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1.
Biofilms wasted from biotrickling filters was dried and used as biosorbent for Cd(II) removal from aqueous solutions. The adsorption condition and effect, adsorption isotherms and kinetics of Cd(II) removal were investigated, and the effects of competitive metal ions on Cd(II) removal were also examined. Results showed that the dry waste biofilms reached the maximum adsorption capacity of 42 mg/g of Cd(II) at 25 °C for 120 min when the initial concentration of Cd(II) and their pH were 50 mg/L and 6.0, respectively. Under these conditions, the removal efficiency of Cd(II) reached to 89.3% when the biosorbent dosage was 2.0 g/L. The Langmuir isotherm model correlated with the isotherm data better than the Freundlich isotherm model, and the pseudo-second-order model fitted the kinetic data better than the pseudo-first-order model. These results indicated that the adsorption was monolayer accompanied with chemical adsorption. In the presence of other metal ions, divalent metal ions of Ca and Zn inhibited the performance of Cd(II) biosorption significantly, while Na(I), K(I) and Fe(III) which had a higher or lower valence than Ca(II) affected slightly when containing 50 mg/L Cd(II), 0.5 g/L adsorbent dosage and pH 6.0. The analyses of scanning electron microscopy and Fourier transform infrared spectroscopy illuminated that the biosorbent had porous structures and the amide group was the majorly responsible for Cd(II) removal. Dry biofilms were novel sorbents for effective removal Cd(II), and it could be reused and recycled if necessary.  相似文献   

2.
We report the crystal structures determined under ambient condition for two Zn2SiO4 polymorphs synthesized at 6.5 GPa and 1,273 K (phase III) and 8 GPa and 1,273 K (phase IV) and also compare their 29Si MAS NMR spectroscopic characteristics with those of other Zn2SiO4 polymorphs (phases I, II and V). Electron microprobe analysis revealed that both of phases III and IV are stoichiometric like the lower-pressure polymorphs (phases I and II), contrary to previous report. The crystal structures were solved using an ab initio structure determination technique from synchrotron powder X-ray diffraction data utilizing local structural information from 29Si MAS NMR as constraints and were further refined with the Rietveld technique. Phase III is orthorhombic (Pnma) with a = 10.2897(5), b = 6.6711(3), c = 5.0691(2) Å. It is isostructural with the high-temperature (Zn1.1Li0.6Si0.3)SiO4 phase and may be regarded as a ‘tetrahedral olivine’ type that resembles the ‘octahedral olivine’ structure in the (approximately hexagonally close packed) oxygen arrangement and tetrahedral Si positions, but has Zn in tetrahedral, rather than octahedral coordination. Phase IV is orthorhombic (Pbca) with a = 10.9179(4), b = 9.6728(4), c = 6.1184(2) Å. It also consists of tetrahedrally coordinated Zn and Si and features unique edge-shared Zn2O6 dimers. The volumes per formula under ambient condition for phases III and IV are both somewhat larger than that of the lower-pressure polymorph, phase II, suggesting that the two phases may have undergone structural changes during temperature quench and/or pressure release.  相似文献   

3.
A batch nitrification process was studied using synthetic wastewater as substrate and Chilean natural zeolite as biomass carrier at ambient temperatures (20 °C). Three groups of experiments were carried out: a first experimental set (I) with and without added zeolite using initial biomass concentrations of 1,000 and 2,000 mg VSS/L; a second set of experiments (II) with added zeolite and at the same initial biomass concentrations. In these two experimental sets, biomass from an activated sludge process located in an urban wastewater treatment plant at La Farfana, Santiago de Chile, was used as inoculum (1). Finally, a third set of experiments (III) was carried out with zeolite at an initial biomass concentration of 1,000 mg VSS/L using an inoculum derived from an activated sludge process treating wastewater from a paper mill (inoculum 2). Nitrifying biomass concentration values in the range of 13,000–18,800 mg VSS/L were achieved when initial biomass concentrations varied between 1,000 and 2,000 mg VSS/L. Inoculum (1) generated higher biomass concentrations than inoculum (2). Ammonium N removals higher than 70 % were obtained in experimental sets II and III when zeolite was used. For both initial biomass concentrations tested, an exponential biomass growth was observed up to the second day of operation, and a slight decrease was evident afterwards, achieving stationary values after 10–12 days of operation. The third experimental set (III) revealed that the highest N consumption took place between days 11 and 16 of digestion.  相似文献   

