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1.
Electric potentials of the (0 0 1) surface of hematite were measured as a function of pH and ionic strength in solutions of sodium nitrate and oxalic acid using the single-crystal electrode approach. The surface is predominantly charge-neutral in the pH 4-14 range, and develops a positive surface potential below pH 4 due to protonation of μ-OH0 sites (pK1,1,0,int = −1.32). This site is resilient to deprotonation up to at least pH 14 (−pK−1,1,0,int ? 19). The associated Stern layer capacitance of 0.31-0.73 F/m2 is smaller than typical values of powders, and possibly arises from a lower degree of surface solvation. Acid-promoted dissolution under elevated concentrations of HNO3 etches the (0 0 1) surface, yielding a convoluted surface populated by sites. The resulting surface potential was therefore larger under these conditions than in the absence of dissolution. Oxalate ions also promoted (0 0 1) dissolution. Associated electric potentials were strongly negative, with values as large as −0.5 V, possibly from metal-bonded interactions with oxalate. The hematite surface can also acquire negative potentials in the pH 7-11 range due to surface complexation and/or precipitation of iron species (0.0038 Fe/nm2) produced from acidic conditions. Oxalate-bearing systems also result in negative potentials in the same pH range, and may include ferric-oxalate surface complexes and/or surface precipitates. All measurements can be modeled by a thermodynamic model that can be used to predict inner-Helmholtz potentials of hematite surfaces. 相似文献
2.
Snorri Gudbrandsson Domenik Wolff-Boenisch Eric H. Oelkers 《Geochimica et cosmochimica acta》2011,75(19):5496-5525
Steady-state element release rates from crystalline basalt dissolution at far-from-equilibrium were measured at pH from 2 to 11 and temperatures from 5 to 75 °C in mixed-flow reactors. Steady-state Si and Ca release rates exhibit a U-shaped variation with pH where rates decrease with increasing pH at acid condition but increase with increasing pH at alkaline conditions. Silicon release rates from crystalline basalt are comparable to Si release rates from basaltic glass of the same chemical composition at low pH and temperatures ?25 °C but slower at alkaline pH and temperatures ?50 °C. In contrast, Mg and Fe release rates decrease continuously with increasing pH at all temperatures. This behaviour is interpreted to stem from the contrasting dissolution behaviours of the three major minerals comprising the basalt: plagioclase, pyroxene, and olivine. Calcium is primarily present in plagioclase, which exhibits a U-shaped dissolution rate dependence on pH. In contrast, Mg and Fe are contained in pyroxene and olivine, minerals whose dissolution rates decrease monotonically with pH. As a result, crystalline basalt preferentially releases Mg and Fe relative to Ca at acidic conditions. The injection of acidic CO2-charged fluids into crystalline basaltic terrain may, therefore, favour the formation of Mg and Fe carbonates rather than calcite. Element release rates estimated from the sum of the volume fraction normalized dissolution rates of plagioclase, pyroxene, and olivine are within one order of magnitude of those measured in this study. 相似文献
3.
