海洋沉积物甲烷厌氧氧化作用(AOM)及其对无机硫循环的影响   总被引：2，自引：0，他引：2  

吴自军  任德章  周怀阳 《地球科学进展》2013,28(7):765-773

甲烷厌氧氧化作用(AOM)在调控全球甲烷收支平衡以及缓解因甲烷引起的温室效应等方面扮演着十分重要的角色,成为近些年来海洋生物地球化学领域的研究热点之一.一般而言,海洋沉积物孔隙水硫酸盐还原主要是通过2种反应途径来完成,即氧化有机质途径和AOM途径.长期以来,与有机质氧化途径相关的硫酸盐还原作用研究已有充分展示,而由AOM驱动的硫酸盐还原及其对自生硫化铁形成与埋藏的重要贡献却被严重低估.侧重从生物地球化学、同位素地球化学等角度,综述近些年来不同环境条件下海洋沉积物AOM作用发生的地球化学证据和AOM对沉积物孔隙水硫酸盐消耗比例的贡献大小及其调控因素.AOM过程产生的H2S会与沉积物中活性铁结合形成自生铁硫化物.与沉积物浅表层条件相比,AOM过程固定的自生铁硫化物不容易发生再氧化,更利于在沉积物中埋藏保存起来.AOM与海洋沉积物硫酸盐还原作用相偶联,由AOM驱动的硫酸盐还原过程对海底自生铁硫化物形成与埋藏的重要贡献不容忽视.该综述有助加深对海洋沉积物AOM作用的认识及其对硫循环的全面理解.  相似文献   

UV/H2O2 Process Under High Intensity UV Irradiation: A Rapid and Effective Method for Methylene Blue Decolorization     

Qian Zhang  Chaolin Li  Ting Li 《洁净——土壤、空气、水》2013,41(12):1201-1207

This study examined the UV/H₂O₂ decolorization efficiency under high UV photon flux (intensity normalized by photon energy) irradiation; the incident UV was ranging from 3.13 × 10^?8 to 3.13 × 10^?6 einstein cm^?2 s^?1. The experimental results showed that complete decolorization of 20 mg L^?1 methylene blue (MB) can be achieved within 5 s and 99% decolorization of 1000 mg L^?1 MB can be achieved in 180 s under the best condition of high UV intensity UV/H₂O₂ process. To the best of our knowledge, UV/H₂O₂ decolorization process in such a short time has not been reported. The electrical energy per order of the process was 16.21 kWh m^?3 order^?1 and it is relatively economical compared with other advanced oxidation processes. The kinetics of decolorization follows pseudo‐first order. There is a linear relationship between rate constant and UV intensity, which indicates that increasing UV intensity does not cause decline in light utilization efficiency. The experiment related to initial substrate concentration shows decolorization rate of different substrate concentration (20–1000 mg L^?1) are closed to each other. Besides, optimal H₂O₂ concentration, comparative study with low photon flux light, decolorization of other types of dyes and TOC removal were also studied.  相似文献   

Does Aqueous‐Phase Oxidation of HCHO Opens a Pathway to Formic Acids in Atmosphere?     

Xu Gang  Lee XinQing  Shao HongBo  Lv YingChun 《洁净——土壤、空气、水》2010,38(11):1006-1009

Formic acid is the major contributor to acid rain in some regions but its sources are not fully understood. We investigated the aqueous‐phase reactions of HCHO (aq) and OH ^. radicals at enlarged rainwater pH values (2.49–5.89) in Guiyang, China from May 2006 to April 2007. Our results show that there were no significant correlation between the [HCOOH]_t/[HCHO] (aq) and the rainwater pH. The ratio did not appear to vary consistently as a function of rainwater pH as predicted by theoretical model. In addition, we saw no clear evidence that oxidation of HCHO (aq) would produce significant HCOOH (aq) which indicates this reaction may be only a minor contribution to the budget of HCOOH (g) in atmosphere. Further investigation is strongly suggested to be carried out in field cloud water, fog water, or rainwater because the ratios would be diverged from equilibrium value as a result of other chemical or physical processes.  相似文献   

Mineralization of Catechol by Fenton and Photo‐Fenton Processes     

Asma M'hemdi  Bechir Dbira  Ridha Abdelhedi  Enric Brillas  Salah Ammar 《洁净——土壤、空气、水》2012,40(8):878-885

Catechol is one of the most abundant phenolic components of olive mill wastewaters. In this article, the mineralization of this compound in synthetic aqueous solutions by the Fenton and photo‐Fenton processes is studied. It has been found that for 1.44 mM catechol, the total organic carbon of solutions is reduced about 94.4% at best after 60 min of Fenton treatment at optimized conditions of pH 3.0, 0.2 mM Fe²⁺, 7.09 mM H₂O₂, and 25°C. A faster and overall mineralization is attained by applying photo‐Fenton with UVA irradiation. o‐Benzoquinone, 1,2,3‐trihydroxybenzene and 1,2,4‐trihydroxybenzene were identified by GC–MS as primary quinonic and polyhydroxylated derivatives. Small amounts of generated carboxylic acids like muconic, maleic, malonic, acetic, oxalic, and formic acids were detected by ion‐exclusion chromatography. The Fe(III) complexes of these acids persist in the medium under Fenton conditions, while their photolysis by UVA light and that of other by‐products account for by the faster degradation and total mineralization achieved in the photo‐Fenton process. A reaction sequence for catechol mineralization by Fenton and photo‐Fenton involving all intermediates detected is proposed.  相似文献   

