共查询到19条相似文献，搜索用时 140 毫秒
1.
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。 相似文献
2.
Fe(Ⅲ)供应速率对无定型施氏矿物形成的影响 总被引：2，自引：0，他引：2
施氏矿物(schwertmannite)已被证实是一种具特异性能的重(类)金属吸附新材料。但在直接由Fe3+或用强氧化剂氧化Fe2+合成该矿物时,常因夹有黄铁矾类物质而降低产品纯度。通过模拟FeSO4-K2SO4-H2O临界成矾体系,发现在嗜酸性氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)作用下存在无定型施氏矿物和晶型黄钾铁矾的合成反应竞争,其中Fe3+供应速率是一个影响铁矿物形成的重要因素,较低的Fe3+供应可以抑制K+的利用,这种变化趋势对无定型施氏矿物合成是有利的。当存在少量K+等成矾导向离子时,可通过合理调低Fe3+供应速率,有利于溶液中Fe3+平缓释放,改善施氏矿物纯度,这为A.ferroxidans菌生物法中直接使用无机盐培养基合成施氏矿物提供了可能。 相似文献
3.
选取酸性矿坑水环境中常见的次生含铁硫酸盐矿物———黄钾铁矾[KFe3(SO4)2(OH)6]为研究对象,用硫酸盐还原菌
Desulfovibriovulgaris 和异化铁还原菌Shewanellaputrefaciens CN32对其进行还原实验,探讨作为重金属治理潜在材料的
黄钾铁矾的微生物稳定性.实验采用非增长型培养基,在中性、厌氧、30℃的条件下进行.采用湿化学方法测量水溶液及还原产
生的总Fe2+ ,利用X射线衍射(X-raydiffraction,简称XRD)来分析反应后残余固体物质的矿物组成,用扫描电镜(scanning
electronicmicroscopy,简称SEM)观察固体残余物的形貌特征.结果表明,没有微生物的参与,黄钾铁矾的稳定性较好.异化铁
还原菌S.putrefaciens CN32和硫酸还原菌D .vulgaris 在营养极其匮乏的中性厌氧条件下均能还原黄钾铁矾晶格中的
Fe3+ ,显示出黄钾铁矾被微生物还原的可能性.S.putrefaciens CN32还原黄钾铁矾晶格中Fe3+ 的最大还原速率和最终Fe3+
还原率分别为0.001mmol·L-1·h-1和0.37%.与S.putrefaciens CN32不同,D .vulgaris 对黄钾铁矾的还原能力较强,不
含有电子穿梭体(Anthraquinone-2,6-disulfonate,简称AQDS)的实验体系中Fe3+ 的最大还原速率和最终Fe3+ 还原率分别为
0.017mmol·L-1·h-1和16.80%,而添加了AQDS的实验体系的则分别达到了0.026mmol·L-1·h-1和24.30%,这可能与
黄钾铁矾中含有SO42- 有关.D .vulgaris 优先还原黄钾铁矾晶格中的SO42- 产生的H2S是强还原剂,也可促进Fe3+ 的还原,
微生物以及H2S的双重作用可能是导致D .vulgaris 体系中Fe3+ 还原率较高的原因.XRD分析表明,黄钾铁矾经过S.putrefaciens
CN32的作用,物相没有发生变化;而经过D .vulgaris 作用后,黄钾铁矾的特征峰消失,固相残余物中出现了菱铁
矿(FeCO3)、蓝铁矿[Fe3(PO4)2·8H2O]等次生矿物.由于培养基中没有添加任何的磷酸盐,因此蓝铁矿的出现可能是由于培
养基中添加的少量酵母浸膏降解后产生的磷酸根与D .vulgaris 还原黄钾铁矾产生的Fe2+ 相互作用的结果.这些认识对深入
理解地球表层铁的生物地球化学循环具有重要意义,为矿山环境重金属的污染治理提供了实验依据. 相似文献
4.
5.
