Oxidation of chalcopyrite by extended milling     

《International Journal of Mineral Processing》2005,77(4):208-216

Chalcopyrite has been milled for up to 50 h in oxygen, air and argon atmospheres using a laboratory ball mill. No phase changes were evident in argon but the XRD peaks were weaker and broader indicating crystalline refinement. In oxygen, even after 1 h milling peaks for CuSO₄·5H₂O were present and these became predominant after 20 h milling where the chalcopyrite peaks were absent. In air, partial oxidation to CuSO₄·5H₂O was evident after 50 h. Leaching of the resultant powders with water showed 80% dissolution after 50 h milling in oxygen, significantly greater than the 20% and 6% dissolution after milling for 50 h in air and argon respectively. Solution analyses showed the Cu/Fe ratio increased with milling time in oxygen suggesting selectivity may be possible. The insoluble residue was found to consist of haematite, elemental sulphur and unreacted chalcopyrite.  相似文献   

Dissolution of illite in saline-acidic solutions at 25 °C     

Irshad Bibi  Ewen Silvester 《Geochimica et cosmochimica acta》2011,75(11):3237-3249

The dissolution rate of illite, a common clay mineral in Australian soils, was studied in saline-acidic solutions under far from equilibrium conditions. The clay fraction of Na-saturated Silver Hill illite (K_1.38Na_0.05)(Al_2.87Mg_0.46Fe³⁺_0.39Fe²⁺_0.28Ti_0.07)[Si_7.02Al_0.98]O₂₀(OH)₄ was used for this study. The dissolution rates were measured using flow-through reactors at 25 ± 1 °C, solution pH range of 1.0-4.25 (H₂SO₄) and at two ionic strengths (0.01 and 0.25 M) maintained using NaCl solution. Illite dissolution rates were calculated from the steady state release rates of Al and Si. The dissolution stoichiometry was determined from Al/Si, K/Si, Mg/Si and Fe/Si ratios. The release rates of cations were highly incongruent during the initial stage of experiments, with a preferential release of Al and K over Si in majority of the experiments. An Al/Si ratio >1 was observed at pH 2 and 3 while a ratio close to the stoichiometric composition was observed at pH 1 and 4 at the higher ionic strength. A relatively higher K⁺ release rate was observed at I = 0.25 in 2-4 pH range than at I = 0.01, possibly due to ion exchange reaction between Na⁺ from the solution and K⁺ from interlayer sites of illite. The steady state release rates of K, Fe and Mg were higher than Si over the entire pH range investigated in the study. From the point of view of the dominant structural cations (Si and Al), stoichiometric dissolution of illite occurred at pH 1-4 in the higher ionic strength experiments and at pH ?3 for the lower ionic strength experiments. The experiment at pH 4.25 and at the lower ionic strength exhibited lower R_Al (dissolution rate calculated from steady state Al release) than R_Si (dissolution rate calculated from steady state Si release), possibly due to the adsorption of dissolved Al as the output solutions were undersaturated with respect to gibbsite. The dissolution of illite appears to proceed with the removal of interlayer K followed by the dissolution of octahedral cations (Fe, Mg and Al), the dissolution of Si is the limiting step in the illite dissolution process. A dissolution rate law showing the dependence of illite dissolution rate on proton concentration in the acid-sulfate solutions was derived from the steady state dissolution rates and can be used in predicting the impact of illite dissolution in saline acid-sulfate environments. The fractional reaction orders of 0.32 (I = 0.25) and 0.36 (I = 0.01) obtained in the study for illite dissolution are similar to the values reported for smectite. The dissolution rate of illite is mainly controlled by solution pH and no effect of ionic strength was observed on the dissolution rates.  相似文献   

