Low-permeability Materials Research Articles

Influence of Chemical Osmosis on Solute Transport and Fluid Velocity in Clay Soils

AbstractSolute transport through the clay liner is a significant process in many waste landfills or unmanaged landfills. At present, researchers mainly focus on the test study about semi-membrane property of clay material, however, the influence of chemical osmosis caused by membrane effect on solute transport and fluid velocity is insufficient. In this investigation, based on the classical advection-diffusion equation, a one-dimensional solute transport model for low-permeable clay material has been proposed, in which the coupled fluid velocity related with hydraulic gradient and concentration gradient is introduced, and the semi-membrane effect is embodied in the diffusion mechanism. The influence of chemical osmosis on fluid velocity and solute transport has been analyzed using COMSOL Multiphysics software. The simulated results show that chemical osmosis has a significant retarded action on fluid velocity and pollutant transport. The proposed model can effectively reveal the change in process of coupled fluid velocity under dual gradient and solute transport, which can provide a theoretical guidance for similar fluid movement in engineering.

Modeling of the groundwater flow system in excavated areas of an abandoned mine

This study evaluated the assumption that back-filled excavated areas of old mine workings can be modeled as porous media, where groundwater flow is governed by Darcy's law. The Yatani mine, located in Yamagata Prefecture, Japan, was selected for this study because several mining methods were used during its operation and detailed drawings of the excavated areas of the mine are available. The model was calibrated using combinations of hydraulic conductivities (k), with the best-matched case being selected by comparing calculated and measured AMD fluxes. Modeled AMD fluxes along the drainage tunnel (−2 L level) were consistent with measured data when the excavated areas were considered to be porous media with a specific hydraulic conductivity, and the presence of faults and permeability were taken into account. The model also successfully predicted the increasing trend of AMD flux from the shaft to adit mouth. In the numerical model, the back-filled excavated areas were assumed to behave as porous media, which was shown to be a valid assumption in this mine. The model demonstrated that back-filling the excavated areas and drainage tunnel with low permeability materials could reduce the flux of Zn in AMD by up to 61%.

Rapid Drawdown in Homogeneous Earth Dam Considering Transient Flow and Suction

The present work intends to demonstrate the advantages of considering transient flow regime in the stability analysis of the upstream slope for the rapid drawdown situation of a homogeneous earth dam. Upstream slope stability evaluations were carried out, considering pore pressure and suction from transient flow analysis while simulating rapid drawdown of the reservoir. The evaluations comprised different geometries of the upstream slope (from 1V:1.1H to 1V:2.5H) and heights varying from 10 m to 50 m, as well as several low permeability materials (SM, SM-SC, SC, ML, ML-CL, CL, MH and CH). In addition, equations relating the safety factor to such slopes or dam height were adjusted to the analysis data, in order to define the minimum slope for a certain dam height or the maximum height for a given upstream slope. The results have shown that, considering the transient flow condition, including suction, within the slope stability analysis of the rapid drawdown situation, increases the safety factor in relation to the simplified analysis that is usually adopted. This also results in much steeper slopes (for a safety factor of 1.1) than the ones recommended by the U.S. Bureau of Reclamation (USBR), suggesting the importance of performing transient flow analysis for rapid drawdown situations and considering its results instability analysis.

Porosity Measurement of Low Permeable Materials Using Gas Expansion Induced Water Intrusion Porosimetry (GEIWIP)

Porosity measurement is a key factor to identify the hydraulic performance of low permeable porous materials (e.g. rock or concrete). Porosimetry tests such as Mercury Intrusion Porosimetry (MIP), Nuclear Magnetic Resonance (NMR), or Gas Expansion (GE) are cost-prohibitive, use hazardous materials, or are incapable of accessing all inter-connected pores. An alternative Gas Expansion Induced Water Intrusion Porosimetry (GEIWIP) method was developed to measure the porosity of a low permeable porous medium using a gas/water intrusion apparatus. This method overcomes the previously mentioned porosimetry drawbacks by using distilled de-aired water (DDW) as a hazard-free liquid which is a wetting fluid to intrude the porous structure and fill the pores. As the DDW has the tendency to fill all inter-connected pores, no back-up pressure is required. This method has lower cost and needs less preparation time comparing to MIP test. Additionally, the GEIWIP set-up, the gas/water intrusion apparatus, can be moved to the field site and provide mobile measurement feasibility. The reliability of the test results was obtained by a repetitive testing process. The porosity of concrete samples with different mixtures was obtained and compared to those of MIP and NMR tests.

