Electrochemical Remediation Research Articles

Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 8. Microscale Simultaneous Photocatalysis

In this article we describe a microscale experiment in which the simultaneous oxidation of an organic compound (citric acid) and the reduction of a metal ion (Cu2+) are photocatalytically performed in an aqueous slurry containing TiO2 irradiated with UV light. This produces electrons (capable of reducing the metal ions) and holes (capable of oxidizing the organic molecule) that can be used for environmental clean up. The experiment allows students to have a better comprehension of the different phenomena involved in a typical photocatalytic process.

Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 7: Microscale Production of Ozone

Ozone, a powerful oxidizing and disinfecting agent, is produced electrochemically in the undergraduate laboratory with simple equipment and under very mild conditions. Tests are given to characterize it, to observe its action in simulated environmental applications, and to measure its rate of production.

Electroremediation part II: A study of the movement of heavy metals during an electroremediation process in Andisol soil

In the Summer 2004 issue of Remediation, the authors presented a study of the influence of buffering behavior in contaminated Andisol soil. This article, Part II, expands on this research by presenting the results of laboratory tests conducted to study the movement of heavy metals in contaminated Andisol soil during the first stage of an electrochemical remediation process. The analysis was performed on the soil after treatment and also on the washing solutions collected during the first four hours. In order to analyze the effectiveness of fast and simple techniques for monitoring the electroremediation process, computer-aided modeling of speciation in the soil solution was performed in connection with the remediation treatment. The results show that the metals moved mainly as positive species in the soil and later occurred as insoluble forms relative to the pH value in the washing solution from the cathode chamber. © 2005 Wiley Periodicals, Inc.

Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 6: Microscale Production of Ferrate

Laboratory Experiments on the Electrochemical Remediation of the Environment. Part 6: Microscale Production of Ferrate

ElectroChemical Remediation Technologies for Metals Remediation in Soil, Sediment and Ground Water, Presentation of Case Histories

ElectroChemical Remediation Technologies (ECRTs) utilize an AC/DC current passed between an electrode pair (one anode and one cathode) in soil, sediment, or ground water to either mineralize organic contaminants through the ElectroChemicalGeoOxidation (ECGO) process, or complex, mobilize, and remove metal contaminants through the Induced Complexation (IC) process, either in-situ or ex-situ. Field remediation data suggest that ECRTs-IC cause electrochemical reactions in soil, sediment, and ground water that generate metallic ion complexes from the target contaminant metals. These complexes, along with naturally occurring dissolved metals, migrate to the electrodes down the electrokinetic gradient and are either concentrated at the electrode (e.g., cesium, strontium) or deposited onto the electrodes (e.g., mercury, cadmium, lead). The metal contaminants concentrated at the electrodes can be pumped and treated, and the metals that deposit on the electrodes can be either disposed of or recycled. ECRTs-IC operates at electrical power levels below those of conventional electrokinetic methods. A unique feature of ECRTs-IC, in marked contrast to electrokinetics, is that metals generally migrate to both the anode and cathode. European field projects include remediation of (1) mercury in brackish water silty sediments, where 76 kg (168 lbs) of mostly mercury were deposited at both electrodes in 26 days of total remediation time; (2) parts per billion ground water contamination of a variety of metals beneath a steel mill waste lagoon, where metal concentration decreases up to 93% were achieved in 30 days of total remediation time; and (3) mercury in sewage sludge contaminated with dental amalgams, which showed an average decrease from 35 mg/kg to 0.185 mg/kg in seven days. A recently completed U.S. laboratory test for the U.S. Department of Energy under fresh water conditions corroborated the European field remediation results. Existing field and laboratory results indicate that ECRTs-IC is a rapid and effective remediation process.

Electrochemical remediation of acid mine drainage

Acid mine drainage (AMD), which has long been a significant environmental problem, results from the microbial oxidation of iron pyrite in the presence of water and air, affording an acidic solution that contains toxic metal ions. Electrochemical treatment of AMD offers possible advantages in terms of operating costs and the opportunity to recover metals, along with cathodic reduction of protons to elemental hydrogen. This work describes the electrolysis of synthetic AMD solutions containing iron, copper and nickel and mixtures of these metals using a flow-through cell divided with an ion exchange membrane. Iron was successfully removed from a synthetic AMD solution composed of FeSO4/H2SO4 via Fe(OH)3 precipitation outside the electrochemical cell by sparging the electrolysed catholyte with air. The work was extended to acidic solutions of Fe2+, Cu2+, and Ni2+, both singly and in combination, and to an authentic AMD sample containing principally iron and nickel.

