Oxidation and Mobility of Trivalent Chromium in Manganese-Enriched Clays during Electrokinetic Remediation

This article presents the results of an investigation that assessed the extent and effect of oxidation of Cr(III) in manganese-enriched clays on the electrokinetic remedial efficiency. Because chromium commonly exists along with nickel and cadmium at contaminated sites, the effects of changes in chromium redox chemistry on the migration of the coexisting nickel and cadmium was also studied. Bench-scale electrokinetic experiments were conducted using two different clays: kaolin, a typical low buffering soil, and glacial till, a high buffering soil. Tests were performed with 1000?mg/kg of Cr(III), 500?mg/kg of Ni(II), and 250?mg/kg of Cd(II), both with and without the presence of 1000?mg/kg of manganese. All of these experiments were conducted under a constant voltage gradient of 1.0?VDC/ cm. The experimental results showed that in the presence of manganese, percentages of oxidation of Cr(III) into Cr(VI) ranged from 67% in kaolin to 28% in glacial till even before the application of induced electric potential. The low extent of oxidation of Cr(III) in glacial till may be attributed to the initial precipitation of Cr(III) as Cr(OH)₃ resulting from high soil pH, reducing aqueous Cr(III) concentrations present within the soil. In kaolin, Cr(III), Ni(II), and Cd(II) under electric potential migrated toward cathode and precipitated near the cathode due to high soil pH. When manganese was present in kaolin, Cr(VI) that was formed due to the oxidation of Cr(III) migrated toward anode and adsorbed to the soil surfaces near the anode region due to low soil pH. However, remaining Cr(III) as well as Ni(II), and Cd(II) migrated towards and precipitated near the cathode due to high soil pH. In kaolin, the migration of Ni(II) and Cd(II) was retarded in the presence of manganese due to a larger soil zone of elevated pH near the cathode. In glacial till, the migration of Cr(III), Ni(II) and Cd(II) was insignificant due to precipitation resulting from high soil pH caused by the high buffering capacity of the soil. Cr(VI) that resulted from the partial oxidation of Cr(III) in the presence of manganese, however, migrated toward the anode. Overall, this study demonstrated that the effects of manganese on Cr(III) oxidation in low buffering soils can be significant, which can in turn affect the extent and direction of chromium migration under induced electric potential.     

Improving the Electrokinetic Remediation of Nickel-, Cadmium-, and Lead-contaminated Sediment

In this work, the simultaneous application of bipolar electrodes and a longer cathodic compartment length without agents addition was used as an enhanced electrokinetic treatment of Ni-, Cd-, and Pb-contaminated sediment. Conventional and enhanced treatments were investigated and their efficacy assessed by comparing the residual metals content in the sediment with values given by Dutch standards. After conventional treatment removals of 20%, 19%, and 31% for Ni, Cd, and Pb were achieved, whereas the enhanced treatment achieved removal efficacies of 36% for Ni, 42% for Cd, and 43% for Pb. Results indicate that the simultaneous application of the techniques mentioned is effective for removing Ni and Pb whereas Cd was not removed to the desired level. Here we show that the addition of chemicals is not necessary to increase the efficacies of electrokinetic sediment treatments, so the simultaneous application of the techniques mentioned can be described as environmentally friendly.     

Extraction,Recovery, and Biostability of EDTA for Remediation of Heavy Metal-Contaminated Soil

Chelation removal of heavy metals from contaminated soil is seen as a viable remediation technique. A useful chelating agent should be strong, reusable, and biostable during metal extraction and recovery operations. This work tested the extraction, recovery, and biostability of EDTA as a potential remediating agent. Parameters, including EDTA concentration, soil type, soil content, washing cycle, precipitant concentration and type, and pH, were varied and tested during metal extraction and recovery operations. Factors, including EDTA concentration, aqueous and 5% soil slurry, presence of Pb, acclimated and unacclimated activated sludges, along with abiotic control, were varied and studied in the biodegradation of EDTA. The results showed that EDTA was able to extract lead completely from the tested soils, amenable to recovery by addition of cationic and anionic precipitants in the alkaline pH range, relatively biostable even under conditions very favorable toward biodegradation. Thus, EDTA is a strong, recoverable, and relatively biostable chelating agent that has potential for soil remediation application.     