铁细菌培养过程中低分子有机酸钠盐对含硫酸根铁矿物形成的影响 总被引：1，自引：0，他引：1
普遍存在环境中的低分子有机酸盐对氧化亚铁硫杆菌的矿化产物(施氏矿和黄钾铁矾等铁矿物)会产生影响,从而导致环境中有毒重金属迁移转化发生变化。本文探讨了低分子有机酸钠盐对铁细菌HX3成长过程中代谢产物铁矿物的影响,并利用XRD、FTIR、FESEM和EDS对形成的铁矿物进行了表征与分析。研究结果表明,低浓度低分子有机酸钠盐的加入对细菌氧化Fe~(2+)的影响不明显,但可加速黄钾铁矾的形成;苹果酸钠的加入较柠檬酸钠和草酸钠更利于施氏矿向黄钾铁矾转变。高浓度低分子有机酸钠盐(苹果酸钠、柠檬酸钠和草酸钠依次为20、40和40mmol/L)的加入对细菌培养过程中Fe~(2+)的氧化有抑制作用;抑制影响从大到小的顺序为:苹果酸钠柠檬酸钠草酸钠。该研究结果可为含氧化亚铁硫杆菌等铁细菌的酸性矿山废水中铁矿物的形成转化和生物矿化机理提供理论参考。 相似文献
6.
一价阳离子和水溶性有机质对生物沥浸中次生铁矿物形成的影响 总被引：2，自引：0，他引：2
在嗜酸性氧化亚铁硫杆菌(Acidithiobacillus ferrooxidans)作用下,污泥生物沥浸体系中常会有次生铁矿物形成,这些矿物对污泥脱水和重金属溶出有重要影响。本研究模拟生物沥浸体系,考察了一价阳离子(K+、NH4+、Na+)和污泥DOM(dissolved organic matter)对次生铁矿物形成的影响。结果表明,一价阳离子生成次生黄铁矾类矿物的能力迥异,其中K+的成矾能力最强,120 mmol/L NH4+和80 mmol/L Na+会抑制体系中黄钾铁矾形成。在1.6 mmol/L K+-120 mmol/L NH4+-40 mmol/L Na+和1.6 mmol/L K+-80 mmol/L NH4+-80 mmol/L Na+两个处理所得矿物的结晶度均低于1.6 mmol/L K+-80 mmol/L NH4+-40 mmol/L Na+处理所得矿物的结晶度。另外,在50 mg/L DOM(以DOC计)存在的生物氧化体系,Fe2+最大氧化速率为4.96 h-1,比没有DOM存在时降低48.1%,矿物结晶度也明显低于后者。可见,过高的一价阳离子和DOM含量会影响A.ferrooxidans菌生理生化活性,降低Fe2+氧化速率,继而影响Fe3+供应,使微环境中的黄铁矾形成动力发生改变,最终在一定程度上影响了次生铁矿物的形成。 相似文献
7.
黄钾铁矾类矿物沉淀去除Cr(Ⅵ)的初步研究 总被引：1，自引：0，他引：1
为探讨黄钾铁矾类矿物沉淀对Cr(Ⅵ)的去除效果,利用黄钾铁矾类矿物沉淀对模拟含Cr(Ⅵ)废水进行了初步实验处理,结果表明,黄钾铁矾类矿物沉淀对含Cr(Ⅵ)废水有较好的去除效果,去除率都在70%以上,最高可达85%。黄钾铁矾与黄铵铁矾沉淀对Cr(Ⅵ)的去除率差别不大;溶液酸碱度对去除率有明显影响,在pH值为2.5~3.2时,时间相同,较高的pH值比低pH值的去除率高。黄钾铁矾类矿物的沉淀过程可用来处理矿山及其他工业废水,去除S、Fe和Cr(Ⅵ)等有毒有害元素。 相似文献
8.
