The oxidation state of manganese in marine sediments and ferromanganese nodules     

James W Murray  Laurie S Balistrieri  Barbara Paul 《Geochimica et cosmochimica acta》1984,48(6):1237-1247

Marine sediments and ferromanganese nodules from the Pacific Ocean have been analyzed for the $\text{O}\text{Mn}$ ratio of solid manganese. We tested six chemical methods and concluded that the iodometric and oxalate methods were equivalent and were the best choice in terms of accuracy and precision on natural samples. We choose the iodometric method for most of our analyses because the oxalate procedure is a method of differences.The ferromanganese nodules that we analyzed were all from MANOP site H and had $\text{Mn}\text{Fe}$ ratios that ranged from 5.6 to 70. These nodules were invariably highly oxidized with $\text{O}\text{Mn}$ values ranging from 1.90 to 2.00. Our most precise analyses suggest that less than 1% of the total manganese is present as Mn(II).We also analyzed red clay and hemipelagic sediments from the eastern tropical Pacific (Baja borderland and MANOP site H) and carbonate ooze samples from the equatorial Pacific. These sediments are also highly oxidized ($\text{O}\text{Mn}\text{= 1.90 to 2.00}$) except when Mn(II) appears in the interstitial water. As dissolved Mn(II) increases the value of the $\text{O}\text{Mn}$ ratio in the solid phase decreases. The $\text{O}\text{Mn}$ ratio decreases to values as low as 1.40. This decrease appears to be due to a decrease in oxidized manganese by reduction, however, an increase in reduced manganese in the solid sediments by adsorption or MnCO₃ formation can not be ruled out in all cases.  相似文献   

Nonequilibrium models for predicting forms of precipitated manganese oxides     

John D. Hem  Carol J. Lind 《Geochimica et cosmochimica acta》1983,47(11):2037-2046

Manganese oxides precipitated by bubbling air through 0.01 molar solutions of MnCl₂, Mn(NO₃)₂, MnSO₄, or Mn(ClO₄)₂ at a constantly maintained pH of 8.5 to 9.5 at temperatures of 25°C or higher consisted mainly of hausmannite, Mn₃O₄. At temperatures near 0°C, but with other conditions the same, the product is feitknechtite, βMnOOH, except that if the initial solution is MnSO₄ and the temperature is near 0°C the product is a mixture of manganite, γMnOOH and groutite, αMnOOH.All these oxides are metastable in aerated solution and alter by irreversible processes to more highly oxidized species during aging. A two-step nonequilibrium thermodynamic model predicts that the least stable species, βMnOOH, should be most readily converted to MnO₂. Some preparations of βMnOOH aged in their native solution at 5°C attained a manganese oxidation state of +3.3 or more after 7 months. Hausmannite aged at 25°C altered to γMnOOH. The latter is more stable than a or βMnOOH, and manganese oxidation states above 3.0 were not reached in hausmannite precipitates during 4 months of aging. Initial precipitation of MnCO₃ rather than a form of oxide is likely only where oxygen availability is very low.Composition of solutions and oxidation state and morphology of solids were determined during the aging process by chemical analyses, X-ray and electron diffraction and transmission electron micrographs.  相似文献   

Rates of manganese oxidation in aqueous systems     

John D. Hem 《Geochimica et cosmochimica acta》1981,45(8):1369-1374

The rate of crystal growth of Mn₃O₄ (hausmannite) and βMnOOH (feitknechtite) in aerated aqueous manganous perchlorate systems, near 0.01 M in total manganese, was determined at pH levels ranging from 7.00 to 9.00 and at temperatures from 0.5 to 37.4°C. The process is autocatalytic, but becomes psuedo first-order in dissolved Mn²⁺ activity when the amount of precipitate surface is large compared to the amount of unreacted manganese. Reaction rates determined by titrations using an automated pH-stat were fitted to an equation for precipitate growth. The rates are proportional to surface area of oxide and degree of supersaturation with respect to Mn²⁺. The oxide obtained at the higher temperature was Mn₃O₄, but at 0.5° C only βMnOOH was formed. At intermediate temperatures, mixtures of these solids were formed. The rate of precipitation of hausmannite is strongly influenced by temperature, and that of feitknechtite much less so. The difference in activation energy may be related to differences in crystal structure of the oxides and the geometry of polymeric hydroxy ion precursors.  相似文献   

