Electromigration of cadmium in contaminated soils driven by single and multiple primary cells

doi:10.1016/j.jhazmat.2007.06.029

Journal of Hazardous Materials

Volume 151, Issues 2–3, 1 March 2008, Pages 594-602

https://doi.org/10.1016/j.jhazmat.2007.06.029 Get rights and content

Abstract

This study tentatively used an iron (Fe) and carbon (C) primary cell, instead of dc electric power, to drive the electromigration of cadmium in contaminated soils. The addition of acid to C compartment increased the electric potential, while the addition of acid to Fe compartment had a slight influence on the potential. It was feasible using the primary cell to drive the electromigration of cadmium in kaolin. The electromigration efficiencies were highly related to the soil pH. Lower pH led to greater migration efficiency. The mechanisms involved the desorption of cadmium from soils to pore solution and the electromigration of cadmium in the pore solution. The desorption was critical to the electromigration process. The series of primary cells could expand the treatment area, but the electromigration efficiencies of cadmium in each cell were less than that achieved by single primary cell. Since the potential gradient produced by the primary cell was rather low, the electromigration rate of pollutants was very low and remediation duration was long. The application would be acceptable in some specific sites, such as acidic soils or artificially controlled acid conditions so that heavy metals have been desorbed from soils.

Introduction

Electrokinetic (EK) remediation is a very effective technique to remove toxic metals from contaminated soils. A comprehensive review of EK soil remediation has been provided in several previous studies [1], [2], [3], [4], [5]. Briefly, with the application of electric field to the polluted site, pollutants will migrate towards anode or cathode by electromigration, electro-osmosis and electrophoresis [1], [2], [3]. Much interest has been focused on the electromigration of heavy metals in soils [6], [7], [8], [9], [10], [11], [12], [13]. It has been well established that the removal mechanism of heavy metals by EK technique involved two steps, the desorption of heavy metals from soils to pore solution and the subsequent movement by electromigration, secondarily by electro-osmosis and diffusion [1], [2], [3]. It is impossible to move the pollutants adsorbed on soils by electromigration.

Generally, about 1 V/cm potential gradient was used in EK remediation in both experimental and field test [3], [4], [5], [14], [15]. Actually, the potential may attribute to the removal efficiencies of heavy metals from two aspects. On one hand, electrolysis of water on anode produces much H⁺, which forms an acidic front towards cathode by electromigration. The acid front may largely contributes to the desorption of heavy metal from contaminated soils into soil pore solution [1], [2], [3]. On the other hand, such a high potential may accelerate the electromigration rate of the positively charged heavy metals in the soil pore solution. Thus, relatively shorter remediation duration was achieved by EK process. High electric energy consumption is one of the most important factors restricting the application of EK technique [15], [16], particularly in developing countries such as China. Therefore, it is very meaningful to develop new methods to reduce the energy consumption. Supposed that the contribution of potential to the desorption was subtracted or the heavy metals have been dissolved in soil pore solutions, much lower potential gradient can be used to drive electromigration. This supposition is reasonable in some specific cases, such as acidic soils or controlled acid conditions artificially so that heavy metals have been desorbed from soils.

In the present study, we tentatively used a primary cell, instead of the traditional dc electric power, to drive the electromigration of heavy metals in soils. The schematic diagram of the technique is shown in Fig. 1. Iron (Fe) and carbon (C) are used as anode and cathode, respectively. When Fe and C are connected with wire, a primary cell is formed due to the difference of electrode potentials. Electrode reaction on C is the evolution of H₂ (reaction (1)) and on Fe is the corrosion of iron (reaction (2)), so the electrode potential on C is higher than that on Fe. Electric current is from C to Fe in the wire and from Fe to C in the soil, as shown in Fig. 1. Cations migrate from Fe to C and anions migrate contrarily:C: 2H⁺ + 2e⁻ → H₂, φ^θ(H⁺, H₂) = 0 VFe: Fe − 2e⁻ → Fe²⁺, φ^θ(Fe²⁺, Fe) = −0.440 V

This study investigated the electromigration of cadmium, a representative heavy metal pollutant, in soils driven by the primary cell. The objectives are (1) to explore the feasibility of using Fe/C primary cell to drive the electromigration of cadmium in soils; (2) to research the effect of acid in Fe and C compartment on the electrokinetic properties and the electromigration of cadmium; (3) to investigate electromigration of cadmium by the series of several primary cells so as to increase the remediation area.

