水库析出物中显微针铁矿的成因差异——以湖北省富水水库及南河水库为例

通过对湖北省富水、南河水库坝基渗漏水及其析出物的研究 ,探讨了不同水库沉积环境中显微针铁矿的成因差异及微生物在铁的生物矿化中的作用和意义。采用化学分析、X射线衍射、红外光谱、穆斯堡尔谱、透射电镜和扫描电镜分析等手段 ,研究了两个水库坝基渗漏水析出物的组成、物相和形貌特征。两个水库坝基渗漏水的成分相似 ,阳离子均以Ca2 + 、Mg2 + 、K+ 、Na+ 为主 ,Fe2 + 和Fe3 + 含量极少 ,阴离子以HCO-3 为主。渗漏水析出物的化学成分以铁的氧化物为主 ,析出物的主要矿物相为针铁矿、石英、伊利石、蒙脱石及微量方解石 ,呈弱结晶状态。穆斯堡尔谱图和SEM显微形貌特征证实了南河水库中针铁矿以化学成因为主 ,系菱铁矿风化而成 ;富水水库中针铁矿的形成受铁细菌的影响 ,以生物成因为主。     

富水水库中微生物成因的显微针铁矿及其对微量元素的富集

通过对湖北省富水水库坝基渗漏水及其析出物的研究，探讨了现代沉积环境（水库）中显微铁矿物形成的机理及微生物在铁的生物矿化中的作用和意义。对析出物中微量元素的富集特征也进行了初步研究。用化学分析方法测试出坝基渗漏水中阳离子以Ca^2 、Mg^2 、K^ 、Na^ 为主，Fe^2 和Fe^3 含量极少，阴离子以HCO3^-为主。析出物的化学成分以铁的氧化物为主。采用X射线衍射、差热分析、红外光谱和穆斯堡尔谱，以及透射电镜和扫描电镜等测试手段，分析研究了析出物的物相和形貌特征。析出物的主要矿物相为针铁矿、石英、伊利石、蒙脱石和微量方解石，呈弱结晶状态。由析出物中显微针铁矿特殊的形貌特征及其特征的穆斯堡尔谱图推测出富水水库沉积环境中显微针铁矿是由铁细菌形成。ICP－MS测试测试结果表明，析出物中不仅富集了铁，还富集了Yb、Pb、Dy、Zn、Co、Be、Eu、Sm和Tb等微量元素。微量元素的富集是微生物与显微针铁矿共同作用的结果。     

A.ferrooxidans培养过程中Al/Fe(摩尔比)对铁矿物形成产物的影响

主要研究了磷酸铝(Al PO4)的加入量对氧化亚铁硫杆菌HX3培养液中铁矿物形成的影响,并对相应沉淀产物进行了结构表征分析。结果表明,Al PO4的加入对细菌培养过程中Fe2+的氧化无明显影响,但可促进Fe3+的水解和初始铁矿物相的形成,也可加速黄钾铁矾的转化形成。Al/Fe(摩尔比)为0. 04～1的培养液中主要形成产物为施威特曼石和黄钾铁矾; Al/Fe为0. 4和1时另有磷酸铁矿形成。较高的Al/Fe比值和磷酸根含量有利于磷酸铁矿的形成。     

Cl-/SO42-铁盐对含可溶性胞外多聚物Acidithiobacillus ferrooxidans溶液中铁矿物形成的影响

铁细菌胞外多聚物作用下聚集的铁可通过氧化或者沉淀作用使铁稳定或沉积,从而形成铁矿物。本文基于铁细菌胞外多聚物(extracellular polymeric substances,EPS)对铁矿物形成的调控作用,介绍了Cl-/SO_4~(2-)的Fe(Ⅲ)或Fe(Ⅱ)盐作用下,含可溶性EPS的氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)溶液中铁矿物的形成,观察了溶液pH值变化及形成铁矿物的矿相与结构,并采用XRD、FTIR和FESEM对其进行表征。结果发现反应溶液中OH-离子可与Fe3+形成微米级"针垫"聚集球状或纳米级小球形施威特曼石和微米级"菱形"块状黄钾铁矾铁矿物沉淀。反应溶液中的可溶性EPS可调控和促进铁矿物的形成,但对Fe2+的氧化未产生影响;外源Fe盐可促进施威特曼石向黄钾铁矾转化。随着Cl-/SO_4~(2-)摩尔比例的增加(即Cl-含量的不断增加),两矿相间的转化明显受到抑制,且铁矿物颗粒之间的集聚作用明显减弱;反之,SO_4~(2-)含量升高时,有利于铁矿物间的转化和聚集球状颗粒形貌结构的形成。     