黄钾铁矾的形成条件研究及其环境意义 总被引：14，自引：0，他引：14
黄钾铁矾的化学合成实验表明,调整合适的pH值及介质浓度,常温常压下可以实现黄钾铁矾的快速形成。影响黄钾铁矾形成的主要因素包括pH值、温度及硫酸铁介质的浓度。常温下,当pH值在2.60~3.10时,24h内即有黄钾铁矾沉淀出现,2d内则有大量黄钾铁矾生成;在90℃左右时,形成黄钾铁矾的溶液pH值范围增大至1.20~3.10,而且在该范围内,pH值越大越利于黄钾铁矾的形成。高硫酸铁浓度有利于黄钾铁矾的形成,硫酸铁浓度较高(大于0.05M)时,形成较纯的黄钾铁矾矿物;而低浓度时,生成的黄钾铁矾常常含有水绿矾及胶体状的红色无定形羟基硫酸铁杂质。黄钾铁矾的沉淀过程可以用来治理矿山及工业废水,去除其中的S、Fe及As、Cr、Hg、Pb等有毒有害元素。常温常压下黄钾铁矾快速形成的实现为在产生酸性废水的矿山废石堆上形成黄钾铁矾类矿物胶体隔离防渗层提供了良好的潜在应用前景。 相似文献
9.
采用X 射线衍射、傅里叶红外光谱、热重分析、透射电子显微镜和穆斯堡尔谱等手段,研究了 Al3+对黑云母溶解/转化过程的影响,重点分析了不同Al3+浓度作用下黑云母转化产物的矿物学特征及黑云母转化机制.结果显示,Al3+通过水解作用产生质子,加速黑云母片层的溶解及转化.当Al3+浓度较低时(0.01～0.10mol/L),Al3+水解产生的较少量质子对黑云母片层结构溶解有一定促进作用,转化产物以蛭石、水黑云母和绿泥石为主,优先溶出的Fe 聚集成核,同时吸附溶出的Si,形成具有核壳结构的球形纳米颗粒和结晶良好的赤铁矿.当Al3+浓度较高时(0.30～0.60mol/L),Al3+水解产生大量质子,显著加速黑云母结构溶解,黑云母转化产物主要为高岭石和弱结晶的铁氧化物.Al3+能明显改变黑云母的溶解速率及转化产物,从而影响黑云母的风化过程. 相似文献
10.
氧化亚铁硫杆菌作用下形成的黄钾铁矾的SEM研究 总被引：29，自引：3，他引：26
黄钾铁矾是金属硫化物在酸性条件下氧化形成的主要次生矿物。很多研究表明,金属硫化物矿区广泛发育的氧化亚铁硫杆菌会影响金属硫化物的氧化分解和次生矿物的形成。为讨论氧化亚铁硫杆菌在黄钾铁矾形成过程中的作用,设计了两组平行实验制备黄钾铁矾：一种采用化学方法合成黄钾铁矾,另一种在相同条件下接种氧化亚铁硫杆菌合成黄钾铁矾。利用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)和能谱分析仪(EDS)等技术对两种实验获得的黄钾铁矾进行定性分析和形貌观察。结果表明：在氧化亚铁硫杆菌充分繁殖的条件下,细菌的参与更利于黄钾铁矾的形成;Fe^2+的氧化速率可能是影响黄钾铁矾结晶的主要因素,氧化亚铁硫杆菌通过提高Fe^2+的供应速度促使黄钾铁矾快速结晶,细菌作用下形成的黄钾铁矾结晶程度好于纯化学方法制备的黄钾铁矾。 相似文献
11.
Xiaofen Yang Hongmei Wang Linfeng Gong Hima Hassane Zhengbo Jiang 《Frontiers of Earth Science》2009,3(2):221-225
Fe2+ oxidation by Acidithiobacillus ferrooxidans in pure and mixed cultures was investigated in batch cultures in the presence of arsenate. The pH value was periodically
monitored and Fe2+ content was analyzed by the 1,10-phenanthroline method. ICP-AES was employed for the analysis of As(V) concentration in the
solution phase. Precipitates were collected and analyzed by X-ray diffraction. Slight enhancement of iron bio-oxidation was
observed in mixed cultures with the two greatest As(V) concentrations (1.0 and 5.0 mg/L As), which were enriched from sediment
samples in an abandoned copper mine site. As(V) concentrations decreased with time, indicating either the co-precipitation
with or the adsorption by jarosite, the major sink of solid phase. Our data suggest that biogenically synthesized jarosite
may play an important role in the attenuation of soluble arsenate in natural aquatic environments. 相似文献
12.
