Amount Of CO2 Research Articles

Performance investigation on a downdraft gasifier using corn waste as a solid biomass and co-feeding with hand gloves and used facemask waste

In India, an abundant source of corn waste is scattered throughout the country, ensure a consistent feedstock supply that can be easily converted into valuable products. Corncob waste, as a solid biomass, has significant potential energy content and can be converted through thermo-chemical processes like gasification. The co-gasification process is a viable solution for managing non-decomposing wastes, such as hand gloves and used face masks, due to their widespread use in domestic and industrial applications. Since hand gloves and used face masks are also difficult to recycle, so that the present investigation aims to utilize the co-gasification process to convert these materials into syngas.A downdraft gasifier, a fixed-bed closed type with a capacity of 5 kW for power generation, was used for the experimental work. The experiment involved using 90% corncob waste co-fed with 5% hand gloves and 5% used face masks. The performance characteristics, including gas composition, product gas composition, char yield, and tar yield, were analyzed. Operating parameters, such as reaction temperature, were varied from 700 to 900 °C, with the equivalence ratio ranging from 0.07 to 0.27.Increasing the reaction temperature led to an increase in the CO and H₂ volume percentages of the producer gas, up to 13.1 vol%, while significantly decreasing the CO₂ amount from 24.6 vol% to 19.3 vol%. CH₄ gas slightly increased from 15.8 vol% at 700 °C to 19.8 vol% at 800 °C but decreased to 19.0 vol% when the reaction temperature was further increased to 900 °C. As a result of the increase in combustible gases, the higher heating value (HHV) of the producer gas also increased with temperature. It was concluded that carbon monoxide (CO) and hydrogen (H₂) yields in the syngas increased at 900 °C, while carbon dioxide (CO₂) and methane (CH₄) decreased. However, further research is needed, especially with pilot-scale autothermal gasifier plants, to investigate the impact of adding hand gloves and used masks on the operations of such gasifiers. The produced green H2 were used an alternate fuel in diesel engine for power production in a localized area such as hospitals, industries, etc., or an effective fuel for fuel cell too.

Influence of Grinding Aids on the Grinding Performance and Rheological Properties of Cementitious Systems.

The cement industry is of great importance in terms of raw materials consumed, energy consumed, and greenhouse gases emitted. Grinding aids (GA) are used to reduce energy consumption and costs, as well as to reduce the amount of CO2 released into the environment. In this study, the effect of GA-polycarboxylate ether-based water-reducing admixture (PCE) compatibility on some fresh, rheological and hardened state properties of cementitious systems was investigated. In order to investigate the rheological properties and thixotropic behavior of the mixtures, a total of 51 cement paste mixtures were prepared, containing 4 different types (molasses, MEG, DEA and ethanol) and ratios (0.025, 0.05, 0.75 and 0.1) of GAs and 2 different ratios (0.08% and 0.16%) of PCE in addition to the control mixture. In addition, the effect of the used GAs on the grinding efficiency and compressive strength value was investigated. Additionally, the predictability of the type of GA, dosage and cure time using the Taguchi method was investigated. It was determined that the highest grinding performance was obtained in mixtures containing MEG. It was determined that in cement paste mixtures containing GAs, the dynamic yield stress and viscosity values generally decrease with the increase in PCE usage rate up to a certain value, and these values may increase if the PCE usage increases further. It was determined that such behavior is not present in cement paste mixtures containing GAs and that the structural build-up value of the mixtures generally increases with the increase in the PCE admixture usage rate. It was determined that the use of GAs had a positive effect on 28-day compressive strength.

Highly Stable Propane Dehydrogenation on a Self‐Supporting Single‐Component Zn2SiO4 Catalyst