Towards Creation of Ceramic-Based Low Permeability Reference Standards

Low-permeable materials, either artificial or natural, are essential components of the current technological development. Their production or processing requires a comprehensive characterization method based on confident reference standards. Permeability standards for values below 10−15 m2 are lacking. In this study, we explored the feasibility of using the ceramic sintering process to reach low, but measurable values of gas permeability in Al2O3 samples, as one of the potential materials for reference standards. The studied samples were produced with a ceramic 3D printer, which enables the manufacturing of low-permeable samples having complex geometrical arrangements. A series of preliminary laboratory testing indicated the available gas permeability range from 2.4 × 10−15 m2 for the pre-sintered samples to 1.8 × 10−21 m2 for the sintered samples. The verification of the permeability reduction was carried out using a unique unsteady state fast and accurate measurement method. The results confirm the possibility of developing a technology for materials manufacturing with low porosity and permeability. Such materials open many areas for application, including manufacturing of ceramics with controlled transport properties and low-permeability standards for calibrating laboratory equipment for geosciences, construction industries, biomedical, and other relevant fields.

A phase field framework for capillary-induced fracture in unsaturated porous media: Drying-induced vs. hydraulic cracking

This manuscript introduces a unified mathematical framework to replicate both desiccation-induced and hydraulic fracturing in low-permeable unsaturated porous materials observed in experiments. The unsaturated porous medium is considered as a three-phase solid–liquid–gas effective medium of which each constituent occupies a fraction of the representative elementary volume. As such, an energy-minimization-based phase-field model (PFM) is formulated along with the Biot’s poroelasticity theory to replicate the sub-critical crack growth in the brittle regime. Unlike hydraulic fracturing where the excess pore liquid pressure plays an important role at the onset and propagation of cracks, desiccation cracks are mainly driven by deformation induced by water retention. Therefore, the wettability of the solid skeleton may affect the evolution of the capillary pressure (suction) and change the path-dependent responses of the porous media. This air–water–solid interaction may either hinder or enhance the cracking occurrence. This difference of capillary effect on crack growth during wetting and drying is replicated by introducing retention-sensitive degradation mechanisms in our phase field fracture approach. To replicate the hydraulic behaviors of the pore space inside the host matrix and that of the cracks, the path-dependent changes of the intrinsic permeability due to crack growth and porosity changes are introduced to model the flow conduit in open and closed cracks. Numerical examples of drying-induced and hydraulic fracturing demonstrate the capability of the proposed model to capture different fracture patterns, which qualitatively agrees with the fracture mechanisms of related experiments documented in the literature.

Actively facilitated permeable reactive barrier for remediation of TCE from a low permeability aquifer: Field application

Proven in situ treatment and remediation approaches are limited for low-permeability aquifers materials, particularly because of limitations to the delivery of reactive chemicals or access to contaminated plumes. In this paper, we describe the development of a cutting-edge solution for the remediation of contaminated groundwater in a low-permeability and low water-bearing aquifer contaminated with the chlorinated hydrocarbon trichloroethylene (TCE). The remediation technique introduced coupling of large-diameter permeable reactive barrier wells (PRB wells) with: (1) extraction wells through in a highly impacted plume; and (2) re-injection wells at the fringe of the plume. A pump-and-treat system (PTS) was employed at the site in a separate plume to reduce the mass of TCE near the second source zone. This research focuses only on the large diameter PRB well system. Conceptual site model development, design considerations, implementation and performance evaluation demonstrated how each of these elements were applied in the field. Approaches for coupling technologies to increase technical and economic feasibility are presented. Extraction and reinjection wells of treated groundwater at the fringe of the plume promoted a positive hydraulic gradient, facilitated groundwater transport through the reactive media, and contained the plume. Detailed geospatial and statistical analysis with over 10 years’ monitoring data showed that dissolved TCE plume delineation shrank, and still concentration continues to decline, and were projected to meet the demands of remediation compliance regulations in the next few years. The results of this study indicate that significant remediation was achieved despite the challenging hydraulic conditions of the aquifer. The developed the remediation technology and conclusions indicate the system’s usefulness at other sites.

