Kinetics of redox cycling of iron coupled with fulvic acid     

Yiwei Deng  Werner Stumm 《Aquatic Sciences - Research Across Boundaries》1993,55(2):103-111

The kinetics of conversion of iron(III) (hydr)oxides to ferrous iron mediated by fulvic acid have been investigated in order to improve the understanding of the redox cycling of iron at the oxic-anoxic boundary in natural waters. Under the conditions similar to natural waters, fulvic acid is able to reduce the iron(III) (hydr)oxide. The kinetics of the reaction depend on the reactivity of iron(III) (hydr)oxides and the reducing power of the fulvic acid. The rate of reaction is 60 nm/h obtained under following conditions: total concentration of Fe(III) 1.0 × 10^–4 M, pH 7.5, fulvic acid 5 mg/L. The rate is considered as a net result of reduction and oxidation in the > Fe^III-OH/Fe(II) wheel coupled with fulvic acid. In a real natural water system, reductants other than fulvic acid may be of importance. The results obtained in the laboratory, however, provide evidence that the Fe(OH)₃(s)/Fe(II) redox couple is able to act as an electron-transfer mediator for the oxidation of natural organic substances, such as fulvic acid by molecular oxygen either in the absence of microorganisms or as a supplement to microbial activity.  相似文献   

冀西北长城纪宣龙式铁矿层中微体植物化石的发现及其意义   总被引：10，自引：0，他引：10  

杜汝霖  刘志礼 《地质论评》1992,38(2):184-189

本文研究的是笔者等在冀西北长城系串岭沟组宣龙式铁矿层中发现的微体植物化石,这些化石都保存在铁质叠层石(肾状赤铁矿)和铁质核形石(鲕状赤铁矿)的基本层中。微化石以丝状体为主,部分为球状体。归属于原核生物蓝藻门颤藻科的两个属和色球藻科的一个属。化石层同位素年龄约在1800—1757Ma。这些化石与北美冈弗林特组微化石比较,既有些相似,又有些区别。该化石的发现为研究铁矿的成因,指示沉积环境及层位对比都很有意义。  相似文献   

Visualization experiments of iron precipitates: Application for in-situ arsenic remediation     

M.I.M. Darwish  V.M. van Beek  J. Bruining 《Journal of Geochemical Exploration》2006,88(1-3):19

Laboratory experiments were carried out to acquire more insight and understanding of the phenomena associated with the in-situ arsenic remediation. Visualization techniques are the most informative for the detection of Fe(II) while flowing in soils. Green Rust (GR) was considered as representative of in-situ iron precipitates. In a visualization flat cell, the change in color of GR to orange, due to oxidation, was monitored by a digital camera and the images were analyzed giving the spatial and temporal distribution of Fe(II). Moreover, both oxygen and pH changes in time were recorded in two sections along the flow direction in the cell. The measured and calculated concentration profiles were compared and the actual reaction rates were predicted. The reaction rate constants measured in this study, under flowing conditions, are in a good agreement with the values obtained from batch experiments reported in the literature.  相似文献   

Speciation of adsorbed arsenate on the surface of hydrous iron oxide     

Yongfeng JIA Xin WANG George Demopoulos 《中国地球化学学报》2006,25(B08):35-35

Adsorption of arsenate on hydrous iron oxide is an important process controlling geochemical cycling of arsenic in environment as well as the fate of arsenic-bearing mining wastes. The widely accepted view on the mechanism of adsorption is that arsenate is adsorbed via bidentate binuclear inner-sphere complexation. In this study, we characterized the arsenate-hydrous iron oxide sorption solids synthesized at pH=3-8 using Fourier transformed infrared spectroscopy （FTIR） and X-ray diffraction （XRD）. It has been determined that poorly crystalline ferric arsenate developed on the surface of iron oxide when arsenate was sorbed at acidic pH, while at alkaline pH the adsorption of arsenate was via bidentate complexation.  相似文献   

XANES analysis of the mechanisms of arsenic removal in biological iron and manganese treatment unit     

