PESA对污泥中铬的萃取研究

An environmentally benign biodegradable chelant,polyepoxysuccinic acid(PESA),was used to separate heavy metals from sewage sludge from the Shanghai Taopu Wastewater Treatment Plant,China,based on chemical extraction technology.The extraction of chromium(Cr) from sewage sludge with an aqueous solution of PESA was studied under various conditions.It was found that the extraction of Cr using PESA was more efficient than that using ethylenediaminetetraacetic acid(EDTA) and S,S-ethylenediaminedisuccinic acid(EDDS) under similar conditions.PESA was capable of extracting Cr from the sewage sludge,and the extraction efficiency was obviously dependent on both the pH and the concentration of the chelating reagent.The extraction efficiency decreased gradually with increasing pH,and the dependence on pH decreased as the concentration of PESA increased.The extraction efficiency reached 58% under conditions of pH = 4 and a ratio of PESA to total heavy metals of 10:1.The extraction efficiency was maintained above 40% within the pH range from 1 to 7 at the high ratio of PESA to total heavy metals of 10:1.Comparing the contents of heavy metals in the sewage sludge before and after the extraction,it was found that the extracted Cr came mainly from the reducible and oxidizable fractions.     

Phytoextraction of Lead from Soil from a Battery Recycling Site: The Use of Citric Acid and NTA

Phytoextraction is a soil remediation technique involving plants that concentrate heavy metals in their shoots, which may be removed from the area by harvest. The application of synthetic chelants to soil increases metal solubility, and therefore enhances phytoextraction. However, synthetic chelants degrade poorly in soil, and metal leaching poses a threat to human and animal health. The aim of this study is to assess the use of two biodegradable chelants (citric acid and nitrilotriacetic acid (NTA)) for Pb phytoextraction by maize from a soil contaminated by battery-casing disposal. In order to assess the behavior of a non-degradable chelant, ethylenediaminetetraacetic acid (EDTA) was also included in the experiment. The chelants NTA and EDTA were applied to soil pots at rates of 0, 3, 5, 7, and 10 mmol kg^?1 of soil. The rates used to citric acid were 0, 5, 10, 15, and 30 mmol kg^?1. Maize plants were grown for 72 days and chelants were applied 9 days before harvest. Soil samples were extracted with CaCl₂ to assess the Pb solubility after chelants application. The results showed that NTA was more efficient than citric acid to solubilize Pb from soil; however, citric acid promoted higher net removal of Pb (120 mg pot^?1) than NTA (57 mg pot^?1). Thus, the use of citric acid, a biodegradable organic acid, could be feasible for enhancing the phytoextraction of Pb from the site studied with no environmental constraints.     

Novel chelant‐based washing method for soil contaminated with Pb and other metals: A pilot‐scale study

Remediation with chelants can restore metal‐contaminated soils for use as a natural resource. Calcareous soil from Meza Valley, Slovenia, and acidic soils from Arnoldstein, Austria, and Pribram, Czech Republic (with 1,028, 862, and 926 mg ∙Pb∙kg⁻¹, respectively), were washed with 60–100 mmol EDTA per kilogram of air‐dried soil in series of 30 batches (50 kg soil batch⁻¹). The approach involves a novel reaction that incorporates alkaline substitution, precipitation and adsorption of toxic metals on polysaccharides, and chelant acidic precipitation via 83% EDTA (on average) and complete process water recycling (no wastewater was generated). The pH gradient was imposed by Ca(OH)₂ and H₂SO₄, and excess reagent was removed with the remediated soil as CaSO₄, thereby preventing the salification of the recycled waters. Remediation removed 60%, 78%, and 71% of the Pb from the Meza, Arnoldstein, and Pribram soils, respectively, and reduced the Pb bioaccessibility levels in the simulated human gastrointestinal phase by 5.0, 7.7, and 8.1 times. Residual emissions (EDTA, toxic metals) were reduced with soil aging and remediated soil deposition on a reactive permeable barrier. The solid waste generated from the process totaled 10.8 kg tons⁻¹ of the air‐dried soil, and the material/energy costs of remediation reached 20.6 € tons⁻¹. These results demonstrate the robustness, efficiency, and safety of this novel approach.     

