污染土壤中硝基苯热脱附研究

以南京黄棕壤和江西红壤为实验土样,通过实验室批量热脱附试验,研究了热脱附温度、热脱附时间、土壤含水率、初始浓度以及土壤类型等对污染土壤中硝基苯热脱附效率的影响。结果表明,当土壤含水率2%,硝基苯初始浓度165.54 mg/kg,脱附温度300℃,脱附时间30 min时,硝基苯的热脱附效率为85.88%,处理后土壤中硝基苯残留浓度为23.37 mg/kg,远低于展览会用地土壤环境质量评价标准（HJ350-2007）（暂行）中的B级标准限值（100 mg/kg）。土壤含水率过高和过低都不利于硝基苯的脱附,当含水率为15% 时,达到了最佳的热脱附效果。硝基苯初始浓度对其脱附效率有较大的影响,随初始浓度的增加,硝基苯脱附效率呈现增大的趋势。而土壤类型对硝基苯热脱附效率的影响较小,在实际修复过程中可以忽略。研究结果可为热脱附法修复硝基苯污染土壤的实际应用提供科学依据。     

复杂有机物污染地块原位热脱附修复技术的研究

鉴于复杂有机物污染地块治理难度大,国内用地形势紧张,因此关于原位热脱附技术在复杂有机物污染地块中的运用越来越受到学术界的广泛关注。综述了三类主要的原位热脱附技术:电阻热脱附、热传导热脱附和蒸汽热脱附,根据污染场地状况总结了各类原位热脱附技术的影响因素和适用范围,并给出了相应的技术路线。阐明了温度、时间、土壤含水率、土壤渗透性等因素对热脱附效果的影响。研究表明温度越高、时间越长、土壤含水率适中、渗透性较好的土壤,有机污染物热脱附性能更好。对于有机物重度污染的难处理地块,相比其他原位修复技术,原位热脱附技术具有更好的运用前景。     

PAHs污染土壤热脱附过程关键影响因素及脱附动力学研究

土壤多环芳烃（PAHs）污染已严重威胁生态环境安全和人类生命健康。通过异位热脱附试验探究了PAHs初始浓度、土壤含水率和土壤粒径对脱附效率的影响,并采用一级、二级动力学和指数衰减模型对PAHs热脱附过程进行拟合,以探究土壤中PAHs热脱附的去除机制。结果表明,在同等条件下,随着PAHs初始浓度的增加,脱附效率随之升高,且在热脱附20~40 min时提高初始浓度可明显提高PAHs的去除率。土壤含水率对于PAHs不同组分的作用具有一定的差异性,当土壤含水率为16%,萘（Nap）、菲（Phe）和蒽（Ant）达到最佳去除率,而荧蒽（Fla）和芘（Pyr）最大去除率对应的土壤含水率为13%。在相同脱附条件下,土壤粒径越小,土壤中PAHs的去除率越高。研究发现指数衰减模型对PAHs各组分的脱附过程具有更好的拟合效果。土壤中PAHs热脱附主要分为两个阶段：①PAHs受到土壤中水的蒸发作用从土壤颗粒表面快速蒸发;②PAHs的蒸发速率受到土壤孔隙内部扩散的限制,以非常缓慢的速度从土壤中脱除。     

污染土壤中PAHs水蒸气剥离法试验研究

对水蒸气剥离法去除污染土壤中多环芳烃(PAHs)进行了研究，研制了实验室规模的污染土壤中PAHs水蒸气剥离法试验装置，获得了多环芳烃脱附的基本试验数据，考察了泥浆质量流量、泥浆浓度和反应温度对脱附效率的影响，对上述影响因素进行了分析，确定了分离工艺的最佳参数范围，为大规模治理污染土壤提供了可靠依据。试验结果表明，泥浆流速增加会显著降低脱附效率，一般应取G≤2 kg/s为好。另外，提高反应温度则会使脱附效率有所增加，故反应器内温度保持在150～200℃范围内较好。     

