首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 62 毫秒
1.
《Chemical Geology》2006,225(3-4):256-265
SeO42− ions can substitute for sulphate in the gypsum structure. In this work crystals of different Ca(SO4,SeO4)·2H2O solid solutions were precipitated by mixing a CaCl2 solution with solutions containing different ratios of Na2SO4 and Na2SeO4. The compositions of the precipitates were analysed by EDS and the cell parameters were determined by X-ray powder diffraction. Moreover, a comparative study on dehydration behaviour of selenate rich and sulfate rich Ca(SO4,SeO4)·2H2O solid solutions was carried out by thermogravimetry.The experimental results show that the Ca(SO4,SeO4)·2H2O solid solution presents a symmetric miscibility gap for compositions ranging from XCaSO4·2H2O = 0.23 to XCaSO4·2H2O = 0.77. By considering a regular solution model a Guggenheim parameter a0 = 2.238 was calculated. The solid phase activity coefficients obtained with this parameter were used to calculate a Lippmann diagram for the system Ca(SO4,SeO4)·2H2O–H2O.  相似文献   

2.
《Applied Geochemistry》2001,16(7-8):947-961
During dry season baseflow conditions approximately 20% of the flow in Boulder Creek is comprised of acidic metals-bearing groundwater. Significant amounts of efflorescent salts accumulate around intermittent seeps and surface streams as a result of evaporation of acid rock drainage. Those salts include the Fe-sulfates — rhomboclase ((H3O)Fe3+(SO4)2·3H2O), ferricopiapite (Fe3+5(SO4)6O(OH)·20H2O), and bilinite (Fe2+Fe23+(SO4)4·22H2O); Al-sulfates — alunogen (Al2(SO4)3·17H2O) and kalinite (KAl(SO4)2·11H2O); and Ca- and Mg-sulfates — gypsum (CaSO4·2H2O), and hexahydrite (MgSO4·6H2O). The dissolution of evaporative sulfate salt accumulations during the first major storm of the wet season at Iron Mountain produces a characteristic hydrogeochemical response (so-called “rinse-out”) in surface waters that is subdued in later storms. Geochemical modeling shows that the solutes from relatively minor amounts of dissolved sulfate salts will maintain the pH of surface streams near 3.0 during a rainstorm. On a weight basis, Fe-sulfate salts are capable of producing more acidity than Al- or Mg-sulfate salts. The primary mechanism for the production of acidity from salts involves the hydrolysis of the dissolved dissolved metals, especially Fe3+. In addition to the lowering of pH values and providing dissolved Fe and Al to surface streams, the soluble salts appear to be a significant source of dissolved Cu, Zn, and other metals during the first significant storm of the season.  相似文献   

3.
The crystal structure of a new compound, (H3O)[(UO2)(SeO4)(SeO2OH)] (monoclinic, P21/n, a = 8.6682(19), b = 10.6545(16), c = 9.846(2) Å, β = 97.881(17)°, V = 900.7(3) Å3), was solved by direct methods and refined to R 1 = 0.050. The structure contains two symmetrically different Se atoms. The Se1 site is coordinated by three O atoms as is characteristic of Se4+ cations. The Se2 site is coordinated by four O atoms and forms selenate anion SeO 4 2? . The structure is based on selenite-selenate sheets [(UO2)(SeO4)(SeO2OH)]? linked by the interlayer H3O? ions. The sheets are parallel to (101). The structure is compared to that of schmiederite, Pb2Cu2(SeO3)(SeO4)(OH)4.  相似文献   

