Comparative evaluation of NTA and EDTA for extractive decontamination of Pb-polluted soils (original) (raw)
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Influence of electrolytes on EDTA extraction of Pb from polluted soil
Water, Air, & Soil Pollution, 1992
Because the economics of soil extraction processes depend on conservation and reuse of costly chelating agents, the ability of various electrolytes to modify EDTA extraction of Pb from a grosslycontaminated soil (Pb T = 21%) was investigated using batch equilibration experiments. In the absence of added electrolyte, a single 5-hr. extraction with 0.04 M EDTA (corresponding to hl Pb T to EDTA ratio) released 65% of Pb T over the pH 5 to 9 range. Under these conditions, Na +-, Li +-, and NH4C104 salts at 0.5 M increased Pb desorption to nearly 80%, probably from exchange displacement of soilbound Pb 2+ and increased solubility of Pb-containing phases at higher ionic strength. Because C1-and C10 4-salts were equally effective, chlorocomplex formation was insignificant. Under slightly acidic conditions, Ca(C104) 2 and Mg(C104) 2 at 0.167 M caused roughly the same elevation in Pb recovery as 0.5M of the monovalent electrolytes. However, with progressively higher pH, Ca, and to a lesser extent Mg, suppressed Pb solubilization by competitive chelation of EDTA. Pb recovery by EDTA soil washing could be enhanced by addition of Ca salts at pH 4 to 6. Subsequent pH elevation in the presence of Ca would promote decomposition of Pb-EDTA complexes and separation of Pb as a hydroxide precipitate.
Sustainability, 2018
This paper presents the results of an experimental study aimed at investigating the applicability of ethylenediamine-N,N-disuccinic acid (EDDS) as a washing solution for the remediation of Pb-contaminated soil. All aspects of the treatment are analyzed and optimized, including the reuse and the final disposal of the EDDS spent solution. Different molar concentrations of the washing solutions and the efficiencies of varying solid/liquid ratio are tested at different pH values. More than 90% of the mobile Pb fraction is removed in about 24 h at pH 6. Accordingly, soil toxicity strongly decreases as a consequence of the treatment. The regenerated solution exhibits a reduced, but not negligible, extractive capacity. The total extraction of Pb is approximately 50% of the initial value after one regeneration cycle, and almost 20% after a second regeneration cycle. Respirometric tests, conducted using an activated sludge sampled in a municipal wastewater treatment plant, indicate that the spent solutions are not biodegradable, but they do not exert any toxic effect on the biomass. On the contrary, tests on regenerated solutions displayed the same biodegradability as the fresh ones.
EDTA-Enhanced Washing for Remediation of Pb and/or Zn-Contaminated Soils
Journal of Environmental Engineering-asce, 2006
The effects of the operating conditions, the initial concentrations of heavy metals in soils, and the competition among heavy metals during ethylenediaminetetraacetic acid ͑EDTA͒-enhanced soil washing were extensively investigated using batch experiments with Pb-and/or Zn-contaminated soils aiming to determine the heavy-metal removal for different types of contaminations and to optimize the process parameters. Pb or Zn removal efficiency was found to be dependent on contact time, pH, concentrations of EDTA, and their initial concentrations in contaminated soils. The experimental results showed that the heavy-metal removal efficiency increased with a higher initial concentration of heavy metals in soils, and the concentrations of heavy metals in the solutions after washing were linearly correlated with their initial concentrations in soils. The study of the competition among heavy metals indicated that when EDTA was present in solution with the concentration less than the stoichiometric requirements, Pb removal efficiency was higher than that of Zn; on the other hand, when EDTA concentration was greater, Pb and Zn removal efficiencies were almost the same.
Electrochemical EDTA recycling after soil washing of Pb, Zn and Cd contaminated soil
Journal of Hazardous Materials, 2011
Recycling of chelant decreases the cost of EDTA-based soil washing. Current methods, however, are not effective when the spent soil washing solution contains more than one contaminating metal. In this study, we applied electrochemical treatment of the washing solution obtained after EDTA extraction of Pb, Zn and Cd contaminated soil. A sacrificial Al anode and stainless steel cathode in a conventional electrolytic cell at pH 10 efficiently removed Pb from the solution. The method efficiency, specific electricity and Al consumption were significantly higher for solutions with a higher initial metal concentration. Partial replacement of NaCl with KNO 3 as an electrolyte (aggressive Cl − are required to prevent passivisation of the Al anode) prevented EDTA degradation during the electrolysis. The addition of FeCl 3 to the acidified washing solution prior to electrolysis improved Zn removal. Using the novel method 98, 73 and 66% of Pb, Zn and Cd, respectively, were removed, while 88% of EDTA was preserved in the treated washing solution. The recycled EDTA retained 86, 84 and 85% of Pb, Zn and Cd extraction potential from contaminated soil, respectively.
