首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到19条相似文献，搜索用时 140 毫秒
1.
实验室合成制得的纳米铁BET比表面积为49.16 m2/g, 直径范围为20~40 nm.通过批实验考察纳米铁对As(Ⅲ)吸附动力学情况.结果表明, 在20℃、pH为7时, 纳米铁能够快速地去除As(Ⅲ), 在60 min内, 0.1 g纳米铁对起始浓度为910 μg/L溶液As(Ⅲ)去除率大于99%.反应遵循准一级反应动力学方程, 标准化后的As(Ⅲ)速率常数kSA为2.6 mL/(m2·min).纳米铁对As(Ⅲ)的吸附等温曲线能够很好地满足Langmuir和Freundlich方程, 相关系数R2＞0.95, 由Langmuir模型获得单层纳米铁的最大吸附量为76.3 mg/g.0.1 mol/L NaOH对吸附在纳米零价铁(NZVI)的As(Ⅲ)解吸率为21%.在竞争阴离子中, SiO32-和H2PO4-对As(Ⅲ)的去除有明显阻碍作用, 而其他离子基本上没有影响.纳米铁对As(Ⅲ)的去除机理主要是吸附和共沉淀.   相似文献   

2.
研究零价铁(Zero-valent iron,ZVI)去除溶液中的U(VI),分析了pH值、反应时间、ZVI投加量、铀溶液初始浓度、其它离子(Mg2+、Mn2+、Cl-、NO-3、CO2-3和Cu2+)等条件因素对U(VI)去除效果的影响,并讨论其去除机理。结果表明:ZVI对溶液中U(VI)有较好的去除作用,在pH=4,振荡时间为120min,ZVI投加量为1.6g/L,铀溶液初始浓度为10mg/L,铀去除量为4mg/g时,U(VI)的去除率可达到63.7%。其它离子实验结果表明:Mg2+、Mn2+、Cl-、NO-3对ZVI去除U(VI)影响不超过3%,CO2-3和Cu2+影响相对较大。ZVI去除溶液中U(VI)以还原沉淀和吸附作用为主,吸附-还原反应遵循一级化学反应动力学方程。  相似文献   

3.
纳米铁去除饮用水中As(Ⅲ)和As(Ⅴ)   总被引：3，自引：1，他引：2  
黄园英  秦臻  刘菲 《岩矿测试》2009,28(6):529-534
在好氧水体中,As(Ⅲ)比As(Ⅴ)更易迁移,而且在水处理过程中去除效率更低。在实验室合成制得BET比表面积为49.16 m2/g,直径范围为20~40 nm的纳米铁。通过批试验考察纳米铁对As(Ⅲ)和As(Ⅴ)去除能力及其反应动力学情况。结果表明,在pH为7,温度20℃时纳米铁能够快速地去除As(Ⅲ)和As(Ⅴ),在60 m in内,0.25 g纳米铁对起始浓度为968.6μg/L As(Ⅲ)和828.9μg/L As(Ⅴ)的去除率大于99.5%。反应遵循准一级反应动力学方程,标准化后的As(Ⅲ)和As(Ⅴ)比表面积速率常数kSA分别为1.30 mL/(m2.m in)和1.64 mL/(m2.m in)。由实验结果可知,具有高反应活性的纳米铁是用于含砷饮用水处理非常有效的吸附材料。  相似文献   

4.
氯代烃的污染治理已成为当今世界最热门的研究领域之一。以水体中最常见的氯代烃污染物1,1-二氯乙烯（1,1-DCE）、林丹（γ-HCH）为主要目标污染物,探讨了不同条件下负载型纳米Pd/Fe对氯代烃的去除效果。负载型纳米Pd/Fe采用浸渍→液相还原→还原沉淀的方法制备,透射电镜显示采用该方法制备的负载型金属钯和铁的平均粒径均在纳米级范围内。负载型纳米Pd/Fe具有较高的表面反应活性,当负载型纳米Pd/Fe 用量为40 g/L、反应时间达2 h时,1.1-二氯乙烯和林丹的去除率分别达到85%和100%。脱氯率与Pd/Fe投加量、钯含量、初始pH值、反应温度等因素有关,与溶液的初始浓度关系不大。负载型纳米Pd/Fe对11-DCE和γ-HCH去除均符合一级反应动力学方程,速率常数分别为0-528 3 h-1及2-012 9 h-1,反应的半衰期t1/2分别为1.31 h和0.34 h。推断在反应过程中,Fe腐蚀产生的H2为主要还原剂,Pd是良好的加氢催化剂,在金属颗粒表面形成高浓度反应相,使反应短时间内完成。  相似文献   