《Applied Geochemistry》2002,17(2):93-103
Mimicking geochemical processes to solve environmental problems was implemented in dealing with waste acidic jarosite and alkaline coal fly ash. By placing these two chemically different materials adjacent to one another, a self-sealing layer was formed at the interface between both wastes, isolating and immobilizing chemical constituents in the process. A series of leaching experiments were performed on each material separately to study the release behavior of the principal constituents. Radiotracer experiments were conducted to explore diffusion and reaction of constituents such as Fe3+ in a combined jarosite/fly ash system. A model has been developed to simulate the coupled processes of diffusion and precipitation taking into account porosity change due to pore filling by precipitates. The formation of a self-sealing isolation layer in a hypothetical jarosite/fly ash disposal site was modelled. Leaching results indicate that the release of elements from jarosite is much larger than that from fly ash, and that the highly pH dependent release of Fe, Al, and Zn was controlled by the solubility of their hydroxides. Leaching results also suggest that precipitation reactions can be expected to occur at the interface between jarosite and alkaline coal fly ash where a large pH gradient exists. Radiotracer experiments showed that accumulation of constituents occurred at the interface. Modeled Fe3+ profiles in layered jarosite/fly ash were well validated by experiments. Modeling results also showed that with the accumulation of constituents at the interface, a new layer with low porosity was formed. Application of this model suggests that there is a potential use to form a self-sealing layer in jarosite/fly ash co-disposal sites. 相似文献
13.
Fifteen samples of (Mg,Fe)SiO3 majorite with varying Fe/Mg composition and one sample of (Mg,Fe)(Si,Al)O3 majorite were synthesized at high pressure and temperature under different conditions of oxygen fugacity using a multianvil press, and examined ex situ using X-ray diffraction and Mössbauer and optical absorption spectroscopy. The relative concentration of Fe3+ increases both with total iron content and increasing oxygen fugacity, but not with Al concentration. Optical absorption spectra indicate the presence of Fe2+–Fe3+ charge transfer, where band intensity increases with increasing Fe3+ concentration. Mössbauer data were used in conjunction with electron microprobe analyses to determine the site distribution of all cations. Both Al and Fe3+ substitute on the octahedral site, and charge balance occurs through the removal of Si. The degree of Mg/Si ordering on the octahedral sites in (Mg,Fe)SiO3 majorite, which affects both the c/a ratio and the unit cell volume, is influenced by the thermal history of the sample. The Fe3+ concentration of (Mg,Fe)(Si,Al)O3 majorite in the mantle will reflect prevailing redox conditions, which are believed to be relatively reducing in the transition zone. Exchange of material across the transition boundary to (Mg,Fe) (Si,Al)O3 perovskite would then require a mechanism to oxidize sufficient iron to satisfy crystal-chemical requirements of the lower-mantle perovskite phase. 相似文献
14.
Jarosite is an important mineral on Earth, and possibly on Mars, where it controls the mobility of iron, sulfate and potentially toxic metals. Atomistic simulations have been used to study the incorporation of Al3+, and the M2+ impurities Cd, Cu and Zn, in the (0 1 2) and (0 0 1) surfaces of jarosite. The calculations show that the incorporation of Al on an Fe site is favorable on all surfaces in which terminal Fe ions are exposed, and especially on the (0 0 1) [Fe3(OH)3]6+ surface. Incorporation of Cd, Cu or Zn on a K site balanced by a K vacancy is predicted to stabilize the surfaces, but calculated endothermic solution energies and the high degree of distortion of the surfaces following incorporation suggest that these substitutions will be limited. The calculations also suggest that incorporation of Cd, Cu and Zn on an Fe site balanced by an OH vacancy, or by coupled substitution on both K and Fe sites, is unfavorable, although this might be compensated for by growth of a new layer of jarosite or goethite, as predicted for bulk jarosite. The results of the simulations show that surface structure will exert an influence on uptake of impurities in the order Cu > Cd > Zn, with the most favorable surfaces for incorporation being (0 1 2) [KFe(OH)4]0 and (0 0 1) [Fe3(OH)3]6+. 相似文献
15.
