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1.
Neutron- and gamma irradiation-induced paramagnetic centers in natural colorless topaz from four different Brazilian localities were studied by electron paramagnetic resonance (EPR) and optical absorption as a function of irradiation dose and thermal treatment. Gamma irradiation doses were applied up to 1,000 kGy with a dose rate of 15 kGy h−1. For the neutron irradiation experiments, a neutron flux of 4 × 1012 cm−2 s−1 was used with an integrated flux of up to 1 × 1018 cm−2. From the experiments, it is concluded that brownish colors are induced by gamma-rays and may be associated with a single broad isotropic EPR line with g = 2.015(2). Both the EPR line and the related optical absorption band at 460 nm (2.7 eV) are lost during thermal treatments between 150 and 200°C. Fast neutrons create the paramagnetic peroxyl radicals O2 − and the paramagnetic O− hole centers. The O− centers have the same thermal stability as the optical absorption band at 620 nm (2.0 eV). It is confirmed that the absorption due to the O− center is responsible for the blue color in topaz. Both color centers and their absorption bands are discussed in the context of O− bound small polarons.  相似文献   

2.
Three types of paramagnetic radiation-induced defects (RID), namely A, A′ (Si-O?-centers) and B (Al-O?-Al center), had been identified in natural kaolinites by means of electron paramagnetic resonance spectroscopy. The A-center, stable at the scale of geological periods, was thought to be of particular relevance to quantify past transits of radionuclides in the geosphere. Alpha radiation being likely the main source of RID in kaolinite, the objective of this paper is to define the role of α-particles on the creation of RID and to test the use of A-centers for an α-dosimetry. Three kaolinites with different crystalline order and containing other clays as impurities were irradiated with He+ ion beams. The radiation dose range (0–750 MGy) was consistent with natural radioactivity in environments from the Earth's surface. Irradiation drastically enhanced the original signals due to RID. An important increase of concentration of the unstable B-center, partly due to unrealistic dose rate provided by accelerator ion beam, was observed from the lower doses. The most stable defects remained of the Atype all along experimental irradiations. The contribution of ancillary phyllosilicates to EPR spectra was negligible. The concentration of the three types of RID was related to radiation doses up to 30 MGy. Dosimetry growth curves for the A-centers exhibited variable efficiencies and saturation levels that were related to the structural order and the chemical purity of the kaolinites: the more ordered and purer the kaolinite, the higher the efficiency and the lower the saturation plateau. Moreover, these results are of geochemical significance: dosimetry based on A-centers could be directly used to quantify past migrations of radioelements in the geosphere, by determination of the naturally-cumulated doses (paleodose) of kaolinites.  相似文献   

3.
We examined the LIII-edge Pb X-ray absorption near-edge structure (XANES) of three natural zircon samples with different amounts of radiation doses (1.9 × 1015 to 6.8 × 1015 α-decay events/mg). The results suggest that the oxidation state of radiogenic Pb in the zircon sample with the highest radiation dose is divalent. The XANES spectra of the two other samples with lower radiation doses suggest that radiogenic Pb(II) is present, and further that some Pb may be tetravalent. This is the first work on the determination of the oxidation state of radiogenic Pb in natural zircon using XANES.  相似文献   

4.
Natural radiation-induced defects were identified in specimens of sudoite (Al–Mg di-trioctahedral chlorite) related to unconformity-type uranium deposits at the base of the Athabasca Group (Saskatchewan, Canada), using electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band frequencies. X-band spectra indicate the presence of a main native defect, named the As-center, whose EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g // = 2,051 and g ⊥ = 2,005, and a secondary defect with apparent component g = 2,025. The study of oriented specimens shows that the main defect has its g // component perpendicular to the (ab) plane of sudoite. The As-center corresponds to an electron hole located on oxygen atoms of the structure and is likely associated with Si, according to the lack of hyperfine structure. The As-center in sudoite has EPR parameters similar to the A-center in kaolinite and dickite, and the Ai-center in illite. The saturation behavior of EPR spectra as a function of power demonstrates that native defects of sudoite are different from those known in other clays, such as kaolinite, dickite or smectite, but are similar to those of illite. The isochronal annealing data suggest that the main defect in sudoite is stable to more than 300°C. The corresponding defects characterized in sudoite may have the potential for tracing past radionuclide migration around unconformity-type uranium deposits.  相似文献   