4.
The aim of this study is the synthesis of CuSeO3·2H2O (chalcomenite analog), ZnSeO3·2H2O, and ZnSeO3·H2O and the investigation of their solubility in water. CuSeO3·2H2O has been synthesized from solutions of Cu nitrate and Na selenite, while Zn selenites were synthesized from solutions of Zn nitrate and Na selenite. The samples obtained have been examined with X-ray diffraction and infrared and Raman spectroscopy. The solubility has been determined using the isothermal saturation method in ampoules at 25°C. The solubility has been calculated using the Geochemist’s Workbench (GMB 9.0) software package. Solubility products have been calculated for CuSeO3·2H2O (10–10.63), ZnSeO3·2H2O (10–8.35), and ZnSeO3·H2O (10–7.96). The database used comprises thermodynamic characteristics of 46 elements, 47 base particles, 48 redox pairs, 551 particles in solution, and 624 solid phases. The Eh–pH diagrams of the Zn–Se–H2O and Cu–Se–H2O systems were plotted for the average contents of these elements in underground water in oxidation zones of sulfide deposits.  相似文献   

5.
 Selenium (Se), an animal toxicant and aquifer contaminant, occurs in coal mine environments of Wyoming. There is a paucity of information on solution-phase Se speciation in mine soils. The objectives of this study were to compare Se extraction efficiencies of various reagents and to characterize SeO2– 3 (selenite), SeO2– 4 (selenate) and organic Se components in these extracts. Forty coal mine soils were extracted using DI (deionized) water, hot water (0.1% CaCl2), AB-DTPA, NaOH, and KH2PO4. Each solution was analyzed for total dissolved Se, and inorganic and organic Se fractions. Both inorganic and organic Se fractions were detected in the soil extracts. The order of Se (total, inorganic, and organic) extraction efficiency for different reagents was DI water < hot water < AB-DTPA < NaOH < KH2PO4. The inorganic–organic Se ratios in DI water, hot water, AB-DTPA, NaOH, and KH2PO4 extracts were 60 : 40, 26 : 74, 61 : 39, 87 : 13, and 52 : 48, respectively, indicating predominance of inorganic Se in all but the hot water extract. Selenite was the dominant inorganic species in AB-DTPA and KH2PO4 extracts, while SeO2– 4 was the major Se species in the DI water, hot water, and NaOH extracts. Significant correlations (P<0.01) were observed among extractable inorganic Se [NaOH and KH2PO4 (r=0.95); hot water and AB-DTPA (r=0.89)], total soluble Se [DI water with hot water (r=0.98) and AB-DTPA (r=0.95)], and Se species [SeO2– 3 in AB-DTPA with SeO2– 4 in NaOH (r=0.94) and SeO2– 3 in KH2PO4 (r=0.88)]. These correlations are indicative of Se extraction efficiency, thermodynamically predicted chemical transformations (such as oxidation of SeO2– 3 to SeO2– 4), and probable interconversions between the organic and inorganic Se fractions (r=0.70 in KH2PO4 extracts); as a whole the correlations can be used as statistical validations of possible geochemical processes. Received: 21 August 1995 · Accepted: 16 October 1995  相似文献   

6.
青海湖是我国唯一报道过的现代湖底沉积物中白云石、方解石和文石等多种碳酸盐矿物共存的高原内陆咸水湖泊。以青海湖水和除菌青海湖水作为载体,以CaCl_2和MgCl_2·6 H_2O作为反应原料,在实验室常温条件下采取控制变量法制备出不同浓度Mg~(2+)参与下的钙质沉淀物,探讨Mg~(2+)浓度对沉淀物类型的影响。仅添加CaCl_2时,青海湖水中的沉淀物主要是石膏(Ca SO_4·2 H_2O)和球霰石(CaCO_3);在添加CaCl_2的同时添加MgCl_2·6 H_2O,沉淀物的石膏消失,完全转变成碳酸盐矿物,包括方解石和球霰石;当湖水中Mg~(2+)浓度为0.62 mol/L时,球霰石消失,沉淀物变为方解石和文石;随着Mg~(2+)浓度继续升高,文石含量稳步增加,方解石含量则逐渐减少,当Mg~(2+)浓度达到1.22 mol/L或更高时,方解石全部消失,沉淀物仅剩文石。实验结果表明,青海湖水中较高浓度的SO_4~(2-)对碳酸钙晶体生长有抑制作用,而额外加入的Mg~(2+)可以解除SO_4~(2-)的抑制作用,使得Ca~(2+)与HCO_3~-和CO_3~(2-)结合形成碳酸钙。此外,碳酸钙的同质多像类型也明显受到Mg~(2+)浓度的控制,随着湖水中Mg~(2+)浓度增加,方解石、球霰石不再稳定,而文石逐渐占主导地位,当Mg/Ca值达到6.1时,反应产物中仅有文石稳定存在。  相似文献   

