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1.
水钠锰矿是土壤与沉积物中最为常见的氧化锰矿物, 依据其MnO6层对称特点分为六方和三斜两种亚结构类型.六方水钠锰矿在表生环境中可通过Mn2+的化学或生物氧化形成, 而环境中三斜水钠锰矿的形成及进一步转化为钙锰矿的途径尚不清楚.以两种六方水钠锰矿(酸性水钠锰矿和水羟锰矿)为前驱物, 采用X射线吸收光谱(EXAFS)、X射线衍射(XRD)、电镜(FESEM/TEM)及化学组成分析等技术方法模拟表生环境研究了水钠锰矿从六方向三斜的亚结构转化及生成钙锰矿的化学条件和矿物学机制.结果表明, 适当Mn(Ⅱ)浓度和弱碱性条件(pH≥8)可使六方水钠锰矿逐渐转化为三斜水钠锰矿, 继而经Mg2+交换、常压回流得到了长纤维状的钙锰矿, 其晶体生长以溶解-结晶为主.Mn(Ⅱ)与六方水钠锰矿MnO6八面体层内的Mn(Ⅳ)反应生成Mn(Ⅲ)并填充层内空位, 使水钠锰矿对称型由六方向三斜转变.与酸性水钠锰矿相比, 水羟锰矿结晶弱、层状堆积混乱度高, 与Mn(Ⅱ)反应迅速, 层结构向三斜水钠锰矿转化快.pH升高, 促进六方水钠锰矿对Mn(Ⅱ)的吸附和Mn(Ⅱ)与Mn(Ⅳ)间的反应, 六方水钠锰矿转化为三斜水钠锰矿的速率加快."六方水钠锰矿→三斜水钠锰矿"可能是环境中三斜水钠锰矿的重要来源, 及进一步形成钙锰矿的重要化学生成机制. 相似文献
2.
水钠锰矿是土壤与沉积物中最为常见的氧化锰矿物,依据其MnO6层对称特点分为六方和三斜两种亚结构类型.六方水钠锰矿在表生环境中可通过Mn2+的化学或生物氧化形成,而环境中三斜水钠锰矿的形成及进一步转化为钙锰矿的途径尚不清楚.以两种六方水钠锰矿(酸性水钠锰矿和水羟锰矿)为前驱物,采用X射线吸收光谱(EXAFS)、X射线衍射(XRD)、电镜(FESEM/TEM)及化学组成分析等技术方法模拟表生环境研究了水钠锰矿从六方向三斜的亚结构转化及生成钙锰矿的化学条件和矿物学机制.结果表明,适当Mn(Ⅱ)浓度和弱碱性条件(pH≥8)可使六方水钠锰矿逐渐转化为三斜水钠锰矿,继而经Mg2+交换、常压回流得到了长纤维状的钙锰矿,其晶体生长以溶解-结晶为主.Mn(Ⅱ)与六方水钠锰矿MnO6八面体层内的Mn(Ⅳ)反应生成Mn(Ⅲ)并填充层内空位,使水钠锰矿对称型由六方向三斜转变.与酸性水钠锰矿相比,水羟锰矿结晶弱、层状堆积混乱度高,与Mn(Ⅱ)反应迅速,层结构向三斜水钠锰矿转化快.pH升高,促进六方水钠锰矿对Mn(Ⅱ)的吸附和Mn(Ⅱ)与Mn(Ⅳ)间的反应,六方水钠锰矿转化为三斜水钠锰矿的速率加快."六方水钠锰矿→三斜水钠锰矿"可能是环境中三斜水钠锰矿的重要来源,及进一步形成钙锰矿的重要化学生成机制. 相似文献
3.
