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The abatement of CO 2 emitted from combustion is a hot research topic. Current CO 2 capture techniques of adsorption, absorption, membrane separation and cryogenics involve high investment and operation costs. For moderate and high temperature exhaust gas, carbonation/decarbonation cycles offer an attractive alternative. An objective assessment method (screening index) was applied to select the most appropriate chemical reactions, with MgO and Mg(OH) 2 being screened as having the highest potential. Macro-thermogravimetric experiments determined a CO 2 capture yield between 60 and 70% for Mg(OH) 2  at temperatures between 260 and 330 °C, and from 85 to 98% for MgO at temperatures of 400-440 °C. Reaction rates were measured for both MgO-CO 2 and Mg(OH) 2 -CO 2 . The reaction kinetics are best fitted by the Jander 3D-diffusion approach. The Arrhenius equation is applied to the reaction rate constant, and both its activation energy and pre-exponential factor are determined. Integrating the Jander expression in the reaction rate equation enables to predict the CO 2 -capture conversion for any selected temperature and/or contact time., Competing Interests: Declaration of competing interest There are no conflicts to declare., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study investigates the addition of 3 wt% of TiO₂, SiO₂, and CeO₂ nanoparticles as an anti-sintering strategy to enhance the reversibility of sodium manganese ferrite for hydrogen production. After preliminary tests, TiO₂ NPs were discarded due to cross-reactivity leading to pronounced sintering. SiO₂ NPs hindered the sintering due to the in-situ formation of NaFeO 2 ,SiO 2 solid solution but ultimately resulted in irreversible H₂ production. In contrast, CeO₂ NPs demonstrated high stability and chemical compatibility, stabilizing H₂ production at approximately 50 μmol/g, while the reference mixture monotonically lost reversibility in 5 cycles. Notably, combining CeO₂ NPs with a eutectoid (Na 0.93 Li 0.07) 2 CO 3 mixture enhanced H₂ production to 0.18/0.19 mmol/g. As a result, the H 2 produced during the 5th cycle was nearly twenty times that of the reference mixture. This improvement was attributed to a synergistic effect between the formation of liquid carbonate and the anti-sintering and oxygen gateway effect of the CeO 2 NPs. [Display omitted] • The addition of NPs is proposed to improve the hydrogen production reversibility. • SiO 2 NPs reduce the sintering but result in no H 2 production reversibility. • CeO 2 NPs reduce the sintering and improve the H 2 production by 5 times. • Combining CeO 2 with eutectoid carbonate boosts increase by 1 order of magnitude. • A synergistic mechanism is proposed to explain the results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Decarbonation of skarn deposits was more efficient than other carbon sources. • Skarn deposits may have contributed to the rise of CO 2 concentration at 145 Ma. • Skarn deposits may have influenced the ecological system in East Asia. Magmatic-hydrothermal systems transport metal, sulfur, and carbon from deep to shallow crust, providing materials to the society and potentially affecting Earth's long-term environment. The fluxes of elements and, accordingly the environmental effects, are ultimately functions of the time-integrated amounts and durations of magmatic-hydrothermal system. In this study, we calculate the duration of prograde metamorphism induced by fluid infiltration and amount of carbon released by skarn ore deposits. This study finds that skarn ore deposits can decarbonize CO 2 at an efficiency up to 1014 g/(y.km3), which is much higher than volcanism on different tectonic settings. The CO 2 flux of skarn deposits increased from late Jurassic to early Cretaceous and reached a maximum value to 7.8 Mt/y at J/K boundary. Our finding provided an previously unquantified but important outgassing source in the subduction zone. This result consistent with global warming pattern based on global sedimentary records. The maximum outgassing at J/K boundary may have important impact on global warming and perhaps mass extinction. [ABSTRACT FROM AUTHOR]