聚环氧琥珀酸对污泥中镉的萃取作用

Polyepoxysuccinic acid (PESA), as an environmental benign biodegradable chelant, was used to remove heavy metals from the sewage sludge of Shanghai Taopu Wastewater Treatment Plant. The extraction of cadmium (Cd) from sewage sludge using aqueous solution of PESA was studied. It was found that PESA was capable of extracting Cd from the sludge, and the extraction efficiency was dependent on both pH and the concentration of the chelating reagent. The extraction efficiency decreased gradually with increasing of pH, whereas the dependency on pH decreased as the concentration of PESA increased. In the case of the high PESA to total metal ratio, e.g., 10:1, the extraction efficiency reached above 70% within the pH range from 1 to 7. The highest extraction efficiency obtained in the experiment was 78％. By comparing the contents of the heavy metals in sewage sludge before and after the extraction, it was found that the extracted Cd came mainly from the four fractions: acid-soluble, reducible, oxidizable, and water-soluble fractions.     

Mixed chelators of EDTA,GLDA, and citric acid as washing agent effectively remove Cd,Zn, Pb,and Cu from soils

Purpose

Soil washing with chelators is a viable treatment alternative for remediating multi-contaminated soils. The aim of this study was to investigate the removal efficiencies of Cd, Zn, Pb, and Cu in alkaline and acid multi-metal-contaminated soils by washing with the mixed chelators (MC).

Materials and methods

The batch experiments were carried out to evaluate the removal efficiencies of heavy metals in contaminated soils by the MC with different molar ratios of EDTA, GLDA, and citric acid, and evaluated the washing factors, including contact time, pH, MC concentration, and single and multiple washings at the same MC dose, on the removal efficiencies.

Results and discussion

Results showed that the removal efficiencies for Cd, Zn, Pb, and Cu by the MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) were as much as those of the only EDTA washing from both soil at the same application dose of total chelators; moreover, the application dose of EDTA decreased by 80%. For the alkaline-contaminated soil, the removal efficiencies of Cd, Zn, Pb, and Cu decreased with the increasing of the solution pH, which was opposite to acid-contaminated soil. This was attributed to that the metal-ligand complex could be obviously re-adsorbed on the soil surface sites, particularly in low pH values. The removal efficiencies of Cd, Zn, Pb, and Cu depended on MC concentration. A higher MC concentration led to a more effective removal of Cd, Zn, Pb, and Cu in alkaline-contaminated soil; however, their changes were slightly increased in acid-contaminated soil. At the same dose of MC, single washing with higher MC concentration might be favorable to remove heavy metals, moreover, with much less wastewater generation.

Conclusions

The MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) may be a useful, environmentally friendly, and cost-effective chelators to remediate heavily multi-metal-contaminated soil.

     

EDTA Leaching of Cu Contaminated Soils Using Ozone/UV for Treatment and Reuse of Washing Solution in a Closed Loop

Ozone and UV irradiation were used for oxidative decomposition of EDTA-Cu complexes in washing solution obtained during multi-step leaching of Cu (344,1?±?36.5 mg kg^?1) contaminated vineyard soil with EDTA as a chelant. The released Cu was absorbed from the washing solution on a commercial mixture of metal absorbing minerals, and the treated washing solution then reused for removal of soil residual Cu-EDTA complexes in a closed-loop process. Six consecutive leaching steps (6?×?2.5 mmol kg^?1 of EDTA) removed 38.8 % of Cu from soils, and reduced Cu soil mobility, determined using the toxicity characteristic leaching test (TCLP), by 28.5%. The final washing solution obtained after soil remediation was colourless, with a pH close to neutral (7.5?±?0.2) and with low concentrations of Cu and EDTA (0.51?±?0.22 mg L^?1 and 0.083 mM, respectively). The proposed remediation method has therefore potential not just to recycle and save process water, but also not to produce toxic wastewaters. Soil treatment did not substantially alter the soil properties determined by pedological analysis, and had relatively little impact on soil hydraulic conductivity and soil water sorption capacity.     