膏盐层氧化障在长江中下游玢岩铁矿成矿中的作用

长江中下游是我国著名的铁铜金等多金属成矿带,其中宁芜和庐枞盆地产出一系列与白垩纪中基性火山-次火山岩有关的玢岩铁矿床。前人根据玢岩铁矿的地质特征、空间分布规律及其与火山-次火山岩的关系建立了著名玢岩铁矿成矿模式,发展了成矿理论,有效指导了玢岩铁矿找矿工作。但三叠系膏盐层在成矿中的作用没有引起应有的重视,深部矿化基本没有涉及。最新研究和勘查结果揭示中下三叠统周冲村组顶部膏盐层与矿化关系密切,但膏盐层的控矿机理还不清楚,"膏盐层氧化障"在玢岩铁矿成矿中的作用鲜有报道,宁芜-庐枞盆地深部矿化类型和矿体赋存部位知之甚少。本文研究了长江中下游玢岩铁矿的硫同位素组成,探讨了膏盐层氧化障在玢岩铁矿成矿中的作用。宁芜和庐枞盆地玢岩铁矿、硫铁矿中普遍含有石膏,玢岩铁矿、硫铁矿和石膏矿三者密切共生。玢岩铁矿及伴生硫铁矿中黄铁矿的δ34SV-CDT值异常高,平均值均在5‰以上,石膏的δ34SV-CDT值大部分位于20‰左右,与海相硫酸盐的值相似,指示矿床中硫主要来自三叠纪膏盐层。矿床中黄铁矿的硫同位素组成与矿床成因类型密切相关。宁芜盆地姑山矿田的δ34SV-CDT值最高,为10.8‰,梅山矿田次之,为7.85‰,凹山矿田最低,为5.01‰;矿床成因类型也发生相应变化,矿浆型→矿浆-热液型→热液型。矿床中黄铁矿的硫同位素变化主要由硫酸盐的还原温度和原始岩浆硫所占比例不同引起,还原温度越高,δ34S值越高;原始岩浆硫所占比例越高,δ34S值越低。计算结果表明矿床中约60%~80%的硫来自膏盐层硫酸盐的还原,还原温度多在450℃以上,但硫化物的沉淀温度相对较低,就位时间稍晚。提出膏盐层(富含碳酸盐、石膏和石盐等)不仅可以为成矿提供大量Na+、Cl-、CO32-等矿化剂,使围岩发生钠长石化、方柱石化(氯化)和矽卡岩化等蚀变,使Fe2+以NaFeCl3等络合物形式搬运,膏盐层还是地壳深处最重要的氧化障,能够将硅酸盐熔体和成矿溶液中的Fe2+氧化成Fe3+,富集形成铁矿床,是玢岩铁矿成矿的关键因素。当炽热的岩浆与膏盐层(CaSO4)发生同化混染时,SO42-将硅酸盐熔体中的Fe2+氧化成Fe3+,Fe3+无法进入硅酸盐矿物晶格之中,而形成铁氧化物Fe3O4/Fe2O3和贫铁的硅酸盐矿物透辉石/阳起石、透闪石等。铁氧化物在磷、水和氯化钠等盐类物质的作用下在岩浆房中与硅酸盐熔体发生液态不混熔,熔离形成铁矿浆。铁矿浆粘滞性强,迁移距离不远,在岩体与膏盐层的接触带附近,沿构造有利部位贯入,形成姑山、梅山等矿浆型铁矿床。以铁的络合物形式搬运的成矿热液流动性强,迁移距离远,可以在远离岩体与膏盐层接触带部位、在上部白垩纪火山岩中富集沉淀。长江中下游玢岩铁矿中矿浆充填型和热液交代-充填型矿体同时存在,二者在空间上具有明显的分带,具"双层成矿结构"。在盆地深部岩体与膏盐层的接触部位产出"大冶式"矿浆充填-接触交代型富铁矿床,规模可能超过了赋存于浅部火山-次火山中的狭义"玢岩铁矿"。位于宁芜盆地南北两端的姑山和梅山矿田是找寻"大冶式"矿浆充填-接触交代型富铁矿的有利地段。在SO42-氧化Fe2+的同时自身被还原为S2-,S2-与Fe2+结合形成硫铁矿,在铁矿的上部或边部富集形成硫铁矿矿床;这是石膏矿、铁矿和硫铁矿密切共生的根本原因。     

