In order to improve the heavy metal removal ability of traditional single washing agents and explore the removal mechanism of heavy metals. Then, the washing reagents that mixed by low-molecular weight organic acids (citric acid, oxalic acid, and tartaric acid) and artificial chelating compound ethylenediaminetetraacetic acid disodium (EDTA) were selected. Furthermore, the effect of soil washing parameters, the variation of leaching toxicity, mobility, stability and speciation of heavy metals were also considered. The results of soil washing experiments showed that mixing an equal volume of 0.05 M EDTA and 0.2 M organic acids (citric acid, oxalic acid, and tartaric acid) could remove more than about 80% heavy metals from soil under the optimal conditions. In addition, the soil leaching toxicity was decreased and the stability of remaining heavy metals was increased, indicating that EDTA-organic acid washing reagents could effectively reduce the ecological risk of contaminated soil. EDTA had a stronger chelating ability with heavy metals than the organic acids, and the organic acids could not only chelate heavy metals but also decrease the pH of the mixture for promoting the desorption of heavy metals. Thus, mixing EDTA and organic acids was advisable method to improve soil washing technology. 相似文献
In this work, the rheological, thermal and mechanical properties of melt-compounded flax fiber-reinforced polylactide composites were investigated. The effect of compounding on fiber length and diameter, and the relationship between fiber content and the crystallization behavior of the biocomposites, at various temperatures, were also examined. After melt-compounding, fiber bundles initially present were, to a large extent, broken into individual fibers and the fiber length was decreased by 75 %, while the aspect ratio was decreased by nearly 50 %. The crystallization half-time was found to decrease with increasing flax fiber content, and showed a minimum value at 105 °C for all systems. The elastic modulus was increased by 50 % in the presence of 20 wt% flax fibers. The addition of maleic anhydride-grafted polylactide had a positive effect on the mechanical properties of the biocomposite. This system is particularly interesting in the context of sustainable development as it is entirely based on renewable resources and biodegradable. 相似文献
The influence exerted by the conditions of the mechanochemical synthesis [time (100–100 min), air pressure (1–9 atm), temperature (30–90°C), amount of ammonia (0.5–3.0 g g?1 raw material)] on the content of nitrogen and functional groups in the products of oxidative ammonolysis of flax boon was studied. The resulting products were tested as nitrogen-containing ion exchangers in sorption of heavy metals. 相似文献
Biodegradation of flax fibers differing in the chemical composition, structure of cellulose, and content of concomitant natural
impurities (pectin compounds, lignin, hemicellulose) was studied. The effect exerted on the biodegradation by silver nanoparticles
immobilized in the fiber was evaluated. 相似文献
There are growing research interests in flax fibers due to their renewable ‘green’ origin and high strength. However, these natural fibers easily absorb moisture and have poor adhesion with polymer matrix leading to low interfacial strength for the composites. A hybrid chemical treatment technique combining alkali (sodium hydroxide) and silane treatments is adopted in the current study to modify flax fibers for improved performances of flax/polypropylene composites. Changes in chemical composition, microstructure, wettability, surface morphology, crystallinity and tensile properties of single flax fiber before and after chemical treatments were comprehensively characterized using techniques including SEM, FTIR, AFM, XRD, micro-fiber tester, etc. It was found that hemicellulose and lignin at the fiber surface were removed due to alkali treatment, which helped to reduce moisture absorption of the composites. Alkali-treated flax fibers were later subjected to silane treatment, which helped to improve the compatibility between flax fiber and polypropylene matrix. After alkali-silane hybrid chemical treatment, moisture absorption of the composites was further decreased. At the same time, the interfacial bonding strength between flax and polypropylene is significantly enhanced. All these results validate the great advantage of the hybrid chemical treatment approach for flax/polypropylene composites, which has the potential to promote the application of chemical treatment techniques in the plant fiber composite industry.