Cu and Fe chalcopyrite leach activation energies and the effect of added Fe     

K. Kaplun 《Geochimica et cosmochimica acta》2011,75(20):5865-5878

The leaching kinetics of chalcopyrite (CuFeS₂) concentrate in sulfuric acid leach media with and without the initial addition of Fe³⁺ under carefully controlled solution conditions (E_h 750 mV SHE, pH 1) at various temperatures from 55 to 85 °C were measured. Kinetic analyses by (i) apparent rate (not surface area normalised), and rate dependence using (ii) a shrinking core model and (iii) a shrinking core model in conjunction with Fe³⁺ activity, were performed to estimate the activation energies (E_a) for Cu and Fe dissolution.The E_a values determined for Cu and Fe leaching in the absence of added Fe³⁺ are within experimental error, 80 ± 10 kJ mol⁻¹ and 84 ± 10 kJ mol⁻¹, respectively (type iii analyses E_a are quoted unless stated otherwise), and are indicative of a chemical reaction controlled process. On addition of Fe³⁺ the initial Cu leach rate (up to 10 h) was increased and Cu was released to solution preferentially over Fe, with the E_a value of 21 ± 5 kJ mol⁻¹ (type ii analysis) suggestive of a transport controlled rate determining process. However, the rate of leaching rapidly decreased until it was consistently slower than for the equivalent leaches where Fe³⁺ was not added. The resulting E_a value for this leach regime of 83 ± 10 kJ mol⁻¹ is within experimental error of that determined in the absence of added Fe³⁺. In contrast to Cu release, Fe release to solution was consistent with a chemical reaction controlled leach rate throughout. The Fe release E_a of 76 ± 10 kJ mol⁻¹ is also within experimental error of that determined in the absence of added Fe³⁺. Where type (ii) and (iii) analyses were both successfully carried out (in all cases except for Cu leaching with added Fe³⁺, <10 h) the E_a derived are within experimental error. However, the type (iii) analyses of the leaches in the presence of added Fe³⁺ (>10 h), as compared to in the absence of added Fe³⁺, returned a considerably smaller pre-exponential factors for both Cu and Fe leach analyses commensurate with the considerably slower leach rate, suggestive of a more applicable kinetic analysis.XPS examination of leached chalcopyrite showed that the surface concentration of polysulfide and sulfate was significantly increased when Fe³⁺ was added to the leach liquor. Complementary SEM analysis revealed the surface features of chalcopyrite, most likely due to the nature of the polysulfide formed, are subtly different with greater surface roughness upon leaching in the absence of added Fe³⁺ as compared to a continuous smooth surface layer formed in the presence of added Fe³⁺. These observations suggest that the effect of Fe³⁺ addition on the rate of leaching is not due to the change in the chemical reaction controlled mechanism but due to a change in the available surface area for reaction.  相似文献   

Copper isotope fractionation in acid mine drainage   总被引：4，自引：0，他引：4  

B.E. Kimball  R. Mathur  A.J. Wall  S.L. Brantley 《Geochimica et cosmochimica acta》2009,73(5):1247-1263

We measured the Cu isotopic composition of primary minerals and stream water affected by acid mine drainage in a mineralized watershed (Colorado, USA). The δ⁶⁵Cu values (based on ⁶⁵Cu/⁶³Cu) of enargite (δ⁶⁵Cu = −0.01 ± 0.10‰; 2σ) and chalcopyrite (δ⁶⁵Cu = 0.16 ± 0.10‰) are within the range of reported values for terrestrial primary Cu sulfides (−1‰ < δ⁶⁵Cu < 1‰). These mineral samples show lower δ⁶⁵Cu values than stream waters (1.38‰ ? δ⁶⁵Cu ? 1.69‰). The average isotopic fractionation (Δ_aq-min = δ⁶⁵Cu_aq − δ⁶⁵Cu_min, where the latter is measured on mineral samples from the field system), equals 1.43 ± 0.14‰ and 1.60 ± 0.14‰ for chalcopyrite and enargite, respectively. To interpret this field survey, we leached chalcopyrite and enargite in batch experiments and found that, as in the field, the leachate is enriched in ⁶⁵Cu relative to chalcopyrite (1.37 ± 0.14‰) and enargite (0.98 ± 0.14‰) when microorganisms are absent. Leaching of minerals in the presence of Acidithiobacillus ferrooxidans results in smaller average fractionation in the opposite direction for chalcopyrite (Δ_aq-min^o=-0.57±0.14‰, where min^o refers to the starting mineral) and no apparent fractionation for enargite (Δ_aq-min^o=0.14±0.14‰). Abiotic fractionation is attributed to preferential oxidation of ⁶⁵Cu⁺ at the interface of the isotopically homogeneous mineral and the surface oxidized layer, followed by solubilization. When microorganisms are present, the abiotic fractionation is most likely not seen due to preferential association of ⁶⁵Cu_aq with A. ferrooxidans cells and related precipitates. In the biotic experiments, Cu was observed under TEM to occur in precipitates around bacteria and in intracellular polyphosphate granules. Thus, the values of δ⁶⁵Cu in the field and laboratory systems are presumably determined by the balance of Cu released abiotically and Cu that interacts with cells and related precipitates. Such isotopic signatures resulting from Cu sulfide dissolution should be useful for acid mine drainage remediation and ore prospecting purposes.  相似文献   

