Separation of H<Subscript>2</Subscript>S from CH<Subscript>4</Subscript> by polymeric membranes at different H<Subscript>2</Subscript>S concentrations

In this work, permeation of mixed gases H₂S/CH₄ through commercial polyphenylene oxide (PPO) hollow fiber and poly (ester urethane) urea (PEUU) flat membranes was studied at pressures of 345–689 kPa, at ambient temperature and at 313.15 K. Various H₂S concentrations of about 100–5000 ppm in CH₄ binary synthetic gas mixtures as well as a real natural gas sample obtained from a gas refinery containing 0.3360 mol.% H₂S (equivalent to 3360 ppm) were tested. It was observed that the permeance of components was affected by the balance between competitive sorption and plasticization effects. Separation factors of H₂S/CH₄ were in the range of 1.3–2.9, 1.8–3.1 and 2.2–4.3 at pressures of 345, 517 and 689 kPa, respectively. In the range of 101–5008 ppm of H₂S in CH₄, the effect of temperature on the separation factor was nearly negligible; however, permeances of both components of the mixtures increased with temperature. Additionally, the results obtained by PEUU membrane indicated that it was a better choice for hydrogen sulfide separation from H₂S/CH₄ mixtures than PPO. For PPO membrane, removal of hydrogen sulfide from high-concentration (up to 5008 ppm) binary mixtures of H₂S/CH₄ was compared with that of low concentration (as low as 101 ppm) through PPO. At concentrations of 101–968 ppm, plasticization was dominant compared with the competitive sorption, while for the H₂S feed concentrations of 3048 ppm, the competitive sorption effect was dominant. For H₂S concentration of 5008 ppm, the balance between these two effects played an important role for explanation of its trend.     

Preparation of carbon molecular sieves and its impregnation with Co and Ni for CO<Subscript>2</Subscript>/N<Subscript>2</Subscript> separation

The carbon molecular sieves (CMSs) prepared by carbonaceous materials as precursors are effective in CO₂/N₂ separation. However, selectivity of these materials is too low, since hydrocarbon cracking for developing the desired microporosity in carbonaceous materials has not been done effectively. Hence, in this study, cobalt and nickel impregnation on the precursor was conducted to introduce catalysts for hydrocarbon cracking. Cobalt and nickel impregnation, carbonization under N₂ atmosphere, and chemical vapor deposition (CVD) by benzene were conducted on the extruded mixtures of activated carbon and coal tar pitch under different conditions to prepare CMSs. The best CMS prepared by carbon deposition on the cobalt-impregnated samples exhibited CO₂ adsorption capacity of 54.79 mg/g and uptake ratio of 28.9 at 0 °C and 1 bar. In terms of CO₂ adsorption capacity and uptake ratio, CMSs prepared by carbon deposition on non-impregnated and cobalt-impregnated samples presented the best results, respectively. As benzene concentration and CVD time increased, equilibrium adsorption capacity of CO₂ decreased, and uptake ratio increased. Cobalt was found to be the best catalyst for benzene cracking in the CVD process.     

Feasibility of CO<Subscript>2</Subscript> adsorption by solid adsorbents: a review on low-temperature systems

In the last few decades of industrialization, the concentration of CO₂ in the atmosphere had increased rapidly. Different organizations have invested considerable funds in research activities worldwide for CO₂ capture and storage. To date, significant work has been done and various technologies have been proposed for CO₂ capture and storage. Both adsorption and absorption are promising techniques for CO₂ capture, but low-temperature adsorption processes using solid adsorbents are the prevailing technique nowadays. In this review paper, a variety of adsorbents such as carbonaceous materials, dry alkali metal-based sorbents, zeolites, metal–organic frameworks (MOFs) and microporous organic polymers (MOPs) have been studied. Various methods of chemical or physical modification and the effects of supporting materials have been discussed to enhance CO₂ capture capacity of these adsorbents. Low-temperature (<100 °C) adsorption processes for CO₂ capture are critically analyzed and concluded on the basis of information available so far in the literature. All the information in CO₂ adsorption using different routes has been discussed, summarized and thoroughly presented in this review article. The most important comparative study of relatively new material MOFs and MOPs is carried out between the groups and with other sorbent as well.     

