Large Amounts Of CO2 Research Articles

Carbonation of concretes containing LC³ cements with different supplementary materials

Due to the clinkerization process during the Portland cement production, large amounts of CO2 are emitted, increasing the effects related to climate change (approximately 5-10% of global CO2 emissions come from cement production), consequently, the seek for alternatives to mitigate these high emissions are necessary. The use of supplementary cementitious materials (SCM) to partial replace of Portand clinker/cement has been the subject of different research, including the use of LC3 cements (Limestone Calcined Clay Cements), where up to 50% of Portland clinker can be replaced, however, cement industry has already used othersupplementary cementitious materials with pozzolanic activities in commercial cements. In this sense, this work evaluates the performance of concretes containing LC3 mixtures with the presence of different SCM (silica fume, fly ash, sugarcane bagasse ash and açaí stone ash) regarding durability issues by carbonation. The results showed that all concretes with LC3 presented higher carbonation fronts in relation to the reference concrete, with Portland cement, due to the lower availability of calcium to react with the CO2 that penetrates into the concrete pores, so the adoption of curing procedures and coatings are recommended.

Investigation of enhanced CO2 storage in deep saline aquifers by WAG and brine extraction in the Minnelusa sandstone, Wyoming

Geological CO2 sequestration in deep saline aquifers has been extendedly investigated to reach the goal of carbon neutral as large amount of CO2 can be reduced in a short time. This study investigates the feasibility of water-alternating-gas (WAG) injection and brine extraction on enhancing CO2 storage in a target deep saline aquifer, Minnelusa Sandstone in the Powder River Basin (PRB) of Wyoming. An integrated numerical model is developed to account for four scenarios: (1) CO2 continuous injection (CI) through one injection well, (2) WAG injection through one injection well, (3) CO2 CI through one injection well and brine extraction through one producer, (4) WAG injection through one injection well and brine extraction through one producer. Simulation results suggest that WAG injection and brine extraction corporately make it possible to enhance CO2 injectivity while securing CO2 storage safety. For instance, WAG injection considerably reduces structural trapping contribution while enhances dissolved and residual trapping contributions. As for brine extraction, it can decrease the maximum averaged reservoir pressure by 37% and 22% for CI and WAG injection, respectively. Besides, sensitive analyses of the operational parameters for the fourth scenarios are performed. Results reveal that, when the amount of total CO2 injection has been predetermined, CO2 injection time and rate within each period of WAG should be small whereas it is preferable to have large water injection time and rate. This is to secure desirable dissolved and residual trapping contributions (store CO2 with safety). Sensitive degree results confirm that CO2 injection rate, water injection time, and CO2 injection time of WAG injection exhibit significant effects on CO2 storage whereas the impacts of producer bottom-hole pressure (BHP), water injection rate, and CO2-water injection time are relatively weaker. This study not only sheds light on achieving double-win goal: enhance CO2 injectivity and store CO2 with safety, but also can be a critical reference for other CO2 storage in deep saline aquifers.

Influence of Oxidative Properties of CexZr1−xO2 Catalyst on Partial Oxidation of Dimethyl Ether

Partial oxidation of dimethyl ether (DME) to hydrogen is an efficient route for hydrogen production for application in SOFC. However, quite a large amount of CO2 as a byproduct has been an important obstacle. In this work, cerium–zirconium solid solution (CexZr1−xO2) was applied to determine how the oxidative properties of the catalyst affect the production of CO2 in the partial oxidation of DME. The results show that the catalyst with more adsorbed oxygen (Oads) rather than the lattice oxygen has stronger oxidizability and gives higher DME conversion as well as higher CO2 yield, due to the overoxidation of CO.

Evaluating the Feasibility of Using Brick Powder and Clay Powder in Cement Replacement.

The cement industry generates very large amounts of CO2 into the atmosphere. In recent years, there has been a search for alternative cementitious materials and micro-fillers that could partially or fully replace cement in cement composites without compromising their durability. This paper investigates the possibility of using brick powder (BP) and clay powder (CP) as a partial replacement for cement (up to 20% by weight) in cement paste. The raw materials were characterized, and the physical and mechanical properties of the modified cement pastes were studied, as well as their resistance to a short-term thermal shock at 250 °C. The study was supplemented by intelligent modelling of compressive strength using the support vector machine (SVM) algorithms. The results indicated a significant increase in tensile strength (up to 100%) and an increase in thermal resistance of cement pastes modified with BP and CP. The proposed SVM model had high accuracy (R2 = 0.90), indicating its suitability to predict the compressive strength of the modified cement matrix. This study complements the knowledge in the field of inter alia, the effect of a short-term thermal shock at elevated temperature on the properties of BP and CP modified cement paste, and the effect of BP, which, due to its grain size, plays more the role of a microfiller than a pozzolanic additive.

