providing large surface area usually depleting the concentration of several metal ions below 0.1 ppm. For design porpoises of these electrodes, it is necessary to study the influence of geometry (cathode thickness), flow rate and concentration on potential distribution.Numerical simulations of primary, secondary and tertiary current distributions on the porous cathode of a packed bed electrochemical reactor (Figure 1) were calculated. For primary and secondary current distribution, Laplace equations with its respective boundary conditions (constant potential for primary current distribution and charge transfer kinetics described by a Tafel approximation in secondary current distribution) were evaluated using the finite element method. For tertiary current distribution, the influence of hydrodynamics was taken in account, considering Navier-Stokes model with Brinkman extension for porous media. Once Brinkman equations was solved and local velocity distributions were obtained, local mass transfer coefficients were evaluated by means of following relationship: Kma=cvb where Km is local mass transport coefficient, a is the specific area, v is local velocity, c and b are empirical constants taken from literature. The effects of flow rate, ion concentration, matrix conductivity and thicknes on the distribution of current on porous cathode are analyzed. Results of current distribution obtained by Nava et. al 2008 [1] enable comparisons with the simulations.

Electrocoagulation in a packed bed reactor-complete treatment of color and cod from real textile wastewater

This paper deals with the efficiency of electrocoagulation (EC) for the abatement of COD and absorbance (i.e. color) from real textile wastewater using a packed bed electrochemical reactor in a unique design, not previously encountered in the literature for the treatment of textile wastewater by electrocoagulation. The cylindrical iron reactor was used as a cathode while the packed bed formed from wrapped iron wire netting was used as an anode. Various operating parameters, such as current density, initial pH, wastewater recirculation flow rate and continuous flow regime, were examined for intensifying the performance of the process. Also, calculation of electrical energy consumption and the characterization of sludge formed during electrocoagulation have been performed. The initial COD concentration of 1953 mg/L was reduced to 61 mg/L with a removal efficiency of 96.88%, while the color of the wastewater was almost completely removed. The experimental results, throughout the present study, have indicate that electrocoagulation of textile wastewater using a uniquely designed reactor was very effective and direct dischargeable effluent, complying with legal requirements, was obtained. The XRD analysis of the sludge produced during EC reveals that maghemite (Fe2O3) is the main by-product formed after EC.

The role of multi-sulfidic mineral binary and ternary galvanic interactions in gold cyanidation in a multi-layer packed-bed electrochemical reactor

A multi-layer packed-bed electrochemical reactor (PBER) approach was used for studying the leaching behavior of associated and free (silica-trapped) gold from a series of synthetic multi-mineral systems consisting of pyrite, silica, Au, and successively, X=chalcopyrite, sphalerite and chalcocite. The PBER was filled with sieved powders of sulfidic minerals (pyrite, X), gold and silica arranged as electrically-isolated three-layer ||pyrite||X||silica|| and two-layer ||pyrite+X||silica|| systems. Introduction of gold successively in each layer of the three- and two-layer PBER systems highlighted the role of Au-pyrite, Au-X and pyrite-X binary, and Au-pyrite-X ternary galvanic interactions in the leaching of associated and free gold. The highest Au recovery was achieved within the pyrite layer while the lowest was within the silica layer. For the ||pyrite||chalcocite||silica|| system, depletion of free cyanide and surface passivation inhibited strongly gold leaching. Cyanidation experiments performed in the mixed ||sulfide||silica|| systems showed that the effect of Au-sulfide galvanic interactions largely depend on the mineralogical association between phases. The presence of galvanic effects between the associated minerals in the PBER was confirmed by a conjunction of electrochemical and chemical speciation studies. Increasing the pyrite-Au areal ratio increased gold leaching as a result of increased cathodic areas for oxygen reduction. However, gold leaching from mixed multi-mineral systems where multi-factorial galvanic contacts were enabled was controlled mostly by the relative area ratios between the associated sulfide minerals.

Leveraging strategies to increase gold cyanidation in the presence of sulfide minerals — Packed-bed electrochemical reactor approach

Several leveraging strategies were explored to improve gold leaching during cyanidation in the presence of pyrite, chalcopyrite, sphalerite and chalcocite. Galena, used a source of lead, was found to largely neutralize the negative effect of sulfide minerals dissolution on gold leaching, especially in the cases of pyrite, chalcopyrite and sphalerite. Pyrite–galena galvanic interactions improved gold leaching while for chalcopyrite, sphalerite and chalcocite active galvanic interactions with galena were found to be detrimental to gold leaching. Pre-oxidation of metal sulfides prior to cyanidation significantly increased gold leaching rate when gold–pyrite galvanic interactions were disabled, while their enablement identified pyrite pre-oxidation as counter-productive. Pre-oxidation of mixed mineral systems of pyrite–chalcopyrite and pyrite–sphalerite showed that enabling galvanic interactions between the associated minerals during pre-oxidation controlled gold leaching in the subsequent cyanidation process. For pyrite, lead nitrate addition during pre-oxidation resulted in a significant increase of gold leaching, whereas its addition to subsequent cyanidation canceled the positive effects of pre-oxidation on gold dissolution.