Correction to: A Two-Parametric Model for Gas Flow in Low-Permeable Porous Materials

Correction to: A Two-Parametric Model for Gas Flow in Low-Permeable Porous Materials

A Two-Parametric Model for Gas Flow in Low-Permeable Porous Materials

Capillary flow at low pressure gradients is determined by the pore structure of the matrix and the viscosity of the fluid. Traditionally, the conductivity of porous materials is characterized by a single parameter—the coefficient of permeability—which includes all geometric and structural resistances of the capillary structure. The fluid is described by its dynamic viscosity, which is independent of pressure in liquids. Gases, on the other hand, are highly compressible which means that their coefficient of permeability is becoming pressure dependent. The Klinkenberg effect takes account of this behaviour by introducing the notion of intrinsic permeability; nevertheless, it remains applicable only to a limited pressure range. At low- and high-pressure gradients, the Klinkenberg linearization deviates considerably from the real flow behaviour. This paper demonstrates that microporous capillary resistance to gas flow cannot be adequately described by a single material parameter. On the basis of ideal gas law conditions, the mass flow is derived by a two-parametric power law. Pore pressure decline is characterized by a permeability exponent n and a reference velocity v1, replacing both dynamic viscosity of the fluid and permeability. The actual pressure distribution over the flow path is expressed by means of an equation of motion which leads to a logarithmic linearization of the material parameters. Velocity and acceleration vectors are derived and discussed in relation to the actual pressure distribution. The two parameters n and v1 remain constant throughout and independent of pore pressure and are thus used to describe the flow rates over the entire pressure range. This model is then validated by means of flow analyses based on data given in the literature and compared to the classical theory of permeability.

Water hammers tremors during plate convergence

Research Article| October 23, 2018 Water hammers tremors during plate convergence An Yin An Yin * 1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California 90095-156702, USA *E-mail: ayin54@gmail.com Search for other works by this author on: GSW Google Scholar Geology (2018) 46 (12): 1031–1034. https://doi.org/10.1130/G45261.1 Article history received: 12 Jun 2018 rev-recd: 19 Sep 2018 accepted: 25 Sep 2018 first online: 23 Oct 2018 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Tools Icon Tools Get Permissions Search Site Citation An Yin; Water hammers tremors during plate convergence. Geology 2018;; 46 (12): 1031–1034. doi: https://doi.org/10.1130/G45261.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyGeology Search Advanced Search Abstract In this study, I show that rapid (∼100 km/h) dip-parallel tremor migration at seismic-aseismic transition depths (15–55 km) of a convergent margin can result from pressure-wave propagation in an anisotropic viscoplastic shear zone. The anisotropy is characterized by slip-parallel conduits in the dip direction composed of high-permeability brittle mafic rocks embedded in low-permeability ductile felsic materials. At the onset of a slow-slip event, the initial compaction of a mafic conduit causes permeability reduction that in turn can lead to partial or complete blockage of flow path. Due to the water-hammer effect, the sudden blockage of flow paths can trigger a propagating pressure wave with an elevated pore-fluid pressure, which is capable of initiating a progressive shear failure expressed as migrating tectonic tremors along the conduit. For a mafic conduit with a pre-slip static permeability of ∼10−13 m2 and a syn-slip dynamic permeability of 10−15 m2, the water-hammer model generates a pressure jump of up to 50 kPa, sufficient to initiate tremors along subduction zones and shear-zone deformation during the same slow-slip event. You do not currently have access to this article.

Lead (II) Removal from Contaminated Soils by Electrokinetic Remediation Coupled with Modified Eggshell Waste

Electrokinetic remediation deserves particular attention in soil treatment due to its peculiar advantages, including the capability of treating fine and low permeability materials, and achieving consolidation, dewatering and removal of salts and inorganic contaminants like heavy metals in a single stage. In this study, the remediation of artificially lead (II) contaminated soil by electrokinetic process, coupled with Eggshell Inorganic Fraction Powder (EGGIF) permeable reactive barrier (PRB), was investigated. An electric field of 2 V cm-1was applied and was used an EGGIF/soil ratio of 30 g kg-1 of contaminated soil for the preparation of the permeable reactive barrier (PRB) in each test. It was obtained high removal rates of lead in both experiments, especially near the cathode. In the normalized distance to cathode of 0.2 it was achieved a maximum removal rate of lead (II) of 68, 78 and 83% in initial lead (II) concentration of 500 mg-1, 200 mg-1 and 100 mg-1, respectively. EGGIF (Eggshell Inorganic Fraction) proved that can be used as permeable reactive barrier (PRB) since in all the performed tests were achieved adsorptions yields higher than 90%.

