As a result of the collapse of the Aznalcollar mine tailings dam, a large extension of the Guadiamar valley in SW Spain was covered with a layer of pyrite sludge. Although most of the sludge was removed, a small amount remains in the soil, constituting a potential source of water pollution. A column experiment was carried out in order to determine the rate of sludge oxidation in the soil, and the existence of metal retention processes. The column was filled with a mixture of sludge and a sandy soil common in the region. At different time intervals, the column was leached with water and the resulting solution analysed.
The pH of the water dropped to values around 2 after 260 days and then remained constant due to the buffering role of silicate dissolution. The concentration of Zn, Cd and Co in the leachates matched the expected values from flow-through experiments at atmospheric oxygen pressure. This indicates that oxygen diffusion in the pores was complete. Moreover, no efficient processes existed for retaining Zn, Cd and Co, which formed soluble salts and were entirely incorporated into the infiltrating water. During the first 2 months of the experiment, when pH was higher than 4.5, the concentrations of Fe and Al were very low. Saturation indices showed that the solution was in equilibrium with amorphous Fe(OH)3 and Al(OH)3. Subsequently, at lower pH values, jarosite [(Na,K)Fe3(SO4)2(OH)6] formed. This solid phase was identified by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). Jarosite was also responsible for the depletion of As, Pb, Sb and probably Tl in the water resulting from infiltration. 相似文献
Cu-poor meneghinite from La Lauzière Massif (Savoy, France) has the composition (electron microprobe) (in wt%): Pb 59.50, Sb 20.33, Bi 1.19, Cu 0.87, Ag 0.05, Fe 0.03, S 17.62, Se 0.05, Total 99.64. Its crystal structure (X-ray on a single crystal) was solved with R1=0.0506, wR2=0.1026, with an orthorhombic symmetry, space group Pnma, and a=24.080(5) Å, b=4.1276(8) Å, c=11.369(2) Å, V=1130.0(4) Å3, Z=4. Relatively to the model of Euler and Hellner (1960), this structure shows a significantly lower site occupancy factor for the tetrahedral Cu site (0.146 against 0.25). Among the five other metallic sites, Bi appears in the one with predominant Sb. Developed structural formula: Cu0.15Pb2(Pb0.53Sb0.47)(Pb0.46Sb0.54)(Sb0.75Pb0.19Bi0.06)S6; the reduced one: Cu0.58Pb12.72(Sb7.04Bi0.24)S24. The formation of such a Cu-poor variety seems to be related to specific paragenetic conditions (absence of coexisting galena), or to crystallochemical constraints (minor Bi). To cite this article: Y. Moëlo et al., C. R. Geoscience 334 (2002) 529–536.相似文献
Interatomic potential parameters have been derived at simulated temperatures of 0 K and 300 K to model pyrite FeS2. The predicted pyrite structures are within 1% of those determined experimentally, while the calculated bulk modulus is within 7%. The model is also able to simulate the properties of marcasite, even though no data for this phase were included in the fitting procedure. There is almost no difference in results obtained for pyrite using the two potential sets; however, when used to model FeS2 marcasite, the potential fitted at 0 K performs better. The potentials have also been used to study the high-pressure behaviour of pyrite up to 44 GPa. The calculated equation of state gives good agreement with experiment and shows that the Fe–S bonds shorten more rapidly that the S–S dimer bonds. The behaviour of marcasite at high pressure is found to be similar to that of pyrite. 相似文献
The nature and style of emplacement of Continental Flood Basalt (CFB) lava flows has been a matter of great interest as well
as considerable controversy in the recent past. However, even a cursory review of published literature reveals that the Columbia
River Basalt Group (CRBG) and Hawaiian volcanoes provide most of the data relevant to this topic. It is interesting to note,
however, that the CRBG lava flows and their palaeotopographic control is atypical of other CFB provinces in the world. In
this paper, we first present a short overview of important studies pertaining to the emplacement of flood basalt flows. We
then briefly review the morphology of lava flows from the Deccan Volcanic Province (DVP) and the Columbia-Oregon Plateau flood
basalts. The review underscores the existence of significant variations in lava flow morphology between different provinces,
and even within the same province. It is quite likely that there were more than one way of emplacing the voluminous and extensive
CFB lava flows. We argue that the establishment of general models of emplacement must be based on a comprehensive documentation
of lava flow morphology from all CFB provinces. 相似文献
Abstract Spatial and temporal variations in radiative fluxes influence glacier mass‐balance in mountain areas. The primary goal of this study was to assess differences in solar radiation on three glacial cirques located in the Maladeta Mountain massif (Central Spanish Pyrenees), and analyse their implications on glacier development and morphology. A quantitative approach is adopted to obtain the values of solar radiation (direct, diffuse and global radiation), combining several field data parameters (measured at 55 control‐points) with the solar radiation modelling package Ecosim. The data obtained confirm that the morphologies of the glacial bodies developed in the three cirques have a good correlation with the spatial variation on solar radiation inputs, favouring also the conservation (Aneto and Coronas cirques) or total vanishing (Llosás cirque) of the glacial remnants analysed here. The study shows how strongly in this Alpine‐Mediterranean context solar radiation — firstly as a function of latitude and time of year, and locally as a function of topographic slope, aspect and shadowing — controls the mass‐balance and the spatial distribution of melting in small glaciers, having an effect on the development of their morphologies. 相似文献
In this paper, a comparative study has been made for physical and engineering properties of low calcium and high calcium Indian
fly ash. The grain size distribution of fly ash is independent of lime content. Fly ash particles of size >75 μm are mostly irregular in shape whereas finer fractions are spherical for low calcium fly ash. For high calcium fly ash, chemical
and mineralogical differences have been observed for different size fractions. Compared to low calcium fly ash, optimum moisture
content is low and maximum dry density is high for high calcium fly ash. Optimum moisture content is directly proportional
and maximum dry density is inversely proportional to the carbon content. The mode and duration of curing have significant
effect on strength and stress–strain behavior of compacted fly ash. The gain in strength with time for high calcium fly ash
is very high compared to that of low calcium fly ash due to presence of reactive minerals and glassy phase. 相似文献
The role of municipal solid waste (MSW) landfill leachate on the genesis of minor amounts of pyrite associated with gypsum
in an otherwise predominantly evaporitic sequence was studied in geological and geochemical terms. The potential association
between landfill leachate and the conditions required for bacterial reduction of sulfate and fixation of H2S as pyrite were examined. The lithological column was generally found to contain little or no Fe. The δ34S values for sulfates were consistent with previously reported data; however, the measured δ18O values were slightly higher. Sulfides disseminated in the marl/lutite exhibited higher δ34S values (≈−8‰) than gypsum-coating pyrite crystals (δ34S < −30‰). Dissolution of gypsum to sulfate and the supply of metabolizable organic matter and Fe required for H2S fixation as sulfides may have originated from landfill leachate. Intermittent availability of leachate, a result of the
precipitation regime, can facilitate sulfur disproportionation and lead to fractionations as high as 相似文献