共查询到18条相似文献，搜索用时 683 毫秒
1.
地下水中三氯乙烯(TCE)严重威胁公众健康和环境安全,纳米零价铁原位注射技术可以还原降解TCE,但是应用中,纳米零价铁存在易氧化团聚而失活、迁移性差等问题。为此,利用天然高分子壳聚糖作包覆剂增强分散性和稳定性,镍作催化剂增强反应活性,成功制备获得壳聚糖包覆纳米铁镍双金属颗粒(CS Fe Ni)。沉降光谱实验表明包覆壳聚糖后纳米铁的分散稳定性得到增强,Zeta电位测试进一步证实颗粒表面负电荷增加,提高了静电排斥力,使得CS Fe Ni分散稳定性明显改善。柱迁移实验表明改性后的CS Fe Ni迁移能力得到提高。批实验表明CS Fe Ni能够高效降解TCE并能完全脱氯,研究结果为纳米铁原位注射技术的实际应用提供了理论基础和实验参考。 相似文献
2.
零价纳米铁(NZVI)具有较高活性,近年受到人们关注并将其应用于地下水污染原位修复,但在实际应用中NZVI易发生氧化与团聚,容易失活。因此尝试运用环境友好型材料对NZVI进行表面改性,选择羧甲基纤维素(CMC)对纳米铁进行表面包覆获得CNZVI,研究不同CMC含量包覆NZVI的分散稳定性和CNZVI对水中六价铬的去除效果。结果表明：经过改性后的CNZVI分散稳定性要明显优于商用纳米铁RNIP,包覆CMC的比例越高,CNZVI的稳定性越好,在较高的CMC包覆比例下,纳米铁不易失活并具有良好的反应活性,对溶液中六价铬有很好的去除效果。 相似文献
3.
不同种类纳米零价铁的毒性比较研究 总被引：1，自引：1，他引：0
纳米零价铁是一种高效的环境修复材料,可以处理多种污染物;然而,纳米粒子的尺寸效应可能导致其在自然界中存在潜在毒性风险。选择几种常用包覆型、负载型和裸露的纳米铁,通过大肠杆菌的耐受性实验,比较3种纳米铁的毒性。研究表明,负载型纳米铁的分散性最好,而裸露纳米铁最差。3种纳米铁虽然对大肠杆菌都表现出毒性,但是负载型纳米铁的毒性最小。通过毒性减缓的机理分析,说明纳米铁改性后阻止了纳米颗粒与细菌的直接接触,这是空间位阻效应的作用。研究结果进一步证实了在使用纳米材料前应充分评估潜在毒性和环境效应的重要性。 相似文献
4.
膨润土负载纳米铁去除地下水中六价铬研究 总被引：4，自引：1，他引：3
随着人民生活水平的提高和城市化进程的加快,有机污染物及重金属高强度场地污染对人类健康、生态环境及社会安全构成了严重威胁。地下水中的重金属Cr(Ⅵ)污染逐渐受到重视,纳米零价铁可以有效地将六价铬还原成三价铬,使其沉淀固定下来,从而将污染源区的污染物消减固定,防止其向周围扩散。然而由于纳米铁颗粒微小,易被氧化,极易团聚,自身活性受到限制,因此,纳米铁的分散性、稳定性、良好活性研究至关重要。采用低成本环境友好型粘土矿膨润土作为负载材料制备膨润土负载纳米铁（B-NZVI）,批实验和柱实验研究B NZVI去除模拟地下水中Cr(Ⅵ)。结果表明：(1)自制的膨润土负载纳米铁个体呈球形,呈分散状负载于膨润土;(2)相同铁含量的B-NZVI处理Cr(Ⅵ)的效率远大于纳米铁,还原反应符合伪一级反应动力学模型,表观速率常数K随着B NZVI初始浓度的减小而减小;(3)B NZVI在石英砂柱中基本无迁移,适用于点源污染,Cr(Ⅵ)穿透曲线为B-NZVI的实际应用提供了理论和实验基础。 相似文献
5.