聚氯乙烯行业汞污染场地土壤修复技术研究进展

聚氯乙烯行业将成为我国汞公约履约的最重要领域,相关产业生产、升级、腾退转型导致的汞污染地块潜在数量与风险巨大,需要提前开展相关修复技术储备和工程应用实践研究;通过调研总结我国聚氯乙烯行业产业特点、生产工艺导致的汞污染途径与风险特征,对国内外汞污染地块土壤修复常用的修复技术有固化稳定化、热脱附和土壤淋洗等;从污染源控制、污染扩散阻隔、污染土壤及地下水修复等多方面和技术特性、工程实施两个维度,选取修复技术指标,提出多层次构建修复技术筛选矩阵标准;以期为聚氯乙烯行业汞污染地块环境评估与修复提供技术参考。     

一种准确测定土壤空气汞浓度的采样方法研究

自然源汞释放对全球大气汞的贡献和循环具有重要影响,地表过程释汞是大气汞重要的自然源,土壤空气汞浓度与大气汞浓度差决定着土壤/大气汞的交换通量。基于目前测定土壤空气中汞浓度的缺点,建立了一种新的测定土壤空气汞浓度的方法。本研究在南京六合循环农业生态区采集了水稻土壤剖面空气,并对样品总汞浓度进行了分析。利用本实验装置,真空泵在低流量下连续抽取土壤剖面空气并预富集于金管上,并结合冷原子荧光法(CVAFS)测定。实验结果显示方法检出限为0.023 ng m-3,水稻土壤空气汞浓度变化范围在6.0~18.9 ng m-3。平行实验装置在同时测定实验室大气和农田土壤空气汞浓度时,相对标准偏差(RSD)均小于15%,同时对比实验证明没有采集土壤表层大气。实验装置简单,野外操作方便,能准确和精确的测定水分不饱和土壤空气中汞浓度。     

pH及共存金属离子对生物质炭吸附铅稳定性的影响

生物质炭对重金属吸附性能的稳定性是评价生物质炭修复效果的重要指标。本文研究了不同pH、金属离子Cd和Al存在下,Pb在不同炭化温度(100℃、400℃、700℃)生物质炭上的脱附性能及脱附过程。结果表明,pH越低,Pb的脱附率越大。其主要是由于H~+的竞争效应,以及生物质炭表面官能团的质子化,促进了Pb的重新活化。在Cd和Al共存时,Pb的脱附率进一步增加。当pH=3.5时,Cd和Al的存在分别使Pb从CM100、CM400和ZKZ700上的脱附率提高了13.9%、1.0%、3.4%和26.8%、13.0%、11.3%。这主要归因于多金属的水解使得更多的H~+得以释放,进而促进了Pb的脱附。Pb在生物质炭上的脱附率随脱附时间的延长而不断增加,反应前4 h,脱附率迅速增加并均已达最大脱附率的70%,4 h后脱附速率减慢。Pb的脱附动力学符合伪一级动力学模型及颗粒内扩散模型(前4 h)。当Cd和Al存在时,解吸液对Cd、Al易解吸态的优先脱附降低了Pb的脱附速率并延长了其脱附所达平衡的时间。     

邻苯二胺对铜在红壤和砂姜黑土中吸附和解吸的影响

研究了铜在红壤和砂姜黑土中的吸附和解吸过程以及有机污染物邻苯二胺对铜在两种土壤中吸附和解吸行为的影响。结果表明 ,砂姜黑土较红壤对铜具有更高的吸附量 ,同时 ,被吸附的铜离子从土壤中的脱附百分数也是砂姜黑土大于红壤 ,吸附在砂姜黑土中的铜较红壤更易被 1molL- 1 MgCl2 所置换。pH 3 .5～ 7.5范围内 ,土壤对铜的吸附量均随溶液pH的升高而升高 ,呈现S形。邻苯二胺增加了红壤对铜的吸附量 ,同时也增加了铜的脱附百分数。而邻苯二胺虽未改变砂姜黑土对铜的吸附量 ,但却显著改变了铜的脱附百分数。文中对邻苯二胺与铜的交互作用过程及其机理进行了推测     

陕西渭北苹果园土壤中汞、镉污染与分布特征研究

该文研究了陕西优势苹果产区果园土壤中汞和镉含量、污染情况、分布特征及对苹果绿色食品生产的影响.2003～2006年在陕西全部27个苹果基地县481个代表苹果园,每一果园采用"S"形法选取20个样点,采集0～40 cm层土样,分析了土壤中汞、镉含量.结果表明,果园土壤受到汞、镉的轻度污染;土壤中汞、镉频数分布为对数正态分布,其含量适宜的表示方法为几何平均值,汞,0.051 mg/kg,镉,0.055 mg/kg;土壤中汞、镉浓度与pH值相关性极显著,在pH值7.6～9.7范围内,土壤pH值越高越有利汞、镉的累积.果园土壤受到汞、镉的轻度污染,对绿色食品苹果生产不存在威胁.     