Yoko Fujikawa Daisuke Yoneda Atushi Minami Hiroshi Yashima Toshio Tonokai Sotoji Tani Masami Fukui Tatuhide Hamasaki Masataka Sugahara 《中国地球化学学报》2006,25(B08):113-113

Biological iron and manganese removal utilizing indigenous iron and manganese oxidizing bacteria （IRB hereafter） in groundwater can also be applied to arsenic removal according to our pilot-scale test. The arsenic removal probably occurred through sorption and complexation of arsenic to iron and manganese oxides formed by enzymic action of IRB. We investigated the chemical properties of iron and manganese oxides in IRB floc and the valence state of arsenic sorbed to the floc to clarify the mechanisms of the arsenic [especially As （Ⅲ）] removal. The floc samples were collected from two drinking water plants using IRB （Jyoyo and Yamatokoriyama, Japan）, and our pilot - scale test site where arsenic and iron removal using IRB is under way （Mukoh, Japan）. The Jyoyo and Yamatokoriyama IRB floc samples were subjected to As （Ⅲ） and As（Ⅴ） sorption experiments. The elemental composition of the floc samples was measured. XANES spectra were collected on As, Fe and Mn K-edges at synchrotron radiation facility Spring 8 （Hyogo, Japan）. FT-IR and the X-ray diffraction spectra of the samples were also obtained. The IRB floc contained ca. 35 % Fe, 0.3%-3.5% Mn and 2%-6% P. The samples were highly amorphous and contained ferrihidrites and hydrated iron phosphate. According to XANES analyses of IRB, As associated with IRB was in ＋5 valence state when As （Ⅲ） （or As （Ⅴ）） was added in laboratory sorption test, Fe in ＋3 valence state, and Mn a mixture of＋3 and ＋4 valence states. Small shift was observed in the XANES spectra of IRB on As K-edge as the equilibration time of the sorption experiment was increased. Gradual oxidation of a small amount of As （Ⅲ） associated with IRB or change in arsenic binding with sorption site were the probable mechanism.  相似文献   

Adsorption of Pentachlorophenol onto Oxide and Clay Minerals： Surface Reaction Model and Environmental Implications     

WU Daqing DIAO Guiyi YUAN Peng PENG Jinlian 《《地质学报》英文版》2006,80(2):192-199

The adsorption of pentachlorophenol （PCP） onto quartz, kaolinite, illite, montmorillonite and iron oxides has been investigated by batch equilibrium techniques. The pH-dependent isotherms are curves with peak values, the position of which is at about pH = 5-6 depending on the mineral species. Based on distribution of both speciation of surface hydroxyls on minerals and PCP in solution a surface reaction model involving surface complexation and surface electrostatic attraction is presented to fit the pH-dependent isotherms, and both reaction constants are calculated. The results show that on quartz and phyllosilicate minerals the predominant adsorption reaction is surface complexation, meanwhile both of surface electrostatic attraction and surface complexation are involved on the iron oxide minerals. The reaction constants of surface electrostatic adsorption are usually one to three orders in magnitude, larger than that of surface complexation. The concentration-dependent isotherms can be well fitted by Langmnir equation with the correlation coefficient R〉0.93 for kaolinite and iron oxides. The maximum adsorption is found in the order： hematite 〉 lepidocrocite 〉 goethite 〉 kaolinite 〉 quartz 〉 montmorillonite ≈ illite, which can be interpreted by consideration of both reaction mechanism and surface hydroxyl density. The significant adsorption of PCP onto mineral surfaces suggests that clay and iron oxide minerals will play an important role as HIOCs are adsorbed in laterite or latertoid soil, which is widespread in South China.  相似文献   