鞍山-本溪地区条带状铁矿的Fe同位素特征及其对成矿机理和地球早期海洋环境的制约

本文报道了鞍山-本溪地区晚太古代条带状铁建造的主量元素、微量元素、稀土元素和Fe同位素的分析结果.结果显示:铁矿主要由Fe2O3T和SiO2组成,具有较低的Al2O3和TiO2含量;微量元素含量和稀土总量均较低;经页岩标准化的稀土元素配分模式呈现轻稀土亏损、重稀土富集;具有明显的La、Eu、Y的正异常;较高的Y/Ho比值.这些特征均表明鞍山-本溪地区条带状铁矿是由极少碎屑物质加入的化学沉积岩,成矿物质主要来源于海底热液的贡献.相对于标准物质IRMM-014,条带状铁矿石的Fe同位素组成最突出的特征是均为正值,这是由于二价铁溶液经部分氧化和沉淀形成富集重铁同位素的三价铁氧化物或氢氧化物的结果,且沉淀程度的不同是控制Fe同位素组成变化的重要因素.条带状铁矿无明显的Ce负异常和Fe同位素组成为正值的特征暗示了铁矿沉淀时的海水为低氧逸度环境.     

铁还原细菌矿化产物及其对铁建造沉积的指示意义

铁还原细菌是微生物诱导矿化的典范之一,它可以利用有机质或氢气作为电子供体还原三价铁,并在细胞外矿化形成多种含铁矿物,比如磁铁矿、菱铁矿、蓝铁矿和绿锈等矿物,从而广泛参与自然界中铁元素的生物地球化学循环过程。本文主要介绍铁还原细菌矿化产物的矿物特征、形成条件和影响因素。此外,通过实验室内建立严格厌氧的环境体系,以与微量元素共沉淀的水合氧化铁为底物,本研究分别利用Fe_ap²⁺和铁还原细菌Shewanella oneidensis MR-4合成非生物成因和生物成因的磁铁矿,结果发现微量元素的存在会改变磁铁矿的形貌和粒径。结合前人提出的微生物可能参与铁建造沉积的过程,本文评估了微量元素作为识别矿物成因指标的有效性,探讨铁还原细菌矿化产物对铁建造沉积的潜在贡献。     

铁细菌胞外多聚物对铁矿物的调控形成及其环境意义

环境介质溶液中铁的水解作用和稳定化作用主要受铁细菌及其代谢有机物质的影响。铁细菌普遍存在于自然环境中,可利用低价铁源为自身生长所需能量。铁细菌胞外有机物的主要组分如多糖和蛋白质等可与铁结合,并通过氧化或沉淀作用使铁稳定、沉积而形成铁矿物;此外铁细菌胞外多聚物可催化铁的氧化或促进铁的聚集。这些生物成因铁矿物因具有良好的表面吸附与氧化还原等化学活性,及有效固定环境中的重金属、放射性核素和催化降解有机污染物的良好环境属性,在环境生物矿物材料和环境治理研究领域被日益重视。故本文基于铁细菌及其胞外多聚物对铁矿物矿化形成的重要调控作用,介绍了环境中存在的铁细菌及其生物矿化特征,重点阐述了铁细菌胞外多聚物(组分、结构及特性)及其在铁矿物矿化过程中的作用,同时对铁细菌胞外多聚物及生物成因铁矿物的环境意义进行了概述。     