AbstractCurrent industrial propane dehydrogenation (PDH) processes predominantly use either toxic Cr‐based or expensive Pt‐based catalysts, necessitating urgent exploration for alternatives. Herein, we present Zn2SiO4, an easily prepared, cost‐effective material, as a highly efficient and stable catalyst for PDH. Uniquely, Zn2SiO4 nanocrystals do not require dispersion on support materials, commonly needed for catalytic active oxide clusters, but function as a self‐supporting catalyst instead. During the reaction‘s induction period, surface Zn species on the Zn2SiO4 crystal reduce to coordinately unsaturated ZnOx single sites, serving as highly active catalytic centers. The Zn2SiO4 catalyst demonstrates a stable performance over 200 hours of PDH operation at 550 °C. We further find that introducing a minuscule amount of CO2 into the propane feed significantly extends the catalyst lifespan to over 2000 hours. This enhancement arises from the special role of CO2 in facilitating the removal of strongly adsorbed H*, preventing the complete reduction of ZnOx. After prolonged reaction, the activity of Zn2SiO4 can be fully restored by etching the surface layer to expose fresh Zn species, available throughout the crystals. The combination of CO2introduction and catalytic site regeneration strategies is expected to enable a year‐long PDH operation using a single batch of Zn2SiO4 catalyst.

Highly Stable Propane Dehydrogenation on a Self-Supporting Single-Component Zn2SiO4 Catalyst.

Current industrial propane dehydrogenation (PDH) processes predominantly use either toxic Cr-based or expensive Pt-based catalysts, necessitating urgent exploration for alternatives. Herein, we present Zn2SiO4, an easily prepared, cost-effective material, as a highly efficient and stable catalyst for PDH. Uniquely, Zn2SiO4 nanocrystals do not require dispersion on support materials, commonly needed for catalytic active oxide clusters, but function as a self-supporting catalyst instead. During the reaction's induction period, surface Zn species on the Zn2SiO4 crystal reduce to coordinately unsaturated ZnOx single sites, serving as highly active catalytic centers. The Zn2SiO4 catalyst demonstrates a stable performance over 200 hours of PDH operation at 550 °C. We further find that introducing a minuscule amount of CO2 into the propane feed significantly extends the catalyst lifespan to over 2000 hours. This enhancement arises from the special role of CO2 in facilitating the removal of strongly adsorbed H*, preventing the complete reduction of ZnOx. After prolonged reaction, the activity of Zn2SiO4 can be fully restored by etching the surface layer to expose fresh Zn species, available throughout the crystals. The combination of CO2introduction and catalytic site regeneration strategies is expected to enable a year-long PDH operation using a single batch of Zn2SiO4 catalyst.

Enhancing carbon dioxide adsorption in a hybrid fixed bed via structuring and thermal management: a numerical study

Systems based on physical sorption are an attractive solution for CO2 capture from flue gases, biogas upgrading or gas storage. Besides the sorbent choice, one of the most important factors related to the design of such systems is proper heat management. Commonly used sorbents typically have low thermal conductivity. Nevertheless, catalyst particles characterized by high conductivity are inherently present in adsorptive (hybrid) reactors. Thus, appropriate structuring of hybrid beds can be used for controlling temperature profiles and improving the bed performance. In this study, the behaviour of a nonadiabatic adsorptive reactor described by a two-dimensional model was analysed for the adsorption step. The effect on the CO2 adsorption performance of different spatial distributions of functionalities in the bed was investigated. The optimality problem for nonuniform radial distribution of sorbent and catalyst in the bed was solved, indicating that such a configuration is a potentially important direction for structuring hybrid beds. Results demonstrate that the optimal configuration of radially distributed functionalities significantly increases the amount of CO2 absorbed under identical boundary and initial conditions for the bed. It appears that precise control of the heat generated and removed from the bed is achievable. Such control could be advantageous for the regeneration phase.

Sustainable Processing of Ultralow-Cost Petroleum Cokes Into Ultrastable Self-Doped Fe3C@CNT Catalysts for High-Efficiency HER.

Petroleum cokes are largely used as low-cost anodes in aluminum industries and general fuels in cement industries, where large amounts of CO2 are generated. To reduce CO2 release, it is challenging to develop green strategies for processing abundant petroleum cokes into high-value products, because there are abundant hetero-atoms in petroleum cokes. To overcome such issues, a sustainable electrochemical approach is proposed to convert ultralow-cost high sulfur petroleum coke and iron powders into high-efficiency catalysts for hydrogen evolution reaction (HER). During molten-salt electrolysis, raw petroleum cokes are converted into CNTs via heteroatom removal and the catalytic effect of Fe, forming Fe3C nanoparticles on the sulfur and nitrogen co-dopped carbon nanotubes (Fe3C@S, N-CNTs). The electrochemical reaction analysis using the continuum model suggested that the rate-determining step referred to the slow transport of mobile ions inside the porous cathode. Because the self-doped S and N atoms massively alleviated the energy barrier for H* absorption and H2 desorption (i.e., promoting HER kinetics), the as-prepared Fe3C@S, N-CNTs exhibited low overpotentials at 10mAcm-2 in acidic (96mV) and alkaline (106mV) solutions with ultralong-term duration (200h). This study offers a sustainable approach to convert ultralow-cost petroleum cokes into ultrastable catalysts for high-efficiency HER.