Literature Review of 2-D Laboratory Experiments in NAPL Flow,Transport, and Remediation

The migration of nonaqueous phase liquid (NAPL) contaminants in the subsurface results in a complex multiphase environment due in part to heterogeneity in both the soil and fluid saturations. To accurately predict the flow, transport, and remediation of NAPL contaminants, research has focused on laboratory and numerical modeling of the subsurface environment. Within this research, 2-D laboratory model are advantageous due to the fact that the capillary, viscous, and buoyancy forces found in the subsurface environment can be reproduced. Thus, they can be used to study flow and transport, test and develop remediation technologies, and verify numerical models. However, to date a comprehensive review of the 2-D experimental work has not been compiled. The review presented in this article should be of interest to geohydrologists, engineers and scientists involved in both applied and research aspects of NAPL-contaminated aquifers.     

Oxalate Extraction of Pb and Zn from Polluted Soils: Solubility Limitations

Oxalate (Ox) was used to extract Pb and Zn from industrially contaminated soils. Although Ox effectively releases metals bound by hydrous oxide soil components, it forms insoluble salts with some heavy metals unlike conventional extractants (e.g., EDTA). The insolubility of PbOx(s) (K_sp=2.74 × 10^?11) precluded the use of Ox as a single-step extractant even for soils mildly contaminated with Pb. The usefulness of Ox as a Zn extractant, however, depends on the level of soil contamination. A Zn solubility model, based on published equilibrium constants, was developed to assess Ox suitability as a function of system conditions. Precipitation of ZnOx(s) hindered Zn recovery under acidic conditions where formation of soluble oxalato complexes was small. For pH<3, the presence of 1?M Ox actually reduced Zn release compared to simple acid washing. Although Ox displaces oxide-bound metals and thus is potentially useful in soil washing, solubility limitations must be defined for effective remediation of metal-laden soils.     

Pulsed Electrokinetic Removal of Chromium,Mercury and Cadmium from Contaminated Mixed Clay Soils

Electrokinetic remediation (EKR) processes are energy intense systems as they are mainly run under continuous constant current supply mode. In this study, pulsed electrokinetic remediation (PEKR) technique was employed for the removal of Cd, Hg and Cr from mixed contaminated natural clay and bentonite soils. The effects of voltage gradient, pulse duty cycle and bentonite/clay ratio on the simultaneous removal efficiencies of the heavy metals and specific energy consumption were investigated. Fifteen (15) PEKR experiments were conducted according to Box–Behnken design (BBD) with each experiment allowed to continuously run for 21 days. Increase in the proportion of the bentonite significantly decreased the removal efficiency of the heavy metals while having insignificant effect on the energy consumption. Conversely, increase in both voltage gradient and pulse duty cycle increased the heavy metals removal efficiencies, though at the expense of increase in energy consumption due to combine effects of increase in the soil electrical conductivity, amount of current needed to sustain the applied voltage gradient as well as the raise in the soil pH. The maximum achievable removal efficiencies for Cd, Hg and Cr were 21.87, 78.06 and 89.64% respectively. The specific energy consumption significantly increased from the range of 91.67–154.17 kwh/m³ to 1700–2441.67 kwh/m³ as a result of combined effect of increasing voltage gradient and pulse duty cycle. This demonstrated that effective PEKR could be achieved with significance reduction in the energy consumption via appropriate selection of pulse duty and voltage gradient for clay soils of different proportion of montmorillonite.     