Role of molecular oxygen in the dissolution of siderite and rhodochrosite     

Owen W Duckworth 《Geochimica et cosmochimica acta》2004,68(3):607-621

The dissolution of siderite (FeCO₃) and rhodochrosite (MnCO₃) under oxic and anoxic conditions is investigated at 298 K. The anoxic dissolution rate of siderite is 10^−8.65 mol m⁻² s⁻¹ for 5.5 < pH < 12 and increases as [H⁺]^0.75 for pH < 5.5. The pH dependence is consistent with parallel proton-promoted and water hydrolysis dissolution pathways. Atomic force microscopy (AFM) reveals a change in pit morphology from rhombohedral pits for pH > 4 to pits elongated at one vertex for pH < 4. Under oxic conditions the dissolution rate decreases to below the detection limit of 10⁻¹⁰ mol m⁻² s⁻¹ for 6.0 < pH < 10.3, and hillock precipitation preferential to steps is observed in concurrent AFM micrographs. X-ray photoelectron spectroscopy (XPS) and thermodynamic analysis identify the precipitate as ferrihydrite. At pH > 10.3, the oxic dissolution rate is as high as 10^−7.5 mol m⁻² s⁻¹, which is greater than under the corresponding anoxic conditions. A fast electron transfer reaction between solution O₂ or [Fe³⁺(OH)₄]⁻ species and surficial >Fe^II hydroxyl groups is hypothesized to explain the dissolution kinetics. AFM micrographs do not show precipitation under these conditions. Anoxic dissolution of rhodochrosite is physically observed as rhombohedral pit expansion for 3.7 < pH < 10.3 and is chemically explained by parallel proton- and water-promoted pathways. The dissolution rate law is 10^−4.93[H⁺] + 10^−8.45 mol m⁻² s⁻¹. For 5.8 < pH < 7.7 under oxic conditions, the AFM micrographs show a tabular precipitate growing by preferential expansion along the a-axis, though the macroscopic dissolution rate is apparently unaffected. For pH > 7.7 under oxic conditions, the dissolution rate decreases from 10^−8.45 to 10^−9.0 mol m⁻² s⁻¹. Flattened hillock precipitates grow across the entire surface without apparent morphological influence by the underlying rhodochrosite surface. XPS spectra and thermodynamic calculations implicate the precipitate as bixbyite for 5.8 < pH < 7.7 and MnOOH (possibly feitnkechtite) for pH >7.7.  相似文献   

Kinetics of biotite dissolution and Fe behavior under low O₂ conditions and their implications for Precambrian weathering     

Hirokazu Sugimori  Takashi Murakami 《Geochimica et cosmochimica acta》2009,73(13):3767-3781

