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1.
《Applied Geochemistry》2001,16(5):559-570
Fe(II)–Fe(III) layered double hydroxysalt green rusts, GRs, are very reactive compounds with the general formula, [FeII(1−x) FeIIIx (OH)2]x+·[(x/n) An−·(m/n) H2O]x−, where x is the ratio FeIII/Fetot, and reflects the structure in which brucite-like layers alternate with interlayers of anions An− and water molecules. Two types of crystal structure for GRs, GR1 and GR2, represented by the hydroxychloride GR1(Cl−) and the hydroxysulphate GR2(SO42−) are distinguished by X-ray diffraction due to different stacking. By analogy with GR1(Cl−) the structure of the fougerite GR mineral, [FeII(1−x) FeIIIx (OH)2]x+·[x OH−·(1−x) H2O]x- Fe(OH)(2+x)·(1−x) H2O, is proposed displaying interlayers made of OH− ions and water molecules (in situ deprotonation of water molecules is necessary for explaining the flexibility of its composition). The space group of mineral GR1(OH−) would be R3̄m, with lattice parameters a≅0.32 and c≅2.25 nm. Stability conditions and the Eh-pH diagram of Fe(OH)(2+x) (the water molecules are omitted) are determined from hydromorphic soil solution equilibria with GR mineral in Brittany (France). Computed Gibbs free energies of formation from soil solution/mineral equilibrium fit well with a regular solid solution model: μ°[Fe(OH)(2+x)]=(1−x) μ°[Fe(OH)2]+x μ°[Fe(OH)3]+RT [(1−x) ln (1−x)+x ln x]+A0 x (1−x), where μ°[Fe(OH)2]=−492.5 kJ mol−1, μ°[Fe(OH)3]=−641 kJ mol−1 and A0=−243.9 kJ mol−1 at the average temperature of 9±1°C. The upper limit of occurrence of GR mineral at x=2/3, i.e. Fe3(OH)8, is explained by its unstability vs. α-FeOOH and/or magnetite; Fe(OH)3 is thus a hypothetical compound with a GR structure which cannot be observed. These thermodynamic data and Eh-pH diagrams of Fe(OH)(2+x) can be used most importantly to predict the possibility that GR minerals reduce some anions in contaminated soils. The cases of NO3−, Se(VI) or Cr(VI) are fully illustrated. 相似文献
2.
《Geochimica et cosmochimica acta》1999,63(19-20):3407-3416
The apparent solubilities of schwertmannite and ferrihydrite were estimated from the H+, OH−, Fe3+, and SO42− activities of the natural stream waters in Korea and mine drainage in Ohio, USA. Both chemical composition of the stream waters and the mineralogy of the precipitates were determined for samples from two streams polluted by coal mine drainage. This study combines these new results with previous data from Ohio, USA to redetermine solubilities. The activities of the dissolved species necessary for the solubility determinations were calculated from the chemical compositions of the waters with the WATEQ4F computer code.Laboratory analyses of precipitates indicated that the main minerals present in Imgok and Osheep creek were schwertmannite and ferrihydrite, respectively. The schwertmannite from Imgok creek had a variable chemical formula of Fe8O8(OH)8−2x(SO4)x· nH2O, where 1.74 ≤ x ≤ 1.86 and 8.17 ≤ n ≤ 8.62. The chemical formula of ferrihydrite was Fe2O3· 1.6H2O. With known mineralogy of the precipitates from each stream, the activities of H+, OH−, Fe3+, and SO42− in the waters were plotted on logarithmic activity-activity diagrams to determine apparent solubilities of schwertmannite and ferrihydrite. The best estimate for the logarithm of the solubility product of schwertmannite, logKs, was 10.5 ± 2.5 around 15°C. This value of logKs constrains the logarithm of the solubility product of ferrihydrite, logKf, to be 4.3 ± 0.5 to maintain the stability boundary with schwertmannite observed in natural waters. 相似文献
3.