Effect of the Secondary Electrode Configuration in Removing Metal Contaminants from Soils by the CEHIXM Process

The effect of the secondary electrode configuration in removal of metal contaminants from soils under coupled electric hydraulic gradient assisted by ion exchange medium (CEHIXM) process was investigated. Soil samples using a blend of spent foundry sand and millpond sludge were used to investigate the contribution and cost-effectiveness of the secondary electrode configuration in removal of primarily four heavy metals (Pb, Cd, Zn, and Mn). A number of tests were conducted at an optimum constant DC electric voltage of 50 V and an optimum constant flow velocity of 0.00713 cm/sec for a period of 200 hours. The experimental results demonstrated the removal efficiencies of approximately 89.84% of Pb, 96.63% of Cd, 92.89% of Zn, and 91.14% of Mn with the primary electrode (PE) configuration. In case of the secondary electrode (SE) configuration, the removal efficiencies were about 87.34% of Pb, 91.68% of Cd, 95.30% of Zn, and 90.44% of Mn. In the case of the combined PE and SE configuration, the removal efficiencies were about 90.16% of Pb, 93.27% of Cd, 96.34% of Zn, and 90.44% of Mn. The energy expenditures were about 480 kWh/m³ and 522 kWh/m³ of soil in the case of the PE and the SE configurations, respectively. It appeared that the use of the SE configuration and/or combination of the PE and SE configuration was not cost-effective and advantageous over the use of the PE configuration in removing heavy metals from the contaminated soils by the CEHIXM process.     

The Detoxification of Heavy Metals in the Phosphate Tailing-contaminated Soil through Sequential Microbial Pretreatment and Electrokinetic Remediation

In this paper, the heavy metals (HMs) in the phosphate tailing-contaminated soil were detoxified using the microbial pretreatment in combination with electrokinetic remediation (EKR).. This study provides compelling evidence that the sequential usage of the bioleaching and electrokinetics is superior to the individual method for the detoxification of Pb, Cu, Zn, Cd, and As from the contaminated soil. In the sequential system, the detoxification efficiency of Zn was the highest and that of As was the lowest. Except the element As, the detoxification efficiencies of HMs in the sequential system were generally higher than that using the single biological treatment and EKR technique. Bioleaching, generation of the passivation, and migration direction of the ions are concluded as the factors attributable to the final results; and, the initial increase in the inoculation doping of Thiobacillus ferrooxidans considered has no obvious impact on improving the final detoxification efficiency rates.     

Electronic (EK) remediation of a contaminated soil at several Pb concentrations and applied voltages

The in situ remediation of a lead‐contaminated silt loam by electrokinetic (EK) soil flushing was studied. Two initial soil Pb concentrations (150 and 1000 mg/kg of Pb) and applied voltages (30 and 60 V) were investigated. The EK soil flushing process was less efficient for the 150 mg/kg of Pb soils despite these tests being operated for longer durations, having larger EO flows and energy inputs, and lower soil pHs. The decrease in effectiveness was attributed to a larger average metal‐soil binding energy for the lower contaminated soil. Increasing the voltage increased the EO flow, current, energy input (kW‐hr/kg of soil), and provided a more evolved low pH front, resulting in more soil being remediated. There appeared to be a correlation between the amount of EO flow and the desorption and transport of soil‐bound lead. Because complete soil remediation did not occur in any of the tests, the final energy input per kilogram of soil could not be calculated.     