作为表生土壤环境中易生成且分布广泛的氧化锰矿物,水锰矿(γ-MnOOH)能参与铁氧化物的生成过程,影响Fe_(2+)的迁移、转化和归趋。本文考察了pH值为3.0~7.0的模拟水溶液体系中水锰矿与Fe_(2+)的相互作用及其生成铁氧化物的过程,分析了Fe_(2+)浓度、pH值和空气(氧气)对Fe(Ⅲ)氧化物晶体结构类型、化学组成和反应速率的影响。研究结果表明,水锰矿氧化Fe_(2+)产物主要为针铁矿和纤铁矿;pH值为3.0~5.0时产物为针铁矿,而pH值为7.0时产物为针铁矿与纤铁矿的混合物,且高浓度Fe_(2+)会促使纤铁矿生成;引入空气利于针铁矿生成;反应速率随着pH值升高、氧气分压的增大而加快。本工作丰富了对铁氧化物在常见锰氧化物表面形成和转化过程的认识。 相似文献
4.
碱性介质中合成水钠锰矿的几个影响因素 总被引：8，自引：0，他引：8
水钠锰矿是土壤和沉积物中常见的氧化锰矿物。较系统地研究了碱性介质中合成水钠锰矿几个影响因素的作用规律。结果表明,在实验条件下,反应液的流动速率和氧气流量是合成水钠锰矿的主要影响因素,在反应中使用机械搅拌,可以使水钠锰矿的合成简单易行;而反应前通氮气处理和反应温度对水钠锰矿的合成没有影响;实验合成单相水钠锰矿的条件为:OH-/Mn摩尔比为13.7,O2的流量2L/min,在常温和机械搅拌下氧化5h;其平均化学组成为Na0.25MnO2.07·0.66H2O。 相似文献
5.
利用锰矿山现有初级产品MnSO4.H2O低成本制备锰钾矿型八面体分子筛。在液相环境中MnSO4和KOH反应生成Mn(OH)2沉淀后,在溶解氧和OH-的参与下,生成K型水钠锰矿,在高温下发生结构的调整转化为锰钾矿。通过实验获得的最佳条件为:在500mL反应体系中用0.2M的MnSO4.H2O与1M的KOH在室温环境中、通空气流量为30L/min、振荡搅拌转速为100r/min的条件下反应3h,离心洗涤至pH=12,样品干燥后在600℃下煅烧1h。为大规模开展锰矿山产品的深加工提供了重要的实验依据。 相似文献
6.
探讨了人工合成的高价锰氧化物与紫外光(UV)联用时降解苯酚废水的特性。结果表明,氧化锰矿物在无UV时对苯酚的降解能力差异大,1 g/L的氧化锰4 h对200 mg/L苯酚废水的降解率和COD去除率分别为:锰钾矿97.51%、酸性水钠锰矿89.07%、碱性水钠锰矿11.36%、钙锰矿9.67%;锰钾矿87.79%、酸性水钠锰矿53.11%、碱性水钠锰矿6.42%、钙锰矿1.43%。UV光照下,氧化锰矿物对苯酚的降解率有不同程度的提高,且表现出显著的表面光催化性质,增加了苯酚的深度降解,COD去除率显著提高。UV下氧化锰4 h对苯酚的降解率分别为:锰钾矿99.48%、酸性水钠锰矿91.86%、碱性水钠锰矿40.15%、钙锰矿35.95%);COD的去除率分别为:锰钾矿98.11%、酸性水钠锰矿68.45%、钙锰矿27.57%、碱性水钠锰矿24.27%。MnO2-UV联用时降解苯酚可能包括两种主要作用机制:氧化锰矿物的直接化学氧化降解和UV下MnO2的表面光催化降解。 相似文献
7.
《矿物岩石地球化学通报》2017,(3)
锰氧化物是常见的半导体材料之一,本文利用XRD、Raman、X射线吸收-发射谱及Zeta电位测试技术对合成的4种锰氧化物矿物(酸性水钠锰矿、碱性水钠锰矿、δ-MnO_2、锰钾矿)的能带结构进行了理论计算。结果表明,4种矿物均是可见光响应的半导体矿物,其禁带宽度分别为2.32 eV、1.77 eV、1.36 eV、1.23 eV;在p H等于6时,4种锰氧化物矿物对应的导带电势分别为-0.32 V、0.09 V、0.39 V、0.46 V(vs.NHE),价带电势分别为2.00 V、1.86 V、1.75 V、1.69 V(vs.NHE)。与腐殖质氧化还原电势相比较,4种锰氧化物矿物在任何pH条件下均能吸收可见光催化氧化腐殖质。从结构上比较,层状结构比隧道结构的锰氧化物可见光催化氧化还原能力更强。 相似文献
8.