Chemosphere, 2008
The feasibility of a novel two-phase method for remediation of Pb (1374 mg kg À1 ), Zn (1007 mg kg À1 ), and Cd (9.1 mg kg À1 ) contaminated soil was evaluated. In the first phase we used EDTA for leaching heavy metals from the soil. In the second phase we used an electrochemical advanced oxidation process (EAOP) for the treatment and reuse of washing solution for soil rinsing (removal of the soilretained, chelant-mobilized metallic species). In EAOP, a boron-doped diamond anode was used for the generation of hydroxyl radicals and oxidative decomposition of EDTA-metal complexes at a constant current density (15 mA cm À2 ). The released metals were removed from the solution by filtration as insoluble participate and by electro-deposition on the cathode. Four consecutive additions of 5.0 mmol kg À1 EDTA (total 20 mmol kg À1 ) removed 44% Pb, 14% Zn and 35% Cd from the soil. The mobility of the Pb, Zn and Cd (Toxicity Characteristic Leaching Procedure) left in the soil after remediation was reduced by 1.6, 3.4 and 1.5 times, respectively. The Pb oral availability (Physiologically Based Extraction Test) in the simulated stomach phase was reduced by 2.4 and in the intestinal phase by 1.7 times. The discharge solution was clear, almost colorless, with pH 7.73 and 0.47 mg L À1 Pb, 1.03 mg L À1 Zn, bellow the limits of quantification of Cd and 0.023 mM EDTA. The novel method enables soil leaching with small water requirements and no wastewater generation or other emissions into the environment.
Multi-step leaching of Pb and Zn contaminated soils with EDTA
Chemosphere, 2007
The efficiency of multi-step leaching of heavy metal contaminated soils was evaluated in a laboratory scale study. Four different soils contaminated with Pb (1136 ± 16-4424 ± 313 mg kg À1 ) and Zn (288 ± 5-5489 ± 471 mg kg À1 ) were obtained from industrial sites in the Mežica Valley, Slovenia and Príbram district, Czech Republic. Different dosages (2.5-40 mmol kg À1 ) of ethylenediamine tetraacetate (EDTA) were used to treat soils in 1-10 leaching steps. Higher EDTA dosages did not result in a proportional gain in Pb and Zn removal. EDTA extracted Pb more efficiently than Zn from three of four tested soils. The percentage of removed Zn did not exceed 75% regardless of the soil, EDTA dosage and leaching steps. Significantly more Pb (in three of four soils) and Zn were removed from soils when the same amount of EDTA was applied in several leaching steps. The interference of major soil cations Fe and Ca with EDTA complexation as a possible factor affecting Pb and Zn removal efficiency with multi-step heap leaching was examined and is discussed. The results of our study indicate that, for some soils, using multi-step leaching instead of the more traditionally used single dose EDTA treatment could improve heavy metal removal efficiency and thus the economics of soil remediation.
Remediation of Lead-Contaminated Soil with Edta : B Atch and Column Studies
1996
Chelate extraction using ethylenediaminetetraacetic acid (EDTA) and other chelates has been demonstrated to be an effective method of removal of Pb from many contaminated soils. However, column leaching of Pb from alkaline soils with EDTA has been problematic due to extremely low soil permeability. The purpose of this study was to determine the effect of the addition of KOH and Ca(Cl) 2 to K2H2EDTA extraction solution on Pb removal and hydraulic conductivity. A Pb-contaminated soil was sampled from an abandoned lead-acid battery recycling facility. Both batch shaker extractions and column l eaching experiments were completed using five different EDTA extract solutions. Addition of Ca(Cl) 2 only to K2H2EDTA did not change the amount of Pb removed by batch extraction, and Pb solubility was only slightly decreased by the addition of both Ca(Cl) 2 and KOH. Lead solub ility was observed to decrease as pH was increased by the addition of KOH. The amount of time required to l each 6.0 l of...