Section snippets

Chemicals and materials

CdCl₂·2.5H₂O (Tingxin Chemical Reagent Factory, China, >99.0%) was used as the source of cadmium. Scrap iron was provided from the mechanical factory of Huazhong University of Science and Technology, China. It was first washed in boiling NaOH (1%) solution for 20 min to remove oil and then in H₂SO₄ (1%) to remove rust. Finally, it was washed with tap water and deionized water to be neutral. Crustose carbon was purchased from Kexin Chemical Co. Ltd., China. It was washed by tap water and

Effect of aqueous solution on electric potential

The standard potential between C and Fe is 0.440 V [21]. However, the potential was affected by the concentration of H⁺ and Fe²⁺, which can be described by Nernst equation [21]:E = φ(H⁺, H₂) − φ(Fe²⁺, Fe)E = φ^θ(H⁺, H₂) − φ^θ(Fe²⁺, Fe) + RT/2F ln[α(H⁺)²α(Fe)/α(H₂)α(Fe²⁺)]E = 0.440 − RT/2F ln[α(Fe²⁺)p(H₂)] − 0.059pHwhere R is the Avogadro number, T the standard temperature, F the Coulomb constant, and α(H⁺), α(Fe), α(H₂) and α(Fe²⁺) are the activities of the corresponding species in the brackets. Generally, the

Conclusions

The present study investigated the feasibility of using Fe/C primary cell to drive the electromigration of cadmium in soils. The effect of acid in Fe and C compartment on the electrokinetic properties and the electromigration of cadmium were studied. Furthermore, the electromigration of cadmium by the series of several primary cells was also researched. The main conclusions were drawn as follows:

(1)
In the primary cell system, the addition of acid to C compartment increased the electric potential,

Acknowledgement

This work was supported by the key project of Natural Science Foundation of Hubei Province (no. 2006ABD005).

References (22)

J. Virkutyte et al.
Electrokinetic soil remediation—critical overview
Sci. Total Environ.
(2002)
R. Lageman et al.
Electro-reclamation, a versatile soil remediation solution
Eng. Geol.
(2005)
S.K. Puppala et al.
Enhanced electrokinetic remediation of high sorption capacity soil
J. Hazard. Mater.
(1997)
D.M. Zhou et al.
Electrokinetic remediation of a Cu contaminated red soil by conditioning catholyte pH with different enhancing chemical reagents
Chemosphere
(2004)
D.M. Zhou et al.
Pilot-scale electrokinetic treatment of a Cu contaminated red soil
Chemosphere
(2006)
A. Giannis et al.
Washing enhanced electrokinetic remediation for removal cadmium from real contaminated soil
J. Hazard. Mater.
(2005)
S.H. Yuan et al.
Electrokinetic movement of hexachlorobenzene in clayed soils enhanced by Tween 80 and β-cyclodextrin
J. Hazard. Mater.
(2006)
S.H. Yuan et al.
Desorption of copper and cadmium from kaolin enhanced by organic acids
Chemosphere
(2007)
R.F. Probstein et al.
Removal of contaminants from soils by electric field
Science
(1993)
Y.B. Acar et al.
Principles of electrokinetic remediation
Environ. Sci. Technol.
(1993)

M.M. Page et al.