On modelling of consolidation processes in geological materials

Low-permeablity materials may be seen as natural geological barriers for radioactive waste repositories. However, to ensure their safe performance, a good understanding of their mechanical properties is required. Although the standard Biot's poroelastic model is widely used to estimate the key properties of these materials, experimental observations differ from this mathematical formulation and suggest that a more complex rock deformation behaviour to include a creep effect is needed. In this study, the Biot's differential equations are modified to include a rheological skeleton. In comparison with other existing models, here we propose a formulation with a minimal parametric uncertainty: we show that with just one additional physically-based parameter, the experimental creep behaviour is properly described. This enhanced model is implemented within a finite element framework and employed in a fitting algorithm to extract the hydro-mechanical properties from experimental data. To illustrate its generality, we analyse laboratory tests performed on three different types of materials: (a) an unlithified lower Oligocene clay from Belgium (Boom Clay), (b) an indurated Jurassic mudrock (Callovo-Oxfordian mudstone) and (c) a Triassic siltstone (Mercia Mudstone Formation). Numerical fits to the data support the validity of this approach and demonstrate its applicability to a range of low-permeability materials regardless of mineralogy or burial history.

KG²B, a collaborative benchmarking exercise for estimating the permeability of the Grimsel granodiorite – Part 1: measurements, pressure dependence and pore-fluid effects

Measuring the permeability of tight rocks remains a challenging task. In addition to the traditional sources of errors that affect more permeable formations (e.g. sample selection, non-representative specimens, disturbance introduced during sample acquisition and preparation), tight rocks can be particularly prone to solid–fluid interactions and thus more sensitive to the methods, procedures and techniques used to measure permeability. To address this problem, it is desirable to collect, for a single material, measurements obtained by different methods and pore-fluids. For that purpose a collaborative benchmarking exercise involving 24 laboratories was organized for measuring the permeability of a single low permeability material, the Grimsel granodiorite, at a common effective confining pressure (5 MPa). The objectives of the benchmark were: (i) to compare the results for a given method, (ii) to compare the results between different methods, (iii) to analyze the accuracy of each method, (iv) to study the influence of experimental conditions (especially the nature of pore fluid), (v) to discuss the relevance of indirect methods and models and finally (vi) to suggest good practice for low permeability measurements. In total 39 measurements were collected that allowed us to discuss the influence of (i) pore-fluid, (ii) measurement method, (iii) sample size and (iv) pressure sensitivity. Discarding some outliers from the bulk data set (4 out of 39) an average permeability of 1.11 × 10−18 m² with a standard deviation of 0.57 × 10−18 m² was obtained. The most striking result was the large difference in permeability for gas measurements compared to liquid measurements. Regardless of the method used, gas permeability was higher than liquid permeability by a factor approximately 2 (kgas = 1.28 × 10−18 m² compared to kliquid = 0.65 × 10−18 m²). Possible explanations are that (i) liquid permeability was underestimated due to fluid-rock interactions (ii) gas permeability was overestimated due to insufficient correction for gas slippage and/or (iii) gases and liquids do not probe exactly the same porous networks. The analysis of Knudsen numbers shows that the gas permeability measurements were performed in conditions for which the Klinkenberg correction is sufficient. Smaller samples had a larger scatter of permeability values, suggesting that their volume were below the Representative Elementary Volume. The pressure dependence of permeability was studied by some of the participating teams in the range 1–30 MPa and could be fitted to an exponential law k = ko.exp(–γPeff) with γ = 0.093 MPa−1. Good practice rules for measuring permeability in tight materials are also provided.

KG²B, a collaborative benchmarking exercise for estimating the permeability of the Grimsel granodiorite—Part 2: modelling, microstructures and complementary data