贵州省万山汞矿区周围土壤中不同形态汞的空间分布特征

利用连续提取法对贵州省万山汞矿区周边土壤的形态与分布特征进行了测试分析。结果表明,研究区土壤中汞含量在1.34～291.71mg·kg-1之间,明显高于我国土壤汞背景值。表层土壤中汞含量在东部区域普遍较高,西部区域相对较低,并呈现随距污染源距离的增加逐渐降低的趋势。剖面土壤中的汞则表现出明显的表层富集规律。研究区土壤中汞的形态主要以残渣态、难氧化降解有机质及某些硫化物结合态和易氧化降解有机质结合态汞为主,且不同形态的汞含量与总汞含量具有较大的相关性。     

不同类型土壤对汞和砷的吸附解吸特征研究

为了探明不同类型土壤对重金属汞和砷吸附、解吸的影响,以性质差异显著的红壤、黑土和潮土为供试土壤,采用批量平衡法,研究了Hg(Ⅱ)和As(Ⅴ)在不同土壤中的吸附-解吸行为。结果表明:(1)Freundlich方程和Langmuir方程均能较好地拟合这3种土壤对Hg(Ⅱ)和As(Ⅴ)的吸附,其中Hg(Ⅱ)的最大吸附量分别为451.33、1699.46和1635.21mg/kg,大小顺序为黑土>潮土>红壤,相关系数(R2)在0.8533～0.9911之间;As(Ⅴ)的最大吸附量分别为818.44、561.87和112.77mg/kg,大小顺序为:红壤>黑土>潮土,相关系数(R2)在0.9223～0.9949之间;而线性方程则不能较好地拟合这3种土壤对Hg(Ⅱ)和As(Ⅴ)的等温吸附。(2)Hg(Ⅱ)和As(Ⅴ)的解吸量随Hg(Ⅱ)和As(Ⅴ)吸附量的增加而增加,两者之间呈显著或极显著的线性正相关,Hg(Ⅱ)的相关系数(R2)分别为0.8668**、0.8971**、0.9969**,As(Ⅴ)的相关系数(R2)分别为0.9987**、0.9964**、0.9858**。研究结果对于探明土壤中汞和砷的环境行为具有重要意义。     

纳米TiO2对土壤Hg2+吸附解吸性能的影响

为了研究纳米TiO_2对土壤吸附解吸汞性能的影响,以三峡水库消落区土壤为代表,选择2种晶型(锐钛矿和金红石)的纳米TiO_2颗粒,设置3个浓度梯度(2,4,8g/kg),制成含有不同浓度纳米TiO_2颗粒的土样,配制不同浓度的Hg~(2+)溶液,进行吸附解吸试验。结果表明:纳米TiO_2颗粒可提高土壤对Hg~(2+)的吸附量,但受颗粒的晶型和浓度的影响;锐钛矿颗粒对土壤吸附解吸Hg~(2+)的影响更大,其吸附作用力更强,不易解吸,其中4g/kg处理组吸附作用最强,与对照相比,最大吸附量可提高32.65%,且其解吸率低于对照组;金红石颗粒处理组对Hg~(2+)的吸附量随颗粒浓度的升高而增大,但吸附作用力较弱,容易被解吸,8g/kg处理组影响最大,与对照相比,最大吸附量提高18.18%,但其解吸率也最大。因此,纳米TiO_2颗粒增强土壤对汞的吸附作用,从而可能影响汞在环境中的迁移转化过程,特别是锐钛矿型颗粒。     

Effect of carboxylic and thiol ligands (oxalate, cysteine) on the kinetics of desorption of Hg(II) from kaolinite