Manganese carbonate overgrowths on foraminifera tests     

Edward A. Boyle 《Geochimica et cosmochimica acta》1983,47(10):1815-1819

Below the zone where manganese is remobilized as Mn²⁺(aq), reductively cleaned foraminifera in deep sea sediments have much higher $\text{Mn}\text{Ca}$ than those in core tops and sediment traps. $\text{Mn}\text{Ca}$ ranges from less than 20 × 10^?6 in and above the MnO₂ maximum to as high as 700 × 10^?6 in reducing Panama Basin sediments. The most plausible explanation for this enrichment is that the tests are coated with Mn carbonate overgrowths. These coatings can account for a significant proportion of the Mn in reduced deep-sea sediments. Uptake of manganous ion by carbonate may explain the absence of Mn nodules in areas of high carbonate accumulation. Extreme degrees of overgrowth can alter foram trace element values, but this artifact can be avoided by avoiding foraminifera with high Mn/Ca.  相似文献   

On the distribution of iron and manganese at the sediment/water interface: thermodynamic versus kinetic control     

Wolfgang Balzer 《Geochimica et cosmochimica acta》1982,46(7):1153-1161

Iron and manganese solubility at the sediment/water interface has been studied at a water depth of 20 m in Kiel Bight, Western Baltic. By means of an in situ bell jar system enclosing 3.14 m² sediment surface and 2094 l water a complete redox turn-over in the bottom water was simulated in an experiment lasting 99 days. The concentration of dissolved Fe in the bell jar water never exceeded 0.041 μmol · dm^?3during the first 50 days of the experiment and then rose abruptly as the Eh fell from +600 to ?200 mV. The concentration of dissolved Fe under oxic and anoxic conditions seems to be limited by equilibria with solid Fe-phases (hydroxides and amorphous sulphide, respectively). In contrast to Fe, manganese was released continuously from the bottom during the first 50 days of the experiment leading to exponentially increasing manganese concentrations in the bell jar water. During this time dissolved O₂ had become ready depleted and pH had dropped from 8.3 to 7.5. Contrary to iron, manganese being solubilized in reduced sediment layers can penetrate oxic strata in metastable form due to slow oxidation kinetics; when the redoxcline moves upwards Mn²⁺ is enriched in bottom waters. The maximum concentration of dissolved Mn under anoxic conditions is controlled by a solid phase with solubility properties similar to MnCO₃ (rhodochrosite). Bottom water enrichment in dissolved Mn²⁺ could be traced to originate from excess solid manganese within the top 3 cm of the sediment.  相似文献   

Permanganate oxidation of arsenic(III): Reaction stoichiometry and the characterization of solid product     

Giehyeon Lee  Kyungsun Song  Jongseong Bae 《Geochimica et cosmochimica acta》2011,75(17):4713-4727

