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Climate change induced partly by emissions of carbon dioxide (CO2) is an urgent issue worldwide, calling for advanced methods of carbon sequestration. Since CO2-emitting industries often generate alkaline waste, sequestrating CO2 by mineral carbonation of alkaline waste is promising both for carbon capture and utilization, and for preventing waste disposal. Here we review the principles of mineral carbonation and we discuss mineral carbonation of alkaline waste and byproducts in Taiwan. We focus on wastes such as iron and steel slag, cement and concrete waste, incineration ash, coal combustion ash, and paper waste. We evaluate the CO2 reduction potential to reveal promising materials and industries. We found that 4.2 Mt CO2 can be directly sequestered annually. Moreover, the use of alternative materials in the cement and concrete industries can indirectly facilitate CO2 sequestration. [ABSTRACT FROM AUTHOR]

The paper presents processing techniques of waste newsprint paper. Wastepaper was soaked in a soda or a hydrochloric solution and heated in a reactor with limited air access or in an autoclave. In the first stage, at 300°C, we obtained brittle carbonated coal with particle sizes of 10-50 µm, which can be used after milling as an additive in poor coals in the production of a coal-water slurry fuel. At the second stage, at 500-600°C, we obtained an amorphous carbon containing of up to 91.2% of C, which is widely used in the tire, rubber, and paint and varnish industries. [ABSTRACT FROM AUTHOR]

This study aimed to maximise the amount of CO2 storage by indirect carbonation using paper sludge ash (PSA), which is an alkaline industrial waste. The properties of the following three types of solvents were considered: acids (acetic acid and hydrochloric acid), ammonium salts (ammonium chloride and ammonium acetate) and others (sodium citrate and water). When carbon dioxide was injected into calcium leachates prepared from PSA using acids, carbonation did not occur, and using ammonium salts as solvent, the carbonation efficiency was low. However, after pH swing of the leachates using sodium hydroxide and ammonia solution for acid and ammonium salt solvents, up to 324 kg CO2/(ton PSA) and 175 kg CO2/(ton PSA) were stored, respectively. When carbon dioxide was injected into calcium leachates prepared from PSA using sodium citrate or water, solid was initially generated which later dissolved. In order to solve this problem, CO2 injection was stopped just before the pH of the solution reached 10.5 for sodium citrate and 8.3 for water, resulting in the storage of 136 kg CO2/(ton PSA) and 29 kg CO2/(ton PSA), respectively. Solids obtained through carbonation were pure calcium carbonate. [ABSTRACT FROM AUTHOR]

The utilization of recycled aggregates (RA) for concrete production has the potential to offer substantial environmental and economic advantages. However, RA concrete is plagued with considerable durability concerns, particularly carbonation. To advance the application of RA concrete, the establishment of a reliable model for predicting the carbonation is needed. On the one hand, concrete carbonation is a long and slow process and thus consumes a lot of time and energy to monitor. On the other hand, carbonation is influenced by many factors and is hard to predict. Regarding this, this paper proposes the use of machine learning techniques to establish accurate prediction models for the carbonation depth (CD) of RA concrete. Three types of regression techniques and meta-heuristic algorithms were employed to provide more alternative predictive tools. It was found that the best prediction performance was obtained from extreme gradient boosting-multi-universe optimizer (XGB-MVO) with R2 value of 0.9949 and 0.9398 for training and testing sets, respectively. XGB-MVO was used for evaluating physical laws of carbonation and it was found that the developed XGB-MVO model could provide reasonable predictions when new data were investigated. It also showed better generalization capabilities when compared with different models in the literature. Overall, this paper emphasizes the need for sustainable solutions in the construction industry to reduce its environmental impact and contribute to sustainable and low-carbon economies. [ABSTRACT FROM AUTHOR]

This paper presents comprehensive research of the advantages and applicability of various concrete carbonation detection methods. Employing a combination of Phenolphthalein indicator (PI), Thermogravimetric analysis (TGA), X-ray phase analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and Quantitative calcium carbonate analysis (CA), a detailed comparison to determine the carbonation depth in the partial carbonation zone of concrete specimens is conducted. Among the quantitative analysis methods, CA measures CaCO3 content based on chemical reactions, while TGA obtains the concentration distribution of Ca(OH)2 and CaCO3. Among qualitative analysis methods, XRD tested the intensity distribution of Ca(OH)2 and CaCO3, while FTIR traced the characteristic peaks of C-O functional groups in a specific spectral range to determine the depth of carbonation of concrete. Results indicate that the depth of carbonation values measured by CA, TGA, XRDA, and FTIR are 2–3 times higher than those measured by PI. This research may provide valuable insights for the design of carbonation detection in concrete. [ABSTRACT FROM AUTHOR]

Basic oxygen furnace (BOF) slag is an industrial waste produced from steel-making. It can be utilized as building material, but its high content of free CaO (f-CaO) causes volume expansion of materials and limits its utilization. However, carbonation of BOF slag can decrease the f-CaO content, improve stability, and reduce carbon emissions. This study investigated the influence of temperature, pressure, liquid to solid, reaction time, and stirring pattern on f-CaO consumption and CO2 sequestration, which reached a maximum f-CaO consumption and CO2 sequestration of 99.58% and 5.12% (51.2 g CO2/Kg BOF slag), respectively, under optimum conditions. According to the results of the XRD patterns of carbonated slag, no peaks of CaO were detected, the peaks of Ca2Fe2O5 and Ca2SiO4 were slightly reduced, and new peaks of CaCO3 were detected. The reaction process has been described by a shrinking core model revealing that the diffusion of reactants through the product layer was the rate-limiting step for carbonation. The kinetic equation for CO2 sequestration was derived as: InK = − 2132.83·T−1–9.1543. This approach presents a green, cost-effective, and rapid method for enhancing steel slag utilization while capturing and storing CO2. The method proposed in this paper holds significant potential for wider adoption. [ABSTRACT FROM AUTHOR]

Environmental global issues affecting global warming, such as carbon dioxide (CO2), have attracted the attention of researchers around the world. This paper reviews and discusses the ground improvement and its contribution to reducing CO2 in the atmosphere. The approach is divided into three parts: the Streamlined Energy and Emissions Assessment Model (SEEAM), the replacement of soil stabilisation materials that lead to the emission of a large amount of CO2 with alternatives and mineral carbonation. A brief discussion about the first two is reviewed in this paper and a detailed discussion about mineral carbonation and its role in enhancing soil strength while absorbing a large amount of CO2. It is emphasised that natural mineral carbonation requires a very long time for a material to reach its full capacity to form CO2; as a result, different acceleration processes can be done from increasing pressure, temperature, the concentration of CO2 and the addition of various additives. In conclusion, it was found that magnesium is more attractive than calcium, and calcium is complicated in terms of strength behaviour. Magnesium has a larger capacity for CO2 sequestration and it has a greater potential to increase soil strength than calcium. [ABSTRACT FROM AUTHOR]