Bi‐Doped TiO2 Electro‐Catalytic System as Fast‐Oxidizing Process for Hydrogen‐Bond Stabilized System          下载免费PDF全文

Wu‐Jang Huang  Sheng‐Jhih Hong  Yaw‐Jian Lin 《洁净——土壤、空气、水》2014,42(8):1154-1156

  相似文献   

U–Th–Pb–REE systematics of organic-rich shales from the ca. 2.15 Ga Sengoma Argillite Formation, Botswana: Evidence for oxidative continental weathering during the Great Oxidation Event     

Gerald D. Pollack  Eirik J. Krogstad  Andrey Bekker   《Chemical Geology》2009,260(3-4):172-185

The redox-sensitive geochemical behavior of uranium permits the use of Th/U ratios as a geochemical proxy for the oxidation state of the atmosphere during deposition. Due to the effects of post-depositional uranium mobility on Th/U ratios during events involving oxygenated fluids, direct measurements of Th/U ratios are often misleading even for drill core samples. Because both of these elements radioactively decay and produce lead isotopes, the Pb isotope composition may reflect the depositional Th/U ratio, although the Th/U ratios induced by changes shortly after deposition may not be distinguished from the true depositional Th/U ratios. In order to effectively evaluate the time-integrated Th/U ratio (κ_a), values for the initial depositional Pb isotope composition must be determined or accepted from the models for the whole Earth.While the timing for the rise of atmospheric oxygen is reasonably well constrained now, its effect on continental weathering and ocean redox state remains poorly constrained and debated. The ca. 2.15 Ga Sengoma Argillite Formation of Botswana contains organic-rich shales deposited during the Great Oxidation Event. The slope of the ²⁰⁷Pb/²⁰⁴Pb–²⁰⁶Pb/²⁰⁴Pb array of shales from the Sengoma Argillite Formation corresponds to a Pb–Pb age that is within analytical error of the depositional age and is, therefore, inferred to be the time by which the time-integrated thorogenic and uranogenic lead growth started. The time-integrated lead growth corresponds to an average κ_a of 2.63 (± 0.62, 1σ) for the organic-rich shales of the Sengoma Argillite Formation. This is lower than Th/U ratios measured in Archean shale suites or estimated for the Archean–Proterozoic average upper continental crust [Taylor, S.R. and McLennan, S.M., 1985. The Continental Crust: Its Composition and Evolution. Blackwell, Oxford, 312 pp.], which indicates that these samples were enriched in uranium with respect to thorium (and perhaps lead) at the time of deposition. In the modern ocean, sediments are enriched in uranium under reducing conditions by reduction of the water-soluble uranyl ion, which is delivered to the ocean by oxidative weathering of continental crust. To evaluate the potential mobility of Th, U, and Pb during post-depositional processes, the concentrations of the rare earth elements (REE) were also determined. Interelement ratios of the largely immobile REE (in this study, La/Nd and Gd/Er) can be used as a proxy for the Th/U ratio, as the geochemical behavior of the lanthanide and actinide elements is similar under a variety of conditions. Furthermore, close similarity in the chondrite-normalized REE patterns and small range in La/Nd and Gd/Er ratios in studied samples indicate that variations in κ_a values are not likely to have been controlled by mixing of one or more REE-, Th-, and U-rich heavy minerals from the multiple detrital sources. Our study of shales from the ca. 2.15 Ga Sengoma Argillite Formation indicates that decoupling of U from Th, most likely related to the oxidative continental weathering, began by 2.15 Ga, at the latest.  相似文献   