《Applied Geochemistry》2000,15(8):1203-1218
Ca6[Al(OH)6]2(CrO4)3·26H2O, the chromate analog of the sulfate mineral ettringite, was synthesized and characterized by X-ray diffraction, Fourier transform infra-red spectroscopy, thermogravimetric analyses, energy dispersive X-ray spectrometry, and bulk chemical analyses. The solubility of the synthesized solid was measured in a series of dissolution and precipitation experiments conducted at 5–75°C and at initial pH values between 10.5 and 12.5. The ion activity product (IAP) for the reaction Ca6[Al(OH)6]2(CrO4)3·26H2O⇌6Ca2++2Al(OH)−4+3CrO2−4+4OH−+26H2O varies with pH unless a CaCrO4(aq) complex is included in the speciation model. The log K for the formation of this complex by the reaction Ca2++CrO2−4=CaCrO4(aq) was obtained by minimizing the variance in the IAP for Ca6[Al(OH)6]2(CrO4)3·26H2O. There is no significant trend in the formation constant with temperature and the average log K is 2.77±0.16 over the temperature range 5–75°C. The log solubility product (log KSP) of Ca6[Al(OH)6]2(CrO4)3·26H2O at 25°C is −41.46±0.30. The temperature dependence of the log KSP is log KSP=A−B/T+D log(T) where A=498.94±48.99, B=27,499±2257, and D=−181.11±16.74. The values of ΔG0r,298 and ΔH0r,298 for the dissolution reaction are 236.6±3.9 and 77.5±2.4 kJ mol−1. the values of ΔC0P,r,298 and ΔS0r,298 are −1506±140 and −534±83 J mol−1 K−1. Using these values and published standard state partial molal quantities for constituent ions, ΔG0f,298=−15,131±19 kJ mol−1, ΔH0f,298=−17,330±8.6 kJ mol−1, ΔS0298=2.19±0.10 kJ mol−1 K−1, and ΔC0Pf,298=2.12±0.53 kJ mol−1 K−1, were calculated. 相似文献
4.
《Geochimica et cosmochimica acta》1999,63(13-14):1969-1980
The solubility of ettringite (Ca6[Al(OH)6]2(SO4)3 · 26H2O) was measured in a series of dissolution and precipitation experiments at 5–75°C and at pH between 10.5 and 13.0 using synthesized material. Equilibrium was established within 4 to 6 days, with samples collected between 10 and 36 days. The log KSP for the reaction Ca6[Al(OH)6]2(SO4)3 · 26H2O ⇌ 6Ca2+ + 2Al(OH)4− + 3SO42− + 4OH− + 26H2O at 25°C calculated for dissolution experiments (−45.0 ± 0.2) is not significantly different from the log KSP calculated for precipitation experiments (−44.8 ± 0.4) at the 95% confidence level. There is no apparent trend in log KSP with pH and the mean log KSP,298 is −44.9 ± 0.3. The solubility product decreased linearly with the inverse of temperature indicating a constant enthalpy of reaction from 5 to 75°C. The enthalpy and entropy of reaction ΔH°r and ΔS°r, were determined from the linear regression to be 204.6 ± 0.6 kJ mol−1 and 170 ± 38 J mol−1 K−1. Using our values for log KSP, ΔH°r, and ΔS°r and published partial molal quantities for the constituent ions, we calculated the free energy of formation ΔG°f,298, the enthalpy of formation ΔH°f,298, and the entropy of formation ΔS°f,298 to be −15211 ± 20, −17550 ± 16 kJ mol−1, and 1867 ± 59 J mol−1 K−1. Assuming ΔCP,r is zero, the heat capacity of ettringite is 590 ± 140 J mol−1 K−1. 相似文献
5.