Effects from different types of construction refuse in the soil on electrodialytic remediation

At abandoned industrial sites some of the previous buildings are often left behind. If the soil at such site is polluted with heavy metals and is to be remediated by an electrochemical method, the construction refuse within the soil matrix will influence the remediation action. The influence of different sorts of construction refuse on electrodialytic soil remediation was investigated in laboratory cells. An insulator, a stone, resulted in an uneven Cu removal in the close vicinity of the stone itself. An electric conductive screw disturbed the Cu removal due to the redox reactions occurring at the surface of the screw causing pH changes in the soil. Two types of refuse with ionic conducting properties were placed within the test cell, a piece of brick and concrete. The brick did not influence the Cu removal from the soil to a high extent, but it was seen that during the remediation the Cu concentration in the brick itself increased. In the case of concrete the Cu mobilized from the soil was simply found to adsorb very strongly to the concrete and thus the Cu could not be removed from the soil and the concrete as a whole. Furthermore, the removal of Cu in the soil next to the concrete was quite poor. It is very important to be aware of the presence of construction refuse at such sites when planning an electrochemical remediation action. All the refuse types investigated here influenced the Cu removal negatively compared to the reference experiment.

Electrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated soil

AbstractElectrokinetic remediation of lead‐, zinc‐ and cadmium‐contaminated sand and clayey soils has been investigated under laboratory‐scale conditions. Soil extracts of heavy metals (by 1 M HCl solution) were analysed by optical emission spectrometry. The efficiency of electrochemical remediation was partially dependent on the pH of the soil media. With pH increase, the migration of heavy metal ions toward the cathode was limited. When acetic acid was added to the sandy soil, almost complete remediation was achieved. A clay layer inserted in the cathode area did enhance the remediation rate. The most effective clean‐up was achieved for zinc and cadmium, with less effective clean‐up being achieved for lead. The effectiveness of the electrokinetic remediation of heavy metal‐contaminated clayey soil was low. The appropriate acidity was not achieved using acetic acid because of the high buffering capacity of clay, and metal ion migration was impeded by its sorption onto some clay components. The conclusion was made that clays could be used as immobilizing media for heavy metal ions by electrokinetic remediation of various soils.© 2001 Society of Chemical Industry

Laboratory Experiments on Electrochemical Remediation of the Environment. Part 5: Indirect H2S Remediation

Many polluting gases can be transformed to nonpolluting--or at least, less polluting--forms by changing the oxidation states of one or more of their constituent atoms. This can often be achieved by transferring electrons to or from the pollutant from or to an electrified interface. Since electrochemical remediation methods require an ion-conducting medium to perform their function, this can be accomplished either by using an absorption medium in an electrochemical cell (inner-cell process) or by absorbing the gas first and then transferring the absorption medium into the electrochemical cell to be treated (outer-cell process). Also, in such methods the polluting species can either undergo electron transfer on an electrode surface (direct method), or electrons can be shuttled to or from the electrode by an electron carrier (indirect method). We report here an experiment to demonstrate one way in which the electrochemical treatment of H2S can be accomplished by bubbling it through an iodine solution. A dramatic change in color occurs, due to the oxidation of S2- ions by I2, producing a suspension of yellow elemental S and colorless iodide ions. The resulting solution is then electrolyzed, regenerating the iodine and producing pure hydrogen. This cycle can be repeated many times with the same solution.