Extractive Decontamination of Metal-Polluted Soils Using Oxalate

Oxalate (Ox) was investigated as an extractant for decontaminating two metal-polluted soils, one with elevated total zinc (ZnT = 2700 mg kg-1) from the Palmerton, Pennsylvania smelter site and the other from a grossly contaminated (PbT = 210 000 mg kg-1) automobile battery recycling facility in Indiana. Metal retention within the soils was substantially different as shown by sequential fractionation experiments. High Zn removal (>80%) was achieved with 1.0 M Ox when Zn existed predominantly in non-detrital metal fractions. However, Ox was an unsuitable Pb extractant due to the sparing solubility of PbOx(s). Despite the dramatically higher stability of ZnEDTA2- (log K = 16.5) compared to ZnOx° (log K = 3.4), Ox released more Zn than EDTA from the Palmerton soil because 40% of ZnT was associated with the oxide fraction. Extract analysis indicated that Ox, but nor EDTA, dissolved soil Fe oxides in the 24 hr extraction period. When contaminating metals are associated with soil oxides, Ox may be a superior extractant to powerful chelants like EDTA. It is essential to establish thoroughly metal solution chemistry and fixation behavior within the soil when extractive decontamination is proposed for site remediation.     

外源铜和镍在土壤中的化学形态及其老化研究

采用连续提取法测定了外源铜和镍进入田间土壤后的化学形态分布,比较研究了这2种重金属在3种不同类型土壤(红壤,水稻土和潮土)中随老化时间的形态转化和分布.结果表明,外源铜以残留态(40%～60%)和EDTA可提取态(40%)为主;随老化时间,EDTA可提取态、易还原锰结合态及铁铝氧化态向残留态转化;外源镍在酸性红壤中以可交换态(40%)和残留态(30%～50%)为主,在中性水稻土中以EDTA可提取态(30%)和残留态(30%～50%)为主,在碱性潮土中以铁铝氧化态(20%)和残留态(40%)为主.随老化时间,水溶态、可交换态、EDTA可提取态等向残留态转化.土壤pH较低时水溶态和可交换态含量较高,但是同时随老化时间的降低量也明显;pH较高时有利于易还原锰结合态和有机质结合态的转化.     

Extraction kinetics of copper,zinc, iron,and manganese from contaminated sediment using Disodium Ethylenediaminetetraacetate

One technique for cleansing heavy metal contaminated soils is to wash the excavated soil with an extraction solution of a chelating agent. The rate of extraction is an important parameter when considering the length of time needed for soil clean-up and the amount and concentration of wash solution required. The extraction kinetics of copper, zinc, iron and manganese from a contaminated sediment of the Clark Fork River in western Montana, U.S.A., with Disodiun Ethylenediaminetetraacetate (Na₂EDTA) as the extraction agent, were investigated. The results showed the extraction process consisted of rapid extraction in the first minutes followed by much slower extraction for the remainder of the experiment. The rate of extraction, particularly in the rapid phase, demonstrated clear pH dependence: the lower the pH, the faster the extraction rate. In the EDTA concentration range of 0.01 M to 0.05 M, the effect of the EDTA concentration on the extraction rate was not important compared with that of the solution pH. Extraction kinetics for different size particles were similar, although in the first few minutes, EDTA extracted more metals from clay and silt than sand. The two reaction, diffusion, and two-constant kinetic models were compared to experimental results. The two reaction model did not fit any of the data well, and only iron extraction could be described with a simple diffusion model. In general the extraction rates can be well described by the two-constant model, C=A t ^B, up to 600 minutes and under different conditions such as solution pH, EDTA concentration, and different sediment particle size.     

