Impact of carbonate on the efficiency of heavy metal removal from kaolinite soil by the electrokinetic soil remediation method

While the feasibility of using electrokinetics to decontaminate soils has been studied by several authors, the effects of soil composition on the efficiency of this method of decontamination has yet to be fully studied. This study focuses its attention on the effect of “calcite or carbonate” (CaCO₃) on removal efficiency in electrokinetic soil remediation. Bench scale experiments were conducted on two soils: kaolinite and natural-soil of a landfill in Hamedan, Iran. Prescribed quantities of carbonates were mixed with these soils which were subsequently contaminated with zinc nitrate. After that, electrokinetic experiments were conducted to determine the efficiency of electrokinetic remediation. The results showed that an increase in the quantity of carbonate caused a noticeable increase on the contaminant retention of soil and on the resistance of soil to the contaminant removal by electrokinetic method. Because the presence of carbonates in the soil increases its buffering capacity, acidification is reduced, resulting in a decrease in the rate of heavy metal removed from the contaminant soil. This conclusion was validated by the evaluation of efficiency of electrokinetic method on a soil sample from the liner of a waste disposal site, with 28% carbonates.     

Zeta potential of soils with surfactants and its relevance to electrokinetic remediation

There are numerous studies on the application of electrokinetic decontamination technique to remediate heavy metal contaminated fine-grained soils. In recent studies, surfactants have been used to increase the efficiency of contaminant removal. However, there is limited data available on how physicochemical parameters such as zeta potential (ζ) of soils changes in the presence of surfactants. Understanding the ζ potential variations of soils with surfactant addition is important because it controls the direction and magnitude of electro-osmotic permeability, which plays important role on the efficiency of electrokinetic remediation. In this study, ζ potentials of kaolinite, montmorillonite and quartz powder with Li⁺, Ca⁺², Cu⁺², Pb⁺² and Al⁺³ in the presence of anionic, cationic and non-ionic surfactants were determined. The results indicate that anionic surfactants produce negative ζ potentials. The other surfactants produce both positive and negative ζ potentials depending on soil type and ion present in the system. The results also indicate that the ζ potential of kaolinite and quartz powder with surfactants showed similar trends; however, the absolute magnitude of the ζ potential of quartz powder is higher than that of kaolinite. The ζ potential of montmorillonite commonly shows a different trend from those of kaolinite and quartz powder. Based on the test results, it is recommended that ζ potential of soils be determined before the electrokinetic decontamination in order to maximize the efficiency of the technique.     

Comparison of electrodialytic removal of Cu from spiked kaolinite, spiked soil and industrially polluted soil

Electrokinetic remediation methods for removal of heavy metals from polluted soils have been subjected for quite intense research during the past years since these methods are well suitable for fine-grained soils where other remediation methods fail. Electrodialytic remediation is an electrokinetic remediation method which is based on applying an electric dc field and the use of ion exchange membranes that ensures the main transport of heavy metals to be out of the pollutes soil. An experimental investigation was made with electrodialytic removal of Cu from spiked kaolinite, spiked soil and industrially polluted soil under the same operational conditions (constant current density 0.2 mA/cm(2) and duration 28 days). The results of the present paper show that caution must be taken when generalising results obtained in spiked kaolinite to remediation of industrially polluted soils, as it was shown that the removal rate was higher in kaolinite than in both spiked soil and industrial polluted soil. The duration of spiking was found to be an important factor too, when attempting to relate remediation of spiked soil or kaolinite to remediation of industrially polluted soils. Spiking for 2 days was too short. However, spiking for 30 days resulted in a pattern that was more similar to that of industrially polluted soils with similar compositions both regarding sequential extraction and electrodialytic remediation result, though the remediation still progressed slightly faster in the spiked soil. Generalisation of remediation results to a variety of soil types must on the other hand be done with caution since the remediation results of different industrially polluted soils were very different. In one soil a total of 76% Cu was removed and in another soil no Cu was removed only redistributed within the soil. The factor with the highest influence on removal success was soil pH, which must be low in order to mobilize Cu, and thus the buffering capacity against acidification was the key soil characteristics determining the Cu removal rate.     