为了模拟浅海环境下锰氧化物微生物还原作用诱导碳酸盐沉淀的过程,选取最常见的锰氧化物-水钠锰矿(K_(0.33)Mn_7O_(14)·7H_2O)为研究对象,在不同种类与浓度盐离子(Mg~(2+)、SO_4~(2-))存在条件下开展异化锰还原菌Dietzia cercidiphylli 45-1b好氧还原水钠锰矿的实验研究.通过测试体系蛋白、Mn~(2+)等离子浓度变化,利用X射线衍射(XRD)和X射线吸收谱(XAS)表征反应前后矿物结构变化,来探讨不同初始Mg~(2+)和SO_4~(2-)浓度对于菌株45-1b还原水钠锰矿及诱导碳酸盐矿物沉淀的影响.结果显示体系pH值在4天内从7.0迅速上升至9.3,Mn~(2+)浓度在2天内迅速上升至166μmol/L,随后迅速下降至8μmol/L(第4天),其好氧还原产物为菱锰矿(MnCO3),且其产生量随Mg~(2+)浓度的升高而降低,随SO_4~(2-)浓度的升高而升高.上述实验结果表明好氧环境下菌株45-1b能够利用乙酸为电子供体,水钠锰矿为电子受体还原水钠锰矿释放Mn~(2+),最终转化有机碳为无机碳酸盐矿物菱锰矿.Mg~(2+)通过影响微生物生长和菱锰矿成核对水钠锰矿的还原及菱锰矿沉淀产生抑制作用,而SO_4~(2-)可以缓解Mg~(2+)的抑制作用并促进水钠锰矿的还原及菱锰矿沉淀. 相似文献
9.
湘潭锰矿床的锰矿层赋存于新元古代南华系(成冰系)大塘坡组底部含锰黑色页岩中,含锰矿物主要为菱锰矿。湘潭锰矿的Fe/Mn值低,Th/U、V/(V+Ni)和V/Cr值等地球化学指标显示其发育在氧化-次氧化的沉积环境中,暗示菱锰矿并不是由Mn~(2+)和CO_3~(2-)直接沉淀形成的。湘潭锰矿稀土元素含量高,稀土元素配分模式存在轻微的中稀土元素富集,具有明显的Ce正异常,这些特征指示湘潭锰矿含锰矿物是以锰氧化物或氢氧化物的形式沉淀的。同时,锰矿的碳同位素富集碳的轻同位素,说明有机物参与了菱锰矿的形成过程。综合分析表明,湘潭锰矿成矿过程可以分为沉淀和转化两个阶段:在氧化性的水体中,Mn以氧化物或氢氧化物的形式沉淀;在缺氧且富含有机物质的成岩环境中,Mn氧化物或氢氧化物被有机物还原而转化生成菱锰矿。这与华南地区其他几个典型的大塘坡式锰矿的成矿机制一致。 相似文献
10.