7.
Polarized electronic absorption spectra of the kieserite-type compounds CoSO4 · H2O and CoSeO4 · H2O have been obtained at room temperature (spectral range 35 000-5000 cm-1) and at liquid nitrogen temperature (visible spectral region), using microscope-spectrometric techniques. The spectra are interpreted and evaluated in terms of a tetragonal crystal field formalism for the d7 configuration, in regard to the pseudotetragonal elongation of the CoO4(H2O)2 octahedra, known from previous X-ray structure investigations, employing the tetragonal parameters Dq, Dt, and Ds, and the Racah parameters B and C. The observed and calculated energy levels are in good agreement for the following parameter sets: CoSO4 · H2O: Dq=826, Dt=40, Ds=350, B=856, C=3580 cm-1; CoSeO4· H2O: Dq=817, Dt=44, Ds=406, B=841, C=3490 cm-1; corresponding ‘cubic’ crystal field strengths Dqcub are 803 and 792 cm-1, respectively. The values of Dq(cub), Racah B and C are in the common range for Co2+ ions in (pseudo) octahedral fields of oxygen ligands, and their differences in CoSO4· H2O compared to CoSeO4 · H2O are consistent with somewhat different mean Co-O bond lengths and with a slightly higher covalent contribution to Co-O bonding in the selenate compound. The values found for the parameter Dt, which is directly correlated to the extent of tetragonal distortion, are much lower than expected from purely geometrical considerations, thus confirming a significantly higher position of H2O ligands in the spectrochemical series compared to oxygen ligands belonging to SO4 or SeO4 groups.  相似文献   

8.
The crystal structure of a new compound, [(H5O2)(H3O)(H2O)][(UO2)(SeO4)2] (monoclinic, P21/n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) Å, β = 103.880(13)°, V = 1182.4(3) Å3), has been solved by direct methods and refined to R 1 = 0.036. The structure is based on [(UO2)(SeO4)2]2? sheet complexes formed by corner-shared UO7 pentagonal bipyramids and SeO4 tetrahedrons. The sheets are parallel to the ( $ \bar 1 The crystal structure of a new compound, [(H5O2)(H3O)(H2O)][(UO2)(SeO4)2] (monoclinic, P21/n a = 8.3105(15), b = 11.0799(14), c = 13.227(2) ?, β = 103.880(13)°, V = 1182.4(3) ?3), has been solved by direct methods and refined to R 1 = 0.036. The structure is based on [(UO2)(SeO4)2]2− sheet complexes formed by corner-shared UO7 pentagonal bipyramids and SeO4 tetrahedrons. The sheets are parallel to the (01) plane. Oxonium ions and water molecules forming [(H3O)·(H2O)·(H5O2)]2+ complexes are interlayer. Among minerals, the existence of (H5O2)+ has been unambiguously confirmed only in rhomboclase, (H5O2)+[Fe2(SO4)2(H2O)2]. Original Russian Text ? S.V. Krivovichev, 2008, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2008, No. 2, pp. 123–130.  相似文献   