Cronobacter sakazakii还原作用对针铁矿晶体结构的影响

厌氧条件下,Cronobacter sakazakii以乙酸钠作为电子供体,针铁矿中Fe(Ⅲ)作为电子受体进行生命活动,其新陈代谢过程伴随Fe(Ⅲ)的还原。细菌增殖和稳定生长过程中不停还原针铁矿并大量累积Fe(Ⅱ);当细菌衰亡时,Fe(Ⅱ)的产生随之减缓;细菌的活动停止时,Fe(Ⅱ)不再积累并最终保持稳定。同步辐射XRD测试表明,微生物还原作用后针铁矿出现了一系列新衍射峰：4.8、6.03、6.13、6.84、7.7和11.4 峰,可能形成具层状结构的新物相。在XANES图谱中Fe主吸收峰向低能量方向移动1 eV,边前峰峰位中心向低能量方向移动且峰面积减小,表明Cronobacter sakazakii的异化Fe(Ⅲ)还原作用使针铁矿中Fe氧化态降低,矿物晶体结构发生了变化。     

辽宁鞍本地区沉积变质型富铁矿的成因：Fe、Si、O、S同位素证据

辽宁鞍本地区是我国最重要的鞍山式沉积变质型(BIF)铁矿矿集区,弓长岭铁矿是我国唯一的由鞍山式贫铁矿经后期热液改造形成的大型磁铁富矿.本文在前人工作基础上,对比研究了鞍本地区贫铁矿、富铁矿和蚀变围岩的铁、硅、氧、硫同位素组成特征和空间变化规律,结合磁铁富矿的地质特征,对成矿流体的性质、来源、成矿作用和富矿成矿机制提出了新的认识.指出鞍本地区富铁矿的成矿作用与辽东地区古元古代造山运动结束后(1.85 Ga)地壳抬升引发的非造山岩浆侵入和热液活动有关,成矿溶液由大气降水演化形成,而非变质热液或混合岩化热液;成矿溶液淋滤了辽河群蒸发盐地层中富13C碳酸盐、富34S石膏、CH4等成矿物质,成矿溶液具偏酸性弱还原特征;铁质活化再富集是鞍本地区富铁矿形成的重要机制,成矿溶液与贫铁矿及围岩反应使铁质以Fe2+形式活化迁移.温度降低、氧逸度升高或与大气降水混合是溶液中Fe2+氧化形成磁铁矿沉淀的主要原因;在Fe2+被氧化形成磁铁矿的同时,成矿溶液中的CH4被氧化形成石墨,与磁铁矿一起沉淀下来,形成含石墨磁铁富矿;溶液中SO42-被还原形成富34S黄铁矿.     

Fe(Ⅱ)/铁氧化物表面结合铁系统还原有机污染物的研究进展

在土壤和沉积物的自然厌氧环境中,铁氧化物可被铁还原菌等微生物异化还原产生Fe(Ⅱ),形成的Fe(Ⅱ)/铁氧化物表面结合铁系统具有还原活性,可使有机污染物还原转化。综述了含卤和含硝基有机污染物的非生物还原转化过程和表面结合铁系统与有机污染物之间的界面反应机理,进而揭示了污染物在环境中的赋存状态和迁移转化规律;重点分析了影响该还原过程的因素,如铁氧化物类型、pH值、Fe(Ⅱ)与铁氧化物接触时间,以及过渡金属、腐殖酸等竞争因子对反应过程的影响。强化自然界中天然的Fe(Ⅱ)/铁氧化物表面结合铁系统在有机污染治理中的作用,在受污染环境修复领域具有广阔的应用前景。 [HT5H]关 键 词:[HT5K]     

Dependence of microbial magnetite formation on humic substance and ferrihydrite concentrations