不同氧化度碱性水钠锰矿氧化As(Ⅲ)和Cr(Ⅲ) 的动力学特性 总被引：1，自引：0，他引：1
用批量法研究了Mn平均氧化度分别为4.02、3.85和3.70的碱性水钠锰矿对As(Ⅲ)和Cr(Ⅲ)氧化的动力学特性。结果表明,碱性水钠锰矿氧化As(Ⅲ)和Cr(Ⅲ)先经历准一级动力学反应阶段,随后表观速率常数(kobs)逐渐减小至趋近零,达到反应平衡,kobs逐渐减小除了逆反应影响外,还与产物在矿物表面不断积累,钝化反应位点有关。初始反应阶段kobs随氧化度增加而增大,氧化As(Ⅲ)的kobs分别为: 0.095 1、0.039 6和0.007 1 min-1;氧化Cr(Ⅲ)的kobs分别为0.034 2、0.017 8和0.014 8 min-1。氧化As(Ⅲ)的初始反应阶段生成的Mn(Ⅱ)基本保留在矿物表面,对反应位点钝化大,使kobs减小速度快。而Cr(Ⅲ) 氧化初始阶段,Mn(Ⅱ)释放明显滞后于Cr(Ⅵ)释放,但随反应进行逐渐增加,与Cr(Ⅵ)释放量比值接近于反应计量比。故Cr(Ⅲ) 氧化生成Mn(Ⅱ)对位点的钝化远小于As(Ⅲ)氧化,其初始反应阶段后kobs减小速度较慢,且氧化度越高,保持一级动力学的初始反应阶段越长,kobs减小越慢。因此,水钠锰矿的Mn氧化度越高,氧化As(Ⅲ)和Cr(Ⅲ)的反应速率越快,As(Ⅲ)和Cr(Ⅲ)在碱性水钠锰矿表面氧化产物的释放行为是影响其反应动力学特性的重要因素。 相似文献
11.
CHEN Xiaoye LU Xiancai LIU Huan LI Juan XIANG Wanli ZHANG Rui LU Jianjun 《《地质学报》英文版》2017,91(4):1276-1285
The formation of manganese oxides in nature is commonly mediated by microorganisms.In this study,the mineralization of biogenic manganese oxidation mediated by Pseudomanas putida has been experimentally investigated by employing various characterization techniques,including SEM,FESEM,TEM,XRD,and STXM-NEXAFS.The results indicate that Mn~(2+) ions can be oxidized into Mn(Ⅳ) minerals(birnessite and pyrolusite) and Mn(Ⅲ) minerals(hausmannite and feitknechtite),successively.The primary products(birnessite and pyrolusite) further transformed into hausmannite and feitknechtite under Mn~(2+) ion-enriched conditions.However,birnessite and pyrolusite are the endproducts of the continuous microbial oxidation processes.These biogenic Mn oxides are poorly crystallized,which provides them with a high potential for usage in environmental restoration of contaminated soils and waters contaminated with heavy metals.The approaches employed in this study will also enrich genesis research of biological oxidation of Mn(Ⅱ) species in nature. 相似文献
12.
Samantha L. Shumlas Soujanya Singireddy Akila C. Thenuwara Nuwan H. Attanayake Richard J. Reeder Daniel R. Strongin 《Geochemical transactions》2016,17(1):5
The effect of simulated solar radiation on the oxidation of arsenite [As(III)] to arsenate [As(V)] on the layered manganese oxide, birnessite, was investigated. Experiments were conducted where birnessite suspensions, under both anoxic and oxic conditions, were irradiated with simulated solar radiation in the presence of As(III) at pH 5, 7, and 9. X-ray absorption spectroscopy (XAS) was used to determine the nature of the adsorbed product on the surface of the birnessite. The oxidation of As(III) in the presence of birnessite under simulated solar light irradiation occurred at a rate that was faster than in the absence of light at pH 5. At pH 7 and 9, As(V) production was significantly less than at pH 5 and the amount of As(V) production for a given reaction time was the same under dark and light conditions. The first order rate constant (kobs) for As(III) oxidation in the presence of light and in the dark at pH 5 were determined to be 0.07 and 0.04 h?1, respectively. The As(V) product was released into solution along with Mn(II), with the latter product resulting from the reduction of Mn(IV) and/or Mn(III) during the As(III) oxidation process. Post-reaction XAS analysis of As(III) exposed birnessite showed that arsenic was present on the surface as As(V). Experimental results also showed no evidence that reactive oxygen species played a role in the As(III) oxidation process. 相似文献
13.