Neutralization and CO2 fixation behavior of alkaline recycled soil using column tests with CO2 ventilation

AbstractColumn tests were conducted to elucidate the pH neutralization and CO2 fixation behavior of alkaline recycled soils permeated with CO2. The ventilation period required for complete CO2 fixation (tEOF) was estimated from the test results of each column. The maximum amount of CO2 captured per gram of dry soil ((mCO2)max) was determined based on the inflow and outflow of CO2 for each specimen. The investigation into the effects of soil density, specimen height, CO2 gas concentration, and flow rate on tEOF and (mCO2)max revealed that tEOF increased with higher dry density (ρd) or specimen height (H), as a denser and larger specimen consumed more CO2 gas. Conversely, tEOF decreased with a higher CO2 gas concentration (C) or flow volume (Q) because a low C or Q resulted in an insufficient CO2 gas supply to match the consumption induced by the reaction. Lower C and Q tended to yield higher (mCO2)max, whereas higher ρd and H resulted in higher (mCO2)max. Furthermore, (mCO2)max increased with tEOF, with a slight reduction in pH after neutralization with increased tEOF. This phenomenon was attributed to the longer ventilation period enabling more Ca to react with the CO2 gas and maintain the equilibrium state of the reaction. Finally, the evaluation of the CO2 consumption rate (CSR) for each column specimen revealed that a higher C and Q resulted in a lower CSR, whereas a higher H resulted in a higher CSR. Additionally, a longer tEOF was associated with a higher CSR, although some variation was observed.

Synthesis and Characterization of an Alkali-Activated Binder from Blast Furnace Slag and Marble Waste.

This study reports an alkali-activated binder including blast furnace slag (BFS) together with marble waste (MW). Cement is an industrial product that emits a significant amount of CO2 during its production and incurs high energy costs. MW is generated during the extraction, cutting, and processing of marble in production facilities, where dust mixes with water to form a settling sludge. This sludge is an environmentally harmful waste that must be disposed of in accordance with legal regulations. In this study, a substantial amount of MW, a by-product with considerable environmental and economic impacts worldwide, was utilized in the production of a binder through the alkaline activation of BFS. In doing this, different experimental parameters were tested to obtain the best binder samples according to workability and mechanical properties. Then, some experiments such as drying shrinkage determination, strength testing, and microstructure analyses were fulfilled through samples with the best values. The findings supported the improvement of the rapid-setting property of BFS by means of the addition of MW. MW reduced the time-dependent drying shrinkage values of BFS by 55%, especially in slag alkaline activation systems with a low or moderate alkali activator content. The substitution of MW (≤50%) in BFS increased flexural and compressive strengths (4.5 and 61.7 MPa), while a reference sample contained BFS only. Although the use of MW did not create a new phase, it contributed to a C-S-H bonding structure during the alkali activation of BFS in a microstructure analysis.

Thermogravimetric Analysis of Combustion of Semi-Coke Obtained from Coniferous Wood and Mixtures on Their Basis