Influence of chlorine substitution on adsorption of gaseous chlorinated phenolics on multi-walled carbon nanotubes embedded in SiO<Subscript>2</Subscript>

Multi-walled carbon nanotubes (MWCNTs) embedded in SiO₂ particles were prepared through the floating-catalyst chemical vapor deposition method. The parameters reaction time and flow rate of the carbon source (CH₄) were studied to obtain optimum conditions for MWCNT synthesis. The obtained MWCNTs were characterized by transmission electron microscopy, scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy to confirm their morphology and crystallinity. The optimum conditions were a CH₄ flow rate of 100 ml/min in a H₂–Ar mixture at a flow rate of 500 ml/min and a reaction time of 20 min. Under these conditions, MWCNTs with average outer and inner diameters of around 50 and 10 nm, respectively, were obtained. SiO₂ particles with embedded MWCNTs were studied for their adsorption of gaseous chlorinated phenolic compounds (CPCs), with emphasis on the effect of number of chlorine substituents. The CPC compounds of 2-chlorophenol (CP) and 2,4-dichlorophenol (DCP) were compared against phenol (P). Adsorption of P and CPCs on the particles fit well the Langmuir isotherm. The adsorption capacities of P, CP, and DCP on SiO₂ particles with embedded MWCNTs were found to be 3.12, 13.83, and 44.25 mg/g, respectively. Desorption activation energy was determined by thermogravimetric analysis. Chlorine substitution on P changed the adsorption process from physical to chemical adsorption. The particles showed high potential for use as a pre-concentration unit for solid-phase microextraction.     

The effect of alkalis and polymerization on the solubility of H<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> in alkali-rich silicate melts

The effect of alkalis on the solubility of H₂O and CO₂ in alkali-rich silicate melts was investigated at 500 MPa and 1,250 °C in the systems with H₂O/(H₂O + CO₂) ratio varying from 0 to 1. Using a synthetic analog of phonotephritic magma from Alban Hills (AH1) as a base composition, the Na/(Na + K) ratio was varied from 0.28 (AH1) to 0.60 (AH2) and 0.85 (AH3) at roughly constant total alkali content. The obtained results were compared with the data for shoshonitic and latitic melts having similar total alkali content but different structural characteristics, e.g., NBO/T parameter (the ratio of non-bridging oxygens over tetrahedrally coordinated cations), as those of the AH compositions. Little variation was observed in H₂O solubility (melt equilibrated with pure H₂O fluid) for the whole compositional range in this study with values ranging between 9.7 and 10.2 wt. As previously shown, the maximum CO₂ content in melts equilibrated with CO₂-rich fluids increases strongly with the NBO/T from 0.29 wt % for latite (NBO/T = 0.17) to 0.45 wt % for shoshonite (NBO/T = 0.38) to 0.90 wt % for AH2 (NBO/T = 0.55). The highest CO₂ contents determined for AH3 and AH1 are 1.18 ± 0.05 wt % and 0.86 ± 0.12 wt %, respectively, indicating that Na is promoting carbonate incorporation stronger than potassium. At near constant NBO/T, CO₂ solubility increases from 0.86 ± 0.12 wt % in AH1 [Na/(Na + K)] = 0.28, to 1.18 ± 0.05 wt % in AH3 [Na/(Na + K)] = 0.85, suggesting that Na favors CO₂ solubility on an equimolar basis. An empirical equation is proposed to predict the maximum CO₂ solubility at 500 MPa and 1,100–1,300 °C in various silicate melts as a function of the NBO/T, (Na + K)/∑cations and Na/(Na + K) parameters: \({\text{wt}}\% \;{\text{CO}}_{2} = - 0.246 + 0.014\exp \left( {6.995 \cdot \frac{\text{NBO}}{T}} \right) + 3.150 \cdot \frac{{{\text{Na}} + {\text{K}}}}{{\varSigma {\text{cations}}}} + 0.222 \cdot \frac{\text{Na}}{{{\text{Na}} + {\text{K}}}}.\) This model is valid for melt compositions with NBO/T between 0.0 and 0.6, (Na + K)/∑cation between 0.08 and 0.36 and Na/(Na + K) ratio from 0.25 to 0.95 at oxygen fugacities around the quartz–fayalite–magnetite buffer and above.     