This paper reports for the first time the use and application of a novel technique in the characterization of mineral carbonation reaction and CO2 sequestration in soil stabilization using flow meters. Soils based on SiO2 with two different sizes were tested. Lime (Ca(OH)2) was used as the reactant. Instant CO2 flow rate (L/min), total CO2 volume (L), temperature (°C), and absolute pressure (kPa) were monitored and recorded for 1 h by flow meters connected to the mold inlet and outlet. It was determined that the mineral carbonation reaction started in the first seconds and ended before the 5th minute. The mineral carbonation is a short-term and potential reaction, and it is not a time-dependent reaction. It is separated from other carbonation reactions with these characteristics. The highest CO2 captured value was obtained in the soil mixed with 5% lime, where fines were not used. The second highest CO2 captured value was obtained in soil mixed with 1% lime, where fines were not used. CO2 captured with 1% lime is more than CO2 captured with 5% lime in the soil containing fines. Accordingly, 1–5% lime can be used in soil carbonation studies. According to the soil properties, the highest CO2 captured and the CO2 efficiency was achieved with the use of 6–7% water by weight. [ABSTRACT FROM AUTHOR]

Alkali-activated slag (AAS) cement is one type of alkali-activated binders free from Portland cement. The main problems of this type of cement are its high drying shrinkage and low carbonation resistance that hinder its wide use. In the current paper, the authors tried to suppress this high drying shrinkage and enhance the carbonation resistance of this type of binder by incorporating quartz powder (QP). For that reason, slag was partially replaced with QP at ratios of 10–30 wt%. The flowability of each mixture was measured using a hand-driven flow table. The initial reading of drying shrinkage was monitored after 24 h from casting and continued up to 90 days. After initial curing, some specimens were exposed to atmospheric natural carbonation for one year, whilst the remaining specimens were sealed and used as references. Different techniques such as thermogravimetric analysis and its derivative (TGA/DTG), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) were used to analyze the results. The results showed that the incorporation of QP in the matrix increased the flowability and compressive strength, decreased the drying shrinkage, increased the carbonation resistance, and refined the microstructure. [ABSTRACT FROM AUTHOR]

Calcium carbonate micro- and nanoparticles are considered as chemically inert materials. Therefore, they are widely considered in the field of biosensing, drug delivery, and as filler material in plastic, paper, paint, sealant, and adhesive industries. The unusual properties of calcium carbonate-based nanomaterials, such as biocompatibility, high surface-to-volume ratio, robust nature, easy synthesis, and surface functionalization, and ability to exist in a variety of morphologies and polymorphs, make them an ideal candidate for both industrial and biomedical applications. Significant research efforts have been devoted for developing novel synthesis methods of calcium carbonate particles in micrometer and nanometer dimensions. This review highlights different approaches of the synthesis of calcium carbonate micro- and nanoparticles, such as precipitation, slow carbonation, emulsion, polymer-mediated method, including in-situ polymerization, mechano-chemical, microwave-assisted method, and biological methods. The applications of these versatile calcium carbonate micro- and nanoparticles in the biomedical field (such as in drug delivery, therapeutics, tissue engineering, antimicrobial activity, biosensing applications), in industries, and environmental sector has also been comprehensively covered. [ABSTRACT FROM AUTHOR]

Extensive carbonation of peridotite results in listvenite, a rock composed of magnesite and quartz. At Gråberget, Røros, SE-Norway, a variably serpentinized peridotite body, surrounded by the Røros schists, a former abyssal sediment displays all stages of transformation of peridotite to quartzite. In this paper we record the sequence of steps in this process by combining the observation of mineral assemblages, textural relationships and geochemistry, and variations in Pb isotopic compositions. Initial serpentinization, a stage that also involved an enrichment in fluid-mobile elements (Pb, Sb and As), was followed by carbonation through CO2 fluids that formed soapstone, and eventually listvenite. The listvenite grades by decreasing amounts of carbonates into fuchsite bearing quartzite. The carbonates dissolved during supergene alteration and formed pores coated with oxides of Fe, Mn and Ni resulting in a brown rock color. The quartzite displays porous stylolites enriched in Pb, As and Sb and fuchsite with porous chromite grains as the only relicts of the original mineralogy in the peridotite. The dissolution of the carbonate occurred at oxidizing conditions at temperatures below 150 °C, where the solubility of magnesite is higher than that of quartz. Formation of quartzite from peridotite is supported by low REE contents and lack of zircons in the two rock types. The transformation involved enrichment of Pb, coupled with the elimination of Mg and enrichment of Si. This chemical fractionation and selective transfer of elements to the continents is an important mechanism and needs to be taken into account in models of continental evolution. [ABSTRACT FROM AUTHOR]

Geopolymers are considered as environmentally friendly binders with a high potential not only to lower the prices of binders, but mainly to decrease the significant carbon footprint originating from the production of traditionally used Portland cement. Their production is very different compared to Portland cement as they are usually prepared by activating alumino-silicates in an alkaline solution. Similarly, to concrete, pozzolana active materials, such as fly ash, blast-furnace slag, or metakaolin were successfully used for geopolymer production. Nevertheless, the utilization of fine ceramic waste powder, also pozzolana active, has rarely been reported in geopolymer production. In this paper, series of ceramic-based geopolymers were prepared with the utilization of ceramic waste powder, alkali activated by the mixtures of sodium hydroxide and sodium silicate (water glass) with the silicate moduli ranging from 0.8 to 1.4. The studied samples were cured for 7 days at temperatures of 60 °C to speed up geopolymerization of ceramics, and after 28 days, they were exposed to 20 ± 2% CO2 at 85% RH for 10 months. The effect of the accelerated carbonation conditions on the composition changes and thermal stability of the studied materials was determined by means of X-ray diffraction and thermal analysis. These results were supported by evolved gas analysis. Mechanical properties, such as compressive and flexural strength, were also analyzed. The accelerated carbonation conditions along with higher curing temperatures led to a partial enhancement of mechanical properties, reduction of efflorescence and non-negligible microstructural changes of exposed geopolymers compared to those stored in laboratory conditions. [ABSTRACT FROM AUTHOR]

Carbonation induced corrosion is one of the major durability issues for reinforced concrete structures. To address this issue, it is essential to understand the underlying mechanism of carbonation by detecting the ingress of the CO2 and carbonation depth quantitatively. This paper demonstrates the potential of Raman spectroscopy, as a powerful technique, to implement quantification analysis of cement paste carbonation. In present work, the correlation between the content of the CO32− and the Raman peak intensity was initially established by using several standard specimens premixed with certain amount of CO32−. The established correlation was then used to investigate the carbonation of the cement paste in a CO2 diffusion scenario, and the results show a good agreement with that obtained by thermogravimetry measurements. Therefore, the feasibility of the Raman spectroscopy to quantify the carbonation degree of the cement paste can be demonstrated. [ABSTRACT FROM AUTHOR]