Jong-Sik Ryu Andrew D. Jacobson Craig Lundstrom 《Geochimica et cosmochimica acta》2011,75(20):6004-7046
We dissolved Boulder Creek Granodiorite in a plug flow reactor for 5794 h at pH = 1 and T = 25 °C. The primary purpose of the experiment was to identify controls on dissolved δ44/40Ca, δ44/42Ca, and δ26/24Mg values during granite weathering. Herein, we also examine the origin of Ca and Mg isotopic variability among minerals composing the Boulder Creek Granodiorite, and we constrain fundamental characteristics of granite weathering important for quantifying the elemental and isotopic geochemistry of the reactor output. Nine Ca-bearing minerals display an 8.80‰ range of δ44/40Ca values and a 0.51‰ range of δ44/42Ca values. Three Mg-bearing minerals display a 1.53‰ range of δ26/24Mg values. These ranges expressed at the mineralogical scale are higher than the ranges thus far reported for bulk igneous rocks. Most of the δ44/40Ca variability reflects 40Ca enrichment in K-feldspar, and to a lesser extent, biotite, due to the radioactive decay of 40K over the 1.7 Ga age of the rock, whereas the entire range of δ44/42Ca values reflects mass-dependent isotope fractionation during igneous differentiation and crystallization. The range of δ26/24Mg values may represent either fractionation during the chloritization of biotite or interaction of the Boulder Creek Granodiorite with Mg-rich metamorphic fluids having low δ26/24Mg values.The elemental and isotopic composition of the reactor output varied substantially during the experiment. We synthesize the mineralogical and fluid data using coupled mass-conservation equations solved at non-steady-state. Model calculations reveal an intricate balance between increasing specific surface area and decreasing mineral concentrations. While surface area normalized dissolution rate constants were time-invariant, specific surface area increased as a power-law function of time through positive feedbacks between mechanical disaggregation, chemical dissolution, and mineral depletion. Variations in dissolved δ44/40Ca, δ44/42Ca, and δ26/24Mg values reflect conservative mixing rather than fractionation. Apatite and calcite initially control δ44/40Ca and δ44/42Ca values, followed by biotite, titanite, epidote, hornblende, and plagioclase. The release of radiogenic 40Ca clearly defines the period where biotite dissolution dominates. The brucite layer of chlorite initially controls δ26/24Mg values, followed by biotite, the TOT layer of chlorite, and hornblende. Through direct isotopic tracking, these results demonstrate that trace minerals, such as apatite and calcite in the case of Ca and brucite in the case of Mg, dominate elemental release during the incipient stages of granite weathering. The results further show that biotite dissolution dominates the middle stages of granite weathering and that plagioclase dissolution only becomes important during relatively late stages. The Ca and Mg isotope variations associated with these stages are distinct and potentially resolvable in soil mineral weathering studies. 相似文献
4.
Fang Lin 《Geochimica et cosmochimica acta》2010,74(11):3260-5902
The pressure-volume-temperature-composition (PVTX) properties of H2O-CH4 were determined from the bubble point curve to 500 °C and 3 kbar for compositions ?4 mol.% CH4 using the synthetic fluid inclusion technique. H2O-CH4 inclusions were produced by loading known amounts of Al3C4 and H2O into platinum capsules along with pre-fractured and inclusion-free quartz cores. During heating the Al3C4 and H2O react to produce CH4, and the H2O-CH4 homogeneous mixture was trapped as inclusions during fracture healing at elevated temperature and pressure. The composition of the fluid in the inclusion was confirmed using the weight loss technique after the experiment and by Raman spectroscopic analysis of the inclusions.Homogenization temperatures of the inclusions were determined and the results were used to construct iso-Th lines, defined as a line connecting the formation temperature and pressure with the homogenization temperature and pressure. The pressure in the inclusion at the homogenization temperature was calculated from the Duan equation of state (EOS). The slope (ΔP/ΔT) of each iso-Th line was calculated and the results fitted to a polynomial equation using step-wise multiple regression analysis to estimate the slope of the iso-Th line as a function of the homogenization temperature and composition according to:
(ΔP/ΔT)=a+b·m+c·m4+d·(Th)2+e·m·Th+f·m·(Th)4, 相似文献
5.
