Release of colloidal particles in natural porous media by monovalent and divalent cations

We study mobilization of colloidal particles from natural porous media, such as soils and groundwater aquifers. Extensive laboratory scale column experiments of particle release from four different subsurface materials are presented. The important characteristics of the release process are (i) its non-exponential kinetics, (ii) the finite supply of colloidal particles and (iii) the strong dependence of the release kinetic on the nature of the adsorbed cations. Particle release depends most sensitively on the relative saturation of the medium with divalent cations. We propose a mathematic model, which captures all these aspects quantitatively, and can be used to describe the coupling between transport of major cations and the release of colloidal particles. The present experimental investigations as well as the developed modeling framework represent an important step towards the understanding of colloid-facilitated transport phenomena in natural porous media.     

阳离子交换膜对Cu2+离子交换的动力学及热力学研究

对阳离子交换膜离子交换Cu2+的动力学及热力学现象进行了研究,结果表明:温度25℃,溶液pH=6时,干膜对Cu2+饱和交换容量为0.506 mmol/g;随Cu2+初始浓度的升高,离子交换速率常数随之增加;随温度升高,离子交换速率常数随之增加;随转速升高,离子交换速率常数随之增加;离子交换过程与一级反应速率方程拟合结果良好;△G0<0,表明离子交换反应能自发进行;△H0m>0,表明的交换反应为吸热反应;△S0>0,表明交换反应是熵变增加的反应。     

阳离子交换膜对Cu~（2＋）离子交换的动力学及热力学研究

对阳离子交换膜离子交换Cu2＋的动力学及热力学现象进行了研究,结果表明：温度25℃,溶液pH=6时,干膜对Cu2＋饱和交换容量为0.506 mmol/g;随Cu2＋初始浓度的升高,离子交换速率常数随之增加;随温度升高,离子交换速率常数随之增加;随转速升高,离子交换速率常数随之增加;离子交换过程与一级反应速率方程拟合结果良好;△G0〈0,表明离子交换反应能自发进行;△H0m〉0,表明的交换反应为吸热反应;△S0〉0,表明交换反应是熵变增加的反应。     

Cesium migration in Hanford sediment: a multisite cation exchange model based on laboratory transport experiments

Cs+ transport experiments carried out in columns packed with uncontaminated Hanford formation sediment from the SX tank farm provide strong support for the use of a multisite, multicomponent cation exchange model to describe Cs+ migration in the Hanford vadose zone. The experimental results indicate a strong dependence of the effective Cs+ Kd on the concentrations of other cations, including Na+ that is present at high to extremely high concentrations in fluids leaking from the Hanford SX tanks. A strong dependence of the Cs+ Kd on the aqueous Cs+ concentration is also apparent, with retardation of Cs+ increasing from a value of 41 at a Cs+ concentration of 10(-4) M in the feed solution to as much as 282 at a Cs+ concentration of 5x10(-7) M, all in a background of 1 M NaNO3. The total cation exchange capacity (CEC) of the Hanford sediment was determined using 22Na isotopic equilibrium exchange in a flow-through column experiment. The value for the CEC of 120 microeq/g determined with this method is compatible with a value of 121.9 microeq/g determined by multi-cation elution. While two distinct exchange sites were proposed by Zachara et al. [Geochim. Cosmochim. Acta 66 (2002) 193] based on binary batch exchange experiments, a third site is proposed in this study to improve the fit of the Cs+-Na+ and Cs+-Ca+ exchange data and to capture self-sharpened Cs+ breakthrough curves at low concentrations of Cs+. Two of the proposed exchange sites represent frayed edge sites (FES) on weathered micas and constitute 0.02% and 0.22% of the total CEC. Both of the FES show a very strong selectivity for Cs+ over Na+ (K(Na-Cs)=10(7.22) and 10(4.93), respectively). The third site, accounting for over 99% of the total CEC, is associated with planar sites on expansible clays and shows a smaller Na+-Cs+ selectivity coefficient of 10(1.99). Parameters derived from a fit of binary batch experiments alone tend to under predict Cs+ retardation in the column experiments. The transport experiments indicate 72-90% of the Cs+ sorbed in experiments targeting exchange on FES was desorbed over a 10- and 24-day period, respectively. At high Cs+ concentrations, where sorption is controlled primarily by exchange on planar sites, 95% of the Cs+ desorption was desorbed. Most of the difficulty in desorbing Cs+ from FES is a result of the extremely high selectivity of these sites for Cs+, although truly irreversible sorption as high as 23% was suggested in one experiment. The conclusion that Cs+ exchange is largely reversible in a thermodynamic sense is supported by the ability to match Cs+ desorption curves almost quantitatively with an equilibrium reactive transport simulation. The model for Cs+ retardation developed here qualitatively explains the behavior of Cs+ in the Hanford vadose zone underneath a variety of leaking tanks with differing salt concentrations. The high selectivity of FES for Cs+ implies that future desorption and migration is very unlikely to occur under natural recharge conditions.     

