Total CO2 Uptake Research Articles

Ultrasonic Non-Destructive Testing of Accelerated Carbonation Cured-Eco-Bricks

This study aimed to investigate the behavior of accelerated carbonation-cured laboratory specimens using the ultrasonic non-destructive testing (UNDT) method and compare the results with the destructive testing (DT) method. The materials used in the study included a blend of lime kiln dust and ground granulated blast furnace slag (LKD-GBFS) wastes, natural fine aggregate (sand), and alternative fine aggregates from waste tires. The chemical analysis of the LKD and GBFS samples highlighted them as suitable alternatives to OPC, hence their utilization in the study. A 60:40 (LKD-GBFS) blending ratio and a 1:2 mix design (one part LKD-GBFS blend and two part sand) was considered. The natural fine aggregate was partially replaced with fine waste tire rubber crumbs (TRCs) in stepped increments of 0, 5, and 10% by the volume of the sand. The samples produced were cured using three curing regimens: humid curing (HC), accelerated carbonation curing (ACC) with no water curing (NWC) afterwards, and water curing after carbonation (WC). From the results, an exponential model was developed, which showed a direct correlation between the UNDT and DT results. The developed model is a useful tool that can predict the CS of carbonated samples when cast samples are unavailable. Lastly, a total CO2 uptake of 15,912 g (15.9 kg) was recorded, which underscores ACC as a promising curing technique that can be utilized in the construction industry. This technique will bring about savings in terms of the time required to produce masonry units while promoting a change in the basic assumptions of a safer and cleaner environment.

Substantial CO2 uptake by biomass ashes under natural condition in China

A considerable amount of biomass ashes, resulting from agricultural waste field burning, wildfire, and solid biofuel incineration, is typically discarded in field or stored in dumps, where the alkaline oxides (CaO, MgO) they contain undergo carbonation and weathering-erosion processes over extended periods, continuously absorbing CO2 from the atmosphere and soil. However, their CO2 absorption behavior under natural conditions remains insufficiently explored in China. Using life cycle assessment (LCA) and material flow analysis (MFA) methods, this study developed a CO2 absorption analysis model for biomass ashes under natural conditions. We estimated the CO2 absorption of 9 different types of biomass ash from 1950 to 2022 through Monte Carlo uncertainty simulation. The results show that biomass ashes in China absorbed approximately 24.17Mt/year (95 % CI, 11.10–43.56) of CO2 under nature conditions, with the annual average CO2 uptake showing a steady increase from 1950 to 2022. The total CO2 uptake reached 856.85Mt (95 % CI, 368.73–1526.01) over these decades, mainly due to the significant contribution of biomass ash produced by domestic straw burning and fuelwood combustion, which accounted for 51.97 % and 22.08 %, respectively. Our findings highlight the substantial carbon sink benefits of biomass ash, providing valuable insights for further studies on carbon cycles in natural ecosystems and the potential integration of biomass ash in Carbon Capture, Utilization, and Storage (CCUS) technologies.

Towards low-cost and sustainable activated carbon production: Influence of microwave activation time on yield and CO2 uptake of PET-derived adsorbents

Microwave (MW) heating is proposed as a method to transform polyethylene terephthalate (PET) into porous adsorbents. The yield, textural properties, and CO2 uptake of the PET-derived adsorbents irradiated at different durations (3 – 35 min) at 400 °C were assessed. MW activation time influenced both the physical properties and CO2 uptake capacities of the resulting adsorbents. The yield decreased with activation time, but the surface area, total pore volume, micropore volume, and CO2 uptake capacities all increased with MW activation time before declining. The optimal sample (produced with 5 min of MW activation time) showed improved textural properties as well as higher equilibrium and dynamic CO2 uptakes than the commercial activated carbon used as reference. This adsorbent also possesses good selectivity for CO2 in the binary 10:90%vol/vol CO2: N2 mixture. Additionally, an excellent recyclability over 20 cycles, (Regeneration Efficiency > 97%) was observed, and the CO2 adsorption kinetics best fits Lagergren’s pseudo-second-order model. This study has shown that a low activation temperature (400 °C), a short MW activation time (5 min), and a low amount of chemical agent (KOH, 0.72 M) could produce CO2 adsorbents from a cheap and abundant material (PET-waste) with better CO2 uptake to that of a commercial activated carbon.