Permanganate (MnO₄⁻) has widely been used as an effective oxidant for drinking water treatment systems, as well as for in situ treatment of groundwater impacted by various organic contaminants. The reaction stoichiometry of As(III) oxidation by permanganate has been assumed to be 1.5, based on the formation of solid product, which is putatively considered to be MnO₂(s). This study determined the stoichiometric ratio (SR) of the oxidation reaction with varying doses of As(III) (3-300 μM) and MnO₄⁻ (0.5 or 300 μM) under circumneutral pH conditions (pH 4.5-7.5). We also characterized the solid product that was recovered ∼1 min after the oxidation of 2.16 mM As(III) by 0.97 mM MnO₄⁻ at pH 6.9 and examined the feasibility of secondary heterogeneous As(III) oxidation by the solid product. When permanganate was in excess of As(III), the SR of As(III) to Mn(VII) was 2.07 ± 0.07, regardless of the solution pH; however, it increased to 2.49 ± 0.09 when As(III) was in excess. The solid product was analogous to vernadite, a poorly crystalline manganese oxide based on XRD analysis. The average valence of structural Mn in the solid product corresponded to +III according to the splitting interval of the Mn3s peaks (5.5 eV), determined using X-ray photoelectron spectroscopy (XPS). The relative proportions of the structural Mn(IV):Mn(III):Mn(II) were quantified as 19:62:19 by fitting the Mn2p_3/2 spectrum of the solid with the five multiplet binding energy spectra for each Mn valence. Additionally, the O1s spectrum of the solid was comparable to that of Mn-oxide but not of Mn-hydroxide. These results suggest that the solid product resembled a poorly crystalline hydrous Mn-oxide such as (Mn^II_0.19Mn^III_0.62Mn^IV_0.19)₂O₃·nH₂O, in which Mn(II) and Mn(IV) were presumably produced from the disproportionation of aqueous phase Mn(III). Thermodynamic calculations also show that the formation of Mn(III) oxide is more favorable than that of Mn(IV) oxide from As(III) oxidation by permanganate under circumneutral pH conditions. Arsenic(III), when it remained in the solution after all of the permanganate was consumed, was effectively oxidized by the solid product. This secondary heterogeneous As(III) oxidation consisted of three steps: sorption to and oxidation on the solid surface and desorption of As(V) into solution, with the first step being the rate-limiting process as observed in As(III) oxidation by various Mn (oxyhydr)oxides reported elsewhere. We also discussed a potential reaction pathway of the permanganate oxidation of As(III).  相似文献   

Ferromanganese oxide deposits from the Central Pacific Ocean,I. Encrustations from the Line Islands Archipelago     

Andrew C Aplin  David S Cronan 《Geochimica et cosmochimica acta》1985,49(2):427-436

Chemical and mineralogical analyses of a well-controlled suite of ferromanganese encrustations from the Line Islands Archipelago (Central Pacific) suggest that they represent purely hydrogenous deposits—i.e. they have formed through the slow accumulation of trace metal-enriched oxides directly from the water-column. Mineralogically they consist predominantly of δMnO₂ and amorphous FeOOHxH₂O. Compositionally, they are similar to δMnO₂ nodules from adjoining basinal areas but are enriched in both Mn (mean = 20.4%, max = 29.3%) and Co (mean = 0.55%, max = 1.57%). δMnO₂ is the most important trace metal bearing phase; strong associations are noted between it and Co, Mo, Ni, Zn, and Cd, whilst only Be is associated specifically with FeOOH. V, Sr and Pb are partitioned between the authigenic oxide phases, whilst Ti most probably occurs as TiO₂xH₂O. Cu is contained in both aluminosilicate contaminant phases and Fe oxide phases. These relations are considered to reflect the differing scavenging behaviour of Mn and Fe oxides in the water column.Crusts from ~1–2 km are enriched in Mn and the Mn-related elements and exhibit higher $\text{Mn}\text{Fe}$ ratios than deeper crusts, which are compositionally constant. The higher $\text{Mn}\text{Fe}$ ratios may result from a supply of Mn from continental borderland sediments at these depths, which is transported horizontally by advective-diffusive processes. Since manganophile elements are enriched relative to Mn in the 1–2 km crusts, it is considered that the supply of Mn is scavenged by existing oxides, is oxidised and effectively occludes them. A higher proportion of oxide particles thus exhibit Mn oxide scavenging properties in the 1–2 km depth zone. The increased vertical flux of Mn resulting from the supply at ~1–2 km is not reflected by higher $\text{Mn}\text{Fe}$ ratios in deeper crusts, so that the vertical flux of oxides is not simply related to the standing crop. The $\text{Mn}\text{Fe}$ ratios of the crusts thus reflect the composition of suspended oxides at similar depths.  相似文献   

Oxidation of aqueous Cr(III) at birnessite surfaces: constraints on reaction mechanism     