无机离子及天然有机物对纤维负载Fe0还原溴酸盐的影响

为了考察水中存在的NO3-、PO43-、SO42-、HCO3-和Cl-几种阴离子及天然有机物腐殖酸HA对纤维负载Fe0还原溴酸盐的影响,实验以接枝丙烯酸(AA)的聚丙烯(PP)纤维为载体,采用配位技术和液相还原法制备出了纤维负载Fe0(PP-g-AA-Fe0)材料,对纤维负载Fe0还原溴酸盐的反应效能进行了研究。结果表明,NO3-存在会与BrO3-产生竞争使还原反应速率有所降低,但这种竞争没有影响BrO3-完全被还原去除;PO43-、SO42-和HA存在对BrO3-还原反应影响不大,表观反应速率常数较单纯BrO3-还原体系略有增加,未出现文献报道中所说的明显抑制现象;HCO3-、Cl-的存在明显促进了纤维负载Fe0对BrO3-的还原。     

Influence of metal ion on sorption of p-nitrophenol onto sediment in the presence of cetylpyridinium chloride

Heavy metals and surfactants have a significant effect on the sorption of organic contaminants. In this study, batch equilibrium experiments were carried out to investigate the influence of Pb(NO(3))(2) on the sorption of p-nitrophenol (PNP) onto sediments in the presence of cationic surfactant cetylpyridinium chloride (CPC). Results indicated that in the complex system containing PNP, Pb(NO(3))(2) and CPC, the sorption of PNP decreased with increasing concentration of Pb(NO(3))(2) due primarily to competing for adsorption sites. Likewise, partitioning of PNP in adsorbed surfactant layers and micelles decreased with increasing level of Pb(NO(3))(2). Moreover, the influence of different metal ions (Pb(2+), Cd(2+), Zn(2+)) was examined and results indicated that the presence of heavy metals inhibited the sorption of PNP in the order: Pb(2+)>Cd(2+)>Zn(2+). The competitive effect of the heavy metals was in agreement with the hydration energy and hydrated radius. The results are believed to provide a useful insight into describing the transport and fate of PNP in natural environments.     

Effects of natural organic matter on the microporous sorption sites of black carbon in a Yangtze River sediment

Black carbon (BC), characterized by high microporosity and high specific surface area (SSA), has been demonstrated to have substantial contributions to the sorption of hydrophobic organic chemicals in soils and sediments. Other naturally occurring organic matters provide soft and penetrable sorption domains while may cling to BC and affect its original surface properties. In this work, we studied the sorption sites of a Yangtze River sediment sample with organic carbon (OC) content of 3.3 % and the preheated sediment (combusted at 375 °C) with reduced OC content (defined as BC) of 0.4 % by gas and pyrene sorption. The SSA and microporosity of the pristine and preheated sediments were characterized by N₂ and CO₂ adsorption. The results suggest that the adsorption of N₂ was hindered by amorphous organic carbon (AOC) in the pristine sediment but CO₂ was not. Instead, the uptake of CO₂ was higher in the presence of AOC, likely due to the partition of CO₂ molecules into the organic matter. The pyrene adsorptions to BC in pristine and preheated sediments show a similar adsorption capacity at high concentration, suggesting that AOC of ca. 2.9 % in the pristine sediment does not reduce the accessibility to the sorption sites on BC for pyrene.     