Hydrated goethite (α-FeOOH) (1 0 0) interface structure: Ordered water and surface functional groups
Sanjit K. Ghose Glenn A. Waychunas Peter J. Eng 《Geochimica et cosmochimica acta》2010,74(7):1943-2587
Goethite(α-FeOOH), an abundant and highly reactive iron oxyhydroxide mineral, has been the subject of numerous studies of environmental interface reactivity. However, such studies have been hampered by the lack of experimental constraints on aqueous interface structure, and especially of the surface water molecular arrangements. Structural information of this type is crucial because reactivity is dictated by the nature of the surface functional groups and the structure or distribution of water and electrolyte at the solid-solution interface. In this study we have investigated the goethite (1 0 0) surface using surface diffraction techniques, and have determined the relaxed surface structure, the surface functional groups, and the three dimensional nature of two distinct sorbed water layers. The crystal truncation rod (CTR) results show that the interface structure consists of a double hydroxyl, double water terminated interface with significant atom relaxations. Further, the double hydroxyl terminated surface dominates with an 89% contribution having a chiral subdomain structure on the (1 0 0) cleavage faces. The proposed interface stoichiometry is ((H2O)(H2O)OH2OHFeOOFeR) with two types of terminal hydroxyls; a bidentate (B-type) hydroxo group and a monodentate (A-type) aquo group. Using the bond-valence approach the protonation states of the terminal hydroxyls are predicted to be OH type (bidentate hydroxyl with oxygen coupled to two Fe3+ ions) and OH2 type (monodentate hydroxyl with oxygen tied to only one Fe3+). A double layer three dimensional ordered water structure at the interface was determined from refinement of fits to the experimental data. Application of bond-valence constraints to the terminal hydroxyls with appropriate rotation of the water dipole moments allowed a plausible dipole orientation model as predicted. The structural results are discussed in terms of protonation and H-bonding at the interface, and the results provide an ideal basis for testing theoretical predictions of characteristic surface properties such as pKa , sorption equilibria, and surface water permittivity. 相似文献
6.
Mario Tribaudino Fabrizio Nestola Marco Bruno Tiziana Boffa Ballaran Christian Liebske 《Physics and Chemistry of Minerals》2008,35(5):241-248
The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal
expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V
0) = α(T − T
0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant
between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was
observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis
shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral
planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature
in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature
and high-pressure strain are differently oriented. 相似文献
7.
异构比φiC4 /φnC4 和φiC5 /φnC5 的石油地质意义 总被引:6,自引:1,他引:6
同分子量的正构烷烃和异构烷烃存在着物理化学性质差异,在运移过程中受围岩的物理化学性质及其它外部因素的影响必然产生分异效应,从而使二者在空间分布上具有一定的特征和规律,异构比指标可以在一定程度上反映出这种特征和规律性。用异构比φiC4 /φnC4 和φiC5 /φnC5 指标可以判断有机质的成熟度,研究轻烃运移的途径、方向、生成环境及轻烃的生物降解。 相似文献
8.
通过密度泛函理论模拟了H_2O_2和SO_2气体在矿物氧化物(α-Fe_2O_3)表面上的非均相反应,研究了H_2O_2和SO_2在α-Fe_2O_3(001)表面的吸附机制和氧化机制。研究结果表明,SO_2、H_2O_2均在α-Fe_2O_3(001)表面通过Fe原子进行吸附,H_2O_2相比于SO_2优先吸附在α-Fe_2O_3(001)表面,且H_2O_2在表面的赋存形式趋向于两个·OH形式吸附。通过二者共吸附的局域态密度、差分电荷密度、Mulliken电荷布局分析结果发现,SO_2和H_2O_2的共吸附形式是通过H_2O_2产生的·OH吸附在α-Fe_2O_3(001)表面,同时SO_2被H_2O_2产生的·OH氧化[S(SO_2)-电荷布局:0. 79 e→1. 32 e; O(H_2O_2)-电荷布局:-0. 77 e→-1. 11 e]形成·OH+SO_2团簇。模拟结果表明大气微量气体H_2O_2能够在矿物氧化物表面介导SO_2吸附并促进SO_2的转化,为理解H_2O_2在大气中非均相氧化SO_2的反应过程提供了理论依据。 相似文献
9.