土壤Hg污染及修复技术研究

早在 2 0世纪 6 0年代初期 ,日本查明了“水俣病”[1] 是由甲基Ｈｇ污染造成的 ,引起世界范围内人们对Ｈｇ污染危害的重视 ,使其研究日益增多。Ｈｇ通过不同途径进入土壤环境 ,土壤中的Ｈｇ经过复杂的物理、化学反应 ,大部分以各种形态滞留在土壤中 ,同时Ｈｇ在作物可食部分积累并进入食物链循环 ,对人体健康构成威胁。我国被Ｈｇ污染的耕地面积有 3.2× 10 4 ｈａ ,每年产生污染环境的Ｈｇ达 1.9× 10 8ｋｇ[2 ] 。土壤一旦遭受Ｈｇ污染 ,对人类健康构成潜在的危害 ,因此土壤Ｈｇ污染的治理及生物修复技术研究应运而生。重金属污染治理的传…     

地下水硝酸类氮污染的修复技术

近年来,以氮化合物为代表的各种化学物质对地下水和土壤的污染,已引起了人们的广泛关注,硝酸类氮污染的地下饮用水,已严重地危害了人们的健康。在国外,硝酸类氮和亚硝酸类氮自来水水质标准的浓度及ＷＨＯ的标准,分别限制在Ｎ113ｍｇ·Ｌ-1和10ｍｇ·Ｌ-1以下。我国采用20ｍｇ·Ｌ-1为基准值。饮用水中含有的大量硝酸性氮化物对健康的主要影响是引起高铁血红蛋白血症和高癌症发病率。地下水中硝酸类氮浓度上升的原因,主要与酸雨和污水中的氮化物向地下渗透,所施氮肥和家畜排泄物中含氮成分在土壤硝化作用形成硝酸类化合物有关。在我国,硝酸类…     

我国污染土壤修复研究现状与展望

介绍了我国土壤污染的突出特点及其危害,回顾了污染土壤从清洁技术研究到物理、化学和生物修复研究的历程,总结了污染土壤修复取得的初步成果,提出了污染土壤修复的实质和系统技术方法。根据我国土壤污染的实际和修复需求,本文提出了当前本领域急需开展的研究内容,预测了污染土壤修复研究对环境科学相关学科的推动作用。     

Remediation of contaminated soils by biotechnology with nanomaterials: bio-behavior,applications, and perspectives

Soil contamination caused by heavy metals and organic pollutants has drawn world-wide concern. Biotechnology has been applied for many years to the decontamination of soils polluted with organic and inorganic contaminants, and novel nanomaterials (NMs) has attracted much concern due to their high capacity for the removal/stabilization/degradation of pollutants. Recently, developing advanced biotechnology with NMs for the remediation of contaminated soils has become a hot research topic. Some researchers found that bioremediation efficiency of contaminated soils was enhanced by the addition of NMs, while others demonstrated that the toxicity of NMs to the organism negatively influenced the repair capacity of polluted soils. This paper reviews the application of biotechnology and NMs in soil remediation, and further provides a critical view of the effects of NMs on the phytoremediation and micro-remediation of contaminated soils. This review also discusses the future research needs for the combined application of biotechnology and NMs in soil remediation.     

Chemically Assisted Phytoextraction: A Review of Potential Soil Amendments for Increasing Plant Uptake of Heavy Metals

The contamination of soils by trace metals has been an unfortunate sideeffect of industrialization. Some of these contaminants can interfere with vulnerable enduses of soil, such as agriculture or nature, already at relatively low levels of contamination. Reversely, conventional civil–technical soil-remediation techniques are too expensive to remediate extended areas of moderately contaminated soil. Phytoextraction has been proposed as a more economic complementary approach to deal with this specific niche of soil contamination. However, phytoextraction has been shown to be a slow-working process due to the low amounts of metals that can be annually removed from the soil under normal agronomic conditions. Therefore, extensive research has been conducted on process optimization by means of chemically improving plant availability and the uptake of heavy metals. A wide range of potential amendments has been proposed in the literature, with considerable attention being spent on aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA). However, these compounds have received increasing criticism due to their environmental persistence and associated risks for leaching. This review presents an overview of potential soil amendments that can be employed for enhancing metal uptake by phytoextraction crops, with a distinct focus on more degradable alternatives to persistent compounds such as EDTA.     