The research presented herein is the first attempt to probe the chemical nature of lignocellulosic samples by the application of carbon near edge X-ray absorption fine structure spectroscopy (C-NEXAFS). C-NEXAFS is a soft X-ray technique that principally provides selective interrogation of discrete atomic moieties using photoelectrons of variable energies. The X1A beam line of the National Synchrotron Light Source was employed for the specific purpose of observing carboxylic acid moieties that display a signature absorption band centered at 289 eV. This study caps a larger effort to support the mechanistic basis for lignocellulosic fiber chemical degradation induced by the disproportionation of hydrogen peroxiduring fiber bleaching trials. It is shown that fibers that have been bleached with a hydrogen peroxide phase without removal of resident pendant metals (Mn, Cu, Fe) sustain significant macroscopic damage likely via classical Fenton-type radical reactions, as evidenced by a tensile reduction by over 30%. We present X-ray absorption spectra obtained using a scanning transmission X-ray microscope (STXM) at the end of a 2.5 GeV electron synchrotron that provided 1s * contrast-enhanced micrographs illustrating a random distribution of acid functionalities that were principally located on fiber surfaces. Control studies using non-bleached fibers demonstrated that very little signature carboxylic acid absorption patterns were present in the fibers, suggesting that these groups are an incriminating fingerprint for macroscopic fiber strength damage during non-radical suppressed bleaching trials. 相似文献
Anodic stripping voltammetry using a mercury film electrode (MFE) and hanging mercury drop electrode (HMDE) was applied for
the determination of trace amounts of lead, cadmium, zinc and copper leached from plates by 4% acetic acid standard solution.
The use of a MFE, the fast scan rate (1000 mV/s) by DC voltammetry with subtraction of background current allowed to determine
low concentrations of heavy metals. The amounts of metals leached from ware were Pb: 0.1 to 25, Cd: 0.015 to 0.44, Zn: 0.07
to 1.06, Cu: 0.14 to 0.40 μg/mL, depending on the kind of plate and manufacture. Determinations of copper and zinc were carried
out using the HMDE electrode in the leachate, determination of tin after medium exchange, and thallium after complexing of
lead by EDTA. A significant decrease of metals leached during the second leaching and after washing with detergent solution
was found for plates with overglaze decoration.
Received: 5 November 1997 / Revised: 24 February 1998 / Accepted: 26 February 1998 相似文献
EPDM composites filled with short flax fibers were prepared by melt blending procedure. The effects of fiber loading on the mechanical, thermal and water uptake characteristics were studied. The physico-mechanical, morphological thermal properties and water absorption behavior were discussed using tensile testing, differential scanning calorimetry, thermogravimetrical analysis and scanning electron microscopy. Scanning electron microscopy revealed that the flax fibers were well dispersed in the polymer matrix. The tensile strength and hardness of the composites were found to be improved at higher fiber loading. The water absorption pattern of EPDM/fiber composites at room temperature follows a Fickian behavior for composites with 10, 15 and 20 phr flax fiber. 相似文献
Flax fiber was treated with acetic anhydride or with ethylene plasma to improve adhesion with poly(3-hydroxybutyrate) (PHB). The flax fiber surface became hydrophobic by the surface treatments. The ethylene plasma treated flax fiber has better thermal resistance and shows higher interfacial adhesion strength in flax/PHB biocomposite than the chemically modified flax fiber with acetic anhydride. Optimum conditions of the ethylene plasma treatment were found to be 0.5 cm3/sec of the ethylene flow rate and 50 W of the plasma power with 5 min of the treatment time. 相似文献
Heavy-metal-containing humic colloids from seepage water samples of three different municipal waste disposal plants were characterized in terms of molecular weight, hydrodynamic radius and heavy metal content. The size distribution of the colloids was determined with ultrafiltration (UF) and flow field-flow fractionation (flow FFF). The humic colloids in the seepage water samples were characterized using an off-line coupling of flow FFF with an enzyme-linked immunosorbent assay (ELISA) for humic substances. The heavy metals in the different size fractions obtained by UF and flow FFF were determined using atomic absorption spectroscopy (AAS). The colloid size distributions obtained with UF showed a maximum of the distribution in the range 1–10 nm. Seepage water samples with high colloid concentrations had a second maximum