Astrid Holzheid Marina V. Charykova Vladimir G. Krivovichev Brendan Ledwig Elena L. Fokina Ksenia L. Poroshina Natalia V. Platonova Vladislav V. Gurzhiy 《Chemie der Erde / Geochemistry》2018,78(2):228-240
Any progress in our understanding of low-temperature mineral assemblages and of quantitative physico-chemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56–87?°C and ends at 226–237?°C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180?°C) and the remaining two molecules of water will be lost in the second stage (>180?°C) or (b) four molecules of water will be lost in the first stage up to 180?°C and the last molecule of water will be lost at a temperature above 180?°C. Based on XRD measurements and thermal analyses we were able to deduce Fe2(SeO3)3·(6-x)H2O (x?=?0.0–1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected. 相似文献
10.
1974年在一水晶矿石英脉晶洞中,发现了一种含Ba、Li的硅酸盐新矿物--纤钡锂石。我们对纤钡锂石进行了光性研究、比重测定、差热及热失重分析、红外光谱分析、X射线单晶结构分析等工作,现分述如下。 相似文献
12.
E. Yu. Li D. V. Grichuk S. N. Shilobreeva D. A. Chareev 《Moscow University Geology Bulletin》2011,66(6):413-422
A thermodynamic model for gas-rock interactions in the system [basalt-SO2-O2±S2] is suggested. Calculations are performed for a wide range of temperatures (100–850°C) and pressures (1–1000 bars). The high-temperature
part of this model was verified by experimental research, which was carried out at 850, 650 and 450°C. The modeling prediction
of interactions in the system [(alumino)silicates SO2-O2±S2] at relatively low temperatures (100–300°C) gives steady mineral associations that are typical for natural secondary quartzites:
quartz-pyrite-hematite-Al-silicates-metal sulfates (Ca, Mg, Na, K, Al, and Fe). The formation of sulfates stabilizes the level
of SO2 concentration in the gas phase; this level falls with a temperature decrease. 相似文献
13.
纤钡锂石产于湖南临武香花岭地区一水晶矿锂云母石英脉晶洞中,与锂云母、石英等矿物共生。矿物为浅黄白色,丝绢光泽,呈针状、纤维状、放射状或平行束状集合体,纤维长达1厘米。经X射线单晶及粉晶衍射测定:该矿物属斜方晶系,空间群Ccca,晶胞参数:a=13.60(?),b=20.24(?),e=5.16(?)。最强衍射线为:10.12(?)(100) 4.05(?)(78) 3.39(?)(91) 2.605(?)(31)2.390(?)(28)。 相似文献
14.
根据X射线衍射(XRD)分析发现: A Fe3(SO4)2(OH)6(A=K+、H3O+)系列铁钒的XRD数据十分相近,难以用XRD区别,需通过能谱(EDS)辅助分析,才能区分此类铁矾。另外,此类铁矾的003和107面网间距d随K+含量增大而增大,且呈一元三次方程的关系;而033和220面网间距d随K+含量增大而减小,呈一元二次方程的关系。对该现象从铁矾晶体结构方面进行解释:K+、H3O+离子位于较大空隙中,且沿着Z轴方向排列,当K+、H3O+离子之间相互替换时,会导致该铁矾晶体结构在Z轴方向有较明显的变化。 相似文献
15.
采用CO碳化SiO2和Al3O4负载的Co(NO3)2的方法制备了SiO2和Al3O4负载的Co2C催化剂,采用N2物理吸附、X射线衍射和H2-程序升温还原技术对催化剂进行了表征,并用于催化费托合成反应中.结果显示,需要较长碳化时间才可合成负载的Co2C催化剂;所制催化剂表现出CO加氢生成高碳醇的催化性能,其原因可能在于催化剂表面存在的金属Co物种使CO解离,表面Co物种有利于CO插入,从而导致醇的生成,但体相Co2C则不具有催化活性. 相似文献
16.
17.