This paper attempts to evaluate the mineralogical and chemical composition of sedimentary limestone mine waste alongside its mineral carbonation potential. The limestone mine wastes were recovered as the waste materials after mining and crushing processes and were analyzed for mineral, major and trace metal elements. The major mineral composition discovered was calcite (CaCO3) and dolomite [CaMg(CO3)2], alongside other minerals such as bustamite [(Ca,Mn)SiO3] and akermanite (Ca2MgSi2O7). Calcium oxide constituted the greatest composition of major oxide components of between 72 and 82%. The presence of CaO facilitated the transformation of carbon dioxide into carbonate form, suggesting potential mineral carbonation of the mine waste material. Geochemical assessment indicated that mean metal(loid) concentrations were found in the order of Al > Fe > Sr > Pb > Mn > Zn > As > Cd > Cu > Ni > Cr > Co in which Cd, Pb and As exceeded some regulatory guideline values. Ecological risk assessment demonstrated that the mine wastes were majorly influenced by Cd as being classified having moderate risk. Geochemical indices depicted that Cd was moderately accumulated and highly enriched in some of the mine waste deposited areas. In conclusion, the limestone mine waste material has the potential for sequestering CO2; however, the presence of some trace metals could be another important aspect that needs to be considered. Therefore, it has been shown that limestone mine waste can be regarded as a valuable feedstock for mineral carbonation process. Despite this, the presence of metal(loid) elements should be of another concern to minimize potential ecological implication due to recovery of this waste material. [ABSTRACT FROM AUTHOR]

The application of three simple and cost-effective technologies for ex situ remediation of the sediment of Begej River in Serbia is presented in this paper. In the first step, conventional electrokinetic treatment (EK) was carried out to reduce the amount of contaminated sediment and enhance the accumulation of metals. Subsequently, stabilization/solidification (S/S) treatment was applied to the remaining portion of polluted sediment to immobilize the accumulated metals. At the same time, the influence of accelerated carbonation on the effectiveness of the treatment was evaluated. The immobilizing agents used in this study included bio ash produced by combustion of wheat and soy straw mixture and bio ash derived from molasses incineration. After the treatments, the risk assessment was performed by using the sequential extraction procedure (SEP) and TCLP and DIN 3841-4 S4 leaching tests. The results obtained after the EK treatment revealed a reduction in the amount of polluted sediment to a half. Leaching tests and SEP performed on S/S mixtures after a 28-day maturation period indicated that accelerated carbonation decreased the mobility of critical metals, especially in wheat and soy straw mixtures. Moreover, based on the leaching tests, all prepared mixtures were categorized as non-hazardous and safe for disposal according to the relevant Serbian regulations. The newly developed method that combines EK and S/S treatments with the addition of accelerated carbonation produced reduced volumes of stabilized sediment which is safe for disposal. [ABSTRACT FROM AUTHOR]

In the paper, a multi-scale experimental investigation on the occurrence of carbonation and its effect on chemo-mechanical behaviour of lime-treated soil has been presented. Carbonation affects chemo-mineralogical evolution of lime-treated soils depending on the time scale at which reaction mechanism takes place. In the short term, a progressive carbonation of portlandite is responsible for the formation of calcium carbonate with consumption of available lime for pozzolanic reactions (lime carbonation). In the long term, carbonation of the secondary phases resulting from pozzolanic reactions weakens the bonding effects induced by hydrated compounds (carbonation of secondary reaction products). Mineralogical and microstructural features of lime-treated and carbonated samples have been monitored at increasing curing times by means of microstructural analyses. Triaxial drained compression tests have been performed on treated samples cured in different conditions for short and long term. Mineralogical investigations showed precipitation of calcium carbonate for lime-treated samples exposed to atmospheric CO2 since the very short term. Exposure of lime-treated sample to CO2 after precipitation of hydrated phases favoured decalcification of cementitious compounds and formation of calcium carbonate. In both cases, precipitation of calcite relevantly affects the mechanical behaviour of lime-treated samples. From the observed behaviours, it will be possible to take into account relevant factors for performing the best practice finalized to efficient and durable soil treatment. [ABSTRACT FROM AUTHOR]

In this article, a new process for treating steel slag and CO2 simultaneously and preparing calcium carbonate, metallic iron, and glass ceramics without wastewater or gas production is proposed. The reduction of iron and preparation of diopside glass ceramics are studied in this paper, and the results show that the carbon thermal reduction product of the original slag does not reach its melting point, and the slag and iron are well separated in the samples containing the leached steel slag and added silica. Part of the parent glass is converted into a glass ceramic after heat treatment, and the crystalline phases of samples are melilite, diopside, and partial melilite, and diopside and anorthite, respectively. The crystallization activation energy of the best sample in this article is E = 660.664 kJ/mol. The Avrami indices calculated at different heating rates are all less than 3, which indicates that the crystallization mode of the glass involves surface crystallization. This finding is consistent with the results for the prepared glass ceramics. [ABSTRACT FROM AUTHOR]

The progress achieved with the use of volcanic ash for geopolymer synthesis has been critically reviewed in this paper. This consists of an overview of mineralogy and chemistry of volcanic ash. The role of chemical composition and mineral contents of volcanic ash on their reactivity during geopolymerization reaction and, consequently, mechanical properties have been accessed. An attempt has been made to establish a relationship between synthesis factors and final properties. A critical assessment of some synthesis conditions has been addressed and some practical recommendations given along with suggestions of future works that have to be done. All this has shown that there are still many works such as durability tests (carbonation, freeze-thaw, resistance, etc.), life cycle analysis, etc. that need to be done in order to satisfy both suitability and sustainability criteria for a large-scale or industrial application. [ABSTRACT FROM AUTHOR]

This paper presents a study on the carbonation behaviors of hydraulic and non-hydraulic calcium silicate phases, including tricalcium silicate (3CaO·SiO or CS), γ-dicalcium silicate (γ-2CaO·SiO or γ-CS), β-dicalcium silicate (β-2CaO·SiO or β-CS), rankinite (3CaO·2SiO or CS), and wollastonite (CaO·SiO or CS). These calcium silicate phases were subjected to carbonation reaction at different CO concentration and temperatures. Thermogravimetric analysis (TGA) tests were performed to quantify the amounts of carbonates formed during the carbonation reactions, which were eventually used to monitor the degree of reactions of the calcium silicate phases. Both hydraulic and non-hydraulic calcium silicates demonstrated higher reaction rate in case of carbonation reaction than that of the hydration reaction. Under specific carbonation scenario, non-hydraulic low-lime calcium silicates such as γ-CS, CS and CS were found to achieve a reaction rate close to that of CS. Fourier transformed infrared (FTIR) spectroscopy and scanning electron microscope (SEM) tests were performed to characterize the carbonation reaction products of the calcium silicate phases. The FTIR spectra during the early stage of carbonation reaction showed formation of calcium silicate hydrate (C-S-H) from CS, γ-CS, β-CS, and CS phases with a similar degree of polymerization as that of the C-S-H that forms during the hydration reaction of CS. However, upon further exposure to CO, these C-S-H phases decompose and eventually converted to calcium-modified (Ca-modified) silica gel phase with higher degree of silicate polymerization. Contradictorily, CS phase started forming Ca-modified silica gel phase even at the early stage of carbonation reaction. This paper also revealed the stoichiometry of the Ca-modified silica gel that formed during the carbonation reaction of the calcium silicate phases using the SEM/energy dispersive spectroscopy (EDS) and TGA results. [ABSTRACT FROM AUTHOR]

