超声强化EDDS/EGTA淋洗修复重金属污染土壤

采用响应面法中的Box-Behnken实验设计,研究了超声强化N,N'-乙二胺二琥珀酸(EDDS)和乙二醇双(2-氨基乙基醚)四乙酸(EGTA)复合淋洗对土壤中Cu、Zn、Pb 和Cd 等4种重金属的去除效果,拟合了各重金属去除率、潜在生态风险指数削减率与EDDS投加量、EGTA投加量、超声功率和初始pH等淋洗条件之间的关系,模拟值与观测值相关性高,模拟精度较高。EGTA在较广pH范围对高生理毒性的Cd具有较强的洗脱效果,酸性条件下可有效洗脱Zn;Cu去除率在酸性条件下随着EDDS投加量的增加而显著提高,Pb去除率则在碱性条件随着EDDS投加量的增加而显著提高。基于模型优化结果的验证实验显示,当EDDS/重金属摩尔质量比为0.81、EGTA/重金属摩尔质量比为3.92、超声功率为569.85 W、pH为3.95时,潜在生态风险指数削减率最大,达到86.05%,Cu、Zn、Pb和Cd去除率分别为72.48%、62.40%、59.25%和87.45%,与模型拟合结果偏差较小,表明模型具有较好的拟合和预测能力。     

微生物矿化修复重金属污染土壤

以选矿厂附近土壤为研究对象,分析了土壤中交换态重金属含量,As、Pb、Cd、Zn和Cu的交换态浓度为14.01、4.95、0.64、33.46和12.95 mg/kg。基于生物矿化原理,利用碳酸盐矿化菌生长代谢过程产生的脲酶来分解底物尿素,产生碳酸根离子,固结重金属离子,使得土壤中活泼的重金属离子转变为碳酸盐矿物态,降低其危险。研究了温度、pH和重金属离子对酶活性的影响,发现环境30℃温度有利于促进酶活性;在弱酸性条件下,底物分解量减少15%;重金属离子在低浓度时对脲酶活性影响不大,浓度提高后对酶活性抑制作用没有加剧。将制备好的微生物矿化修复制剂喷洒于1 000 m2的污染土壤中,实验结果发现,土壤中交换态重金属离子含量在0～20 cm范围内明显减少,As、Pb、Cd、Zn和Cu的交换态浓度分别减少至2.37、1.25、0.31、16.67和3.42 mg/kg。     

Solvent extraction for heavy crude oil removal from contaminated soils

A new strategy of heavy crude oil removal from contaminated soils was studied. The hexane-acetone solvent mixture was used to investigate the ability of solvent extraction technique for cleaning up soils under various extraction conditions. The mixtures of hexane and acetone (25 vol%) were demonstrated to be the most effective in removing petroleum hydrocarbons from contaminated soils and approx 90% of saturates, naphthene aromatics, polar aromatics, and 60% of nC₇-asphaltenes were removed. Kinetic experiments demonstrated that the equilibrium was reached in 5 min and the majority of the oil pollutants were removed within 0.5 min. The effect of the ratio between solvent and soil on the extraction efficiency was also studied and results showed that the efficiency would increase following the higher solvent soil ratio. Then the multistage continuous extraction was considered to enhance the removal efficiency of oil pollutants. Three stages crosscurrent and countercurrent solvent extraction with the solvent soil ratio 6:1 removed 97% oil contaminants from soil. Clearly the results showed that the mixed-solvent of hexane and acetone (25 vol%) with character of low-toxic, acceptable cost and high efficiency was promising in solvent extraction to remove heavy oil fractions as well as petroleum hydrocarbons from contaminated soils.     