零价铁纳米颗粒具有许多异于本体物质的独特性质,在废水处理方面应用潜力巨大。以蒙脱石为载体和分散剂,通过硼氢化钠液相还原法制备了零价铁纳米颗粒。采用电镜及多种谱学技术手段对所得铁纳米颗粒进行了表征。结果表明,铁纳米颗粒大致呈球状形貌,平均粒径约为55 nm,在蒙脱石表面分散良好,具有零价铁内核-铁氧化物外壳结构,提高了纳米铁在空气氛中的稳定性。通过批次实验考察了负载型铁纳米颗粒净化Cr(Ⅵ)的效率、过程及机理。净化效果受p H值影响显著,在最优p H值为1.0条件下,零价铁内核因其表面氧化膜酸溶而出露,可作为有效成分快速高效去除水体中Cr(Ⅵ)污染物,机理为零价铁将吸附至其表面的Cr(Ⅵ)异相还原为Cr(Ⅲ)而去除。属自发放热吸附过程,动力学行为符合准二级模型,吸附等温线可用Langmuir方程较好拟合。研究成果为新型纳米零价铁材料的制备及其铬污染治理提供了理论支撑。 相似文献
6.
应用纳米零价铁进行地下水污染治理是近年迅速发展的环境修复新技术,但在实际应用中,纳米零价铁的反应活性受到环境条件的影响,其中自然界中广泛存在的天然有机质就是重要影响因素。通过批实验研究腐殖酸(天然有机质代表物)对纳米零价铁去除水中六价铬的影响,结果表明,腐殖酸的存在能够极大地抑制纳米铁去除六价铬的反应速度和去除效率,原因在于纳米铁对腐殖酸具有一定的吸附作用,从而减少了纳米铁表面的有效活性位点,降低了对六价铬的作用。此外发现,水体中溶解氧的存在有利于纳米铁对六价铬的去除。关于腐殖酸-纳米零价铁-六价铬的相互作用研究,对于进一步揭示修复体系作用机制具有重要的理论和应用价值。 相似文献
7.
纳米零价铁在多孔介质中的运动能力影响其作为污染地下水修复材料的应用潜力。已有研究多采用一维柱试验研究纳米零价铁的运动行为,对于其二维运动行为的报道有限。自主研发了模拟多孔介质中纳米颗粒运动的模型试验系统,采用细、中、粗3种不同粒径的玻璃珠模拟土体,通过取样测量和图像分析等方法获得了磷负载纳米铁在多孔介质中的运动行为。一维柱试验结果表明磷负载纳米铁在中玻璃珠和粗玻璃珠中均有一定的运动能力,其液相回收率分别为50.3%和41.0%,而在细玻璃珠中运动能力较差;二维模型试验表明磷负载纳米铁在中玻璃珠中的滞留量随距离逐渐降低,而在粗玻璃珠中则呈现出滞留量随距离先升高后降低的趋势。由模型试验结果分析可知,磷负载纳米铁的运动和滞留过程与多孔介质孔隙结构和流速密切相关,颗粒阻塞与表面沉积等不同物理过程的共同作用导致了其在不同粒径多孔介质中运动特性的差异。研究成果可用于评估磷负载纳米铁的运动能力及分析其在多孔介质中的运移和滞留机制,为纳米零价铁技术的工程应用和环境风险评价提供参考依据。 相似文献
8.
《地质科技情报》2017,(3)
运用纳米零价铁进行地下水污染原位处理是近年新发展的环境修复新技术,传统合成纳米零价铁一般多采用无氧条件(通氮气保护)液相法,操作繁琐,不适合批量生产。为了达到纳米零价铁液相法大规模制备和便于现场应用的目的,通过对比传统方法(通氮气除氧),提出在空气氛围中(有氧)制备纳米零价铁。透射电镜和X射线衍射分析表明,空气中直接制备的纳米零价铁Fe@Fe_2O_3有明显核壳结构,粒径40~100nm,内核零价铁,外壳氧化铁厚4~5nm。纳米铁降解水中甲基橙和去除六价铬的实验表明,空气氛围中制备的纳米铁反应活性最好,10min内0.4g/L(RO)Fe@Fe_2O_3能够把200mg/L甲基橙降解98.6%,30min内0.2g/L(RO)Fe@Fe_2O_3能够把20mg/L六价铬去除84.7%。因此,省略了氮气保护环节,成功合成核壳结构纳米零价铁,这有利于现场应用时现配现用,并降低运输保管纳米铁的成本和风险,对开展原位现场污染修复具有启示和应用价值。 相似文献
9.