Using lime mud (LM) purified by sucrose method, derived from paper-making industry, as calcium precursor, and using mineral rejects-bauxite-tailings (BTs) from aluminum production as dopant, the CaO-based sorbents for high-temperature CO capture were prepared. Effects of BTs content, precalcining time, and temperature on CO cyclic absorption stability were illustrated. The cyclic carbonation behavior was investigated in a thermogravimetric analyzer (TGA). Phase composition and morphologies were analyzed by XRD and SEM. The results reflected that the as-synthesized CaO-based sorbent doped with 10 wt% BTs showed a superior CO cyclic absorption-desorption conversion during multiple cycles, with conversion being >38 % after 50 cycles. Occurrence of CaAlO phase during precalcination was probably responsible for the excellent CO cyclic stability. [ABSTRACT FROM AUTHOR]

Carbon capture and sequestration (CCS) has been employed to reduce global warming, which is one of the critical environmental issues gained the attention of scientific and industrial communities worldwide. Once implemented successfully, CCS can store at least 5 billion tons of CO2 per year as an effective and technologically safe method. However, there have been a few issues raised in recent years, indicating the potential leakages paths created during and after injection. One of the major issues might be the chemical interaction of supercritical CO2 with the cement, which may lead to the partial or total loss of the cement sheath. There have been many approaches presented to improve the physical and mechanical properties of the cement against CO2 attack such as changing the water-to-cement ratio, employing pozzolanic materials, and considering non-Portland cements. However, a limited success has been reported to the application of these approaches once implemented in a real-field condition. To date, only a few studies reported the application of nanoparticles as sophisticated additives which can reinforce oil well cements. This paper provides a review on the possible application of nanomaterials in the cement industry where physical and mechanical characteristics of the cement can be modified to have a better resistance against corrosive environments such as CO2 storage sites. The results obtained indicated that adding 0.5 wt% of Carbon NanoTubes (CNTs) and NanoGlass Flakes (NGFs) can reinforce the thermal stability and coating characteristics of the cement which are required to increase the chance of survival in a CO2 sequestrated site. Nanosilica can also be a good choice and added to the cement by as much as 3.0 wt% to improve pozzolanic reactivity and thermal stability as per the reports of recent studies. [ABSTRACT FROM AUTHOR]

This paper studies hydration stages and phase transformation mechanism of the Sr2+-doped calcium zirconium aluminate cement at room temperature. Features of different hydration stages of this cement paste are identified by X-ray diffraction, scanning electron microscopy, differential thermal analysis, thermogravimetric analysis, evolved gas analysis and heat evolution test. It was found that the partial isovalent substitution of Ca2+ for Sr2+ such as Ca7−xSrxZrAl6O18, with x = 0.3, 0.6, 1.0, reduced the hydraulic reactivity of Ca7ZrAl6O18 phase. The course of hydration of mixed oxides of the type 6CaO·SrO·3Al2O3·ZrO2 documented using microcalorimetry was supported by investigations of the solid hydration products. Research showed that the hexagonal hydrates were stable at early and middle curing ages, an indication that including Sr in solid solution could effectively inhibit the conversion from both C4AH13–19 and C2AH8 to C3AH6 and AH3. Calcium monocarboaluminate C4AC¯H11 phases were also found in this system due to the carbonation process of C4AH13 phase. Substitution of Ca2+ ions by Sr2+ ions in hexagonal calcium aluminate hydrates causes structural disorder and then contributes to the broadening of lines in the powder X-ray diffraction patterns of layered structures of metastable hydrates. At later curing ages, the formation of two hydrogarnet phases, one Sr-rich (C,Sr)3AH6 and the other Ca-rich (C,Sr)3AH6, was proved. [ABSTRACT FROM AUTHOR]

It was previously revealed that the total CO concentration in seawater decreased during the Late Archean. In this paper, to assess the secular change of total CO concentration in seawater, we focused on the Paleoproterozoic era when the Earth experienced its first recorded global glaciation. The 2.4 Ga Ongeluk Formation outcrops in the Kaapvaal Craton, South Africa. The formation consists mainly of submarine volcanic rocks that have erupted during the global glaciation. The undeformed lavas are mostly carbonate-free but contain rare disseminated calcites. The carbon isotope ratio of the disseminated calcite (δC vs. VPDB) ranges from − 31.9 to − 13.2 ‰. The relatively low δC values clearly indicate that the carbonation was partially contributed by C-depleted CO derived from decomposition of organic matter beneath the seafloor. The absence of δC higher than − 13.2‰ is consistent with the exceptionally C-depleted CO in the Ongeluk seawater during glaciation. The results suggest that carbonation occurred during subseafloor hydrothermal circulation just after the eruption of the lavas. Previously, it was reported that the carbonate content in the uppermost subseafloor crust decreased from 3.2 to 2.6 Ga, indicating a decrease in total CO concentration in seawater during that time. However, the average CO (as carbonate) content in the Ongeluk lavas (< 0.001 wt%) is much lower than those of 2.6 Ga representatives and even of modern equivalents. This finding suggests that the total CO concentration in seawater further decreased during the period between 2.6 and 2.4 Ga. Thus, the very low content of carbonate in the Ongeluk lavas is probable evidence for the extremely low CO concentration in seawater during the global glaciation. Considering that the carbonate content of the subseafloor crusts also shows a good correlation with independently estimated atmospheric pCO levels through the Earth history, it seem highly likely that the low carbonate content in the Ongeluk lavas reflects the low atmospheric pCO at that time. We conclude that the continuous decrease in CO concentration of seawater/atm. from 3.2 Ga was one of the contributing factors to the Paleoproterozoic global glaciation. [ABSTRACT FROM AUTHOR]

Rapid decarbonization of the cement industry is critical to meeting climate goals. Oversimplification of direct air capture benefits from hydrated cement carbonation has skewed the ability to derive decarbonization solutions. Here, we present both global cement carbonation magnitude and its dynamic effect on cumulative radiative forcing. From 1930–2015, models suggest approximately 13.8 billion metric tons (Gt) of CO2 was re-absorbed globally. However, we show that the slow rate of carbonation leads to a climate effect that is approximately 60% smaller than these apparent benefits. Further, we show that on a per kilogram (kg) basis, demolition emissions from crushing concrete at end-of-life could roughly equal the magnitude of carbon-uptake during the demolition phase. We investigate the sensitivity of common decarbonization strategies, such as utilizing supplementary cementitious materials, on the carbonation process and highlight the importance of the timing of emissions release and uptake on influencing cumulative radiative forcing. Given the urgency of determining effective pathways for decarbonizing cement, this work provides a reference for overcoming some flawed interpretations of the benefits of carbonation. The time-dependent effects of cement production emissions and CO2 uptake through carbonation of hydrated cement at a global scale were quantified. The results show the climate benefits of the CO2 uptake by cement are being significantly over-estimated. [ABSTRACT FROM AUTHOR]

The current experimental work aimed at developing PCC through two major process steps: dissolution and precipitation, using raw materials domestically available as SL, which are intensively used in construction inputs. The pH level was the decisive parameter used to determine the time required to complete the dissolution and carbonation processes during precipitation. The optimal pH levels were found to be 13 for dissolution and 7.1 for precipitation, respectively. The produced PCC was characterized based on chemical analysis, crystallinity, and morphology, showing an increment of CaCO3 content exceeding 99%, sharper crystal peaks, and predominantly calcite PCC. The compatibility of the PCC was assessed by incorporating 25%, 50%, 75%, and 100% of PCC with commercial filler, followed by selected mechanical tests, such as stress at yield, density, and elongation at break. The results indicated that mixing ratios of 25%, 50%, and 75% of PCC with the commercial filler met the standards, with stress at a yield above 45 MPa and density within the range of 1.35 to 1.46 g/cm3. However, complete substitution slightly lowered these properties. Nevertheless, the elongation at break was acceptable at all treatment levels. [ABSTRACT FROM AUTHOR]