Aqueous fluids are essential to extract slab‐trapped carbon at forearc to subarc depths and interpret the decarbonation efficiency of global subduction zones. A large amount of carbon survives beyond subarc depths. The behavior of such carbon, however, remains unclear owing to a lack of experimental studies. Here, we investigate the decarbonation behavior of carbonated oceanic crust containing different amounts of H2O at pressures from subarc depths to the top of the mantle transition zone. We find that calcium‐rich carbonatitic liquids can form at temperatures of ∼950–1,150°C at depths below ∼150–300 km, corresponding to warm/cold thermal regimes in most subduction zones. Therefore, hydrous carbonatitic liquids should be pervasive in subduction zones, while extensive dehydration reactions and fluid activities are critical for creating carbonatitic liquids and preventing most of the surviving carbon from being subducted into the deep Earth. Plain Language Summary: The deep recycling of CO2 and H2O in subduction zones is key for understanding the habitability and climate change of Earth. Here, we use a high‐pressure and high‐temperature instrument, the multi‐anvil press, to investigate the fate of subducted carbon in oceanic crust. We find that H2O can depress the decarbonation temperature of subducted oceanic crust by hundreds of °C. Most of the surviving carbon that descends to depths below ∼150 km may be released into the upper mantle by hydrous carbonatitic liquids, rather than entering the lower mantle. The fate of such carbon has not been well constrained, but it is important to understand this process because CO2 released into the convecting upper mantle is key to constraining the origin of the deep carbon reservoir. Key Points: Effect of H2O on the decarbonation behavior of subducted oceanic crust was investigatedHydrous carbonatitic liquids can form at ∼950–1,150°C at depths below ∼150 kmFluid activity is critical for removing most of the surviving carbon beyond subarc depths [ABSTRACT FROM AUTHOR]

The carbonation behavior of calcium-containing sorbents, CaO and Ca(OH)2, was investigated under pressurized CO2 at nominal room temperature. The carbonation reaction was mechanically driven via reactive ball milling. The carbonation rate was determined by monitoring the CO2 pressure inside the sealed milling jar. Two different versions of CaO were fabricated as starting materials. The addition of citric acid in CaO synthesis resulted in a significant increase in sorbent surface area, bringing up the conversion of CO2 from 18% to 41% after 3 h of reactive milling. The hydroxide formation from these two oxides closed the surface area gap. Nevertheless, we found that hydroxides had a higher initial carbonation rate and greater final CO2 uptake than their oxide counterparts. However, the formation of byproduct water limited the further carbonation of Ca(OH)2. When we added a controlled amount of water to the CaO-containing milling jar, the highest carbonation rate and most extensive CO2 uptake were attained due to the in situ formation of reactive Ca(OH)2 nanoparticles. We saw CaCO3 X-ray diffraction peaks only when Ca(OH)2 was involved in this low-temperature carbonation, indicating that the grain growth of CaCO3 is easier on the Ca(OH)2 surface than on the CaO surface. We used the Friedman isoconversional method to calculate the effective activation energy of decarbonation for the high surface area CaO sorbent milled with water. The average effective activation energy was found to be about 72 kJ mol−1, and its magnitude started to decrease significantly from 50% sorbent regeneration. The drastic change of the effective activation energy during decarbonation suggests that CaCO3, formed at nominal room temperature by reactive milling under pressurized CO2, should undergo a more drastic morphology change than the typical thermally carbonated CaCO3. [ABSTRACT FROM AUTHOR]

The accumulation of CO 2 in some natural gas fields represents a risk for exploration, and calls for a way of integrating its occurrence in basin modelling. Among several possible sources we investigate mineral reactions able to take place within bottom sediments of particularly deep and hot sedimentary basins, i.e. at conditions of low-grade metamorphism (up to 500 °C and 2500 bar). These reactions involve lithologies where carbonate and alumino-silicate minerals are combined to form a « mixed composition ». For appraising decarbonation quantitatively we propose a method founded on thermodynamic calculations, that follows a modelling approach commonly used in metamorphic petrology. At given bulk composition and temperature-pressure (T-P) conditions, the composition and proportions of solid and fluid phases that coexist at equilibrium are computed using a Gibbs Energy Minimization (GEM) algorithm. On the basis of R.G. Berman's database we incorporate thermodynamic parameters for a variety of solid solutions including clay minerals, and for a CH 4 –CO 2 –H 2 O fluid mixture represented by the CPA-Electrolyte equation of state. A large range of decarbonation reactions is explored through a systematics involving 85 model compositions, and a unique T-P path typical of the targeted basins. We confirm that pure carbonate lithologies do not behave as CO 2 source in the conditions explored. In contrast, we demonstrate that mixed compositions are likely to yield CO 2 from successive mineral reactions, in which clay minerals play a prominent role. We also show that the temperature of incipient decarbonation, staggered over 325–425 °C, depends on the Ca/Mg/Fe composition ratio of the bulk sediment. CO 2 -prone reactions occurring from a selection of natural sediments are then presented. The CO 2 -prolific character of particular facies associated to the rift phase of a basin evolution is illustrated, notably in the case of lacustrine oil shales. Finally, we indicate a protocol that integrates the decarbonation scheme derived from thermodynamics into a CO 2 -generation formalism compatible with the usual formalism of a basin model. [ABSTRACT FROM AUTHOR]