4.
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5.
Gaza central seawater desalination plant is a promising solution to alleviate the problem of water crisis in the Gaza Strip. The plant in the short term, phase (I), will desalinate seawater for potable uses with a capacity of 55 million cubic meters per year, while in the long term, phase (II), the plant capacity will be doubled to 110 million cubic meters per year of freshwater. As a product from the reverse osmosis process, a huge amount of brine with salinity reaches to 75,000 mg/L will be redirected to seawater; nearly 12,200 m3/h of brine will be rejected from phase (I) while in the long term, a brine flow rate of 24,400 m3/h will be disposed from phase (II). In order to minimize the negative impacts of the rejected brine on the marine environment, it is urgent to modeling numerically the impact of the discharged brine through various disposal systems to define the most environmental system. Various scenarios were defined and simulated using CORMIX model to study the efficiencies of onshore surface open channel, offshore submerged single port as well as offshore submerged multiport outfalls taking salinity variations as an indicator. Sensitivity analysis was conducted to identify the most influencing input parameters on the simulation results as well as to evaluate the optimal environmental disposal system which can mitigate the adverse impacts of brine on the marine ecosystem as much as possible in the worst seawater conditions. The simulation results showed that the discharge via surface open channel is not environmentally feasible where the seawater salinity rose by more than 2000 mg/L at RMZ. The single-port scenario can meet the regulations at RMZ but the standard at GMZ was not met, where the rejected brine from phase (I) through single port at 1500 m offshore raises the seawater salinity at GMZ by more than 600  mg/L. The staged multiport outfall, capped by 24 ports, achieves acceptable brine dilution at seawater depth of about 7.5  m, and in the worst ambient conditions in the case of phase (II) in operation, the brine’s excess salinity was 536, 497, and 379 mg/L above the salinity of seawater at RMZ, GMZ, and ROI, respectively.  相似文献   

6.
The late Early Permian (273 – 271 Ma) Wandrawandian Siltstone in the southern Sydney Basin of New South Wales represents a marine highstand that can be correlated over 2000 km. A mainly fine-grained terrigenous clastic succession, the Wandrawandian Siltstone contains evidence for cold, possibly glacial conditions based on the presence of outsized clasts and glendonites, mineral pseudomorphs after ikaite, a mineral that forms in cold (0 – 7°C) marine sediments. A lithostratigraphic and facies analysis of the unit was conducted, based on extensive coastal outcrops and continuous drillcores. Eight facies associations were identified: (i) siltstone; (ii) siltstone with minor interbedded sandstone; (iii) interbedded tabular sandstone and siltstone; (iv) admixed sandstone and siltstone to medium-grained sandstone; (v) discrete, discontinuous sandstone intervals; (vi) chaotic conglomerate and sandstone in large channel forms; (vii) chaotically bedded and pervasively soft-sediment-deformed intervals; and (viii) tuffaceous siltstone and claystone. Using lithology and ichnology, relative water depths were ascribed to each facies association. Based on these associations, the unit was divided into five informal members that reveal a history of significant relative sea-level fluctuations throughout the formation: member I, interbedded/admixed sandstone and siltstone; member II, siltstone; member III, slumped masses of members I and II; member IV, siltstone and erosionally based lensoid sandstone beds and channel bodies; and member V, interbedded/admixed sandstone and siltstone with abundant tuffs. Member I marks an initial marine transgression from shoreface to offshore depths. Member II records the maximum water depth of the shelf. Member III is interpreted to be a slump sheet; plausible mechanisms for its emplacement include seismicity produced by tectonism or glacio-isostatic rebound, changes in pore-water pressures due to sea-level fluctuations, or an increase in sedimentation rates. Members IV and V record minor fluctuations in depositional environments from offshore to shoreface water depths. Member IV includes regionally extensive, large channel bodies, with composite fills that are interpreted as storm-influenced mass-flow deposits. Member V includes a greater abundance of volcanic ash. Glacial controls (isostasy, eustasy) and tectonic affects may have worked in concert to produce the changes in depositional environments observed in the Wandrawandian Siltstone.  相似文献   

