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Kozai N Inada K Kozaki T Sato S Ohashi H Banba T 《Journal of contaminant hydrology》2001,47(2-4):149-158
Diffusion of neptunium (V) in compacted Na-montmorillonite was studied through the non-steady state diffusion method. In this study, two experimental attempts were carried out to understand the diffusion mechanism of neptunium. One was to establish the diffusion activation energy, which was then used to determine the diffusion process in the montmorillonite. The other was the measurement of the distribution of neptunium in the montmorillonite by a sequential batch extraction. The apparent diffusion coefficients of neptunium in the montmorillonite at a dry density of 1.0 Mg m-3 were from 3.7 x 10(-12) m2 s-1 at 288 K to 9.2 x 10(-12) m2 s-1 at 323 K. At a dry density of 1.6 Mg m-3, the apparent diffusion coefficients ranged between 1.5 x 10(-13) m2 s-1 at 288 K and 8.7 x 10(-13) m2 s-1 at 323 K. The activation energy for the diffusion of neptunium at a dry density of 1.0 Mg m-3 was 17.5 +/- 1.9 kJ mol-1. This value is similar to those reported for diffusion of other ions in free water, e.g., 18.4 and 17.4 kJ mol-1 for Na+ and Cl-, respectively. At a dry density of 1.6 Mg.m-3, the activation energy was 39.8 +/- 1.9 kJ mol-1. The change in the activation energy suggests that the diffusion process changes depending on the dry density of the compacted montmorillonite. A characteristic distribution profile was obtained by the sequential extraction procedure for neptunium diffused in compacted montmorillonite. The estimated fraction of neptunium in the pore water was between 3% and 11% at a dry density of 1.6 Mg m-3 and at a temperature of 313 K. The major fraction of the neptunium in the montmorillonite was identified as neptunyl ions sorbed on the outer surface of the montmorillonite. These findings suggested that the activation energy for diffusion and the distribution profile of the involved nuclides could become powerful parameters in understanding the diffusion mechanism. 相似文献
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Three perovskite-type catalysts prepared by citric acid method are applied to remove phenol from gas streams with the total flow rate of 300 mL/min, corresponding to a GHSV of10,000/hr. LaMnO_3 catalyst is first prepared and further partially substituted with Sr and Cu to prepare La_(0.8)Sr_(0.2)MnO_3 and La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3, and catalytic activities and fundamental characteristics of these three catalysts are compared. The results show that phenol removal efficiency achieved with La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3 reaches 100% with the operating temperature of 200°C and the rate of mineralization at 300°C is up to 100%, while the phenol removal efficiencies achieved with La_(0.8)Sr_(0.2)MnO_3 and LaMnO_3 are up to 100% with the operating temperature of 300°C and 400°C, respectively. X-ray photoelectron spectroscopy(XPS) analysis shows that the addition of Sr and Cu increases the lattice oxygen of La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3, and further increases mobility or availability of lattice oxygen. The results indicate that La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3 has the best activity for phenol removal among three catalysts prepared and the catalytic activity of phenol oxidation is enhanced by the introduction of Sr and Cu into LaMnO_3. Apparent activation energy of 48 k J/mol is calculated by Mars–Van Krevelen Model for phenol oxidation with La_(0.8)Sr_(0.2)Mn_(0.8)Cu_(0.2)O_3 as catalyst. 相似文献
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《Process Safety and Environmental Protection》2014,92(6):879-887
The purpose of this study is to find an optimal mixture ratio of the platinum-loaded carbon catalyst and the electrolyte in a membrane electrode assembly (MEA) of a proton exchange membrane fuel cell for reducing the activation resistance, which influences the electrochemical surface area, activation polarization, and maximum power density of the MEA. First, mixture ratios of 10, 20, 40, and 60 wt% platinum-loaded carbon catalysts and electrolyte were examined. The results indicated that the fuel cell performance improved for mixing weight ratios of 1.0:2.0 in 10 wt% Pt/C, 1.0:1.8 in 20 wt% Pt/C, 1.0:1.1 in 40 wt% Pt/C, and 1.0:0.5 in 60 wt% Pt/C. Next, we evaluated the activation resistances of the MEA from the AC impedance characteristics using the optimal mixing weight ratio of the platinum-loaded carbon catalyst and the electrolyte. It was found that the activation resistances of the anode and cathode decrease with an increase in the weight ratio of platinum-loaded carbon in the catalyst layer. 相似文献
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Eduard Hanslík Diana Ivanovová Eva Juranová Pavel Šimonek Věra Jedináková-Křížová 《Journal of environmental radioactivity》2009