EDTA Extraction of Heavy Metals from Different Soil Fractions and Synthetic Soils

A laboratory-prepared contaminated soil was partitioned into four fractions, namely carbonate, Fe/Mn oxides, organic matter and clay mineral, according to the form in which the heavy metal bound with soil constituents. Individual contaminated soil fractions and synthetic soils were prepared for the study of soil extraction using ethylenediaminetetraacetic acid (EDTA). The effect of contact time and EDTA concentration were evaluated for both individual soil fractions and synthetic soils. The extraction reached equilibrium rapidly, after about 30 min. A 0.01 M EDTA solution was less effective than a 0.05 M or a 0.10 M EDTA. EDTA was proved to be effective for metal removal from the four individual soil fractions and synthetic soils. In general, approximately 90% of metals were removed from synthetic soils by 0.10 M EDTA. EDTA extraction of Pb from a contaminated carbonate fraction was thought to be affected by the formation of lead carbonates. A simple equation based on the sum of the released heavy metal from the individual components is used to check if there are interactions among the different soil components when mixed. The estimated values agreed well with the experimentally measured results only for the 0.10 M EDTA system.     

Enriched stable isotopes for determining the isotopically exchangeable element content in soils

The proportion of metals in soils in equilibrium with soil solution can be determined using isotopic dilution. For this purpose, an isotope dilution mass spectrometric (IDMS) technique has been applied for the elements Cd, Cr, Cu, Mo, Ni, Pb, Tl and Zn. Conventionally, sorbed amounts of heavy metals in soils are analysed by ethylenediamine tetra-acetic acid (EDTA) extraction. The IDMS technique and EDTA extraction were both applied to 115 soil samples and compared. For Cd, Cu, Ni, Pb and Zn, the results of the IDMS technique correlated well with the results of EDTA extractions ( r _s(Cd) = 0.965, r _s(Cu) = 0.916, r _s(Ni) = 0.878, r _s(Pb) = 0.922, r _s(Zn) = 0.962; all at P < 0.001). For Cd and Zn, no significant differences between the results of both methods could be observed, which suggests that EDTA and IDMS determined the same pool. EDTA extracted more Cu, Ni and Pb than was determined by IDMS (7, 26 and 13%, respectively). The correlation between EDTA extraction and IDMS for Cr was significant but weak ( r _s(Cr) = 0.361). For Tl and Mo, EDTA extraction and IDMS did not correlate, and IDMS yielded larger concentrations than EDTA. This can be explained by the fact that Tl and Mo do not form stable EDTA complexes, which are essential for the EDTA technique. Recovery experiments demonstrated that added Cd, Cu, Mo, Ni, Pb, Tl and Zn could be recovered successfully by IDMS analysis (mean recovery = 103 ± 9%). Adsorption isotherms for soil samples were determined for Tl, thereby demonstrating that IDMS gave a better estimation of the native content of sorbed Tl in soils than EDTA extraction.     

Comparison of Prewashing Procedures for the Assessment of Phosphate Rock Dissolution in Soils

When evaluating phosphate rock (PR) dissolution, previous to the extraction with sodium hydroxide (NaOH), dry soil samples with PR were extracted with three solutions to remove exchangeable and solution calcium (Ca) [sodium chloride (NaCl) 1 M, buffered NaCl with ethylenediaminetetraacetic acid (EDTA) (NaCl–EDTA), and NaCl buffered at pH 7 with triethanolamine (TEA) (NaCl–TEA)] for comparison with the extraction of soil samples without any prewash. In acidic soils, up to 51% of applied P was recovered during the NaCl extraction because of the high exchangeable acidity released during the extraction. In soils with exchangeable Ca>2 cmol₍₊₎kg^?1, high EDTA quantities also promoted PR dissolution. The NaCl–TEA solution efficiently removed Ca, avoiding PR dissolution and P retention by calcium hydroxide [Ca(OH)₂] during the NaOH extraction. Thus, when evaluating PR dissolution we recommend the use of NaCl–TEA to remove Ca. We also recommend the same procedure when applying the Chang and Jackson fractionation to calcareous soils and soils submitted to PR application.     