Pure-iron end-member hibbingite, Fe2(OH)3Cl(s), may be important to geological repositories in salt formations, as it may be a dominant corrosion product of steel waste canisters in an anoxic environment in Na–Cl- and Na–Mg–Cl-dominated brines. In this study, the solubility of Fe2(OH)3Cl(s), the pure-iron end-member of hibbingite (FeII, Mg)2(OH)3Cl(s), and Fe(OH)2(s) in 0.04 m to 6 m NaCl brines has been determined. For the reactionFe2(OH)3Cl(s) + 3H+ ? 3 H2O + 2 Fe2+ + Cl?,the solubility constant of Fe2(OH)3Cl(s) at infinite dilution and 25 °C has been found to be log10 K = 17.12 ± 0.15 (95% confidence interval using F statistics for 36 data points and 3 parameters). For the reactionFe(OH)2(s) + 2H+ ? 2 H2O + Fe2+,the solubility constant of Fe(OH)2 at infinite dilution and 25 °C has been found to be log10 K = 12.95 ± 0.13 (95 % confidence interval using F statistics for 36 data points and 3 parameters). For the combined set of solubility data for Fe2(OH)3Cl(s) and Fe(OH)2(s), the Na+–Fe2+ pair Pitzer interaction parameter θNa+/Fe2+ has been found to be 0.08 ± 0.03 (95% confidence interval using F statistics for 36 data points and 3 parameters). In nearly saturated NaCl brine we observed evidence for the conversion of Fe(OH)2(s) to Fe2(OH)3Cl(s). Additionally, when Fe2(OH)3Cl(s) was added to sodium sulfate brines, the formation of green rust(II) sulfate was observed, along with the generation of hydrogen gas. The results presented here provide insight into understanding and modeling the geochemistry and performance assessment of nuclear waste repositories in salt formations. 相似文献
6.
《Geochimica et cosmochimica acta》1999,63(19-20):3487-3497
The solubility of iron(III) hydroxide as a function of pH was investigated in NaCl solutions at different temperatures (5–50°C) and ionic strengths (0–5 M). Our results at 25°C and 0.7 M in the acidic range are similar to the solubility in seawater. The results between 7.5 to 9 are constant (close to 10−11 M) and are lower than those found in seawater (>10−10) in this pH range. The solubility subsequently increases as the pH increases from 9 to 12. The solubility between 6 and 7.5 has a change of slope that cannot be accounted for by changes in the speciation of Fe(III). This effect has been attributed to a solid-state transformation of Fe(OH)3 to FeOOH. The effect of ionic strength from 0.1 to 5 M at a pH near 8 was quite small. The solubility at 5°C is considerably higher than at 25°C at neutral pH range. The effects of temperature and ionic strength on the solubility at low and high pH have been attributed to the effects on the solubility product and the formation of FeOH2+ and Fe(OH)4−. The results have been used to determine the solubility products of Fe(OH)3, K1Fe(OH)3 and hydrolysis constants, β11, β12, β13, and β14 as a function of temperature (T, K) and ionic strength (I):log K1Fe(OH)3 = −13.486 − 0.1856 I0.5 + 0.3073 I + 5254/T (σ = 0.08)log β11 = 2.517 − 0.8885 I0.5 + 0.2139 I − 1320/T (σ = 0.03)log β12 = 0.4511 − 0.3305 I0.5 − 1996/T (σ = 0.1)log β13 = −0.2965 − 0.7881 I0.5 − 4086/T (σ = 0.6)log β14 = 4.4466 − 0.8505 I0.5 − 7980/T. (σ = 0.2)Both strong ethylenediaminetetraacetic acid and weak (HA) organic ligands greatly affect iron solubility. The additions of ethylenediaminetetraacetic acid and humic material were shown to increase the solubility near pH 8. The higher solubility of Fe(III) in seawater compared to 0.7 M NaCl may be caused by natural organic ligands. 相似文献
7.
Ilvaite samples from six different localities in Japan are found to be members of a solid-solution series varying from Ca(Fe2+,Fe3+)2Fe2+(OH)O Si2O7 to approaximately Ca(Fe2+,Fe3+)2Fe 0.5 2+ Mn 0.5 2+ (OH)O Si2O7, and have been studied by Mössbauer spectrometry and magnetic measurements. The variation in intensity of Mössbauer doublets confirms that Mn substitutes for Fe2+ in the M(B) cation site. An temperatures decreasing from 300 K to 4K, an abrupt change in the reciprocal mass magnetic susceptibility, 1/x g, occurs about 120 K; 1/x g depends linearly upon temperature above 120 K. This change, which is characterized by an unusual mode of decrease in 1/x g, has been interpreted based on Mössbauer spectra at 80 K: the spectra of Fe2+ and Fe3+ in the M(A) site show Zeeman splitting, whereas those of Fe2+ in the M(B) site do not show the effect. This Mössbauer evidence suggests that magnetic spins of Fe in M(A) are in an ordered state, very likely of antiparallel coupling, whereas those of Fe in M(B) are randomly oriented, showing that below 120 K ilvaite has two different magnetic states for Fe ions. As there is a line of evidence that the spins of Fe in M(B) would take an ordered state at extremely low temperatures, ilvaite magnetism may be regarded as basically antiferromagnetic. The magnetic spins of Fe in M(A) and M(B) undergo magnetic transitions at different specific temperatures, thus giving as a whole unusual features of magnetism. 相似文献
8.