Biotite dissolution experiments were carried out to better understand the dissolution kinetics and Fe behavior under low O₂ conditions, and to give an insight into the Precambrian weathering. Mineral dissolution with a continuous flow-through reactor was employed at 25 °C for up to 65 days varying partial pressure of atmospheric oxygen (PO₂), pH (6.86 and 3.01) and Fe content in mineral (1.06 and 0.11 mol of Fe per O₁₀(OH,F)₂ for biotite and phlogopite, respectively) independently for the examination of their effects on biotite dissolution. Low PO₂ conditions were achieved in a newly developed glove box (PO₂ ? 6 × 10⁻⁴ atm; referred to as anoxic conditions), which was compared to the present, ambient air conditions (0.2 atm of PO₂; oxic conditions). The biotite dissolution rate was slightly faster under anoxic conditions at pH 6.86 while it was not affected by PO₂ at pH 3.01. There was no direct effect of Fe content on dissolution rate at pH 6.86 while there was a small difference in dissolution rate between biotite and phlogopite at pH 3.01. The 1.5 order-of-magnitude faster release rate of Fe under anoxic conditions for biotite dissolution at pH 6.86 resulted from the difference in ratio of Fe³⁺ precipitates remaining in the reactor to Fe dissolved (about 60% and 100% under anoxic and oxic conditions, respectively), which is caused mainly by the difference in PO₂. The results infer that the Fe²⁺ and Fe³⁺ contents in the Paleoproterozoic paleosols, fossil weathering profiles, are reflected by atmospheric oxygen levels at the time of weathering.  相似文献   

The oxidation states of copper and iron in mineral sulfides, and the oxides formed on initial exposure of chalcopyrite and bornite to air     

Siew Wei Goh  Robert N. Lamb  Damian Moran 《Geochimica et cosmochimica acta》2006,70(9):2210-2228

Metal L_2,3, sulfur K and oxygen K near-edge X-ray absorption fine structure (NEXAFS) spectra for chalcopyrite, bornite, chalcocite, covellite, pyrrhotite and pyrite have been determined from single-piece natural mineral specimens in order to assess claims that chalcopyrite should be regarded as Cu^IIFe^IIS₂ rather than Cu^IFe^IIIS₂, and that copper oxide species are the principal initial oxidation products on chalcopyrite and bornite exposed to air. Spectra were obtained using both fluorescence and electron yields to obtain information representative of the bulk as well as the surface. Where appropriate, NEXAFS spectra have been interpreted by comparison with the densities of unfilled states and simulated spectra derived from ab initio calculations using primarily the FEFF8 code and to a lesser extent WIEN2k. Metal 2p and S 2p photoelectron spectra excited by monochromatised Al K_α X-rays were determined for each of the surfaces characterised by NEXAFS spectroscopy. The X-ray excited Cu LMM Auger spectrum was also determined for each copper-containing sulfide. FEFF8 calculations were able to simulate the experimental NEXAFS spectra quite well in most cases. For covellite and chalcocite, it was found that FEFF8 did not provide a good simulation of the Cu L₃-edge spectra, but WIEN2k simulations were in close agreement with the experimental spectra. Largely on the basis of these simulations, it was concluded that there was no convincing evidence for chalcopyrite to be represented as Cu^IIFe^IIS₂, and no strong argument for some of the Cu in either bornite or covellite to be regarded as Cu(II). The ab initio calculations for chalcopyrite and bornite indicated that the density of Cu d-states immediately above the Fermi level was sufficient to account for the Cu L₃-edge absorption spectrum, however these incompletely filled Cu d-states should not be interpreted as indicating some Cu(II) in the sulfide structure. It was also concluded that the X-ray absorption spectra were quite consistent with the initial oxidation products on chalcopyrite and bornite surfaces being iron oxide species, and inconsistent with the concomitant formation of copper-oxygen species.  相似文献   

Mechanism of kaolinite dissolution at room temperature and pressure Part II: kinetic study     