To satisfy the requirements regarding a precise analytical method for carbonated beverages, a sample preparation method to selectively and efficiently remove dissolved carbon dioxide (CO) from carbonated beverages is presented in this work. The key element of this development is a membrane module with semipermeable hollow fibre membranes. The CO permeates in the membrane module as the sample stream flows through the membrane into a stripping gas stream. A specifically developed phase splitter induces a two-phase flow (gas and liquid) of the beverage sample, which results in an accumulation of the dissolved CO in the gas phase. In addition to the development of the membrane decarbonation unit and the significant parameters, an extensive study comparing the unit with common decarbonation techniques has been carried out. More than 96 % of the CO was removed from the carbonated sample, resulting in a residual CO concentration of <0.1 g/L in the decarbonated sample. [ABSTRACT FROM AUTHOR]

Abstract: Between January 2011 and April 2012, Santorini volcano (Greece) experienced a period of unrest characterised by the onset of detectable seismicity and caldera-wide uplift. This episode of inflation represented the first sizeable intrusion of magma beneath Santorini in the past 50 years. We employ a new approach using 222Rn– systematics to identify and quantify the source of diffuse degassing at Santorini during the period of renewed activity. Soil CO2 flux measurements were made across a network of sites on Nea Kameni between September 2010 and January 2012. Gas samples were collected in April and September 2011 for isotopic analysis of CO2 ( ), and radon detectors were deployed during September 2011 to measure (222Rn). Our results reveal a change in the pattern of degassing from the summit of the volcano (Nea Kameni) and suggest an increase in diffuse CO2 emissions between September 2010 and January 2012. High-CO2-flux soil gas samples have . Using this value and other evidence from the literature we conclude that these CO2 emissions from Santorini were a mixture between CO2 sourced from magma, and CO2 released by the thermal or metamorphic breakdown of crustal limestone. We suggest that this mixing of magmatic and crustal carbonate sources may account more broadly for the typical range of values of CO2 (from to ) in diffuse volcanic and fumarole gas emissions around the Mediterranean, without the need to invoke unusual mantle source compositions. At Santorini a mixing model involving magmatic CO2 (with of and elevated (222Rn)/CO2 ratios ) and CO2 released from decarbonation of crustal limestone (with (222Rn)/CO2 ∼ 30–300 Bq kg−1, and of ) can account for the and (222Rn)/CO2 characteristics of the ‘high flux’ gas source. This model suggests of the carbon in the high flux deep CO2 end member is of magmatic origin. This combination of and (222Rn) measurements has potential to quantify magmatic and crustal contributions to the diffuse outgassing of CO2 in volcanic areas, especially those where breakdown of crustal limestone is likely to contribute significantly to the CO2 flux. [Copyright &y& Elsevier]