Iron mineral (trans)formation during microbial Fe(III) reduction is of environmental relevance as it can influence the fate of pollutants such as toxic metal ions or hydrocarbons. Magnetite is an important biomineralization product of microbial iron reduction and influences soil magnetic properties that are used for paleoclimate reconstruction and were suggested to assist in the localization of organic and inorganic pollutants. However, it is not well understood how different concentrations of Fe(III) minerals and humic substances (HS) affect magnetite formation during microbial Fe(III) reduction. We therefore used wet-chemical extractions, magnetic susceptibility measurements and X-ray diffraction analyses to determine systematically how (i) different initial ferrihydrite (FH) concentrations and (ii) different concentrations of HS (i.e. the presence of either only adsorbed HS or adsorbed and dissolved HS) affect magnetite formation during FH reduction by Shewanella oneidensis MR-1. In our experiments magnetite formation did not occur at FH concentrations lower than 5 mM, even though rapid iron reduction took place. At higher FH concentrations a minimum fraction of Fe(II) of 25-30% of the total iron present was necessary to initiate magnetite formation. The Fe(II) fraction at which magnetite formation started decreased with increasing FH concentration, which might be due to aggregation of the FH particles reducing the FH surface area at higher FH concentrations. HS concentrations of 215-393 mg HS/g FH slowed down (at partial FH surface coverage with sorbed HS) or even completely inhibited (at complete FH surface coverage with sorbed HS) magnetite formation due to blocking of surface sites by adsorbed HS. These results indicate the requirement of Fe(II) adsorption to, and subsequent interaction with, the FH surface for the transformation of FH into magnetite. Additionally, we found that the microbially formed magnetite was further reduced by strain MR-1 leading to the formation of either dissolved Fe(II), i.e. Fe²⁺, in HEPES buffered medium or Fe(II) carbonate (siderite) in bicarbonate buffered medium. Besides the different identity of the Fe(II) compound formed at the end of Fe(III) reduction, there was no difference in the maximum rate and extent of microbial iron reduction and magnetite formation during FH reduction in the two buffer systems used. Our findings indicate that microbial magnetite formation during iron reduction depends on the geochemical conditions and can be of minor importance at low FH concentrations or be inhibited by adsorption of HS to the FH surface. Such scenarios could occur in soils with low iron mineral or high organic matter content.     

Shallow-marine ironstones formed by microaerophilic iron-oxidizing bacteria in terminal Paleoproterozoic

The microbial origin of Precambrian iron formations is debated due to the lack of direct fossil evidence. In order to reveal the genesis of ironstones under low-oxygen levels, integrative studies of sedimentology, petrography, mineralogy, and geochemistry were conducted on the intertidal to shallow subtidal ooidal and stromatolitic ironstones from the terminal Paleoproterozoic Chuanlinggou Formation (ca. 1.65–1.64 Ga) of North China, using microscopy, SEM, EDS, ICP-OES, ICP-MS and MC-ICP-MS techniques. Mineralogical study shows that the Fe-rich mineral is predominantly hematite that resulted from dehydration of amorphous Fe-oxyhydroxide during diagenesis. Petrographic observation indicates that the iron was oxidized and precipitated from seawater rather than sourced from terrestrial detritus. Basinward increases of the ironstone abundance, Eu anomalies (from 1.39 to 1.56) and δ⁵⁶Fe values of the ironstones (from +0.5‰ to +1.0‰) suggest that the iron was mainly sourced from seafloor hydrothermal fluids, and partially oxidized and precipitated in shallow subtidal to intertidal environments. The common existence of Fe-oxide coated sheaths, spiral stalks, residual extracellular polymer substances (EPS) and other biogenic fabrics indicates that microaerophilic iron-oxidizing bacteria (FeOB) may have played an important role in precipitating the Chuanlinggou ironstones. The extremely low oxygen concentrations implied by the proliferation of microaerophilic FeOB in the shallow waters, the weak positive Ce anomalies (0.94–1.12) and low Mn concentrations in the ironstones are broadly consistent with the previous result of a Cr isotope study. Thus the establishment of a microaerophilic FeOB genetic model for the widespread Chuanlinggou ironstones in North China provides new insight into the origin of Precambrian iron formations and the redox evolution of ocean-atmosphere systems during the “Boring Billion”.     