Although the literature presents intensive studies based on monitoring cement hydration in adiabatic and semi-adiabatic environments, such as non-conventional differential thermal analysis (NCDTA) systems, studies of cement hydration in controlled climatic chambers are very rare. Using three W/C ratios (0.5, 0.6 and 0.7) and three relative humidity conditions (60, 80 and 100%) at 25 °C, the authors analyzed in real time the evolution of cement hydration reaction during the first 24 h in an environmental-controlled chamber. The main objective of this paper is to present two new developed systems of NCDTA (NNCDTA) and non-conventional TG and to show, using high-strength sulfate-resistant Portland cement pastes in a controlled chamber as application examples, how the developed systems measure on real time the thermal effects and the mass changes that occur during hydration and carbonation reactions. The captured CO mass can be quantified as it occurs by carbonation curves. The results are in agreement with the mechanical and structural properties of the used pastes and with their TG/DTG data, after being processed by different operational conditions. Carbonation for 24 h alters significantly the cement hydrated paste composition, resulting in final poor mechanical resistance properties. However, carbonation for 1 h, in specific conditions, enhances them when compared to a non-carbonated reference paste, due to a final higher content of silica and alumina hydrated phases and to a lower mass ratio between that of their combined water and their total mass as well. [ABSTRACT FROM AUTHOR]

This paper presents a study on rapid hardening behaviors of β-CS by accelerated carbonation curing. β-CS cubes compacted at various molding pressures were subjected to different CO concentration for accelerated carbonation curing. The CO uptake and microstructure changes were analyzed by thermogravimetric analysis (TG), QXRD, FT-IR and MAS-NMR. The results indicated that CO uptake was affected by molding pressure and CO concentration seriously. TG analysis indicated that the carbonation reaction was rapid in the first hour. The carbonation degree reached 21.6% and giving a compressive strength of 85.7 MPa after 6 h carbonation in 99.9% CO concentration. And it showed a much less carbonation degree in 20.0% CO. Calcite, vaterite and amorphous silica-rich phase formed in the carbonation progress. The FT-IR and NMR analysis indicated β-CS was decalcified to C-S-H gel and further decalcified to formation of an amorphous silica gel composed of Q and Q silicate tetrahedral. The chain length of C-S-H gel increased from to 2.67 to 6.36 with prolonged carbonation time, showing a lower C/S ratio and higher polymerization and also resulting in a lower C-S-H content. [ABSTRACT FROM AUTHOR]

In this paper, waste gypsum from wet flue gas desulfurization (WFGD) mixed with NH·HO was applied for CO absorption in the solid-liquid-gas phase system. The effects of operation temperature, CO flow rates, and ammonia-to-gypsum ratio on carbonation process were discussed. Meanwhile, a model for CO absorption in the suspension of WFGD gypsum and ammonia was established. The results indicate that higher temperature favors the reaction, and WFGD gypsum conversion can be achieved above 90% even at lower ammonia-to-gypsum ratio, while CO conversion reaches 90% and ammonia utilization is up to 83.69%. The model fits well with the experimental results at various CO flow rates and predicts the concentration distribution of the main species, including CO absorbed, NHCOO, and HCO . [ABSTRACT FROM AUTHOR]

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CO mineralization is a promising utilization option for reducing CO emissions. Hard water (e.g. seawater, salt water and brine) rich in Ca and Mg ions, has potential for fixation of CO. But to date there is no effective way to use these ions for CO mineralization. In this paper, a novel method based on membrane electrolysis was proposed and used for carbonation and separation of calcium and magnesium ions from hard water in low voltage. Compared with traditional electrolysis, membrane electrolysis can reduce the voltage by about 1.3 V, which reducing the energy consumption for CO mineralization dramatically. This method was proved effective to remove the Ca/Mg ions from hard water. And CO was finally transformed into marketable pure magnesium carbonate and precipitated calcium carbonate. According to this study, 1000 m of concentrated seawater could mineralize 4.65 tons of CO. In addition, 9.97 tons of magnesium carbonate hydroxide and 2.02 tons of precipitated calcium carbonate could be produced with only a total electric power consumption of 5676 kWh. Therefore, this method affords a new route for CO mineralization by transforming hard water into high value-added industrial products with low energy consumption. [ABSTRACT FROM AUTHOR]

Gas-solid interfacial phenomena always play a significant role in the multiphase process in atmospheric chemistry. The mineral aerosols have desirable interfacial reactivity on the carbonation of kaolinite. In addition, carbonation of kaolinite may play a role in carbon dioxide capture. It is not well-known about the mechanisms of this reaction. In this paper, the carbonation of kaolinite cluster models with or without water on the atomic scale is studied. We simulate the corresponding reaction paths and accurately calculate the transition states with the homologous enthalpies via using the density functional theory (DFT) method. The study shows that the reaction barriers are lowered down seriously with the existence of water. In addition, water can help stabilize the reaction regions thereby firming the structure of carbonated product. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical and long-term durability behaviour of structural lightweight concrete (LWC) produced with natural lightweight scoria aggregate (LWSA) from the Azores is analysed. Among the properties studied are the compressive and tensile strength, modulus of elasticity, shrinkage, capillary absorption, carbonation and chloride resistance. To this end, a comprehensive experimental study was carried out on different concrete compositions involving common and high-performance structural concrete produced with coarse or coarse and fine volcanic scoria aggregate. Generally, all the mechanical properties worsened with the incorporation of LWSA. It is concluded that the most efficient LWC with LWSA can attain compressive strength up to about 35 MPa. On the other hand, the production of LWC of more than 50 MPa implies a marked reduction in compressive strength for a small reduction in density. The long-term shrinkage increased with the replacement of normal-weight aggregate by LWA and was higher when coarse and fine scoria were used. However, the early age shrinkage can be counterbalanced by the internal curing effect provided by LWSA. The capillary absorption, chloride and carbonation resistance were affected by the high porosity of LWSA. The absence of the outer shell in scoria aggregate and the surface effects during tests can partly explain the lower performance of the LWC. Nevertheless, it is shown that LWC with scoria can be durable, and even for low- to moderate-strength LWC the corrosion induced by carbonation may not be relevant. [ABSTRACT FROM AUTHOR]