Effect of humic substances on Cu(II) solubility in kaolin-sand soil

The type and amount of organic matter present in industrially contaminated soils will influence the risk they pose. Previous studies have shown the importance of humic and fulvic acids (FAs) (important components of soil organic matter) in increasing the solubility of toxic metals but were not carried out using toxic metal levels and the pH range typical of industrially contaminated soils. This study investigated the influence of three humic substances (HSs: humates, fulvates and humins) on the solubility of copper(II) ions in kaolinitic soil spiked with Cu at levels representative of industrially contaminated soil. Humates, fulvates and humin were extracted from Irish moss peat, and controlled pH batch leaching tests were conducted on an artificial kaolin-sand soil that was spiked with each. Further leaching tests were conducted on soil spiked with each HS and copper nitrate. Dissolved organic contents were determined by titration and total and free aqueous copper concentrations in the leachate were measured using AAS and ion selective electrode (ISE) potentiometry respectively (dissolved complexed copper levels were determined by difference). It was found that humates and fulvates are partially sorbed by the soil, probably by chemisorption on positively charged gibbsite (Al-hydroxide) sites in the kaolinite. The addition of 340 mg/kg Cu(II) ions did not significantly affect the amount of humate or fulvate sorbed. Dissolved humates and fulvates form soluble complexes with copper over the pH range 3-11. However, in the presence of kaolinite, soluble copper humates and fulvates are unable to compete with the kaolinite for Cu ions at pH 6-7. Above pH 8, humate and fulvate complexes are the only forms of dissolved Cu. Humin is largely insoluble and has little effect on Cu mobility between pH 2 and 12. The implication of this study is that measurement of total soil organic content and water leaching tests should be a standard part of contaminated site investigation.     

A new method to control electrolytes pH by circulation system in electrokinetic soil remediation

To simultaneously avoid a decrease of electro-osmotic flow by hydrogen ions and to increase heavy metal precipitation due to hydroxide ions, simulated electrokinetic remediation was conducted in saturated kaolinite specimens loaded with lead(II) using an electrolyte circulation method to control electrolyte pH. At an electrolyte circulation rate of 1.1 ml/min, it was possible to increase the anolyte pH from 2 to 4 and decrease the catholyte pH from 12 to 8. Using electrolyte circulation, it was observed that the rate of decrease of clay pH due to the change of electrolyte pH was reduced. As a result, the operable period was extended and the removal efficiency for lead(II) was also increased. It was observed that most of the effluent lead(II) from the cathode compartment was electroplated onto the cathode and that residual effluent lead(II) did not precipitate onto, or adsorb to, the clay at the anode compartment during circulation. Therefore, there was no need to treat the electrolyte because there was virtually no effluent from the cathode compartment in the circulation system. It was also found that the electrolyte volume required to sustain the electrolytic reaction was sufficient for the whole electrokinetic remediation process.     

Numerical analysis for electrokinetic soil processing enhanced by chemical conditioning of the electrode reservoirs

A numerical analysis was undertaken for enhanced electrokinetic soil processing. To perform chemical conditioning of the electrode reservoirs, the electrokinetic soil process employed a membrane as a barrier between the electrode reservoirs and the contaminated soil. An alkaline solution was purged in the anode reservoir that was bounded by the membrane. A mathematical model was used for demonstration of pH change and phenol removal from a kaolinite soil bed, the prediction of pH variations in both electrode reservoirs, and the determination of an optimized injection time of the anode-purging solution. The time-dependent dispersion coefficient was employed in consideration of the averaging effect of the velocity profile on a one-dimensional transport. The estimation of pH and phenol profiles in the soil bed reasonably agreed with the experimental data. The simulation revealed that the removal efficiency of phenol from the kaolinite soil could be improved by maintaining pH of the anode solution.     