粘土矿物修复重金属污染土壤

简要介绍了我国土壤重金属污染的现状与危害.通过粘土矿物在重金属污染土壤中净化功能的阐述,提出利用粘土矿物修复土壤重金属污染的观点.继而从天然和改性粘土矿物特性,叙述了粘土矿物修复土壤重金属污染的机制与应用进展及其影响因素.最后讨论了粘土矿物在修复土壤重金属污染过程中值得注意的几个问题,并展望了粘土矿物在该领域应用中的发展方向.     

Removal of heavy metals and arsenic from contaminated soils using bioremediation and chelant extraction techniques

A combined chemical and biological treatment scheme was evaluated in this study aiming at obtaining the simultaneous removal of metalloid arsenic and cationic heavy metals from contaminated soils. The treatment involved the use of the iron reducing microorganism Desulfuromonas palmitatis, whose activity was combined with the chelating strength of EDTA. Taking into consideration that soil iron oxides are the main scavengers of As, treatment with iron reducing microorganisms aimed at inducing the reductive dissolution of soil oxides and thus obtaining the release of the retained As. The main objective of using EDTA was the removal of metal contaminants, such as Pb and Zn, through the formation of soluble metal chelates. Experimental results however indicated that EDTA was also indispensable for the biological reduction of Fe(III) oxides. The bacterial activity was found to have a pronounced positive effect on the removal of arsenic, which increased from the value of 35% obtained during the pure chemical treatment up to 90% in the presence of D. palmitatis. In the case of Pb, the major part, i.e. approximately 85%, was removed from soil with purely chemical mechanisms, whereas the biological activity slightly improved the extraction, increasing the final removal up to 90%. Co-treatment had negative effect only for Zn, whose removal was reduced from 80% under abiotic condition to approximately 50% in the presence of bacteria.     

铁改性生物炭的制备及其在重金属污染土壤修复技术中的应用进展

生物炭已被广泛应用于修复重金属污染土壤,但粒径大、力学性能差、吸附点位较少等缺点限制了其应用。由铁基化合物和生物炭制备的铁改性生物炭,可优化生物炭的性能,弥补生物炭修复能力的不足,表现出良好的重金属钝化效果。综述了铁改性生物炭的制备方法,以及该材料对重金属污染土壤修复的研究进展：介绍了铁改性生物炭的制备方法和常用表征手段;总结了制备及修复过程中的主要影响因素 (原材料、温度、投加量、修复时间等) ;从静电作用、离子交换、络合、氧化还原、共沉淀作用等方面阐明了铁改性生物炭对重金属的固定化机制;分析了施用铁改性生物炭对土壤微生态的影响;最后指出了铁改性生物炭材料在应用中可能存在的问题。以期为铁改性生物炭在重金属污染土壤修复中的应用提供理论依据。     

Degradability of ethylenediaminedisuccinic acid (EDDS) in metal contaminated soils: implications for its use soil remediation

Previous research has identified ethylenediaminedisuccinate (EDDS) as a promising biodegradable alternative for persistent compounds such as EDTA for application in soil washing or enhanced phytoextraction of heavy metals. This study examines heavy metal mobilization in three polluted soils varying in soil composition, with specific attention for competitive behaviour for complexation between the various metals and major elements, such as Al, Fe, Mn, Ca and Mg. In addition, amendment biodegradability was compared between the different soil types. The selected soils included a moderately contaminated calcareous clayey soil, a dredged sediment derived surface soil with similar soil characteristics yet more heavily polluted with Cd, Cr and Zn, and a sandy soil moderately contaminated by historical smelter activity (atmospheric deposition). Biodegradability of EDDS in the three soils varied distinctly. This was mainly expressed in the duration of the lag phase prior to metal complex degradation, and not so much in the half life when degradation effectively did set in. Differences in the lag phase were attributed to differences in soil pollution. However, EDDS was fully degraded within a period of 54 d in all soils regardless of initial delay. Assessment of the cation mobilisation patterns in the three soils under study revealed that mainly Ca, Fe and Al can reduce effectiveness of heavy metal mobilisation by competition for complexation.     