Adsorption of methylene blue and crystal violet on low-cost adsorbent: waste fruits of <Emphasis Type="Italic">Rapanea ferruginea</Emphasis> (ethanol-treated and H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-treated)

This study assesses the ability of two low-cost adsorbents made from waste of Rapanea ferruginea treated with ethanol (WRf) and its H₂SO₄-treated analog (WRf/H₂SO₄) for the removal of two cationic dyes methylene blue (MB) and crystal violet (CV) from aqueous solutions. The adsorbent was characterized by scanning electron microscopy, Fourier transform infrared spectrometry, thermogravimetric analysis, point of zero charge (pH_pzc), specific surface, and functional groups. The adsorption of dye onto the adsorbents was studied as a function of pH solution (2–12), contact time (up to 120 min) and initial concentration (20–120 mg/L), and temperature (25, 35, and 55 °C). The influence of these parameters on adsorption capacity was studied using the batch process. The response surface methodology (RSM) was used in the experimental design, modeling of the process, and optimizing of the variables and was optimized by the response involving Box–Behnken factorial design (15 runs). The results show that the data correlated well with the Sips isotherm. The maximum adsorption capacities of MB and CV onto WRf were found to be 69 and 106 mg/g, and onto WRf/H₂SO₄, the adsorption capacities were 33 and 125 mg/g, respectively. The kinetic data revealed that adsorption of cationic dyes onto the adsorbents closely follows the pseudo-second-order kinetic model. Regression analysis showed good fit of the experimental data to the second-order polynomial model, with coefficient of determination (R²) values for MB (R²?=?0.9685) and MB (R²?=?0.9832) for WRf and CV (R²?=?0.9685) and CV (R²?=?0.9832) for WRf/H₂SO₄ indicated that regression analysis is able to give a good prediction of response for the adsorption process in the range studied. The results revealed that waste from R. ferruginea is potentially an efficient and low-cost adsorbent for adsorption of MB and CV.     

CO<Subscript>2</Subscript> mineralization of natural wollastonite into porous silica and CaCO<Subscript>3</Subscript> powders promoted via membrane electrolysis

CO₂ is a greenhouse gas, whose emissions threaten the existence of human beings. Its inherently safe sequestration can be performed via CO₂ mineralization, which is relatively slow under natural conditions. In this work, an energy-saving membrane electrolysis technique was proposed for accelerating the CO₂ mineralization of wollastonite into SiO₂ and CaCO₃ products. The electrolysis process involved splitting NH₄Cl into HCl and NH₃·H₂O via hydrogen oxidation and water reduction at the anode and cathode of the electrolytic system, respectively. In contrast to the chlor-alkali electrolysis, this method did not involve Cl^? oxidation and the standard potential of the anode was reduced. Additionally, NH₄Cl was used as the electrolyte instead of NaCl; as a result, the generation of NH₃·H₂O instead of NaOH occurred in the catholyte and the cathodic pH dramatically decreased, thus reducing the cathodic potential for hydrogen evolution. The observed changes led to a 73.5% decrease in the energy consumption. Moreover, after the process of CO₂ mineralization was optimized, SiO₂ with a specific surface area of 221.8 m² g^?1 and CaCO₃ with a purity of 99.9% were obtained.     

