Robert J. Gale

Electrokinetic remediation: Basics and technology status

Abstract Electrokinetic remediation, variably named as electrochemical soil processing, electromigration, electrokinetic decontamination or electroreclamation uses electric currents to extract radionuclides, heavy metals, certain organic compounds, or mixed inorganic species and some organic wastes from soils and slurries. An overview of the principals of the electrokinetic remediation technique in soils is presented. The types of waste and media in which the technology could potentially be applicable are outlined and some envisioned environmental uses of conduction phenomena in soils under electric fields are presented. The current status of the electrokinetic remediation technique and its limitations are discussed through a review of the bench-scale and pilot-scale tests. The recent findings of research on different techniques that may improve the technologys effectiveness are mentioned and the status of ongoing efforts in wide-scale implementation and commercialization of the technique in the USA are described.

ENHANCED ELECTROKINETIC REMEDIATION OF HIGH SORPTION CAPACITY SOIL

Abstract In unenhanced electrokinetic remediation of metals, electrolysis reactions at the cathode generate a high pH medium that results in metal precipitation and immobilization in the soil. Different enhancement procedures could be utilized at the electrodes to prevent or hinder the generation and transport of this alkaline medium into the soil. This study investigates the feasibility of enhanced extraction of metals from high sorption capacity soils by the use of acetic acid to neutralize the cathode electrolysis reaction and also the use of an ion selective (Nafion TM ) membrane to prevent back-transport of the OH − generated at the cathode. Synthetic soil samples spiked with lead were used in the testing. Synthetic soils were a mixture of 40% illite, 8% kaolinite, 5% Na-montmorillonite and 47% fine sand representing an illitic deposit. The results demonstrate the feasibility of extracting lead from the deposit. Acetic acid and Nafion enhancement resulted in better removal efficiencies and lead electrodepositions at the cathode compared to unenhanced tests. However, higher energy expenditure and longer processing periods were required when compared to enhanced extraction of lead from kaolinite. Acetic acid tests required less energy than membrane tests.

Fundamentals of extracting species from soils by electrokinetics

Abstract Bench-scale and pilot-scale studies demonstrate that ionic contaminant species, some organic contaminants, and certain radionuclides can be removed efficiently from fine-grained deposits by application of electrical currents across a soil mass, through electrodes that allow gress and ingress of a pore fluid. This technique (electrokinetic remediation or electrochemical soil processing) results in soil acidification, contaminant desorption, transport, accumulation, and removal. A review of the fundamentals of the process and the theoretical development, together with a review of considerations and limitations for full-scale application of the technique for site remediation, are presented.

Electrochemical processing of soils: Theory of pH gradient development by diffusion, migration, and linear convection

Abstract A theory, based on the Nernst‐Planck equations, is presented for pH gradient development during the electrochemical processing of soils. Its premises and consequences are discussed in terms of using electrochemical techniques for the decontamination of polluted media. Formation of an acidic front at the anode from water electrolysis and the induced electro‐osmotic flow of pore fluid contribute to facilitate removal of contaminants. The model provides a first‐order, mathematical framework to examine the flow patterns and chemistry generated in electro‐osmosis. Analytical solutions are compared with the numerical results obtained by the finite element method (FEM) and with some preliminary experimental results. Upstream‐downstream effects are included but consolidation effects, neutralization, and ion exchange reactions need to be quantified and incorporated into the model. The physical basis of electro‐osmosis phenomenon needs to be better established. Modelling approaches of this type should assi...

Optimization of 2-D Electrode Configuration for Electrokinetic Remediation

A practical evaluation of one- and two-dimensional applications of electric fields for in situ extraction of contaminants is provided. The evaluation is based on contaminant transport by electroosmosis and ion migration. Parameters evaluated include electrode requirements, effectiveness of electric field distribution, remediation time, and energy expenditure. Formulation is provided for calculating cost components of the process, including electrode, energy, chemicals, posttreatment, fixed, and variable costs. Equations are also provided for evaluating optimum electrode spacings based on energy and time requirements. The derivations show that spacing between same-polarity electrodes is as significant in cost calculations and in process effectiveness as that between anodes and cathodes. Decreasing the same-polarity electrode spacing to half the anode-cathode spacing will result in a 100% increase in electrode requirements, but will decrease the area of the ineffective electric field by one half. Selection ...

ELECTROKINETIC SOIL PROCESSING COMPLICATING FEATURES OF ELECTROKINETIC REMEDIATION OF SOILS AND SLURRIES: SATURATION EFFECTS AND THE ROLE OF THE CATHODE ELECTROLYSIS.