《Geochimica et cosmochimica acta》1999,63(11-12):1671-1687

X-ray Photoelectron Spectroscopy (XPS) was used to investigate oxidation of aqueous Cr(III) at the surface of 7 Å-birnessite [MnO_1.75(OH)_0.25]. Special emphasis was placed on detection of intermediate oxidation states of chromium due to their critical environmental significance. No previous studies have been able to identify these intermediate oxidation states of chromium (namely, Cr[IV] and Cr[V]) on mineral surfaces or in natural solutions. Mn(2p_3/2), Cr(2p_3/2) and O(1s) spectra of the reacted surfaces reveal that Mn(IV) of synthetic birnessite undergoes reductive dissolution in two steps. The first step involves Mn(IV) reduction to Mn(III),that forms at the oxide surface probably as an oxyhydroxide (MnOOH), and in the second step Mn(III) is reduced to Mn(II) that is subsequently taken into solution. Each reductive reaction step involves transfer of only one electron to the Mn ion. After Cr(III)_aq is adsorbed onto the MnO₂ surface, it undergoes oxidation in three separate steps, each involving the loss of one electron to Mn ions, so that Cr(IV), Cr(V) and Cr(VI) are produced. The intermediate reaction products, namely Mn(III), and Cr(V) were positively identified by XPS spectral analyses. Similarity in XPS binding energy values of Cr(III) and Cr(IV) as well as that of Cr(V) and Cr(VI), however, preclude separate identification of Cr(III) from Cr(IV) and Cr(VI) from Cr(V) multiplets on the near-surface of the solid. A parallel reaction scheme (exclusive of sorption reactions) best describes the birnessite-Cr(III)_aq redox reactions. The two parallel reactions proceed by separate mechanisms with a monodentate complex formed in one mechanism and a bidentate complex in another. The bulk of Cr(IV) probably is formed via the monodentate complex and Cr(V) via the bidentate complex. The rate expressions associated with these reactions display near-perfect correlation with changing surface abundances of Cr(IV) and Cr(V) as a function of reaction time. Copyright © 1999 Elsevier Science Ltd.  相似文献   

Oxidative Ce3+ sequestration by fungal manganese oxides with an associated Mn(II) oxidase activity     

《Applied Geochemistry》2016

Sequestration of Ce³⁺ by biogenic manganese oxides (BMOs) formed by a Mn(II)-oxidizing fungus, Acremonium strictum strain KR21-2, was examined at pH 6.0. In anaerobic Ce³⁺ solution, newly formed BMOs exhibited stoichiometric Ce³⁺ oxidation, where the molar ratio of Ce³⁺ sequestered (Ce_seq) relative to Mn²⁺ released (Mn_rel) was maintained at approximately two throughout the reaction. A similar Ce³⁺ sequestration trend was observed in anaerobic treatment of BMOs in which the associated Mn(II) oxidase was completely inactivated by heating at 85 °C for 1 h or by adding 50 mM NaN₃. Aerobic Ce³⁺ treatment of newly formed BMO (enzymatically active) resulted in excessive Ce³⁺ sequestration over Mn²⁺ release, yielding Ce_seq/Mn_rel > 200, whereas heated or poisoned BMOs released a significant amount of Mn²⁺ with lower Ce³⁺ sequestration efficiency. Consequently, self-regeneration by the Mn(II) oxidase in newly formed BMO effectively suppressed Mn²⁺ release and enhanced oxidative Ce³⁺ sequestration under aerobic conditions. Repeated treatments of heated or poisoned BMOs under aerobic conditions confirmed that oxidative Ce³⁺ sequestration continued even after most Mn oxide was released from the solid phase, indicating auto-catalytic Ce³⁺ oxidation at the solid phase produced through primary Ce³⁺ oxidation by BMO. From X-ray diffraction analysis, the resultant solid phases formed through Ce³⁺ oxidation by BMO under both aerobic and anaerobic conditions consisted of cerianite with crystal sizes of 5.00–7.23 Å. Such nano-sized CeO₂ (CeO_2,BMO) showed faster auto-catalytic Ce³⁺ oxidation than that on well-crystalized cerianite under aerobic conditions, where the normalized pseudo-first order rate constants for auto-catalytic Ce³⁺ oxidation on CeO_2,BMO was two orders of magnitude higher. Consequently, we concluded that Ce³⁺ contact with BMOs sequesters Ce³⁺ through two oxidation paths: primary Ce³⁺ oxidation by BMOs produces nano-sized crystalline cerianite, and subsequent auto-catalytic Ce³⁺ oxidation efficiently occurs using dissolved oxygen as the oxidizing agent. Pretreatment of newly formed BMOs with La³⁺ solution resulted in decreased rate constants for primary Ce³⁺ oxidation by BMO due to site blocking by La³⁺ sorption. The results presented herein increase our understanding of the role of BMO in oxidative Ce³⁺ sequestration process(es) through enzymatic and abiotic paths in natural environments and provide supporting evidence for the potential application of BMOs towards the recovery of Ce³⁺ from contaminated waters.  相似文献   