Effect of humic acids and iron hydroxides deposited on the surface of clay minerals on the 137Cs immobilization

The effect exerted on the relationships of ¹³⁷Cs sorption by humic acids and iron hydroxides deposited on the surface of clay minerals, montmorillonite and kaolinite, differing in the exchange capacity, was studied. The presence of humic acids and Fe(OH)₃ deposited on the mineral surface leads to an increase in the ¹³⁷Cs sorption in a wide pH range (pH 4–9), suggesting the participation of functional groups of humic acids and ferrinol groups of iron(III) hydroxide in binding of the metal ions. The Na⁺, K⁺, and Ca²⁺ ions, on the contrary, with an increase in their concentration in aqueous solution decrease the immobilization of cesium radionuclides and favor their migration in the environment.     

Preparation and characterization of novel nanocomposites based on polyacrylonitrile/kaolinite

A novel intercalation nanocomposite based on polyacrylonitrile (PAN)/kaolinite was prepared by a simple in situ emulsion polymerization in the presence of organically modified layered silicates (kaolinite). The crude kaolinite (K₀) was firstly modified by dimethylsulfoxide-methanol and potassium acetate-aqueous systems; acrylonitrile monomer was then intercalated into kaolinite by displacing potassium acetate from KAc-kaolinite (the kaolinite modified by KAc, marked as K₂). The polymer/kaolinite composites were prepared by in situ emulsion polymerization, and characterized by means of X-ray diffraction, scanning electron microscope, transmission electron microscope and thermal gravimetric analysis. Experimental results indicate that the clay layers of kaolinite in PAN/K₂ composites are well distributed and delaminated. The weight-average molecular weights were measured by small-angle X-ray scattering for all samples. The presence of clay results in an increase in molecular weights compared to pure PAN polymer due to the highly crosslinked structure.     

Effect of sequestration on PAH degradability with Fenton's reagent: roles of total organic carbon,humin, and soil porosity

The phenomenon of contaminant sequestration—and the physicochemical soil parameters which drive this process—has recently been studied by several authors with regard to microbial contaminant degradation. Very little work has been done to determine the effects of contaminant sequestration on the chemical treatability (oxidizability) of soil contaminants; the current study was conducted to address this data gap. A suite of six model soils, ranging in organic matter content from 2.32 to 24.28%, were extensively characterized. Measured parameters included: (1) levels of total organic carbon (TOC); (2) contents of humic acid (HA); fulvic acid (FA) and humin; and (3) total porosity and surface area. Each soil was then spiked with coal tar and, after varying periods of aging/sequestration, subjected to slurry-phase Fenton’s reagent oxidation. Percent recoveries of 12 PAHs, ranging from 3 to 6 aromatic rings, were determined. Results indicated that the susceptibility of each PAH to chemical oxidation was a function of TOC in four of the soils (those with TOC greater than approximately 5%), but was strongly dependent on soil porosity for low-TOC soils. The importance of these two parameters changed with increasing sequestration time, with the relative contribution of porosity-mediated sequestration becoming more important over time. Porosity-mediated effects were more rapid and significant with lower-molecular-weight PAHs (e.g. those with three or four aromatic rings) than with higher-molecular-weight, more hydrophobic compounds. These observations are discussed in light of current physicochemical models of the contaminant sequestration process.     

PZC modification on mechanochemically treated kaolinite

The effect of mechanochemical treatment (oscillating mill) on the surface charge and the point of zero charge (PZC) of kaolinite is discussed.Values of PZC increase with grinding time, reaching a maximum of pH 4.0 after a 120-s treatment. This increase in PZC is attributed mainly to the release of structural aluminium and subsequent formation of polymeric species in solution, and possibly on the surface of the kaolinite particles.The effect of specific Al³⁺ adsorption also has been considered, since the observed pH shift of the interception points for the ground samples was opposite to the expected one if specific Al³⁺ adsorption were the only effect.The electrokinetic behavior is related to the physicochemical and structural changes induced through the grinding process, mainly specific surface area (Sg) and cation exchange capacity (CEC).The results obtained suggest that the system acts as a mechanical mixture of polymeric aluminium species and kaolinite.     