Effects of Particle Size on the Gas Uptake Kinetics and Physical Properties of Type III Porous Liquids.

Type III porous liquids (PLs) consist of porous solid particles dispersed in a size-excluded liquid phase and are attracting much attention as novel media for applications such as gas separation. However, the effects of fundamental variables such as particle size on their physical properties are currently largely unknown. Here we study the effects of particle size in a series of porous liquids based on solid Al(OH)(fumarate) (a microporous metal-organic framework, MOF) with particle sizes of 60 nm, 200-600 nm, or 800-1000 dispersed in liquid polydimethylsiloxane (PDMS). Properties examined include physical stability of the dispersion, viscosity, total CO2 uptake, and kinetics of CO2 uptake. As expected, both physical stability and viscosity decreased with increasing particle size. Unexpectedly, total gravimetric gas uptake also varied with particle size, being greatest for the largest particles, which we ascribe to larger particles having a lower relative content of surface-bound FMA ligands. Various models for the gas uptake kinetic data were considered, specifically adsorption reaction models such as pseudo-first-order, pseudo-second-order, and Elovich models. In contrast to pure PDMS, which showed first-order kinetics, all PLs fit best to the Elovich model confirming that their uptake mechanism is more complex than for a simple liquid. Adsorption diffusion models, specifically Weber and Morris' intraparticle model and Boyd's model, were also applied which revealed a three-step process in which a combination of diffusion through a surface layer and intraparticle diffusion were rate-limiting. The rate of gas uptake follows the order PDMS < PL1 < PL2 < PL3, showing that the porous liquids take up gas more rapidly than does PDMS and that this rate increases with particle size. Overall, the study suggests that for high gas uptake and fast uptake kinetics, large particles may be preferred. Also, the fact that large particles resulted in low viscosity may be advantageous in reducing the pumping energy needed in flow separation systems. Therefore, the work suggests that finding ways to stabilize PLs with large particles against phase separation could be advantageous for optimizing the properties of PLs toward applications.

Carbon dioxide sequestration in mortars with excavated soil: Engineering performances and environmental benefits

Globally, substantial volume of excavated soils is generated during construction and demolition activities, which can be utilized in the manufacturing stabilized earth-based construction materials. Furthermore, increasing amount of CO2 is being released into the environment from growing industrial operations that can sequestered in earth-based materials without compromising the engineering properties. This article attempts to explore the effect of CO2 sequestration through accelerated carbonation curing on engineering properties, micro-structure and phase composition of cement-lime stabilized soil mortars. Lateritic soil (clay content of 42 %) is used to replace 25 % and 50 % of natural sand by mass. The experimental findings demonstrate an increase in CO2 uptake by 15–23 % and 33–40 % due to addition of 25 % and 50 % soil respectively compared to control (0 % soil). Precipitation of meta-stable calcium carbonates majorly contributes to the total CO2 uptake, accounting for 62–69 % and 78–87 % of the carbonates formed in 25 % soil-mortars and 50 % soil mortars. These are substantially higher compared to 40–50 % in the case of control mixes. The mentioned finding is attributed to the formation of additional calcium-silicate-hydrate and calcium-aluminate-hydrate due to clay-lime reaction, that binds CO2 and precipitate meta-stable polymorphs of calcium carbonate. Addition of lime and carbon sequestration are found to substantially enhance 1-day strength of cement-soil and cement-lime-soil mortars by 31–36 %, although no prominent effect at 7-day and 28-day marks are observed. Furthermore, capillary water absorption at 28-day age is reduced by 18–31 % in lime-added cement-soil mortars compared to the ones without lime, that reduces moisture sensitivity of the mortars. Overall, the carbon sequestered mortars demonstrate satisfactory strength (20–37 MPa) and water absorption performance of the stabilized mortars for masonry applications, which will provide a promising means to manufacture low-carbon and more durable construction products.