采用液相还原法成功制备纳米零价铁,并组装出生物质炭负载纳米零价铁复合材料(NZVI/BC)。XRD图谱显示,NZVI/BC由生物质炭(BC)和纳米零价铁(NZVI)两种成分复合而成;SEM图像显示,加入生物质炭之后,NZVI颗粒在炭表面分散良好。研究考察溶液p H值、还原剂投加量、铁/炭比和NO-3初始浓度等因素对NZVI/BC还原性能的影响。结果表明,NZVI/BC显示出优良的还原性能。在相同条件下,反应2 h,NZVI对NO-3的去除率为75%,而NZVI/BC对NO-3的去除率为96%。NZVI/BC是一种具有应用前景的硝态氮净化材料。 相似文献
10.
纳米零价铁（NZVI）是粒径在1～100nm之间的铁颗粒,它的比表面积和反应活性远远大于普通铁屑和铁粉,可以直接注入到含水层的重污染区,形成一个高效的原位反应带,灵活、高效、低成本地治理地下水污染。NZVI不仅可以降解各种卤代烃,还可以降解部分不含卤族元素的有机污染物,吸附或降解地下水中的重金属离子和多种无机阴离子。NZVI地下水修复技术在发达国家已经得到工程应用并正在迅速推广,原位场地因素对NZVI地下水修复效果的影响是今后该领域重要发展方向。NZVI在含水层中的有效分散和运移是今后NZVI用于地下水修复的主要突破点。 相似文献
11.
《Geochimica et cosmochimica acta》1999,63(19-20):2891-2901
A long-standing problem in aquatic geochemistry has been the incorporation of natural organic matter (NOM) into speciation models. The general effect of NOM on metal ion sorption by particles has been understood for some time, and significant progress has been made in elucidating some of the details of the role of NOM through the use of surrogate organic acids such as citric acid. However, a gap exists between the general observations that have been made of NOM behavior and the inclusion of NOM in surface chemical models for metal ion sorption. In this paper, we report on the results of a study on the sorption of U(VI) by hematite in the absence and presence of Suwannee river humic acid (HA) and over a range of other system conditions (e.g., pH, I). Essential HA characteristics (e.g., its acid/base, metal binding, and surface chemical properties) were “captured” by representing the HA as an assembly of monoprotic acids with assumed pK values and without explicit correction for electrostatic effects. The ternary system (hematite/HA/U(VI)) was simulated through the combination of the binary submodels (i.e., CO32−/hematite, U(VI)/HA, U(VI)/hematite, and HA/hematite) with model constants fixed at the values determined from simulations of the respective experimental systems. However, the “summed-binary” approach undersimulated experimental results, and the ternary system model required the postulation of two ternary surface (Type A) complexes composed of the uranyl ion, hematite surface sites, and the model ligands comprising the HA. Consideration of the HA in this manner permitted the simulation of HA effects on U(VI) sorption by hematite over a range of solution conditions using a general speciation model. 相似文献
12.
Transport of trace metals by natural organic matter (NOM) is potentially an important vector for trace metal incorporation in secondary cave precipitates [speleothems], yet little is known about the size distribution, speciation and metal binding properties of NOM in cave dripwaters. A hyperalkaline cave environment (ca. pH 11) was selected to provide information on colloid-metal interactions in cave waters, and to address the lack of high-pH data in natural systems in general. Colloidal (1 nm-1 μm) NOM in hyperalkaline cave dripwater from Poole’s Cavern, UK, was characterised by flow field-flow fractionation (FlFFF) coupled to UV and fluorescence detectors and transmission electron microscopy (TEM) coupled to X-ray energy-dispersive spectroscopy (X-EDS); trace-metal lability was examined by diffusive gradients in thin films (DGT). Colloidal aggregates and small particulates (>1 μm) imaged by TEM were morphologically heterogeneous with qualitative elemental compositions (X-EDS spectra; n = 41) consistent with NOM aggregates containing aluminosilicates, and iron and titanium oxides. Globular organic colloids, with diameters between ca. 1 and 10 nm were the most numerous colloidal class and exhibited high UV-absorbance (254 nm) and fluorescence intensity (320:400 nm excitation: emission) in optical regions characteristic of humic-like compounds. Metal binding with humic substances was modelled using the WHAM 6.1 (model VI) and visual MINTEQ 3.0 (NICA-Donnan) speciation codes. At pH 11, both models predicted dominant humic binding of Cu (ca. 100%) and minimal binding of Ni and Co (ca. <1-7%). A DGT depletion experiment (7 days duration) with the hyperalkaline dripwater showed that the available proportion of each metal was much lower than its total concentration. Metal availability for DGT in the initial stages (24 h) was consistent with weaker binding of alkaline earth metals by humic substances (Ba > Sr > V > Cu > Ni > Co), compared to the transition metals. Integrated over the entire experiment, the DGT-available proportion of transition metals (Ni > Cu & V >> Co) differed greatly from the expected hierarchy from WHAM and MINTEQ, indicating unusually strong complexation of Co. Total metal concentrations of Cu, Ni, and Co in raw and filtered PE1 dripwater samples (n = 53) were well correlated (Cu vs. Ni, R2 = 0.8; Cu vs. Co, R2 = 0.5) and were strongly reduced (> ca. 50%) by filtration at ca. 100 and 1 nm, indicating a common colloidal association. Our results demonstrate that soil-derived colloids reach speleothems, despite transport through a karst zone with potential for adsorption, and that NOM is a dominant complexant of trace metals in high pH speleothem-forming groundwaters. 相似文献
13.