Study of carbon dioxide and methane equilibrium adsorption on silicoaluminophosphate-34 zeotype and T-type zeolite as adsorbent

Carbon dioxide is known as a hazardous material with acidic property that can be found as impurity in natural gas reservoirs with a broad range of 2 up to 40 %. Therefore, many efforts have been directed to remove and separate carbon dioxide from methane to prevent corrosion problems as well as improving the natural gas energy content. In this study, two molecular sieves, silicoaluminophosphate-34 (SAPO-34) zeotype and T-type zeolite, were synthesized by the hydrothermal method for the comparative study of adsorptive separation of carbon dioxide from methane. The synthesized adsorbents were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Brunner–Emmett–Teller techniques. These characterization tests confirmed formation of both materials with acceptable crystallinity. Both adsorbents were tested in equilibrium adsorption experiments in order to evaluate maximum capacity and adsorption affinity. Adsorption capacity of carbon dioxide and methane on SAPO-34 and zeolite T were measured in a pressure range of 0.1–2.0 MPa and temperature of 288, 298, and 308 K and fitted with the Sips and Langmuir isotherm models. The ideal selectivity of CO₂/CH₄ was determined for SAPO-34 and zeolite T at the studied pressures and temperatures, indicating that the molecular sieves can be properly used for CO₂–CH₄ separation or CO₂ capturing from natural gas.     

The Role of CaCO<Subscript>3</Subscript> Reactions in the Contemporary Oceanic CO<Subscript>2</Subscript> Cycle

The present analysis adjusts previous estimates of global ocean CaCO₃ production rates substantially upward, to 133 × 10¹² mol yr^?1 plankton production and 42 × 10¹² mol yr^?1 shelf benthos production. The plankton adjustment is consistent with recent satellite-based estimates; the benthos adjustment includes primarily an upward adjustment of CaCO₃ production on so-called carbonate-poor sedimentary shelves and secondarily pays greater attention to high CaCO₃ mass (calcimass) and turnover of shelf communities on temperate and polar shelves. Estimated CaCO₃ sediment accumulation rates remain about the same as they have been for some years: ~20 × 10¹² mol yr^?1 on shelves and 11 × 10¹² mol yr^?1 in the deep ocean. The differences between production and accumulation of calcareous materials call for dissolution of ~22 × 10¹² mol yr^?1 (~50 %) of shelf benthonic carbonate production and 122 × 10¹² mol yr^?1 (>90 %) of planktonic production. Most CaCO₃ production, whether planktonic or benthonic, is assumed to take place in water depths of <100 m, while most dissolution is assumed to occur below this depth. The molar ratio of CO₂ release to CaCO₃ precipitation (CO₂↑/CaCO₃↓) is <1.0 and varies with depth. This ratio, Ψ, is presently about 0.66 in surface seawater and 0.85 in ocean waters deeper than about 1000 m. The net flux of CO₂ associated with CaCO₃ reactions in the global ocean in late preindustrial time is estimated to be an apparent influx from the atmosphere to the ocean, of +7 × 10¹² mol C yr^?1, at a time scale of 10²–10³ years. The CaCO₃-mediated influx of CO₂ is approximately offset by CO₂ release from organic C oxidation in the water column. Continuing ocean acidification will have effects on CaCO₃ and organic C metabolic responses to the oceanic inorganic C cycle, although those responses remain poorly quantified.     