《Geochimica et cosmochimica acta》1999,63(19-20):3261-3275

Studies on the dissolution kinetics of kaolinite were performed using batch reactors at 25°C and in the pH range from 1 to 13. A rapid initial dissolution step was first observed, followed by a linear kinetic stage reached after approximately 600 hr of reaction during which the kaolinite dissolves congruently at pH < 4 and pH > 11. The apparent incongruency between pH 5 and 10 was due to the precipitation of an Al–hydroxide phase. The true dissolution rates were computed from the amount of Si released into solution. The rate dependence on pH can be described by: r = 10−12.19aH+0.55 + 10−14.36 + 10−10.71aOH−0.75Between pH 5 and 10, the rate is approximately constant, although a smooth minimum was observed at pH close to 9. mAn attempt was made to obtain a general rate law based on the coordination theory, which was first applied to the mineral dissolution studies by Stumm and co-workers. The kinetic data were combined with the results obtained for the surface speciation by Huertas et al. (1998). It is possible to express the linear dissolution rate as a simple power function of the concentration of the surface sites active in various pH ranges: r = 10−8.25 [>Al2OH2+] + 10−10.82 [>AlOH2+]0.5 + 10−9.1 [>Al2OH + >AlOH + >SiOH] + 103.78 [>Al2O− + >AlO−]3This equation assumes that the dissolution mechanism is mainly controlled by the two Al surface sites (external and internal structural hydroxyls, and aluminol at the crystal edges) under both acidic and alkaline conditions. The model reflects well the important contribution of the crystal basal planes to the dissolution of kaolinite.  相似文献   

Connections between surface complexation and geometric models of mineral dissolution investigated for rhodochrosite     

Owen W Duckworth 《Geochimica et cosmochimica acta》2003,67(10):1787-1801

Mineral dissolution rates have been rationalized in the literature by surface complexation models (SCM) and morphological and geometric models (GM), and reconciliation of these conceptually different yet separately highly successful models is an important goal. In the current work, morphological alterations of the surface are observed in real time at the microscopic level by atomic force microscopy (AFM) while dissolution rates are simultaneously measured at the macroscopic level by utilizing the AFM fluid cell as a classic flow-through reactor. Rhodochrosite dissolution is studied from pH = 2 to 11 at 298 K, and quantitative agreement is found between the dissolution rates determined from microscopic and macroscopic observations. Application of a SCM model for the interpretation of the kinetic data indicates that the surface concentration of >CO₃H regulates dissolution for pH < 7 while the surface concentration of >MnOH₂⁺ regulates dissolution for pH > 7. A GM model explains well the microscopic observations, from which it is apparent that dissolution occurs at steps associated with anisotropic pit expansion. On the basis of the observations, we combine the SCM and GM models to propose a step-site surface complexation model (SSCM), in which the dissolution rates are quantitatively related to the surface chemical speciation of steps. The governing SSCM equation is as follows: R = χ_1/2(k_co + k_ca)[>CO₃H] + χ_1/2(k_mo + k_ma)[>MnOH₂⁺ ], where R is the dissolution rate (mol m⁻² s⁻¹), 2χ_1/2 is the fraction of surface sites located at steps, [>CO₃H] and [>MnOH₂⁺ ] are surface concentrations (mol m⁻²), and k_co, k_ca, k_mo, and k_ma are the respective dissolution rate coefficients (s⁻¹) for the >CO₃H and the >MnOH₂⁺ surface species on obtuse and acute steps. We find k_co = 2.7 s⁻¹, k_ca = 2.1 × 10⁻¹ s⁻¹, k_mo = 4.1 × 10⁻² s⁻¹, k_ma = 3.7 × 10⁻² s⁻¹, and χ_1/2 = 0.015 ± 0.005. The rate coefficients quantify the net result of complex surface step processes, including double-kink initiation and single-kink propagation. We propose that the SSCM model may have general applicability for dissolution far from equilibrium of flat mineral surfaces of ionic crystals, at least those that dissolve by step retreat.  相似文献   

Equilibrium and kinetic aspects of soddyite dissolution and secondary phase precipitation in aqueous suspension     

Daniel E. Giammar  Janet G. Hering 《Geochimica et cosmochimica acta》2002,66(18):3235-3245