凹凸棒石黏土-腐植酸复合吸附剂吸附Cr(Ⅵ)的性能研究

为促进凹凸棒石黏土-腐植酸复合吸附剂在水处理中的应用,用酸改性的甘肃靖远凹凸棒石黏土和天祝褐煤提取的腐植酸制备出凹凸棒石黏土-腐植酸复合吸附剂,通过SEM、XRD、FT-IR等分析方法对复合吸附剂的结构进行了表征,考察了物料配比及吸附时间、pH值、温度、投加量和初始浓度对Cr(Ⅵ)吸附率的影响。结果表明:靖远凹凸棒石黏土最佳酸改性条件为盐酸5 mol/L,酸化时间120 min,酸用量固液比为1∶10。当Cr(Ⅵ)的起始浓度为0.1 g/L,体积为50 m L,复合吸附剂用量为1.2 g,吸附时间为6 h,p H值为6,温度25℃,酸改性的凹凸棒石黏土与腐植酸的最佳复合比为1∶3时,复合吸附剂对Cr(Ⅵ)的吸附率达到91.7%。复合吸附剂对Cr(Ⅵ)的吸附满足Freundlich模型。在25~45℃条件下,吸附过程ΔG <0、ΔS=87.46 J/(mol·K)、ΔH=-21.2 kJ/mol,表明该吸附是一个自发、熵增、放热的过程。     

Separation and detection of explosives on a microchip using micellar electrokinetic chromatography and indirect laser-induced fluorescence

A new approach for sensitive detection on a microfabricated chip is presented. Indirect laser-induced-fluorescence (IDLIF) was used to detect explosive compounds after separation by micellar electrokinetic chromatography (MEKC). The detection setup was used in an epifluorescence configuration with excitation provided by a near-IR diode laser operating at 750 nm. To achieve indirect detection, a low concentration of a dye (5 microM Cy7) was added to the running buffer as a visualizing agent. Using this methodology, a sample containing 14 explosives (EPA 8330 mixture) was examined. Concentrations of 1 ppm of trinitrobenzene (TNB), trinitrotoluene (TNT), dinitrobenzene (DNB), tetryl, and 2,4-dinitrotoluene (2,4-DNT) could be detected with S/N ratios between 3 and 10. Analyses showing 10 peaks, with plate numbers on the order of 60000, were completed within 60 s using a 65 mm long separation channel. The three isomers of nitrotoluene (2-, 3-, and 4-nitrotoluene) were not resolved. Additionally, the two nitramines (HMX and RDX) could only be detected at much higher concentrations, likely due to the low fluorescence quenching efficiencies of these compounds. The analysis method was also used to separate and detect nitroaromatic compounds in extracts from spiked soil samples. The presence of 1 ppm (1 microg of analyte/1 g of soil) of TNB, DNB, TNT, tetryl, 2,4-DNT, 2,6-DNT, 2-NH2-4,6-DNT, and 4-NH2-2,6-DNT could readily be detected. In the interest of increasing the sensitivity of the analysis, various on-chip injection schemes were evaluated. It was found that a 250 microm double-T injector gave a 35% increase in peak signal compared to a straight-cross injector, which is less than expected based on injected volume.     

Removal of Pb(II) from aqueous solution using modified and unmodified kaolinite clay

Modified kaolinite clay with 25% (w/w) aluminium sulphate and unmodified kaolin were investigated as adsorbents to remove Pb(II) from aqueous solution. The results show that amount of Pb(II) adsorbed onto modified kaolin (20 mg/g) was more than 4.5-fold than that adsorbed onto unmodified kaolin (4.2 mg/g) under the optimized condition. In addition, the linear Langmuir and Freundlich models were used to describe equilibrium isotherm. It is observed that the data from both adsorbents fitted well to the Langmuir isotherm. The kinetic adsorption of modified and unmodified kaolinite clay fitted well to the pseudo-second-order model. Furthermore, both modified and unmodified kaolinite clay were characterized by X-ray diffraction, Fourier transform infrared (FT-IR) and scanning electron microscope (SEM). Finally, both modified and unmodified kaolinite clay were used to remove metal ions from real wastewater, and results show that higher amount of Pb(II) (the concentration reduced from 178 to 27.5 mg/L) and other metal ions were removed by modified kaolinite clay compared with using unmodified adsorbent (the concentration reduced from 178 to 168 mg/L).     