Coal remains one of the most used solid fuels for heat and electricity generation but burning coal releases large amounts of CO2 into the urban atmosphere in addition to harmful substances. In order to reduce the consumption of solid fossil fuels, it is necessary to search for fuels capable of replacing coal in terms of its thermal and environmental characteristics. One of the best alternative fuels is biomass, which is considered carbon neutral, but its thermal characteristics are worse than those of solid fossil fuels. In this work, an alternative to coal was studied for the first time, which was semi-coke, obtained by gasification at a temperature of 700–900 °C, the heat of combustion of which turned out to be higher than that of biomass before thermal treatment by 75%. We also studied fuel mixtures based on the resulting semi-coke. The aim of the work is to determine the main characteristics of combustion of semi-coke obtained from coniferous wood and mixtures based on them. The method of thermogravimetric analysis in oxidising medium at a heating rate of 20 °C/min was applied for the research. According to the results of this analysis, the ignition and burnout temperatures were determined, the combustion index was determined, the duration of coke residue combustion was determined, and synergetic interactions between the mixture components influencing the combustion characteristics were established. It was found that the ignition temperature of semi-coke is more than 50% higher than that of biomass and the burnout temperature is 10% higher. Adding 50% of biomass to semi-coke increases the combustion index by more than 30% and decreases the ignition temperature and burnout temperature. The mixture components synergistically interact with each other during combustion to reduce the value of maximum mass loss rate. It was found that the atomic ratios of O/C and H/C in semi-coke are lower than in biomass before gasification.

Demonstration of the carbon capture with building make-up air unit

Building-integrated carbon capture technology has the potential to reduce the cost of CO2 capture while improving indoor air quality (IAQ). To promote the adoption of CO2 capture in a building environment, this study investigated the possibility of integrating carbon capture technology with an existing rooftop make-up air unit (MAU) system to trap CO2. Here, a modular compact CO2 capture system containing amine-functionalized polymer fibers was examined. The system, which was installed at the exhaust of the MAU, captures CO2 before it leaves the building to enter the atmosphere as a greenhouse gas. The demonstrated average amount of CO2 captured was 1.1–1.4 mmol/g of adsorbent material. Techno-economic analysis (TEA) was further performed on the CO2 capture system, considering material costs, energy costs, as well as transportation and regeneration costs. These results were then used to estimate the levelized cost per ton CO2 captured (LCOC). To achieve LCOC below $100/t-CO2, adsorbents should have working capacities of 4.9 t and 3 t-CO2/year for 5 years and 10 years of operation, respectively. In summary, this study highlights a viable path toward the decarbonization of the commercial buildings sector and provides quantitative performance and economic insight on the suitability of building-integrated carbon capture technology.

Mineralization reaction between CO2 and coal ash produced from underground coal gasification: Implication for in situ carbon sequestration

Underground coal gasification (UCG) represents a promising clean and low-carbon energy technology, which could create a suitable cavity for in situ carbon sequestration by mineralization reaction between CO2 and coal ash produced from UCG. This may assist in achieving a net-zero carbon emission goal for UCG projects. To determine the carbonation efficiency and mineralization potential of CO2 mineral sequestration in abandoned UCG cavity, coal ash produced from the gasification of three different low-rank coal samples was used in this study. A comparative experiment was conducted using a group of high-calcium fly ash from a coal-fired power plant. All mineralization reaction experiments were performed in a high-temperature and high-pressure reactor, with CO2 pressures ranging from 2 to 8 MPa and temperatures ranging from 40 to 80°C. These conditions were selected to simulate the sequestration conditions in the UCG cavity. Real-time monitoring of CO2 pressure in the reactor was used to assess the impact of solid-to-water ratio, temperature, and pressure on the CO2 mineralization. X-ray diffraction and scanning electron microscopy were employed to identify the presence of newly formed carbonate minerals associated with mineralization reaction. The results indicated that the coal ash produced by gasification pretreatment at 900°C contains a substantial quantity of alkaline-earth oxides, such as calcium oxide (CaO), with a relative mass fraction reaching 25.9%. It provided an adequate supply of alkali metal ions for the mineralization reaction, which exhibited comparable efficacy in mineralizing CO2 to that observed in high-calcium fly ash. Without stirring, at lower solid-to-water ratio, the maximum amount of CO2 consumed through mineralization was increased by up to 74.12%. Carbonation efficiency decreased with rising temperatures below 70°C due to the limited dissolution of CO2 in water, it increased with elevated pressure but decreased in the supercritical state, potentially attributable to the dissolution of carbonate minerals in a supercritical CO2 environment. The process of mineralization reaction between CO2 and coal ash aligned well with the Surface Coverage Model (R2 values ranging from 0.92 to 0.99). A preliminary estimation based on Chinese coal reserves revealed that the potential of CO2 sequestration capacity in UCG cavities by mineralization ranging from 29 to 102 Gt, an additional 517 Gt CO2 may be stored when filled with fly ash. This paper provides theoretical bases for predicting the maximum carbonation efficiency under high-pressure and high-temperature conditions in UCG cavities, and research directions for achieving a net-zero carbon emission goal for UCG projects.