Risk-Based Zoning Strategy for Soil Remediation at an Industrial Site

After determining at an early stage of the project that the future land use of this New Jersey chemical manufacturing site remain industrial in nature, the site was zoned according to risk. The chemicals of concern (COCs) at the site included relatively low levels of mono- and polynuclear aromatic hydrocarbons, chlorinated aliphatics, as well as other volatile and semivolatile compounds. Direct human exposure scenarios were the key to the mitigation of risks related to soils because the groundwater migration pathway was already interrupted using groundwater recovery. A focused remedial strategy was developed to ensure that the exposure pathways (inhalation, ingestion, and dermal contact) are alleviated and the remedial measures are protective to the workers operating and/or maintaining the site. The risk evaluation process included a preliminary risk assessment (Tier 1) based on a comparison with pertinent soil cleanup criteria, a prioritization analysis to rank zones, chemicals and pathways of concern, and an application of the Risk Based Corrective Action (RBCA) approach (Tier 2) for construction worker exposure scenario. The risk assessment identified selected areas that would benefit from remedial actions. Prioritization Analysis classified the site into five high-priority (comprising 97% of the total health-based risk), three medium-priority (contributing to remaining 2 to 3% of the risk), and adequately protected areas. The boundaries and volumes of affected areas were delineated based on confirmatory soil sampling and statistical analyses. The remedial technologies selected for the site have achieved appropriate reduction in risk to comply with all State regulations and include (in addition to the institutional controls): ??Capping the site where only immobilesemivolatile contaminants are present ??Excavation and on-site treatment of the soils impacted by volatile organic com pounds through ex situ low temperature desorption, or alternative “biopile” treatment and natural attenuation, and ??Excavation and off-site disposal of limited volumes of soils This risk-based, integral approach helped identify the real significance of contamination present at the site and facilitated the development of suitable and adequate remedies. Had not it been for this approach, the mere comparison with soil cleanup criteria would have unnecessarily resulted in denoting all areas as nuisance contributors, and thus requiring some actions. New Jersey Department of Environmental Protection (NJDEP) has approved this approach and contributed to its accomplishment.     

基于文献计量的细菌-生物炭协同修复重金属污染土壤研究进展

为提高重金属污染土壤可持续修复效能,研究生物炭与细菌对重金属污染土壤的协同修复作用。基于文献计量学分析及重金属污染土壤修复背景,总结了细菌与生物炭对土壤重金属的稳定化特征及菌炭间的相互作用,分析了单一生物炭或细菌对重金属污染土壤修复的局限性,强调了细菌-生物炭协同修复技术的优势,阐述了细菌与生物炭主要通过离子交换、固定作用、氧化还原作用和迁移作用等重要机制有效修复重金属污染土壤,揭示了细菌-生物炭协同作用在重金属污染土壤修复中的巨大应用价值。文献计量学研究表明,生物炭与细菌对重金属污染土壤的协同修复已得到广泛关注。目前认为:生物炭与细菌的协同作用可有效改良土壤理化性质及提高土壤修复效率,也可促进植物生长及植物修复进程;生物炭对细菌影响具有双重性质,可促进细菌生长,也可能对细菌产生毒害;细菌可改变生物炭的理化性质,进而强化生物炭的重金属固定性能;细菌协同生物炭联合修复重金属污染土壤过程中,生物炭主导吸附和固定,细菌则发挥活化和解毒等功能;优化细菌-生物炭组合形式,发展混合细菌与多种类生物炭协同技术,是复合重金属污染土壤可持续修复亟待解决的重要问题;进一步揭示细菌与生物炭对重金属污染土壤的耦合作用及长效作用机制,规避生物炭生产和应用中的潜在生态健康风险,研发新型高效能细菌与生物炭复合体是细菌协同生物炭可持续修复重金属污染土壤应用领域面临的挑战。     