5.
This study presents the first unequivocal identification of natural radiation-induced defects in illites. Middle Proterozoic illites related to unconformity-type uranium deposits of Canada and Australia were studied using electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band frequencies. The saturation behaviour of EPR spectra as a function of power demonstrates that native defects of illites are different from those known in other clays as kaolinite, dickite or smectite. Q-band spectra indicate the presence of several––at least two––native defects. The EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g ∥ = 2.032 and g ⊥ = 1.993. The corresponding defect is named as Ai center. The study of oriented specimen confirms the strong anisotropy, and shows that the main defect has its g ∥ component perpendicular to the (ab) plane of illite. These defects in illite correspond to electron holes located on oxygen atoms of the structure and likely associated to Si, according to the lack of hyperfine structure. The Ai center in illite has similar EPR parameters to the A center in kaolinite and dickite. The isochronal annealing data suggest that illite can be used as a dosimeter in the geosphere. However, the determination of half-life and activation energy of the Ai center requires additional work.  相似文献   

6.
Thermoluminescence, electron paramagnetic resonance and optical absorption properties of rhodonite, a natural silicate mineral, have been investigated and compared to those of synthetic crystal, pure and doped. The TL peaks grow linearly for radiation dose up to 4 kGy, and then saturate. In all the synthetic samples, 140 and 340°C TL peaks are observed; the difference occurs in their relative intensities, but only 340°C peak grows strongly for high doses. Al2O3 and Al2O3 + CaO-doped synthetic samples presented several decades intenser TL compared to that of synthetic samples doped with other impurities. A heating rate of 4°C/s has been used in all the TL readings. The EPR spectrum of natural rhodonite mineral has only one huge signal around g = 2.0 with width extending from 1,000 to 6,000 G. This is due to Mn dipolar interaction, a fact proved by numerical calculation based on Van Vleck dipolar broadening expression. The optical absorption spectrum is rich in absorption bands in near-UV, visible and near-IR intervals. Several bands in the region from 540 to 340 nm are interpreted as being due to Mn3+ in distorted octahedral environment. A broad and intense band around 1,040 nm is due to Fe2+. It decays under heating up to 900°C. At this temperature it is reduced by 80% of its original intensity. The pink, natural rhodonite, heated in air starts becoming black at approximately 600°C.  相似文献   

7.
Vibrational properties of diaspore, α-AlOOH, have been re-investigated using room-temperature single-crystal Raman spectroscopy and low-temperature powder infrared (IR) transmission spectroscopy. First-principles harmonic calculations based on density functional theory provide a convincing assignment of the major Raman peaks and infrared absorption bands. The large width of the Raman band related to OH stretching modes is ascribed to mode–mode anharmonic coupling due to medium-strength H-bonding. Additional broadening in the powder IR spectrum arises from depolarization effects in powder particles. The temperature dependence of the IR spectrum provides a further insight into the anharmonic properties of diaspore. Based on their frequency and temperature behavior, narrow absorption features at ~2,000 cm−1 and anti-resonance at ~2,966 cm−1 in the IR spectrum are interpreted as overtones of fundamental bending bands.  相似文献   

8.
Uranium(VI) sorption onto kaolinite was investigated as a function of pH (3–12), sorbate/sorbent ratio (1 × 10?6–1 × 10?4 M U(VI) with 2 g/L kaolinite), ionic strength (0.001–0.1 M NaNO3), and pCO2 (0–5%) in the presence or absence of 1 × 10?2–1 × 10?4 M citric acid, 1 × 10?2–1 × 10?4 M EDTA, and 10 or 20 mg/L fulvic acid. Control experiments without-solids, containing 1 × 10?6–1 × 10?4 M U(VI) in 0.01 M NaNO3 were used to evaluate sorption to the container wall and precipitation of U phases as a function of pH. Control experiments demonstrate significant loss (up to 100%) of U from solution. Although some loss, particularly in 1 × 10?5 and 1 × 10?4 M U experiments, is expected due to precipitation of schoepite, adsorption on the container walls is significant, particularly in 1 × 10?6 M U experiments. In the absence of ligands, U(VI) sorption on kaolinite increases from pH ～3 to 7 and decreases from pH ～7.5 to 12. Increasing ionic strength from 0.001 to 0.1 M produces only a slight decrease in U(VI) sorption at pH < 7, whereas 10% pCO2 greatly diminishes U(VI) sorption between pH ～5.5 and 11. Addition of fulvic acid produces a small increase in U(VI) sorption at pH < 5; in contrast, between pH 5 and 10 fulvic acid, citric acid, and EDTA all decrease U(VI) sorption. This suggests that fulvic acid enhances U(VI) sorption slightly via formation of ternary ligand bridges at low pH, whereas EDTA and citric acid do not form ternary surface complexes with the U(VI), and that all three ligands, as well as carbonate, form aqueous uranyl complexes that keep U(VI) in solution at higher pH.  相似文献   