《Chemie der Erde / Geochemistry》2016,76(3):419-428
Tooeleite, nominally Fe63+(As3+O3)4(SO4)(OH)4·4H2O, is a relatively uncommon mineral of some acid-mine drainage systems. Yet, if it does occur, it does so in large quantities, indicating that some specific conditions favor the formation of this mineral in the system Fe-As-S-O-H. In this contribution, we report the thermodynamic properties of synthetic tooeleite. The sample was characterized by powder X-ray diffraction, scanning electron microscopy, extended X-ray absorption fine-structure spectroscopy, and Mössbauer spectroscopy. These methods confirmed that the sample is pure, devoid of amorphous impurities of iron oxides, and that the oxidation state of arsenic is 3+. Using acid-solution calorimetry, the enthalpy of formation of this mineral from the elements at the standard conditions was determined as −6196.6 ± 8.6 kJ mol−1. The entropy of tooeleite, calculated from low-temperature heat capacity data measured by relaxation calorimetry, is 899.0 ± 10.8 J mol−1 K−1. The calculated standard Gibbs free energy of formation is −5396.3 ± 9.3 kJ mol−1. The log Ksp value, calculated for the reaction Fe6(AsO3)4(SO4)(OH)4·4H2O + 16H+ = 6Fe3+ + 4H3AsO3 + SO42− + 8H2O, is −17.25 ± 1.80. Tooeleite has stability field only at very high activities of aqueous sulfate and arsenate. As such, it does not appear to be a good candidate for arsenic immobilization at polluted sites. An inspection of speciation diagrams shows that the predominance field of Fe3+ and As3+ overlap only at strongly basic conditions. The formation of tooeleite, therefore, requires strictly selective oxidation of Fe2+ to Fe3+ and, at the same time, firm conservation of the trivalent oxidation state of arsenic. Such conditions can be realized only by biological systems (microorganisms) which can selectively oxidize one redox-active element but leave the other ones untouched. Hence, tooeleite is the first example of an “obligatory” biomineral under the conditions prevailing at or near the Earth's surface because its formation under these conditions necessitates the action of microorganisms. 相似文献
9.
Manganoan lipscombite (Fe x /2+ , M y /2+ ) Fe 3?(x +y)/3+ [OH)3?(x+y)(PO4)2] was synthesized from pure chemicals. From the study of the Mn2+/Fe2+ atomic ratio by Mössbauer spectra, solubility, and electrokinetic properties, it was found that the crystal structure of lipscombite is not changed substantially by the manganese substitution. The unit cell parameters were determined from Guinier-Hägg X-ray diffraction patterns, which are identical for both synthetic ferrous-ferric and manganoan lipscombite. The two compounds crystallize in the tetragonal system with a=5.3020±0.0005 Å and c=12.8800±0.0005 Å. 相似文献
10.
The transformation of vivianite and the direct synthesis starting from pure chemicals lead to the formation of lipscombite {Fe x 2+ Fe 3?x 3+ [(OH)3?x/(PO4)2]} with varying Fe2+/Fe3+ molar ratios. The influence of this ratio on the Mössbauer spectra, solubility, electrokinetic potential and infrared spectra has been studied. By means of Mössbauer spectroscopy, the distribution of the Fe2+ and Fe3+ ions between the octahedral sites I and II has been investigated. The unit cell dimensions have been determined from Guinier-Hägg X-ray diffraction patterns. The crystal system is tetragonal for synthetic lipscombite with a=5.3020±0.0005 Å and c=12.8800±0.0005 Å. Lipscombite has been found to show a negative and time-dependent zeta-potential which, moreover, is influenced by the pH of the suspension and the Fe2+/Fe3+ molar ratio. An explanation of the time-dependence of the zeta-potential on variations of solubility is proposed. Infrared absorption spectrum only is characterized by two absorption bands: v OH(3,500 cm?1) and v P?O(1,100-960 cm?1). The density at 25° C is determined in toluene as 3.36±0.01 g·cm?3. 相似文献
11.