Mathematical Modeling of Electrochemical Remediation for Soils under Galvanostatic Conditions

This work proposes a mathematical model for the electrochemical remediation of clayey soils based on the total volume concept for a two-phase system. The mathematical formulation was done including contributions from theories for: groundwater, membranes, porous electrodes and environmental soil chemistry. The resulting model accounts for: free and complexed species in the soil matrix and the pore solution; chemical reactions taking place on either phase and/or between phases; a dynamic soil surface charge affected by the ion content of the pore solution; and electroneutrality of the total volume. Soil surface charge was included in a modified Ohm's law (voltage gradient) and in a modified Schlög's law (convective movement). Numerical implementation was done using orthogonal collocation on finite elements for spatial derivatives, and forward finite differences for time derivatives. Visual Fortran supported by IMSL subroutines was used for computer simulation. Model predictions were successfully compared with reported experimental data. Also, an analysis of pH profiles through the soil is provided for conditions when parameters including hydrostatic head, applied current density and initial pH are modified.

Electrochemical remediation of copper (II) from an industrial effluent

Electrochemical remediation of copper (II) from an industrial effluent

Incorporation of Radioactive Contaminants into Pyroaurite-Like Phases by Electrochemical Synthesis

AbstractDuring electrochemical remediation of radionuclide, 235U, 238U, and 99Tc-contaminated aqueous solutions, pyroaurite-like phases, ideally [M(II)M(III)(OH)16CO3·4H2O] where M = Fe, were synthesized following coprecipitation with iron from metal iron electrodes. The effect of radionuclides on the transformation of amorphous precipitates to crystalline pyroaurite-like phases was investigated using X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray analysis, Fourier-transform infrared (FTIR) spectroscopy, and fluorescence spectroscopy. The synthetic iron carbonate hydroxide phases showed primary XRD peaks at 0.7 and 0.35 nm and FTIR spectra that indicated the presence of a brucite-like sheet structure with carbonate anions occupying the interlayer. Divalent and trivalent iron, eroded from the electrode, occupies the octahedral sites of the brucite-like sheets. The carbonate anions in the interlayer balance the excess positive charge from isomorphous substitution of the Fe2+ or Fe3+ by reduced uranium (U4+) and technetium (Tc4+). Because of the lower solubility associated with crystalline phases than amorphous phases, incorporation of radioactive contaminants into pyroaurite-like phases by electrochemical syntheses represents a more effective approach for removing U and Tc from contaminated aqueous solutions than traditional technologies.

Electrochemical remediation of copper (II) from an industrial effluent Part II: three-dimensional foam electrodes

A batch recycle removal of copper ions from an industrial effluent by means of copper foam cathodes was tested. A constant current of 750 A was applied to the cell in order to perform the reduction. Copper depletion was investigated at different solution flow rates and a removal greater than 98% was obtained with a flow rate of 1000 l/h. The influence of initial metal concentration on copper deposition and current efficiency is also discussed.

Electrochemical remediation of copper (II) from an industrial effluent

Abstract Many studies indicate that flow-through reactors with three-dimensional electrodes can be successfully used for metal removal from dilute streams, but they present high capital costs. So the simplest titanium and stainless steel AISI 904L plate were chosen as cathode materials in tank reactors. A three cell plant was used for cathodic deposition of copper from an industrial effluent containing copper (II). The influence of the flow rate and the initial copper concentration on the removal efficiency and current yield was studied.

Electrochemical remediation of heavy metal contaminated soils

AbstractOver the years, many soils have been contaminated with toxic heavy metals as a result of a variety of industrial and military activities. Electrokinetic soil treatment is an emerging technology that could prove to be very effective in the remediation of these sites. “Real‐world” heavy metal contaminated (Pb(II), Cd(II), and Cr(III)) soils from three military sites with varying soil properties were subjected to electrokinetic treatment in the laboratory. Metal extractants (chelating agents and acids) were studied and found to be effective in enhancing the electrokinetic process. Results indicated that heavy metal removal efficiencies varied in the three soils tested. In one case, removal efficiencies of 90 percent and 60 percent were obtained for Cd and Cr, respectively, for the nitric acid amended experiments. For another case, over 60 percent of the total Pb in the system was deposited near the cathode for the non‐amended and the citric‐acid amended tests. Conversely, in the third case, the electrokinetic soil‐washing treatment process failed to produce significant removal of any metal contaminant. The discrepancies that exist between the metal removal results of the three soils were attributed to the different physiochemical characteristics of each soil.