9.
Rock magnetic properties have been measured in a loess–paleosol sequence in the Gorina Quarry, which previously have been suggested to contain records of the Brunhes and part of the Matuyama polarity chrons. Lowest susceptibility values (below 50 × 10−8 m3/kg) are generally related to intensive weathered horizons, whereas highest values are obtained in loess layers (250 × 10−8 m3/kg) as a result of the greater ferromagnetic content in the parent material. The frequency-dependent part of susceptibility ranges between 0.5% and 6.8%; the higher value was obtained in B horizons of paleosols, which can be attributed to superparamagnetic contributions. Hysteresis loops indicate that the differences in ferrimagnetic and paramagnetic content in the sequence reflect the degree of pedogenesis. The same conclusion can be drawn with isothermal remanent magnetization. This point is relevant for determining past climatic changes because the wind-blown titanomagnetites from Cordillera de Los Andes during glacial periods were altered during interglacial periods. The mode of pedogenesis appears not only to control such alterations but also to produce other magnetic minerals.  相似文献   

10.
Synthetic ZrSiO4 and (mildly to strongly radiation-damaged) natural zircon samples were irradiated with 8.8 MeV 4He2+ ions (fluences in the range 1 × 1013–5 × 1016 ions/cm2). For comparison, an additional irradiation experiment was done with 30 MeV 16O6+ ions (fluence 1 × 1015 ions/cm2). The light-ion irradiation resulted in the generation of new (synthetic ZrSiO4) or additional (mildly to strongly metamict natural samples) damage. The maximum extent of the damage is observed in a shallow depth range approximately 32–33 μm (8.8 MeV He) and ~12 μm (30 MeV O) below the sample surface, i.e. near the end of the ion trajectories. These depth values, and the observed damage distribution, correspond well to defect distribution patterns as predicted by Monte Carlo simulations. The irradiation damage is recognised from the notable broadening of Raman-active vibrational modes, lowered interference colours (i.e. decreased birefringence), and changes in the optical activity (i.e. luminescence emission). At very low damage levels, a broad-band yellow emission centre is generated whereas at elevated damage levels, this centre is suppressed and samples experience a general decrease in their emission intensity. Most remarkably, there is no indication of notable structural recovery in pre-damaged natural zircon as induced by the light-ion irradiation, which questions the relevance of alpha-assisted annealing of radiation damage in natural zircon.  相似文献   

11.
Synthetic Co-doped quartz was grown hydrothermally in steel autoclaves at the Technological Center of Minas Gerais (CETEC), Brazil. The quartz samples, originally yellow in the as-grown state acquired blue coloration after prolonged heat treatment times at 500°C near the alpha–beta transition temperature. UV–VIS–NIR absorption spectroscopy shows the characteristic spectra of Co3+ before heat treatment. After heat treatment, the optical absorption spectrum is dominated by two split-triplet bands the first in the near infrared region centered at about 6,700 cm−1 (1,490 nm) and the second in the visible spectral range at about 16,900 cm−1 (590 nm). Both split-triplet bands are typical for Co2+ ions in tetrahedral coordination environments. From the absence of electron paramagnetic resonance (EPR) spectra, we conclude that the Co2+ found in the optical absorption spectra of the blue quartz is not due to an isolated structural site in the quartz lattice. Instead, the blue color is associated with electronic transitions of Co2+ in small inclusions in which the Co site has tetrahedral symmetry. The non-observation of polarization-depend optical absorption spectra is also in agreement with this model. The results for Co2+ in quartz are different from Co-bearing spinel and staurolite and other silicates like orthopyroxene, olivine, and beryls. The formation process of the color center is discussed.  相似文献   