Caesium selectivity and fixation by vermiculite in the presence of various competing cations

Caesium selectivity coefficients (k(G)) that were determined with respect to Na-, Mg-, Ca-, Sr- and Ba-ions, for Kent and Libby vermiculites,ranged from 4.8 to 11 (litres/mol) [Formula: see text], much higher than those with respect to K- and NH(4)-ions (0.01 to 0.06), indicating the high affinity of vermiculite for the weakly hydrated cations. Higher K(G) values were also found for low and extremely low Cs concentrations. Vermiculite samples were very effective in removing (137)Cs from solutions containing traces of (137)Cs (4 ng litre(-1)) and extremely higher quantities of K-, NH(4)-, Na-, Mg- and Ca-ions (500 mg litre(-1)). 0.5N chloride solutions of H, NH(4), K, Na, Mg and Ca were unable to remove Cs from Cs-saturated v vermiculite samples which had undergone heating at 110 degrees C. Significant quantities (50-65%) of fixed Cs were removed from these samples only after treatment with strong acids. The high preference and fixing ability of vermiculite for Cs suggests the use of this mineral as a radioactive Cs decontaminating agent.     

Influence of natural dissolved organic carbon on the bioavailability of mercury to a freshwater alga

Bioavailability of mercury (Hg) to Selenastrum capricornutum was assessed in bioassays containing field-collected freshwater of varying dissolved organic carbon (DOC) concentrations. Bioconcentration factor (BCF) was measured using stable isotopes of methylmercury (MeHg) and inorganic Hg(II). BCFs for MeHg in low-DOC lake water were significantly larger than those in mixtures of lake water and high-DOC river water. The BCF for MeHg in rainwater (lowest DOC) was the largest of any treatment. Rainwater and lake water also had larger BCFs for Hg(II) than river water. Moreover, in freshwater collected from several US and Canadian field sites, BCFs for Hg(II) and MeHg were low when DOC concentrations were >5mg L(-1). These results suggest high concentrations of DOC inhibit bioavailability, while low concentrations may provide optimal conditions for algal uptake of Hg. However, variability of BCFs at low DOC indicates that DOC composition or other ligands may determine site-specific bioavailability of Hg.     

天然有机物对零价铁去除水体中砷的影响研究

在研究零价铁对水体中砷去除动力学的基础上,着重探讨了天然有机物腐殖酸对零价铁除砷的影响.并对零价铁的腐蚀产物进行了分析.结果表明,水体中的砷可以通过在零价铁腐蚀产物上的吸附得到快速去除.腐殖酸显著降低了砷的去除率,这归因于腐殖酸与零价铁腐蚀产生的铁离子形成络合物,阻止了Fe(OH)3(或Fe(OH)2)沉淀的产生.腐殖酸浓度越高.砷的去除率越低.1.00 mg腐殖酸最多可以络合约0.75 mg铁离子.当铁离子与腐殖酸的络合达到饱和后,零价铁进一步腐蚀产生的铁离子可形成Fe(OH)3(或Fe(OH)2)沉淀,这些沉淀物可吸附水体中的腐殖酸和砷,从而加速砷的去除.冷冻干燥后的零价铁腐蚀产物的结构以无定型为主,含有少量的结晶化合物,包括γ-Fe2O3、γ-FeO(OH)和Fe3O4等.腐殖酸的存在可进一步增加腐蚀产物中的无定型成分.光电能谱(XPS)分析结果显示,吸附在腐蚀产物上的砷为5价,没有发现5价砷被还原成3价砷.在应用零价铁修复砷污染水体时,应考虑腐殖酸的影响.     