Soil organic phosphorus in tropical forests: an assessment of the NaOH–EDTA extraction procedure for quantitative analysis by solution 31P NMR spectroscopy

The extraction of soil organic phosphorus by the NaOH–EDTA procedure was assessed in detail for a tropical forest soil (clay‐loam, pH 4.3, total carbon 2.7%). Optimum conditions for the quantification of soil organic phosphorus and characterization of its composition by solution ³¹P NMR spectroscopy were extraction in a solution containing 0.25 m NaOH and 50 mm Na₂EDTA in a 1:20 solid to solution ratio for 4 hours at ambient laboratory temperature. Replicate analyses yielded a coefficient of variation of 3% for organic phosphorus as a proportion of the spectral area. There was no significant difference in total phosphorus extraction from fresh and air‐dried soil, although slightly more organic phosphorus and less paramagnetic ions were extracted from dried soil. The procedure was not improved by changing the concentration of NaOH or EDTA, extraction time, or solid to solution ratio. Pre‐extraction with HCl or Na₂EDTA did not increase subsequent organic phosphorus extraction in NaOH–EDTA or improve spectral resolution in solution ³¹P NMR spectroscopy. Post‐extraction treatment with Chelex resin did not improve spectral resolution, but removed small concentrations of phosphorus from the extracts. Increasing the pH of NaOH–EDTA extracts (up to 1.0 m NaOH) increased the concentration of phosphate monoesters, but decreased DNA to an undetectable level, indicating its hydrolysis in strong alkali. The standardized NaOH–EDTA extraction procedure is therefore recommended for the analysis of organic phosphorus in tropical forest soils.     

Use of Single Extraction Methods to Predict Bioavailability of Heavy Metals in Polluted Soils to Rice

Human exposure to toxic heavy metals via dietary intake is of increasing concern. Heavy-metal pollution of a rice production system can pose a threat to human health. Thus, it was necessary to develop a suitable extraction procedure that would represent the content of metal available to rice plants (Oryza sativa L.). The aim of this study was to predict, on the basis of single extraction procedures of soil heavy metals, the accumulation of heavy metals (cadium, lead, copper, and zinc) in rice plants. Six extracting agents [Mehlich 1, Mehlich 3, EDTA (ethylenediaminetetraacetic acid), DTPA–TEA (diethylenetriaminepentaacetic acid–triethanolamine), ammonium acetate (NH₄OAc), and calcium chloride (CaCl₂)] were tested to evaluate the bioavailability of heavy metals from paddy soils contaminated with lead–zinc mine tailings to rice. The extraction capacity of the metals was found to be of the order EDTA > Mehlich 3 > Mehlich 1 > DTPA–TEA > NH₄OAc > CaCl₂. The correlation analysis between metals extracted with different extractants and concentrations of the metals in the grain and stalk of the plant showed positive correlations with all metals. The greatest values of correlation coefficients were determined between the NH₄OAc- and CaCl₂-soluble fractions of soil and contents in plants in all four metals studied. Therefore, NH₄OAc and CaCl₂ were the most suitable extractants for predicting bioavailability of heavy metals in the polluted soils to rice. The results suggested that uptake of heavy metals by rice was mostly from exchangeable and water-soluble fractions of the metals in the soils. Soil-extractable metals were more significantly correlated with metal accumulation in the stalk than in the grain. The pH had more significant influence on availability of heavy metals in the soils than total content of metals and other soil properties. The bioavailability of metals for rice plants would be high in acidic soils.     

Enhanced Sequential Flushing Process for Removal of Mixed Contaminants from Soils