9.
Hydrothermal scheelite was synthesized using Na2WO4 · 2 H2O mixed with CaCl2 · H2O, CaSO4 · 2 H2O or CaF2 at different temperatures (270–720° C) and 108 Pa. The morphology of the crystals depends on the starting products. The observed faces include the {112}, {114}, {011}, and {013} forms. Pure or REE doped scheelites were studied by thermoluminescence (TL), fluorescence and electron paramagnetic resonance (EPR). The main TL peaks are located near 88, 149, 216, 277, and 315 K. Results obtained with EPR or optical fluorescence have been correlated with TL measurements and show that the trivalent lanthanide elements substitute for calcium ions without site distortion. The differences in TL observed between Eu and the other doping elements are related to the greater stability of Eu2+ caused by X-irradiation.  相似文献   

10.
  相似文献   

11.
《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   

12.
The crystal structures of two new compounds (H3O)2[(UO2)(SeO4)2(H2O)](H2O)2 (1, orthorhombic, Pnma, a = 14.0328(18), b = 11.6412(13), c = 8.2146(13) Å, V = 134.9(3) Å3) and (H3O)2[(UO2)(SeO4)2(H2O)](H2O) (2, monoclinic, P21/c, a = 7.8670(12), b = 7.5357(7), c = 21.386(3) Å, β = 101.484(12)°, V = 1242.5(3) Å3) have been solved by direct methods and refined to R 1 = 0.076 and 0.080, respectively. The structures of both compounds contain sheet complexes [(UO2)(SeO4)2]2? formed by cornershared [(UO2)O4(H2O)] bipyramids and SeO4 tetrahedrons. The sheets are parallel to the (100) plane in structure 1 and to (?102) in structure 2. The [(UO2)(SeO4)2(H2O)]2? layers are linked by hydrogen bonds via interlayer groups H2O and H3O+. The sheet topologies in structures 1 and 2 are different and correspond to the topologies of octahedral and tetrahedral complexes in rhomboclase (H2O2)+[Fe(SO4)2(H2O)2] and goldichite K[Fe(SO4)2(H2O)2](H2O)2, respectively.  相似文献   

13.
Analysis and speciation of selenium ions in mine environments   总被引：2，自引：1，他引：1  
 Aqueous extracts of five mine soil samples and a set of selenite (SeO3 2–)–selenate (SeO4 2–) solutions (0.5, 1, 5, 10 and 25 mg/l) were speciated using atomic absorption spectroscopy with hydride generation (AAS-HG) and ion chromatography (IC) to compare these methods for Se speciation. In another experiment, a SeO3 2––SeO4 2––SO4 2– solution (25 mg/l) was reacted with CaO, MgO, MnO2, CuO, La2O3, and WO3 to evaluate the relative distribution of the Se species and SO4 2– in the SORB (sorbed ions that were desorbed by NaOH), SOLN (equilibrium concentrations), CMPX (irreversibly sorbed and neutral ion pair complexes) fractions. The AAS-HG method was capable of analyzing Se as low as 0.002 mg/l, which was below the detection limit of IC. High concentration of SO4 2– affected the chromatographic Se speciation either by shifting or overlapping Se peaks, in which AAS-HG was more useful. However, IC was capable of speciating aqueous SeO3 2––SeO4 2– directly without any sample pretreatment, whereas AAS-HG measured SeO3 2–+SeO4 2–, and SeO3 2– in separate runs and SeO4 2– was calculated from the difference, i.e., spectrophotometric speciation was an indirect method. For both Se species, AAS-HG and IC data were comparable within detection standard deviations. Ratios of different Se species at measured soil pH and pe indicated that SeO3 2– or SeO4 2– would be the dominant Se species; the p(SeO4 2–/SeO3 2–) values further suggested SeO4 2– would be the major solution species. Except for CaO and MgO treatments, the %SeO3 2– in the SORB fraction was ≥%SeO4 2–. In the SOLN fraction %SeO4 2– was ≥%SeO3 2– for all oxides but CaO, whereas in the CMPX fraction this order was observed for only CaO and MnO2. The %SeO3 2– was highest in the SOLN fraction for all oxides but MgO and La2O3 for these two oxides SeO3 2– dominated in CMPX and SORB fractions, respectively. The SOLN fraction also contained the highest %SeO4 2– for all oxides but MgO which retained SeO4 2– primarily in the SORB fraction. The %SeO3 2– and %SeO4 2– in the CMPX fraction were highest for MgO, thus, suggesting a possible formation of MgSeO3 0 and MgSeO4 0. A similar trend of SORB %SO4 2– and SORB %SeO4 2– was attributed to the analogous adsorption mechanisms (outer-sphere complexation). For all oxides but MgO, %SO4 2– was <%SeO4 2– in the SOLN fraction and ≥%SeO4 2– in the CMPX fraction. Comparative ionic distributions provide an overall picture of the relative abundance of different Se species in various fractions associated with different oxides present in micro- and macrolevels in soils and geological materials. Received: 27 December 1995 · Accepted: 29 April 1997  相似文献   