5.
零价铁（Fe0） 被广泛用于地下水中硝酸盐原位与异位修复,但二价铁（Fe2+） 的存在对具有氧化膜的Fe0还原硝酸盐的作用效应仍有待研究。以100 目的未经酸化的颗粒状零价铁作为还原剂,采用室内批试验方法,研究了Fe2+在零价铁还原去除NO3-系统中的作用效应。实验结果表明,Fe2+可显著提高Fe0对于NO3-的去除速率与去除效率,且Fe2+浓度越高,去除速率与效率越高;由于未经酸化的Fe0具有氧化膜,反应初期的NO3-还原速率较慢。Fe2+将零价铁表面的Fe2O3氧化膜转化为Fe3O4,加速电子由Fe0向NO3-的转移,促进NO3-还原。此外,在反应系统中加入Fe3O4,可进一步提高Fe0对于硝酸盐的去除能力,若Fe2+不存在,仅添加Fe3O4,NO3-的去除效率没有提高。  相似文献   

6.
As(Ⅲ)毒性高,易迁移,且是厌氧条件下地下水中主要存在形式。纳米铁颗粒在含砷水体处理中受到广泛关注,而锌具有比铁更低的氧化还原电位且更易保存,被认为是用于氯代有机化合物还原的最佳金属,但有关纳米锌用于水体中砷的研究很少。本文研究了纳米锌吸附As(Ⅲ)的反应动力学性质和吸附As(Ⅲ)的主要影响因素。通过应用准一级动力学、准二级动力学和粒内扩散三种模型对吸附过程进行模拟,结果显示纳米锌吸附As(Ⅲ)的过程更符合二级反应动力学模型,速率常数k2为0.18 g/(mg·min),吸附量为0.47 mg/g,且去除机理以化学吸附为主。批实验结果表明,纳米锌对As(Ⅲ)吸附最佳条件为:振荡时间120 min,纳米锌投加量2.5 g/L,pH值2~7。在最佳实验条件下,纳米锌对起始浓度为0.565 mg/L As(Ⅲ)和0.568 mg/L As(Ⅴ)进行吸附试验,As(Ⅲ)和As(Ⅴ)的去除率均能达到99.5%以上,表明纳米锌对As(Ⅲ)和As(Ⅴ)都有很好的去除效果,可作为处理水体中砷的吸附材料之一。以纳米锌作为吸附材料与传统方法相比,并不需要将As(Ⅲ)预氧化成As(Ⅴ),在实际应用中可简化水处理程序,节约处理成本。  相似文献   

7.
采用液相还原法制备纳米铁粒子,粒径约为50 nm,主要成分为ɑ-Fe。实验研究了纳米铁还原高浓度硝基苯的效果及反应动力学。结果表明:自制的纳米铁具有很高的活性,短时间内能将高浓度硝基苯彻底还原,效果远优于普通铁粉。当摩尔比满足n纳米铁∶n硝基苯=4∶1时,纳米铁还原硝基苯属于一级反应动力学,反应速率常数和半衰期分别为0.159 3 h-1和4.351 2 h。整个实验过程中,ρ(DO)在0.5 mg/L以下,pH值约为9.0,体系呈弱碱性的厌氧环境,有利于厌氧微生物的生长。纳米铁反应后的产物为Fe6(OH)12CO3和MgFe3O4,且以Fe6(OH)12CO3为主。纳米铁反应后较以前比粒径变化不大,分散性较好,但表面被严重腐蚀。  相似文献   

8.
采用液相还原法成功制备纳米零价铁,并组装出生物质炭负载纳米零价铁复合材料(NZVI/BC)。XRD图谱显示,NZVI/BC由生物质炭(BC)和纳米零价铁(NZVI)两种成分复合而成;SEM图像显示,加入生物质炭之后,NZVI颗粒在炭表面分散良好。研究考察溶液p H值、还原剂投加量、铁/炭比和NO-3初始浓度等因素对NZVI/BC还原性能的影响。结果表明,NZVI/BC显示出优良的还原性能。在相同条件下,反应2 h,NZVI对NO-3的去除率为75%,而NZVI/BC对NO-3的去除率为96%。NZVI/BC是一种具有应用前景的硝态氮净化材料。  相似文献   