This study focused on the ferric sulfate precipitates formed during the culture of Acidithiobacillus ferrooxidans (A. ferrooxidans) in a modified 9K medium by applying a potential control on the electrode. X-ray diffraction (XRD), environmental scanning
electron microscope (ESEM), Raman spectroscopy (Raman) and Fourier Transform Infrared spectroscopy (FTIR) were carried out
to characterize and identify the precipitates which were formed, respectively, in the electrochemical cultivation with a fixed
cathode potential (bias-experiment) and in the conventional batch cultivation without cathode potential control (no-bias-experiment).
The results indicated that K-jarosite presented in both experiments while NH4-jarosite and schwertmannite were only found in the no-bias-experiment. The formation of different precipitates could be attributed
to the different growth statuses and rates of A. ferrooxidans and the different concentrations of Fe3+. In the bias-experiment, external electrons reproduced Fe2+ and promoted the growth of A. ferrooxidans, thus resulting in the low Fe3+ concentration and the rapid depletion of NH4
+ as the nitrogen source, in which K-jarosite was preferentially formed. In the no-bias-experiment, the lower concentration
of A. ferrooxidans was observed, which was due to the continuous consumption of Fe2+ by bacteria, thus resulting in the relatively higher Fe3+ and the NH4
+ concentration in culture. The high concentration of Fe3+ favored the precipitation of the solid solution of K-NH4-H3O jarosite, and led to the formation of schwertmannite after K+ and NH4
+ were depleted. 相似文献
16.
Sven-Ulf Weber Michael Grodzicki Werner Lottermoser Günther J. Redhammer Gerold Tippelt Johann Ponahlo Georg Amthauer 《Physics and Chemistry of Minerals》2007,34(7):507-515
Natural alexandrite Al2BeO4:Cr from Malyshevo near Terem Tschanka, Sverdlovsk, Ural, Russia, has been characterized by 57Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine oxidation state and location of iron. The sample contains 0.3 wt% of total iron oxide. The 57Fe Mössbauer spectrum can be resolved into three doublets. Two of them with hyperfine parameters typical for octahedrally coordinated high-spin Fe3+ and Fe2+, respectively, are assigned to iron substituting for Al in the octahedral M2-site. The third doublet is attributed to Fe3+ in hematite. Electronic structure calculations in the local spin density approximation are in reasonable agreement with experimental data provided that expansion and/or distortion of the coordination octahedra are presumed upon iron substitution. The calculated hyperfine parameters of Fe3+ are almost identical for the M1 and M2 positions, but the calculated ligand-field splitting is by far too large for high-spin Fe3+ on M1. 相似文献
17.
S. Lauterbach C. A. McCammon P. van Aken F. Langenhorst F. Seifert 《Contributions to Mineralogy and Petrology》2000,138(1):17-26
(Mg,Fe)(Si,Al)O3 perovskite samples with varying Fe and Al concentration were synthesised at high pressure and temperature at varying conditions of oxygen fugacity using a multianvil press, and were characterised using ex?situ X-ray diffraction, electron microprobe, Mössbauer spectroscopy and analytical transmission electron microscopy. The Fe3+/ΣFe ratio was determined from Mössbauer spectra recorded at 293 and 80?K, and shows a nearly linear dependence of Fe3+/ΣFe with Al composition of (Mg,Fe)(Si,Al)O3 perovskite. The Fe3+/ΣFe values were obtained for selected samples of (Mg,Fe)(Si,Al)O3 perovskite using electron energy-loss near-edge structure (ELNES) spectroscopy, and are in excellent agreement with Mössbauer data, demonstrating that Fe3+/ΣFe can be determined with a spatial resolution on the order of nm. Oxygen concentrations were determined by combining bulk chemical data with Fe3+/ΣFe data determined by Mössbauer spectroscopy, and show a significant concentration of oxygen vacancies in (Mg,Fe)(Si,Al)O3 perovskite. 相似文献
18.
