Alkaline Front Research Articles

Iron slag/activated carbon-electrokinetic system with anolyte recycling for single and mixture heavy metals remediation

The electrokinetic process has been proposed for in-situ soil remediation to minimize excavation work and exposure to hazardous materials. The precipitation of heavy metals in alkaline pH near the cathode is still challenging. Reactive filter media and enhancement agents have been used in electrokinetics to enhance the removal of heavy metals. This study investigated coupling industrial iron slag waste and iron slag-activated carbon reactive filter media with electrokinetic for a single and mixture of heavy metals treatment. Instead of using acid enhancement agents, the anolyte solution was recycled to neutralize the alkaline front at the cathode, reducing the operation cost and chemical use. Experiments were conducted for 2 and 3 weeks at 20 mA electric current. Copper removal increased from 3.11 % to 23 % when iron slag reactive filter media was coupled with electrokinetic. Copper removal increased to 70.14 % in the electrokinetic experiment with iron slag-activated carbon reactive filter media. The copper removal increased to 89.21 % when the anolyte solution was recycled to the cathode compartment. Copper removal reached 93.45 % when the reactive filter media-electrokinetic process with anolyte recirculation was extended to 3 weeks. The reactive filter media- an electrokinetic process with anolyte recycling was evaluated for removing copper, nickel, and zinc mixture, and results revealed 81.1 % copper removal, 89.04 % nickel removal, and 92.31 % zinc removal in a 3-week experiment. The greater nickel and zinc removal is attributed to their higher solubility than copper. The results demonstrated the cost-effectiveness and efficiency of the electrokinetic with iron slag-activated carbon reactive filter media with anolyte recirculation for soil remediation from heavy metals.

Permeable reactive composite approaching cathode enhanced Cr removal in soil using the byproduct of electrokinetic technology: emphasized energy utilization efficiency.

Cost-effective techniques with significant removal rates and low energy consumption are urgently required for in-situ Cr-contaminated soil remediation to reduce potential environmental toxicity to the ecosystem and human bodies. Electrokinetic technology is a valuable and promising soil remediation technology; however, the acidic and alkaline fronts evolutioninduced by the electrokinetic byproducts (H+, OH-) has significant hindering characteristics for ion removal. To effectively utilize the byproducts for enhancing Cr elimination, this paper proposed the permeable reactive composite approaching cathode with rhamnolipid-modified biochar as reactive material. Power utilization efficiency (η) was presented to comprehensively evaluate the target species elimination effect, considering removal rate and energy consumption. Results suggested that biosurfactant rhamnolipid stimulated Cr removal in acid and base fronts. Acid front induced rhamnolipid protonation reducing anolyte Cr(VI) to Cr(III), and base front induced rhamnolipid deprotonation complexing with Cr(III) and expediting Cr(VI) dissolution by electrostatic repulsion. Permeable reactive composite approaching cathode induced the maximum removal rate of Cr(VI) and Cr(III) in each section by impelling the alkaline front. Approaching cathode caused increased resistance and energy consumption in the near-anode regions, ultimately decreasing energy utilization efficiency. Optimized moving frequency and applied potential magnitude could adjust power consumption distribution in a single soil layer to obtain better electrokinetic removal performance of contaminates. This work provided essential scientific and practical importance for in-situ electrokinetic remediation of Cr(VI) and Cr(III), considering elimination efficiency and energy consumption in the future.

Effect of electrokinetic treatment time on energy consumption and salt ions removal from clayey soils