The feasibility of a sequentially enhanced process for the remediation of soils contaminated by mixed contaminants, specifically multiple polycyclic aromatic hydrocarbons (PAHs) and heavy metals, was investigated. This process consists of sequential flushing using two chemical agents: a surfactant and a chelate. A series of laboratory column experiments was conducted with three different sequential schemes, designated as SEQ1, SEQ2, and SEQ3, in two distinct flushing stages, to remove PAHs and heavy metals from a field-contaminated soil. The SEQ1 scheme involved flushing 0.2 M ethylenediaminetetraacetic acid (EDTA) followed by flushing 5 % Igepal. The SEQ2 scheme involved flushing 5 % Igepal followed by flushing 0.2 M EDTA. SEQ1 was investigated under a constant hydraulic gradient of 1.2, while the SEQ2 scheme was investigated under hydraulic gradients that increased from 1.2 to 4.0. The SEQ3 scheme consisted of sequential flushing of 5 % Igepal (first stage) and 0.2 M EDTA (second stage) under a constant low hydraulic gradient of 0.2. The selected sequential schemes allowed an assessment of the efficacy of sequencing the surfactant and chelating flushing for the removal of multiple heavy metals and PAHs under various hydraulic gradients. The hydraulic conductivity (or flow) was found to vary depending on the flushing agent and the sequence scheme. Under the high hydraulic gradient, the hydraulic conductivity was lower during chelant flushing stage as compared with surfactant flushing stage in both SEQ1 and SEQ2. However, under a low gradient condition (SEQ3), the hydraulic conductivity was approximately the same during both chelant and surfactant flushing stages. The contaminant removal was also significantly affected by the flushing agent and sequence and the applied hydraulic gradient. Heavy metals were removed during chelant flushing, while PAHs were removed during surfactant flushing. The total removal efficiencies of Pb, Zn, and Cu were 76 %, 63 %, and 11 % in SEQ1 and 42 %, 40 %, and 7 % in SEQ2, respectively, while the total removal efficiencies of phenanthrene, anthracene, benz(a)anthracene, and pyrene were 51 %, 35 %, 58 %, and 39 % in SEQ1 and 69 %, 50 %, 65 %, and 69 % in SEQ2, respectively. Overall, the total mass removal of heavy metals and PAHs was higher in SEQ1 as compared with SEQ2, demonstrating that SEQ1 is the effective sequence scheme. Comparison of the results of high and low gradient conditions (SEQ2 and SEQ3) reveals that the removal of contaminants, especially heavy metals, is rate-limited. Overall, this study showed that the removal of co-existing heavy metals and PAHs from soils is possible through the careful selection of the sequence under which the flushing of chelant and surfactant occurs and depends on the site-specific soil and contaminant conditions. Additional research is needed to establish the most optimal flushing scheme (sequence duration and flow velocity) to remove the mixed contaminants effectively and efficiently.     

Inorganic Amendments to Decrease metal Availability in Soils of Recreational Urban Areas: Limitations to their Efficiency and Possible Drawbacks

The use of three inorganic materials as potential immobilizers of metals in soils has been studied by monitoring metal availability by EDTA extraction, the Simple Bioaccessibility Extraction Test (SBET) and extraction with a mixture of organic acids (OA). The SBET test was the most suitable for risk assessment in soils of recreational areas. The materials were a 4A-type zeolite, tri-calcium phosphate and ‘slovakite’, a synthetic sorbent developed for remediation of metal-polluted soils. Adsorption/desorption experiments of metals by the isolated materials showed that all materials caused a strong retention of metals from solutions, with negligible release by dilution. When added to soils of three parks, zeolite and, to a much lesser extent, slovakite caused some increase in soil pH. Despite this increase of pH, zeolite is often the least effective amendment for decreasing metal availability estimated by any method, and even sometimes seems to cause some increase, as well as an increase of soil electrical conductivity. In contrast, slovakite causes a decrease of available metals as estimated by EDTA and SBET, but by SBET the effect seems to be steadily reduced after the first samplings, so that after 300 days the metals extracted by this method are very similar to the data for the blanks. Despite the differences in pseudo-total metal contents, few differences are noticeable among parks. In general, these amendments are scarcely efficient in the case of neutral urban soils like those studied here. Other techniques are needed for controlling and, eventually, decreasing metal pollution hazard in soils of recreational areas.     

Dissolution of Poorly Crystalline Iron Oxides in Soils by EDTA and Oxalate

Poorly crystalline iron oxides in soils are often estimated by 2 hours oxalate extraction at pH 3 and less often by 3–7 months EDTA extraction at pH 7.5–10.5. Calculated solubility products (Ksp) of iron oxides in equilibrium with EDTA and oxalate showed EDTA to dissolve only iron oxides with Ksp > 10^?40-10^?41 at pH > 10, whereas at pH 3 oxalate (and EDTA) should theoretically dissolve all iron oxides. The different pHs could largely account for the great difference in extraction speed between the two methods. Although EDTA and oxalate seem to act by surface complexation, where the adsorbed ligand by attenuating lattice Fe-O bonds causes iron detachment, the mechanisms are considered to be different. Possibly EDTA forms tetranuclear surface complexes, which are considered to inhibit dissolution of well crystallized but not poorly crystallized iron oxides due to differences in bond strengths. Oxalate forming binuclear and mononuclear surface complexes can probably also act as an electron bridge between iron(II) in solution and surface iron(III) leading to iron(II) catalyzed dissolution of iron oxides. This mechanism is obviously of particular importance in the dissolution of magnetite and maghemite. Despite the great theoretical differences the published methods with EDTA and oxalate dissolve comparable amounts of iron from many soils and the dissolved iron corresponds to poorly crystalline (highly reactive) iron oxides, mainly ferrihydrite.     