Chlorophenols in leachates originating from different landfills and aerobic composting plants

Both type and concentration of organic contaminants in landfill leachates show great variation depending on many factors, such as type of wastes, rate of water application, moisture content, landfill design and operation age. In this paper, highly toxic chlorophenol derivatives, poorly biodegradable, carcinogenic existence and recalcitrant properties are determined by solid phase microextraction (SPME)-GC/FID in different leachates from landfill and composting plant in Istanbul. Leachates originated from acidogenic, methanogenic phases of Odayeri sanitary landfill (OSL) and from an aerobic composting plant are considered for different chlorophenol types. It is observed that acidogenic leachate from Odayeri landfill includes 2,4-dichlorophenol, 2,6-dichlorophenol, 2,3,4-trichlorophenol, 2,3,4,5-tetrachlorophenol and 2,3,4,6-tetrachlorophenol at concentration ranges, 15-130, 18-65, 8-40, 5-20 and 10-25 microg/l, respectively. Whereas, only 2,4-dichlorophenol at a concentration range 8-40 microg/l is determined in the methanogenic leachate of the landfill, which can be considered as an indication of reductive dechlorination. There is no chlorophenol derivative in aerobic composting leachate. It is determined that acidogenic leachate from Odayeri landfill includes more species of chlorinated phenols at higher concentration.     

Low-temperature thermal desorption of diesel polluted soil: influence of temperature and soil texture on contaminant removal kinetics

Five soil size aggregate fractions, corresponding to coarse (500-840 μm), medium (200-350 μm), fine (75-200 μm) sand, silt (10-75 μm) and clay (<4 μm), were artificially contaminated with diesel, and thermally treated using a laboratory scale apparatus to investigate the effect of soil texture on contaminant adsorption and removal. Ex situ thermal process was simulated using helium as the carrier gas at a flow rate of 1.5 L min(-1), different temperatures (100-300 °C) and different treatment times (5-30 min). The amount of contaminant adsorbed on the soil and the residual amount after thermal treatment was determined by gas chromatography. Results showed that adsorption phenomena and desorption efficiency were affected by the soil texture and that temperature and time of treatment were key factors in remedial process. A temperature of 175 °C is sufficient to remedy diesel polluted sandy and silty soils, whereas a higher temperature (250 °C) is needed for clays. Thermal desorption of diesel polluted soil was shown to be governed by first-order kinetics. Results are of practical interest and may be used in scaling-up and designing desorption systems for preliminary cost and optimal condition assessment.     

合成系绿色高吸水树脂研究进展

综述了无机粘土(包括蒙脱石、海泡石和高岭土)、天然可再生基质(包括蛋白类、海藻酸类、甲壳素/壳聚糖类及腐植酸类)与有机高吸水树脂的复合改性研究进展,介绍了天然原材料的加入对复合吸水树脂的耐盐吸盐水性、吸水倍率、凝胶强度、降解性等性能的影响,最后提出了复合吸水树脂研究有待解决的问题。     

The use of non-uniform electrokinetics to enhance in situ bioremediation of phenol-contaminated soil

In situ bioremediation is an attractive and often cost-effective technology for the cleanup of organics-contaminated sites, but it often requires extended treatment time under field conditions. This study explored the feasibility of using non-uniform electrokinetic transport processes to enhance in situ bioremediation. A bench-scale non-uniform electrokinetic system with periodic polarity-reversal was developed for this purpose, and tested by using a sandy loam spiked with phenol as a model organic pollutant. The results demonstrated that non-uniform electrokinetic processes could accelerate the movement and in situ biodegradation of phenol in the soil. Bidirectional operation enhanced the phenol biodegradation more effectively than unidirectional operation. At the same time, a smaller polarity-reversing interval induced a higher and more uniform removal of phenol from the soil. The results also showed that reversing the polarity of electric field applied could maintain the soil pH and moisture, but it increased the consumption of electricity.     