9.
以Pt为阳极,以Ti纳米管为基底修饰一薄层Pd和Cu构成的多金属纳米电极为阴极,搭建电化学反应器进行去除硝酸盐氮(NO3- N)研究,观察了在不同电流密度、初始浓度和pH值条件下该多金属纳米电极对NO3- N去除率的影响。结果表明,在电流密度为30 mA/cm2,添加050 g/L的 Na2SO4作为支持电解质的条件下,电解90 min后Cu Pd TiO2多金属纳米电极对硝酸盐的去除率可达81%,而相同条件下金属Ti做阴极时对硝酸盐的去除率仅为245%。溶液pH值的改变对 NO3- N的去除效果几乎没有影响;随着电流密度的增高,NO3- N的去除效率也随之提高;而随着溶液初始浓度的升高,NO3- N的去除率反而略有下降。  相似文献   

10.
废水中的铅极难降解,本研究基于石墨烯负载纳米铁材料对铅的还原和高效吸附,以市售石墨稀为原料,采用液相还原法合成了石墨烯负载纳米铁材料(Graphene-supported nanoscale zero-valent iron,G-nZVI)。借助扫描电子显微镜(SEM)、红外光谱分析仪(FTIR)表征,研究了以G-nZVI为材料,应用于水体中铅的去除的影响因素,结果显示:室温下,当G-nZVI投加量为0.6g/L,铅的初始浓度为200mg/L,初始pH值为3.0时,铅的去除率达到99%以上。G-nZVI材料对铅的去除高效、快速,去除产物可通过外加磁力方法达到与水体分离的目的,防止对水体的二次污染。在环境重金属污染治理方面具有较好的应用前景。  相似文献   

11.
Exposure to high concentration of nitrate through drinking water poses a threat to human health and environment. Electrocoagulation (EC) is an alternative water treatment process that involves electrogeneration of coagulant agents. In the present study, EC was exerted for the nitrate removal in a batch reactor using aluminum and iron anodes simultaneously. The effects of the main parameters including electrical current, initial pH, NaCl dosage, initial nitrate concentration and presence of turbidity on NO3 ? removal were investigated. NO2 ? as a by-product was monitored during electrolysis, and nitrate–nitrite index was calculated. The results indicated that optimum condition was pH of 5, 300 mA electrical current, 100 mg/L NaCl and electrolysis time of 40 min, under which removal efficiency was 81.5 %. Nitrite anion was generated during electrolysis of nitrate solution which increases nitrate–nitrite index at the first reaction time, and it was eliminated after 20-min electrolysis time. Reaction kinetic of nitrate removal in the absence and presence of turbidity was first-order and zero-order, respectively.  相似文献   

12.
In this work, a new process called advanced reduction process (ARP) was used for nitrate removal from water. This ARP process combines sodium dithionite as reducing agent with ultraviolet irradiation using medium pressure lamps (UV-M) as an activating method. Experimental results showed that UV-M/S2O4 2? process achieved almost complete removal of nitrate from aqueous solutions containing 25 mg NO3 ?/L using stoichiometric dose of dithionite of 68.8 mg/L at neutral pH conditions. Analysis of final products and material balance confirmed that NO3 ? ions were reduced to ammonium with formation of nitrite as intermediates in addition to the formation of small amounts of volatile species, mainly ammonia and nitrogen gas. Effects of certain experimental parameters including dithionite dose, initial pH, initial nitrate concentration, and UV light source on the kinetics and efficiency of nitrate reduction were evaluated. Increasing dithionite dose augmented the rate of nitrate reduction and enhanced the efficiency of ARP process. Dithionite doses higher than stoichiometric ratios led to complete removal of nitrate in shorter reaction time. UV-M/S2O4 2? process was found to be effective only under neutral pH or alkaline conditions, and its removal efficiency is negligible in acidic medium (pH < 4). Irradiation with UV-M was more effective than low pressure or narrow band lamps. These results can be attributed to the contribution of several mechanisms for nitrate reduction to ammonium. These include the following: direct photolysis, chemical reduction of nitrate dithionite, and mediated reduction of nitrate by free reducing radicals.  相似文献   