《Geochimica et cosmochimica acta》1993,57(16):3847-3853
Ab initio, molecular orbital calculations at the 6-31G1 level including second-order Møller-Plesset electron correlation predict that the species [Si(OH)5]1− is dynamically stable in a distorted trigonal bipyramid configuration. Reaction pathways for Si(OH)4 + (OH)− → [Si(OH)5]1− → [(OH)3SiO]1−—H2O are also calculated. The first reaction represents the formation of pentacoordinate Si from orthosilicic acid and hydroxide. The activation energy for adding a fifth Si-(OH)− bond to the Si(OH)4 molecule is ≈0.1 eV /molec (≈10kJ/mol). The second reaction is the deprotonation of the Si(OH)4 which forms as a hydroxyl group leaves the [Si(OH)5]1− molecule. Removal of a bond from this complex requires 0.9 eV/molecule (≈85 kJ/mol). Lengthening the Si—OH2 distance results in the isolated molecules [(OH)3SiO]1− + H2O. This represents dehydration of the deprotonated orthosilicic acid.[Si(OH)5]1− and [(OH)3SiO]1−- H2O have the same energetic stability within the accuracy of these calculations. The potential energies of the isolated molecular systems [(OH)3SiO]1−+ H2O and Si(OH)4 + (OH)− are considerably higher. These results suggest that [Si(OH)5]1− may be a stable species or reaction intermediate in dissolution of silicate minerals in basic aqueous solutions. 相似文献
12.
B. Ghazi-Bayat M. Behruzi F. J. Litterst W. Lottermoser G. Amthauer 《Physics and Chemistry of Minerals》1992,18(8):491-496
The dependence of the electronic and the crystallographic structure on temperature of synthetic Mnbearing ilvaites CaFe2+ 2-xMn2+ xFe3+ [Si2O7/O/OH] with 0≤x≤0.19 has been investigated. The change of the electronic structure was studied by 57Fe Mössbauer spectroscopy. The spectra show an increasing valence fluctuation rate between Fe2+ and Fe3+ in the double chain of edge-sharing octahedra with increasing temperature resulting in a mixed valent state of iron. The valence fluctuation rate is distinctly increased by the Mnsubstitution. The temperature of the crystallographic phase transition T x as studied by a high temperature Guinier method is distinctly lowered by the Mn-substitution (x = 0.0, T x=390K; x = 0.12, T x =370K; x = 0.19, T x=295K). The reasons for this behaviour are discussed in terms of Fe2 +, Fe3 + cation order-disorder, electronic relaxation rate, and relaxation of the lattice. In the monoclinic phase there is electron hopping between Fe2 +, Fe3 + pairs whereas in the orthorhombic phase there is extended electron delocalization via a narrow, d-band mechanism. 相似文献
13.
Gennaro Ventruti Fernando Scordari Giancarlo Della Ventura Fabio Bellatreccia Alessandro F. Gualtieri Andrea Lausi 《Physics and Chemistry of Minerals》2013,40(8):659-670
The thermal stability of sideronatrite, ideally Na2Fe3+(SO4)2(OH)·3(H2O), and its decomposition products were investigated by combining thermogravimetric and differential thermal analysis, in situ high-temperature X-ray powder diffraction (HT-XRPD) and Fourier transform infrared spectroscopy (HT-FTIR). The data show that for increasing temperature there are four main dehydration/transformation steps in sideronatrite: (a) between 30 and 40 °C sideronatrite transforms into metasideronatrite after the loss of two water molecules; both XRD and FTIR suggest that this transformation occurs via minor adjustments in the building block. (b) between 120 and 300 °C metasideronatrite transforms into metasideronatrite II, a still poorly characterized phase with possible orthorhombic symmetry, consequently to the loss of an additional water molecule; X-ray diffraction data suggest that metasideronatrite disappears from the assemblage above 175 °C. (c) between 315 and 415 °C metasideronatrite II transforms into the anhydrous Na3Fe(SO4)3 compound. This step occurs via the loss of hydroxyl groups that involves the breakdown of the [Fe3+(SO4)2(OH)] ∞ 2? chains and the formation of an intermediate transient amorphous phase precursor of Na3Fe(SO4)3. (d) for T > 500 °C, the Na3Fe(SO4)3 compound is replaced by the Na-sulfate thenardite, Na2SO4, plus Fe-oxides, according to the Na3Fe3+(SO4)3 → 3/2 Na2(SO4) + 1/2 Fe2O3 + SOx reaction products. The Na–Fe sulfate disappears around 540 °C. For higher temperatures, the Na-sulfates decomposes and only hematite survives in the final product. The understanding of the thermal behavior of minerals such as sideronatrite and related sulfates is important both from an environmental point of view, due to the presence of these phases in evaporitic deposits, soils and sediments including extraterrestrial occurrences, and from the technological point of view, due to the use of these materials in many industrial applications. 相似文献
14.