Decomposition of heavy metal contaminated nettles (Urtica dioica L.) in soils subjected to heavy metal pollution by river sediments

Two incubation experiments were conducted to evaluate differences in the microbial use of non-contaminated and heavy metal contaminated nettle (Urtica dioica L.) shoot residues in three soils subjected to heavy metal pollution (Zn, Pb, Cu, and Cd) by river sediments. The microbial use of shoot residues was monitored by changes in microbial biomass C, biomass N, biomass P, ergosterol, N mineralisation, CO(2) production and O(2) consumption rates. Microbial biomass C, N, and P were estimated by fumigation extraction. In the non-amended soils, the mean microbial biomass C to soil organic C ratio decreased from 2.3% in the low metal soil to 1.1% in the high metal soils. In the 42-d incubation experiment, the addition of 2% nettle residues resulted in markedly increased contents of microbial biomass P (+240%), biomass C (+270%), biomass N (+310%), and ergosterol (+360%). The relative increase in the four microbial properties was similar for the three soils and did not show any clear heavy metal effect. The contents of microbial biomass C, N and P and ergosterol contents declined approximately by 30% during the incubation as in the non-amended soils. The ratios microbial biomass C to N, microbial biomass C to P, and ergosterol to microbial biomass C remained constant at 5.2, 26, and 0.5%, respectively. In the 6-d incubation experiment, the respiratory quotient CO(2)/O(2) increased from 0.74 in the low metal soil to 1.58 in the high metal soil in the non-amended soils. In the treatments amended with 4% nettle residues, the respiratory quotient was constant at 1.13, without any effects of the three soils or the two nettle treatments. Contaminated nettle residues led generally to significantly lower N mineralisation, CO(2) production and O(2) consumption rates than non-contaminated nettle residues. However, the absolute differences were small.     

重金属-多氯联苯复合污染土壤同步洗脱

电子垃圾拆解区土壤具有重金属与有机物复合污染的特性,尤其以Cu、Pb、Cd和多氯联苯(PCBs)的复合污染较为突出。为了同步脱除土壤中重金属与PCBs,选用增溶物质:Tween 80、TX-100、SDBS、β-环糊精与螯合剂柠檬酸依次组合进行复合污染土壤淋洗实验,应用批量平衡震荡法研究它们对重金属(Cu、Pb、Cd)与PCBs(Aroclor 1254)的洗脱效果。通过比较洗脱效果、环境友好性等方面,得出非离子表面活性剂Tween 80与天然螯合剂柠檬酸2种淋洗剂复合最佳;进一步研究两者的淋洗先后顺序、浓度配比、洗脱时间及淋洗剂pH对污染土壤洗脱效果的影响,结果表明,在Tween 80和柠檬酸均为10 g/L、pH=6、淋洗时间12 h时淋洗效果达到最佳,对Cu、Pb、Cd及PCBs的洗脱率分别达到98.77%、55.92%、66.82%和58.01%。因此,利用Tween80和柠檬酸组合可同时有效去除土壤重金属和PCBs,是复合污染土壤淋洗修复的有效淋洗剂。     

Leaching of heavy metals from contaminated soils using EDTA

Ethylenediaminetetraacetic acid (EDTA) extraction of Zn, Cd, Cu and Pb from four contaminated soils was studied using batch and column leaching experiments. In the batch experiment, the heavy metals extracted were virtually all as 1:1 metal-EDTA complexes. The ratios of Zn, Cd, Cu and Pb of the extracted were similar to those in the soils, suggesting that EDTA extracted the four heavy metals with similar efficiency. In contrast, different elution patterns were obtained for Zn, Cd, Cu and Pb in the column leaching experiment using 0.01 M EDTA. Cu was either the most mobile or among the most mobile of the four heavy metals, and its peak concentration corresponded with the arrival of full strength EDTA in the leachate. The mobility of Zn and Cd was usually slightly lower than that of Cu. Pb was the least mobile, and its elution increased after the peaks of Cu and Zn. Sequential fractionations of leached and un-leached soils showed that heavy metals in various operationally defined fractions contributed to the removal by EDTA. Considerable mobilisation of Fe occurred in two of the four soils during EDTA leaching. Decreases in the Fe and Mn oxide fraction of heavy metals after EDTA leaching occurred in both soils, as well as in a third soil that showed little Fe mobilisation. The results suggest that the lability of metals in soil, the kinetics of metal desorption/dissolution and the mode of EDTA addition were the main factors controlling the behaviour of metal leaching with EDTA.     