12.
《Applied Geochemistry》2002,17(4):445-454
Processing waters contain up to 10 mg l−1 dissolved As at the Macraes mine, New Zealand, and this is all removed by adsorption as the water percolates through a large earth dam. Laboratory experiments were set up to identify which mineral is the most effective substrate for this adsorption of As. The experiments were conducted using infrared (IR) spectroscopy of thin mineral films adhering to a ZnSe prism. Silicates, including kaolinite, adsorbed only small amounts of As which was readily washed off. Hydrated Fe oxides (HFO) were extremely effective at adsorbing As, particularly the natural amorphous HFO currently being deposited from dam discharge waters at the Macraes mine. An adsorption isotherm determined for this natural material has the adsorption constant, Kads=(1.9±0.4)×104 M−1, and the substrate becomes saturated with adsorbed As when solution concentrations exceed about 50 mg l−1. Saturation is not being reached at the Macraes mine. Arsenic adsorbed on to natural HFO has a distinctive IR spectrum with the absorption peak varying from 800 cm−1 (alkaline solutions) to 820 cm−1 (neutral to acid solutions). Much of this adsorbed As is strongly bound and difficult to wash off. Arsenate ions adsorb in a bidentate structure which may be a precursor for scorodite crystallisation.  相似文献   

13.
《Chemical Geology》2007,236(1-2):92-111
Complexly zoned zircons (19 grains, ∼ 3.3 Ga) from a porphyritic granite in the Jack Hills, Western Australia, have been investigated using electron microprobe analysis (EMPA) and transmission electron microscopy (TEM) in order to examine the effects of radiation as a function of dose, as well as the nano-scale microstructure and composition of impurities and secondary alteration phases. In back-scattered electron (BSE) images, zones with bright contrast consist of an almost unaltered zircon with limited amounts of impurity elements. In contrast, the dark zones contain higher concentrations of trace elements: U, Th, Pb, Fe, Y, Ce, Ca and Al. The cumulative doses due to alpha-decay in the dark zones are calculated to be 0.21–1.0 × 1017 (alpha-decay events/mg), equivalent to 1.0–4.7 dpa (displacements per atom). These doses are much higher than the dose required for radiation-induced amorphization, as determined by ion-beam irradiation of synthetic zircon, 0.3–1.0 dpa (0–600 °C). However, based on high-resolution TEM observations, none of the zircons are fully amorphous, to the result of annealing under ambient conditions. The concentrations of Ca and Al, which was considered to indicate alteration, increase dramatically at a cumulative dose of 1.6 × 1016 (alpha-decay events/mg). This is the dose at which the first percolation point occurs, as amorphous domains overlap and form an interconnected network. In the altered zones, nanocrystallites of zircon are present with a random orientation, and the amorphous matrix contains the impurity elements. Although the Ce-concentration is extremely high, 1–2 wt.%, the Ce anomaly, Ce/Ce⁎, does not vary significantly as a function of dose or degree of alteration, indicating that the LREE patterns were overprinted by the fluids with a similar Ce-anomaly. The valence of Ce analyzed by EELS (electron energy loss spectroscopy) is tetravalent in the altered zone, suggesting that the altering fluids were oxidizing.  相似文献   

14.
Characterization of lattice strain induced by neutron irradiation   总被引：1，自引：0，他引：1  
Powder X-ray diffraction and Rietveld refinement have been used to study structural damage induced by neutron irradiation of orthoclase (Or94) from Benson Mines, New York. X-ray diffraction profiles of samples exposed to total neutron doses in excess of 6.3×1018 n/ cm2 exhibit small but measurable peak broadening in comparison with unirradiated orthoclase. Rietveld structure refinements and transmission electron microscope observations indicate that the X-ray peak broadening arises primarily from the effect of strain rather than particle size. The results reveal a positive correlation between the neutron dose and the anisotropic strain percentage calculated from the Lorentzian profile parameters. This strain-induced broadening probably stems from numerous point defects created by recoiling atoms during neutron collisions. These observations have important implications for the diffusive behavior of 39Ar and 40Ar.  相似文献   