Analysis of organic and inorganic species on the surface of atmospheric aerosol using time-of-flight secondary ion mass spectrometry (TOF-SIMS)

This work explores the utility of time-of-flight static secondary-ion mass spectrometry (TOF-SIMS) for the analysis of the surface organic layer on individual atmospheric aerosol particles. The surface sensitivity and minimal fragmentation available with TOF-SIMS suggest that it can be a powerful tool for the examination of the organic and inorganic species on the surface of individual particles. Cascade impactors were used to collect aerosol from summer 2000 Montana forest fires, winter snowmobile samples in Yellowstone National Park, Hawaiian lava and sea salt, from an Asian Dust event reaching Salt Lake City, Utah in April 2001 and from Salt Lake Valley summer urban aerosol. TOF-SIMS analysis and multivariate statistical techniques combined gave chemical and morphological information about the particles. Surfaces of the aerosol from forest fires, snowmobile exhaust, and sea salt were all dominated by aliphatic hydrocarbons and their amphiphilic derivatives. Each source showed a different organic chemical signature. The extent and composition of the organics layer which typically covers the surface of atmospheric particles are expected to effect all of the surface related aerosol properties such as health effects, the ability of the particle to activate and form cloud droplets, and the aggregation of particles as well as reactions between the particle and gas phase species.     

Evaluation of ion exchange resins for the removal of dissolved organic matter from biologically treated paper mill effluent

In this study, the efficiency of six ion exchange resins to reduce the dissolved organic matter (DOM) from a biologically treated newsprint mill effluent was evaluated and the dominant removal mechanism of residual organics was established using advanced organic characterisations techniques. Among the resins screened, TAN1 possessed favourable Freundlich parameters, high resin capacity and solute affinity, closely followed by Marathon MSA and Marathon WBA. The removal efficiency of colour and lignin residuals was generally good for the anion exchange resins, greater than 50% and 75% respectively. In terms of the DOM fractions removal measured through liquid chromatography–organic carbon and nitrogen detector (LC–OCND), the resins mainly targeted the removal of humic and fulvic acids of molecular weight ranging between 500 and 1000 g mol^?1, the portion expected to contribute the most to the aromaticity of the effluent. For the anion exchange resins, physical adsorption operated along with ion exchange mechanism assisting to remove neutral and transphilic acid fractions of DOM. The column studies confirmed TAN1 being the best of those screened, exhibited the longest mass transfer zone and maximum treatable volume of effluent. The treatable effluent volume with 50% reduction in dissolved organic carbon (DOC) was 4.8 L for TAN1 followed by Marathon MSA – 3.6 L, Marathon 11 – 2.0 L, 21K-XLT – 1.5 L and Marathon WBA – 1.2 L. The cation exchange resin G26 was not effective in DOM removal as the maximum DOC removal obtained was only 27%. The resin capacity could not be completely restored for any of the resins; however, a maximum restoration up to 74% and 93% was achieved for TAN1 and Marathon WBA resins. While this feasibility study indicates the potential option of using ion exchange resins for the reclamation of paper mill effluent, the need for improving the regeneration protocols to restore the resin efficiency is also identified. Similarly, care should be taken while employing LC–OCND for characterising resin-treated effluents, as the resin degradation is expected to contribute some organic carbon moieties misleading the actual performance of resin.     

Observations on long-term air-soil exchange of organic contaminants

Evidence for long-term changes in the soil composition of selected organic compounds, brought about by exchanges with the atmosphere, is briefly reviewed. In the case of some compounds — such as benzo(a)pyrene and octachlorodibenzo-p-dioxin, soils may be significant long-term environmental sinks for atmospherically-derived material. In other cases — such as phenanthrene and some of the lighter PCBs, de-gassing or volatilisation from soil back to the air can occur under certain conditions. Hence the soil may act as a “short-term” sink, and a potential source to atmosphere. Indeed, for some ‘semi-volatile’ compounds used in large quantities in the past — such as PCBs, soil outgassing may actually be an extremely important source to contemporary air. Furthermore, soil outgassing from areas of former high use may provide an important driving mechanism for continued “global cycling” of a range of semi-volatile organochlorine compounds.     