一次造成乌鲁木齐市电网瑶线铁塔倒塌事故的气象原因分析     

窦新英  宾建华蒋军 《沙漠与绿洲气象(新疆气象)》2005,28(5):32-34

为了解2004年11月24日乌鲁木齐市两座电网瑶线铁塔倒塌事故的气象原因，通过实地调查，并对高低空环流形势场、加密气象站信息等进行了分析。结果表明，乌鲁木齐地区不同地理位置风速差异很大，红雁池和头屯河区瞬间极大风速分别比市区大12．8m／s和18．4m／s。纠正了过去认为东南大风的强中心只出现在红雁池附近的说法，为今后制作大风分区预报提供了参考，也可为城区高层建筑及相关设计规范的修正提供借鉴。  相似文献   

金刚石工具富铁胎体掺杂稀土的研究   总被引：5，自引：0，他引：5  

段隆臣  田永常  邹庆化  杨凯华 《地质科技情报》2002,21(3):101-103,107

稀土的加入量、加入形态和在混料中的均匀弥散性直接影响热压富铁金刚石复合材料的性能。改进的稀土掺杂工艺，保证了稀土在胎体中的均匀弥散性；通过试验研究了稀土的加入量与富铁胎体的抗弯强度、抗冲击韧性和孔隙率的关系，从而确定了稀土的最优加入量。通过差热分析试验，认为稀土可以改变富铁胎体的热物理特性。  相似文献   

华北陆块北缘西段中元古代与裂谷作用有关的铁、稀土、多金属矿床特征及成因     

曹秀兰 《华北地质》2002,(Z1)

华北陆块北缘西段狼山—白云鄂博裂谷系中元古代形成的大型多金属矿床 ,是我国重要的铁、稀土、铜、铅、锌矿产地。矿床为产于沉积岩中热水沉积型多金属矿床。其形成受地层、构造控制 ,与裂谷作用有着密切的关系。裂谷系内外分支的地质环境及矿床矿种不同 ,导致矿床特征及成因具有一定差异。白云鄂博铁、稀土矿床为钾、钠、磷等含量较高的热水沉积型 ,霍各乞铜、铅、锌多金属矿床为与中基性火山岩有关的过渡热水沉积型 ,东升庙和甲生盘等铅、锌多金属矿床为热水沉积型。文中将对上述矿床分别进行论述。  相似文献   

Negative Ce Anomaly in the Indian Banded Iron Formations: Evidence for the Emergence of Oxygenated Deep-Sea at 2.9-2.7 Ga     

Yasuhiro KATO  Takashi KANO  Keitaro KUNUGIZA 《Resource Geology》2002,52(2):101-110

Abstract: Major and rare earth element contents are reported for Late Archean banded iron formations (BIFs) in the Bababudan Group of the Dharwar Craton, South India. The BIFs are mostly composed of SiO₂ (average1ρ = 54.88.1 wt%) and Fe₂O₃* (44.38.2 wt%). The Al₂O₃ and TiO₂ contents are remarkably low, suggesting that detrital components were starved during the BIF deposition. The BIFs have a LREE-enriched pattern with a relatively high (La/Yb)_N (6.644.07). Total REE concentrations (RE) vary from 5.2 to 65.3 ppm. The REE patterns are characterized by the presence of a very large negative Ce anomaly (Ce/Ce*: 0.13-0.83) and a positive Eu anomaly (Eu/Eu*: 0.96-2.45). The Eu/Eu* decreases and (La/Yb)_N increases with a increase of RE. These correlations of REE indices are similar to those of modern hydrothermal iron-rich sediments near a mid-ocean ridge (MOR). Greenstones associated with the BIFs have MORB-like geochemical features. These geochemical and geological lines of evidence indicate that the depositional site of the BIFs was remote from a continent and/or island arc and that the BIFs were in situ hydrothermal sediments near a MOR. A striking negative Ce anomaly in the BIFs indicates that oxygenated deep-sea environments emerged at 2.9-2.7 Ga. The existence of contemporaneous Mn deposits in the Dharwar Craton supports this assertion. Our scenario of oxygen in the Earth's surface of the Late Archean is different from long-held notion that the atmosphere and ocean were persistently anoxic throughout the Archean.  相似文献