in the range 0.1–1 m. The determination of colloid size with flow FFF gave different colloid size distributions for the three waste disposal seepage waters, whereas water from the oldest disposal plant showed the smallest colloid size with a maximum at 0.9 nm and water from the most recent plant showed the largest colloid size with a maximum at 1.3 nm. The determination of particle classes with regard to the chemical composition using a scanning electron microscope with energy dispersive X-ray fluorescence detector (SEM/EDX) showed that the particles can be divided into five classes: silicates, insoluble salts, iron(hydr)oxides, carbonates and organic colloids (humic colloids). Flow FFF/ELISA off-line coupling showed that the most frequently occurring colloids of the seepage waters were humic colloids and investigation of the UF-size-fractions with AAS showed that up to 77% of the total mass of a heavy metal element can be bound to particles, especially to humic colloids. Additionally, the distributions of the heavy metals Fe, Cu and Zn were investigated with flow FFF/AAS off-line coupling. These results also showed that a substantial amount of these heavy metals (up to 46%) was bound to humic colloids. 相似文献
The aim of this work was to quantify the content of elements present in textile materials since it is known that textiles containing metals may represent a health hazard to consumers. Determination of metal content can be also useful to the textile industry since some metals present in textiles may contribute to problems during textile production. Extraction of metals from different textile materials was performed in an artificial acidic sweat solution according to the Öko Tex standard for materials coming into direct contact with the skin. After extraction from textile products made of cotton, flax, wool, silk, viscose, and polyester materials, all elements were determined by means of inductively coupled plasma-optical emission spectrometry (ICP-OES). Results in the sweat extracts (minimum-maximum in μg/mL) were: Al 0.11-1.58, Cd 0.02-0.05, Cr 0.01-0.32, Cu 0.05-1.95, Mn 0.01-2.17, and Ni 0.05-0.10. Concentrations of other elements were bellow detection limits. The total amount of metals present was determined after microwave assisted acidic digestion of textile materials with 7 M nitric acid. According to the results, the majority of the detected elements were below the concentration limits given by the Öko Tex, and for this reason the textile materials investigated do not represent a health hazard to consumers. 相似文献
Pollution of soils and sediments by heavy metals is an environmental concern. Among the remedial techniques, soil washing is proving to be reliable. Biosurfactant rhamnolipid has shown its potential as a washing agent. In this research, small angle neutron scattering (SANS) was employed to investigate the size and morphology of rhamnolipid aggregates and micelle structure in the presence of heavy metals Cu, Zn, and Ni. The results indicate the importance of the pH of the system in the morphology of the aggregates in the rhamnolipid solution. Creation of a basic condition by addition of 1% NaOH led to the formation of large aggregates (>2000 A) + micelles with RG approximately 17 A while in the acidic environment with 1% NaCl, large polydisperse vesicles with a radius about 550-600 A were formed. The size of the aggregates in both acidic and basic condition is fine enough to ease the flow of the rhamnolipid solution through the porous media with the pore sizes as small as 200 nm. 相似文献
The precision of the determination of the of heavy metals in aerosols by X-ray fluorescence after their collection on a paper
filter is evaluated depending on the chemical composition and weight of unsaturated samples. Recommendations on the choice
of the optimal shape of the calibration function and on the conditions for the determination of its coefficients used for
the X-ray analysis of unsaturated samples are formulated. A procedure for the X-ray determination of metals in aerosols collected
on paper filters is developed; its performance characteristics are presented. 相似文献
The distribution of heavy metals Cr, Ni, Zn, Cu, Cd, and Pb among the truly dissolved (molecular weight cutoff <1 kD), colloidal (1 kD-0.20 µm and 0.20-0.45 µm) and particulate (>0.45 µm) fractions was investigated in the soil solution and surface water. In 15 soil solutions heavy metals were mainly present in the truly dissolved fraction (<1 kD) with occasional exceptions. And a good correlation was also found between the concentrations of metals in the truly dissolved fractions and the cation exchange capacity of soils. As for the surface water samples, the distribution pattern was more complicated one depending on metal properties and sampling sites. 相似文献