The formation of todorokite and birnessite in sea water pumped from under ground     

N Takematsu  Y Sato  S Okabe 《Geochimica et cosmochimica acta》1984,48(5):1099-1106

Manganese oxides precipitated from aerated well sea water at the Marine Science Museum, Tokai University, have been analyzed chemically and mineralogically. The $\text{O}\text{Mn}$ ratios are lower in todorokite than in birnessite but these minerals have similar contents of minor transition metals, which can be taken up additionally from sea water after the precipitation of Mn oxides. On the basis of these results, the genesis of Mn minerals is discussed in relation to marine Mn nodules.  相似文献   

Reaction of Mn (hydr)oxides with oxalic acid, glyoxylic acid, phosphonoformic acid, and structurally-related organic compounds     

Yun Wang  Alan T. Stone 《Geochimica et cosmochimica acta》2006,70(17):4477-4490

Phosphonoformic acid, oxalic acid, glyoxylic acid, and 10 additional organic compounds that are structurally related to them have been reacted with synthetic MnO₂ (birnessite), consisting of 22% Mn^III and 78% Mn^IV, and synthetic MnOOH (manganite), consisting solely of Mn^III. Significant concentrations of dissolved Mn^III were detected in reactions of phosphonoformic acid with MnOOH, indicating that ligand-assisted dissolution took place. Reaction of phosphonoformic acid with MnO₂, and reaction of all other organic reactants with either MnOOH or MnO₂, yielded only Mn^II, indicating that reductive dissolution was predominant. As far as reductive dissolution reactions are concerned, MnO₂ yields a range of reactivity that is nearly 20-times greater than that of MnOOH. Oxidation converts phosphonoformic acid into orthophosphate ion, glyoxylic acid into formic acid, pyruvic acid into acetic acid, and 2,3-butanedione into acetic acid. When differences in surface area loading are accounted for, oxalic acid, pyruvic acid, and 2,3-butanedione yield virtually the same dissolution rates for the two (hydr)oxides. At pH 5.0, glyoxylic acid reacts 14-times faster with MnO₂ than with MnOOH. MnO₂ reacts more slowly than MnOOH by a factor of 1/16th with oxamic acid, 1/20th with lactic acid, and 1/33rd with dimethyl oxalate. Adsorptive, complexant, and reductant properties of the 13 organic reactants are believed responsible for the observed reactivity differences.  相似文献   

Titan-aegirine from early Tertiary ash layers in northern Denmark     

J.G Rønsbo  A.K Pedersen  J Engell 《Lithos》1977,10(3):193-204

Microprobe analyses on a xenocrystic suite of salites, aegirine-augites, aegirines, titan-aegirines and acmites from a lower Tertiary ash layer in northern Denmark are presented. The sodic pyroxenes show an unusual titan-enrichment and up to 42 mol.% of the component $\text{NaTi}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{4+}}\text{M}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{2+}}\text{Si}{}_3\text{O}{}_6\text{(}\text{M = Fe}{}^{\mathrm{2+}}\text{,}\text{Mn or Mg}\text{)}$, is estimated. Optical absorption measurements show no evidence for Ti³⁺. The titan-aegirines were formed during late to post-magmatic crystallization in a system with a high Ti⁴⁺/Fe²⁺ ratio and were followed by acmite showing enrichment in jadeite. Comparison with experimentally investigated titan-aegirine indicates crystallization far below the Mn₂O₃Mn₃O₄f₀₂ buffer.  相似文献   