S.-U. Weber M. Grodzicki C. A. Geiger W. Lottermoser G. Tippelt G. J. Redhammer M. Bernroider G. Amthauer 《Physics and Chemistry of Minerals》2007,34(1):1-9
Three natural lawsonites from Syke Rock, Mendocino Co., Reed Ranch, Marin Co., and Blake Gardens, Sonoma Co., all from the Coast Range Region in California, were studied by 57Fe Mössbauer spectroscopy, electron microprobe analysis, and X-ray powder diffraction. The samples contain about 0.6, 1.0, and 1.4 wt% of total iron oxide, respectively. 57Fe Mössbauer spectra are consistent with the assumption that high-spin Fe3+ substitutes for Al in the octahedrally coordinated site. The Mössbauer spectrum of lawsonite from Syke Rock exhibits a second doublet with 57Fe hyperfine parameters typical for octahedrally coordinated high-spin Fe2+. Electronic structure calculations in the local spin density approximation yield quadrupole splittings for Fe3+ in quantitative agreement with experiment indicating, however, that substitution of Al by Fe3+ must be accompanied by local distortion around the octahedral site. Model calculations also reproduce the room temperature hyperfine parameters of ferrous high-spin iron assuming the substitution of Ca by Fe2+. However, it cannot be excluded that Fe2+ may occupy a more asymmetric site within the microstructural cavity occupied by Ca and a H2O molecule. 相似文献
19.
Bjorn O. Mysen 《Geochimica et cosmochimica acta》2006,70(9):2337-2353
Iron-57 resonant absorption Mössbauer spectroscopy was used to describe the redox relations and structural roles of Fe3+ and Fe2+ in meta-aluminosilicate glasses. Melts were formed at 1500 °C in equilibrium with air and quenched to glass in liquid H2O with quenching rates exceeding 200 °C/s. The aluminosilicate compositions were NaAlSi2O6, Ca0.5AlSi2O6, and Mg0.5AlSi2O6. Iron oxide was added in the form of Fe2O3, NaFeO2, CaFe2O4, and MgFe2O4 with total iron oxide content in the range ∼0.9 to ∼5.6 mol% as Fe2O3. The Mössbauer spectra, which were deconvoluted by assuming Gaussian distributions of the hyperfine field, are consistent with one absorption doublet of Fe2+ and one of Fe3+. From the area ratios of the Fe2+ and Fe3+ absorption doublets, with corrections for differences in recoil-fractions of Fe3+ and Fe2+, the Fe3+/ΣFe is positively correlated with increasing total iron content and with decreasing ionization potential of the alkali and alkaline earth cation. There is a distribution of hyperfine parameters from the Mössbauer spectra of these glasses. The maximum in the isomer shift distribution function of Fe3+, δFe3+, ranges from about 0.25 to 0.49 mm/s (at 298 K relative to Fe metal) with the quadrupole splitting maximum, ΔFe3+, ranging from ∼1.2 to ∼1.6 mm/s. Both δFe3+ and δFe2+ are negatively correlated with total iron oxide content and Fe3+/ΣFe. The dominant oxygen coordination number Fe3+ changes from 4 to 6 with decreasing Fe3+/ΣFe. The distortion of the Fe3+-O polyhedra of the quenched melts (glasses) decreases as the Fe3+/ΣFe increases. These polyhedra do, however, coexist with lesser proportions of polyhedra with different oxygen coordination numbers. The δFe2+ and ΔFe2+ distribution maxima at 298 K range from ∼0.95 to 1.15 mm/s and 1.9 to 2.0 mm/s, respectively, and decrease with increasing Fe3+/ΣFe. We suggest that these hyperfine parameter values for the most part are more consistent with Fe2+ in a range of coordination states from 4- to 6-fold. The lower δFe2+-values for the most oxidized melts are consistent with a larger proportion of Fe2+ in 4-fold coordination compared with more reduced glasses and melts. 相似文献