Reinventing rice husk ash: derived NaX zeolite as a high-performing CO<Subscript>2</Subscript> adsorbent

In this work, rice husk ash was used as silica source to synthesize NaX zeolite potentially suitable for CO₂ adsorption. The produced material, denoted NaX-RHA, was characterized employing X-ray diffraction, scanning electron microscopy and gas adsorption porosimetry, in order to verify the occurred production of well-crystallized NaX zeolite with a significant degree of purity. CO₂ adsorption isotherms on NaX-RHA were volumetrically evaluated in the 298–348 K temperature range up to standard pressure, revealing performances that are higher than those reported for commercial similar substrates. The experimental data regarding CO₂ adsorption on NaX-RHA were very satisfyingly fitted by the semiempirical Sips model. Analyzing the best fitting values of model parameters allowed to conclude that the synthesized adsorbent could be quite suitable for applications like CO₂ capture from flue gas.     

The influence of degradation of the swamp and alpine meadows on CH<Subscript>4</Subscript> and CO<Subscript>2</Subscript> fluxes on the Qinghai-Tibetan Plateau

CH₄ and CO₂ fluxes from a high-cold swamp meadow and an alpine meadow on the Qinghai-Tibetan Plateau, subject to different degrees of degradation, were measured over a 12-month period. Air temperature, soil temperature and moisture, and the depths of the water table and thawing-freezing layer were determined. For swamp meadows, the greater the degradation, the lesser the carbon efflux. CH₄ emissions at the nondegraded swamp meadow site were 1.09–3.5 and 2.5–11.27 times greater, and CO₂ emissions 1.08–1.69 and 1.41–4.43 times greater, respectively, than those from moderately and severely degraded sites. For alpine meadows, the greater the degradation, the greater the CH₄ consumption and CO₂ emissions. CH₄ consumption at the severely degraded alpine meadow site was 6.6–21 and 1.1–5.25 times greater, and CO₂ emissions 1.05–78.5 and 1.04–6.28 times greater, respectively, than those from the nondegraded and moderately degraded sites. The CH₄ and CO₂ fluxes at both sites were significantly correlated (R ² > 0.59, P < 0.05) with air temperature, soil temperature, and topsoil (0–5 cm depth) moisture, indicating these to be the main environmental factors affecting such fluxes.     

Compressibility of strontium orthophosphate Sr<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript> at high pressure

High pressure in situ synchrotron X-ray diffraction experiment of strontium orthophosphate Sr₃(PO₄)₂ has been carried out to 20.0 GPa at room temperature using multianvil apparatus. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a volume of V ₀ = 498.0 ± 0.1 Å³, an isothermal bulk modulus of K _T  = 89.5 ± 1.7 GPa, and first pressure derivative of K _T ′ = 6.57 ± 0.34. If K _T ′ is fixed at 4, K _T is obtained as 104.4 ± 1.2 GPa. Analysis of axial compressible modulus shows that the a-axis (K _a  = 79.6 ± 3.2 GPa) is more compressible than the c-axis (K _c  = 116.4 ± 4.3 GPa). Based on the high pressure Raman spectroscopic results, the mode Grüneisen parameters are determined and the average mode Grüneisen parameter of PO₄ vibrations of Sr₃(PO₄)₂ is calculated to be 0.30(2).     

Pressure induced phase transition in Pb<Subscript>6</Subscript>Bi<Subscript>2</Subscript>S<Subscript>9</Subscript>

The crystal structure of Pb₆Bi₂S₉ is investigated at pressures between 0 and 5.6 GPa with X-ray diffraction on single-crystals. The pressure is applied using diamond anvil cells. Heyrovskyite (Bbmm, a = 13.719(4) Å, b = 31.393(9) Å, c = 4.1319(10) Å, Z = 4) is the stable phase of Pb₆Bi₂S₉ at ambient conditions and is built from distorted moduli of PbS-archetype structure with a low stereochemical activity of the Pb²⁺ and Bi³⁺ lone electron pairs. Heyrovskyite is stable until at least 3.9 GPa and a first-order phase transition occurs between 3.9 and 4.8 GPa. A single-crystal is retained after the reversible phase transition despite an anisotropic contraction of the unit cell and a volume decrease of 4.2%. The crystal structure of the high pressure phase, β-Pb₆Bi₂S₉, is solved in Pna2 ₁ (a = 25.302(7) Å, b = 30.819(9) Å, c = 4.0640(13) Å, Z = 8) from synchrotron data at 5.06 GPa. This structure consists of two types of moduli with SnS/TlI-archetype structure in which the Pb and Bi lone pairs are strongly expressed. The mechanism of the phase transition is described in detail and the results are compared to the closely related phase transition in Pb₃Bi₂S₆ (lillianite).     