Electrokinetics effectively removes contaminants, but its field-scale applications are limited mainly due to its high energy cost. In previous studies, the energy consumption was determined either by changing the soil’s specimens initial salt concentration while keeping the treatment time fixed or by changing the treatment time and keeping the same initial salt concentrations for all the specimens. Since both the initial salt concentration and treatment time are important parameters in determining reclamation cost, therefore, in this study, the soil specimens intentionally contaminated with different concentrations of sodium chloride (NaCl), i.e., varying from 3.7 to 15.5 g kg−1, were exposed to a constant DC electric field of 1 V cm−1 for different time durations, i.e., varying from 6 to 72 h. The results show that electroosmotic flow (EOF) was directed from the anode to the cathode and higher for specimens contaminated with relatively low salt concentration, i.e., up to 7.6 g kg−1. Therefore, for these specimens, due to the combined effect of electroosmosis and electromigration, the removal of Na+ was higher than the Cl−. However, for the specimen contaminated with a higher salt concentration, i.e., 15.5 g kg−1, the Cl− removal exceeded Na+ due to the marginalization of EOF. Regardless of initial salt concentration, the electroosmotic flow and salt ions removal rates decreased with increasing treatment time, which might be attributed to the development of acidic and alkaline environments in soil. The collision of acidic and alkaline fronts resulted in a large potential gradient in a narrow soil region of pH jump, diminishing it everywhere else. This nonlinearity in the electric potential distribution in soil reduced the EOF and electromigration of salt ions.

Investigating immobilization efficiency of Pb in solution and loess soil using bio-inspired carbonate precipitation

Lead (Pb) metal accumulation in surrounding environments can cause serious threats to human health, causing liver and kidney function damage. This work explored the potential of applying the MICP technology to remediate Pb-rich water bodies and Pb-contaminated loess soil sites. In the test tube experiments, the Pb immobilization efficiency of above 85% is attained through PbCO3 and Pb(CO3)2(OH)2 precipitation. Notwithstanding that, in the loess soil column tests, the Pb immobilization efficiency decreases with the increase in depth and could be as low as approximately 40% in the deep ground. PbCO3 and Pb(CO3)2(OH)2 precipitation has not been detected as the majority of Pb2+ combines with –OH (hydroxyl group) when subjected to 500 mg/kg Pb2+. The alkaline front promotes the chemisorption of Pb2+ with CO32− reducing the depletion of quartz mineral close to the surface. However, OH− is in shortage in the deep ground retarding the Pb immobilization. The Pb immobilization efficiency thus decreases with the increase in depth. Quartz and albite minerals, when subjected to 16,000 mg/kg Pb2+, appear not to intervene in the chemisorption with Pb2+ where the chemisorption of Pb2+ with CO32− plays a major role in the Pb immobilization. Compared to the nanoscale urease applied to the enzyme-induced carbonate precipitation (EICP) technology, the micrometer scale ureolytic bacteria penetrate into the deep ground with difficulty. The ‘size’ issue remains to be addressed in near future.

Enhanced remediation of surface-bound hexavalent chromium in soils using the acidic and alkaline fronts of electrokinetic technology

In the subsurface environment, highly toxic hexavalent chromium (Cr(VI)) control and remediation are essential to avoid further ecological impacts and reduce environmental risks. This paper investigated the enhanced Cr(VI) electrokinetic removal in the soil through the approaching cathode method. Besides, a novel four-step sequential fractionation method was used to reflect the strength of Cr(VI) binding to the soil. The approaching cathode enhanced the electrokinetic delivery of surface-bound Cr(VI) by advancing the alkaline front for Cr(VI) desorption and improving the electric potential flattening of the soil layers. Desorption of Cr(VI) by the alkaline front involved converting the inner-sphere complexes form of Cr(VI) to a weakly adsorbed form susceptible to ionic strength. In addition, the acidic front provided a favorable environment for the photochemical reduction of Cr(VI) by soil species or the added citrate as the electron donors. Improving the potential distribution could regulate the energy consumption of individual soil layers and efficiently operate the electrokinetic transfer of pollutants. The work results have significant scientific and practical significance for applying the in-situ electrokinetic technique in subsurface pollution control.