Precipitation of iron in microbial mats of the spring waters of Borra Caves,Vishakapatnam, India: some geomicrobiological aspects

The Borra caves, Vishakapatnam, India, can be described as a speleothem cave with significant amounts of unexplored microbial mats in spring waters. Here, we present the first observations and hypotheses on the possible impact of the microorganisms in these mats on the cave formation, focusing on their role on iron mineral precipitation. The spring waters (pH neutral 7.5–7.7) contained dissolved metals like iron and the organic mat sludge (pH 7.0–7.3) had a TOC content of approximately 5.4 wt%. Geochemically, the spring waters deep below the microbial mats contained Fe 369 ppb, Sr 198 ppb; and the organic mat sludge contained Mg 9 ppm, Fe 427 ppb, Zn 149 ppb, Sr 190 ppb. XRD observations displayed Fe minerals (dominantly hematite), minor amounts of zinc gallium sulfide and nitrofuryl compounds. At least four groups of bacteria identified by direct microscopy and SEM-EDX on the basis of morphology could be observed in all samples: Leptothrix-like organisms, entombed bacterial mineral sheaths, a few stalks of Gallionella-like organisms and some additional bacteria that could not be further identified. Leptothrix-like organisms contained 43.22–60.08 wt % Fe and the mineral precipitated near and around these bacteria (in the actual unaltered samples on site) contained 30.76–45.22 wt% Fe as identified and quantified by SEM-EDX. This study indicates that the precipitation of these iron-rich mats in the spring waters could be linked to the presence of abundant active communities of iron precipitating bacteria at Borra caves, Vishakapatanam.     

陕西木龙沟矽卡岩型铁多金属矿床地质特征

陕西木龙沟铁矿床为接触交代矽卡岩型矿床,地质构造单元归属华北古大陆南缘华山一熊耳山陆缘带。矿床主要围岩地层为蓟县系巡检司组,岩体分叉侵入,矿体产于燕山中期花岗闪长斑岩体与巡检司组内、外接触带。矿石成分简单,以磁铁矿为主,其他具有工业意义的金属有钼、锌、铅、铜。通过对该矿床的矿体、矿石特征、蚀变特征的研究,认为该矿床成矿作用主要受构造及中酸性岩浆活动控制,钙镁碳酸盐是成矿的有利围岩。     

Iron biomineralization by anaerobic neutrophilic iron-oxidizing bacteria

Minerals formed by bio-oxidation of ferrous iron (Fe(II)) at neutral pH, their association with bacterial ultrastructures as well as their impact on the metabolism of iron-oxidizing bacteria remain poorly understood. Here, we investigated iron biomineralization by the anaerobic nitrate-dependent iron-oxidizing bacterium Acidovorax sp. strain BoFeN1 in the presence of dissolved Fe(II) using electron microscopy and Scanning Transmission X-ray Microscopy (STXM). All detected minerals consisted mainly of amorphous iron phosphates, but based on their morphology and localization, three types of precipitates could be discriminated: (1) mineralized filaments at distance from the cells, (2) globules of 100 ± 25 nm in diameter, at the cell surface and (3) a 40-nm thick mineralized layer within the periplasm. All of those phases were shown to be intimately associated with organic molecules. Periplasmic encrustation was accompanied by an accumulation of protein moieties. In the same way, exopolysaccharides were associated with the extracellular mineralized filaments. The evolution of cell encrustation was followed by TEM over the time course of a culture: cell encrustation proceeded progressively, with rapid precipitation in the periplasm (in a few tens of minutes), followed by the formation of surface-bound globules. Moreover, we frequently observed an asymmetric mineral thickening at the cell poles. In parallel, the evolution of iron oxidation was quantified by STXM: iron both contained in the bacteria and in the extracellular precipitates reached complete oxidation within 6 days. While a progressive oxidation of Fe in the bacteria and in the medium could be observed, spatial redox (oxido-reduction state) heterogeneities were detected at the cell poles and in the extracellular precipitates after 1 day. All these findings provide new information to further the understanding of molecular processes involved in iron biomineralization by anaerobic iron-oxidizing bacteria and offer potential signatures of those metabolisms that can be looked for in the geological record.     