Optimising thermochemical energy storage: a comprehensive analysis of CaCO3 composites with CaSiO3, CaTiO3, and CaZrO3.

With the increasing amount of renewable energy produced, many governments and industries are pushing for the installation of battery energy storage system (BESS) solutions. Thermal batteries are systems that store heat made from various energy sources, and can be used to produce electricity upon demand. These systems are easily scalable and can be installed in cities, homes and remote locations. Thermochemical energy storage (TCES) uses the enthalpy of a chemical reaction to store and release heat through endothermic and exothermic processes, respectively. CaCO3 has been identified as an ideal TCES material as it is cheap and abundant, but maximising long-term cyclability is key to ensure battery longevity. This article investigates the addition of CaSiO3, CaTiO3 and CaZrO3 to CaCO3 in a 1 : 1 ratio to ascertain the reaction properties and cyclic capacity over time. Cycling longevity and thermodynamic properties were determined using simultaneous differential scanning calorimetry and thermogravimetric analysis (DSC-TGA) along with the Sieverts technique, and their reaction pathway studied by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The low cost of the CaCO3-CaSiO3 material of $1.8 USD per kW hth suggests that if a suitable particle refinement agent were to be employed to ensure cycling longevity this material would be an excellent TCES material. Despite the CO2 cycling capacity of the CaCO3-CaZrO3 system only reducing by 16 wt% over 100 cycles, the cost of ZrO2 brings the materials cost to $30.9 USD per kW hth, making this material currently unsuitable for application. The CaCO3-CaTiO3 system showed only a 17% drop in total CO2 uptake over 100 cycles, although the cost was $11.1 USD per kW hth.

Enhanced Southern Ocean CO2 outgassing as a result of stronger and poleward shifted southern hemispheric westerlies

Abstract. While the Southern Ocean (SO) provides the largest oceanic sink of carbon, some observational studies have suggested that the SO total CO2 (tCO2) uptake exhibited large (∼ 0.3 GtC yr−1) decadal-scale variability over the last 30 years, with a similar SO tCO2 uptake in 2016 as in the early 1990s. Here, using an eddy-rich ocean, sea-ice, carbon cycle model, with a nominal resolution of 0.1∘, we explore the changes in total, natural and anthropogenic SO CO2 fluxes over the period 1980–2021 and the processes leading to the CO2 flux variability. The simulated tCO2 flux exhibits decadal-scale variability with an amplitude of ∼ 0.1 GtC yr−1 globally in phase with observations. Notably, two stagnations in tCO2 uptake are simulated: between 1982 and 2000, and between 2003 and 2011, while re-invigorations are simulated between 2000 and 2003, as well as since 2012. This decadal-scale variability is primarily due to changes in natural CO2 (nCO2) fluxes south of the polar front associated with variability in the Southern Annular Mode (SAM). Positive phases of the SAM, i.e. stronger and poleward shifted southern hemispheric (SH) westerlies, lead to enhanced SO nCO2 outgassing due to higher surface natural dissolved inorganic carbon (DIC) brought about by a combination of Ekman-driven vertical advection and DIC diffusion at the base of the mixed layer. The pattern of the CO2 flux anomalies indicate a dominant control of the interaction between the mean flow south of the polar front and the main topographic features. While positive phases of the SAM also lead to enhanced anthropogenic CO2 (aCO2) uptake south of the polar front, the amplitude of the changes in aCO2 fluxes is only 25 % of the changes in nCO2 fluxes. Due to the larger nCO2 outgassing compared to aCO2 uptake as the SH westerlies strengthen and shift poleward, the SO tCO2 uptake capability thus reduced since 1980 in response to the shift towards positive phases of the SAM. Our results indicate that, even in an eddy-rich ocean model, a strengthening and/or poleward shift of the SH westerlies enhance CO2 outgassing. The projected poleward strengthening of the SH westerlies over the coming century will, thus, reduce the capability of the SO to mitigate the increase in atmospheric CO2.