Abstract: Water–rock interaction experiments have been performed to investigate the production of CO2-rich gas in the deep reservoir of the geothermal system of Mt Amiata (Italy) through the interaction between a natural phyllite sample (coming from 1115m below ground level and considered representative of the deep reservoir) and a coexisting fluid phase. Experiments were conducted with an externally heated pressure vessel, a chamber furnace and a stirred micro-reactor at 300°C and at P up to 35MPa, using different solid/liquid ratios, and also under nominally anhydrous conditions. Experimental results show that CO2-rich gases containing variable amount of CO, CH4 and other aliphatic and aromatic hydrocarbons were produced by fluid–rock interaction. Compositional data of the gas, coupled with solid residua characterization, show that thermal decomposition of magnesian siderite in phyllite is the process responsible for the gas genesis. This process is particularly effective when aqueous solutions interact with phyllite and it may represent the thermometamorphic reaction mainly responsible of the production of CO2-rich gas under hydrothermal conditions similar to those of the main reservoir in the Mt Amiata geothermal area. [Copyright &y& Elsevier]

Abstract: This work studied the characteristic changes of a continuous electrolytic decarbonation and recovery of a carbonate salt solution from a metal-contaminated carbonate solution with changes of operational variables in an electrolytic system which consisted of a cell-stacked electrolyzer equipped with a cation exchange membrane and a gas absorber. The system could completely recover the carbonate salt solution from a uranyl carbonato complex solution in a continuous operation. The cathodic feed rate could control the carbonate concentration of the recovered solution and it affected the most transient pH drop phenomenon of a well type within the gas absorber before a steady state was reached, which caused the possibility of a CO2 gas slip from the gas absorber. The pH drop problem could be overcome by temporarily increasing the OH− concentration of the cathodic solution flowing down within the gas absorber only during the time required for a steady state to be obtained in the case without the addition of outside NaOH. An overshooting peak of the carbonate concentration in the recovered solution before a steady state was observed, which was ascribed to the decarbonation of the initial solution filled within the stacked cells by a redundant current leftover from the complete decarbonation of the feeding carbonate solution. [Copyright &y& Elsevier]

Abstract: By using acetate–buffer (sodium acetate and acetic acid)/NaCl mixed solutions, the deintercalation of carbonate ions (CO2− 3) was conducted on MgAl-LDHs at different Mg/Al ratios—LDH2 (LDH with Mg/Al≈2) and LDH3 (LDH with Mg/Al≈3). When only an acetate–buffer solution was used, decarbonation did not take place even if the buffer solution was made acidic enough to dissolve LDH itself; however, the addition of NaCl to the buffer solution caused deintercalation of the carbonate ions from the MgAl-LDHs and the reaction was conducted without any morphological and weight change at 25 °C. Under the optimum conditions, full decarbonation was attained for the two MgAl-LDHs in minutes, and the obtained LDHs contained Cl− in the interlayer space without incorporation of any acetate anions due to their extremely low anion selectivity of acetate ion. The allowable range for the concentration of the decarbonation solution is wide, and the change in pH due to the decarbonation reaction is slight because of the buffering effect. The decarbonation was affected by the Mg/Al ratio of the LDH; i.e., the present LDH2 was slightly more difficult to decarbonate than LDH3, probably due to the higher layer-charge density of LDH2. [Copyright &y& Elsevier]

Calcium oxalates are naturally occurring biominerals and can be found as a byproduct of some industrial processes. Recently, a new and green method for carbon capture and sequestration in stable calcium oxalate from oxalic acid produced by carbon dioxide reduction was proposed. The reaction resulted in high-quality weddellite crystals. Assessing the stability of these weddellite crystals is crucial to forecast their reuse as solid-state reservoir of pure CO2 and CaO in a circular economy perspective or, eventually, their disposal. The thermal decomposition of weddellite obtained from the new method of carbon capture and storage was studied by coupling in-situ high-temperature X-ray powder diffraction and thermogravimetric analysis, in order to evaluate the dehydration, decarbonation, and the possible production of unwanted volatile species during heating. At low temperature (119–255 °C), structural water release was superimposed to an early CO2 feeble evolution, resulting in a water-carbon dioxide mixture that should be separated for reuse. Furthermore, the storage temperature limit must be considered bearing in mind this CO2 release low-temperature event. In the range 390–550 °C, a two-component mixture of carbon monoxide and dioxide is evolved, requiring oxidation of the former or gas separation to reuse pure gases. Finally, the last decarbonation reaction produced pure CO2 starting from 550 °C. [ABSTRACT FROM AUTHOR]