Toxicity and environmental aspects of surfactants

Abstract As the single largest class of specialty chemicals, surfactants are consumed in huge quantities in our daily life and in many industrial areas. In the past, the attention was focused entirely on technical performance. However, starting from the 1970s and 80s, surfactant related environmental concerns have become the main driving force to upgrade surfactant production technology to make more benign or “greener” products. For this reason, environmental issues, dermatological effects, and oral toxicity are the main priorities when surfactants are considered for a specific purpose. In this paper, we present five cases to demonstrate how the surfactant industry tackles these challenges to mitigate the environmental and health effects associated with surfactant consumption. We also discuss the important role played by surfactants in a current carbon capture and storage (CCS) strategy to reduce the CO2 level in the atmosphere. Surfactant-based stable CO2 foam flooding is a well-established enhanced oil recovery technique. It has been considered to be an economically realistic procedure to sequester large amounts of CO2 in geological formations.

Environmental impact assessment in microalgal lipid production: carbon footprint and net emissions

This study focuses on analyzing the role of microalgae in mitigating climate change through CO2 capture and lipid production, which can be used in the development of energy products and commercially relevant products. The objective was to evaluate the net CO2 emissions in three lipid production scenarios from microalgae, in addition to analyzing the impact of various biomass pretreatment technologies before lipid extraction. For this purpose, only the emissions directly generated by energy consumption in the process and the amount of CO2 that can be captured by microalgae cultivation were considered. In all three scenarios, CO2 capture during biomass cultivation and emissions associated with maintaining the process in operation were evaluated. The results show that the emissions generated by energy consumption were 3.56 kg-CO2/kg-oil, 2.19 kg-CO2/kg-oil, and 2.36 kg-CO2/kg-oil in scenarios 1, 2, and 3, respectively, while the CO2 emissions captured in microalgae cultivation were three to four times higher, ultimately resulting in negative emissions in all scenarios. The efficiency of CO2 capture per kilogram of oil produced varies between scenarios, suggesting that the choice of technology and process conditions significantly influence the overall environmental impact. This analysis identifies areas of opportunity to improve microalgal biomass utilization processes, highlighting the stages of the process with the greatest impact on the carbon footprint and enabling the comparison of different technologies on the same basis.

Investigating the generation mechanism of nanobubbles and the ion-transport regulation on nanofiltration membranes for efficient salt-salt separation

Nanofoaming-assisted interfacial polymerization (IP) exhibits strong potential to regulate the structure and the separation performance of thin film composite (TFC) membranes. At present, it is recognized that when NaHCO3 is employed as an aqueous foaming agent, the generation of nanobubbles is ascribed to the NaHCO3 acidification and may be enhanced by increasing the NaHCO3 dosage. However, to more accurately measure the generation of nanobubbles, it is necessary to analyze the content and composition of carbonates in the aqueous solution at the initial and final states of interfacial polymerization, which is currently lacking in research. In this work, based on the chemical equilibrium theory, the aqueous carbonate chemistry and the quantity of CO2 released during IP was evaluated through monitoring the pH changes near the interface and calculating the carbonate distribution fraction. Results showed that the pH of the aqueous solution changed from 10.3 to 11.4 to 6.0–6.5 during interfacial polymerization when the NaHCO3 dosage was 0.00–0.10 wt%. However, this variation in pH was subtle (from ∼9.3 to ∼8.8) when 1.00 wt% NaHCO3 was added, leading to limited transformation of carbonate into H2CO3 and, consequently, less generation of CO2. In the whole dosage range of NaHCO3, 0.10 wt% NaHCO3 contributed to the maximum quantity of CO2 during IP, which was also confirmed by the vesicle-like membrane morphology. The resultant membrane achieved a superior salt-salt separation, with selectivity for Mg2+ and Li+/Na+/K+ enhancements of more than 2 times compared to the membrane without NaHCO3 dosage. This work proposed a new approach to evaluate the inner relationship between NaHCO3 dosage and nanobubble quantity during IP, which provides an ion-transport regulation mechanism of nanofiltration membranes for efficient salt-salt separation.