Electroremediation of contaminated soils

J. Environ. Eng.

(2002)

Cited by (12)

Comprehensive review of progress made in soil electrokinetic research during 1993–2020, Part I: Process design modifications with brief summaries of main output
2023, South African Journal of Chemical Engineering
Since the early 1990s, soil electrokinetic remediation (SEKR) has been exploited for removing organic, inorganic, and radioactive material from contaminated soil. However, the application of SEKR has been met with multiple obstacles; thus, trials have been introduced to overcome these limitations. The present study provides a comprehensive review of various modifications applied to SEKR process designs. We classified the SEKR designs in horizontal, vertical, and mixed (horizontal and vertical) types as per the movement of contaminants. SEKR is conducted via four mechanisms, namely electromigration, electroosmosis, diffusion, and electrophoresis, when a direct current electrical field is applied among two electrodes to achieve contaminant movement from one location to another. During SEKR operation, the removal rate can be adversely affected by factors such as the formation of a pH jumping zone, very high (low) pH around the cathode (anode), polarization, and reduced current efficiency with increase in time. Accordingly, in a previous research, the regular design of SEKR has been modified to address these and other limitations. Moreover, soil electrokinetic (SEK) has been used for other applications such as land restoration, geophysics, dewatering, and consolidation. This review primarily aims to provide a comprehensive summary of the major design modification made to SEK processes in the past 28 years, (1993–2020) to facilitate research on the major aspects of SEK. As per our extensive literature survey, most relevant studies focused on the horizontal SEK design. This study discusses relevant SEK studies in which process design modification is considered.
Role of DDL processes during electrolytic reduction of Cu(II) in a low oxygen environment
2013, Journal of Hazardous Materials
Citation Excerpt :
The slurry was stirred for 24–48 h undisturbed, in order to equilibrate the Cu with the clay mixture. In previous experiments, it was determined that as little as 24 h, but no more than 48 h, is necessary for uniform distribution of the electrolytes in the clay matrix [19,23]. At the end of the equilibration period, the system was purged with N2 for 1 h and an initial DO (dissolved oxygen) reading was taken.
Heavy metals typically accumulate in reduced bottom sediments after being discharged into waterways by industrial and municipal processes. A laboratory experiment was conducted in order to determine if abundance of clay in the bottom sediments of a Cu-contaminated aqueous ecosystem could enhance electrolytic reduction of the heavy metal. Cu(NO₃)₂·2.5H₂O was added to simulate a moderately contaminated system with 650 μg Cu/ml kaolinite clay-water slurry. A constant electrical potential of 1.0 V/cm was applied across platinum wire electrodes inserted into the continuously stirred system for four days while the system ORP² was monitored and periodic sub-samples were taken for analysis. The electrical as well as the chemical results indicate that the quantity of Cu(II) being reduced to Cu(I), especially within the aqueous phase, is increased within the first 48 h of experimentation by the presence of kaolinite clay up to 0.05 mg clay/l slurry.
Near-anode focusing phenomenon caused by the high anolyte concentration in the electrokinetic remediation of chromium(VI)-contaminated soil
2012, Journal of Hazardous Materials
Citation Excerpt :
EKR techniques are also applied in mine tailings, sewage sludge, and marine sediments [2–5]. Many enhancement or hybrid techniques have been developed to enhance the efficacy and efficiency of EKR [2,6–14]. The bench-scale tests for EKR techniques normally achieve good results, but only few field tests achieved similar efficacies.