Sorption and desorption of Hg(II) on clay minerals can impact the biogeochemical cycle and bio-uptake of Hg in the environment. We studied the kinetics of the desorption of Hg(II) from kaolinite as affected by oxalate and cysteine, representing the ligands with carboxylic and thiol groups of different affinities for Hg(II). The effects of pH (3, 5, and 7), ligand concentration (0.25 and 1.0?mM), and temperature (15??C, 25??C, and 35??C) on the Hg(II) desorption were investigated through desorption kinetics. Our study showed that the Hg(II) desorption was pH dependent. In the absence of any organic ligand, >90% of the previously adsorbed Hg(II) desorbed at pH?3 within 2?h, compared to <10% at pH?7. Similar results were observed in the presence of oxalate, showing that it hardly affected the Hg(II) desorption. Cysteine inhibited the Hg(II) desorption significantly at all the pH tested, especially in the first 80?min with the desorption less than 20%, but the inhibition of the desorption appeared to be less prominent afterwards. The effect of the ligand concentration on the Hg(II) desorption was small, especially in the presence of oxalate. The effect of temperature on the Hg(II) desorption was nearly insignificant. The effect of the organic acids on the Hg(II) sorption and desorption is explained by the formation of the ternary surface complexes involving the mineral, ligand, and Hg(II). The competition for Hg(II) between the cysteine molecules adsorbed on the particle surfaces and in the solution phase probably can also affect the Hg(II) desorption.     

Mercury in the natural gas industry in Canada

There are an estimated 1,500 natural gas facilities across Canada, most of which used mercury (Hg) in metering equipment at one time or another. Although the use of mercury has ceased, many gas industry buildings still contain detectable levels of Hg in air. Air Hg levels are generally low but indoor remediation is suggested. Worker exposure to the air Hg levels is not considered a significant hazard. Very high soil Hg levels have been observed at numerous sites. Soil Hg levels do not pose an immediate human hazard but are sufficient to be hazardous to ecological receptors. The area of soil contamination, is generally within the buildings or within a few metres of the nearest door. Downward movement of the Hg does not generally extend more than one metre. Remediation of contaminated soil with on-site thermal desorption is recommended as the appropriate soil clean-up technology.     

汞在山东省三种森林土壤上的吸附解吸特征研究

As one of the most toxic heavy metals with persistence, bioaccumulation, and toxicity in environment, mercury and its envi- ronmental problems have caused a global concern. To fully understand the behavior and fate of mercury (Hg)(Ⅱ) in forest soils, a series of batch experiments were conducted to determine the adsorption and desorption characteristics of Hg(Ⅱ) by three dark brown forest soils from Mount Taishan, Laoshan Mountain, and Fanggan Village in Shandong Province, China. The adsorption solution was prepared using 0.1 mol L-1 NaNO3 as background electrolyte, with Hg(Ⅱ) at rising concentration gradients of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 mg L-1 . Fourier transform infrared (FTIR) spectroscopy was adopted to characterize the soil samples and soil-Hg complexes. It was found that Hg(Ⅱ) adsorption isotherms could be well fitted with both Langmuir and Freundlich equations. The soil from Mount Taishan had the largest potential Hg(Ⅱ) adsorption capacity, though with less adsorptive intensity. The percentages of Hg(Ⅱ) desorbed from all soil samples were less than 0.6%, which suggested that all the soils studied had a high binding strength for Hg(Ⅱ). The soil from Mount Taishan had a higher Hg(Ⅱ) desorption capacity than the other soils, which indicated that the Hg(Ⅱ) deposited on the topsoil of Mount Taishan from atmosphere may easily discharge to surface water through runoff. Results of the FTIR spectroscopy showed that the three soils contained the same functional groups. The relative absorbencies of soil-Hg complexes changed significantly compared with those of the soil samples and the adsorption of Hg(Ⅱ) mainly acted on the O-H, C-O, and C=O groups of the soils.     

The behavior of mercury in the soil with special emphasis on complexation and adsorption processes - A review of the literature

The behavior of Hg in the soil is mainly controlled by adsorption and desorption processes depending on complexation, the most important ligands in solution being OH^?, Cl^?, and organic anions. Since the solubility of HgCl₂ and Hg(OH)₂ is rather high, the affinity of Hg to these ligands leads to an increased mobility. This is especially true for HgCl₂, whereas the hydrolysis of Hg²⁺ may result in the specific adsorption of Hg on mineral colloids. The high affinity of Hg to S explains the strong binding of Hg to soil organic matter and also the stability of HgS. Further precipitation products than HgS are unlikely to occur, since the activity of Hg²⁺ remains too low to exceed the solubility product of any other defined Hg compound. It is mainly the physical fractioning of soil organic matter (dissolved vs adsorbed) that determines the behavior and distribution of Hg in soils.     