Chloride Transport in Concrete Subjected to Electric Field

Chloride transport in concrete is often subject to an electric field. This may arise from an internal source, such as the development of a membrane potential, or it may be imposed on the concrete by an external source, as is often the case when electrochemical remediation techniques are applied and accelerated chloride diffusion tests are undertaken. In this work the theory of chloride migration and its practical applications are reviewed. The migration of ions in an electric field differs from other transport processes in that positive and negative ions move in opposite directions, and the condition of electroneutrality does not impose the same constraint on the transport of ions as would otherwise be the case. Well established laws with appropriate boundary conditions have been used to model chloride transport in concrete under electrochemical chloride extraction and cathodic protection conditions, as well as in accelerated chloride diffusion tests. The minimum electric field that will prevent further chloride contamination may be regarded as the threshold requirement for chloride removal and also provides a basis for a corrosion prevention measure in its own right. The quantification of the membrane effects of concrete on the transport of chloride ions and the time dependence of chloride binding and dissolution require further research.

Laboratory Experiments on the Electrochemical Remediation of Environment. Part 4: Color Removal of Simulated Wastewater by Electrocoagulation-Electroflotation

Due to the large production of aqueous waste streams from textile mills and dye production plants, several processes have been under intense study. Electrochemical processes offer some distinctive advantages, including effects due to: 1) the production of electrolysis gases, and 2) the production of polyvalent cations from the oxidation of corrodible anodes (like Fe and Al). The gas bubbles can carry the pollutant to the top of the solution where it can be more easily concentrated, collected and removed. The metallic ions can react with the OH- ions produced at the cathode during the evolution of H2 gas to yield insoluble hydroxides that will adsorb pollutants out of the solution and also contribute to coagulation by neutralizing any negatively charged colloidal particles that might be present. In this experiment an iron electrode (paper clip) is used in conjunction with pH indicator dyes, so dramatic color changes will be noticed.

Laboratory Experiments on Electrochemical Remediation of the Environment Part 3: Microscale Electrokinetic Processing of Soils

Electrochemical remediation of the environment is gaining widespread acceptance due to the mild conditions used, the cleanliness of the electron as a reagent, the easiness for automation, its versatility, etc. In this paper three phenomena are presented at the microscale level, originating from the application of an electric field to a simulated soil sample: a) Demonstration of metal ion migration, b) Demonstration of the creation and movement of an acidic and a basic front, and c) Demonstration of water movement through soil.

Electrochemical remediation of metal-bearing wastewaters Part II: Corrosion-based inhibition of copper removal by iron (iii)

A hitherto undocumented inhibition to electrodeposition of Cu(ii) from dilute (<200 mg L−1) wastewaters was traced to the presence of Fe(iii) at concentrations comparable to those of copper ion. This inhibition was found to differ from heterogeneous side-reduction of Fe(iii) that is well known to decrease faradaic efficiency for copper removal. Based on bench-scale electrolysis as well as cyclic voltammetry studies, an inhibition mechanism was qualitatively identified that involved copper corrosion by Fe(iii). This corrosion process was found to be strongly favoured by sluggish heterogeneous reduction of Fe(iii) at carbon electrode materials. One procedure shown to substantially improve copper removal from solutions demonstrating corrosion inhibition was alkali precipitation of iron. Real mine drainage wastewater that was pretreated in this manner was consistently depleted of copper by flow-through electrolysis to levels below 50 μg L−1.

Laboratory Experiments on Electrochemical Remediation of the Environment. Part 2: Microscale Indirect Electrolytic Destruction of Organic Wastes

The objective of this experiment is to destroy, at the microscale level, a sample of surrogate organic waste by generating a powerful oxidizer at the anode of an electrochemical cell. This generated species oxidizes the waste to harmless products. The oxidizer can then be regenerated and recycled. Specifically, this experiment utilizes a redox mediator with a high standard potential (i.e., the Co (III/II) couple, E° = 1.82 V) to destroy a surrogate organic waste (e.g., glycerin or acetic acid) by converting it into CO2 and water. Students can observe the end of the reaction signaled by a color change of the electrolytic medium (from pink to gray-light purple) as well as the evolution of CO2 which precipitates CaCO3 from a Ca(OH)2 solution. The Co(II) solution and the electrodes can then be reused.