Assimilation of S5P/TROPOMI carbon monoxide data with the global CAMS near-real-time system

Abstract. The Tropospheric Monitoring Instrument (TROPOMI) on the Copernicus Sentinel 5 Precursor (S5P) satellite, launched in October 2017, provides a wealth of atmospheric composition data, including total columns of carbon monoxide (TCCO) at high horizontal resolution (5.5 km × 7 km). Near-real-time TROPOMI TCCO data have been monitored in the global data assimilation system of the Copernicus Atmosphere Monitoring Service (CAMS) since November 2018 to assess the quality of the data. The CAMS system already routinely assimilates TCCO data from the Measurement of Pollution in the Troposphere (MOPITT) instrument and the Infrared Atmospheric Sounding Interferometer (IASI) outside the polar regions. The assimilation of TROPOMI TCCO data in the CAMS system was tested for the period 6 July to 31 December 2021, i.e. after the TROPOMI algorithm update to version 02.02.00 in July 2021. By assimilating TROPOMI TCCO observations, the CAMS CO columns increase by on average 8 %, resulting in an improved fit to independent observations (IAGOS aircraft profiles and NDACC Fourier transform infrared (FTIR) tropospheric and total-column CO data) compared to a version of the CAMS system where only TCCO from MOPITT and IASI is assimilated. The largest absolute and relative changes from the assimilation of TROPOMI CO are found in the lower and middle troposphere, i.e. that part of the atmosphere that is not already well constrained by the assimilated TIR MOPITT and IASI data. The largest impact near the surface comes from clear-sky TROPOMI data over land, and additional vertical information comes from the retrievals of measurements in cloudy conditions. July and August 2021 saw record numbers of boreal wildfires over North America and Russia, leading to large amounts of CO being released into the atmosphere. The paper assesses the impact of TROPOMI CO assimilation on selected CO plumes more closely. While the CO column can be well constrained by the assimilation of TROPOMI CO data, and the fit to individual IAGOS CO profiles in the lower and middle troposphere is considerably improved, the TROPOMI CO columns do not provide further constraints on individual plumes that are transported across continents and oceans at altitudes above 500 hPa.

Decarbonisation potential of dimethyl ether/hydrogen mixtures in a flameless furnace: Reactive structures and pollutant emissions

This article sheds light on the combustion characteristics of dimethyl ether and its mixtures with methane/hydrogen under flameless conditions at different equivalence ratios. It was found that combustion of 100% dimethyl ether in flameless conditions minimises the NO formation, keeping it less than 10 ppm with no CO or unburned hydrocarbons. Progressive addition of methane was found to reduce the NO, reaching up to zero value at 50% methane in molar fraction along with a marginal CO2 reduction. However, large amounts of CO were found for higher methane levels, greater than 60% CH4 in molar fraction. Reactive structures based on OH∗ chemiluminescence revealed that adding methane results in increased ignition delay times and, consequently, a more distributed reaction zone characterised by reduced temperature gradients. No visible flame was observed for pure dimethyl ether as well as dimethyl ether/methane mixtures. Furthermore, a more intense and narrower reaction zone, characterised by the presence of a visible flame, was formed upon hydrogen addition. Adding hydrogen by 50% in molar fraction did not cause a noticeable rise in NO levels; however, CO2 was lowered by about 18%. Further addition of hydrogen resulted in increased peak temperatures of about 1700 K and higher NO emissions of about 50 ppm. Additionally, a skeletal Chemical Reactor Network was built and simulated with the commercial software CHEMKIN Pro to investigate the effect of the different mixtures and operating conditions on NO formation from a chemical point of view. N2O pathway was observed to be the root source of NO emissions for pure DME and DME/CH4 mixtures, however; the thermal pathway became gradually more important as hydrogen concentration was increased in the mixture.