Elastic behavior of vanadinite,Pb<Subscript>10</Subscript>(VO<Subscript>4</Subscript>)<Subscript>6</Subscript>Cl<Subscript>2</Subscript>, a microporous non-zeolitic mineral

The high-pressure behavior of a vanadinite (Pb₁₀(VO₄)₆Cl₂, a = b = 10.3254(5), c = 7.3450(4) Å, space group P6₃/m), a natural microporous mineral, has been investigated using in-situ HP-synchrotron X-ray powder diffraction up to 7.67 GPa with a diamond anvil cell under hydrostatic conditions. No phase transition has been observed within the pressure range investigated. Axial and volume isothermal Equations of State (EoS) of vanadinite were determined. Fitting the P–V data with a third-order Birch-Murnaghan (BM) EoS, using the data weighted by the uncertainties in P and V, we obtained: V ₀ = 681(1) Å³, K ₀ = 41(5) GPa, and K′ = 12.5(2.5). The evolution of the lattice constants with P shows a strong anisotropic compression pattern. The axial bulk moduli were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: a ₀ = 10.3302(2) Å, K ₀(a) = 35(2) GPa and K′(a) = 10(1) for the a-axis; c ₀ = 7.3520(3) Å, K ₀(c) = 98(4) GPa, and K′(c) = 9(2) for the c-axis (K ₀(a):K ₀(c) = 1:2.80). Axial and volume Eulerian-finite strain (fe) at different normalized stress (Fe) were calculated. The weighted linear regression through the data points yields the following intercept values: Fe _a (0) = 35(2) GPa for the a-axis, Fe _c (0) = 98(4) GPa for the c-axis and Fe _V (0) = 45(2) GPa for the unit-cell volume. The slope of the regression lines gives rise to K′ values of 10(1) for the a-axis, 9(2) for the c-axis and 11(1) for the unit cell-volume. A comparison between the HP-elastic response of vanadinite and the iso-structural apatite is carried out. The possible reasons of the elastic anisotropy are discussed.     

Influences of activated sludge surface properties on adsorption of aqueous fullerene C<Subscript>60</Subscript> nanoparticles

Rapid increases in the amounts of fullerene C₆₀ nanoparticles (nC₆₀) being produced and used will inevitably lead to increases in the amounts released into the aquatic environment. This will have implications for human and ecosystem health. Wastewater treatment plants are key barriers to nC₆₀ being released into aquatic systems, but little information is available on how adsorption processes in wastewater treatment plants affect the fates of nC₆₀. We investigated the effects of the surface properties of activated sludge on the adsorption of nC₆₀ and related mechanisms by modeling the adsorption kinetics and equilibrium process and performing correlation analyses. The adsorption of nC₆₀ closely followed the pseudo-second-order kinetic model (R > 0.983), the Freundlich isotherm model (R > 0.990), and the linear partitioning isotherm model (R > 0.966). Different adsorption coefficients, 1.070–4.623 for the Freundlich partitioning model and 1.788–6.148 for the linear partitioning model, were found for different types of activated sludge. The adsorption coefficients significantly positively correlated with the zeta (ζ) potential (R = 0.877) and hydrophobicity (R = 0.661) and negatively correlated with particle size (R = ?0.750). The results show that nC₆₀ adsorption is strongly affected by the surface properties of activated sludge because changes in surface properties cause changes in the electrostatic and hydrophobic interactions that occur.     