Air-sea CO2 fluxes and cross-shelf exchange of inorganic carbon in the East China Sea from a coupled physical-biogeochemical model

The East China Sea (ECS) has been reported to be a significant sink of atmospheric CO2, but less is known about horizontal transport of dissolved inorganic carbon (DIC) across the shelf. A coupled physical-biogeochemical model has been implemented for the ECS to simulate the inorganic carbon system and estimate CO2 fluxes and cross-shelf DIC transport in the ECS. A 6-year model hindcast (2013–2018) was performed and assessed. Multiple existing datasets from in-situ observations are used to constrain and validate the model. The model reproduces the spatial and temporal patterns of nitrogen, chlorophyll and CO2 parameters in general agreement with observations. Modeling estimation reveals that the ECS takes up CO2 at an annual mean rate of about 8.20 ± 3.13 mmol m−2 d−1, and experiences substantial seasonal variability. The total annual CO2 uptake in the ECS is about 21.55 Tg C yr−1. Modeling estimation suggests that the biological processes contribute to about 15 % of the shelf CO2 uptake in the ECS, leaving ~80 % of the shelf uptake contributed by other physical-chemical processes, e.g., physical pump and/or solubility pump. The horizontal fluxes of DIC between the ECS and the adjacent ocean are more than two orders of magnitude larger than the air-sea CO2 flux on the ECS and result in a net DIC export of about ~33.8 ± 14.87 Tg C yr−1 from the shelf area. Modeling results suggest that this conveyance of DIC to the open ocean is equivalent to about 70 % of the inorganic carbon inflow from riverine and atmospheric pathways in the annual scale.

Rethinking the deployment of static chambers for CO2 flux measurement in dry desert soils

Abstract. The mechanisms underlying the soil CO2 flux (Fs) in dry desert soils are not fully understood. To better understand these processes, we must accurately estimate these small fluxes. The most commonly used method, static chambers, inherently alters the conditions that affect the flux and may introduce errors of the same order of magnitude as the flux itself. Regional and global assessments of annual soil respiration rates are based on extrapolating point measurements conducted with flux chambers. Yet, studies conducted in desert ecosystems rarely discuss potential errors associated with using static chambers in dry and bare soils. We hypothesized that a main source of error is the collar protrusion above the soil surface. During the 2021 dry season, we deployed four automated chambers on collars with different configurations in the Negev, Israel. Fs exhibited a repetitive diel cycle of nocturnal uptake and daytime efflux. CO2 uptake measured over the conventionally protruding collars was significantly lower than over the collars flushed with the soil surface. Using thermal imaging, we proved that the protruding collar walls distorted the ambient heating and cooling regime of the topsoil layer, increasing the mean surface temperatures. Higher soil temperatures during the night suppressed the flux driving forces, i.e., soil–atmosphere CO2 and temperature gradients, ultimately leading to an underestimation of up to 50 % of the actual Fs. Accordingly, the total daily CO2 uptake by the soil in the conventionally deployed collars was underestimated by 35 %. This suggests that desert soils are a larger carbon sink than previously reported and that drylands, which cover approximately 40 % of Earth's terrestrial surface, may play a significant role in the global carbon balance.