生物酶生态修复重金属污染土壤

以多种重金属污染的土壤为材料,研究了酶对重金属的去除效果.在单因素实验基础上,采用响应面法对重金属去除的反应条件进行优化,结果表明,α-淀粉酶质量浓度0.2%、pH 3.5、反应时间12 h为最佳淋洗修复条件,Cd、Cr、Cu、Ni、Zn去除率分别为82.36%、75.02%、38.38%、34.69%和57.54%,去除率的大小顺序为Cd >Cr >Zn >Cu >Ni.酶作为土壤的组成部分,利用酶修复重金属污染的土壤,可以降低环境风险,具有较好应用前景.     

Sorption of phenanthrene by soils contaminated with heavy metals

The fate of polycyclic aromatic hydrocarbons (PAHs) in soils with co-contaminants of heavy metals has yet to be elucidated. This study examined sorption of phenanthrene as a representative of PAHs by three soils contaminated with Pb, Zn or Cu. Phenanthrene sorption was clearly higher after the addition of heavy metals. The distribution coefficient (K(d)) and the organic carbon-normalized distribution coefficient (K(oc)) for phenanthrene sorption by soils spiked with Pb, Zn or Cu (0-1000 mg kg(-1)) were approximately 24% larger than those by unspiked ones, and the higher contents of heavy metals added into soils resulted in the larger K(d) and K(oc) values. The enhanced sorption of phenanthrene in the case of heavy metal-contaminated soils could be ascribed to the decreased dissolved organic matter (DOM) in solution and increased soil organic matter (SOM) as a consequence of DOM sorption onto soil solids. Concentrations of DOM in equilibrium solution for phenanthrene sorption were lower in the case of the heavy metal-spiked than unspiked soils. However, the decreased DOM in solution contributed little to the enhanced sorption of phenanthrene in the presence of metals. On the other hand, the sorbed DOM on soil solids after the addition of heavy metals in soils was found to be much more reactive and have far stronger capacity of phenanthrene uptake than the inherent SOM. The distribution coefficients of phenanthrene between water and the sorbed DOM on soil solids (K(ph/soc)) were about 2-3 magnitude larger than K(d) between water and inherent SOM, which may be the dominant mechanism of the enhanced sorption of phenanthrene by soils with the addition of heavy metals.     

Remediation of heavy metals contaminated soils by ball milling

In the present work, the use of ball milling reactors for the remediation of lead contaminated soils was investigated. Lead immobilization was achieved without the use of additional reactants but only through the exploitation of weak transformations induced on the treated soil by mechanical loads taking place during collisions among milling media. The degree of metal immobilization was evaluated by analyzing the leachable fraction of Pb(II) obtained through the "synthetic precipitation leaching procedure". The reduction of leachable Pb(II) from certain synthetic soils, i.e., bentonitic, sandy and kaolinitc ones, was obtained under specific milling regimes. For example, for the case of bentonitic soils characterized by a Pb(II) concentration in the solid phase equal to 954.4 mg kg(-1), leachable Pb(II) was reduced, after 7 h of mechanical treatment, from 1.3 mg l(-1) to a concentration lower than the USEPA regulatory threshold (i.e., 0.015 mg l(-1) for drinkable water). Similar results were obtained for sandy and kaolinitic soils. X-ray diffraction, scanning electron microscopy, electron dispersive spectroscopy and granulometric analyses revealed no significant alterations of the intrinsic character of sandy and bentonitic soils after milling except for a relatively small increase of particles size and a partial amorphization of the treated soil. On the other hand, the mechanical treatment caused the total amorphization of kaolinitic soil. The increase of immobilization efficiency can be probably ascribed to specific phenomena induced by mechanical treatment such as entrapment of Pb(II) into aggregates due to aggregation, solid diffusion of Pb(II) into crystalline reticulum of soil particles as well as the formation of new fresh surfaces (through particle breakage) onto which Pb(II) may be irreversibly adsorbed.     