Rutile/TiO<Subscript>2</Subscript>II phase equilibria

The transition between rutile and α-PbO₂ structured TiO₂ (TiO₂II) has been investigated at 700–1,200 °C and 4.2–9.6 GPa. Hydrothermal phase equilibrium experiments were performed in the multi-anvil apparatus to bracket the phase boundary at 700, 1,000, and 1,200 °C. The equilibrium phase boundary is described by the equation: P (GPa)=1.29+0.0065 T ( °C). In addition, growth of TiO₂II was observed in experiments at 500 and 600 °C, although growth of rutile was too slow to bracket unambiguously the equilibrium boundary at these temperatures. Water was not detected in either rutile or TiO₂II, and dry synthesis experiments at 1,200 °C were consistent with the phase boundary determined in the fluid-bearing experiments, suggesting that the equilibrium is unaffected by the presence of water. Our bracket of the phase boundary at 700 °C is consistent with the reversed, dry experiments of Akaogi et al. (1992) and the reversals of Olsen et al. (1999). The new data suggest that the phase boundary is linear, in agreement with Akaogi et al. (1992), but in striking contrast to the phase diagram inferred by Olsen et al. (1999). The natural occurrence of TiO₂II requires formation pressures considerably higher than the graphite–diamond phase boundary.     

CO<Subscript>2</Subscript> fluid inclusions in Jack Hills zircons

The discovery of Hadean to Paleoarchean zircons in a metaconglomerate from Jack Hills, Western Australia, has catalyzed intensive study of these zircons and their mineral inclusions, as they represent unique geochemical archives that can be used to unravel the geological evolution of early Earth. Here, we report the occurrence and physical properties of previously undetected CO₂ inclusions that were identified in 3.36–3.47 Ga and 3.80–4.13 Ga zircon grains by confocal micro-Raman spectroscopy. Minimum P–T conditions of zircon formation were determined from the highest density of the inclusions, determined from the density-dependence of the Fermi diad splitting in the Raman spectrum and Ti-in-zircon thermometry. For both age periods, the CO₂ densities and Ti-in-zircon temperatures correspond to high-grade metamorphic conditions (≥5 to ≥7 kbar/~670 to 770 °C) that are typical of mid-crustal regional metamorphism throughout Earth’s history. In addition, fully enclosed, highly disordered graphitic carbon inclusions were identified in two zircon grains from the older population that also contained CO₂ inclusions. Transmission electron microscopy on one of these inclusions revealed that carbon forms a thin amorphous film on the inclusion wall, whereas the rest of the volume was probably occupied by CO₂ prior to analysis. This indicates a close relationship between CO₂ and the reduced carbon inclusions and, in particular that the carbon precipitated from a CO₂-rich fluid, which is inconsistent with the recently proposed biogenic origin of carbon inclusions found in Hadean zircons from Jack Hills.     

Effects of nitrogen on the ecosystem respiration,CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions to the atmosphere from the freshwater marshes in northeast China

Freshwater marshes could be a source of greenhouse gases emission because they contain large amounts of soil carbon and nitrogen. These emissions are strongly influenced by exogenous nitrogen. We investigate the effects of exogenous nitrogen on ecosystem respiration (CO₂), CH₄ and N₂O emissions from freshwater marshes in situ in the Sanjiang Plain Northeast of China during the growing seasons of 2004 and 2005, using a field fertilizer experiment and the static opaque chamber/GC techniques. The results show that there were no significant differences in patterns of seasonal variations of CO₂ and CH₄ among the fertilizer and non-fertilizer treatments, but the seasonal patterns of N₂O emission were significantly influenced by the exogenous nitrogen. Seasonal averages of the CO₂ flux from non-fertilizer and fertilizer were 987.74 and 1,344.35 mg m ⁻² h ⁻¹, respectively, in 2004, and 898.59 and 2,154.17 mg m ⁻² h ⁻¹, respectively, in 2005. And the CH₄ from the control and fertilizer treatments were 6.05 and 13.56 mg m ⁻² h ⁻¹ and 0.72 and 1.88 mg m ⁻² h ⁻¹, respectively, in 2004 and 2005. The difference of N₂O flux between the fertilizer and non-fertilizer treatments is also significant either in 2004 and 2005. On the time scale of 20-, 100-, and 500-year periods, the integrated global warming potential (GWP) of CO₂ + CH₄ + N₂O released during the two growing seasons for the treatment of fertilizer was 97, 94 and 89%, respectively, higher than that for the control, which suggested that the nitrogen fertilizer can enhance the GWP of the CH₄ and N₂O either in long time or short time scale.     

