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A comparison of CaOs produced by calcining two types of hydrated lime and calcium carbonate was made for decomposition of trichloroethylene and in-situ dry sorption of the decomposed Cl-products using a lab-scale gas flow type tubular packed bed reactor. About 20 mg of CaO sample was mixed with about 2 g of Al2O3 particles and packed in the reactor and allowed to react with a flowing standard gas containing 500 ppm of C2HCl3 (N2 balance) at 673 and 873 K, under the condition that the reaction of CaO with C2HCl3 might be completed within a few hours.It was found that no thermal decomposition of C2HCl3 at or below 673 K was observed in a reactor packed only with Al2O3 particles. However, a considerable amount of decomposition of C2HCl3 was obtained in a reactor packed with CaO and Al2O3, even at 673 K. For 1 mol of CaO prepared by calcining highly reactive Ca(OH)2 at 673 K, decomposition of 0.42 mol of C2HCl3 and in-situ absorption product of 0.53 mol of CaCl2 were obtained. At 873 K, about 46% of C2HCl3 was thermally decomposed. The total amount of C2HCl3 decomposed in CaO-Al2O3 particle bed at 873 K became nearly twice larger than that at 673 K. For 1 mol of CaO prepared by calcining highly reactive Ca(OH)2 at 873 K, decomposition of 0.59 mol of C2HCl3 and in-situ absorption product of 0.67 mol of CaCl2 were obtained. Small amounts of C2Cl2, C2Cl4, CCl4, etc. were detected during decomposition of C2HCl3 at 673 and 873 K.It was recognized that the data on decomposition of C2HCl3 as well as in-situ dry sorption of Cl-products in CaO particle bed were correlated with specific surface area of the CaO employed. 相似文献
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Numerical simulation is used to examine the relative velocities of DNAPL and aqueous phase plumes in sandy aquifers where lateral spreading of DNAPL has occurred at the base of the aquifer. The scenario being modeled is one where a permeable aquifer is underlain by a sloping aquitard, which results in lateral migration of the DNAPL down the slope, in addition to lateral migration of an aqueous phase plume subject to a specified hydraulic gradient. A sensitivity analysis is presented to the impacts of both DNAPL properties and geologic properties. The most important chemical properties governing the relative velocities of the DNAPL and the shallow aqueous phase plume are the DNAPL viscosity and the aqueous component soil-water partition coefficient (Kd). The dip of the underlying aquitard was found to be relatively unimportant, at least for the range of values studied. The scenario under consideration can be important in conceptual model development and remedial design, as in certain cases DNAPL could be migrating in areas without the evidence of a well-developed aqueous phase plume. The implication of this work is that the absence of a shallow aqueous phase plume directly downgradient of a DNAPL source zone does not rule out the possibility of deep occurrences of DNAPL beyond the shallow monitoring well network. A further finding of this study is that the occurrence of a highly sorbing compound in groundwater at virtually any concentration may indicate the immediate upgradient presence of residual or pooled DNAPL. 相似文献
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Hydrodechlorination is a promising technology for the remediation of water body contaminated with trichloroethylene (TCE). In this work, the liquid-phase hydrogenation of TCE by Raney Ni (R-Ni) and Pd/C under an open system have been studied, in which nascent H2 (Nas-H2) generated in situ from the cathode acted as a hydrogen source. Experimental results showed that TCE was completely eliminate from the solution through the synergistic effects of hydrodechlorination and air flotation due to the formation of continuous micro/nano-sized Nas-H2 bubbles from the cathode. Furthermore, the effects of inorganic anions and organic solvents on R-Ni and Pd/C hydrogenation activity were investigated, respectively. The results showed that NO3? and acetonitrile can form a competitive reaction with TCE; Sulfur with lone-pair electrons will cause irreversible poisoning to these two catalysts, and have a stronger inhibitory effect on Pd/C. This work helps to realize the separation of volatile halogenated compounds from water environment and provides certain data support for the choice of catalyst in the actual liquid-phase hydrogenation system. 相似文献