The dissolution and transformation of soddyite ([UO₂]₂SiO₄ · 2H₂O) have been examined in aqueous suspension at pH 6 and 0.01 M NaNO₃. Soddyite is an important component of the paragenetic sequence of secondary minerals that arises from the weathering of uraninite ore deposits and corrosion of spent nuclear fuel. A soddyite of high purity and crystallinity was synthesized in the laboratory for use in dissolution experiments. In batch experiments, rapid dissolution occurred over an initial period of several hours followed by continuing steady-state dissolution for up to 700 h. Up to 200 h, U and Si were released into solution at their stoichiometric 2:1 ratio in soddyite. A decrease in the dissolved U concentration was observed at longer times, indicating the precipitation of a new phase. Even after precipitation of the secondary phase, the continuing dissolution of soddyite could be inferred from increasing dissolved Si concentrations. Through the use of X-ray diffraction, Raman spectroscopy, and scanning electron microscopy, the precipitated phase was identified as a clarkeite-like sodium uranyl oxide hydrate. The sodium uranyl oxide hydrate was ultimately the solubility-controlling solid, despite being only a minor component. Soddyite dissolution rates were quantified in flow-through experiments, in which reaction products were flushed from the reactors, thereby avoiding reprecipitation of U. The measured dissolution rate at pH 6 was 0.71 μmol U m⁻² h⁻¹. A slower dissolution rate of 0.44 μmol U m⁻² h⁻¹ was observed when 100 μM dissolved Si was added to the reactor influent.  相似文献   

Magnesia mixture as a regulator in the separation of pyrite from chalcopyrite and arsenopyrite     

A.M. Abeidu  A.M. Almahdy 《International Journal of Mineral Processing》1980,6(4):285-302

The aim of this paper is to find an effective method for the separation of the undesirable constituents, namely, chalcopyrite and arsenopyrite from pyrite used for the production of H₂SO₄. A new effective method is developed for co-depressing chalcopyrite with arsenopyrite by AsI₃, followed by the addition of magnesia mixture. This method has been shown to be based on the fact that iron sites exist in the three minerals, whereas copper and arsenic sites exist only in chalcopyrite and arsenopyrite, respectively. This is coupled with the ability of both Cu(I) and Cu(II) to precipitate As(III) in the form of insoluble copper arsenides, namely Cu₃As, Cu₃As₂. In contrast, neither Fe(II) nor Fe(III) form stable arsenides. Consequently, As³⁺ ions are selectively adsorbed onto the surface of chalcopyrite. The facility for oxidizability of As(III) is well known and hence it adsorbs oxygen from the pulp and changes to As(V) of higher valency and smaller size, with ionic potential over 10. Accordingly, it yields a stable complex anion with covalent bonding, namely, [AsO₄]^3?. These newly created arsenate sites on the surface of chalcopyrite, as well as the corresponding original arsenate sites on the surface of arsenopyrite combine with magnesia mixture to form cations leading to the formation of tightly abutting strongly hydrophilic layers of … AsO₄NH₄Mg.6H₂O. The spread of this hydrophilic film on arsenopyrite and chalcopyrite surfaces leads to the screening of their surfaces, making them difficult of access for the collector, ethyl xanthate. Since the pK_a of xanthic acid occurs at pH below 3, xanthate species predominate at pH above 8 and are adsorbed selectively on the pyrite surface in sufficient quantity for its selective flotation and hence for its separation to take place in the pH range 8–9.  相似文献   

Far from equilibrium enstatite dissolution rates in alkaline solutions at earth surface conditions     

Sougata Halder  John V. Walther 《Geochimica et cosmochimica acta》2011,75(23):7486-7493

Far from equilibrium enstatite dissolution rates both open to atmospheric CO₂ and CO₂ purged were measured as a function of solution pH from 8 to 13 in batch reactors at room temperature. Congruent dissolution was observed after an initial period of incongruent dissolution with preferential Si release from the enstatite. Steady-state dissolution rates in open to atmospheric CO₂ conditions decrease with increase in solution pH from 8 to 12 similar to the behavior reported by other investigators. Judging from the pH 13 dissolution rate, rates increase with pH above pH 12. This is thought to occur because of the increase in overall negative surface charges on enstatite as Mg surface sites become negative above pH 12.4, the pH of zero surface charge of MgO.Steady-state dissolution rates of enstatite increase above pH 10 when CO₂ was purged by performing the experiments in a N₂ atmosphere. This suggests inhibition of dissolution rates above pH 10 when experiments were open to the atmosphere. The dissolved carbonate in these solutions becomes dominantly CO₃²⁻ above pH 10.33. It is argued that CO₃²⁻ forms a >Mg₂-CO₃ complex at positively charged Mg surface sites on enstatite, resulting in stabilization of the surface Si-O bonds. Therefore, removal of solution carbonate results in an increase in dissolution rates of enstatite above pH 10. The log rate of CO₂-purged enstatite dissolution in moles per cm² per s as a function of increasing pH above pH 10 is equal to 0.35. This is consistent with the model of silicate mineral dissolution in the absence of surface carbonation in alkaline solutions proposed earlier in the literature.  相似文献   