Abstract Electrokinetic soil processing is an emerging technology for decontamination of certain radionuclides, heavy metals, or organic species from soils or slurries. Tests reveal that the process efficiencies in partially saturated kaolinite samples (without contaminants) are high, since water supplied at the anode eventually flushed across the specimens and saturated the deposits. Consolidation settlements are expected in the vicinity of anodes in fine-grained soils, even when both electrodes allow ingess or egress of the water. Uranyl ion at 1000 pCi/g could be effectively removed from kaolinite but the removal efficiency decreased close to the cathode due to the high pH in this region. A yellow uranium hydroxide precipitate was collected at the cathode. Thorium ion, even at 300 pCi/g, could not be efficiently removed throughout the cell because of its high adsorptive capacity, facile hydrolysis, and the precipitation of insoluble hydroxide. Methods are required to prevent hydroxide ion formation by ...

In situ TCE bioremediation study using electrokinetic cometabolite injection

Abstract The feasibility was evaluated of using electrokinetic injection of benzoic acid cometabolite to enhance the biodegradation of a representative recalcitrant contaminant, trichloroethene (TCE). Whereas in flask studies, sulfate ion alone enhanced TCE (at 6 ppm) degradation rates over those found in the absence of suitable additives, benzoic acid showed enhanced degradation rates for TCE at 6–50 ppm levels. Following injection of benzoic acid cometabolite into a 1 m column of TCE contaminated Loess clay, the TCE first order degradation rate at the periphery was determined to be (0.039±0.007) day −1 , a value in good agreement with an anaerobic slurry flask tests at 30°C, (0.047±0.009) day −1 . However, unless the rate of injection of an additive is made compatible with its rate of consumption, these column results and a theoretical model reveal that homogeneous penetration of additive is not achieved. It is cautioned that knowledge of the rate of degradation of a carbon source enhancer (or additive) is critical for engineering its homogeneous injection, whether by hydraulic or electrokinetic methods. These results demonstrate that electrokinetic degradation of recalcitrant wastes may be practical, in particular for those sites whose soil media have low coefficients of hydraulic permeability (clay deposits, silty clays, etc.) where traditional pump and treat technology is ineffective.

Surfactant Enhanced Desorption of TNT from Soil

Surfactant enhanced desorption of 2,4,6-trinitrotoluene (TNT) from contaminated soils at a military site was investigated. Anionic (SDS and DOWFAX 8390), cationic (CTAC and CTAB), and nonionic (Tween 80 and Brij 35) surfactants were first tested at concentrations ranging from 0.1 to 1%. The anionic and nonionic surfactants were further tested at concentrations of up to 10%. Anionic surfactants, particularly SDS, provided the best desorption of TNT from the soil. There was not any increase in TNT desorption for both the nonionics and cationics at concentrations ranging between 0.1 to 1% and the extent of desorption was found to be lower than the TNT desorption only by water. The competition of the negatively charged soil surfaces for the positively charged cationics and the neutral nonionic surfactants may constitute the underlying reason. TNT was significantly desorbed when the concentrations of Tween 80, DOWFAX 80 and SDS were increased up to 10%.

Lithium Ion Association with Sodium Phytate and the Effects on the Conformational Equilibria. Implications in the Physiological Effects of Lithium

Abstract 31P NMR was employed to examine the solution interactions of lithium and potassium ions with sodium phytate. The phytate molecular conformation was found to be pH and concentration dependent. The conformational equilibria of sodium phytate in aqueous solution was not affected by the addition of potassium ions, however, it was influenced by added lithium ions and was dependent on lithium ion concentration. Furthesmore, the phytate molecule showed some selectivity for lithium ion association over potassium and sodium ions. Possible implications in the physiological effects of lithium are discussed.

Remediation of Soils Contaminated with Tetraethyl Lead by Electric Fields

Four tests were conducted to investigate potential uses of electric fields for remediation of high buffering capacity soils contaminated with high lead concentrations (11 percent by dry weight). The soil samples were collected from a site in Louisiana where tetraethyl lead was used extensively for increasing the octane rating of leaded gasoline. Calcium was present at relatively high concentrations (9 percent by dry weight). Initial soil pH was basic (about 8.5). Two enhancement procedures were used: acetic acid for neutralizing the cathode and membranes to prevent migration of hydroxyl ions from the cathode. Current densities applied were in the order of 5 A/m2 to 10 A/m2. Tests were processed for up to 3,220 hours. Lead extraction rates were significantly affected by high calcium concentration. Energy expenditure was very high (up to 20 667 kWh/m3 in the unenhanced test). The study showed that the soil buffering capacity significantly affected energy requirements, cost-effectiveness, and success of the process. Efficient extraction of lead in soils will be controlled by the presence of high concentrations of soluble ions (such as calcium) in the soil.