Measuring and modelling the permeability of tight rocks remains a challenging task. In addition to the traditional sources of errors that affect more permeable formations (e.g. sample selection, non-representative specimens, disturbance introduced during sample acquisition and preparation), tight rocks can be particularly prone to solid–fluid interactions and thus more sensitive to the methods, procedures and techniques used to measure permeability. To address this problem, it is desirable to collect, for a single material, measurements obtained by different methods and pore fluids. For that purpose, a benchmarking exercise involving 24 laboratories was organized for measuring and modelling the permeability of a single low-permeability material, the Grimsel granodiorite. The objectives of the benchmark were: (i) to compare the results for a given method, (ii) to compare the results between different methods, (iii) to analyse the accuracy of each method, (iv) to study the influence of experimental conditions (especially the nature of pore fluid), (v) to discuss the relevance of indirect methods and models and finally (vi) to suggest good practice for low-permeability measurements. To complement the data set of permeability measurements presented in a companion paper, we focus here on (i) quantitative analysis of microstructures and pore size distribution, (ii) permeability modelling and (iii) complementary measurements of permeability anisotropy and poroelastic parameters. Broad ion beam—scanning electron microscopy, micro-computerized tomography, mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) methods were used to characterize the microstructures and provided the input parameters for permeability modelling. Several models were used: (i) basic statistical models, (ii) 3-D pore network and effective medium models, (iii) percolation model using MICP data and (iv) free-fluid model using NMR data. The models were generally successful in predicting the actual range of measured permeability. Statistical models overestimate the permeability because they do not adequately account for the heterogeneity of the crack network. Pore network and effective medium models provide additional constraints on crack parameters such as aspect ratio, aperture, density and connectivity. MICP and advanced microscopy techniques are very useful tools providing important input data for permeability estimation. Permeability measured—orthogonal to foliation is lower that—parallel to foliation. Combining the experimental and modelling results provide a unique and rich data set.

Stretchable Seal.

Many stretchable electronic devices require stretchable hermetic seals. However, stretchability and permeability are inextricably linked at the molecular level: stretchable, low-permeability materials do not exist. We collect data for the permeation of water and oxygen in many materials and describe the scaling relations for both flat and wrinkled seals. Whereas flat seals struggle to fulfill the simultaneous requirements of stretchability, low stiffness, and low transmissibility, wrinkled seals can fulfill them readily. We further explore the behavior of wrinkled seals under cyclic stretch using aluminum, polyethylene, and silica films on elastomer substrates. The wrinkled aluminum develops fatigue cracks after a small number of cycles, but the wrinkled polyethylene and silica maintain low transmissibility after 10 000 cycles of tensile strain.

Numerical study of tritium transport characteristics in Thorium Molten Salt Reactor with Solid Fuel (TMSR-SF)

Abstract Tritium control is one of the most key issues for the development of Molten Salt Reactor (MSR). The tritium transport characteristics in 2MWth Thorium Molten Salt Reactor-Solid Fuel (TMSR-SF) proposed by Shanghai INstitute of Applied Physics (SINAP) is studied in this paper. Three works are conducted: Firstly, an integrated numerical model is established, including tritium production, adsorption, diffusion, corrosion and permeation. Secondly, the Tritium trAnsPort chAracteristics analysiS code (TAPAS) for TMSR-SF is developed and benchmarked. The results prove the fidelity and accuracy of TAPAS. Finally, the distributions of the key variables including TF, T2 and Cr2+ in TMSR-SF system at both steady and transient state are obtained. In addition, some methods for tritium mitigation are evaluated by TAPAS. Numerical results show that tritium can be efficiently removed from the molten salt via graphite absorption. The amount of T2 at steady state is two orders of magnitude more than TF. Tritium permeation can be prevented by increasing 7Li enrichment and reducing redox potential. Tungsten or similar low-permeability material is a candidate for tritium barrier when covered on the surface of the heat exchanger wall. This work provides some valuable considerations for the tritium control in the MSR.

Electrokinetic in situ leaching of gold from intact ore

Electrokinetic in situ leaching (EK-ISL) is a novel in situ mining technology that uses an electric field to induce the migration of lixiviants through the subsurface to extract target commodities. Based on previous experiments with fine-grained unconsolidated material, this study assesses the feasibility of EK-ISL of gold from consolidated, unfractured, low-permeability ore material. Under the initially tested laboratory conditions, substantial ionic transport through low-permeability rock was achieved by applying a constant voltage. Subsequently, synthetic gold ore was positioned in between two rock sections and gold was successfully mobilised from the synthetic ore, transported through the second rock piece and collected in the target reservoir, albeit at a fairly slow rate. EK-ISL was then applied to two different gold ore samples. Both ores consumed considerable amounts of lixiviant before gold breakthrough occurred. Within the experimental timeframe, only a trace of gold was leached from Ore Sample 1. Nevertheless, over 50% of gold was recovered from Ore Sample 2 within a month after initial breakthrough. These experiments show that EK-ISL of gold from intact rocks is feasible, and also highlight the importance of characterising the reactivity of the host rock with respect to the selected lixiviant system prior to attempting EK-ISL. It was also found that during EK-ISL the hydraulic permeability of the ore was increased as a result of the dissolution of gangue minerals, which enhanced electro-migration of ions over the investigation timeframe.