14.
Brine extremely rich in potassium, boron and bromine has been discovered from the Middle Triassic Leikoupo Formation at a depth of 4300 m in Sichuan Province. It contains ～50 g/L of K+, >92 g/L of Na+, >12 g/L of B2O3, >2.36 g/L of Br? and ～0.030 g/L of I+. The solid precipitates during evaporation at 25°C include KB5O8·4H2O, K2B4O7·3H2O, MgCl2·6H2O and KMgCl3·6H2O. The brine ranges from 2.2‰ to 2.8‰ (SMOW) in δ18O, ? 38‰ – ? 53‰ (SMOW) in δD, 15.6‰ in δ34S, and 13.5‰–15.1‰ in δ11B. These data, particularly the isotopic composition of boron, indicate that the brine has a composite derivation from marine and nonmarine brines and dissolved marine evaporites in the Triassic system.  相似文献   

15.
《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   

16.
《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   

17.
The JEB Tailings Management Facility (TMF) is central to reducing the environmental impact of the McClean Lake uranium mill facility that is operated by AREVA Resources Canada. This facility has been designed around the idea that elements of concern (e.g., U, As, Ni, Se, Mo) will be controlled through equilibrium with precipitants. Confirming the presence of calcium-containing carbonates in the JEB TMF is the first step in determining if gypsum (CaSO4·2H2O) controls the concentration of HCO3− (aq), limiting the formation of soluble uranyl bicarbonate complexes. A combination of X-ray diffraction (XRD), X-ray absorption near-edge spectroscopy (XANES), and microprobe X-ray fluorescence (XRF) mapping was used to analyze a series of tailings samples from the JEB TMF. Calcium carbonate in the form of calcite (CaCO3), aragonite (CaCO3), and dolomite (CaMg(CO3)2) were identified by analysing Ca K-edge μ-XANES spectra coupled with microprobe XRF mapping. This is the first observation of these phases in the JEB TMF. The combination of μ-XANES and XRF mapping provided a greater sensitivity to low concentration calcium species compared to the other techniques used, which were only sensitive to the major species present (e.g., gypsum).  相似文献   

18.
The crystal structure of a new compound [Mg(H2O)4(SeO4)]2(H2O) (monoclinic, P2 1/a, a = 7.2549(12), b = 20.059(5), c = 10.3934(17) Å, β = 101.989(13), V = 1479.5(5) Å3) has been solved by direct methods and refined to R 1 = 0.059 for 2577 observed reflections with |F hkl | ≥ 4σ|F hkl |. The structure consists of [Mg(H2O)4(SeO4)]0 chains formed by alternating corner-sharing Mg octahedrons and (SeO4)2? tetrahedrons. O atoms of Mg octahedrons that are shared with selenate tetrahedrons are in a trans orientation. The heteropoly-hedral octahedral-tetrahedral chains are parallel to the c axis and undulate within the (010) plane. The adjacent chains are linked by hydrogen bonds involving H2O molecules not bound with M2+ cations.  相似文献   