FENG Xionghan TAN Wenfeng LIU Fan Huada Daniel RUAN HE Jizheng 《《地质学报》英文版》2006,80(2):249-256
Oxidation of As^Ⅲ by three types of manganese oxide minerals affected by goethite was investigated by chemical analysis, equilibrium redox, X-ray diffraction （XRD） and transmission electron microscopy （TEM）. Three synthesized Mn oxide minerals of different types, birnessite, todorokite, and hausmannite, could actively oxidize As^Ⅲ to Asv, and greatly varied in their oxidation ability. Layer structured birnessite exhibited the highest capacity of As^Ⅲ oxidation, followed by the tunnel structured todorokite. Lower oxide hansmannite possessed much low capacity of As^Ⅲ oxidation, and released more Mn^2＋ than birnessite and todorokite during the oxidation. The maximum amount of Asv produced during the oxidation of As^Ⅲ by Mn oxide minerals was in the order： birnessite （480.4 mmol/kg） 〉 todorokite （279.6 mmol/kg） 〉 hansmannite （117.9 mmol/kg）. The oxidation capacity of the Mn oxide minerals was found to be relative to the composition, crystallinity, and surface properties. In the presence of goethite oxidation of As^Ⅲ by Mn oxide minerals increased, with maximum amounts of Asv being 651.0 mmol/kg for birnessite, 332.3 mmol/kg for todorokite and 159.4 mmol/kg for hansmannite. Goethite promoted As^Ⅲ oxidation on the surface of Mn oxide minerals through adsorption of the Asv produced, incurring the decrease of Asv concentration in solutions. Thus, the combined effects of the oxidation （by Mn oxide minerals）-adsorption （by goethite） lead to rapid oxidation and immobilization of As in soils and sediments and alleviation of the As^Ⅲ toxicity in the environments. 相似文献
14.
Manganese (Mn) oxides are among the strongest oxidants and sorbents in the environment, impacting the transport and speciation of metals, cycling of carbon, and flow of electrons within soils and sediments. The oxidation of Mn(II) to Mn(III/IV) oxides has been primarily attributed to biological processes, due in part to the faster rates of bacterial Mn(II) oxidation compared to observed mineral-induced and other abiotic rates. Here we explore the reactivity of biogenic Mn oxides formed by a common marine bacterium (Roseobacter sp. AzwK-3b), which has been previously shown to oxidize Mn(II) via the production of extracellular superoxide. Oxidation of Mn(II) by superoxide results in the formation of highly reactive colloidal birnessite with hexagonal symmetry. The colloidal oxides induce the rapid oxidation of Mn(II), with dramatically accelerated rates in the presence of organics, presumably due to mineral surface-catalyzed organic radical generation. Mn(II) oxidation by the colloids is further accelerated in presence of both organics and light, implicating reactive oxygen species in aiding abiotic oxidation. Indeed, the enhancement of Mn(II) oxidation is negated when the colloids are reacted with Mn(II) in the presence of superoxide dismutase, an enzyme that scavenges the reactive oxygen species (ROS) superoxide. The reactivity of the colloidal phase is short-lived due to the rapid evolution of the birnessite from hexagonal to pseudo-orthogonal symmetry. The secondary particulate triclinic birnessite phase exhibits a distinct lack of Mn(II) oxidation and subsequent Mn oxide formation. Thus, the evolution of initial reactive hexagonal birnessite to non-reactive triclinic birnessite imposes the need for continuous production of new colloidal hexagonal particles for Mn(II) oxidation to be sustained, illustrating an intimate dependency of enzymatic and mineral-based reactions in Mn(II) oxidation. Further, the coupled enzymatic and mineral-induced pathways are linked such that enzymatic formation of Mn oxide is requisite for the mineral-induced pathway to occur. Here, we show that Mn(II) oxidation involves a complex network of abiotic and biotic processes, including enzymatically produced superoxide, mineral catalysis, organic reactions with mineral surfaces, and likely photo-production of ROS. The complexity of coupled reactions involved in Mn(II) oxidation here highlights the need for further investigations of microbially-mediated Mn oxide formation, including identifying the role of Mn oxide surfaces, organics, reactive oxygen species, and light in Mn(II) oxidation and Mn oxide phase evolution. 相似文献
15.
