共查询到20条相似文献，搜索用时 140 毫秒
1.
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
2.
实验研究了不同的pH值、初始离子浓度、矿物用量、温度以及时间等因素对针铁矿和软锰矿吸附镉的影响。结果表明:在pH值从酸性到近中性的范围内,两种氧化矿物对镉的吸附量增加较快,然后在碱性条件下吸附量保持着最大值;反应前后两种氧化矿物溶液的pH值均有不同程度的变化,其中针铁矿和软锰矿的临界pH值分别为8和6.5;两种矿物对镉的吸附在6 h左右达到了吸附平衡,吸附等温线都较好地符合Freundlich等温方程式;随着两种氧化物用量的增加,其吸附量也有增加;室温下,针铁矿和软锰矿对镉的吸附效果较好。 相似文献
3.
天然锰氧化物矿物氧化废水中苯酚的动力学研究 总被引：1，自引：0，他引：1
利用天然锰氧化物矿物在酸性条件下的强氧化性,研究其氧化水中苯酚的动力学,模拟锰氧化物矿物氧化苯酚的反应过程。通过测定初始浓度为100~1000 mg/L,pH值为1~2,温度为293~333 K时不同氧化时间锰氧化物矿物对苯酚的氧化结果,比较伪一级和伪二级反应方程的线性拟合情况;结果表明,该反应动力学曲线用伪二级反应模型拟合时相关系数高于用伪一级反应方程线性的拟合,所以这个反应可用来模拟伪二级反应。根据动力学数据得出Arrhenius反应活化能Ea为11.62 kJ/mol,说明温度对该反应影响不显著,且是一个扩散控制反应。 相似文献
4.
在酸性条件下进行了锰钾矿氧化降解水体中苯酚的实验研究，结果表明：室内自然光照和氧气环境不影响苯酚降解；反应溶液酸度越大，反应进行得越快；样品用量越多、粒径越小，越有利于降解反应；反应温度升高与振荡速度增大也有利于降解反应的进行；共存电解质氯化钠、氯化钙不影响降解反应，而磷酸钠与醋酸钠则不利于降解反应。当介质pH值为2、1，160～200目锰钾矿用量为10g／L，反应温度为25℃，振荡速度为200r／min，反应8h，对50mL浓度为100mg／L苯酚的降解率基本上达到100％，达到了工业排放标准。从反应产物初步推断，苯酚降解的实质是锰钾矿氧化降解作用，为处理苯酚废水增加了一种有效的方法，并拓宽了天然锰钾矿的开发应用前景。 相似文献
5.
不同氧化锰矿物对光催化降解苯酚的影响 总被引：1，自引：0，他引：1
合成层状结构的酸性和碱性水钠锰矿以及隧道结构的锰钾矿和钙锰矿,将其用于苯酚的光催化降解研究。分别采用X射线衍射(XRD)、原子吸收光谱(AAS)、扫描电镜(SEM)、BET氮气吸附法和紫外可见漫反射光谱(UV-Vis DRS)对供试锰氧化物的晶体结构、化学组成、微观形貌、比表面积以及光吸收性能等进行了表征。研究表明,暗反应条件锰氧化物对苯酚的降解作用较弱,而UV-Vis光照能显著促进锰氧化物对苯酚的降解。光照反应12 h后,锰钾矿、酸性水钠锰矿、钙锰矿以及碱性水钠锰矿的苯酚降解率分别为92.1%、77.3%、57.4%和45.8%;对应的TOC去除率分别由暗反应时的6.3%、11.2%、2.0%和4.6%提高至62.1%、43.1%、25.4%和22.5%。4种供试锰氧化物均具有光催化活性,其大小顺序为:锰钾矿>酸性水钠锰矿>钙锰矿>碱性水钠锰矿。UV-Vis光照下氧化锰矿物光化学降解苯酚主要存在3种降解机制———苯酚的直接光解,锰氧化物的化学氧化和锰氧化物的光化学催化,其中光催化降解起主导作用。 相似文献
6.
7.
锰的氧化物和氢氧化物在污染水体净化中的应用研究现状 总被引：17，自引：1，他引：17
经过对锰的氧化物和氢氧化物在净化污染水体中的应用综合研究，发现该氧化物和氢氧化物样品能有效去除污染水体中的有毒有害金属离子和 氧化降解苯酚、2－丙醇、苯及印染废水等有机物，其污染净化能力主要是基于表面络合反应、表面离子交换作用和变价元素的氧化还原作用。同时介绍了锰氧化物和氢氧化物所具有的4个环境属性；离子交换、氧化还原、粒径效应和孔道效应，提出将结构特征与环境化学有机结合，深入探讨其环境属性与污染净化能力之间的关系是目前主要的研究方向。 相似文献
8.