Fractionation of sulfur isotopes and selenium between coexisting sulfide minerals from the Besshi deposit,Central Shikoku,Japan     

M. Yamamoto  K. Kase  M. Tsutsumi 《Mineralium Deposita》1984,19(3):237-242

Fractionation of sulfur isotopes and selenium was measured between coexisting pyrite and chalcopyrite and between coexisting pyrrhotite and chalcopyrite from the Besshi deposit of Kieslager-type, Central Shikoku, Japan. In all the pyrite-chalcopyrite pairs studied, ³⁴S is enriched in pyrite relative to chalcopyrite, while selenium is enriched conversely in chalcopyrite relative to pyrite. The mean ³⁴S_py-cp value is +0.53±0.36 per mil, and the mean value of the distribution coefficient of selenium, D_cp-py, is 2.58±0.64. In all the pyrrhotite-chalcopyrite pairs studied, the two minerals are very close to each other both in sulfur isotope and Se/S ratios. The mean ³⁴S_po-cp value is –0.08±0.16 per mil and the mean D_cp-po value is 0.99±0.05. The results have been discussed in comparison with similar data obtained for the Hitachi deposits of Kieslager-type, Japan (Yamamoto et al. 1983).  相似文献   

Calcite dissolution driven by benthic mineralization in the deep-sea: in situ measurements of Ca2+, pH,pCO2 and O2     

《Geochimica et cosmochimica acta》2001,65(16):2677-2690

In situ measured microprofiles of Ca²⁺, pCO₂, pH and O₂ were performed to quantify the CaCO₃ dissolution and organic matter mineralization in marine sediments in the eastern South Atlantic. A numerical model simulating the organic matter decay with oxygen was used to estimate the calcite dissolution rate. From the oxygen microprofiles measured at four stations along a 1300-m isobath of the eastern African margin and one in front of the river Niger at a water depth of 2200 m the diffusive oxygen uptake (DOU) and oxygen penetration depth (OPD) was calculated. DOU rates were in the range of 0.3 to 3 mmol m⁻² d⁻¹ and showed a decrease with increasing water depth, corresponding to an increase in OPD. The calculated amount of degradated organic matter is in the range of 1 to 8.5 gC m⁻² a⁻¹. The metabolic CO₂, released from mineralization of the organic matter drives calcite dissolution in these sediments overlain by calcite-supersaturated water. Fluxes across the sediment water interface calculated from the in situ Ca²⁺ microprofiles were 0.6 mmol m⁻² d⁻¹ for two stations at a water depth of 1300 m. The ratio of calcite dissolution flux and organic C degradation is 0.53 and 0.97, respectively. The microprofiles indicate that CO₂ produced within the upper oxic sediment layer dissolves up to 85% of the calcite rain to the seafloor. Modeling our O₂, pH and Ca²⁺ profiles from one station predicted a calcite dissolution rate constant for this calcite-poor site of 1000 mol kgw⁻¹ a⁻¹ (mol per kg water and year), which equals 95% d⁻¹. This rate constant is at the upper end of reported in situ values.  相似文献   

Rates of silicate dissolution in deep-sea sediment: In situ measurement using U/U of pore fluids     

Katharine Maher  Donald J. DePaolo  Jo Chiu-Fang Lin 《Geochimica et cosmochimica acta》2004,68(22):4629-4648