19.
The leaching behaviour of electrostatic precipitator dust from the Mufulira Cu smelter (Copperbelt, Zambia) was studied using a 48-h pH-static leaching experiment (CEN/TS 14997). The release of metals (Cd, Co, Cu, Ni, Pb and Zn) and changes in mineralogical composition using X-ray diffraction and PHREEQC-2 modelling were investigated in the pH range of 3–7. The highest concentrations of metals were released at pH 3–4.5, which encompasses the natural pH of the dust suspension (～4.3). About 40% of the total Cu was leached at pH 3, yielding 107 g/kg. Chalcanthite (CuSO4·5H2O), magnetite (Fe3O4) and delafossite (CuFeO2) represented the principal phases of the studied dust. In contact with water, chalcanthite was dissolved and hydrated Cu sulphates precipitated at pH 4–7. Gypsum (CaSO4·2H2O) and secondary Fe or Al phases were observed in the leached residues. Serious environmental impact due to leaching may occur in dust-contaminated soil systems in the vicinity of the smelting plants.  相似文献   

20.
We study the phase relations and mineral chemistry in the systems muscovite–NH3–N2-H2O and eclogite + muscovite–NH3–N2-H2O at 6.3–7.8 GPa, 1000–1200 °C, and oxygen fugacity (fO2) from ∼IW (Fe–FeO) to ∼ NNO (Ni–NiO) equilibria. The quenched H2O-bearing fluids differ in nitrogen speciation from NH3-rich to N2–rich, and the respective N2/(NH3+N2) ratio varies from <0.1 to ∼ 1. N-bearing K-cymrite is obtained in association with a kyanite-garnet-jadeite ± muscovite ± corundum assemblage in the muscovite–NH3–N2-H2O system and coexists with pyrope-almandine garnet and omphacite in the eclogite + muscovite–NH3–N2-H2O system. The presence of an N-bearing fluid in the studied systems stabilizes the K-cymrite structure. Muscovite does not convert to K-cymrite in the absence of NH3–N2-bearing fluid up to 7.8 GPa and 1070–1120 °C. According to FTIR and Raman spectroscopy, K-cymrite in equilibrium with an N-rich fluid can capture a huge amount of nitrogen in cages of its framework, mainly as N2 molecules at fO2 ∼NNO and predominantly as NH3 molecules at fO2 ∼IW. The storage capacity of K-cymrite with respect to nitrogen increases from 2.9 to 6.3 wt% with increase of fO2. FTIR spectroscopy of muscovite equilibrated with K-cymrite shows that the clathrate mechanism of nitrogen entrapment by aluminosilicates (as neutral N2 and NH3 molecules) is much more efficient than the K+ → (NH4)+ substitution. The structure of N-bearing K-cymrite (K,(NH4+))[AlSi3O8]·(N2,NH3,H2O) determined using X-ray single-crystal diffraction is very similar to that of H2O-bearing K- and Ba-cymrites. It includes aluminosilicate layers consisting of double six-membered tetrahedral rings and cation sites statistically occupied with K+, Ba2+ and (NH4)+ on the six-fold symmetry axis in interlayer space. The N2 and NH3 molecules are located near the cage centers and, unlike H2O molecules, are included in the coordination environment of the cations. Our study confirms that NH3- and N2-rich K-cymrite may be stable in metapelites and can act as a redox insensitive carrier of nitrogen to >250 km mantle depths in downgoing slabs. The stability field of N-rich K-cymrite in the presence of an N2–H2O–NH3-bearing fluid is inferred to be P ≥ 4 GPa in metasediments rich in K-feldspar and P ≥ 6 GPa in those containing phengite. As the slab material sinks deeper than 250–300 km where N-bearing K-cymrite may lose stability, the releasing nitrogen may migrate to metal-saturated mantle and become stored there in γ−Fe, Fe3C, metal melt, or even iron nitride phases.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号