Modeling of adsorption-controlled binary gas transport in ultratight porous media

Organic-rich ultratight porous media such as shales have complicated pore types and sizes, dictating their unique fluid transport and storage mechanisms. This paper introduces a diffusion-based binary gas (CH4 and CO2) transport model in such porous media, incorporating key transport and storage mechanisms. Binary gas mixture within the pore volume is divided into two domains: the free-phase and the sorbed-phase, both of which contribute to gas mass transport. Thermodynamic properties of the free phase are determined using the Peng-Robinson equation of state, while a modified extended Langmuir isotherm describes the sorbed phase. The bulk diffusion, Knudsen diffusion, and viscous diffusion are reconciled to describe binary gas transport in the free phase, while the surface diffusion is considered in the sorbed phase. The mass flux is finally related to the effective diffusion coefficient and the free-phase concentration gradient through coupling all transport mechanisms via the equivalent resister network model. The governing equations are solved numerically using a finite difference approach to simulate co-diffusion and counter-diffusion of a binary gas mixture in two nanoporous media, shale and coal.The results reveal that surface diffusion is more pronounced in coal than in shale due to coal's higher adsorption capacity. In co-diffusion cases, both free-phase and sorbed-phase concentrations decrease over time. However, the decline of sorbed-phase concentrations is slower than that of the free-phase. Moreover, CO2 tends to remain adsorbed within the coal matrix due to its stronger adsorption affinity, unlike CH4, which is more likely to flow out. In counter-diffusion cases, injected CO2 first accumulates near the fracture region and then diffuses further into the matrix. Despite shale's pore volume being twice that of coal, similar amounts of CO2 are injected, which can be attributed to coal's higher CO2 adsorption capacity.

Numerical modeling of an offshore shellfish farm exposed to extreme wave conditions

Shellfish cultivation is a sustainable method of providing human food and can help remove large amounts of CO2 from the atmosphere. Over the last two decades, longline-based structures have dominated farming systems. So far, the innovative technologies for open-ocean shellfish farming remain stagnant and need to be developed. As such, this paper preliminarily studies the operation and survivability abilities of an innovative shellfish farm under extreme wave conditions. To that end, an efficient numerical scheme with a robust implicit finite element method is established. First, the numerical modeling of a single module of the shellfish farm is conducted and the numerical results are verified against physical model tests. Then, the numerical modeling is implemented in a full-scale shellfish farm containing nine floating rafts with suspended lantern nets in a 3×3 configuration exposed to extreme wave conditions. Different angles of wave attack and shellfish rafts with and without lantern nets are fully considered, allowing an assessment of the operation and survivability abilities of the shellfish farm under extreme wave conditions in various situations. The results highlight that the angle of wave attack significantly affected the energy absorption of the mooring system. Moreover, non-linear instability such as subharmonics, which existed in the motion dynamics, can be manipulated to avoid resonant motions. This study provides insights into the evaluation of the safety design of a shellfish farm at both operational and survivability levels. The numerical method can also model other advanced offshore marine structures with multi-modules, such as floating bridges, airports, and even floating energy islands.

Preparation of aragonite from calcium carbonate via wet carbonation to improve properties of steel slag building materials

Smelting in steel mills emitted large amounts of CO2 and produced the waste product steel slag (SS). Therefore, the use of SS to fix CO2 and produce value-added products could treat waste with waste and promote the effective use of resources. In this study, aragonite-type calcium carbonate was prepared by wet carbonation of SS, and the aragonite-rich SS (ASS) was pressed and moulded in the raw material of SS for semi-dry carbonation to obtain SS products. Through a series of experiments, the optimal conditions for the modulation and the formation mechanism of aragonite whiskers were investigated, and the effects of aragonite as a crystal seed on the properties and the degree of carbonation of SS products were also explored. In this experiment, the carbonation products were characterised microscopically by XRD, TGA, FT-IR and SEM, and the strength was tested by press machine. The results showed that aragonite phase was produced by wet carbonation of SS suspension containing 0.1 M/L MgCl2 at 120 °C for 2 h. The compressive strength, flexural strength, and secondary carbonation degree of the prepared SS products were increased when 5 % ASS was added.