Thermogravimetric analysis is finding increasing utility in investigations of reaction paths and carbonation behaviors of CO sorbent. Potassium-based sorbents are currently suggested as new options for capturing CO from flue gas after combustion or removing CO from confined space, such as submarines, space crafts, and aircrafts. In this paper, KCO/AC, KCO/AlO, KCO/5A, KCO/13X, and KCO/SG were prepared with the impregnation of KCO on activated carbon (AC), AlO, zeolite 5A, zeolite 13X, and silica aerogels (SG), respectively. The carbonation paths and behaviors of these sorbents in low temperature and CO concentration were revealed with TG. The carbonation conversions and average reaction rates were measured under different conditions by changing support material, temperature, CO concentration, and HO concentration. The carbonation conversions for KCO/AC, KCO/AlO, KCO/5A, KCO/13X, and KCO/SG are 93.3, 67.3, 34.5, 60.0, and 10.1 %, respectively. The reaction paths of KCO/AC and KCO/SG are found out that the hydration reaction occurs first to form KCO·1.5HO and KH(CO)·1.5HO, then KHCO is produced rapidly. In the case of KCO/AlO, KCO/5A, and KCO/13X, a new phase of KAl(CO)(OH) is formed which requires a higher temperature of 350 °C to be decomposed. The carbonation conversions increase with the increase of the CO concentration and HO concentration, but decrease with the increase of temperature. The average reaction rate increases when the aforementioned variables increase to a high value. The support material is the key factor that affects the carbonation conversion and average reaction rate. Choosing a proper support material is most important for obtaining enhanced CO capture capacity of potassium-based sorbent. [ABSTRACT FROM AUTHOR]

This paper is devoted to a micromechanical study of mechanical properties of cement-based materials by taking into account effects of water saturation degree and carbonation process. To this end, the cement-based materials are considered as a composite material constituted with a cement matrix and aggregates (inclusions). Further, the cement matrix is seen as a porous medium with a solid phase (CSH) and pores. Using a two-step homogenization procedure, a closed-form micromechanical model is first formulated to describe the basic mechanical behavior of materials. This model is then extended to partially saturated materials in order to account for the effects of water saturation degree on the mechanical properties. Finally, considering the solid phase change and porosity variation related to the carbonation process, the micromechanical model is coupled with the chemical reaction and is able to describe the consequences of carbonation on the macroscopic mechanical properties of material. Some comparisons between numerical results and experimental data are presented. [ABSTRACT FROM AUTHOR]

This study developed a prediction model of the carbonation depth of concrete containing mineral admixtures based on an intelligent algorithm. A carbonation test database of mineral admixture concrete was established considering the influence of 17 parameters. The intelligent algorithm and three existing carbonation depth prediction models were analysed based on the database. The evaluation results indicated that the prediction accuracy of the back-propagation neural network is higher than that of the support vector machine, and the prediction accuracies of the two intelligent algorithms are higher than those of the existing numerical prediction models for carbonation depth. A variable importance analysis indicated that the content of fly ash in mineral admixture has a relatively large influence on the carbonation depth, and the carbonation time is the most critical factor affecting the carbonation depth of concrete containing mineral admixture. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrated a new approach to CO mineral sequestration using wollastonite carbonation assisted by sulfuric acid and ammonia. Samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, and Si nuclear magnetic resonance. The change in Gibbs free energy from −223 kJ/mol for the leaching reaction of wollastonite to −101 kJ/mol for the carbonation reaction indicated that these two reactions can proceed spontaneously. The leached and carbonated wollastonite showed fibrous bassanite and granular calcium carbonate, respectively, while the crystal structure of pristine wollastonite was destroyed and the majority of the Ca in pristine wollastonite leached. The chemical changes in the phases were monitored during the whole process. A high carbonation rate of 91.1 % could be obtained under the action of sulfuric acid and ammonia at 30 °C at normal atmospheric pressure, indicating its potential use for CO sequestration. [ABSTRACT FROM AUTHOR]

Purpose: Blended cements use waste products to replace Portland cement, the main contributor to CO emissions in concrete manufacture. Using blended cements reduces the embodied greenhouse gas emissions; however, little attention has been paid to the reduction in CO capture (carbonation) and durability. The aim of this study is to determine if the reduction in production emissions of blended cements compensates for the reduced durability and CO capture. Methods: This study evaluates CO emissions and CO capture for a reinforced concrete column during its service life and after demolition and reuse as gravel filling material. Concrete depletion, due to carbonation and the unavoidable steel embedded corrosion, is studied, as this process consequently ends the concrete service life. Carbonation deepens progressively during service life and captures CO even after demolition due to the greater exposed surface area. In this study, results are presented as a function of cement replaced by fly ash (FA) and blast furnace slag (BFS). Results and discussion: Concrete made with Portland cement, FA (35 % FA), and BFS blended cements (80 % BFS) captures 47, 41, and 20 % of CO emissions, respectively. The service life of blended cements with high amounts of cement replacement, like CEM III/A (50 % BFS), CEM III/B (80 % BFS), and CEM II/B-V (35 % FA), was about 10 % shorter, given the higher carbonation rate coefficient. Compared to Portland cement and despite the reduced CO capture and service life, CEM III/B emitted 20 % less CO per year. Conclusions: To obtain reliable results in a life cycle assessment, it is crucial to consider carbonation during use and after demolition. Replacing Portland cement with FA, instead of BFS, leads to a lower material emission factor, since FA needs less processing after being collected, and transport distances are usually shorter. However, greater reductions were achieved using BFS, since a larger amount of cement can be replaced. Blended cements emit less CO per year during the life cycle of a structure, although a high cement replacement reduces the service life notably. If the demolished concrete is crushed and recycled as gravel filling material, carbonation can cut CO emissions by half. A case study is presented in this paper demonstrating how the results may be utilized. [ABSTRACT FROM AUTHOR]

The type and kinetics of metamorphic CO 2-producing processes in metacarbonate rocks is of importance to understand the nature and magnitude of orogenic CO 2 cycle. This paper focuses on CO 2 production by garnet-forming reactions occurring in calc-silicate rocks. Phase equilibria in the CaO–FeO–Al 2O 3–SiO 2–CO 2–H 2O (CFAS–CO 2–H 2O) system are investigated using P– T phase diagrams at fixed fluid composition, isobaric T– X(CO 2) phase diagram sections and phase diagram projections in which fluid composition is unconstrained. The relevance of the CFAS–CO 2–H 2O garnet-bearing equilibria during metamorphic evolution of calc-silicate rocks is discussed in the light of the observed microstructures and measured mineral compositions in two representative samples of calc-silicate rocks from eastern Nepal Himalaya. The results of this study demonstrate that calc-silicate rocks may act as a significant CO 2 source during prograde heating and/or early decompression. However, if the system remains closed, fluid–rock interactions may induce hydration of the calc-silicate assemblages and the in situ precipitation of graphite. The interplay between these two contrasting processes (production of CO 2-rich fluids vs. carbon sequestration through graphite precipitation) must be considered when dealing with a global estimate of the role exerted by decarbonation processes on the orogenic CO 2 cycle. [ABSTRACT FROM AUTHOR]

Gypsum-based mortars were widely used during the Mudejar artistic period in Spain from the 12th to 16th century. During restoration works, compatibility between the new repair mortars and the original components is essential for an adequate intervention on the monument. The increasing interest of knowing the properties of the gypsum-lime-based mortars for restoration purposes justifies the research carried out. Different mortars compatible with traditional building materials were elaborated by varying the binder proportions, the type of aggregates, the binder/aggregate ratios and the curing time. The main goal of this paper is to characterize the mechanical behaviour and the pore structure of the mortars as a function of curing time. The influence between the different variables used to prepare the mortars and the development of the carbonation process over time is also considered. Mechanical strength and porosity measurements as well as X-ray diffraction and thermal analysis were performed after curing times of 1, 28 and 90 days. The results obtained confirmed a progressive increase in mechanical strength linked to the carbonation of the mortars prepared. Less lime binder and also aggregate contents showed the highest rise in strength over time, related to the highest initial porosity which favoured the carbon dioxide flow. The use of siliceous aggregates (GL-QS mortars) obtained the best results in the development of physico-mechanical properties over curing time. The knowledge obtained from the studied mortars provides practical information to establish a suitable mortar mixture for restoration works on historic buildings and modern architecture where gypsum-lime-based mortars are used. [ABSTRACT FROM AUTHOR]

