High CO2 permeation using a new Ce0.85Gd0.15O2-δ-LaNiO3 composite ceramic-carbonate dual-phase membrane

This work shows the synthesis, characterization and evaluation of dense-ceramic membranes made of Ce0.85Gd0.15O2-δ-LaNiO3 (CG-LN) composites, where the fluorite-perovskite ratio (CG:LN) was varied as follows: 75:25, 80:20 and 85:15 wt.%. Supports were initially characterized by XRD, SEM and electrical conductivity (using vacuum and oxygen atmospheres), to determine the composition, microstructural and ionic-electronic conductivity properties. Later, supports were infiltrated with an eutectic carbonates mixture, producing the corresponding dense dual-phase membranes, in which CO2 permeation tests were conducted. Here, CO2 permeation experiments were performed from 900 to 700°C, in the presence and absence of oxygen (flowed in the sweep membrane side). Results showed that these composites possess high CO2 permeation properties, where the O2 addition significantly improves the ionic conduction on the sweep membrane side. Specifically, the GC80-LN20 composition presented the best results due to the following physicochemical characteristics: high electronic and ionic conductivity, appropriate porosity, interconnected porous channels, as well as thermal and chemical stabilities between the composite support and carbonate phases.

Effects of different oxidants on the behaviour of microplastic hetero-aggregates

Microplastic hetero-aggregates are stable forms of microplastics in the aqueous environment. However, when disinfecting water containing microplastic hetero-aggregates, the response of them in water to different oxidizing agents and the effect on water quality have not been reported. Our results showed that Ca(ClO)2, K2S2O8, and sodium percarbonate (SPC) treatment could lead to the disaggregation of microplastic hetero-aggregates as well as a rise in cell membrane permeability, which caused a large amount of organic matter to be released. When the amount of oxidant dosing is insufficient, the oxidant cannot completely degrade the released organic matter, resulting in DOC, DTN, DTP and other indicators being higher than before oxidation, thus causing secondary pollution of the water body. In comparison, K2FeO4 can purify the water body stably without destroying the microplastic hetero-aggregates, but it only weakly inhibits the toxic cyanobacteria Microcystis and Pseudanabaena, which may cause cyanobacterial bloom as well as algal toxin and odorant contamination in practical application. Compared with the other oxidizers, K2S2O8 provides better inhibition of toxic cyanobacteria and has better ecological safety. Therefore, when treating microplastic-containing water bodies, we should consider both water purification and ecological safety, and select appropriate oxidant types and dosages to optimize the water treatment.

Deterioration phenomenon of Pb-contaminated aqueous solution remediation and enhancement mechanism of nano-hydroxyapatite-assisted biomineralization

Modern metallurgical and smelting activities discharge the lead-containing wastewater, causing serious threats to human health. Bacteria and urease applied to microbial-induced carbonate precipitation (MICP) and enzyme-induced carbonate precipitation (EICP) are denatured under high Pb2+ concentration. The nano-hydroxyapatite (nHAP)-assisted biomineralization technology was applied in this study for Pb immobilization. Results showed that the extracellular polymers and cell membranes failed to secure the urease activity when subjected to 60 mM Pb2+. The immobilization efficiency dropped to below 50% under MICP, whereas it due to a lack of extracellular polymers and cell membranes dropped to below 30% under EICP. nHAP prevented the attachment of Pb2+ either through competing with bacteria and urease or promoting Ca2+/Pb2+ ion exchange. Furthermore, CO32- from ureolysis replaced the hydroxyl (-OH) in hydroxylpyromorphite to encourage the formation of carbonate-bearing hydroxylpyromorphite of higher stability (Pb10(PO4)6CO3). Moreover, nHAP application overcame an inability to provide nucleation sites by urease. As a result, the immobilization efficiency, when subjected to 60 mM Pb2+, elevated to above 80% under MICP-nHAP and to some 70% under EICP-nHAP. The findings highlight the potential of applying the nHAP-assisted biomineralization technology to Pb-containing water bodies remediation.

Statistical modelling, optimization, and mechanistic exploration of novel ureolytic Enterobacter hormaechei IITISM-SA3 in cadmium immobilization under microbial inclusive and cell-free conditions through microbially induced calcite precipitation

The study aimed to evaluate the potential of a novel isolated ureolytic Enterobacter hormaechei IITISM-SA3 in cadmium bioremoval through MICP. The optimization and modelling of the biotic and abiotic factors affecting the process of mineralization were also performed. In addition, the underlying mechanism of MICP-driven Cd mineralization under microbial-inclusive and cell-free conditions was revealed and supported through the characterization of the bio-precipitates obtained using various characterization techniques. The results indicated that the isolate could remove 97.18% Cd2+ of 11.4 ppm under optimized conditions of 36.86 h, pH 7.63, and biomass dose of 1.75 ml. Besides, the presence and absence of bacterial cells were found to influence both the morphologies and crystalline structures of precipitates. The precipitates obtained under microbial-inclusive conditions showed typical rhombohedral crystalline structures of the composition comprising CaCO3, CdCO3, and 0.67Ca0.33CdCO3. However, the crystalline nature of the precipitate reduced to a nano-sized granular structure in cell-free media. Unlike the cadmium mineralization process under microbial-inclusive media, where bacterial cells serve as nucleation sites for crystallization, the carbonate precipitation effectively captures Cd2+ through co-precipitation, chemisorption, or alternative mechanisms involving interactions between metal ions and CaCO3 under cell-free conditions. The findings presented suggest that using cell-free culture supernatant enriched with carbonate ions provides an avenue that could be harnessed for sustainable metal remediation.