7.
This paper presents detailed mineral chemical, element geochemical and Sr–Nd–Hf isotopic data for the Late Jurassic (155?±?4 Ma) lamprophyre dikes in the Liaodong Peninsula, NE China. The lamprophyres are shoshonitic and geochemically fall into three groups: Group I has relatively high SiO2 (52.5–57.0 wt.%), low MgO (5.5–8.3 wt.%) and compatible trace element (e.g. Cr?=?128–470 ppm) contents, high initial 87Sr/86Sr ratios (0.7093–0.7117), and low εNd (T) values (?9.6 to ?12.1); Group II has relatively low SiO2 (44.8–50.0 wt.%), high MgO (10.8–14.2 wt.%) and compatible trace element (e.g. Cr?=?456–1,041 ppm) contents, low initial 87Sr/86Sr ratios (0.7073–0.7087), and high εNd (T) values (?1.4 to ?2.9); Group III is transitional between the two in all elemental and isotopic compositions. Interpretation of the elemental and isotopic data suggests that the lamprophyric melts were derived by partial melting of subcontinental lithospheric mantle (SCLM) at a depth of 60–80 km (group I), decompression melting of upwelling asthenosphere at 60–100 km (group II), and mixing between the SCLM-derived and asthenosphere-derived melts (group III). It is assumed that the local SCLM was detached at a depth of 60–80 km by the 155 Ma ago. A continental arc-rifting related to the Palaeo-Pacific plate subduction is favored as a geodynamic force for such a cratonic lithosphere detachment.  相似文献   

8.
Phytoremediation is a proven low-cost and sustainable method for the removal of toxic pollutants from water. This green technology has been practiced for the past several years all over the world. In the present study, the interaction of fluoride on the surface of the floating aquatic plant water lettuce (Pistia stratiotes) during fluoride removal was investigated. Batch kinetic studies were performed to examine the fluoride uptake capacity of the plant with different initial fluoride concentrations such as 3, 5, 10, and 20 mg/L. The effects of various process parameters on fluoride uptake dynamics such as pH, plant biomass, initial fluoride concentration, and time were examined. Freundlich’s isotherm model was found to (R 2 = 0.957) fit well to the experimental data. The nature of reaction order followed pseudo-first-order kinetics, when the initial fluoride level in the solution was 5 mg/L. The experimental findings showed that the removal mechanism was driven by biosorption phenomenon. High fluoride concentration in the solution reduced the growth ratio of P. stratiotes. The lowest growth ratio of this aquatic macrophyte was found to be 76.80 ± 3.73% at 20 mg/L fluoride concentration. At lower fluoride concentrations such as 3 and 5 mg/L, the growth ratio of the plant was not reduced significantly.  相似文献   

9.
The Pb(II) and Ni(II) biosorption of a fungal biomass isolated from mine drainage of metal-processing industries in Balya (Bal?kesir province, Turkey) was optimized using a response surface methodology by altering parameters such as pH, initial metal concentration, contact time and biosorbent dosage. This strain was shown to be highly similar to Penicillium sp. Furthermore, zeta potential measurements and Fourier transform infrared spectroscopy were performed to understand the adsorption mechanism. A Box–Behnken design with 29 experiments was used to evaluate the interactions between independent variables. The results showed that the fungal biomass isolated from the metal mine drainage could have a significant environmental impact through the biosorption of Pb(II) and Ni(II) in waters polluted with heavy metals, particularly in the drainage from metal mines. The maximum removal values were 76 and 47 % at pH 4.5 for both Pb(II) and Ni(II), with 123 and 33 mg/L initial metal concentrations, 65 and 89 min contact times and 0.2 and 1.6 g/L biosorbent, respectively.  相似文献   

10.
In recent years, the need for safe and economical methods to eliminate heavy metals from contaminated waters has necessitated research on the production of low-cost alternatives to commercially available activated carbon. In the present work, in order to enhance the removal of heavy metals from contaminated water, Zizyphus vulgaris wastes were modified chemically to produce an adsorbent rich in carboxylic groups to enhance the removal of heavy metals from contaminated water. Adsorption of Zn(II) ions on the produced adsorbent was then optimized. The optimal ratio for esterification involved the treatment of Z. vulgaris wastes (1 g) with 0.0037 mmol malic acid in the presence of a very small amount of water for 2 h at 140 °C. The maximum values for adsorption capacity, q max, were 28.7 and 164.6 mg/g on native and modified Z. vulgaris wastes, respectively, at pH 5 and 30 °C with a contact time 2 h and an initial metal ion concentration of 400 mg/L. The equilibrium data were well fitted by the Langmuir and Freundlich adsorption models and demonstrated the significant capacity for Z. vulgaris wastes in the removal of Zn(II) ions from aqueous solutions.  相似文献   