Exploring the mechanism associated with methane emissions during composting: Inoculation with lignocellulose-degrading microorganisms

Inoculation with microorganisms is an effective strategy for improving traditional composting processes. This study explored the effects of inoculation with lignocellulose-degrading microorganisms (LDM) on the degradation of organic matter (OM), methane (CH4) emissions, and the microbial community (bacteria and methanogens) during composting. The results showed that LDM accelerated the degradation of OM (including the lignocellulose fraction) and increased the CH4 releases in the later thermophilic and cooling stages during composting. At the ending of composting, LDM increased the CH4 emissions by 38.6% compared with the control. Moreover, LDM significantly increased the abundances of members of the bacterial and methanogenic community during the later thermophilic period (P < 0.05). In addition, LDM promoted the growth and activity of major bacterial genera (e.g., Ureibacillus) with the ability to degrade macromolecular OM, as well as affecting key methanogens (e.g., Methanocorpusculum) in the composting system. Network analysis and variance partitioning analysis indicated that OM and temperature were the main factors that affected the bacterial and methanogen community structures. Structural equation modeling demonstrated that the higher CH4 emissions under LDM were related to the growth of methanogens, which was facilitated by the anaerobic environment produced by large amounts of CO2. Thus, aerobic conditions should be improved during the end of the thermophilic and cooling composting period when inoculating with lignocellulose-degrading microorganisms in order to reduce CH4 emissions.

Simple fabrication of homogeneous Co/Co9S8/nitrogen doped carbon nanospheres derived from Prussian blue analogues for high performance supercapacitors

In this paper, an N-doped porous carbon (N-C) nanosphere containing a large amount of Co and Co9S8 nanocrystals (Co/Co9S8/N-C) is described. Among them, ZnCo-PBA (Zn3[Co(CN)6]2) was synthesized by simple method as the sacrificial template and carbon source. After calcination in N2, Co ions are reduced to Co, and zinc ions are vaporized to produce a large number of pores. Finally, it was vulcanized by hydrothermal method to form Co9S8 nanocrystals with high activity. Co/Co9S8/N-C nanomaterials have excellent specific surface area and mesoporous pores, which increase the charge transfer rate in the redox process and the performance. The material not only has excellent specific capacity (141.83 mAh g−1/1542.64 F g−1 at 1 A g−1), but also retains good specific capacity after thousands of charges and discharges. To further test the value of Co/Co9S8/N-C electrodes, an asymmetric supercapacitor (ASC) was assembled with a very high energy density (94.632 Wh kg−1) at 29368.55 W kg−1. The specific capacitance is about 80.70 % of the initial value after 5000 cycles. This strategy of using PBA as template to construct N-doped carbon skeleton embedded with metal sulfide provides a broad idea for supercapacitor electrode materials.

Characterization of Aerosol Properties from the Burning Emissions of Typical Residential Fuels on the Tibetan Plateau.

The Tibet Autonomous Region in China is a unique place with high altitude and special Tibetan culture. The residents have different living habits and domestic fuels from those in other parts of China, however, knowledge on the emission characteristics of local residential fuels remain poorly understood until now. In this study, nine popular residential fuels in the Tibet are burned in situ to study the aerosol chemical compositions, mass spectral signatures, and emission characteristics from their burning emissions. Overall, emissions of particulate and gaseous pollutants depend strongly on the burning conditions, in addition to the fuel constituents themselves. Burning the biofuels of yak dung, WeiSang mixture fuels, and two powdery Tibetan incenses with relatively low combustion efficiencies can emit large amounts of CO and aerosols, especially organic aerosols (>90%) with large diameters. In contrast, burning of wood, coal, ghee lamp, stick-like Tibetan incense, and diesel can release abundant CO2 but fewer aerosols from their flaming combustion. A comprehensive database consisting of the high-resolution mass spectra of organics and emission factors of multiple chemical components are established. Distinctly different mass spectral signatures are found among the different fuels, in particularly those unique Tibetan biofuels. All these findings have significant implications for the identification of aerosol sources, compilation of pollutant emission inventories, and assessment of potential environment effects in this remote region.

Stress and permeability modelling in depleted coal seams during CO2 storage

Depleted coal seam gas reservoirs are considered as one of the best sites for underground CO2 sequestration which can contribute to climate change mitigation. Due to coal's high internal surface area, a large amount of CO2 can be stored in the coal matrix. Despite the high CO2 storage capacity, the swelling of coal near the injection wells remains a major challenge. Most field trials have shown a significant decline in injection rate and permeability in the vicinity of vertical injection wells, while horizontal wells showed no such decline. It is not well studied how matrix swelling and well trajectory affect permeability in horizontal carbon dioxide injection wells. In this study, a mathematical model is developed to determine stress distribution and permeability around vertical and horizontal CO2 injection wells in depleted coal seams. The model incorporates injection pressure, matrix swelling effect, in situ stresses, and wellbore trajectory. The results indicate that during CO2 injection, matrix swelling significantly impacts the stress path and increases both horizontal stresses. Stress distribution and permeability around the well are affected significantly by wellbore trajectory and swelling. As CO2 injection continues in vertical wells, radial, tangential, and mean effective stresses increase near the well and within the reservoir. As a result, permeability declines during injection in a vertical well. In horizontal wells, however, tangential and mean horizontal stress near the wellbore decrease with injection. Hence, the model confirms no decline in permeability near a horizontal injection well which is in good agreement with the field trial observations.