山西五台山滹沱群四集庄冰碛岩碎屑锆石年龄及其对大氧化事件研究意义   总被引：2，自引：0，他引：2  

陈威宇  陈衍景  李秋根  李建荣  李凯月  疏孙平  陈西  佟子达 《地学前缘》2018,25(5):1-18

山西滹沱群四集庄组变质陆源碎屑混杂岩的砾石岩性复杂,分选和磨圆性差,砾石表面可见划痕和凹面,发育落石构造,表明其沉积于冰水过渡带环境,记录了华北克拉通古元古代冰期事件。四集庄组不同层位不同岩石的碎屑锆石U-Pb年龄集中于2.5 Ga左右,下部2件陆源碎屑混杂岩样品的碎屑锆石给出的最小年龄分别为(2 440±40) Ma和(2 400±23) Ma,而上部1件砂岩样品碎屑锆石的最小年龄为(2 121±22) Ma,说明冰川沉积作用发生在2.4 Ga之后, 2.1 Ga之前或2.1 Ga左右,与全球性休伦冰川事件(Huronian Glaciation Event,HGE)发生时间一致。砂岩相最小碎屑锆石年龄2.1 Ga左右,说明五台地区冰川事件之后沉积作用仍未结束,冰川沉积发生在陆缘广海盆地。四集庄组之上的大石岭组具有碳酸盐岩碳同位素正漂移,沉积于2.12 Ga之后,2.08 Ga之前,与全球碳酸盐岩碳同位素正漂移事件时间一致。青石村组的红层沉积于2.08 Ga左右,也与全球红层发育记录一致。华北克拉通滹沱群记录了相对完整的大氧化事件序列。  相似文献   

刘家金矿床基本地质特征     

张万良 《铀矿地质》1996,12(3):156-159

刘家金矿位于扬子准地台南缘，赋存于元古代地槽发展晚期形成的陆相碎屑－火山碎屑岩建造之中，矿体受变凝灰岩（少量板岩）中的褐铁矿化顺层破碎带控制，规模中等，形态呈似层状、透镜状。金矿物以不规则中细粒自然金为主，含微量金银矿，伴生元素少。金矿化是热液作用的结果，更是氧化淋滤作用的产物。  相似文献   

Degradation of Aqueous Atrazine and Metazachlor Solutions by UV and UV/H2O2 — Influence of pH and Herbicide Concentration Abbau von Atrazin und Metazachlor in wäßriger Lösung durch UV und UV/H2O2 — Einfluß von pH und Herbizid-Konzentration     

D. P. Hessler  V. Gorenflo  F. H. Frimmel 《洁净——土壤、空气、水》1993,21(4):209-214

The degradation of two pesticides: atrazine and metazachlor was investigated in aqueous solution under UV-irradiation with and without H₂O₂. Rate constants of the photochemical degradation were determined applying a first order kinetics and quantum yields of the processes were calculated. This approach leads to an apparent decrease of the quantum yield with increasing initial pesticide concentration. At low H₂O₂ initial concentrations, the pesticide degradation was shown to be much more efficient than the degradation under UV-irradiation only. However, at high H₂O₂ concentrations (>2 mmol L^?1), the efficiency of the UV/H₂O₂ system dropped down and the quantum yields of degradation were lower than for the direct photolysis. In the absence of H₂O₂, no influence of the pH value on the photodegradation of the pesticides could be noticed in a range between pH 3 and pH 11. At low H₂O₂ initial concentrations, the photochemical degradation of the pesticides was much faster at pH 3 and pH 7 compared with the degradation at pH 11. The results emphasize the potential of optimized reaction conditions in advanced oxidation.  相似文献   

Structural changes and oxidation of ferroan phlogopite with increasing temperature: in situ neutron powder diffraction and Fourier transform infrared spectroscopy     

Chul-Min Chon  Chul-Kyoo Lee  Yungoo Song  Sin Ae Kim 《Physics and Chemistry of Minerals》2006,33(5):289-299

The thermal response of the natural ferroan phlogopite-1M, K₂(Mg_4.46Fe_0.83Al_{0. 34}Ti_0.22)(Si_5.51Al_{2. 49})O₂₀[OH_3.59F_0.41] from Quebec, Canada, was studied with an in situ neutron powder diffraction. The in situ temperature conditions were set up at ?263, 25, 100°C and thereafter at a 100°C intervals up to 900°C. The crystal structure was refined by the Rietveld method (R _p=2.35–2.78%, R _wp=3.01–3.52%). The orientation of the O–H vector of the sample was determined by the refinement of the diffraction pattern. With increasing temperature, the angle of the OH bond to the (001) plane decreased from 87.3 to 72.5°. At room temperature, a = 5.13 Å, b = 9.20 Å, c = 10.21 Å, β = 100.06° and V(volume) = 491.69 ų. The expansion rate of the unit cell dimensions varied discontinuously with a break at 500°C. The shape of the M-octahedron underwent some significant changes such as flattening at 500°C. At temperatures above 500°C, the octahedral thickness and mean distance was decreased, while the octahedral flattening angle increased. Those results were attributed to the Fe oxidation and dehydroxylation processes. The dehydroxylation mechanism of the ferroan phlogopite was studied by the Fourier transform infrared spectroscopy (FTIR) after heated at temperatures ranging from 25 to 800°C with an electric furnace in a vacuum. In the OH stretching region, the intensity of the OH band associated with Fe²⁺(N _B-band) begun to decrease outstandingly at 500°C. The changes of the IR spectra confirmed that dehydroxylation was closely related to the oxidation in the vacuum of the ferrous iron in the M-octahedron. The decrease in the angle of the OH bond to the (001) plane, with increasing temperature, might be related to the imbalance of charge in the M-octahedra due to Fe oxidation.  相似文献