通过对ET0计算公式研究进展的总结,分析了在世界上三个时期比较有代表性的计算蒸发腾发量(ET0)的主要公式:修正Penman(MP)公式、Penman-Monteith(PM)公式及标准ASCE-PM公式;以20世纪90年代末期和21世纪初期世界上最新的19个用Lysimeter实验值率定ET0计算值的实验成果为基础,对于不同气候条件下ET0计算方法的普适性分析评估认为:虽PM公式应用效果较好的地区较多,但也有不少地区效果欠佳,MP等公式在一部分地区较好,PM与MP公式并非普适性的,要特别关注标准ASCE-PM公式,总之,这类半理论(半经验)公式均有一定的地区性。仅通过MP、PM公式的计算比较,不能简单地评定哪种公式最优或哪种公式计算ET0值大(或值小),应针对不同地理及气候条件,要经Lysimeter的实验结果才能进行率定比较。文中也对今后研究提出相应建议,有助于ET0计算公式学科的深入研究。 相似文献
18.
19.
To understand the aqueous species important for transport of rhenium under supercritical conditions, we conducted a series of solubility experiments on the Re–ReO2 buffer assemblage and ReS2. In these experiments, pH was buffered by the K–feldspar–muscovite–quartz assemblage; in sulfur-free systems was buffered by the Re–ReO2 assemblage; and and in sulfur-containing systems were buffered by the magnetite–pyrite–pyrrhotite assemblage. Our experimental studies indicate that the species ReCl4 0 is dominant at 400°C in slightly acidic to near-neutral, and chloride-rich (total chloride concentrations ranging from 0.5 to 1.0 M) environments, and ReCl3 + may predominate at 500°C in a solution with total chloride concentrations ranging from 0.5 to 1.5 M. The results also demonstrate that the solubility of ReS2 is about two orders of magnitude less than that of ReO2. This finding not only suggests that ReS2 (or a ReS2 component in molybdenite) is the solubility-controlling phase in sulfur-containing, reducing environments but also implies that a mixing process involving an oxidized, rhenium-containing solution and a solution with reduced sulfur is one of the most effective mechanisms for deposition of rhenium. In analogy with Re, TcS2 may be the stable Tc-bearing phase in deep geological repositories of radioactive wastes. 相似文献
20.
G. Iezzi F. Cámara R. Oberti G. Della Ventura G. Pedrazzi J-L Robert 《Physics and Chemistry of Minerals》2004,31(6):375-385
This work reports the synthesis of ferri-clinoholmquistite, nominally Li2(Mg3Fe3+2)Si8O22(OH)2, at varying fO2 conditions. Amphibole compositions were characterized by X-ray (powder and single-crystal) diffraction, microchemical (EMPA) and spectroscopic (FTIR, Mössbauer and Raman) techniques. Under reducing conditions ( NNO+1, where NNO = Nickel–Nickel oxide buffer), the amphibole yield is very high (>90%), but its composition, and in particular the FeO/Fe2O3 ratio, departs significantly from the nominal one. Under oxidizing conditions ( NNO+1.5), the amphibole yield is much lower (<60%, with Li-pyroxene abundant), but its composition is close to the ideal stoichiometry. The exchange vector of relevance for the studied system is M2(Mg,Fe2+) M4(Mg,Fe2+) M2Fe3+–1 M4Li–1, which is still rather unexplored in natural systems. Amphibole crystals of suitable size for structure refinement were obtained only at 800 °C, 0.4 GPa and NNO conditions (sample 152), and have C2/m symmetry. The X-ray powder patterns for all other samples were indexed in the same symmetry; the amphibole closest to ideal composition has a = 9.428(1) Å, b = 17.878(3) Å, c = 5.282(1) Å, = 102.06(2)°, V = 870.8(3) Å3. Mössbauer spectra show that Fe3+ is strongly ordered at M2 in all samples, whereas Fe2+ is disordered over the B and C sites. FTIR analysis shows that the amount of CFe2+ increases for increasingly reducing conditions. FTIR data also provide strong evidence for slight but significant amounts of Li at the A sites. 相似文献