Impact of ecosystem metabolism on CO2 emissions: Insights from high-resolution time series of pH measured in situ

Lakes and reservoirs are important sources/sinks of atmospheric CO2. Primary production and respiration transforming inorganic to organic carbon and vice versa alter CO2 concentrations in the surface waters and thus affect CO2 emissions. Here we investigate the link between net-production (NEP) and CO2 concentrations and emissions at high temporal resolution over more than two months in a German pump storage reservoir. Continuous in-situ pH measurements in combination with few alkalinity measurements provided concentrations of CO2 and dissolved inorganic carbon (DIC) at high temporal resolution over more than 75 days. Time series of metabolic rates of carbon were determined with an open-water diel pH technique, which utilizes the diel changes in DIC obtained from the observed diel changes in pH and data on alkalinity. During the measuring period, average NEP was positive and CO2 concentrations were typically substantially under-saturated. On average, the reservoir acted as a sink for CO2, whereby CO2 uptake was 39% larger in the evening than in the morning. Only few consecutive days with negative NEP were sufficient to turn the reservoir temporally into a source of CO2. Therefore, the average CO2 uptake determined from continuous data can be 80% larger to 30% smaller than estimates of average uptake based on bi-weekly data. Daily mean NEP explained only 9% and 4% of the variance of daily mean DIC and CO2. Note that NEP is proportional to the time derivative of DIC and therefore not expected to correlate well with DIC in general. Because CO2 changes nonlinearly with DIC, NEP explains less variance of CO2 than of DIC. Numerical experiments confirmed the arguments above and revealed that at positive average NEP the total CO2 uptake over several weeks is not well predicted by average NEP but depends on the detailed temporal pattern of NEP. However, if average NEP is negative, average NEP may be a good predictor of total CO2 emissions. Similar conclusions apply for high and low alkalinity waters, but uptake rates and temporal variability of CO2 emissions are smaller in high than in low alkalinity waters. Assessment of the link between NEP and CO2 emissions requires differentiation between lakes with different alkalinity and, because of the non-linear relationship between NEP and CO2, strongly benefits from data with high temporal resolution especially during time-periods with positive net-production.

Re-identification of non-facultative crassulacean acid metabolism behavior for red-fleshed pitaya (Hylocereus polyrhizus) micropropagules in vitro using an Arduino-based open system

A non-facultative crassulacean acid metabolism (CAM) profile has been documented in pitaya, in which closed flow photosynthesis systems have been used to evaluate the CAM capacity and characteristics of plants, albeit with overestimation. By contrast, open-flow systems promote measurement reliability and continuously monitor the photosynthetic profile, which has not been reported in pitaya. Therefore, this study aimed to overview the diel gas exchange capacity of Hylocereus polyrhizus ‘Da Hong’ in an open-flow system, in which the explants were incubated in vitro to prevent measurement deviations caused by microorganism activity. The experimental conditions were 80 µmol/m2/s light intensity at 25 °C under a 16/8 h (D/N) photoperiod. The Arduino-based assembled system contained three subsystems: explant growth, air supplementation, and air sampling and environmental monitoring. The growth vessel had an 83.5% light transmittance with a 3.8 mol/m2/day light intensity. Air ventilation was performed at a flow rate of 1,000 mL/min with 99.9% relative humidity through the filters, which precluded infection and provided a high moisture content environment in the growth vessel during the experiments. A real-time clock library programmed on the development board realized an accurate sampling point and period. The diel gas exchange pattern of pitaya exhibited four phases; explants had a net photosynthetic rate (Pn) of 2.63 μmol/m2/s at midnight, and the total net CO2 uptake over 24 h was 73.98 mmol/m2/day. The positive Pn observed during the daytime was noteworthy. This study successfully measured the photosynthetic profile of pitaya in vitro, providing a diel gas exchange reference. An open-flow whole-canopy system could be used in other explants to evaluate the photosynthesis profile in the era of climate change.