Inhibition characteristics of the electrokinetic removal of inorganic contaminants from soil due to evolution of the acidic and alkaline fronts

This study comprehensively investigates the inhibition characteristics of the electrokinetic removal (EKR) of inorganic pollutants from soil due to evolution of the acidic and alkaline fronts (EAAF). The effects of EAAF on the ion strength of the soil pore fluid, potential distribution, soil colloids, clay minerals, and soil microstructure are systematically examined, in addition to the control effects of non-target charged species on the removal of target pollutants. The results show that the transport of target species near the anode region is mainly inhibited by potential flattening, soil colloid aggregation, and the closure of soil pores. Migration near the cathode region is mainly inhibited by the immobile chemical states of metals, potential flattening, soil dehydration, and a high soil adsorption ability owing to the relatively developed pores. This results also show that H+, OH-, and soluble Al have a significantly control effect on the macroscopic dynamics of EKR of the target contaminants. The injection of acidic solution near the cathode alleviates the potential jump and prevents the formation of metal hydroxides to some extent. The average removal rates of nitrate, Pb, and Cd after EKR improved from 85.5%, 11.1%, and 21.8–98.5%, 35.8% and 47.7%, respectively.

Electro-kinetic washing of a soil contaminated with quinclorac and subsequent electro-oxidation of wash water

This work deals with the remediation of a soil that has been enriched with Quinclorac (QNC), one of the herbicides most used in Chile for weed control in rice fields. Quinclorac damages the microflora and macrofauna of soils and is toxic to some susceptible crops, which results in economic loses during crop rotation. Furthermore, Quinclorac a potential contaminant of water resources and soils, given its high mobility and persistence. This has created the need to lower its concentrations in soils intensively cultivated. In this study, an electro-kinetic soil washing system (EKSW) for mobilizing this pesticide in the soil was explored. The performance of this technology was compared by assessing the effect of direct (DP) and reverse (RP) polarity during 15 days under potentiostatic conditions and applying an electric field of 1 V cm−1 between electrodes. Among the main results, the highest removal of QNC was obtained through the EKSW-RP process, which also contributed to the prevention of acidity and alkaline fronts in the soil, compared to the EKSW-DP system. In both cases, the highest accumulation of QNC occurred in the cathodic well by mobilizing the non-ionized contaminant through the electroosmotic flow (EOF) from anode to cathode. After the treatment with EKSW, the wash water accumulated in the anodic and cathodic wells, which contained an important concentration of pesticide, was subjected to electro-oxidation (EO) by applying different current densities (j). The high generation of •OH on the surface of a boron-doped diamond electrode (BDD) allowed for the complete degradation and mineralization of QNC and its major intermediate compounds to CO2. The results of this study show that the application of both coupled stages in this type of remediation technologies would enable the removal of QNC from the soil without altering its chemical and physical properties, constituting an environmentally friendly process.

Enhanced copper removal from contaminated kaolinite soil by electrokinetic process using compost reactive filter media

Electrokinetic (EK) remediation is a promising technology for soil decontamination, although basic pH in the soil close to cathode has constrained EK effectiveness due to heavy metal precipitation. This study aimed to enhance copper removal from kaolinite soil by integrating EK with compost (C) as recyclable reactive filter media (RFM) for the first time. Compost placed near the cathode served as an adsorbent to bind copper ions while buffering the advancement of the alkaline front in soil. The total copper removal rate increased from 1.03% in EK to 45.65% in EK-100%C under an electric potential of 10 V. Further experiments conducted by using biochar (BC) and compost/biochar (C + BC) mixture RFM at different ratios showed total Cu removal efficiency decreasing as EK-100%C > EK-(10%BC + 90%C) > EK-(20%BC + 80%C) > EK-(30%BC + 70%C) > EK. The application of a constant electric current of 20.00 mA further enhanced copper removal to 84.09% in EK-100%C although did not show significant enhancement in EK-(BC + C). The compost RFM was regenerated by acid extraction and then reused twice, achieving a total removal of 74.11%. The findings demonstrated compost as a promising and reusable RFM for the efficient removal of copper in contaminated soil.