Effective CH4 production and novel CO2 storage through depressurization-assisted replacement in natural gas hydrate-bearing sediment

In this study, the guest exchange behaviors in the hydrate-bearing sediment of a one-dimensional reactor specially designed for depressurization-assisted replacement were experimentally investigated for CH4 production and CO2 storage. The longitudinal distributions of vapor compositions, replacement efficiency, and hydrate weight fractions, as well as the average efficiency for depressurization-assisted replacement, were examined using gas chromatography and powder X-ray diffraction (PXRD). The immediate re-formation of gas hydrates after CO2 injection implied a rapid recovery of the geo-mechanical strength of the sediment. The unique changes in the gas compositions in the pore space caused by the re-formation of gas hydrates resulted in a distinctive longitudinal distribution of the replacement efficiency in the hydrate-bearing sediment. PXRD analysis of the hydrate samples revealed that the gas hydrate saturation nearly recovered after depressurization-assisted replacement. Despite CH4 re-enclathration, the replacement efficiency was remarkably enhanced through depressurization-assisted replacement, and a larger amount of CO2 was stored in the hydrate-bearing sediment than the amount of CH4 produced. Furthermore, the production rate of CH4 through depressurization-assisted replacement was significantly higher than that through replacement only, and the guest exchange rate increased with an increase in the initial hydrate dissociation ratio. The experimental results demonstrated that depressurization-assisted replacement could solve the weakening of the geo-mechanical strength of the sediment for depressurization only and the slow production rate for replacement only; thus, it would be useful for low-carbon energy production from natural gas hydrate-bearing sediments.

Solvay claims soda ash breakthrough

Solvay is piloting a soda ash production process that it claims will reduce CO 2 emissions by half and eliminate limestone in its effluent, which currently contributes to the release of heavy metals into the sea. The company has reached a settlement with the activist investor Bluebell Capital Partners that calls for it to roll out the new process across all of its soda ash plants by 2050. In parallel, Solvay will take shorter-term measures to reduce the amount of limestone released into the sea from its plant in Rosignano, Italy. Solvay is the world’s largest producer of soda ash (sodium carbonate), which is used to make glass and other products. Solvay’s process uses brine and limestone as raw materials and ammonia as a catalyst. The process creates large amounts of CO 2 from the burning of fossil fuels and generates powdery limestone, which contains traces of heavy metals. The

Effective conversion of CO2 into light olefins along with generation of low amounts of CO

Indium-based oxide/zeolite bifunctional catalyst has been shown to be potential for conversion of CO2 into C2=-C4=. However, this type of catalyst generates large amounts of CO with selectivity ≥ 55 %. Thus, a new type of InCeZrOx(n)/H-SAPO-34(x) composite is fabricated here for catalyzing CO2 hydrogenation to light olefins, and its catalytic mechanism is investigated by combining in situ spectroscopy and isotope-labeled experiments. Upon optimization of In content incorporated in CeZrOx, the coupling manner of InCeZrOx with H-SAPO-34 and reaction conditions, this composite gives comparable C2=-C4= yield to previously reported catalysts but a much lower CO selectivity (9.7 %) as a result of C2=-C4= selectivity in hydrocarbons reaching 93.6 %, while those of CH4 and C20-C40 as low as 1.9 % and 2.4 %, respectively. Various characterization and designed experiment results reveal that incorporation of appropriate amounts of In in CeZrOx generates more oxygen vacancies that promotes CO2 activation to form formate and methoxy intermediates at low temperature and pressure, whereas addition of more In species causes some to migrate onto H-SAPO-34(x) and poison acid sites, which leads to quick deactivation of catalysts.