《Applied Geochemistry》1998,13(4):509-520
A gravity-fed, battery-powered, portable continuously-stirred tank reactor has been developed to directly measure aqueous reaction rates in the field. Dye and tracer experiments indicate the reactor is well-mixed. Rates of Fe2+ oxidation at untreated and passively treated coal mine drainage sites in Pennsylvania were measured under ambient conditions and with the addition of either O2 gas or NaOH solutions. Rates at 5 sites ranged from below the detection limit for this technique (approximately 10−9 mol L−1 s−1) to 3.27±0.01×10−6 mol L−1 s−1. Uncertainties in rates ranged from 70% near the lower limit of measurement to as little as 1% at higher rates of reaction. Multiple linear regressions showed no universal correlations of rates to Fe2+, dissolved O2, and pH (Thiobacillus populations were not measured), although data for two more acidic sites were found to fit well for the model log rate=log K+a log [Fe2+]+b log [OH−]+c log [O2]. Field rates of Fe oxidation from this and other studies vary by 4 orders of magnitude. A model using the ambient field rate of Fe oxidation from this study successfully reproduced independently-measured Fe2+ concentrations observed in a passive wetland treatment facility. 相似文献
15.
Zhuming Yang Kuishou Ding Jeffrey de Fourestier Qian Mao He Li 《Mineralogy and Petrology》2013,107(2):163-169
The Fe-rich Li-bearing magnesionigerite-6N6S occurs in the Xianghualing tin-polymetallic ore field, Linwu County, Hunan Province, Peoples Republic of China. It was found near the outer contact zone of the Laizhiling granite body and in the Middle-Upper Devonian carbonate rocks of Qiziqiao Formation. The mineral formed during the skarn stage. Its empirical formula is Sn1.81Li0.67(Fe1.43Zn1.19 Mn0.41)Σ3.03(Al14.89Mg1.46 Ti0.11Si0.01)Σ16.47O30(OH)2. The structure for magnesionigerite-6N6S was solved and refined in space group R-3?m, with a?=?5.7144(8), c?=?55.446(11) Å, V?=?1568.0(4) Å3, to R1?=?0.0528. Based on the structural refinement of single crystal diffraction data the formula of magnesionigerite-6N6S is Sn1.80Li0.97(Fe1.89Zn0.91) Σ2.80 (Al14.60Mg1.63 Ti0.20)Σ16.43O30(OH)2 with Z?=?3. Fe-rich Li-bearing magnesionigerite-6N6S contains 0.74 wt.% Li2O. The idealized charge-balanced composition of magnesionigerite-6N6S may be expressed by bivalent and trivalent cations: (Mg2+)4(Al3+)18O30(OH)2. The simplified general formula for the 6N6S polysomes in the nigerite and högbomite groups can be given as A x B18-x O30(OH)2, x?=?~4, where A?=?Mg2+, Fe2+, Zn2+; B?=?Al3+, Sn4+, Ti4+, Li+, □. 相似文献
16.