The Growth and Physiological Characteristics of the Endangered CAM Plant, Nadopungnan (Sedirea japonica), under Drought and Climate Change Scenarios

No natural habitat of Sedirea japonica has been found in Korea for the past 20 years. This study was conducted to provide basic physiological data for the conservation strategy of this endangered plant in response to climate change. Soil fruit daylight system (SFDS) chambers were used and four treatment groups (2.6LVPD, 2.6HVPD, 8.5LVPD, and 8.5HVPD) were designed based on the RCP scenario (RCP 2.6, and 8.5) and VPD conditions (low VPD; LVPD, and high VPD; HVPD). Air dryness was induced in the HVPD groups during the daytime by increasing the atmospheric vapor pressure deficit (VPD). There was no significant difference based on the RCP scenario. However, the difference between LVPD and HVPD was considerable. Total CO2 uptake and transpiration were lower than those of LVPD due to the duration decrease of Phase I in 2.6HVPD and 8.5HVPD. There was a reduction in total biomass, leaf thickness, length, and the number of leaves. ABS/RC, DI0/RC, φD0, VK, VJ, and other chlorophyll fluorescence markers increased. φP0, RE0/RC, φE0, ψE0, φR0, RC/CS0, Sm, N, PIabs, DFabs, SFIabs, and PIabs,Total declined. Daily drought stresses impact the physiological mechanisms occurring at nighttime. The defense mechanisms against drought stress occur by conserving water by controlling the stomata, inactivating the reaction center, and increasing the dissipated energy through heat. In summary, S. japonica is flexible against drought stress.

Peatland Heterogeneity Impacts on Regional Carbon Flux and Its Radiative Effect Within a Boreal Landscape

AbstractPeatlands, with high spatial variability in ecotypes and microforms, constitute a significant part of the boreal landscape and play an important role in the global carbon (C) cycle. However, the effects of this peatland heterogeneity within the boreal landscape are rarely quantified. Here, we use field‐based measurements, high‐resolution land cover classification, and biogeochemical and atmospheric models to estimate the atmosphere‐ecosystem C fluxes and the corresponding radiative effect (RE) for a boreal landscape (Kaamanen) in northern Finland. Our result shows that the Kaamanen catchment currently functioned as a sink of carbon dioxide (CO2) and a source of methane (CH4). Peatlands (26% of the area) contributed 22% of the total CO2 uptake and 89% of CH4 emissions; forests (61%) accounted for 78% of CO2 uptake and offset 6% of CH4 emissions; water bodies (13%) offset 7% of CO2 uptake and contributed 11% of CH4 emissions. The heterogeneity of peatlands accounted for 11%, 88%, and 75% of the area‐weighted variability (deviation from the area‐weighted mean among different land cover types (LCTs) within the catchment) in CO2 flux, CH4 flux, and the combined RE of CO2 and CH4 exchanges over the 25‐year time horizon, respectively. Aggregating peatland LCTs or misclassifying them as nonpeatland LCTs can significantly (p &lt; 0.05) bias the regional CH4 exchange and RE estimates, while differentiating between drier noninundated and wetter inundated peatlands can effectively reduce the bias. Current land cover products lack such details in peatland heterogeneity, which would be needed to better constrain boreal C budgets and global C‐climate feedbacks.

Valorisation of Recycled Cement Paste: Feasibility of a Short-Duration Carbonation Process.