13.
  相似文献   

14.
A considerable increase in nitrate concentration in groundwater has been observed in many countries. This research focuses on nitrate removal using biodegradable snack ware (BSW) as both carbon source and biofilm support for denitrifiers. The denitrification efficiency of a laboratory-scale denitrification reactor packed with BSW was examined in a low-temperature condition. The nitrate removal efficiency supported by BSW decreased to approximately 40% at 12°C from nearly 100% at 25°C with 50?mg/L of nitrate-nitrogen in the influent and 2?h of hydraulic retention time (HRT). The complete nitrate removal was obtained when nitrate-nitrogen concentration was no more than 15?mg/L at 2?h of HRT and at 12°C. If the initial concentration of nitrate-nitrogen was 50?mg/L, 5?h of HRT was needed for the complete nitrate removal. Nitrite concentration in the treated water decreased evidently as HRT was increased from 2 to 5?h, or as nitrate-nitrogen concentration in the influent decreased to 15?mg/L from 50?mg/L. It was observed that varying HRT and nitrate concentration in the influent had no noticeable effect on dissolved organic carbon content in the effluent under the experimental conditions. This study indicated that the complete nitrate removal could be achieved readily even at 12°C using BSW as carbon source by changing HRT or the initial concentration of nitrate in the influent, which has some useful implications in environmental engineering practice.  相似文献   

15.
In coastal ecosystems, suspension-feeding bivalves can remove nitrogen though uptake and assimilation or enhanced denitrification. Bivalves may also retain nitrogen through increased mineralization and dissimilatory nitrate reduction to ammonium (DNRA). This study investigated the effects of oyster reefs and clam aquaculture on denitrification, DNRA, and nutrient fluxes (NO x , NH4 +, O2). Core incubations were conducted seasonally on sediments adjacent to restored oyster reefs (Crassostrea virginica), clam aquaculture beds (Mercenaria mercenaria) which contained live clams, and bare sediments from Smith Island Bay, Virginia, USA. Denitrification was significantly higher at oyster reef sediments and clam aquaculture site than bare sediment in the summer; however, DNRA was not enhanced. The clam aquaculture site had the highest ammonium production due to clam excretion. While oyster reef and bare sediments exhibited seasonal differences in rate processes, there was no effect of season on denitrification, or dissimilatory nitrate reduction to ammonium (DNRA) or ammonium flux at the clam aquaculture site. This suggests that farm management practices or bivalve metabolism and excretion may override seasonal differences. When water column nitrate concentration was elevated, denitrification increased in clam aquaculture site and oyster reef sediments but not in bare sediment; DNRA was only stimulated at the clam aquaculture site. This, along with a significant and positive relationship between denitrification and sediment organic matter, suggests that labile carbon limited nitrate reduction at the bare sediment site. Bivalve systems can serve as either net sinks or sources of nitrogen to coastal ecosystems, depending mainly on the type of bivalve, location, and management practices.  相似文献   

16.
Nitrate removal from water has been accomplished by heterotrophic biofilms using organic carbon as a source of reducing power. To overcome the natural limitation in organic carbon in water, a poly-ε-caprolactone based biofilm carrier that serves simultaneously as a biofilm carrier and as a source of organic carbon was developed and tested in the present work. The feasibility of the new biofilm carrier for nitrate removal from water was evaluated in a packed bed reactor. The combination of size and structure provided a carrier element having high surface area and void volume, 1,170 m2/m3 and 67 %, respectively. A maximum denitrification rate of 4.4 mg N–NO3 ?/(L.h) (9.2 mg N–NO3 ?/(m2.h)) was achieved in the packed bed reactor at 20 °C and pH 7.0. Main advantages of the biofilm carrier developed in the present work are its mechanical stability in water even after biofilm formation and controlled release of organic carbon by enzymatic reactions. The proposed biotechnology to remove nitrate from groundwater is robust and easy to operate.  相似文献   