11.
In the present work, a continuous catalytic wet peroxide oxidation fixed bed reactor was employed to treat a simulated wastewater sample with malachite green dye, as a contaminant. Natural perlite particle-supported nano-Fe3O4 catalyst was used as a fixed bed inside a reactor, and it was immobilized by a persistent magnetic field. The range of (perlite) particle sizes was from 100 to 1000 nm. The effects of various operating parameters, including temperature of the reactor, pH, initial hydrogen peroxide concentration and initial dye concentration, were investigated on the percentage removal of malachite green dye. Load of catalyst of 2 g and volumetric flow rate of 1 L/h were selected for all the tests. Maximum malachite green degradation was 99.5 ± 0.3%. This removal percentage was attained at temperature of 80 °C, pH = 6, initial dye concentration of 6 mg/L and initial hydrogen peroxide concentration of 100 mg/L. The process was isotherm, and the catalyst showed high catalytic activity in the steady-state condition. The loss of catalyst was less than 0.3%.  相似文献   

12.
The spatial distribution of arsenic (As) concentrations along three classified hydrogeomorphological zones in the Brahmaputra River Valley in Assam (India) have been investigated: zone I, comprising the piedmont and alluvial fans; zone II, comprising the runoff areas; and zone III, comprising the discharge zones. Groundwater (150 samples) from shallow hand-pumped and public water supply wells (2–60 m in depth) was analysed for chemical composition to examine the geochemical processes controlling As mobilization. As concentrations up to 0.134 mg/L were recorded, with concentrations below the World Health Organization and the Bureau of Indian Standards drinking-water limits of 0.01 mg/L being found mainly in the proximal recharge areas. Eh and other redox indicators (i.e., dissolved oxygen, Fe, Mn and As) indicate that, except for samples taken in the recharge zone, groundwater is reducing and exhibits a systematic decrease in redox conditions along the runoff and discharge zones. Hydrogeochemical evaluation indicated that zone I, located along the proximal recharge areas, is characterized by low As concentration, while zones II and III are areas with high and moderate concentrations, respectively. Systematic changes in As concentrations along the three zones support the view that areas of active recharge with high hydraulic gradient are potential areas hosting low-As aquifers.  相似文献   

13.
An alternative iron removal treatment method using liquid-liquid extraction with the room-temperature ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, as a solvent medium was studied. The chelating agent 1,10-phenanthroline was used as the extractant. The extraction of Fe(III) and Fe(II) was influenced significantly by the pH of the aqueous phase. The successful removal of iron was achieved; more than 95 % of the initial iron concentration was removed from the groundwater samples. However, detailed research is needed before the ionic liquid method can replace the conventional groundwater treatment protocol because the recovery rate was very low upon reuse (approximately 25–60 %). This low recovery was due to the ion exchange process; the appearance of anions from ionic liquids was also detected in groundwater samples.  相似文献   

14.
In this study, the performance of moving-bed biofilm sequencing batch reactor in operating the anaerobic/anoxic/oxic (A2O) process for treatment of wastewaters containing nitrogen and phosphorous was evaluated. For this purpose, a pilot system with two bench-scale sequencing batch reactors with a total volume of 30 L and functional volume of 10 L was used. The installation was elaborated using plexiglass, in which 60% of the functional volume consisted of PVC suspended carriers (Kaldnes K3) with a specific surface area of 560 m2/m3. The independent variables used in this study were hydraulic retention time (HRT) (1.5, 2, 2.5, 3, and 3.5 h) and the initial organic load (300, 500, 800, 1000 mg O2/L). The results showed impressive performance in the case of an initial organic load of 300 mg O2/L and HRT of 3 h with maximum removal of COD and TN, respectively, by 95.1 and 89.8%. In the case of an initial organic load of 1000 mg O2/L and HRT of 3.5 h, the maximum total phosphorus removal was 72.3%. Therefore, according to the analysis of data obtained by different HRTs, it was revealed that the system of A2O has greater efficiency in removing organic matter from wastewater in the shortest possible time.  相似文献   

15.
Limestone-based material can reduce concentrations of cadmium below 0.001 mg/L (1 ppb) in water, resulting in > 99% removal efficiency. Thermodynamic constraints appear to be favorable for reactions involving the formation of otavite during cadmium removal. Thermodynamic values for these reactions yield a theoretical removal limit of 0.0015 mg/L or better for cadmium, in reasonable agreement with tests on laboratory and field samples that show cadmium removal at levels less than 0.001 mg/L.  相似文献   