CO<Subscript>2</Subscript>-assisted removal of nutrients from municipal wastewater by microalgae <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> and <Emphasis Type="Italic">Scenedesmus obliquus</Emphasis>

Axenic culture of microalgae Chlorella vulgaris ATCC^® 13482 and Scenedesmus obliquus FACHB 417 was used for phycoremediation of primary municipal wastewater. The main aim of this study was to measure the effects of normal air and CO₂-augmented air on the removal efficacy of nutrients (ammonia N and phosphate P) from municipal wastewater by the two microalgae. Batch experiments were carried out in cylindrical glass bottles of 1 L working volume at 25 °C and cool fluorescent light of 6500 lux maintaining 14/10 h of light/dark cycle with normal air supplied at 0.2 L min^?1 per liter of the liquid for both algal strains for the experimental period. In the next set of experiments, the treatment process was enhanced by using 1, 2 and 5% CO₂/air (vol./vol.) supply into microalgal cultures. The enrichment of inlet air with CO₂ was found to be beneficial. The maximum removal of 76.3 and 76% COD, 94.2 and 92.6% ammonia, and 94.8 and 93.1% phosphate after a period of 10 days was reported for C. vulgaris and S. obliquus, respectively, with 5% CO₂/air supply. Comparing the two microalgae, maximum removal rates of ammonia and phosphate by C. vulgaris were 4.12 and 1.75 mg L^?1 day^?1, respectively, at 5% CO₂/air supply. From kinetic study data, it was found that the specific rates of phosphate utilization (q _phsophate) by C. vulgaris and S. obliquus at 5% CO₂/air supply were 1.98 and 2.11 day^?1, respectively. Scale-up estimation of a reactor removing phosphate (the criteria pollutant) from 50 MLD wastewater influent was also done.     

Equation of state of synthetic qandilite Mg<Subscript>2</Subscript>TiO<Subscript>4</Subscript> at ambient temperature

Using a diamond-anvil cell and synchrotron X-ray diffraction, the compressional behavior of a synthetic qandilite Mg_2.00(1)Ti_1.00(1)O₄ has been investigated up to about 14.9 GPa at 300 K. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state yield an isothermal bulk modulus (K _T0) of 175(5) GPa, with its first derivative \(K_{T0}^{{\prime }}\) attaining 3.5(7). If \(K_{T0}^{{\prime }}\) is fixed as 4, the K _T0 value is 172(1) GPa. This value is substantially larger than the value of the adiabatic bulk modulus (K _S0) previously determined by an ultrasonic pulse echo method (152(7) GPa; Liebermann et al. in Geophys J Int 50:553–586, 1977), but in general agreement with the K _T0 empirically estimated on the basis of crystal chemical systematics (169 GPa; Hazen and Yang in Am Miner 84:1956–1960, 1999). Compared to the K _T0 values of the ulvöspinel (Fe₂TiO₄; ~148(4) GPa with \(K_{T0}^{{\prime }} = 4\)) and the ringwoodite solid solutions along the Mg₂SiO₄–Fe₂SiO₄ join, our finding suggests that the substitution of Mg²⁺ for Fe²⁺ on the T sites of the 4–2 spinels can have more significant effect on the K _T0 than that on the M sites.