17.
Biologically available nitrogen (fixed N) is removed from the oceans by metabolic conversion of inorganic N forms (nitrate and ammonium) to N2 gas. Much of this removal occurs in marine sediments, where reaction rates are thought to be limited by diffusion. We measured the concentration and isotopic composition of major dissolved nitrogen species in anoxic sediments off the coast of California. At depths below the diffusive penetration of nitrate, we found evidence of a large nitrate pool transported into the sediments by motile microorganisms. A ∼20‰ enrichment in 15N and 18O of this biologically transported nitrate over bottom water values and elevated [N2] and δ15N-N2 at depth indicate that this nitrate is consumed by enzymatic redox reactions with the production of N2 as the end product. Elevated N2O concentrations in pore waters below the nitrate diffusion depth confirm that these reactions include the denitrification pathway. A data-constrained model shows that at least 31% of the total N2 production in anoxic sediments is linked to nitrate bio-transport. Under suboxic/anoxic regimes, this nitrate bio-transport augments diffusive transport, thus increasing benthic fixed nitrogen losses and the reducing burial efficiency of sedimentary organic matter.  相似文献   

18.
Filter-feeding bivalves, like oysters, couple pelagic primary production with benthic microbial processes by consuming plankton from the water column and depositing unassimilated material on sediment. Conceptual models suggest that at low to moderate oyster densities, this deposition can stimulate benthic denitrification by providing denitrifying bacteria with organic carbon and nitrogen (N). While enhanced denitrification has been found at oyster reefs, data from oyster aquaculture are limited and equivocal. This study measured seasonal rates of denitrification, as well as dissimilatory nitrate reduction to ammonium (DNRA), and dissolved inorganic N fluxes at a rack and bag eastern oyster (Crassostrea virginica) aquaculture farm. Consistent with models, denitrification was enhanced within the farm, with an average annual increase of 350% compared to a reference site. However, absolute denitrification rates were low relative to other coastal systems, reaching a maximum of 19.2 μmol m?2 h?1. Denitrification appeared to be nitrate (NO3 ?) limited, likely due to inhibited nitrification caused by sediment anoxia. Denitrification may also have been limited by competition for NO3 ? with DNRA, which accounted for an average of 76% of NO3 ? reduction. Consequently, direct release of ammonium (NH4 +) from mineralization to the water column was the most significant benthic N pathway, with seasonal rates exceeding 900 μmol m?2 h?1 within the farm. The enhanced N processes were spatially limited however, with significantly higher rates directly under oysters, compared to in between oyster racks. For commercial aquaculture farms like this, with moderate oyster densities (100–200 oysters m?2), denitrification may be enhanced, but nonetheless limited by biodeposition-induced sediment anoxia. The resulting shift in the sediment N balance toward processes that regenerate reactive N to the water column rather than remove N is an important consideration for water quality.  相似文献   

19.
We used fine-scale porewater profiles and rate measurements together with a multiple component transport–reaction model to investigate carbon degradation pathways and the coupling between electron and proton transfer reactions in Lake Champlain sediments. We measured porewater profiles of O2, Mn2+, Fe2+, HS−, pH and pCO2 at mm resolution by microelectrodes, and profiles of NO3 −, SO4 2−, NH4 +, total inorganic carbon (DIC) and total alkalinity (TA) at cm resolution using standard wet chemical techniques. In addition, sediment–water fluxes of oxygen, DIC, nitrate, ammonium and N2 were measured. Rates of gross and net sulfate reduction were also measured in the sediments. It is shown that organic matter (OM) decomposes via six pathways: oxic respiration (35.2%), denitrification (10.4%), MnO2 reduction (3.6%), FeOOH reduction (9.6%), sulfate reduction (14.9%), and methanogenesis (26.4%). In the lake sediments, about half of the benthic O2 flux is used for aerobic respiration, and the rest is used for the regeneration of other electron acceptors produced during the above diagenetic reactions. There is a strong coupling between O2 usage and Mn2+ oxidation. MnO2 is also an important player in Fe and S cycles and in pH and TA balance. Although nitrate concentrations in the overlying water were low, denitrification becomes a quantitatively important pathway for OM decomposition due to the oxidation of NH4 + to NO3 −. Finally, despite its low concentration in freshwater, sulfate is an important electron acceptor due to its high efficiency of internal cycling. This paper also discusses quantitatively the relationship between redox reactions and the porewater pH values. It is demonstrated here that pH and pCO2 are sensitive variables that reflect various oxidation and precipitation reactions in porewater, while DIC and TA profiles provide effective constraints on the rates of various diagenetic reactions.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号