Thermal and chemical gradients at the boundary of a subducting plate and suprasubduction mantle lead to a variety of poorly understood geologic processes. This paper reports the results of experiments simulating interaction between olivine ( Ol, mantle analog) and carbonated glaucophane schist ( Gls, analog of the upper layer of the subducted crust) under the P-t conditions of a 'hot' subduction zone. The experiments were carried out at a pressure of P = 25 kbar under temperature gradient conditions ( t = 720°C and t = 1000°C) and at a constant temperature of t = 800°C corresponding to the boundary between the materials in the gradient experiment. A comparison of experimental data obtained using two different methods showed that the temperature gradient experiment reproduced the character of schist-olivine interaction under isothermal conditions and provided additional information on the effect of temperature on mineral reactions. Orthopyroxene occurs in the experimental products in different textural positions, forming a layer (with or without magnesite) at the base of the olivine zone or separate grains and intergrowths with magnesite at the boundary of olivine grains. The development of orthopyroxene and carbonate redeposition are described by reactions between olivine and aqueous fluid components, SiO and CO, at $$a_{SiO_2 } = 0.23$$ and $$a_{CO_2 } = 0.07$$. The calculated silica content in the fluid under such thermodynamic conditions is 0.39 mol/kg HO. Given these parameters, the estimated SiO flux at a depth of ∼80 km from the downgoing slab of the Cascadia subduction zone in the northwester United States is 180 t/yr at a very moderate (for the considered depth level) aqueous fluid flux of one million moles per year per kilometer. Modern concepts on convective flows initiated by a subducting slab in the mantle wedge allow us to suggest that orthopyroxene-enriched ultramafic rocks must occur both above the areas of the release of volatile components and silica from the slab and at deeper levels of subduction zones. [ABSTRACT FROM AUTHOR]

The hydrocarbon fossil fuels are considered as the preferable fuels to provide sufficient energies for industrial purposes. Also, extracting oil from the exploration wells might be a concerning issue in the coming decades, and petroleum engineers push themselves into limits ind novel solutions to enhance the oil recovery factor. Wellbore stimulation procedures exert a profound impact on the current production rate enhancement; respect of the way, reservoir productivity index witnesses a steep rise during the production operation and subsequently would virtually eliminate unnecessary expenditures of other methodologies. Appropriate investigation of acidizing procedures and its significant role in the wellbore production enhancement are utterly dependent on the quality and types of additives, types of acid, acidizing operation and types of formation. The objective of this study is to investigate the effect of injected acid in the carbonated reservoir and subsequently its comparison with the acidizing operations model. Therefore, available well-testing experiments are administered to determine the critical reservoir parameters such as skin factor, reservoir pressure, and permeability. Since then by modeling the wellbore condition in the acidizing operation simulator software, the impact of acidizing on the reservoir is simulated. Consequently, the provided information from software is compared with the real data from well-testing operations. As a result, productivity index is increased dramatically owing to successful acidizing procedures. [ABSTRACT FROM AUTHOR]

Magnesium oxide carbonation, especially the reactive magnesia (rMgO), is a new paradigm regarded as a green alternative to the traditional Portland cement. The eco-friendly nature of rMgO binder and the ability to consume industry-derived wastes during carbonation have caused it to receive significant attention in recent years as solutions are being sought for the difficulties facing the cement and construction industry. However, the reaction mechanisms and the carbonation conditions required to achieve an optimized carbonation degree and CO2 uptake are still unclear and not fully understood. This article aimed to review previous studies that investigated the rMgO reaction mechanisms, some factors influencing the carbonation curing of rMgO-based composites, and the application of carbonated rMgO in soil stabilization. Findings revealed that rMgO hydration is a crucial aspect of the reaction process and suggests that factors such as material properties and curing conditions influence the carbonation process. The carbonation treatment utilizes sequestered CO2 to enhance the mechanical and durability performance of carbonated rMgO composites by refining the pore structure and improving the porosity of the carbonated products. Meanwhile, utilizing hydration agents eliminates delayed hydration and improves the overall carbonation efficiency. Finally, recommendations for future research directions on the carbonation of rMgO-based composites were provided. Carbonation of MgO-based binder and CO2 utilization in the construction industry. [ABSTRACT FROM AUTHOR]

Coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) approaches may be important for assessing the long-term durability of cementitious materials. We present a multiphysics approach to overcome past limitations of THMC modelling and validate it based on experimental results of accelerated carbonation tests. Our numerical approach rests on a sequential coupling between Hytec and Cast3m. Hytec computes the evolution of hydraulic and mineralogical fields allowing to compute the micromechanical properties (e.g. Young's modulus). The mineral reactions generate tensile stresses and Cast3M computes the associated strain tensors and the damage evolution represented by the opening or sealing of cracks, impacting subsequent reactive transport processes. Our approach manages to qualitatively represent the crack patterns and non-uniform degradation depths observed on microtomographic images of carbonated cement samples, which can only be explained by the coupled dynamics of chemical and mechanical processes. Our approach can be extended to a wide range of cement-concrete pathologies and contexts. [ABSTRACT FROM AUTHOR]

By-products from the non-ferrous industry are an environmental problem; however, their economic value is high if utilized elsewhere. For example, by-products that contain alkaline compounds can potentially sequestrate CO2 through the mineral carbonation process. This review discusses the potential of these by-products for CO2 reduction through mineral carbonation. The main by-products that are discussed are red mud from the alumina/aluminum industry and metallurgical slag from the copper, zinc, lead, and ferronickel industries. This review summarizes the CO2 equivalent emissions generated by non-ferrous industries and various data about by-products from non-ferrous industries, such as their production quantities, mineralogy, and chemical composition. In terms of production quantities, by-products of non-ferrous industries are often more abundant than the main products (metals). In terms of mineralogy, by-products from the non-ferrous industry are silicate minerals. Nevertheless, non-ferrous industrial by-products have a relatively high content of alkaline compounds, which makes them potential feedstock for mineral carbonation. Theoretically, considering their maximum sequestration capacities (based on their oxide compositions and estimated masses), these by-products could be used in mineral carbonation to reduce CO2 emissions. In addition, this review attempts to identify the difficulties encountered during the use of by-products from non-ferrous industries for mineral carbonation. This review estimated that the total CO2 emissions from the non-ferrous industries could be reduced by up to 9–25%. This study will serve as an important reference, guiding future studies related to the mineral carbonation of by-products from non-ferrous industries. [ABSTRACT FROM AUTHOR]