15.
《Applied Geochemistry》1998,13(7):905-916
Experiments measuring kaolinite and smectite dissolution rates were carried out using batch reactors at 35° and 80°C. No potential catalysts or inhibitors were present in solution. Each reactor was charged with 1 g of clay of the ≤2 μm fraction and 80, 160 or 240 ml of 0.1–4 M KOH solution. An untreated but sized kaolinite from St. Austell and two treated industrial smectites were used in the experiments. One smectite is a nearly pure montmorillonite, while the second has a significant component of beidellitic charge (35%). The change in solution composition and mineralogy was monitored as a function of time. Initially, the 3 clays dissolved congruently. No new formed phases were observed by XRD and SEM during the pure dissolution stage. The kaolinite dissolution is characterized by a linear release of silica and Al as a function of the log of time. This relationship can be explained by a reaction affinity effect which is controlled by the octahedral layer dissolution. Far from equilibrium, dissolution rates are proportional to a0.56±0.12OH− at 35°C and to a0.81±0.12OH− at 80°C. The activation energy of kaolinite dissolution increases from 33±8 kJ/mol in 0.1 M KOH solutions to 51±8 kJ/mol in 3 M KOH solutions. In contrast to kaolinite, the smectites dissolve at much lower rates and independently of the aqueous silica or Al concentrations. The proportionality of the smectite dissolution rate constant at 35 and 80°C was a0.15±0.06OH−. The activation energy of dissolution appears to be independent of pH for smectite and is found to be 52±4 kJ/mol. The differences in behavior between the two kinds of minerals can be explained by structural differences. The hydrolysis of the tetrahedral and the octahedral layer appears as parallel reactions for kaolinite dissolution and as serial reactions for smectite dissolution. The rate limiting step is the dissolution of the octahedral layer in the case of kaolinite, and the tetrahedral layer in the case of smectite.  相似文献   

16.
The intrinsic room temperature magnetic properties of pure calcite were determined from a series of natural crystals, and they were found to be highly dependent on the chemical composition. In general, dia-, para-, and ferromagnetic components contribute to the magnetic susceptibility and the anisotropy of magnetic susceptibility (AMS). With a combination of magnetic measurements and chemical analysis these three contributions were determined and related to their mineralogical sources. The intrinsic diamagnetic susceptibility of pure calcite is − 4.46 ± 0.16 × 10− 9 m3/kg (− 12.09 ± 0.5 × 10− 6 SI) and the susceptibility difference is 4.06 ± 0.03 × 10− 10 m3/kg (1.10 ± 0.01 × 10− 6 SI). These diamagnetic properties are easily dominated by other components. The paramagnetic contribution is due to paramagnetic ions in the crystal lattice that substitute for calcium; these are mainly iron and manganese. The measured paramagnetic susceptibility agrees with the values calculated from the known concentration of paramagnetic ions in the crystals according to the Curie law of paramagnetic susceptibility. Substituted iron leads to an increase in the AMS. The paramagnetic susceptibility difference was found to correlate linearly with the iron content for concentrations between 500 and 10,000 ppm. An empirical relation was determined: (k1 − k3)para (kg/m3) = Fe-content (ppm) × (1 ± 0.1) × 10− 12 (kg/m3/ppm). The maximum susceptibility difference (Δk = k1 − k3) was found to be unaffected by iron contents below 100 ppm. Ferromagnetic contributions due to inclusions of ferromagnetic minerals can dominate the susceptibility. They were detected by acquisition of isothermal remanent magnetization (IRM) and their contribution to the AMS was separated by high-field measurements.  相似文献   

17.
Natural processes and anthropogenic activities may result in the formation and/or introduction of perchlorate (ClO4−) at elevated levels into the environment. Perchlorate in soil environments on Earth and potentially in Mars may modify the dynamics of metal release and their mobilization. Serpentine soils, known for their elevated metal concentrations, provide an opportunity to assess the extent that perchlorate may enhance metal release and availability in natural soil and regolith systems. Here, we assess the release rates and extractability of Ni, Mn, Co and Cr in processed Sri Lankan serpentine soils using a range of perchlorate concentrations (0.10–2.50 w/v ClO4−) via kinetic and incubation experiments. Kinetic experiments revealed an increase of Ni, Mn, Co and Cr dissolution rates (1.33 × 10−11, 2.74 × 10−11, 3.05 × 10−12 and 5.35 × 10−13 mol m−2 s−1, respectively) with increasing perchlorate concentrations. Similarly, sequential and single extractions demonstrated that Ni, Mn, Co and Cr increased with increasing perchlorate concentrations compared to the control soil (i.e., considering all extractions: 1.3–6.2 (Ni), 1.2–126 (Mn), 1.4–34.6 (Co) and 1.2–6.4 (Cr) times greater than the control in all soils). Despite the oxidizing capability of perchlorate and the accelerated release of Cr, the dominant oxidation state of Cr in solution was Cr(III), potentially due to low pH (<2) and Cr(VI) instability. This implies that environmental remediation of perchlorate enriched sites must not only treat the direct hazard of perchlorate, but also the potential indirect hazard of related metal contamination.  相似文献   