Enhanced electrokinetic remediation and simulation of cadmium-contaminated soil by superimposed electric field

The ‘focusing’ effect has become a limiting factor for the removal of heavy metals from soils by electrokinetic (EK) remediation. A superimposed electric field EK (SE-EK) method is proposed to address this problem. Two sets of fixed electrodes placed at different positions were switched to move the ‘focusing’ region of Cd to the cathode by controlling the location of the pH jumping front. Moreover, a model was established to simulate and optimize the process of Cd transport in soil under the superimposed electric field. Results showed that, after 35 d of SE-EK remediation, Cd was mainly accumulated in the soil section near the cathode (S5), where the acid and alkaline fronts converged. The removal rate of Cd in the soil sections from S1 to S4 reached 87.60%, which was 6.13 times that in conventional EK remediation. Meanwhile, the energy utilization efficiency in SE-EK was 6.38 times that in conventional EK. The pH changes and Cd distribution during the SE-EK experiment were simulated well, with good agreement between the modeled and experimental data. The removal of Cd in SE-EK remediation could therefore be optimized through simulating the distribution of Cd in five situations with differences in switching time and electrode position. This research provides valuable technical support for effective EK remediation of heavy metal contaminated soil.

Geochemical conditions for the formation of Mg silicates phases in bentonite and implications for radioactive waste disposal

The present study evaluates the formation of magnesium silicates phases as a result of the alkaline alteration of FEBEX bentonite in long-term experiments. The results are relevant in the context of radioactive waste disposal since the bentonite barrier will partly change its original mineralogy and condition its long-term geochemical behavior. Bentonite samples from an in situ experiment of interaction with a CEM-II-type concrete performed for 13 years in a rock gallery and a laboratory experiment of interaction with a CEM-I-type concrete performed for 10 years provide some experimental evidences on the mineralogical alteration. Results required multiple analytical techniques to resolve the nature of the Mg silicates. X-ray diffraction, thermogravimetric analyses, scanning electron microscopy, infrared spectroscopy and 27Al and 29Si nuclear magnetic resonance have been used. The mineralogical alteration is complex since several Mg silicates may coexist in the same region not only with themselves but also with carbonates and calcium (aluminium) silicate hydrates. Brucite intercalation in the interlayer of smectite, previously reported as a chlorite-like phase in a former study, is observed. In addition, a serpentine-type mineral phase was better observed in the in situ samples, at least by XRD, and a 2:1 trioctahedral phyllosilicates was better observed in the laboratory samples. Formation of Mg silicates in the bentonite barrier may buffer the Ca alkaline front originated in concrete and may decrease the porosity at the concrete-bentonite interface.

Coupling electrokinetic remediation with phytoremediation for depolluting soil with petroleum and the use of electrochemical technologies for treating the effluent generated

Abstract This work aims to investigate the enhancement of the efficiency of phytoremediation (phytoR) by electrokinetic remediation (ER) by using graphite electrodes to depollute soil contaminated with petroleum. It was focused on the effects of electric fields (by applying direct current (DC) of reversal polarity (RP)) as well as the growth of sunflower plants after soil remediation. In this case, five experimental setups were used, phytoR, ER and electro-phytoremediation (ER-PhytoR) by supplying DC (ER-PhytoR-DC) or RP (ER-PhytoR-RP). Regarding the total petroleum hydrocarbon (TPH) removal, it was more efficient for the ER-phytoR-RP carried out at 1 V cm−1 after 20 d where microbial degradation in the rhizosphere and organic compounds transport through the soil associated to the RP (contributing to avoid the acidity and alkaline fronts in the soil), were the key operating parameters. Results clearly showed that the application of RP favoured the germination, growth of plants and high TPH removal after 20 d. It was also demonstrated by higher biomass production achieved at different treatments; 5.22 g for phytoR, 1.137 g for ER-phytoR-DC and 5.89 g for phytoR-ER. Finally, two diamond based-electrochemical technologies (anodic oxidation (AO-H2O2) and electro-Fenton (EF)) have been used for treating the effluents generated by soil decontamination to eliminate the dissolved organic matter.

Lime mortar-compacted bentonite–magnetite interfaces: An experimental study focused on the understanding of the EBS long-term performance for high-level nuclear waste isolation DGR concept