The effects of the concentration and the low pH value of anolyte on the electrokinetic remediation (EKR) of chromium-contaminated soil were investigated using chromium-spiked kaolin-gypsum soil. Results of visual observation and X-ray fluorescence analysis show that high anolyte concentrations could cause an ion-induced potential gradient well trapping effect on the soil near the anode, and consequently cause a focusing phenomenon (FP) without chemical precipitation. This FP significantly prolonged the remediation duration and reduced chromium removal. The low pH value of soil aggravated the FP, resulting in a quasi-dead zone near the anode caused by the reduction in soil resistance, rather than the adsorption of chromium (VI) ions. The high anolyte concentration also resulted in high energy consumption. The FP and low pH value collectively decreased the energy efficiency by more than 96%. This kind of FP can be predicted via the online monitoring of the potential gradient profiles of the soil between the electrodes in the EKR.
Migration of ions and organic matter during electro-dewatering of anaerobic sludge
2010, Journal of Hazardous Materials
This paper reports the migration of ions and organic matter, initially present in anaerobically digested sludge taken from the effluent of an anaerobic digestion unit in Mikkeli Wastewater Treatment Plant (SE Finland) during electro-dewatering process, employing various experimental strategies such as freeze/thaw and polyelectrolyte conditioning and various sludge loading rates. It was found that a decrease in sludge loading rate (from 20 to 5 kg DS m⁻²) resulted in an increase in the maximum current density (145–467 A m⁻²). The principle component analysis (PCA) showed a significant correlation between the dry solid (DS) content in the final sludge cake, sludge loading rate, freezing conditions, energy consumption and maximum current density during electro-dewatering process. The decrease in sludge loading rate resulted in the reduced time to achieve the highest concentrations of Na⁺ and K⁺ in the removed water at the cathode. Moreover, concentration of Na⁺ and K⁺ was reduced by 51 and 78% in the sludge cake, respectively, in comparison to blank experiments. Fe ions, Ca²⁺ and Mg²⁺ concentrations were found lower in the sludge cake at the anode and higher at the cathode. According to the statistical analysis, Fe and Ca ion concentrations at the anode and sludge loading rate had a negative correlation with the volatile solids/dry solids (VS/DS) ratio in sludge at the anode. High P concentration at the anode was only observed in experiments using freeze/thaw conditioned sludge samples and highly depended on the initial sludge freezing temperatures. Furthermore, at the end of experiments, concentration of problematic elements in the sludge cake such as Cr⁶⁺, Zn²⁺ and Mn ions increased from 63 to 100% and decreased from 23 to 70% at the anode, respectively, in comparison to the blank experiment.
Use of solar cell in electrokinetic remediation of cadmium-contaminated soil
2009, Journal of Hazardous Materials
This preliminary study used a solar cell, instead of direct current (DC) power supply, to generate electric field for electrokinetic (EK) remediation of cadmium-contaminated soil. Three EK tests were conducted and compared; one was conducted on a cloudy and rainy day with solar cell, one was conducted on a sunny day with solar cell and another was conducted periodically with DC power supply. It was found that the output potential of solar cell depended on daytime and was influenced by weather conditions; the applied potential in soil was affected by the output potential and weather conditions, and the current achieved by solar cell was comparable with that achieved by DC power supply. Solar cell could be used to drive the electromigration of cadmium in contaminated soil, and removal efficiency achieved by solar cell was comparable with that achieved by DC power supply. Compared with traditional DC power supply, using solar cell as power supply for EK remediation can greatly reduce energy expenditure. This study provided an alternative to improve the EK soil remediation and expanded the use of solar cell in environmental remediation.
Assessment of Acid Enhancement Schemes for Electrokinetic Remediation of Cd/Pb Contaminated Soil
2016, Water, Air, and Soil Pollution

View all citing articles on Scopus

¹: Tel.: +86 27 62798401; fax: +86 27 87792159.

View full text

Electromigration of cadmium in contaminated soils driven by single and multiple primary cells

Abstract

Introduction

Section snippets

Chemicals and materials

Effect of aqueous solution on electric potential

Conclusions

Acknowledgement

Sci. Total Environ.

Eng. Geol.

J. Hazard. Mater.

Chemosphere

Chemosphere

J. Hazard. Mater.

J. Hazard. Mater.

Chemosphere

Removal of contaminants from soils by electric field

Science

Principles of electrokinetic remediation

Environ. Sci. Technol.

Electroremediation of contaminated soils

J. Environ. Eng.