Thermodynamic stability of CoOOH and its coprecipitation with manganese     

John D. Hem  Charles E. Roberson  Carol J. Lind 《Geochimica et cosmochimica acta》1985,49(3):801-810

A precipitate of cobalt oxyhydroxides formed by bubbling oxygen through a dilute solution of Co(NO₃)₂ held at pH 9.0 and 25°C was aged for 23 months in contact with the original solution, with access to atmospheric oxygen. Co₃O₄ and CoOOH were identified in the precipitate by X-ray diffraction. Chemical equilibria involving these solids were evaluated by measurements of solution pH and Co²⁺ activities and by redox potential measurements and gave a $\text{ΔG}{}_{\mathrm{coOOH}}{}^0$ of $\text{?92.3 ± 0.5 kcal/mole}$. This value and other thermodynamic data show relative feasibility of hypothetical reaction steps and changes in reaction paths during automated coprecipitation titrations and subsequent aging of a precipitate that finally contained βMnOOH, MnO₂ (birnessite) and CoOOH.  相似文献   

Oxidative removal of Mn(II) from solution catalysed by the γ-FeOOH (lepidocrocite) surface     

Windsor Sung  James J. Morgan 《Geochimica et cosmochimica acta》1981,45(12):2377-2383

A laboratory study was undertaken to ascertain the role of surface catalysis in Mn(II) oxidative removal. γ-FeOOH, a ferric oxyhydroxide formed by O₂ oxidation of ferrous iron in solution, was studied in the following ways: surface charge characteristics by acid base titration, adsorption of Mn(II) and surface oxidation of Mn(II). A rate law was formulated to account for the effects of pH and the amount of surface on the surface oxidation rate of Mn(II). The presence of milli-molar levels of γ-FeOOH was shown to reduce significantly the half-life of Mn(II) in 0.7 M NaCl from hundreds of hours to hours. The numerical values of the surface rate constants for the γ-FeOOH and that reported for colloidal MnO₂ are comparable in order of magnitude.  相似文献   

Experimental Study of Gold and Platinum Solubility in a Complex Fluid under Hydrothermal Conditions   总被引：2，自引：0，他引：2  