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
9.
广西下雷氧化锰矿床矿石特征及成因分析 总被引：3，自引：0，他引：3
广西下雷锰矿床由原生碳酸锰矿和次生氧化锰矿组成.其中氧化锰矿石的矿物主要有软锰矿、钡锰矿、隐钾锰矿、锂锰矿、钙锰矿、褐锰矿、黑镁铁锰矿等,与之伴生的其他表生矿物主要有赤铁矿、针铁矿、石英、高岭石和蒙脱石.矿石结构主要有交代、隐晶和细晶结构,矿石构造主要有葡萄状、块状、晶洞状、网脉状和条带状构造.与原生碳酸锰矿相比,次生氧化锰矿的矿石品位明显提高,平均在44%以上;Co、Ni、Cu、Zn等微量元素也有一定程度的富集.化学分析和单矿物成分分析结果表明,氧化锰矿石和锰氧化物中的w(Mn)/w(TFe)值均较高(一般大于10),说明风化强度大,铁、锰分离显著.与铁的氧化物相比,锰氧化物中Si和P等有害杂质元素的含量要低得多,因此,铁、锰分离是形成优质锰矿的重要条件.氧化锰矿的次生富集及其在空间上的分布受古气候、构造、含锰地层及地形地貌等多种因素的影响和控制. 相似文献
10.
氧化锰、氧化铁、氧化铝对砷(Ⅲ)的吸附行为研究 总被引：6，自引：0，他引：6
合成了氧化锰、氧化铁、氧化铝三种矿物,以氧化铁、氧化锰为吸附剂研究了pH值、离子强度和时间等因素对吸附As(Ⅲ)的影响,并讨论了氧化锰、氧化铁、氧化铝三种矿物对As(Ⅲ)的饱和吸附容量及等温吸附实验。pH值对氧化锰吸附As(Ⅲ)几乎不影响,对氧化铁吸附As(Ⅲ)在很大的范围内(pH为3.5~8.5)影响不大,离子强度对二者吸附As(Ⅲ)的影响不大,吸附反应在0.5 h左右达到吸附平衡。在优化吸附条件下氧化锰、氧化铁、氧化铝对As(Ⅲ)的饱和吸附容量分别为48.38 mg/g、23.70 mg/g、3.52mg/g,三种合成矿物对As(Ⅲ)的饱和吸附容量:氧化锰氧化铁氧化铝。对实验数据进行Freundlich和Langmuir拟合,相关系数R均在0.98以上,吸附动力学符合Lagergren二级速率方程。 相似文献
11.
David M. Sherman 《Geochimica et cosmochimica acta》2005,69(13):3249-3255
Sunlight-induced reduction and dissolution of colloidal Fe-Mn (hydr)oxide minerals yields elevated concentrations of Fe2+ and Mn2+ in natural waters. Since these elements may be biolimiting micronutrients, photochemical reactions might play a significant role in biogeochemical cycles. Reductive photodissolution of Fe (hydr)oxide minerals may also release sorbed metals. The reactivity of Fe-Mn (hydr)oxide minerals to sunlight-induced photochemical dissolution is determined by the electronic structure of the mineral-water interface. In this work, oxygen K-edge absorption and emission spectra were used to determine the electronic structures of iron(III) (hydr)oxides (hematite, goethite, lepidocrocite, akaganeite and schwertmannite) and manganese(IV) oxides (pyrolusite, birnessite, cryptomelane). The band gaps in the iron(III) (hydr)oxide minerals are near 2.0-2.5 eV; the band gaps in the manganese (IV) oxide phases are 1.0-1.8 eV. Using published values for the electrochemical flat-band potential for hematite together with experimental pHpzc values for the (hydr)oxides, it is possible to predict the electrochemical potentials of the conduction and valence bands in aqueous solutions as a function of pH. The band potentials enable semiquantitative predictions of the susceptibilities of these minerals to photochemical dissolution in aqueous solutions. At pH 2 (e.g., acid-mine waters), photoreduction of iron(III) (hydr)oxides could yield millimolal concentrations of aqueous Fe2+ (assuming surface detachment of Fe2+ is not rate limiting). In seawater (pH 8.3), however, the direct photo-reduction of colloidal iron(III) (hydr)oxides to give nanomolal concentrations of dissolved, uncomplexed, Fe2+ is not thermodynamically feasible. This supports the hypothesis that the apparent photodissolution of iron(III) (hydr)oxides in marines systems results from Fe3+ reduction by photochemically produced superoxide. In contrast, the direct photoreduction of manganese oxides should be energetically feasible at pH 2 and 8.3. 相似文献
12.