Enhanced multi-metal extraction with EDDS of deficient and excess dosages under the influence of dissolved and soil organic matter

This study investigated the influence of dissolved and soil organic matter on metal extraction from an artificially contaminated soil. With high concentration of DOM, the extraction of Cu, Zn and Pb was enhanced by forming additional metal-EDDS complexes under EDDS deficiency. However, the enhancement of metal extraction under EDDS excess was probably due to the soil structure being disrupted owing to humic acid enhanced Al and Fe dissolution, which induced more metals dissolving from the soils. Fulvic acid was found to enhance metal extraction to a greater extent compared with humic acid because of its high content of the carboxylic functional group. Cu extraction from the soil with high organic matter content using EDDS was the lowest due to the high binding affinity of Cu to SOM, whereas Zn extraction became the highest because of a preference for EDDS to extract Zn due to the high stability constant of ZnEDDS.     

In vitro gastro-intestinal method for the assessment of heavy metal bioavailability in contaminated soils

Introduction  

Balya and its associated villages which is a town of the Balikesir region of Turkey have very rich zinc, lead, and manganese mines. These mines have been operating since the thirteenth century and now there is heavy metal contamination in both the soil and natural waters in these areas.     

Arsenic and heavy metal mobility in iron oxide-amended contaminated soils as evaluated by short- and long-term leaching tests

Several iron-bearing additives were evaluated for their effectiveness in the attenuation of arsenic (As) in various contaminated soils. These were selected for their known or potential ability to adsorb As anions, thus changing the speciation of As in a soil system. Three soils with different sources of As contamination were investigated (canal dredgings, coal fly ash deposits, and low-level alkali waste). The amendments used were goethite (alpha-FeOOH), iron grit, iron (II) and (III) sulphates (plus lime), and lime, applied to the soils at a rate of 1% w/w. A series of leachate extraction tests (UKEA, ASTM and modified Dutch column leaching test) were conducted on the equilibrated amended soils. These were used to firstly evaluate the potential of the amendments as immobilising agents, and secondly to compare the short- and long-term durability of their effects. Column tests demonstrated the efficiency of iron oxides over the longer time scale; these treatments significantly reduced concentrations of arsenic in leachates from all treated soils. Amended soils were also observed to contain higher levels of lead (Pb) and cadmium (Cd) in their leachates, signifying that certain Fe-oxides potentially increased heavy metal mobility in treated soils. The conclusions were that whilst Fe-oxides may be used as effective in situ amendments to attenuate As in soils, their effects on other trace elements, such as Pb and Cd, require careful consideration.     

The effects of soil amendments on heavy metal bioavailability in two contaminated Mediterranean soils