The paper summarizes impacts of the Temelín Nuclear Power Plant (NPP) on the Vltava and Labe River basins. The study is based on the results of long-term monitoring carried out before the plant operation (1989–2000), and subsequently during the plant operation (2001–2005). In the first period, the main objective was to determine background radionuclide levels remaining in the environment after global fallout and due to the Chernobyl accident. A decrease in the concentrations of 90Sr, 134Cs and 137Cs, which was observed before the plant operation, continued also during the subsequent period. Apart from tritium, the results of the observation did not indicate any impacts of the plant on the concentrations of activation and fission products in the hydrosphere. The annual average tritium concentrations in the Vltava River were in agreement with predicted values. The maximum annual average tritium concentration (13.5 Bq L−1) was observed in 2004 downstream from the wastewater discharge in the Vltava River at Solenice. Estimated radiation doses for adults due to intakes of river water as drinking water contaminated by tritium are below 0.1 μSv y−1. 相似文献
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《Journal of environmental science and health. Part. B》2013,48(5):677-686
In the present study, a series of activated carbons were prepared from agricultural waste corn cob by chemical and physical activations with potassium hydroxide (KOH)/potassium carbonate (K2CO3) and carbon dioxide (CO2). The effect of process variables such as impregnation ratio, impregnation time, activation temperature and soaking time of CO2 was studied in order to relate these preparation parameters with the physical properties of final carbon products. The resulting activated carbons were characterized by nitrogen adsorption[ch-[chdesorption isotherms at 77 K. The surface areas and pore volumes of carbons were estimated by the BET equation, the Langmuir equation and the t-plot method. Under the experimental conditions investigated, the main parameters in the activation of corn cob were found to be the impregnation ratio and activation temperature. The soaking time of CO2 is another important variable, which had a strong effect on the pore volume development. The BET surface area and total pore volume were as large as about 2000 m2/g and about 1.0 cm3/g, respectively. This study showed that the activation of agricultural waste corn cob with KOH/K2CO3 and CO2 was suitable for the preparation of large-surface-area activated carbons. 相似文献
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Pian Feng Xiaohong Guan Yuankui Sun Wonyong Choi Hejie Qin Jianmin Wang Junlian Qiao Lina Li 《环境科学学报(英文版)》2015,27(5):175-183
Weak magnetic field(WMF) was employed to improve the removal of Cr(VI) by zero-valent iron(ZVI) for the first time. The removal rate of Cr(VI) was elevated by a factor of 1.12–5.89 due to the application of a WMF, and the WMF-induced improvement was more remarkable at higher Cr(VI) concentration and higher p H. Fe2+was not detected until Cr(VI) was exhausted, and there was a positive correlation between the WMF-induced promotion factor of Cr(VI) removal rate and that of Fe2+release rate in the absence of Cr(VI) at pH 4.0–5.5. These phenomena imply that ZVI corrosion with Fe2+release was the limiting step in the process of Cr(VI) removal. The superimposed WMF had negligible influence on the apparent activation energy of Cr(VI) removal by ZVI, indicating that WMF accelerated Cr(VI)removal by ZVI but did not change the mechanism. The passive layer formed with WMF was much more porous than without WMF, thereby facilitating mass transport. Therefore,WMF could accelerate ZVI corrosion and alleviate the detrimental effects of the passive layer, resulting in more rapid removal of Cr(VI) by ZVI. Exploiting the magnetic memory of ZVI, a two-stage process consisting of a small reactor with WMF for ZVI magnetization and a large reactor for removing contaminants by magnetized ZVI can be employed as a new method of ZVI-mediated remediation. 相似文献
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Nonradical reaction driven by peroxymonosulfate (PMS) based advanced oxidation processes has drawn widespread attention in water treatment due to their inherent advantages, but the degradation behavior and mechanism of organic pollutants are still unclear. In this study, the performance, intermediates, mechanism and toxicity of tetracycline (TC) degradation were thoroughly examined in the constructed magnetic nitrogen-doped porous carbon/peroxymonosulfate (Co-N/C-PMS) system. The results showed that 85.4% of TC could be removed within 15 min when Co-N/C and PMS was simultaneously added and the degradation rate was enhanced by 3.4 and 14.7 folds compared with Co-N/C or PMS alone, respectively. Moreover, the performance of Co-N/C was superior to that of most previously reported catalysts. Many lines of evidence indicated that Co-N/C-PMS system was a singlet oxygen-dominated nonradical reaction, which was less interfered by pH and water components, and displayed high adaptability to actual water bodies. Subsequently, the degradation process was elaborated on the basis of three-dimensional excitation-emission matrix spectra and liquid chromatography-mass spectrometry. At last, the toxicity of treated TC was greatly reduced by using microalgae Coelastrella sp. as ecological indicator. This study provides a promising approach based on singlet oxygen-dominated nonradical reaction for eliminating TC in water treatment. 相似文献
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基于改进的Vyazovkin方法,提出了一种新的求解固态反应活化能的等转化率方法。这种方法不仅避开了对反应机理的选择,而且突破了当前等转化率方法不能像拟合法一样求解出明确的活化能的局限。通过对模拟数据及挤塑聚苯乙烯热解实验数据的验证,证实了这种方法对实验噪音具有良好的容许度,并且能够对热重数据的一阶导数据有明显的多峰多歩反应求解出比拟合法更可信的活化能的值。 相似文献