Mercury contaminated sites — Behaviour of mercury and its species in lysimeter experiments

In a polluted site in Germany not only metallic, ionic and MeHg could be detected, but also organomercurials such as methyl- ethyl- and phenyl-mercury. In addition sometimes other organomercurials could be separated but up to now not identified. Extraction of the organomercurials from soil and percolating water was performed by dithizone, differentiation and detection by High-Performance-Liquid-Chromatography and atomic fluorescence detection, respectively. Differentiation between gaseous organic and gaseous elemental mercury was done by adsorption on Carbotrap^® and gold filters, thermal desorption and detection by atomic fluorescence The behaviour of 8 organomercurials in soil is described. For this a lysimeter of a new design was filled with polluted soil. The top layer of the soil was spiked with 8 organomercurials. The percolating water and the air above the soil, were analyzed. Different layers of the soil were also investigated after the experiment. By synthetic rain the movement of Hg species is low: the compounds stay in the first centimeters. Ethoxyethylmercury⁺, tolylmercury⁺, and nitromersol were not detected in the percocolate. Concentrations of phenylmercury⁺ and hydroxymercurybenzoicacid decreased. Methoxymethylmercury⁺ increased. In the head of the lysimeter, volatile Hg(0) concentration increased during 150 hours by a factor of 5, while volatile organic mercury decreased during this time by a factor of 10. The organomercurial-content in soil decreased.A transformation of organic to inorganic Hg is therefore presumed.     

Kinetics of Desorption of Heavy Metals from Polluted Soils: Influence of Soil Type and Metal Source

Kinetics of desorption of heavy metal ions (Cd, Cu, Ni and Zn) from the surface (0–15 cm) samples of an acidic soil (Inceptisol) and a neutral soil (Mollisol) spiked with inorganic salts of these metals or through an acidic sludge were studied by the column method. The rate of desorption of soil applied heavy metals was initially rapid and gradually declined with time. In general, the release of heavy metals from soils polluted by inorganic or sludge sources conformed to a multi-site model of first order kinetics; however, the release of Cd and Ni applied through inorganic sources to the neutral soil could be adequately accounted for by single-site model. The double-site model could adequately explain the release of Cd from sludge amended acidic soil and the release of Zn applied though inorganic salt or sludge to the neutral soil. In acidic soil, the apparent desorption rate coefficients of heavy metals applied through inorganic sources were higher than those for the sludge source. In neutral soil, however, the apparent desorption rate coefficients of heavy metals added through sludge were higher than for inorganic sources. Among the heavy metals, the higher apparent desorption coefficient value and percent desorption of Cd indicated a higher potential of this metal for leaching and ground water contamination. The results also suggested that the acidic soil pH might reduce the ability of the soil to naturally sequester heavy metal cations and lead to their leaching.     

The use of rate equations for a quantitative description of K desorption from soils in an external electric field (electro-ultrafiltration)

Ions can be extracted from soils by applying an external electric field to a soil suspension. When a constant field strength is employed characteristic desorption parameters can be calculated from the results, such as maximum desorbable quantity, halftime, and rate constant. The method consists of a combination of electrodialysis and ultrafiltration and is called electro-ultrafiltration (EUF). It was found that the K transfer from the central compartment A to the cathode compartment B follows a first order rate law, if compartment A contains only the solution of a strong electrolyte such as KCl. If a soil suspension is introduced into compartment A the bulk of K that is transferred to compartment B has first to be desorbed from the soil particles hence the designation as desorption for the transfer from a soil suspension. In this case a second order rate law is followed. The rate equations allow the calculation of the quantity of K involved in the desorption process and the rate with which it is released. It was found that invariably only the exchangeable K takes part in the desorption reaction. The desorption rate differs between soils and depends on clay content and the quantity of exchangeable K present in the soil. It is suggested that the desorption data may provide a means of describing the soil K status by kinetic parameters.