Enhanced microbial reduction of Cr(VI) and U(VI) by different natural organic matter fractions 总被引：1，自引：0，他引：1
Although direct microbial reduction of Cr(VI) and U(VI) is known, few studies have examined the kinetics and the underlying mechanisms of the reduction of these contaminants by different natural organic matter (NOM) fractions in the presence or absence of microorganisms. In this study, NOM was found to chemically reduce Cr(VI) at pH 3, but the reduction rates were negligible at pH ∼7. The abiotic reduction of U(VI) by NOM was not observed, possibly because of the presence of small amounts of nitrate in the reactant solution. However, all NOM fractions, particularly the soil humic acid (HA), enhanced the bioreduction of Cr(VI) or U(VI) in the presence of Shewanella putrefaciens CN32. The reduction rates varied greatly among NOM fractions with different chemical and structural properties: the polyphenolic-rich NOM-PP fraction appeared to be the most reactive in abiotically reducing Cr(VI) at a low pH, but soil HA was more effective in mediating the microbial reduction of Cr(VI) and U(VI) under anaerobic, circumneutral pH conditions. These observations are attributed to an increased solubility and conformational changes of the soil HA with pH and, more importantly, its relatively high contents of polycondensed and conjugated aromatic organic moieties. An important implication of this study is that, depending on chemical and structural properties, different NOM components may play different roles in enhancing the bioreduction of Cr(VI) and U(VI) by microorganisms. Polycondensed aromatic humic materials may be particularly useful in mediating the bioreduction and rapid immobilization of these contaminant metals in soil. 相似文献
14.
The environmental behaviour of colloidal clay in aquatic systems is linked to the properties of their aggregates. Earlier investigations of clay colloids were performed with electron microscope techniques which caused de-hydration of the particles. Information on the structure of colloid aggregates is needed for understanding their sedimentation behaviour, as well as colloid contaminant transport properties in natural systems. Scanning transmission X-ray microspectroscopy successfully produced images of montmorillonite colloid aggregates in a pseudo-equilibrium state in 1 mM NaCl suspensions equilibrated for more than a year. These clay aggregates were revealed at photon energies below the O absorption edges of clay and water. They were spherical or ellipsoidal with diameters of the order of 100–800 nm. The aggregates are porous and gel like with lower densities than the clay mineral. These investigations are important for modelling the occurrence of clay aggregates in aqueous environments. 相似文献
15.