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Minxiang Wang Lili Yang Xiaoyun Liu Zheng Wang Guorui Liu Minghui Zheng 《Frontiers of Environmental Science & Engineering》2021,15(4):60
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Qiong Bin Bin Lin Ke Zhu Yaqian Shen Yuanyuan Man Boyang Wang Changfei Lai Wenjin Chen 《环境科学学报(英文版)》2020,32(2):90-102
Sulfide-modified nanoscale zero-valent iron (S-nZVI) is a promising material for removal of organic pollutants from water, but S-nZVI nanoparticles (NPs) easily agglomerate and have poor contact with organic contaminants. Herein, we propose a new S-nZVI/graphene aerogel (S-nZVI/GA) composite which exhibits superior removal capability for trichloroethylene (TCE) from water. Three-dimensional porous graphene aerogel (GA) can improve the efficiency of electron transport, enhance the adsorption of organic pollutants and restrain the agglomeration of the core-shell S-nZVI NPs. The TCE removal rates of FeS, nZVI, GA and S-nZVI were 27.8%, 42%, 63% and 75% in 2?hr, respectively. Furthermore, TCE was completely removed within 50?min by S-nZVI/GA. The TCE removal rate increased with increasing pH and temperature, and TCE removal followed the pseudo-first-order kinetic model. The results demonstrate the great potential of S-nZVI/GA composite as a low-cost, easily separated and superior monolithic adsorbent for removal of organic pollutants. 相似文献
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The photocatalytic degradation of gaseous trichloroethylene (TCE) without water has been studied. The degradation products were determined to be CO2, HCl and Cl2, and the reaction stoichiometry, was described as . The degradation rate was found to be linear with 0.16 power of the illumination intensity. When the TCE concentration was low (1014 mol L−1 or a little more), its degradation rate model could be considered as first order kinetics. A mechanism of valence band hole oxidation was proposed. 相似文献
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负载型纳米TiO2光催化降解水中微量三氯乙烯 总被引:1,自引:0,他引:1
利用负载型纳米TiO_2作为光催化剂,对水中微量三氯乙烯进行紫外光催化降解处理。研究表明,三氯乙烯光催化降解过程符合表现一级反应动力学规律。不同的三氯乙烯初始浓度、光照强度和催化剂用量,对三氯乙烯的光催化降解具有不同的效果。在一定初始浓度范围内,随着初始浓度的增大,三氯乙烯光催化降解的反应速率常数逐渐减小;光强与反应速率常数呈正比例相关,显示出有一个最佳值;催化剂的用量与反应速率常数并非呈直线相关。此外,还讨论了三氯乙烯光催化降解的机理。 相似文献
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正己烷萃取-气相色谱法快速测定水中三氯乙烯 总被引:3,自引:0,他引:3
采用正己烷萃取法对水中三氯乙烯进行富集,用毛细管柱气相色谱法进行测定;通过正交试验,对气相色谱测定的主要影响因素和条件进行优化选择,并进行定量评价,总结其影响规律,最终确定最佳测定条件。同时对该方法检出限、准确度和精密度进行检验,完成方法验证。结果表明,该方法简单、快速、准确可靠,灵敏度高,在水环境质量监测中具有实用性。 相似文献
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This study investigated the removal of hydrophobic trichloroethylene (TCE) in the presence of methanol (co-metabolite) in a biotrickling filter, which was seeded with fungi at pH 4. Starvation was chosen as the biomass control strategy. Two systems, Biofilter I (methanol:TCE 70:30) and Biofilter II (methanol:TCE 80:20) were run in parallel, each with varying composition ratios. The TCE loading rates for both biofilters ranged from 3.22 to 12.88 g/m3/hr. Depending on the ratio, methanol concentrations varied from 4.08 to 27.95 g/m3/hr. The performance of the systems was evaluated and compared by calculating removal kinetics, carbon mass balance, efficiencies and elimination capacities. Methanol was observed to enhance TCE removal during the initial loading rate. However, methanol later inhibited TCE degradation above 6.44 g TCE/m3/hr (Biofilter I) and 3.22 g TCE/m3/hr (Biofilter II). Conversely, TCE did not impede methanol removal because over 95% methanol elimination was consistently achieved. Overall, Biofilter I was able to outperform Biofilter II due to its greater resistance towards methanol competition. 相似文献