A low-carbon alkali activated slag based ultra-high performance concrete (UHPC): Reaction kinetics and microstructure development

Ultra high performance concrete (UHPC) is a cement-based material with great development prospects. However, the production of cement will produce a large amount of CO 2 , which does not conform to the current global trend of energy conservation and emission reduction, and limits the further development of UHPC. One of the ways to further develop UHPC is to reduce the carbon emissions in the production process of UHPC. The aim of this study is to develop a low-carbon alkali activated slag based Ultra-High Performance Concrete (A-UHPC) with ultra-low moisture content. Firstly, based on the particle dense packing model, an optimized combination of low-carbon cementitious mixture and aggregates skeleton is designed. Then, the effects of moisture content on the macro-properties, hydration mechanism and micro-mechanism of the developed A-UHPC are studied. The experimental results show that the fresh performance and macroscopic mechanical properties of A-UHPC are advanced at low moisture content. When the water-binder ratio is 0.29, the compressive strength at 28 d is the highest, reaching 118 MPa. Besides, low moisture content A-UHPC also shows good microscopic properties: its hydration degree can reach 62.58% and the longest molecular chain length of the polymer is about 4.74. In general, the developed A-UHPC can meet the requirement of high performance and low CO 2 emission simultaneously, which could be one of the most suitable choices to achieve the goal of “Carbon peak and Carbon neutral” in the near future. • A novel method for designing a low carbon UHPC is presented. • The newly developed UHPC exhibits admirable ecological value. • Mineral powder and alkali-activator are adopted in UHPC. • Low moisture content A-UHPC is developed. • 5.The effect of water on the macro and micro properties of A-UHPC is studied.

Catalytic Upgrading of Biomass-Gasification Mixtures Using Ni-Fe/MgAl2O4 as a Bifunctional Catalyst.

Biomass gasification streams typically contain a mixture of CO, H2, CH4, and CO2 as the majority components and frequently require conditioning for downstream processes. Herein, we investigate the catalytic upgrading of surrogate biomass gasifiers through the generation of syngas. Seeking a bifunctional system capable of converting CO2 and CH4 to CO, a reverse water gas shift (RWGS) catalyst based on Fe/MgAl2O4 was decorated with an increasing content of Ni metal and evaluated for producing syngas using different feedstock compositions. This approach proved efficient for gas upgrading, and the incorporation of adequate Ni content increased the CO content by promoting the RWGS and dry reforming of methane (DRM) reactions. The larger CO productivity attained at high temperatures was intimately associated with the generation of FeNi3 alloys. Among the catalysts’ series, Ni-rich catalysts favored the CO productivity in the presence of CH4, but important carbon deposition processes were noticed. On the contrary, 2Ni-Fe/MgAl2O4 resulted in a competitive and cost-effective system delivering large amounts of CO with almost no coke deposits. Overall, the incorporation of a suitable realistic application for valorization of variable composition of biomass-gasification derived mixtures obtaining a syngas-rich stream thus opens new routes for biosyngas production and upgrading.

Study Of Flame-Wall Interaction : Influence Of Effusion Cooling On Pollutant Emissions

For several years, engine manufacturers have had to meet increasingly stringent standards on pollutant emissions. Studying the flame/wall interaction is essential to control pollutant emissions and extend the lifetime of gas turbine. An inherent constraint of combustion chambers is that the walls are cooled by air introduced through multi-perforation (effusion cooling). The problem is that this injection of cold air into the combustion chamber disrupts the oxidation reactions of the fuel either by freezing them, which yields the emission of large quantities of CO, UHC and soot or by bringing fresh air to the rich areas, which is very favourable to the formation of thermal NOx. The focus of this work is to investigate the influence of parameters such as burner flow rate, cooling flow rate and equivalence ratio on the reaction zone. Experiments were conducted with a multi-perforated plate placed above a flat flame burner to simulate the head-on interaction between an aeronautical injector and an effusion cooled liner.

Numerical simulation of residual stress in post internal-welding process of bimetal composite pipe and optimization of welding sequence

With the increasing demand for energy, energy extraction is developing towards a more complex corrosive environment containing a large amount of CO2, H2S and Cl−. Bimetal composite pipes because of both good corrosion resistance and strength are getting more and more research and application. In this paper, L415/316L bimetal mechanical lined pipes were welded by two processes (single-side welding process and post internal-welding process) the residual stress of which was studied by combining numerical simulation and experiment. Then the welding sequences of the post internal-welding process were compared and analyzed. The results show that there is already a certain amount of residual stress in the pipe after overlay welding. The residual stress of single-side welding process and post internal-welding process is too large and distributes in the danger zone, which is easy to lead to failure. By adjusting sequence of the post internal-welding, it can effectively change the level of the residual stress and reduce the stress of the overlay layer, the internal-welding layer and the backing welding layer, which is beneficial to improve the safety of the bimetal mechanical lined pipe.