Brian Fry Richard S Scalan J.Kenneth Winters Patrick L Parker 《Geochimica et cosmochimica acta》1982,46(6):1121-1124
Stable sulfur isotope analyses show that rooted estuarine plants growing in anoxic sediments incorporate substantial amounts of 34S-depleted sulfides, or oxidation products thereof. In roots, this incorporation predominates over sulfate uptake from interstitial porewater. Either the plants incorporate normally toxic sulfides, or they are creating and using a specialized nutrient pool of oxidized sulfides at the root-sediment interface. 相似文献
16.
常见硫化物表面的XPS研究 总被引：6，自引：0，他引：6
采用XPS分析方法,研究了黄铁矿、磁黄铁矿、方铅矿、黄铜矿、闪锌矿和毒砂等常见硫化物矿物表面的化学成分及其化学态,从而探讨硫化物表面的氧化和次生变化。研究发现：（1）硫化物矿物表面在氧逸度较高的情况下很容易发生变化,其氧化产物很复杂,主要是其金属元素的高价态氧化物、氢氧化物和硫酸盐等;（2）就一般常见硫化物而言,相对比较稳定的是黄铁矿;（3）常见硫化物经氧化后,其表面的原子比率常常显示硫富余;（4）在含铁的各种常见硫化物中,除黄铁矿表面的铁相对稳定外,毒砂表面的铁也相对较稳定,而闪锌矿表面的类质同像铁却容易被氧化而发生变化。 相似文献
17.
Mario Villalobos Brandy Toner Garrison Sposito 《Geochimica et cosmochimica acta》2003,67(14):2649-2662
Manganese oxides form typically in natural aqueous environments via Mn(II) oxidation catalyzed by microorganisms, primarily bacteria, but little is known about the structure of the incipient solid-phase products. The Mn oxide produced by a Pseudomonas species representative of soils and freshwaters was characterized as to composition, average Mn oxidation number, and N2 specific surface area. Electron microscopy, X-ray diffraction, and X-ray absorption near edge structure spectroscopy were applied to complement the physicochemical data with morphological and structural information. A series of synthetic Mn oxides also was analyzed by the same methods to gain better comparative understanding of the structure of the biogenic oxide. The latter was found to be a poorly crystalline layer type Mn(IV) oxide with hexagonal symmetry, significant negative structural charge arising from cation vacancies, and a relatively small number of randomly stacked octahedral sheets per particle. Its properties were comparable to those of δ-MnO2 (vernadite) and a poorly crystalline hexagonal birnessite (“acid birnessite”) synthesized by reduction of permanganate with HCl, but they were very different from those of crystalline triclinic birnessite. Overall, the structure and composition of the Mn oxide produced by P. putida were similar to what has been reported for other freshly precipitated Mn oxides in natural weathering environments, yielding further support to the predominance of biological oxidation as the pathway for Mn oxide formation. Despite variations in the degree of sheet stacking and Mn(III) content, all poorly crystalline oxides studied showed hexagonal symmetry. Thus, there is a need to distinguish layer type Mn oxides with structures similar to those of natural birnessites from the synthetic triclinic variety. We propose designating the unit cell symmetry as an addition to the current nomenclature for these minerals. 相似文献
18.
煤矸石-水相互作用的溶解动力学及其环境地球化学效应研究 总被引：17，自引：1，他引：17
党志 《矿物岩石地球化学通报》1997,(4)
煤矸石—水相互作用的溶解动力学及其环境地球化学效应研究党志（中国科学院地球化学研究所，贵阳５５０００２）关键词水—岩作用煤矸石地球化学动力学采煤矿区复垦环境效应收稿日期：１９９７－３－１０作者简介：党志男１９６２年生博士生环境地球化学煤矸石以其量多、... 相似文献