Evaluation of liquid transport properties of hydrophobic polymers of intrinsic microporosity by electrical resistance measurement

In this work, the electrical resistance method was used to get an insight of the liquid transport through the polymers with excess of fractional free volume. The dense films based on the first generation of polymers of intrinsic microporosity, disubstituted polyacetylenes PMP and PTMSP, were used; water-ethanol binary mixtures allowed to adjust the affinity of the liquid phase to selected polymers continuously. In this work, the liquid-membrane interaction was considered as a stepwise occupation of accessible free volume elements within the polymer, while the appearance of continuous (pseudo)liquid channels in the polymeric matrix, so-called percolation clusters, was required for formation of hydrodynamic liquid transport. Since the appearance of such percolation clusters might dramatically change the conductivity of hydrophobic materials, it was proposed to use the electrical resistance method to investigate the evaluation of selected polymers from being a barrier (water) to being permeable (ethanol) with respect to the liquid composition. To highlight the electrical resistance of the swollen films, all water/ethanol solutions contained NaCl (0.5 g/L). The steady-state values of liquid permeation, sorption/swelling, and electrical conductivity data were considered together and discussed. The electric resistance was significantly varied for 30 µm dense films of PMP (1–1300 kΩ) and PTMSP (0.15–910 kΩ) by the adjustment of ethanol content in water. The phase shift (25– 100,000 Hz) illustrated that the behavior of PTMSP and PMP membranes changed from mainly capacitive at low ethanol concentrations to the ion conductive as higher ethanol content. The very good quantitative agreement was found between the relative change of the membrane electrical resistance and the permeability as a function of the ethanol content in the liquid phase. Consequently, electrical resistance measurements could be used as an express method to determine the membrane permeability of low permeable materials, since the time required to get steady-state results was found to be much shorter for electrical resistance measurements than for permeability measurements.

Light transmission method to explore the migration and distribution of Cr(VI) in a sandy aquifer

The migration and distribution of contaminants in heterogeneous aquifers are mostly investigated through numerical simulations. They are rarely examined through experimental simulations because of sampling difficulties. In this study, we used the light transmission method (LTM) to explore the migration and distribution of hexavalent chromium [Cr(VI)] in homogeneous sandy aquifers with or without a low-permeability bottom and lens (heterogeneous aquifer). Experimental phenomena were observed via images obtained with a high-power light source. The migration distances of pollution plume were also monitored. Under heterogeneous conditions, low-permeability aquifer materials considerably inhibited the migration of Cr(VI) and altered the Cr(VI) migration rate of horizontal and vertical plumes spread to a certain extent. Common horizontal and vertical migration curve equations in all three conditions were also obtained through distance–time curve fitting. The difference between high- and low-concentration zones was accurately revealed, and the experimental phenomenon was further explained. The proposed method could be used for the qualitative investigation and visualization of the migration and distribution of Cr(VI).

Low Permeability Zone Remediation via Oxidant Delivered by Electrokinetics and Activated by Electrical Resistance Heating: Proof of Concept.

This study proposes and proves (in concept) a novel approach of combining electrokinetic (EK)-assisted delivery of an oxidant, persulfate (PS), and low temperature electrical resistivity heating (ERH), to activate PS, to achieve remediation of contaminated, low permeability soil. This unique combination is able to overcome existing challenges in remediating low permeability materials, particularly associated with delivering remediants. A further benefit of the approach is the use of the same electrodes for both EK and ERH phases. Experiments were conducted in a laboratory-scale sand tank packed with silt and aqueous tetrachloroethene (PCE) and bracketed on each side by an electrode. EK first delivered unactivated PS throughout the silt. ERH then generated and sustained the target temperature to activate the PS. As a result, PCE concentrations decreased to below detection limit in the silt in a few weeks. Moreover, it was found that activating PS at ∼36 °C eliminated more PCE than activating it at >41 °C. It is expected this results from the reactive SO4•- radical being generated more slowly, which ensures more complete reaction with the contaminant. The novel application of EK-assisted PS delivery followed by low temperature ERH appears to be a viable strategy for low permeability contaminated soil remediation.