18.
Taking advantage of the opportunity provided by the nationally funded Water Resources Integrated Planning and Investigation of China program (WRIPI), a model was established to estimate non-point source pollutant loads in a large-scale basin (ENPS-LSB) on the basis of hydrological processes and pollutant transport. The model made use of Environment for Visualizing Images software (ENVI) and Interactive Data Language (IDL) and took the characteristics of present-day China into account: a huge rural population scattered widely, marginal rural infrastructure and livestock cultivation based on scatter-feeding. The model was divided into two sections: one on dissolved and one on adsorbed pollutant loads. The dissolved loads were divided into four different types: those originating from agricultural fields, urban areas, rural residential areas, and livestock. The study was undertaken in the Yangtze River Basin. The results showed the chemical oxygen demand (COD), the total nitrogen (TN), the total phosphorous (TP), and the ammonia nitrogen (NH3–N) loads to be 2.6 × 106, 1.6 × 106, 9.3 × 105 and 3.1 × 105 tons, respectively, in the year 2000. The dissolved COD resulted mainly from rural residential areas and livestock; 76.8% of the dissolved TN and 86.4% of the dissolved TP produced were from agricultural fields. The Yangtze River Delta, the lower reaches of the Han River, and part of the Dongting Lake, Taihu Lake and Poyang Lake basins all had relatively high dissolved pollutant loads; adsorbed nitrogen and phosphorus loads were mainly observed in the middle and upper reaches of the Yangtze River Basin. Dissolved loads were most affected by human activity, whereas adsorbed loads were most affected by natural factors. The results showed that the model performed well on large scale, describing pollutant loads effectively. This makes it possible to properly consider not only point source pollutant discharge but also non-point source pollution in the Yangtze River Basin. Combining point source discharge investigation with the ENPS-LSB model could assist environmental management with controlling water pollution.  相似文献   

19.
Samples of a natural amethyst, pulverized in air, and irradiated for gamma-ray doses from 0.14 to 70 kGy, have been investigated by powder electron paramagnetic resonance (EPR) spectroscopy from 90 to 294 K. The powder EPR spectra show that the surface Fe3+ species on the gamma-ray-irradiated quartz differ from its counterpart without irradiation in both the effective g value and the observed line shape, suggesting marked radiation effects. This suggestion is supported by quantitatively determined thermodynamic properties, magnetic susceptibility, relaxation times, and geometrical radius. In particular, the surface Fe3+ species on gamma-ray-irradiated quartz has larger Gibbs and activation energies than its non-irradiated counterpart, suggesting radiation-induced chemical reactions. The shorter phase-memory time (T m) but longer spin–lattice relaxation time (T 1) of the surface Fe3+ species on the gamma-ray-irradiated quartz than that without irradiation indicate stronger dipolar interactions in the former. Moreover, the calculated geometrical radius of the surface Fe3+ species on the gamma-ray-irradiated quartz is three orders of magnitude larger than that of its counterpart on the as-is sample. These results provide new insights into radiation-induced aerosol nucleation, with relevance to atmospheric cloud formation and global climate changes.  相似文献   

20.
Flexible-wall hydraulic conductivity tests were carried out on bottom ash, fly ash and compacted specimens of sand with additions of 0, 3, 6, 9 and 18% of bentonite. In order to study the effect of bentonite inclusion and particle morphology on the hydraulic conductivity of the admixtures, an investigation was undertaken based on thin section micrographs. It was found that, for both bottom and fly ash admixtures, bentonite addition reduced only one order of magnitude the hydraulic conductivity, from 1.78 × 10−6 m/s to 1.39 × 10−7 m/s. On the other hand, the sand hydraulic conductivity was reduced five orders of magnitude, from 3.17 × 10−5 m/s to 5.15 × 10−10 m/s. Among several factors that can be responsible for the difficulty in reducing hydraulic conductivity, such as ash grain size distribution and elevated cation concentration (leached from the ash) in pore water, it can also be recalled the high particle voids observed in the ash by means of microscopic analysis. The same is not true with the sand, which has solid particles, without inner voids.  相似文献   

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