A Review on Research Progress of Corrosion Resistance of Alkali-Activated Slag Cement Concrete.

China is the largest producer and user of Ordinary Silicate Cement (OPC), and rapid infrastructure development requires more sustainable building materials for concrete structures. Portland cement emits large amounts of CO2 in production. Given proposals for "carbon peaking and carbon neutralization", it is extremely important to study alternative low-carbon cementitious materials to reduce emissions. Alkali-activated slag (AAS) cement, a new green cementitious material, has high application potential. The chemical corrosion resistance of AAS concrete is important for ensuring durability and prolonging service life. This paper reviews the hydration mechanism of AAS concrete and discusses the composition of hydration products on this basis, examines the corrosion mechanism of AAS concrete in acid, sulfate, and seawater environments, and reviews the impact of its performance due to the corrosion of AAS concrete in different solutions. Further in-depth understanding of its impact on the performance of concrete can provide an important theoretical basis for its use in different environments and provides an important theoretical basis for the application of AAS concrete, so that we can have a certain understanding of the durability of AAS concrete.

Preparation of highly active MgO by carbonate hydrogenation and its application in separation of cobalt and nickel

AbstractAs a significant industrial material, MgO is mainly obtained by the pyrolysis of magnesite (magnesium carbonate) under air conditions, producing large amounts of CO2 and contributing to global warming. In this work, the MgO was prepared using the hydrogenation reduction method. The reaction conditions led to CO2 emissions of <1% and an overall temperature decrease of ~80°C. The highly active MgO prepared by hydrogenation reduction led to a precipitation rate of Co and Ni >99% with a short separation time. Electron paramagnetic resonance, CO2 temperature programmed desorption, and diffuse reflectance infrared spectroscopy analyses showed that the MgO prepared by hydrogenation contained oxygen vacancies, which improved the alkalinity of the MgO and promoted the precipitation of Ni2+ and Co2+ by adsorption of hydroxyl oxygen to induce water dissociation, thereby enhancing their separation efficiency.

Multiple-Win Effects and Beneficial Implications from Analyzing Long-Term Variations of Carbon Exchange in a Subtropical Coniferous Plantation in China

To improve our understanding of the carbon balance, it is significant to study long-term variations of all components of carbon exchange and their driving factors. Gross primary production (GPP), respiration (Re), and net ecosystem productivity (NEP) from the hourly to the annual sums in a subtropical coniferous forest in China during 2003–2017 were calculated using empirical models developed previously in terms of PAR (photosynthetically active radiation), and meteorological parameters, GPP, Re, and NEP were calculated. The calculated GPP, Re, and NEP were in reasonable agreement with the observations, and their seasonal and interannual variations were well reproduced. The model-estimated annual sums of GPP and Re over 2003–2017 were larger than the observations of 11.38% and 5.52%, respectively, and the model-simulated NEP was lower by 34.99%. The GPP, Re, and NEP showed clear interannual variations, and both the calculated and the observed annual sums of GPPs increased on average by 1.04% and 0.93%, respectively, while the Re values increased by 4.57% and 1.06% between 2003 and 2017. The calculated and the observed annual sums of NEPs/NEEs (net ecosystem exchange) decreased/increased by 1.04%/0.93%, respectively, which exhibited an increase of the carbon sink at the experimental site. During the period 2003–2017, the annual averages of PAR and the air temperature decreased by 0.28% and 0.02%, respectively, while the annual average water vapor pressure increased by 0.87%. The increase in water vapor contributed to the increases of GPP, Re, and NEE in 2003–2017. Good linear and non-linear relationships were found between the monthly calculated GPP and the satellite solar-induced fluorescence (SIF) and then applied to compute GPP with relative biases of annual sums of GPP of 5.20% and 4.88%, respectively. Large amounts of CO2 were produced in a clean atmosphere, indicating a clean atmospheric environment will enhance CO2 storage in plants, i.e., clean atmosphere is beneficial to human health and carbon sink, as well as slowing down climate warming.