The aim of this study was to obtain evidences regarding the physical and geochemical processes occurring as a result of the combined effects of cementitious materials from the concrete degradation and magnetite from steel corrosion on the bentonite barrier during disposal of high-level radioactive waste.A series of six experiments were done that attempt to reproduce the repository conditions prevailing from 1000 to 3000years after emplacement of wastes. A lime mortar was used as the source of calcium and alkalinity as this is the presumed reactive product produced during concrete degradation at long-term. Magnetite powder was used to simulate the final corrosion product of cast iron and C-steel under anaerobic conditions. Either a natural FEBEX bentonite or a pretreated “aged” sample, depleted in exchangeable Mg and enriched in K, were used as the swelling clay component. Experiments, with both types of bentonite, were performed simultaneously in cylindrical specimens (50mm diameter, 25mm length), confined in a Teflon® sleeve/steel case cells. These specimens were composed of cement mortar in contact with compacted bentonite, which was in turn in contact with compressed magnetite powder. They were hydrated with an artificial Na+–Ca2+×SO42−type Spanish reference clayey formation water for 18months at 60°C and constant hydraulic pressure applied through the base of the mortar.After dismantling and sampling the specimens, distribution of soluble ions, exchangeable cations and mineralogy were studied in the bentonite by different instrumental techniques. Iron migration or any impact of the corrosion products in the bentonite was not noticeable in the clay. Both, mortar and magnetite acted as sinks of chloride and sulfate. Small quantities of Ca–Al-sulfates and carboaluminates, which can allocate chlorides, were determined near the mortar-bentonite interface. Portlandite dissolved near the bentonite interface and induced the formation of calcium silicates hydrates (C-S-H) phases cementing the clay interface characterizing a calcium front that was developed from the mortar towards the bentonite. Magnesium silicate hydrates (M-S-H) phases were also concentrated at the interface with mortar in the natural bentonite. It was also determined that natural bentonite has potentially higher buffering capacity attenuating the calcium alkaline front than the pretreated clay. In both cases, a low porosity bentonite–mortar zone was experimentally created at the interface. This type of material should be carefully studied in order to predict the potential for further development of a diffusive alkaline alteration, the radionuclides retention and the consequences in the hydration rate of the unaffected bentonite buffer.

Acid Enhanced Electrokinetic Remediation of a Contaminated Soil using Constant Current Density: Strong vs. Weak Acid

The most typical enhancement for electrokinetic remediation (EKR) involves the neutralization of the alkaline front generated at the cathode by the addition of an acid to the catholyte. Although the use of strong and weak acids can be found in the literature, there is still a clear lack of reliable comparisons between them. This paper presents a comparison of the results obtained for a real lead contaminated soil treated by EKR enhanced with nitric or with acetic acid. The divergences that are usually observed in those experimental results obtained when using constant voltage drop are avoided here by the use of EKR with constant current intensity and the disposition in series of the soil lab columns. Important differences are observed in the behavior of the system when the acid was changed. The time needed to achieve the same metal recovery is more than 3 times longer for the nitric acid. A standard sequential extraction procedure was used to fractionate the lead concentration in the soil according to its mobility in a before- and after-treatment way. Regardless of these important differences observed in the remediation time, the fractionation results after the experiments were almost the same for the two acid enhanced EKRs.

Electrokinetic Treatment of Cr-, Cu-, and Zn-Contaminated Sediment: Cathode Modification

Enhanced electrokinetic (EK) removal of Cr, Cu, and Zn from sediment by using original and modified integrated ion exchange (IIX™) cathodes was investigated. IIX cathode design and EK device process modifications were made to improve performance: separation of IIX cathode components (IIXS), combination of modified IIX cathode with pulsed electric field (IIXSP), and separation of IIX cathode components with addition of an anion exchange resin compartment (IIXA). After using the IIXSP, overall Cr, Cu, and Zn removal efficacies were significantly improved compared with the other treatments investigated. No improvements in overall Cr, Cu, and Zn removal efficacies were achieved by utilization of IIXA. Nevertheless, significant removal efficacies occurred at the anode region since distribution of the alkaline front was prevented. However, metal accumulation in the cathode region occurred. This was a consequence of metal cation complexation with Cl- released from the anion exchange resin that changed the direction of metal migration. Enhancing EK remediation of Cr-, Cu-, and Zn-contaminated sediment can be achieved by using a modified IIX cathode.