The pool of iron oxides, available in sediments for reductive dissolution, is usually estimated by wet chemical extraction methods. Such methods are basically empirically defined and calibrated against various synthetic iron oxides. However, in natural sediments, iron oxides are present as part of a complex mixture of iron oxides with variable crystallinity, clays and organics etc. Such a mixture is more accurately described by a reactive continuum covering a range from highly reactive iron oxides to non-reactive iron oxide. The reactivity of the pool of iron oxides in sediment can be determined by reductive dissolution in 10 mM ascorbic acid at pH 3. Parallel dissolution experiments in HCl at pH 3 reveal the release of Fe(II) by proton assisted dissolution. The difference in Fe(II)-release between the two experiments is attributed to reductive dissolution of iron oxides and can be quantified using the rate equation J/m0 = k′(m/m0)γ, where J is the overall rate of dissolution (mol s−1), m0 the initial amount of iron oxide, k′ a rate constant (s−1), m/m0 the proportion of undissolved mineral and γ a parameter describing the change in reaction rate over time. In the Rømø aquifer, Denmark, the reduction of iron oxides is an important electron accepting process for organic matter degradation and is reflected by the steep increase in aqueous Fe2+ over depth. Sediment from the Rømø aquifer was used for reductive dissolution experiments with ascorbic acid. The rate parameters describing the reactivity of iron oxides in the sediment are in the range k′ = 7·10−6 to 1·10−3 s−1 and γ = 1 to 2.4. These values are intermediate between a synthetic 2-line ferrihydrite and a goethite. The rate constant increases by two orders of magnitude over depth suggesting an increase in iron oxide reactivity with depth. This increase was not captured by traditional oxalate and dithionite extractions. 相似文献
13.
Hanne D. Pedersen Dieke Postma Rasmus Jakobsen 《Geochimica et cosmochimica acta》2006,70(16):4116-4129
The behaviour of trace amounts of arsenate coprecipitated with ferrihydrite, lepidocrocite and goethite was studied during reductive dissolution and phase transformation of the iron oxides using [55Fe]- and [73As]-labelled iron oxides. The As/Fe molar ratio ranged from 0 to 0.005 for ferrihydrite and lepidocrocite and from 0 to 0.001 for goethite. For ferrihydrite and lepidocrocite, all the arsenate remained associated with the surface, whereas for goethite only 30% of the arsenate was desorbable. The rate of reductive dissolution in 10 mM ascorbic acid was unaffected by the presence of arsenate for any of the iron oxides and the arsenate was not reduced to arsenite by ascorbic acid. During reductive dissolution of the iron oxides, arsenate was released incongruently with Fe2+ for all the iron oxides. For ferrihydrite and goethite, the arsenate remained adsorbed to the surface and was not released until the surface area became too small to adsorb all the arsenate. In contrast, arsenate preferentially desorbs from the surface of lepidocrocite. During Fe2+ catalysed transformation of ferrihydrite and lepidocrocite, arsenate became bound more strongly to the product phases. X-ray diffractograms showed that ferrihydrite was transformed into lepidocrocite, goethite and magnetite whereas lepidocrocite either remained untransformed or was transformed into magnetite. The rate of recrystallization of ferrihydrite was not affected by the presence of arsenate. The results presented here imply that during reductive dissolution of iron oxides in natural sediments there will be no simple correlation between the release of arsenate and Fe2+. Recrystallization of the more reactive iron oxides into more crystalline phases, induced by the appearance of Fe2+ in anoxic aquifers, may be an important trapping mechanism for arsenic. 相似文献
14.
J. Ostwald 《Mineralium Deposita》1993,28(3):198-209
Supergene manganese oxides, occurring in shales, breccias and dolomites of Proterozoic Age, in the Western Australian Pilbara Manganese Group, have Mn/Fe ranging from 1.9 to 254 and Mn4+ to Mn (Total) of 0.49–0.94. The manganese mineralogy is dominated by tetravalent manganese oxides, especially by cryptomelane, with lesser amounts of pyrolusite, nsutite, manjiroite, romanechite and other manganese oxide minerals. The manganese minerals are commonly associated with iron oxides, chiefly goethite, indicating incomplete separation of Mn from Fe during Tertiary Age arid climate weathering of older, manganiferous formations. These manganese oxides also contain variable amounts of braunite and very minor hausmannite and bixbyite. The braunite occurs in three generations: sedimentary-diagenetic, recrystallised sedimentary-diagenetic, and supergene. The mode of origin of the hausmannite and bixbyite is uncertain but it is possible that they resulted from diagenesis and/or low-grade regional metamorphism. The supergene manganese deposits appear to have been derived from manganiferous Lower Proterozoic banded iron formations and dolomites of the Hamersley Basin and overlying Middle Proterozoic Bangemali Basin braunite-containing sediments. 相似文献
15.