GLDA淋洗参数对污泥中重金属去除效率的影响及其动力学分析

采用GLDA作为淋洗剂对工业污水污泥进行淋洗,确定淋洗的最优参数,为治理工业污泥提供参考依据。通过振荡淋洗研究了GLDA浓度（0.5% ~ 20%）、pH（2 ~ 10）、液固比（10∶1 ~ 80∶1）和淋洗时间（0 ~ 24 h）对污泥中重金属去除率的影响,利用动力学方程对实验数据进行拟合。结果表明,降低pH、增加液固比和延长淋洗时间均可提升重金属的淋洗效率,在pH为2,浓度5%,液固比60∶1,淋洗时间480 min时,GLDA对污泥中的重金属淋洗率达到最优,镍（Zn）、镍（Ni）、镉（Cd）和铬（Cr）的去除率分别为91.21%、76.34%、69.56%和65.01%。准二级动力学方程可以较好的拟合GLDA对4种重金属的淋洗过程,说明重金属淋洗过程以化学淋洗为主。综上所述,在进行淋洗参数优化的基础上,GLDA可用于工业污水污泥中重金属的去除。     

Elemental Uptake and Root-Leaves Transfer in Cistus Ladanifer L. Growing in a Contaminated Pyrite Mining Area (Aljustrel-Portugal)

Soils at the contaminated Aljustrel mining area situated in SWPortugal in the Iberian Pyrite Belt, and Cistusladanifer L., an autochthonal aromatic bush, were investigated to quantify the most relevant elements present in soils and in the plant, and to evaluate the possibility of phytoremediation of that area, particularly concerning the elements of higher pollutant potential.Multielemental (Mg, S, Cl, K, Ca, Cr, Mn, Fe, Cu, Zn, As, Br and Pb) characterisation of the soils and C. ladanifer leaves was carried out by Energy-Dispersive X-Ray Fluorescence spectrometry (EDXRF). Subsequently, due to their abundance in the soil and significant elevation compared to the control site, potential toxicity and/or biological significance, Mn, Cu, Zn, and Pb were determined by Atomic Absorption Spectrometry (AAS) in samples of soils, as well as in the roots and leaves of plants. C. ladanifer is able to survive and grow in soils having high concentrations of such toxic elements and to accumulate Mn.The bioavailability of Mn, Cu, Zn and Pb in the soils was evaluated by determining the contents of the elements in a solution of 0.5 M ammonium acetate, 0.5 M acetic acid and 0.02 M EDTA, pH 4.7, after soil extraction. Comparison of the values obtained with the corresponding element concentration in leaves give us a model of C. ladanifer's capacity to avoid these metals to reach toxic levels in the plant or their toxic effects when such levels are exceed, as in the case of Mn.     

Remediation of Lead Contaminated Soil by EDTA. I. Batch and Column Studies

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 expected, lead solubility was observed to decrease as pH was increased by the addition of KOH. However, Pb solubility was only slightly decreased by the addition of both CaCl₂ and KOH. The amount of time required to leach 6.0 L of extraction solution through the soil columns varied from 2 to 33 days. The addition of CaCl₂ and/or KOH resulted in increased soil hydraulic conductivity relative to the EDTA-only solution. The hydraulic conductivity was related to residual calcium carbonate content, suggesting that dissolution of CaCO₃ and subsequent production of CO₂ gas in the soil pores was partially responsible for the observed reductions in soil permeability. However, Pb removal was diminished with the addition of CaCl₂ and KOH because of the decreased Pb solubility and also kinetic limitations associated with the shorter residence time of the extract solution in the column.