G. G. LIKHOIDOV  L. P. PLYUSNINA  J. A. SCHEKA  T. B. APHANAS EVA 《Resource Geology》2000,50(2):83-92

Abstract: The solubility of gold was studied in water and aqueous NaCl (1– 5 m) solutions under oxygen and sulfur buffered conditions between 300–500C at a constant pressure 1 kb. Two buffer assemblages HMP and PPM were used. Analysis of the scatter in measured values in log m_Au–m_NaCl–T frame fixed linear dependence between log m_Au and T at any studied iso‐pleth (m_NaCl) in the form of log m_Au = a. T(C) + b. Coefficients of the equation were calculated for water and NaCl (1, 3, 5 m) solutions. The maximum solubility characterizes the NaCl‐free system in the presence of HMP. In the case, Au solubility increases from (log m_Au) –6. 72 to –5. 04 at 300 and 500C, respectively. In the presence of PPM, maximum of Au solubility was obtained for the 5 mNaCl solution. In a similar manner solubility rises from –6. 54 to –5. 77 at 300 and 500C, accordingly. In studied f_O2/f_S2 area the behavior of Au solubility testified that: (i) – a composite interaction between chloride and hydrosulfide speciation of gold affects its total solubility; (ii) – in addition of NaCl up to about 1. 5 m the solubility decreases, more pronounced in the presence of HMP; (iii) – the contribution of chloride in total Au solubility is more for PPM despite of lower f_O2value, than for HMP. The solubility of platinum was studied in the Pt–Cl–S–H₂O system between 300 and 500C, 1 kb. PPM solid buffer controlled oxidation state, pH and sulfur activity of solutions (H₂O, 1 mNaCl and 0. 1 mHCl). Under the conditions, PtS precipitated from the solutions with increasing temperature and acidity. The PtS solubility in the 0. 1 m_HCl solutions lowers slightly in the range of 300–500C from –5. 30 to –5. 60 (in log m_Pt) that is typical to the hydrosulfide species. It was deduced that reducing media, regulated by the PPM assemblage, suppress activity of chloride species of Pt. More oxidizing conditions were modeled in runs using mixtures of Mn(II), Mn(III) and Mn(IV) oxides to buffer the aqueous‐chloride solutions between 300 and 500C, 1 kb. It was found that MnO tends to oxidize at T below 400C forming intermediate Mn‐hydroxides (β–MnOOH, Mn (OH)₂ and Mn₂(OH)₃Cl). These phases are metastable and transfer to Mn₃O₄ with increasing duration. Generation of the Mn‐hydroxides leads to a change of physical‐chemical parameters of the solutions, such as water activity, pH and Eh. The last results in abrupt increase in the noble metals dissolution. At stable existence of only Mn₃O₄, the solubility of both Pt and Au lowers to equilibrium values. Essential catalysis effect of Pt on intensity and rate of Mn(II) oxidation was found. The dominant role of chloride of Pt and Au was defined under most oxidized conditions, specified by Mn₂O₃–MnO₂ buffer. So at 400C, dissolved Au (log m_Au) increases from –4. 40 in water to –1. 00 in 0. 1 m_HCl, and ones of Pt (log m_Pt) from –4. 80 to –2. 90 accordingly. Thus, mixing of hydrosulfide and chloride solutions, as well as transformation of the systems to the stable state act upon total solubility of the noble metals.  相似文献   

On the model of Mn,Fe, Ni,Co ore formation in recent basins: Experiments with the synthesis of Me-hydroxide phases on Mn3O4     

I. M. Varentsov  N. V. Bakova  Yu. P. Dikov  T. S. Gendler  R. Giovanoli 《Mineralium Deposita》1979,14(3):281-296

Experiments on the sorption of dissolved Ni, Co, Mn, Fe from seawater by Mn₃O₄ reveal a sequence of reactions taking place: Ion exchange, hydrolysis, then autocatalytic oxidation and layer formation on the interface. The composition of the new compounds depends on the kinetics of i) sorption, and ii) interface oxidation. The highest oxidized Me ions accumulate at low sorption rates, i. e. when sorption does not inhibit interface oxidation: 60% Mn⁴⁺, 30% Ni³⁺ & 30% Co³⁺ are a representative example for that layer type. Iron is present in this layer as amorphous FeOOH·xH₂O according to Mössbauer spectra. Specific for the Me sorption by Mn₃O₄ is the interaction of Ni & Co with Mn²⁺ and Mn³⁺ of the sorbent lattice. Mn is found in the solute phase equivalent to 16, 14% of the adsorbed Co or 17, 96% of the adsorbed Ni. These results confirm the earlier presented model on the transition metal accumulation in recent basins as taking place in distinct stages with interface autocatalysis for the Me oxidation playing the main role.  相似文献   

The oxidation of cobalt(II) adsorbed on manganese dioxide     

James W Murray  John G Dillard 《Geochimica et cosmochimica acta》1979,43(5):781-787

X-ray photoelectron spectroscopy (XPS) measurements of cobalt adsorbed on MnO₂ reveal strong evidence that Co(II) has been oxidized to Co(III). The manganese spectra are characteristic of Mn(IV). Model calculations suggest that Co(II) cannot be oxidized by O₂ to Co(III) in bulk solution at seawater concentrations but that the oxidation can proceed in the presence of the strong electric field at the MnO₂-solution interface. Ni(II), however, cannot be oxidized at the interface except at very high concentrations. These calculations suggest that the oxidation of Co(II) can explain the geochemical separation of cobalt from nickel.  相似文献   

Concentration of Mn and separation from Fe in sediments—I. Kinetics and stoichiometry of the reaction between birnessite and dissolved Fe(II) at 10°C     