Reduction of crystalline iron(III) oxyhydroxides using hydroquinone: Influence of phase and particle size 总被引：1，自引：0，他引：1
Iron oxides and oxyhydroxides are common and important materials in the environment, and they strongly impact the biogeochemical
cycle of iron and other species at the Earth's surface. These materials commonly occur as nanoparticles in the 3–10 nm size
range. This paper presents quantitative results demonstrating that iron oxide reactivity is particle size dependent. The rate
and extent of the reductive dissolution of iron oxyhydroxide nanoparticles by hydroquinone in batch experiments were measured
as a function of particle identity, particle loading, and hydroquinone concentration. Rates were normalized to surface areas
determined by both transmission electron microscopy and Braunauer-Emmett-Teller surface. Results show that surface-area-normalized
rates of reductive dissolution are fastest (by as much as 100 times) in experiments using six-line ferrihydrite versus goethite.
Furthermore, the surface-area-normalized rates for 4 nm ferrihydrite nanoparticles are up to 20 times faster than the rates
for 6 nm ferrihydrite nanoparticles, and the surface-area-normalized rates for 5 × 64 nm goethite nanoparticles are up to
two times faster than the rates for 22 × 367 nm goethite nanoparticles. 相似文献
16.
Eric E. Roden 《Geochimica et cosmochimica acta》2004,68(15):3205-3216
Data from studies of dissimilatory bacterial (108 cells mL−1 of Shewanella putrefaciens strain CN32, pH 6.8) and ascorbate (10 mM, pH 3.0) reduction of two synthetic Fe(III) oxide coated sands and three natural Fe(III) oxide-bearing subsurface materials (all at ca. 10 mmol Fe(III) L−1) were analyzed in relation to a generalized rate law for mineral dissolution (Jt/m0 = k′(m/m0)γ, where Jt is the rate of dissolution and/or reduction at time t, m0 is the initial mass of oxide, and m/m0 is the unreduced or undissolved mineral fraction) in order to evaluate changes in the apparent reactivity of Fe(III) oxides during long-term biological vs. chemical reduction. The natural Fe(III) oxide assemblages demonstrated larger changes in reactivity (higher γ values in the generalized rate law) compared to the synthetic oxides during long-term abiotic reductive dissolution. No such relationship was evident in the bacterial reduction experiments, in which temporal changes in the apparent reactivity of the natural and synthetic oxides were far greater (5-10 fold higher γ values) than in the abiotic reduction experiments. Kinetic and thermodynamic considerations indicated that neither the abundance of electron donor (lactate) nor the accumulation of aqueous end-products of oxide reduction (Fe(II), acetate, dissolved inorganic carbon) are likely to have posed significant limitations on the long-term kinetics of oxide reduction. Rather, accumulation of biogenic Fe(II) on residual oxide surfaces appeared to play a dominant role in governing the long-term kinetics of bacterial crystalline Fe(III) oxide reduction. The experimental findings together with numerical simulations support a conceptual model of bacterial Fe(III) oxide reduction kinetics that differs fundamentally from established models of abiotic Fe(III) oxide reductive dissolution, and indicate that information on Fe(III) oxide reactivity gained through abiotic reductive dissolution techniques cannot be used to predict long-term patterns of reactivity toward enzymatic reduction at circumneutral pH. 相似文献
17.
铁锰氧化物在污染土壤修复中的作用 总被引：22，自引：0，他引：22
矿物学在环境科学中的应用将是21世纪矿物学研究的一个主要方面。土壤污染作为一个制约人类社会可持续发展的基本问题正受到日益广泛的关注，污染土壤的修复已成为环境科学研究的一个重点。污染土壤的修复技术主要有物理、化学、生物等方法，但是，它们都不同程度地存在着缺陷。众所周知，铁和锰是自然界中少数但常见的变价元素。含有变价元素和带有表面电荷的铁锰氧化物具有良好的表面活性，不仅对有毒有害的无机污染物具有良好的净化功能，而且对土壤中有机污染物具有氧化降解作用。利用这些矿物来修复污染土壤，具有成本低、无二次污染等优点，体现出天然净化作用的特色，展现出广阔的环境矿物学应用前景。 相似文献
18.