Simultaneous electrokinetic removal of polycyclic aromatic hydrocarbons and metals from a sediment using mixed enhancing agents

The maintenance of harbor waterways generates large amounts of dredged sediments which are often rich in coexisting organic and inorganic contaminants. Electrokinetic remediation treatments have recently been developed for the simultaneous removal of heavy metals and polycyclic aromatic hydrocarbons (PAHs), using various enhancing agents generally tested sequentially. In this study, different processing fluids were tested, alone or mixed, to improve the decontamination of aged model sediment contaminated with cadmium, lead, chromium, copper, zinc, and five PAHs. Nitric acid (NA) and citric acid (CA) were tested to avoid the formation of an alkaline front into the sediment and favor the metals removal, while an anionic surfactant [sodium dodecyl sulfate (SDS)] and a nonionic surfactant (Tween 20) were tested to solubilize and mobilize PAHs. Processing fluids were circulated under a constant voltage gradient of 1 V cm−1 for 10–14 days. NA showed an excellent potential to remove metals (76.8–99.9 % removal) and PAHs (70.3–89.7 % removal) in a single run. Besides, the mixture of Tween 20 and CA, more environmental friendly, could be considered as a relatively good processing fluid for the simultaneous removal of metals (10.3–90.8 % removal) and PAHs (53.6–61.6 % removal) from the fine-grained sediment, while SDS mixed to CA was not a good candidate for this purpose (0.1–65 % removal for metals and 34.1–41.0 % removal for PAHs).

Inhibition of electrokinetic ion transport in porous materials due to potential drops induced by electrolysis

In this work we present non-destructive measurements of sodium ion concentration profiles during the electrokinetic removal of sodium chloride from porous materials using Nuclear Magnetic Resonance (NMR). The effect of both protons and hydroxyl ions, generated due to the electrolysis of water, on the transport of the salt ions is studied by tracking the acidic and alkaline fronts using pH-indicator paper. In addition, the electrical potential distribution within the specimen is monitored to assess its influence on the process. To support the observations we compare the experimental results with a theoretical model based on the Poisson–Nernst–Plank equations. In this model we use the chemical equilibrium condition for the self-electrolysis of water in the description of the transport of protons and hydroxyl ions. In addition we use the electro-neutrality condition to compute the transport of salt ions through the material. At the edges of the system the electrical current is distributed over the chemical active species, i.e. protons, hydroxyl and chloride ions, according to the Butler–Volmer description for charge transfer at electrodes. Both the experimental and model results show in the final stage of the electrokinetic remediation process a sharp transition from the acidic to alkaline region at one third of the length of the specimen away from the positively biased electrode, i.e. the anode. From the model results we found that the formation of chlorine gas at the anode does not influence the position of this transition area. In this transition region we also observe a large gradient in electrical potential and a corresponding local deficit of ions. As a result of the large potential gradient in this small transition zone the electrical field in the acidic and alkaline region diminishes. Consequently, electrokinetic ion transport though the material will stagnate.

Electrokinetic study of the buffer capacity of some soils from Tenerife.: Comparison with a volumetric technique

During electroremediation treatment applied to polluted soils, secondary reactions may result which can influence the efficiency of a decontamination process. The most important of these secondary reactions is the generation of acid and alkaline fronts as a consequence of the electrolysis of water which occurs at the electrodes. These fronts interact with the soil fraction closest to the electrodes, and their influence on the process of pollutant removal is dependent on the buffer capacity present in the soil. This buffer capacity, related to the presence of specific functional groups, can be determined by volumetric techniques in which the soil is placed in contact with an alkaline material for a given time period, and subsequently analyzed for the resultant pH. This information may not be directly applicable to the electrokinetic process since it may be related to a process involving dynamic changes generated by the continuous electrical field applied to the soil. The objective of the present study was to determine the buffer capacity of the soil by means of quantitative determination of a “buffer function” obtained under identical conditions to those operating during an electroremediation treatment. This function was determined for a group of soils from Tenerife Island, Spain. The results obtained from both techniques are shown and compared, and the findings reveal some discrepancies related to the type of acid–base disturbance applied. In the case of regulatory function, it is possible to relate these variations to some soil properties such as pH and the presence of carbonate.