16.
In this study, sepiolite-nano zero valent iron composite was synthesized and applied for its potential adsorption to remove phosphates from aqueous solution. This composite was characterized by different techniques. For optimization of independent parameters (pH = 3–9; initial phosphate concentration = 5–100 mg/L; adsorbent dosage = 0.2–1 g/L; and contact time = 5–100 min), response surface methodology based on central composite design was used. Adsorption isotherms and kinetic models were done under optimum conditions. The results indicated that maximum adsorption efficiency of 99.43 and 92% for synthetic solution and real surface water sample, respectively, were achieved at optimum conditions of pH 4.5, initial phosphate concentration of 25 mg/L, adsorbent dosage of 0.8 g/L, and 46.26 min contact time. The interaction between adsorbent and adsorbate is better described with the Freundlich isotherm (R 2 = 0.9537), and the kinetic of adsorption process followed pseudo-second-order model. Electrostatic interaction was the major mechanisms of the removal of phosphates from aqueous solution. The findings of this study showed that there is an effective adsorbent for removal of phosphates from aqueous solutions.  相似文献   

17.
Naturally occurring pyroclastic materials, quartz-rich tuffs (Qz) and stellerite tuffs, were evaluated for their capacities to remove As(V) from aqueous solutions. The mechanism of As(V) uptake was evaluated using sequential extraction of As(V)-loaded adsorbent which entailed that the plausible removal mechanism is sorption to short-range ordered hydrous oxides of iron and aluminum. In addition, buffering effects of adsorbents could form favorable charges upon them through hydrolysis of amphoteric oxides, enhancing the performance of sorption. The influence of anions co-existing with As(V) in water such as carbonate, bicarbonate, nitrate, chloride, phosphate, and sulfate was studied in a batch sorption process. The impact of most anions on As(V) removal was found to be negligible except phosphate. The sorption behavior well fitted to Langmuir and Freundlich models. Estimated maximum sorption capacities of 0.42 and 0.23 mg/L were observed using quartz-rich tuffs and stellerite tuffs, respectively. As(V) concentration of 0.8 mg/L was easily decreased to below the drinking water standard of 0.01 mg/L using Qz adsorbent, whereas 0.1 mg/L As(V) decreased to below this limit upon the use of stellerite tuffs under similar conditions. The buffering capacity of quartz-rich tuffs and stellerite tuffs induced a pH increase to 5.76 and 5.40, respectively, from initial pH of 3.50, which will incur an important asset in real applications.  相似文献   

18.
Incidence of high fluoride (F?) in groundwater (>1.5 mg/L) in two tribal belts of eastern India, one around Chukru in the Palamau district of Jharkhand and the other around Karlakot in the Nuapada district of Odisha, has been studied. The maximum concentration of F? in groundwater from dug wells and tube wells is 10.30 mg/L in Chukru and 4.62 mg/L in Karlakot. The groundwaters are mildly alkaline with pH ranges of 7.52–8.22 and 7.33–8.20 in Chukru and Karlakot, respectively. The F? concentration is positively correlated with pH, electrical conductivity and SO4 2? in both areas. The high F? in groundwater resulted mainly from dissolution of biotite and fluorapatite in quartzofeldspathic gneiss. The ionic dominance pattern (in meq/L) is mostly in the order Ca2+ > Na+ > Mg2+ > K+ among cations and HCO3 ? > SO4 2? > < Cl? > F? among anions in the Karlakot groundwater. Preliminary adsorption experiments were conducted on natural haematite iron ore and synthetic magnetite to evaluate their potential for F? removal from water. Effects of different parameters such as contact time, pH, adsorbent dose and initial F? concentration on the adsorption capacity of these materials were investigated. Strong dependence of F? removal on pH was observed for both the adsorbents. With natural haematite iron ore, the maximum F? removal of 66 % occurred at an initial pH of 3.2 for a solution with F? concentration of 3 mg/L, adsorbent dose of 7 g/L and overnight contact time. The haematite iron ore was observed to increase the pH of the F? solution. Adsorption equilibrium was not achieved with this adsorbent even after a contact time of 45.2 h. In the case of synthetic magnetite, 84 % F? removal was achieved after 2 min of contact time for a solution with F? concentration of 6 mg/L, adsorbent dose of 10 g/L and initial pH of 7. The results indicate high potential of both natural haematite iron ore and synthetic magnetite as adsorbents of F? in water.  相似文献   