Dieke Postma 《Geochimica et cosmochimica acta》1985,49(4):1023-1033

Redox reactions between Fe²⁺ in solution and Mn-oxides are proposed as a mechanism for concentration of Mn in sediments both during weathering and diagenesis in marine sediments, e.g. the formation of Mn-nodules.If such a mechanism is to be effective, then reaction rates between Fe²⁺ and Mn-oxides should be fast. The kinetics and stoichiometry of the reaction between dissolved Fe²⁺ and synthetically prepared birnessite (Mn₇O₁₃·5H₂O) were studied experimentally in the pH range 3–6.Results show a stoichiometry which at pH < 4 conforms to a simple reaction between Fe²⁺ and birnessite, releasing Mn²⁺ and Fe³⁺ to the solution. At pH > 4 FeOOH is precipitated and excess Fe²⁺ consumption compared to the theoretical stoichiometry is observed. The excess Fe²⁺ consumption is not due to a formation of a quantitative MnOOH layer but rather to adsorption.Reaction kinetics are very fast at pH < 4 and change at pH 4 to a slower mechanism. At pH > 4 the reaction is fast initially until 17% of the bimessite has dissolved and changes then to a slower stage. The later stage can be described by the equation: $\text{J = km}{}_0\text{(H}{}^{\mathrm{+}}\text{)}{}^{\mathrm{?0.45}}\text{[Fe}{}^{\mathrm{2+}}\text{]}{}^{\mathrm{\gamma }}\text{(}\text{m}\text{m}{}_0\text{)}{}^{\mathrm{\beta }}$ where J is the overall rate of Mn²⁺ release, m₀ and m the mass of birnessite at time t = 0 and t > 0, β = 6.76?0.94 pH and γ has values of 0.76 at pH 5 and 0.39 at pH 6. The rate constant k is 7.2·10^?7 moles s^?1 g^?1 (moles/1)^?0.31 at pH 5 and 9.6·10^?8 moles s^?1 g^?1 (moles/1)^0.06 at pH 6.Diffusion calculations show that the rate is controlled by surface reaction and it is tentatively proposed that the availability of vacancies in octahedral [MnO₆]sheets of the birnessite surface could be rate controlling. It is concluded that reactions between Fe(II) and birnessite, and probably other Mn-oxides, are fast enough to be important in natural environments at the earth surface.  相似文献   

Oxidation state of marine manganese nodules     

D.Z. Piper  J.R. Basler  J.L. Bischoff 《Geochimica et cosmochimica acta》1984,48(11):2347-2355

Analyses of the bulk oxidation state of marine manganese nodules indicates that more than 98% of the Mn in deep ocean nodules is present as Mn(IV). The samples were collected from three quite different areas: the hemipelagic environment of the Guatemala Basin, the pelagic area of the North Pacific, and seamounts in the central Pacific. Results of the study suggest that todorokite in marine nodules is fully oxidized and has the following stoichiometry: (K, Na, Ca, Ba)_.33(Mg, Cu, Ni)_.76Mn₅O₂₂(H₂O)_3.2.  相似文献   

Orthopyroxene-olivine assemblages in diogenites and mesosiderites     

Roger H. Hewins 《Geochimica et cosmochimica acta》1981,45(1):123-126

Diogenites contain equilibrated orthopyroxene-olivine assemblages. Mn is very regularly partitioned between olivine and orthopyroxene in pallasites, diogenites and synthetic eucrite melts, with an $\text{FeO}\text{MnO}$ partition ratio for olivine versus orthopyroxene of 1.6 by weight over a very wide range of FeO contents. In contrast to diogenites, Fe and Mn are not regularly partitioned between the olivine and orthopyroxene of mesosiderites and these minerals were not in equilibrium. Mesosiderite olivine differs from diogenite olivine in $\text{Fe}\text{Mn}$ and $\text{Ca}\text{Mn}$ ratios. Lack of olivine-orthopyroxene equilibrium suggests that olivine in mesosiderites was derived not from a pyroxenite component analogous to diogenites but from dunites.  相似文献