Electromigration of Mn, Fe, Cu and Zn with citric acid in contaminated clay

Metal reactivity, speciation and solubility have an important influence in its transportation through a porous matrix by electrokinetics and, therefore, they dramatically affect the removal efficiency. This work deals with the effect of solubility and transport competition among several metals (Mn, Fe, Cu and Zn) during their transport through polluted clay. The unenhancement electrokinetic treatment results in a limited removal of the tested metals because they were retained into the kaolinite sample by the penetration of the alkaline front. Metals showed a removal degree in accordance with the solubility of the corresponding hydroxide and its formation pH. In 7 days of treatment, the removal results were: 75.6% of Mn; 68.5% of Zn, 40.6% of Cu and 14.8% of Fe. In order to avoid the negative effects of the basic front generated at the cathode, two different techniques were proposed and tested: the addition of citric acid as complexing agent to the polluted kaolinite sample and the use of citric acid to control de pH on the cathode chamber. Both techniques are based on the capability of citric acid to act as a complexing and neutralizing agent. Almost complete removal of Mn, Cu and Zn was achieved when citric acid was used (as neutralizing or complexing agent). But Fe only reached 33% of removal because it formed a negatively charged complex with citrate that retarded its transportation to the cathode.

The hindering effect of experimental strategies on advancement of alkaline front and electroosmotic flow during electrokinetic lake sediment treatment

The current study focused on the hindering of alkaline front during electrokinetic copper migration in artificially contaminated lake sediments and the effect of several experimental strategies on electroosmotic flow. Fourteen laboratory scale experiments in triplicates were performed using plastic container where the distance between electrodes was 30 cm at 40 mA, 60 mA and 120 mA electric currents (under density of 0.15 mA cm −2, 0.23 mA cm −2 and 0.53 mA cm −2, respectively) with different Cu concentrations (500 mg kg −1, 1000 mg kg −1, 1500 mg kg −1, 2000 mg kg −1 and 2500 mg kg −1) for 14 days. Tests were conducted with/without electric current and with/without the employment of membranes or barriers. Selected membranes and barriers proved to be efficient in hindering the alkaline front and thus improving copper migration in the sediments. During electrokinetic treatment and the use of the nylon membrane 85% of Cu was removed from sediments. Additionally, 80% and 70% of Cu was removed when cation exchange membrane and filter paper barrier were used. During the electrokinetic treatment Cu as well as the electroosmotic flow was always directed towards the cathode. The highest electroosmotic flow was observed with the lowest (500 mg kg −1) Cu concentration. Moreover, the electroosmotic flow and electrical gradient increased with the increase in electric current and was found to be the highest at 120 mA. When there were no membranes, barriers or acid used, severe pH jump was observed at a normalized distance of 0.5–0.6 from the anode. However, when membranes or barriers were employed, there was no pH jump present in the sediments.

Improving on electrokinetic remediation in spiked Mn kaolinite by addition of complexing agents

During the electrokinetic treatment of kaolinite polluted with Mn, metal ions migrated to the cathode side, but the alkaline front generated by the reduction of water at the cathode provoked their precipitation as Mn hydroxide. It prevented their collection in the cathode chamber. Most Mn precipitated in a thin soil layer close to the cathode (68%), and only 26% of the initial Mn was found in the cathodic solution. Solubility of manganese can be enhanced with the addition of organic compounds (EDTA, oxalic acid and citric acid) that form complexes or chelates with Mn 2+ ions. Besides, the complexing agents tested in this work are environmentally benign and do not provoked negative effects in soil. The addition of EDTA and oxalic acid to the spiked Mn kaolinite improved metal removal from kaolinite. Thus, 38% of Mn was colleted at the cathode chamber when oxalic acid was used as complexing agent. EDTA was more effective since 42% of Mn reached the cathode. The rest of the Mn remained into the kaolinite, mainly in the last section, close to the cathode. When citric acid was added to kaolinite, the behaviour of the electrokinetic treatment was totally different. Mn was completely removed and no accumulation was detected into the kaolinite. All contaminated metal was recovered in the cathodic solution. This good result was attributed to the complexing activity of citric acid and to the high electro-osmotic flow induced by the presence of citric acid into the kaolinite sample.