《Applied Geochemistry》2004,19(11):1837-1853
Iron monosulfide formation and oxidation processes were studied in the extensively drained acid sulfate soil environment of the Tweed River floodplain in eastern Australia. Porewater profiles of pH, Eh, SO42−, Fe2+, Fe3+, Cl−, HCO3−, and metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) were obtained using in situ dialysis membrane samplers (`peepers'). Concentrations of acid volatile S (AVS), pyrite, total S, reactive Fe, total and organic C, simultaneously extracted metals (SEMs) and total elemental composition by X-ray fluorescence, were determined on sediment samples. The oxidation of pyrite in the surrounding landscape provides a source of acidity, Fe, Al, SO4 and metals, which are exported into the drainage system where they accumulate in the sediments and porewaters. Negative porewater concentration gradients of SO42− and Fe2+, and large AVS concentrations in the sediments, indicate Fe monosulfides form rapidly under reducing conditions and consume acidity and metals. Oxidation of the sediments during previous drought episodes has resulted in the conversion of monosulfides and pyrite to oxidised Fe minerals and the release of acidity, SO42−, Fe3+, and metals to the surface waters. These formation and oxidation cycles show that Fe monosulfides play an important role in controlling water quality in the drainage system. 相似文献
17.
S. G. Eeckhout E. De Grave R. Vochten N. M. Blaton 《Physics and Chemistry of Minerals》1999,26(6):506-512
Mössbauer spectra (MS) of anapaite (Ca2 Fe2+(PO4)2?·?4H2O) and of a sample after being immersed in a 4% H2O2 solution at room temperature (RT) over 12 days (hereafter an4ox) were collected at temperatures in the range 4.2 to 420?K and 11 to 300?K respectively. All MS consist of symmetrical doublets, hence magnetic ordering was not observed. The temperature dependencies of the Fe2+ centre shifts of anapaite and an4ox were analysed with the Debye model for the lattice vibrations. The characteristic Mössbauer temperatures were found as 370?K?±?25?K and 340?K?±?25?K, and the intrinsic isomer shifts as 1.427?±?0.005?mm/s and 1.418?±?0.005?mm/s respectively. From the external-field (60?kOe) MS recorded at 4.2 and 189?K for the non-treated sample, the principal component V zz of the electric field gradient (EFG) is determined to be positive and the asymmetry parameter η?≈?0.2 and 0.4 respectively. The temperature variations of the quadrupole splittings, ΔE Q(T), cannot be interpreted on the basis of the thermal population of the 5 D electronic levels resulting from the tetragonal compression of the O6 co-ordination. The low-temperature linear behaviour of ΔE Q(T) is attributed to a strong orbit-lattice coupling. A field of 60 kOe applied to anapaite at 4.2?K produces magnetic hyperfine splitting with effective hyperfine fields of ?136, ?254 and ?171?kOe along the principal axes Ox, Oy and Oz of the EFG tensor respectively. Additional oxidation treatments in solutions with various H2O2 concentrations up to 20% and subsequent Mössbauer experiments at room temperature, have revealed that the anapaite structure is not sensitive to oxidation since eventually only a small amount of Fe2+ (～6.5%) is converted into Fe3+. 相似文献
18.
Fe57 Mössbauer spectra were measured on compositions of the series Fe1?x/3Ta1+x/3O4, 0≤x≤1. The spectra are characterized by mixed valencies of Fe2+ and Fe3+ ions for 0<x<1. Starting from x=0 with rutile structure, a trirutile structure forms towards x=1. Quadrupole splitting QS of Fe3+ is QS(Fe3+)≈0.55 mm/s and isomer shift IS is IS(Fe3+)≈0.40 mm/s (referred to Fe); both quantities exhibit minor variations along the series. The Fe2+ subspectra for x>0.5 were fitted using one symmetrical doublet; however, for x<0.5 two symmetrical doublets were necessary to describe these patterns. QS(Fe2+)=2.0–3.2 mm/s and IS(Fe2+)=0.90–1.15 mm/s for all compositions. In the case x<0.5, marked temperature dependent QS values appear to exist. This feature may be related to short range order effects and possibly also in part to intervalence electron transfer betwee Fe2+ and Fe3+ ions. 相似文献
19.