Effect of dye compounds on the adsorption of atrazine by natural sediment

The overall objective of this research is to investigate competitive adsorption between atrazine (AT) and dye compounds in the natural aquatic sediment. The sorbent was sediment obtained from Guanting Reservoir (Beijing, China), which contained 25% sand, 67% silt, 8% clay, and 2.06% organic carbon. Batch adsorption experiments were conducted at various Ca2+ concentration, pH levels, temperatures, and introducing conditions of dye compounds. Compared with the dye-free system, both of dyes including Congo red (CR) and methylene blue (MB) reduce the adsorption of atrazine over the range of dye concentrations examined, with the adsorption percentage of atrazine decreasing about 14-30%. And the competition between AT and MB is much stronger than that between AT and CR. The adsorption experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf) of the samples; Kf values range from 1.669 micromol/kg for the MB-AT sample up to 3.738 micromol/kg for the AT-alone sample. By contrast with the single-solute adsorption isotherm, both simultaneous adsorption and dye preloading inhibit the adsorption of atrazine. As for AT preloading, the impacts of CR and MB are different on the desorption of atrazine. As compared to the atrazine desorption without dye compounds, a certain amounts of atrazine molecules are replaced by MB in AT preloading system, while in CR solution AT is adsorbed strongly on the sediment and could not be replaced by CR. The result suggests that micropore constriction by CR reduces the desorption rate of atrazine.     

Occurrence of organic and inorganic biocides in the museum environment

In the museum environment organic and inorganic chemicals can be found, which originate from both outside and inside the building. Many of the contaminants may cause adverse effects on works of art and human health, but in the past, pollution research in museums has focused on the protection of artifacts, while the risk assessment for humans has been neglected. Especially, the application of biocides leads to a conflict of interest: on the one hand cultural assets have to be protected against microorganisms, insects and rodents while on the other hand it is essential to provide healthy conditions for museum staff and visitors. It has recently been shown that the release of organic indoor pollutants from building products is one of the main reasons for deterioration of artifacts. In this work, we present the results of screening measurements on biocides in different locations of German museums. The major components that could be identified were DDT, PCP, lindane, methoxychlor, naphthalene, chlorinated naphthalenes, 1,4-dichlorobenzene, PCBs and arsenic. It is demonstrated that the application of chlorinated organic compounds and arsenic for preventive conservation is one of the prime reasons for indoor pollution in museums and provides a potential for exposure. However, the concentrations in air, dust and material are widely different and a health risk for humans has to be evaluated case by case.     

离子交换纤维对重金属的吸附研究

采用自制强酸性阳离子交换纤维对镉、铅离子的吸附性能进行了初步研究。实验结果表明 ,强酸性阳离子交换纤维对镉、铅离子具有较好的吸附能力 ,其最大吸附容量分别为 2 0 6.6mg g和 10 5 .5mg g ;吸附速度快 ,2 0min即可达到平衡。用Langmuir方程对其吸附等温线进行回归 ,结果显示实测值与理论方程具有较好的一致性     

颗粒物对无电压作用下离子交换膜分离去除铜离子的影响

在无外加电压条件下研究了颗粒物对阳离子交换膜分离去除铜离子效果的影响。选用硅酸、二氧化硅、氧化铝和水杨酸等4种物质作为颗粒物分别进行实验,其添加量均为50 mg/L。Cu2+及其补偿离子K+的浓度分别为0.0787mmol/L(5 mg/L)和0.787 mmol/L,水温为25±1℃,搅拌强度为600 r/min,水力停留时间为12 h。在所述实验条件下运行96 h后,水中无颗粒物干扰时,铜离子去除率为84%;水中存在带负电荷颗粒物(硅酸)和不带电荷颗粒物(二氧化硅和氧化铝)时,铜离子去除率略为下降至81%;而当水中存在带正电荷颗粒物(水杨酸)时,铜离子的去除率进一步下降为79%。研究结果表明带正电荷颗粒物对铜离子的交换去除影响较带负电荷或不带电荷颗粒物大,因为带正电荷颗粒物更易迁移至阳离子交换膜表面甚至进入膜内,并与膜表或膜内离子交换基团结合,从而导致铜离子交换去除明显下降。