Bulk dissolution rates for sediment from ODP Site 984A in the North Atlantic are determined using the ²³⁴U/²³⁸U activity ratios of pore water, bulk sediment, and leachates. Site 984A is one of only several sites where closely spaced pore water samples were obtained from the upper 60 meters of the core; the sedimentation rate is high (11-15 cm/ka), hence the sediments in the upper 60 meters are less than 500 ka old. The sediment is clayey silt and composed mostly of detritus derived from Iceland with a significant component of biogenic carbonate (up to 30%).The pore water ²³⁴U/²³⁸U activity ratios are higher than seawater values, in the range of 1.2 to 1.6, while the bulk sediment ²³⁴U/²³⁸U activity ratios are close to 1.0. The ²³⁴U/²³⁸U of the pore water reflects a balance between the mineral dissolution rate and the supply rate of excess ²³⁴U to the pore fluid by α-recoil injection of ²³⁴Th. The fraction of ²³⁸U decays that result in α-recoil injection of ²³⁴U to pore fluid is estimated to be 0.10 to 0.20 based on the ²³⁴U/²³⁸U of insoluble residue fractions. The calculated bulk dissolution rates, in units of g/g/yr are in the range of 4 × 10⁻⁷ to 2 × 10⁻⁶ yr⁻¹. There is significant down-hole variability in pore water ²³⁴U/²³⁸U activity ratios (and hence dissolution rates) on a scale of ca. 10 m. The inferred bulk dissolution rate constants are 100 to 10⁴ times slower than laboratory-determined rates, 100 times faster than rates inferred for older sediments based on Sr isotopes, and similar to weathering rates determined for terrestrial soils of similar age. The results of this study suggest that U isotopes can be used to measure in situ dissolution rates in fine-grained clastic materials.The rate estimates for sediments from ODP Site 984 confirm the strong dependence of reactivity on the age of the solid material: the bulk dissolution rate (R_d) of soils and deep-sea sediments can be approximately described by the expression R_d ≈ 0.1 Age⁻¹ for ages spanning 1000 to 5 × 10⁸ yr. The age of the material, which encompasses the grain size, surface area, and other chemical factors that contribute to the rate of dissolution, appears to be a much stronger determinant of dissolution rate than any single physical or chemical property of the system.  相似文献   

CO<Subscript>2</Subscript>-rich fluid inclusions with chalcopyrite daughter mineral from the Fenghuangshan Cu–Fe–Au deposit,China: implications for metal transport in vapor     

Jianqing Lai  Guoxiang Chi 《Mineralium Deposita》2007,42(3):293-299

CO₂-rich fluid inclusions containing opaque mineral crystals were found in the Fenghuangshan skarn-porphyry Cu–Fe–Au deposit in Tongling, Anhui, China. These inclusions show variable CO₂ contents and are accompanied by aqueous inclusions, both occurring as secondary inclusions in quartz and being locally associated with chalcopyrite mineralization. Laser Raman microspectroscopic analyses confirm the predominance of CO₂ in the vapor and the presence of H₂S as high as 8 mol%, and identify the opaque mineral with yellow reflectance color in the inclusions as chalcopyrite. More than half of the CO₂-bearing inclusions contains chalcopyrite, whereas few of the associated aqueous inclusions do so. The chalcopyrite, occupying less than 1% (volume) of the inclusions, is interpreted to be a daughter mineral, and calculated Cu concentrations in the inclusions range from 0.1 to 3.4 wt%. Copper is inferred to have been transported in CO₂-dominated fluids as HS⁻ complexes. The occurrence of chalcopyrite daughter crystals in CO₂-rich fluid inclusions indicates that CO₂-rich vapor has the capacity of transporting large amounts of Cu, and possibly Au. This finding has significant implications for metal transport and mineralization in hydrothermal systems enriched in CO₂, such as orogenic-type and granitic intrusion-related gold deposits.  相似文献   

An experimental study of the dissolution rates of simulated aluminoborosilicate waste glasses as a function of pH and temperature under dilute conditions     

Eric M. Pierce  Elsa A. Rodriguez  L.J. Calligan  Wendy J. Shaw  B. Pete McGrail 《Applied Geochemistry》2008

  相似文献