Cement paste powder (CPP) is a by-product of the recycling process of concrete with an elevated carbonation capability and potential to be recycled as a binding material in new concrete batches. The application of a carbonation treatment to CPP improves this potential even more, besides the evident gains in terms of CO2 net balance. However, the long duration usually adopted in this treatment, from 3 to 28 days, hampers the industrial viability of the process. We studied the feasibility of a short-duration carbonation process, with a duration of two hours, carrying out a comprehensive characterization of the material throughout the process. The test was performed on CPP with an average initial water content of 16.9%, exposed to a CO2 concentration of 80%. The results demonstrate two main carbonation rates: a rapid growth rate in the first 18 minutes of the process, involving all the calcium-bearing compounds in CPP, and a slow growth rate afterwards, where only C-S-H contributes to the carbonation reaction. During the 2 h carbonation process, the main CPP compounds, calcium silicate hydrate (C-S-H) and calcium hydroxide (CH), reached different carbonation degrees, 31% and 94%, with, however, close CO2 uptake values, 8% and 11%, respectively. Nevertheless, the total CO2 uptake for this process (≈19%) attained values not distant from the values usually obtained in a carbonation of 12 days or more (19–25%). Hence, these findings highlight the blocking role of C-S-H in the carbonation process, indicating that longer carbonation periods are only going to be useful if an effective carbonation of this compound is accomplished. In the present scenario, where CH is the main contributor to the reaction, the reduction in the process duration is feasible.

Sol-gel processing of a covalent organic framework for the generation of hierarchically porous monolithic adsorbents

Sol-gel processing of a covalent organic framework for the generation of hierarchically porous monolithic adsorbents

A process for CO2 capture and brine salinity reduction through reaction with potassium hydroxide: A multi-stage evaluation

Solvay and modified Solvay processes are facing a major challenge in reducing brine salinity to a level suitable for agriculture and industry. This challenge arises as a result of competing reactions and mixing limits between CO2 gas and brine. Another challenge is the high solubility of sodium bicarbonate (NaHCO3), which results in a low overall desalination efficiency. Previous studies established the effectiveness of a modified Solvay process based on potassium hydroxide (KOH). The first objective of this study is to evaluate a multi-stage treatment for a modified Solvay process on the basis of potassium hydroxide (KOH) to achieve an additional reduction in ion removal from high-salinity brines and an increase in CO2 capture as compared to previously obtained under optimal operating conditions. Three different methods were investigated. The first method evaluated the effectiveness of adding ammonium bicarbonate (NH4HCO3) in reducing the solubility of NaHCO3. Even though the Na+ and Cl− concentrations were reduced by 56.2% and 40%, respectively, the total CO2 uptake slightly improved by 1.2% (67.8 g CO2/1000 ml of treated brine). In the second method, the addition of extra KOH in subsequent stages was investigated to overcome the pH reduction observed in the first method. There was an ∼ 47.3% improvement in CO2 uptake from the first method. Furthermore, the percentages of Na+ and Cl− removal were increased to 65% and 64.5%, respectively. In the third method, the recovery of Ca2+ and Mg2+ was approximately 76.3% and 94.6%, respectively, following the pre-treatment step (filtration), followed by the same stages as in the second method. Reducing these ions decreased the competitive reactions and thus increased CO2 solubility and reactivity with KOH, resulting in higher cumulative CO2 uptake from all stages to 108.2 g CO2/1000 ml, which was 8.3% more than the second method. Additionally, solid products were characterized using scanning electron microscopy, X-ray diffraction, FTIR and Raman analysis. Finally, the dynamic behaviour of the reactor was evaluated using step changes in the inlet gas and liquid flow rate. The results are promising in terms of the reactor system's adaptability to large-scale processes.

Development of Calcium Carbonate-Based Coatings by the Carbonation of Gamma-C2S (γ-C2S).

A calcium carbonate (CaCO3)-based coating with gamma-C2S (γ-C2S) as the main carbonatable binder is proposed to protect the metal substrate against corrosion in this paper. Here, the morphology and phase assemblage of the coatings are studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the corrosion resistance of the coating is evaluated by electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). Results show that the carbonated coating has excellent properties in terms of ultraviolet (UV) aging resistance, salt fog resistance, and electrochemical corrosion resistance. The porosity of deposited coating on steel substrates decreases by 47.1% after carbonation due to the compacted calcium carbonate formation, which is recognized as a self-compacting process during carbonation. The coating also exhibits rapid strength development within the first 2 h of carbonation; both the CO2 uptake efficiency and degree of carbonation (DOC) can reach more than 95% of the total CO2 uptake efficiency and final DOC values. This study provides a novel insight to extend the category of inorganic coating with additional benefits of CO2 solidification.