It is generally recognized that cracks provide easy access to ingress of chlorides in concrete and hence, the initiation of corrosion of steel in cracked concrete occurs at early stage. However, wide variety of results on the effect of crack widths on corrosion of steel in concrete are reported in many studies. Apart from crack width, the crack depths, cracking frequency and healing of cracks also influence the corrosion of steel in concrete. This paper presents a comprehensive review and summarised the results on the effect of cracking on corrosion of steel in concrete. The effect of crack widths on the diffusion of chlorides ions and carbon-dioxide is also discussed in this paper. Among all available results, a correlation between the corrosion current and the crack widths up to 0.3 mm can be established, however, no distinct trends are observed beyond that crack width. Conflicting results on the effect of crack widths on chloride ion diffusion are also reported. The longitudinal crack causes more severe corrosion of steel in concrete than transverse cracks of same width. Cracked concrete containing supplementary cementitious materials exhibited superior corrosion resistance than cracked ordinary Portland cement concrete of same width of transverse as well as longitudinal cracks. The same is also true in the case of lower water–binder ratios of cracked concrete. The increase in crack depth increased the chloride diffusion; however, the corrosion test shows an opposite trend. Conflicting results on the effect of crack frequency on corrosion of steel are also reported. [ABSTRACT FROM AUTHOR]

Waste management is still one of the most significant problems faced by industry. Spent lime cake or carbonation sludge from cane or beet-sugar processing is a major problem for the sugar industries owing to its pollution, storage and disposal issues. The goal of this study was to evaluate beet sugar carbonation sludge (BCS) for use in separation of synthetic dyes from aqueous media. Methylene blue, a synthetic and toxic dye that is widely used in industry was selected as the model coloring agent. The BCS was analyzed by FT-IR, SEM, EDX, TGA, BET and BJH analyses. The adsorption system reached equilibrium after 240 min and followed pseudo-second-order kinetics. The efficiency was nearly constant in the range of pH 4.6–12.2, indicating that BCS can be effectively used for this purpose over a wide pH range. Adsorption efficiency increased with temperature and BCS dosage but decreased with MB concentration. Thermodynamic measurements indicated that the process was endergonic and endothermic. Maximum adsorption capacity and efficiency were 13.05 mg/g and 96.8%, respectively. The isotherm models, Langmuir, Freundlich and Temkin were employed to interpret the data. More than 75% of MB was desorbed using acetonitrile after three consecutive trials and BCS was shown to be re-usable for at least 3 cycles. This study clearly shows the potential use of BCS for the remediation of synthetic and toxic dyes from aqueous media. [ABSTRACT FROM AUTHOR]

Indirect mineral carbonation is considered an ideal CO2 sequestration strategy because of its high carbonation rate and high value-added products. This research explores the carbonation ability of different carbon species—CO32– ions, HCO3– ions, and H2CO3—in their dominant region. When (NH4)2CO3 was used as the carbon source, the Ca2+ ions carbonation rate was hardly affected by pH, while NH4HCO3 was the opposite. When the pH of the leachate decreased from 8.67 to 6.20, the carbonation rate of (NH4)2CO3 decreased from 99.32% to 98.42%, while the carbonation rate of NH4HCO3 decreased from 96.28% to 37.71%. Meanwhile, this research also probed the influence of the nucleating agent on the carbonation rate and carbonation products. The addition of nucleating agent can increase the carbonation rate. For a CH3COOH concentration of 0.6 M for mixed leaching, the carbonation rate was increased by 26.81% with the addition of nucleating agent. Meanwhile, the nucleating agent can also induce the growth of CaCO3 toward the crystal form of the nucleating agent itself. When (NH4)2CO3 and NH4HCO3 were used as the carbon sources, CaCO3 mainly exists in the crystal form of vaterite, and after adding the nucleating agent, the crystal form changes to calcite. [ABSTRACT FROM AUTHOR]

In this work, we studied the phase relationships in the NaAlSi2O6–CaMgSi2O6–CO2 system in the range of 3–6.5 GPa and 900–1500 ℃ using a multianvil press. The duration of most experiments varied from 5 to 9 days. Equilibrium was examined from both sides using oxide-carbonate mixtures and diopside-jadeite glasses with Ag2C2O4 as starting materials. We found that the subsolidus assemblage is represented by clinopyroxene, coesite, dolomite, and CO2 fluid. The solidus of the system passes through 1015 ℃/3 GPa and 1095 ℃/6 GPa, and has a slope of 38 MPa/℃. The near-solidus carbonate melt contains 1–4 mol% SiO2 and 1–4 mol% Na2O. We found that clinopyroxene can be in equilibrium with CO2 fluid under P–T conditions corresponding to the diamond stability field to at least 6–6.5 GPa and 1050–1100 ℃. Yet, the composition of such clinopyroxene corresponds to almost pure jadeite, Jd# 95–97. Thus, the infiltration of CO2 fluid into eclogite under conditions of the continental lithospheric mantle should be accompanied by partial carbonation of clinopyroxene with the formation of a low-Mg carbonate melt with moderate concentrations of sodium. As a result of the reaction, the compositions of clinopyroxenes of eclogites of Groups A and B should shift towards a high-jadeite composition corresponding to eclogites of Group C. [ABSTRACT FROM AUTHOR]

The direct aqueous mineral carbonation of wood combustion ash (WCA), which is a representative high-calcium waste from combustion process, was systematically investigated by varying complex operating conditions, including reaction time, liquid-to-solid ratio (L/S), CO2 concentration, and particle size. The WCA exhibited high CO2 sequestration characteristics with an optimal carbonation efficiency of 76.4%, corresponding to a CO2 sequestration capacity of 0.314 g CO2/g WCA. In addition to solid carbonates, dry residues from liquid products with high potassium contents are potential feedstocks for quality potash fertilizer. Modified shrinking core models based on diffusion-controlled mechanism were proposed to evaluate the carbonation process. The theoretical framework assumes a contracting interface mechanism where active CaO reacts with CO2 to form a product layer. The effective diffusion coefficient of CO2 through the product layer decreases over time, giving deficient carbonation efficiency. The newly proposed models corresponding to different geometrical dimensions provided more perfect fit to the experimental data when compared with the most commonly used kinetic equations. The low apparent activation energy of the carbonation reaction demonstrated the diffusion-controlled mechanism. This work is useful for improving the economics and feasibility of bioenergy carbon capture and storage (CCS) technology chain. [ABSTRACT FROM AUTHOR]

This study investigated the efficiency of CO2 curing in blast-furnace slag pastes activated with three concentrations of KOH solution (3, 4, and 5 M). The CO2 curing was applied into the alkali-activated slag paste for 3 days. The CO2-cured pastes were subjected to subsequent curing in a water bath or exposed to seawater. The mechanical properties and characteristics of the reaction products were compared. Full strength can be obtained within 3 days of the early CO2 curing. The strength remained almost constant regardless of the activator concentration. The CO2-cured samples produced more CaCO3 after exposure to the seawater. The carbonates filled the micropores of the samples, and no strength reduction was observed. The hydrates Ca(OH)2 and C–S–H(I) are carbonated, forming calcite and amorphous CaCO3 during the subsequent curing and exposure to seawater as well as the CO2 curing. A less dense matrix with a lower activator concentration facilitated the diffusion of CO2 and promoted early carbonation in the paste. The polymerization of C–S–H(I) was relatively slow with low activity, and within the period of CO2 curing, more carbonates were produced in the sample prepared at a low activator concentration. [ABSTRACT FROM AUTHOR]