Untangling galvanic and passivation phenomena induced by sulfide minerals on precious metal leaching using a new packed-bed electrochemical cyanidation reactor

Because permanent galvanic contacts between gold rotating disc electrodes and slurried sulfide-rich ores are uneasy to achieve, the standard gold rotating disc electrode/slurry cyanidation arrangement has a tendency to inflate overly the importance of passivation phenomena over the corrective trend of galvanic interactions inherently present within the ore grains. A new packed-bed electrochemical reactor (PBER) was thus developed and tested to decouple and quantify the individual contributions of passivation phenomena (PP) and galvanic interactions (GI) on precious metal (gold and silver, PM) leaching rates during the cyanidation of sulfide-rich ores. The PBER was filled with homogenized mixtures of minerals (pyrite, chalcopyrite, sphalerite, chalcocite, galena, stibnite, and industrial ore), gold and silver powders, which were arranged as electrically isolated sulfide-quartz segregated bilayer(s) with permanent (inter)particle–particle electrical contacts among all constituents in each layer. Implantation of PM powders successively in the quartz layer and then in the sulfide layer, enabled PP and GI to be singled out and quantified separately for each sulfide. Galvanic interactions were found to ameliorate, to various degrees, the leaching of PM. Locating the PM powders in the quartz layer emphasized the negative impact of PP of the sulfide layer on Au and Ag dissolution, except for galena which enhanced gold leaching kinetics. Galvanic interactions due to pyrite, chalcopyrite and an industrial ore were so positive that they largely outweighed the negative impact of PM passivation. The galvanic current measured between Au/Ag electrode and each of the above minerals confirmed the positive effect of GI on gold leaching rate. In close agreement with PM recoveries, stronger galvanic currents were measured for Au-pyrite, Au-chalcopyrite and Au-industrial ore galvanic couples in comparison to those for Au-sphalerite, Au-chalcocite and Au-stibnite.

Electrochemical decolorization of the dye Acid orange 10

In the present study experiments were carried out to decolorize the dye Acid orange 10 using an electrochemical technique. A square packed-bed electrochemical reactor was constructed with a graphite rod as anode and stainless steel as cathode material. Effect of parameters including pH (1.7–7.5) and current intensity (0.1–0.6 A) was investigated. The complete removal of color was achieved within a short period of electrolysis for different concentrations of Acid orange 10. Studies were also made for the removal of chemical oxygen demand (COD) and total organic carbon (TOC).It was found that the electrochemical treatment reduced COD and TOC to 85% and 56% respectively, for 200 mg/L Acid orange and 1.5 g/L sodium chloride concentration. Maximum decolorization was achieved at a current intensity of 0.4 A at a pH of 1.7. Effect of current intensity on color removal was also investigated as a function of electrolysis time (30–210 min) and it showed that maximum removal efficiency (98%) was reached within 60 mi...

Simulation of a Packed-Bed Electrochemical Reactor with Cooled Cathode for Continuously Producing Glyoxylic Acid by Oxalic Acid

Simulation of a Packed-Bed Electrochemical Reactor with Cooled Cathode for Continuously Producing Glyoxylic Acid by Oxalic Acid

Modeling of a packed-bed electrochemical reactor for producing glyoxylic acid from oxalic acid

A two-dimensional reactor model was established for a packed-bed electrochemical reactor with cooled cathode (PERCC) for producing glyoxylic acid from oxalic acid based on the system's reaction kinetics, mass conservation equation, and the equation of charge conservation in terms of solution-cathode potential to describe the distributions of glyoxylic acid concentration and electrolyte potential in the cathode compartment of the PERCC. The equation for a circulating mixer was also presented to account for the accumulation of glyoxylic acid in the catholyte of a batch electroreduction process. Using the orthogonal collocation approach, the partial differential equations of the model could be converted into sets of algebraic equations and be numerically solved. The effects of operating temperature, conductivity of catholyte, operating cathode potential, and volumetric flow rate of the catholyte on the current efficiency and concentration of glyoxylic acid were simulated and discussed, with emphasis on the current densities generated from main and side reactions. The model was used in a batch operation process and a continuous operation process, with the predicted results being generally in good agreement with the experimental data for both the cases.