Komposisi, Struktur dan Cadangan Karbon pada Agroforestri Kopi Arabika di Kabupaten Aceh Tengah, Aceh

Carbon stocks indicates the amount of CO2 that is absorbed and stored in plant biomass coffee, shade trees, undergrowth and litter. Objective research is to analyze the species composition and structure of vegetation and determine the amount of biomass, carbon stocks and CO2 uptake aboveground part in both types of coffee agroforestry with non-destructive methods, using allometric equation, in Central Aceh district. The location of the plot was determined by purposive sampling based on the representation of stands. The dominant value of a species in plants is calculated using the important value index (INP). The composition of agroforestry constituents consisted of 34 species, of which 15 species were found in simple agroforestry and 19 species in complex agroforestry. The horizontal structure of agroforestry consists of 5 diameter classes, with vegetation density decreasing continuously in the number of individuals. Carbon stocks agoforestri types of coffee in a simple decrease with an increase in diameter &lt;10 cm and 10-19.99 cm and the complex agroforestry increases. The highest non-coffee carbon reserves are found at growth rates of 10-19.99 cm in simple agroforestry. The total component of the amount of biomass in simple agroforestry (159. 56 tons ha-1) is greater than the agroforestry complex (142.00 tons ha-1). Total CO2 uptake in both types of agroforestry was (520.16 tonsCO2 ha-1). Total CO2 uptake in simple agroforestry (275.22 tonsCO2 ha-1) was greater than in complex agroforestry (244.94 tonCO2 ha-1).Keywords: arabica coffee, agroforestry, carbon stocks and composition of vegetation

Effect of liquid alkane on carbon dioxide hydrate formation

Hydrophobic surface affects gas hydrate formation. It is an effective method to promote hydrate formation by adding hydrophobic materials into hydrate formation system. However, it is little known about the interaction between hydrate formation and macroalkane. n-Dodecane and n-tetradecane are selected as additives to investigate their effect on CO2 hydrate formation in this work. The addition of liquid alkanes effectively improves hydrate nucleation, shortens the induction time of CO2 hydrate formation, and improves the hydrate growth rate. In addition, the total CO2 uptake at the end of the experiments was increased in the presence of liquid alkanes. Compared with the addition of n-dodecane, n-tetradecane has a weaker effect on CO2 hydrate formation. Increasing the stirring rate can effectively reduce the induction time of hydrate formation and improve hydrate growth rate, but has little effect on gas storage capacity in hydrates. The experimental results also show that the increase of experimental pressure or the decrease of temperature is conducive to hydrate formation.

Significant winter CO2 uptake by saline lakes on the Qinghai-Tibet Plateau.

Direct measuring of CO2 flux remains challenging for global lakes. The traditional sampling and gas transfer models used to estimate lake CO2 fluxes are variable and uncertain, and ice-covered periods are often excluded from the annual carbon budget. Here, the first longtime (2013-2017) direct measurement of CO2 flux by eddy covariance system over the largest saline lake (Qinghai lake) in the Qinghai-Tibet Plateau (QTP) revealed that ice-covered period draws large amounts of CO2 from the atmosphere (-0.87±0.38g C m-2 d-1 ), a value more than twice the CO2 flux rate during the ice-free period (-0.41±0.35g C m-2 d-1 ). The total CO2 uptake by all saline lakes on the QTP was estimated to -10.28±1.65Tg C yr-1 , an equivalent to approximately one third of the net terrestrial ecosystems carbon sink in QTP. Our results indicate large sink for CO2 in winter is controlled by both seasonal hydrochemistry processes and lake ice absorption in saline lakes. This research also demonstrates decreasing CO2 uptake from the atmosphere by saline lakes on the QTP, which may turn carbon sinks to carbon sources with future warming.