Two heavy metal contaminated calcareous soils from the Mediterranean region of Spain were studied. One soil, from the province of Murcia, was characterised by very high total levels of Pb (1572 mg kg(-1)) and Zn (2602 mg kg(-1)), whilst the second, from Valencia, had elevated concentrations of Cu (72 mg kg(-1)) and Pb (190 mg kg(-1)). The effects of two contrasting organic amendments (fresh manure and mature compost) and the chelate ethylenediaminetetraacetic acid (EDTA) on soil fractionation of Cu, Fe, Mn, Pb and Zn, their uptake by plants and plant growth were determined. For Murcia soil, Brassica juncea (L.) Czern. was grown first, followed by radish (Raphanus sativus L.). For Valencia soil, Beta maritima L. was followed by radish. Bioavailability of metals was expressed in terms of concentrations extractable with 0.1 M CaCl2 or diethylenetriaminepentaacetic acid (DTPA). In the Murcia soil, heavy metal bioavailability was decreased more greatly by manure than by the highly-humified compost. EDTA (2 mmol kg(-1) soil) had only a limited effect on metal uptake by plants. The metal-solubilising effect of EDTA was shorter-lived in the less contaminated, more highly calcareous Valencia soil. When correlation coefficients were calculated for plant tissue and bioavailable metals, the clearest relationships were for Beta maritima and radish.     

Enhanced phytoextraction of Pb and other metals from artificially contaminated soils through the combined application of EDTA and EDDS

Chemically enhanced phytoextraction is achieved by the application of chelates to soils. Using pot experiments, the effect of the combined application of EDTA and EDDS on the uptake of Cu, Pb, Zn and Cd by Zea mays L. was studied. Among the tested application ratios of 1:1, 1:2, and 2:1 (EDTA/EDDS), 2:1 of EDTA:EDDS was the most efficient ratio for increasing the concentrations of Cu, Pb, Zn and Cd in the shoots. The combined application of 3.33 mmol kg(-1) soil of EDTA+1.67 mmol kg(-1) soil of EDDS produced 650 mg kg(-1) of Pb in the shoots, which was 2.4 and 5.9 times the concentration of Pb in the shoots treated with 5 mmol kg(-1) of EDTA and EDDS alone, respectively. The total phytoextraction of Pb reached 1710 microg kg(-1) soil, which was 2.1 and 6.1 times the total Pb from 5 mmol kg(-1) EDTA and EDDS alone, respectively. The combined application of EDTA and EDDS also significantly increased the translocation of Pb from the roots to the shoots. The mechanism of enhancing the phytoextraction of Pb by the combined application of EDTA+EDDS did not involve a change in the pH of the soil. The increase in the phytoextraction of Pb by the shoots of Z. mays L. was more pronounced than the increase of Pb in the soil solution with the combined application of EDTA and EDDS. It was thought that the major role of EDDS might be to increase the uptake and translocation of Pb from the roots to the shoots of plants.     

Prosopis juliflora--a green solution to decontaminate heavy metal (Cu and Cd) contaminated soils

Soil and plant samples (root and shoot) of Prosopis juliflora were collected in the vicinity of metal based foundry units in Coimbatore and assessed for their heavy metal content (Cu and Cd) to ascertain the use of P. juliflora as a green solution to decontaminate soils contaminated with Cu and Cd. The results showed that Cu and Cd content was much higher in plant components compared to their extractable level in the soil. Furthermore, there exist a strong correlation between the distance of the sources of industrial units and accumulation of heavy metals in plants. Accumulation of Cd in roots is comparatively higher than that of shoots. However, in case of Cu no such clear trend is seen. Considering the accumulation efficiency and tolerance of P. juliflora to Cd and Cu, this plant can be explored further for the decontamination of metal polluted soils. On the other hand, in view of heavy metal accumulate the practice of providing foliage and pods as fodder for live stock should be avoided.     

EDTA及其回收溶液治理重金属污染土壤的研究

试验结果表明,EDTA能够有效地萃取土壤重金属,由于其价格较贵和不易被降解等特点,限制了它的广泛运用.在运用MINTEQA2模型对萃取液中重金属离子形态分析的基础上,选用Na2S沉淀法将重金属从EDTA萃取液中有效分离.同时将回收的EDTA连续进行萃取土壤重金属,由于回收EDTA浓度下降的原因,其效果比新鲜EDTA的要稍微差一点,但从经济和效率上来说,仍旧可以用来治理重金属污染的土壤.