David M. Cwiertny Robert M. Handler Vicki H. Grassian 《Geochimica et cosmochimica acta》2008,72(5):1365-1380
The Fe(II)/Fe(III) redox couple plays an important role in both the subsurface fate and transport of groundwater pollutants and the global cycling of carbon and nitrogen in iron-limited marine environments. Iron oxide particles involved in these redox processes exhibit broad size distributions, and the recent demonstrations of dramatic nanoscale size-effects with various metal oxides has compelled us, as well as many others, to consider whether the rate and extent of Fe(II)/Fe(III) cycling depends upon oxide particle size in natural systems. Here, we investigated the reaction of Fe(II) with three different goethite particle sizes in pH 7.5 suspensions. Acicular goethite rods with primary particle dimensions ranging from 7 by 80 nm to 25 by 670 nm were studied. Similar behavior with respect to Fe(II) sorption, electron transfer and nitrobenzene reduction was observed on a mass-normalized basis despite almost a threefold difference in goethite specific surface areas. Scanning electron microscopy (SEM) images, dynamic light scattering (DLS) and sedimentation measurements all indicated that, at pH 7.5, significant aggregation occurred with all three sizes of goethite particles. SEM images further revealed that nanoscale particles formed dense aggregates on the order of several microns in diameter. The clear formation of particle aggregates in solution raises questions regarding the use of primary particle surface area as a basis for assessing nanoscale size-effects in iron oxide suspensions at circum-neutral pH values. In our case, normalizing the Fe(II) sorption densities and rate constants for nitrobenzene reduction by BET surface area implies that goethite nanoparticles are less reactive than larger particles. We suspect, however, that aggregation is responsible for this observed size-dependence, and argue that BET values should not be used to assess differences in surface site density or intrinsic surface reactivity in aggregated particle suspensions. In order to realistically assess nanoscale size-effects in environmentally relevant systems that are likely to aggregate, new methods are needed to quantify the amount of surface area accessible for sorption and reaction in wet nanoparticle suspensions, rather than assuming that this value is equivalent to the surface area determined from the characterization of dry nanoparticles. 相似文献
16.
Black carbon (BC), especially biochar, is a potential material for the remediation of hydrophobic organic compounds (HOCs) pollution in soils and sediments. Recent studies have reported that the adsorption capability of BC in sediment was reduced as time increased. It was hypothesised that this behaviour was caused by the presence of natural organic matter (NOM), but few systematic studies have examined the influence of NOM on the sorption ability of BC in sediment (S). The results of this study revealed that a humic acid (HA) coating changed the surface properties, blocked the micropores, and decreased the sorption capacity of rice-straw biochar (RBC) towards pentachlorophenol. With increasing aging time, the reductions in the sorption capacity of the S + RBC and S + HA + RBC systems occurred more rapidly than in the S + HA/RBC (HA-coated RBC) system, and the sorption curves became closer to that of the S + HA/RBC system, indicating that HA may play a primary role in reducing the sorption capacity of RBC in the sediment. With higher HA contents, the sorption capacity of the complex sediments was lower and decreased more rapidly. 相似文献
17.
Maria Fernanda Alvarez Margarita Luisa Osterrieth Julio Luis del Río 《Environmental Earth Sciences》2012,65(2):505-515
Organic matter is a fundamental factor in the biogeochemical cycle of carbon; it influences the chemical, physical, and biological
properties of the soil. The aim of this paper is to determine the organic fractions in the three predominant morphologies
of aggregates found in Typical Argiudolls of the Buenos Aires southeastern area and to link them to different soil uses, as
possible indicators of soil quality. The study was carried out in the basin de Los Padres Pound (General Pueyrredón, Buenos Aires). We analyzed the first 5 cm of mollic epipedons of plots with different soil uses: (a)
cultivated plots, (b) pine and eucalyptus forests, (c) pastures, and (d) a natural plot in the de Los Padres Pound Reserve as a reference. The percentage of soil organic carbon (SOC), light organic carbon (LOC), fulvic acids (FA), humic acids (HA),
and humins (H) in elongated, quadrangular and spherical aggregates were determined. The results show slight variations in
SOC (7.2–8.6%) in the spherical aggregates of all the plots and a greater variability in elongated and quadrangular aggregates
(5.6–10% and 6.9–13.6%, respectively). HA are minimal in the agroecosystems with extreme values of 0.02% in the spherical
aggregates of cultivated plots, and maximal in the elongated and quadrangular aggregates of natural plots (0.3–0.5%). Fulvic
acids display a similar behavior, while H decrease slightly with the morphologies and the different practices. The substantial
decrease of humic substances in cultivated plots translates into a lower biologic activity; this, in turn, influences the
aggregation, thus lowering the structural stability of these plots, which have been under agro-horticultural management for
more than 50 years. 相似文献
18.
This work presents models of the vertical distribution and flux of phytoplankton aggregates, including changes with time in
the distribution of aggregate sizes and sinking speeds. The distribution of sizes is described by two parameters, the mass
and number of aggregates, which greatly reduces the computational cost of the models. Simple experiments demonstrate the effects
of aggregation on the timing and depth distribution of primary production and export. A more detailed ecological model is
applied to sites in the Arabian Sea; it demonstrates that aggregation can be important for deep sedimentation even when its
effect on surface concentrations is small, and it presents the difference in timing between settlement of aggregates and fecal
pellets. 相似文献