19.
Regional study on the impact of variations in input rainfall over groundwater quality and its suitability for utilitarian purposes is essential for its extraction and management. Water chemistry from 456 observations wells for 2007–2011 period in hard rock Basaltic terrain of Upper Godavari basin is supported with 8 field samples (in 2014) in this analysis. Based on mean annual rainfall (MAR), four narrow climatic zones are identified in the basin, defined as “humid” (MAR > 1600 mm), “sub-humid” (1600–1000 mm), “semi-arid” (1000–600 mm), and “arid” (MAR < 600 mm). NICB ratio (<±10%), and anionic percentages demarcated the polluted areas from rest “good data”, composing of 1818 samples. Hydrochemical facies are studied using Piper diagram, secondary alkalinity exceeded 50% and not one cation–anion pair exceeded 50%, and silicate–carbonate plot, arid zone nearer to silicate pole indicated the dominance of SiO2 in Ca/Na vs Mg/Na plot. These geochemical variations emphasize a detailed study on role of climatic gradient on groundwater suitability for different purposes, for groundwater extraction, and its management. Suitability of groundwater for drinking based on water quality indices (WQI) indicated 98% of the samples as suitable (WQI < 50%). TDS in humid zone is 150–500 and 500–1000 mg/L in rest of the zones with ～68% in permissible range, 15% as hard water (TDS > 600 mg/L) and not acceptable for drinking. Suitability of groundwater for irrigation is studied using sodium percentage (Na %), Wilcox diagram, sodium absorption ratio (SAR), US salinity diagram, residual sodium carbonate (RSC), permeability index (PI), Kelly’s ratio (KR), ancd magnesium absorption ratio (MgAR). Na % in four zones is < 60% and permissible for irrigation. Very few water samples fall in “doubtful to unsuitable” and “unsuitable” category of Wilcox diagram. Region is observed to have SAR < 6, indicating that water would not cause any problem to the soil and crop. Humid and sub-humid zones belonged to C1S1 and C2S1 categories (low and medium sodium), while semi-arid extended to C3S1 category (salinity hazard zone) in US salinity plot. RSC for all the three zones ranged from 1 to 1.5 meq/L, with 90–95% of the area safe for irrigation. Out of 1818 samples, 1129 belonged to class 2 of PI classification (PI ranging from 25 to 75%) while rest 689 samples had PI >75% (class 1). KR varied from 0.05 to 12.81, with 70–80% of the area having KR < 1. MgAR ratio ranged from 67% to 96%, with sub-humid, humid zones having higher Mg concentrations (increased salinity). Thus, 90% of the samples indicated non-alkaline water with 1% of normal alkalinity. Hence, the current study systematically analyzed the effect of precipitation and geology on groundwater quality and on its usability for various purposes. This stepwise procedure categorized the regions, and the same can be adopted for any regional hydrogeochemical studies.  相似文献   

20.
A new polymorph of FeS has been observed at pressures above 30 GPa at 1,300 K by in situ synchrotron X-ray diffraction measurements in a laser-heated diamond anvil cell. It is stable up to, at least, 170 GPa at 1,300 K. The new phase (here called FeS VI) has an orthorhombic unit cell with lattice parameters a = 4.8322 (17) Å, b = 3.0321 (6) Å, and c = 5.0209 (8) Å at 85 GPa and 300 K. Its topological framework is based on the NiAs-type structure as is the case for the other reported polymorphs (FeS I-V). The unit cell of FeS VI is, however, more distorted (contracted) along the [010] direction of the original NiAs-type cell. For example, the c/b axial ratio is ～1.66 at 85 GPa and 300 K, which is considerably smaller than that of orthorhombic FeS II (～1.72) and NiAs-type hexagonal FeS V (=√3 ≈ 1.73). The phase boundary between FeS IV and VI is expected to be located around 30 GPa at 1,300 K. The phase transition is accompanied by gradual and continuous changes in volume and axial ratios and may be second order. At room temperature, FeS VI becomes stable over FeS III at pressures above 36 GPa. It is, therefore, suggested that the phase boundary of FeS III–VI and/or FeS IV–VI has negative pressure dependence.  相似文献   

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