赤泥在重金属污染治理中的应用研究进展

尽管赤泥在重金属污染环境修复研究中的应用越来越受到重视,但赤泥给污染环境修复带来突破的同时也给环境带来风险.目前,在赤泥的重金属环境修复研究中,针对赤泥的修复效果和修复过程研究较多,而对赤泥的钝化机理研究不够深入,赤泥修复的环境安全风险评价才刚起步.本文对近年来国内外关于赤泥修复重金属污染的研究进行综述,并指出了赤泥在今后的重金属污染治理中应加强的方向:一是深入赤泥对重金属钝化机制的研究;二是探索有效的赤泥安全评价方法;三是联合赤泥修复和生物修复技术(植物和微生物)对重金属和有机物复合污染进行修复.     

Impact of Humin on Soil Adsorption and Remediation of Cd(II), Pb(II), and Cu(II)

In situ immobilization constitutes a promising technology for the mitigation of contaminants, through the reduction of metal bioavailability and mobility. This study investigated the adsorption isotherms and kinetic characteristics of humin extracted from peat soils. We also studied the influences of the pH, ionic strengths, and soluble organic matter concentrations of soil solutions on the adsorptive properties of humin, and compared its ability to detoxify potentially toxic metals in both actual and simulated soil solutions. The study results indicated that humin contains a massive population of oxygen-containing functional groups. Its adsorption capacity for Pb(II) was greater than that for Cu(II), which exceeded that for Cd(II). The adsorption of humin for Pb(II) conformed to the Freundlich model, while the adsorption of humin for Cd(II) and Cu(II) followed the Langmuir model. The adsorption kinetics of humin with respect to potentially toxic metals aligned well with second-order kinetics equations. As the pH was elevated, the potentially toxic metal adsorption by humin increased rapidly. Electrolyte ions and tartaric acids in solution both inhibited the adsorption of potentially toxic metals by humin, and its ability to inactivate potentially toxic metals. This was shown to be improved in actual field soil solutions in contrast to simulated soil solutions.     

The Importance of Nickel Phytoavailable Chemical Species Characterization in Soil for Phytoremediation Applicability

In this work Ni speciation in natural and spiked soils (with similar total concentration) was studied. Spiked soils were prepared by addition of NiSO₄.6H₂O to obtain concentration similar to the one in natural soils. In soils mobile species were determined with a simplified sequential extraction as follows: H₂O for water-soluble metal, KNO₃ for exchangeable species, DTPA for complexed/adsorbed species. Results show that in spiked soils the exchangeable and adsorbed Ni concentrations are considerably higher than in natural soils. A study of plant uptake was carried out in order to evaluate the relation between mobile species and phyto-availability. Alfalfa (Medicago sativa L.), even though it is not a hyperaccumulator, was selected for its tolerance to high metal concentrations in soil. Preliminary results show a very high correlation between Ni mobile species and Ni uptake by alfalfa. Significant differences were found between spiked and natural soils. In the latter, high levels of total Ni did not correspond to relevant uptake as in the case of spiked soil. Results stress the importance of evaluating preliminarly heavy metal speciation in soil before planning phytoremediation procedures.     

重金属污染土壤修复技术中有关淋洗剂的研究进展

淋洗法是修复污染土壤的一种很有效的方法 ,是对污染土壤生物修复的一种补充 ,使污染土壤修复的系统化成为可能。淋洗法就是使用淋洗剂来清洗土壤 ,使土壤中污染物随淋洗液流出 ,然后对淋洗液及土壤进行后续处理 ,从而达到修复污染土壤的目的。而淋洗剂的选择是影响这一技术效率高低的主要因素之一。本文对目前淋洗剂的应用情况 ,作用机制进行了总结和评价。探讨了天然有机酸、生物表面活性剂等对环境影响小的淋洗液的应用前景。并根据“以废治污”的指导思想提出并分析了以柠檬酸废水和味精废水作为淋洗剂修复重金属污染土壤的可行性。