铁氧化物矿物对苯酚和溶解性有机质表面吸附的初步研究 总被引：2，自引：0，他引：2
文中以铁氧化物矿物对苯酚和溶解性有机质(DOM)的吸附研究为例开展生态矿物学研究。铁氧化物矿物的吸附作用存在多种机制,这些吸附机制发生作用的条件主要取决于溶液化学性质和吸附质的理化性质。批处理实验研究表明,苯酚吸附在酸性微酸性条件下不强,吸附等温线符合Langmuir方程,属于表面分子吸附模型;DOM的吸附强并发生吸附分异,配体交换、憎水键和范氏力等多种模式并存,在酸性中性条件下对DOM在针铁矿上的吸附起着重要贡献。本文实验条件下DOM吸附等温线近于线性,不能采用Langmuir方程拟合,可能原因是DOM浓度较低。矿物表面荷电性对吸附影响显著,例如,当矿物表面净电荷为零(pH=pHpzc)时,矿物表面水化膜减薄甚至消失,苯酚分子、憎水DOM分子或片断都会倾向于在矿物表面上吸附。由于苯酚吸附机制单一,其受到的影响很明显,所以苯酚在pH值7～8范围内出现吸附最大值;由于配体交换作用主要发生在酸性微酸性条件下,所以在本文pH值约7.5的实验条件下,尽管配体交换仍在发生作用,但它不是主要吸附机制,针铁矿对DOM吸附的主要贡献应是憎水键和范氏力作用,此外,DOM吸附等温方程近于线性还可能与此有关。显然,铁矿物表面作用在对有机质含量低而铁矿物含量高的红壤中污染物和DOM的固定与归宿控制中扮演着重要的角色。 相似文献
19.
M. Taillefert V. C. Hover T. F. Rozan S. M. Theberge G. W. Luther 《Estuaries and Coasts》2002,25(6):1088-1096
Solid and colloidal iron oxides are commonly involved in early diagenesis. More readily available soluble Fe(III) should accelerate the cycling of iron (Fe) and sulfur (S) in sediments. Experiments with synthetic solutions (Taillefert et al. 2000) showed that soluble Fe(III) (i.e., <50 nm diameter) reacts at a mercury voltammetric electrode at circumneutral pH if it is complexed by an organic ligand. The reactivity of soluble organic-Fe(III) with sulfide is greatly increased compared to its solid equivalent (e.g., amorphous hydrous iron oxides or goethite). We report here data from two different creeks of the Hackensack Meadowlands District (New Jersey) collected with solid state Au/Hg voltammetric microelectrodes and other conventional techniques, which confirm the existence of soluble organic-Fe(III) in sediments and its interaction with sulfide. Chemical profiles in these two anoxic sediments show the interaction between iron and sulfur during early diagenesis. Soluble organic-Fe(III) and Fe(II) are dominant in a creek where sulfide is negligible. This dominance suggests that the reductive dissolution of iron oxides goes through the dissolution of solid Fe(III), then reduction to Fe(II), or that soluble organic-Fe(III) is formed by chemical or microbial oxidation of organic-Fe(II) complexes. In a creek sediment where sulfide occurs in significant concentration, the reductive dissolution of Fe(III) is followed by formation of FeS(aq), which further precipitates. Dissolved sulfide may influence the fate of soluble organic-Fe(III), but the pH may be the key variable behind this process. The high reactivity of soluble organic-Fe(III) and its mobility may result in the shifting of local reactions, at depths where other electron acceptors are used. These data also suggest that estuarine and coastal sediments may not always be at steady state. 相似文献
20.
氧化铁矿物催化分解苯酚的动力学速率及其产物特征 总被引：3，自引：0，他引：3
本文研究了针铁矿、纤铁矿、赤铁矿和磁铁矿在过氧化氢参与下催化分解苯酚的动力学速率与溶液pH值的关系,并用紫外吸收谱测定了反应产物的谱学特征。结果表明,纤铁矿反应体系催化分解苯酚的速率常数(k)最大,其余依次为磁铁矿、针铁矿和赤铁矿。在纤铁矿反应体系中又以pH=3.8时反应速率常数最大。除赤铁矿反应体系外,当溶液pH=3~4时苯酚被完全分解,并有50%~65%的有机碳(TOC)被矿化。在pH=3.25的赤铁矿反应体系中,苯酚大多仅被转化为多酚,小部分苯环被打开形成己烯酸。当溶液pH=4~5时,苯酚一般仅被转化为多酚类化合物,但TOC基本不变。当溶液pH>5时,苯酚没有发生明显的转化和矿化现象。 相似文献