Evaluation of Extraction Procedures for Removing Lead from Contaminated Soil
Journal of Environmental Science and Health Part A-toxic/hazardous Substances & Environmental Engineering, 2005
Soil extraction of lead contaminated soil collected from sites near an abandoned battery recycling and secondary lead-smelting factory was investigated for potential use in decontaminating soil at the sites. A fractionation study was conducted to elucidate soil retention mechanism for Pb at the site. Three soil pits were selected from an area surrounding the factory based on level of Pb contamination. Soil samples were collected from each pit in two layers: surface soil and subsoil (0–15 cm and 15–30 cm). Soil physical analysis showed that the soil texture was sandy loam and sandy clay loam with clay content between 11–21%. Soil pH was strongly acid to moderately acid (pH 4.8–5.9). Pb levels in the surface soil were 1620 and 153 mg kg−1 (air-dried basis) respectively for heavily and slightly contaminated soil. A reference soil site contained 15 mg kg−1 of Pb. Partitioning studies indicated that more than 90% of total Pb in the soil existed in three primary fractions: exchangeable, carbonate, and Fe-Mn oxide. This suggested that Pb sources entering the soil from the Pb factory remained in relatively weakly bound forms, which are mobile and have potentially biological availability. Mobility of Pb as in the soil assessed by mobility factor (MF) was as high as 75% indicating a high potential of Pb remobilization. Due to high mobility, the Pb would be amendable to remediation or removal by soil extraction procedures. To determine if such weekly bound Pb could be easily removed, both soil washing (ex situ) and soil flushing (in situ) techniques were evaluated for potential Pb remediation procedure. Particle size separation of soil into coarse (2.0–0.25 mm), medium (0.25–0.15 mm), and fine size (<0.15 mm) was conducted before initiating soil washing for comparing Pb removal efficiency in these fractions with the indigenous soil fraction. Using EDTA (2:1 mole to Pb) as a washing solution up to 85–95% of Pb was removed under the optimum conditions (retention time = 60 min), and liquid to solid ratio (L/S) at 5:1 for coarse fraction and 10:1 for smaller fraction. Pb could be removed from contaminated soil using EDTA extraction; however, the efficiency was higher in the coarse texture soil fraction. As a result particle size separation is recommended before application of the soil washing procedure. For smaller soil particle size fraction a series of extraction was needed for obtaining an adequate extraction efficiency. Three solvents tested as flushing solution showed 85, 84, and 74% of Pb was removed by EDTA (2:1 mole to Pb), 1 M HNO3, and 0.2 M ammonium citrate, respectively after flushing with 20 pore volumes. The capacity of the three flushing solutions to remove Pb from the contaminated soil were ranked in the order: EDTA ≈ 1 M HNO3 > 0.2 N ammonium citrate. However, in highly contaminated soil all solvent extract required several Pb leaching cycles. The flushing process using 1 M HNO3 increased soil acidity to extreme acid conditions (pH 2.0) resulting in adverse effects to physicochemical properties of the treated soil. In general, results showed three factors influenced Pb removal by the extraction techniques: (i) initial Pb concentrations, (ii) Pb partitioning within soil, and (iii) particle size of soil matrix.
Environmental Science and Pollution Research, 2011
The effectiveness of five waste materials (blast furnace slag, water treatment sludge, red mud, sugar mill mud and green waste compost) as metal immobilizing agents in a Pb-and Zn-contaminated soil was investigated. Materials were incubated with the soil for a period of 12 weeks at rates of 5 and 10% w/w. Addition of blast furnace slag, water treatment sludge and red mud markedly reduced EDTA-extractable Zn levels, while additions of water treatment sludge, red mud and mill mud reduced EDTA-extractable Pb concenbtrations. A sequential extraction procedure revealed that reductions in acetic acid-extractable (exchangeable and adsorbed) Pb induced by additions of mill mud and compost were accompanied by increases in the oxidisable (organic) and residual Pb fractions. For Zn, reductions in the percentage present in the exchangeable/adsorbed and organic fractions following additions of water treatment sludge, red mud and mill mud were accompanied by increases in the percentages present in the residual fraction. Materials such as water treatment sludge, red mud, mill mud and blast furnace slag showed good potential as immobilizing agents.
Remediation of Lead Contaminated Soil by EDTA. I. Batch and Column Studies
Water Air and Soil Pollution - WATER AIR SOIL POLLUT, 1999
Extraction using ethylenediaminetetraacetic acid (EDTA), and other chelates has been demonstrated to be an effective method of removal of Pb from many contaminated soils. However, column leaching of Pb from alkaline soils with EDTA has been problematic due to extremely low soil permeability. The first purpose of this study was to develop batch extraction procedures and methods of analysis of batch extraction data to provide Pb solubility information which can be used to model the column extraction of Pb from soils. The second purpose was to determine the effect of the addition of KOH and CaCl2 to K2H2EDTA extract solution on both hydraulic conductivity and Pb removal. A Pb-contaminated soil sample was collected from an abandoned battery recycling facility. Both batch shaker extractions and column leaching experiments were completed using 5 different EDTA extract solutions. When only CaCl2 was added to EDTA no change in the amount of Pb removed by batch extraction was observed. As ex...