Characterization of interlayer Cs+ in clay samples using secondary ion mass spectrometry with laser sample modification

Ultraviolet laser irradiation was used to greatly enhance the secondary ion mass spectrometry (SIMS) detection of Cs(+) adsorbed to soil consisting of clay and quartz. Imaging SIMS showed that the enhancement of the Cs(+) signal was spatially heterogeneous: the intensity of the Cs(+) peak was increased by factors up to 100 for some particles but not at all for others. Analysis of standard clay samples exposed to Cs(+) showed a variable response to laser irradiation depending on the type of clay analyzed. The Cs(+) abundance was significantly enhanced when Cs(+)-exposed montmorillonite was irradiated and then analyzed using SIMS, which contrasted with the behavior of Cs(+)-exposed kaolinite, which displayed no Cs(+) enhancement. Exposed illitic clays displayed modest enhancement of Cs(+) upon laser irradiation, intermediate between that of kaolinite and montmorillonite. The results for Cs(+) were rationalized in terms of adsorption to interlayer sites within the montmorillonite, which is an expandable phyllosilicate. In these locations, Cs(+) was not initially detectable using SIMS. Upon irradiation, Cs(+) was thermally redistributed, which enabled detection using SIMS. Since neither the illite nor the kaolinite is an expandable clay, adsorption to inner-layer sites does not occur, and either modest or no laser enhancement of the Cs(+) signal is observed. Laser irradiation also produced unexpected enhancement of Ti(+) from illite and kaolinite clays that contained small quantities of Ti, which indicates the presence of microscopic titanium oxide phases in the clay materials.     

Enhancement of electrokinetic remediation of arsenic spiked soil by chemical reagents

An enhanced electrokinetic remediation process for removal of arsenic, presented as As(V) form, from spiked soil has been investigated with groundwater (GW) and chemical reagents of cetylpyridinium chloride (CPC, a cationic surfactant), ethylenediaminetetraacetic acid (EDTA) and citric acid (CA) under potential gradient of 2.0-3.3V/cm for 5 days treatment. The removal efficiency of As(V) in EK-EDTA system was better than that in other two EK systems. As potential gradient increased from 2.0V/cm to 3.0V/cm, the removal efficiency of As(V) was increased from 35.4% to 44.8% in EK-EDTA system. It showed that the arsenic removal could be enhanced by selecting suitable chemical reagent and increasing potential gradient. The intensive of electroosmotic flow towards the cathode caused a significant retardation of electromigration of arsenic towards the anode. The quantity of As(V) collected in anode reservoir was 1.4-2.5 times greater than that in cathode reservoir for all EK systems. It implied that As(V) removal was directly related to the electromigration rather than electroosmosis mechanism in EK systems. A further investigation need to be conducted to achieve higher removal efficiency of As(V).     

Assessment of cement kiln dust (CKD) for stabilization/solidification (S/S) of arsenic contaminated soils

A stabilization/solidification (S/S) process for arsenic (As) contaminated soils was evaluated using cement kiln dust (CKD). Laboratory-prepared slurries, made of either kaolinite or montmorillonite, and field soils spiked with either As(3+) or As(5+) were prepared and treated with CKD ranging from 10 to 25 wt%. Sodium arsenite and sodium arsenate at 0.1 wt% were used to simulate arsenite (As(3+)) and arsenate (As(5+)) source contamination in soils, respectively. The effectiveness of treatment was evaluated at curing periods of 1- and 7-days based on the toxicity characteristic leaching procedure (TCLP). As-CKD and As-clay-CKD slurries were also spiked at 10 wt% to evaluate As immobilization mechanism using X-ray powder diffraction (XRPD) analyses. Overall, the TCLP results showed that only the As(5+) concentrations in kaolinite amended with 25 wt% CKD after 1 day of curing were less than the TCLP regulatory limit of 5mg/L. Moreover, at 7 days of curing, all As(3+) and As(5+) concentrations obtained from kaolinite soils were less than the TCLP criteria. However, none of the CKD-amended montmorillonite samples satisfied the TCLP-As criteria at 7 days. Only field soil samples amended with 20 wt% CKD complied with the TCLP criteria within 1 day of curing, where the source contamination was As(5+). XRPD and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDX) results showed that Ca-As-O and NaCaAsO(4).7.5H(2)O were the primary phases responsible for As(3+) and As(5+) immobilization in the soils, respectively.