Biomineralization of lepidocrocite and goethite by nitrate-reducing Fe(II)-oxidizing bacteria: Effect of pH, bicarbonate, phosphate, and humic acids

Fe(III) solid phases are the products of Fe(II) oxidation by Fe(II)-oxidizing bacteria, but the Fe(III) phases reported to form within growth experiments are, at times, poorly crystalline and therefore difficult to identify, possibly due to the presence of ligands (e.g., phosphate, carbonate) that complex iron and disrupt iron (hydr)oxide precipitation. The scope of this study was to investigate the influences of geochemical solution conditions (pH, carbonate, phosphate, humic acids) on the Fe(II) oxidation rate and Fe(III) mineralogy. Fe(III) mineral characterization was performed using ⁵⁷Fe-Mössbauer spectroscopy and μ-X-ray diffraction after oxidation of dissolved Fe(II) within Mops-buffered cell suspensions of Acidovorax sp. BoFeN1, a nitrate-reducing, Fe(II)-oxidizing bacterium. Lepidocrocite (γ-FeOOH) (90%), which also forms after chemical oxidation of Fe(II) by dissolved O₂, and goethite (α-FeOOH) (10%) were produced at pH 7.0 in the absence of any strongly complexing ligands. Higher solution pH, increasing concentrations of carbonate species, and increasing concentrations of humic acids promoted goethite formation and caused little or no changes in Fe(II) oxidation rates. Phosphate species resulted in Fe(III) solids unidentifiable to our methods and significantly slowed Fe(II) oxidation rates. Our results suggest that Fe(III) mineralogy formed by bacterial Fe(II) oxidation is strongly influenced by solution chemistry, and the geochemical conditions studied here suggest lepidocrocite and goethite may coexist in aquatic environments where nitrate-reducing, Fe(II)-oxidizing bacteria are active.     

新疆东昆仑西段铁矿预测区的圈定及资源量估算-基于ArcGIS平台

研究区属华北板块的柴达木地块的早古生代陆缘活动带（祁曼塔格裂陷槽）,即祁漫塔格早古生代岩浆型被动陆缘。本文基于ArcGIS平台,通过建立研究区铁矿资源潜力评价模型,以沉积变质型铁矿为例,对新疆东昆仑西段的铁矿资源进行预测区的圈定,并对圈定的靶区进行优选。由于沉积变质型铁矿主要与沉积地层、岩石分布状况有关,总结出本研究区沉积变质型铁矿主要控矿因素包括沉积地层、Fe元素异常、岩石组合等。本文选取（1）沉积地层、（2）Fe元素异常这两个方面的证据图层对研究区铁矿资源进行预测,共固定了3个沉积变质型预测区,其中A类1处,C类2处。在成矿区带圈定的基础上,估计区带内未发现矿床的个数;对预测区矿点的分布、品位、矿石量（吨位）的分布特征进行模拟,来获得资源量的估算,对研究区铁矿资源潜力做出快速、准确的评价。此次研究表明新疆东昆仑西段具有一定的铁矿资源潜力。     

Distribution of protons and Cd between bacterial surfaces and dissolved humic substances determined through chemical equilibrium modeling

Bacteria and dissolved humic substances are capable of binding significant concentrations of metals in natural environments. Recent advances in understanding bacteria-metal and humic-metal complexation have provided a framework for directly comparing the binding capacities of these components. In this study, we use chemical equilibrium modeling to construct an internally consistent set of thermodynamic equilibrium constants for proton and Cd binding onto dissolved humic substances, using a variety of published data sets. Our modeling approach allows for the direct comparison of humic substance binding constants and site densities to those previously published for proton and Cd binding onto natural consortia of bacteria. We then combine these constants into a unified model that accounts for the competition between bacterial surfaces and humic and fulvic acids in order to determine the relative importance of each component on the total Cd budget. The combined model is used to examine the relative contributions of bacteria and dissolved humic substances to Cd complexation in natural settings. Calculations are performed for three representative systems: (1) one with a maximum realistic concentration of bacteria and a minimum realistic concentration of humic substance, (2) one with a maximum realistic concentration of humic substance and a minimum concentration of bacteria, and (3) one with an intermediate concentration of both components.Our modeling results indicate that dissolved humic substances have 2 orders of magnitude more available binding sites than bacterial surfaces (per gram). Humic substances also have a greater affinity than bacterial surfaces for binding Cd over circumneutral pH ranges. The combined model results demonstrate that, depending upon their relative concentrations, both Cd-humic and Cd-bacteria complexes are capable of dominating Cd-speciation in specific natural environments. This modeling approach is useful in that it can easily be extended to include other metals and binding ligands; however, thermodynamic data must be gathered on additional components to facilitate the modeling of more realistic systems.