Experimental investigation of the phase equilibria in the Tb-Co and Tb-Co-Fe systems and magnetic properties of phases

Phase equilibria in the Tb-Co and Tb-Co-Fe systems were investigated experimentally for the first time by a combination of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and differential thermal analysis (DTA). Based on the experimental data from the present work, the Tb-Co system was constructed. Magnetic properties of Tb2Co17 and Tb2Co7 were measured with vibrating-sample magnetometer (VSM). The liquidus and solidus projections, the melting diagram, the isothermal sections at 1200 and 1000 °C, the vertical sections on isoconcentrates 20, 30 and 40 at% Tb and the Scheil reaction scheme for the Tb-Co-Fe system over the whole concentration range were constructed. No ternary intermetallic phase exists in the system, but the three continuous solid solutions Tb2(Co,Fe)17, Tb(Co,Fe)3 and Tb(Co,Fe)2 were found and the TbCo5 and Tb2Co7 phases have extended homogeneity ranges in the ternary system, where large amounts of Co can be substituted by Fe in both cases. The ternary Tb-Co-Fe system contains five four-phase invariant reactions encompassing one of E- and four of U-type reactions. The system also contains two three-phase invariant reactions.

Integrated environmental influences quantification of pilot-scale constructed wetlands based on modified ecological footprint assessment

Constructed wetlands (CWs) are widely used for non-point source pollution control and water environmental quality improvement. Though it is effective in water quality improvement under most conditions, the overall impacts on the ecological environment in terms of greenhouse gases (GHGs) emissions is a growing concern. Besides, large area requirement has limited further applications of the technology in urban areas. A novel assessment tool of integrating grey water footprint into the ecological footprint framework is established for the assessment of pilot-scale CWs. Findings are compared with a natural riparian wetland adjacent to the researched CWs which were monitored simultaneously. Results demonstrated the CWs had relatively good water quality polishing performance, especially for nitrogen removal. Nonetheless, a large amount of CO2 and some CH4 and N2O emissions were recorded. Meanwhile, a substantial amount of CO2 was also sequestrated by wetland plants via photosynthesis. The strong reducing environment of the CWs inhibited CO2 and N2O generation to a great extent. Calculation of all gaseous emissions and sequestration in CO2 equivalents demonstrated that CWs are an efficient carbon sink. By contrast, the natural wetland was a carbon source because of the high emission of CO2 and N2O under its weak reducing environment conditions and low gross primary production. The carbon footprints of the constructed and natural wetlands were −24.24 and 12.99 gha respectively. Modified ecological footprint values were determined by integrating the carbon footprint, water footprint and build-up lands footprint, and a value of −24.36 gha was obtained for the CWs and 12.99 gha for the natural wetlands. The results indicated that the CWs had substantial beneficial impacts on the ecological environment. On account of the multifunctional service values provided by the CWs, a typical paradigm for water pollution remediation and carbon sequestration was presented for ecological and environmental governance, especially for riparian areas.

Diapirism of carbonate platforms subducted into the upper mantle

Abstract Subduction of lithospheric plates at convergent margins leads to transport of materials once close to or at the surface of Earth to great depths. Some of them later return to the surface by magmatism or degassing, whereas others end up being stored in the mantle for long periods of time. The fate of carbon-bearing minerals in subduction is of particular interest because they can arbitrate the long-term availability of CO2 at the surface. However, there are major gaps in the understanding of even the most fundamental processes that modulate carbon pathways at mantle depths. We use geodynamic models to understand carbonate pathways upon subduction in the form of large carbonate platforms, which were common in the Tethys realm of Europe. We conducted a series of geodynamic forward models for a 1-km-thick carbonate platform entering subduction. We show that most of the carbonate load detaches from the subducting slab and rises up diapirically through the mantle wedge and eventually mixes with the mantle lithosphere. A smaller fraction gets accreted under the forearc, whereas an even smaller fraction descends deeper into the mantle. The cold diapiric plume has a significant role in retarding silicate mantle melting above these subduction zones and promoting the formation of small-volume carbonate-rich melts and, in some cases, alkaline silica-undersaturated silicate melts. We propose that large amounts of CO2 can be stored as carbonate in the shallow uppermost lithospheric mantle.