A. Kühberger T. Fehr H. G. Huckenholz G. Amthauer 《Physics and Chemistry of Minerals》1989,16(8):734-740
Ti-andradites were synthesized at a pressure of P(H2O)=3 kbar and temperatures of 700–800° C. Oxygen fugacities were controlled by solid state buffers (Ni/NiO; SiO2 + Fe/Fe2SiO4). The Fe2+-and Fe3+-distribution was determined by low temperature Mössbauer spectroscopy. The water content was measured by a solid's moisture analyzer. The chemical composition of the synthetic and the natural sample has been determined by electron microprobe. Ti-andradites from runs at high oxygen fugacities have Fe3+ on octahedral and tetrahedral sites; Ti-andradites from runs at low oxygen fugacities have tetrahedrally and octahedrally coordinated Fe2+ as well. These “reduced” garnets must also contain Ti3+ on octahedral sites. Charge balance is maintained due to substitution of O2? by (OH)? by two mechanisms: (SiO4)4? ? (O4H4)4? and (Fe3+O6)9? ? (Fe2+O5OH)9?. FTIR spectra of the synthetic samples do show the presence of structurally bound (OH)?. In a natural sample tetrahedrally and octahedrally coordinated Fe3+ are observed together with Fe2+ on all three cation sites of the garnet structure. 相似文献
20.
I. V. Pekov E. V. Sereda Yu. S. Polekhovsky S. N. Britvin N. V. Chukanov V. O. Yapaskurt I. A. Bryzgalov 《Geology of Ore Deposits》2013,55(7):567-574
A new mineral, ferrotochilinite, ideally 6FeS · 5Fe(OH)2, was found at the Oktyabr’sky Mine, Oktyabr’skoe Cu-Ni deposit, Noril’sk, Krasnoyarsk krai, Siberia, Russia. It is associated with ferrovalleriite, magnetite and Fe-rich, chlorite-like phyllosilicate in the cavities of pentlandite-mooihoekite-cubanite ore with subordinate magnetite and chalcopyrite. Ferrotochilinite occurs as flattened on [001], prismatic to elongated lamellar crystals up to 0.1 × 0.5 × 3.2 mm, typically split and curved. Aggregates (up to 6.5 mm in size) are fanlike, rosette-like, or chaotic. Ferrotochilinite is dark bronze. The streak is black. The luster is moderately metallic. The Mohs’ hardness is ca. 1; VHN is 13 kg/mm2. Cleavage is {001} perfect, micalike. Individuals are flexible, inelastic. D(calc) = 3.467 g/cm3. In reflected light, ferrotochilinite is gray, with the hue changing from pale beige to bluish; bireflectance is distinct. Anisotropy is distinct, with gray bluish to yellowish beige rotation colors. No internal reflections. Reflectance values [R min-R max, % (λ, nm)] are: 11.6–11.4 (470), 11.2–12.4 (546), 11.1–13.6 (589), 11.0–15.5 (650). The IR spectrum shows the presence of (OH) groups bonded with Fe cations and the absence of H2O molecules. Chemical composition (wt %; electron probe; H content is calculated) is as follows: 0.02 Mg, 61.92 Fe, 0.03 Ni, 0.09 Cu, 19.45 S, 16.3 O, 1.03 H calc; the total is 98.84. The empirical formula calculated on the basis of 6 S atoms is: Mg0.01Fe10.96Ni0.005Cu0.015S6(OH)10.07 = (Fe5.98Cu0.0015Ni0.005)Σ6S6(OH)9.80(Fe 4.89 2+ Mg0.01)Σ4.90(OH)9.80Fe 0.09 3+ (OH)0.27. Ferrotochilinite is monoclinic, space group is C2/m, Cm or C2, the unit-cell dimensions are: a = 5.463(5), b = 15.865(17), c = 10.825(12) Å, β = 93.7(1)°, V = 936(3) Å3, Z = 2. The strongest reflections in the X-ray powder diffraction pattern (d, Å-I[hkl]) are: 10.83-13[001], 5.392-100[002], 3.281-7[023], 2.777-7[150], 2.696-12[004, $20\bar 1$ ], 2.524-12[ $22\bar 1$ , $20\bar 2$ ], 2.152-8[134, 153], 1.837-11[135, $17\bar 3$ ]. Ferrotochilinite is a structural analog of tochilinite, with Fe2+ instead of Mg in the hydroxide part. The type specimen is deposited in Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow. 相似文献