Interaction of microorganisms with carbonates from the micro to the macro scales during sedimentation: Insights into the early stage of biodegradation

The assembly process of Organic Matter (OM) from single molecules to polymers and the formation process of Ca-CO3 ion-pairs are explored at the micro-scale, and then the relationship between OM and carbonate based on the results of microbially-induced carbonate precipitation (MICP) laboratory experiments is established at the macro-scale. Molecular dynamics (MD) is used to model the assembly of OM (a) in an aqueous solution, (b) on surfaces of calcite (10 1‾ 4) crystals and (c) on defective calcite (101‾ 4) crystal surfaces. From the MICP experiments, carbonate minerals containing abundant OM were precipitated and were characterized by Scanning Electron Microscopy (SEM), X-Ray Diffractometry (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The results of the MD show that OM is assembled into polymers in all three simulation systems. Although the Ca-CO3 ion-pairs and OM were briefly combined, the aggregation assembly of OM molecules and the precipitation of carbonate calcium are not related in the long run. The highly specific surface area of the defective calcite shows an increase in the adsorption of OM. The van der Waals forces, which are primarily responsible for controlling the assembly of OM molecules, increase with the degree of aggregation. According to the MICP experiments, OM is enriched on the mineral surfaces, and more OM is found at the steps of defective crystals with their larger surface areas. Through MD and MICP laboratory experiments, this work systematically describes the interaction of OM and carbonate minerals from the micro to the macro scales, and this provides insight into the interaction between OM and carbonates and biogeochemical processes related to the accumulation of OM in sediments.

Porous Nano-Fiber Structure of Modified Electrospun Chitosan GBR Membranes Improve Osteoblast Calcium Phosphate Deposition in Osteoblast-Fibroblast Co-Cultures

Desirable characteristics of electrospun chitosan membranes (ESCM) for guided bone regeneration are their nanofiber structure that mimics the extracellular fiber matrix and porosity for the exchange of signals between bone and soft tissue compartments. However, ESCM are susceptible to swelling and loss of nanofiber and porous structure in physiological environments. A novel post-electrospinning method using di-tert-butyl dicarbonate (tBOC) prevents swelling and loss of nanofibrous structure better than sodium carbonate treatments. This study aimed to evaluate the hypothesis that retention of nanofiber morphology and high porosity of tBOC-modified ESCM (tBOC-ESCM) would support more bone mineralization in osteoblast-fibroblast co-cultures compared to Na2CO3 treated membranes (Na2CO3-ESCM) and solution-cast chitosan solid films (CM-film). The results showed that only the tBOC-ESCM retained the nanofibrous structure and had approximately 14 times more pore volume than Na2CO3-ESCM and thousands of times more pore volume than CM-films, respectively. In co-cultures, the tBOC-ESCM resulted in a significantly greater calcium-phosphate deposition by osteoblasts than either the Na2CO3-ESCM or CM-film (p < 0.05). This work supports the study hypothesis that tBOC-ESCM with nanofiber structure and high porosity promotes the exchange of signals between osteoblasts and fibroblasts, leading to improved mineralization in vitro and thus potentially improved bone healing and regeneration in guided bone regeneration applications.

Implications of dietary carbon incorporation in fish carbonates for the global carbon cycle

Marine bony fish are important participants in Earth's carbon cycle through their contributions to the biological pump and the marine inorganic carbon cycle. However, uncertainties in the composition and magnitude of fish contributions preclude their integration into fully coupled carbon-climate models. Here, we consider recent upwards revisions to global fish biomass estimates (2.7-9.5×) and provide new stable carbon isotope measurements that show marine fish are prodigious producers of carbonate with unique composition. Assuming the median increase (4.17×) in fish biomass estimates is linearly reflected in fish carbonate (ichthyocarbonate) production rate, marine fish are estimated to produce between 1.43 and 3.99 Pg CaCO3 yr-1, but potentially as much as 9.03 Pg CaCO3 yr-1. Thus, marine fish carbonate production is equivalent to or potentially higher than contributions by coccolithophores or pelagic foraminifera. New stable carbon isotope analyses indicate that a significant proportion of ichthyocarbonate is derived from dietary carbon, rather than seawater dissolved inorganic carbon. Using a statistical mixing model to derive source contributions, we estimate ichthyocarbonate contains up to 81 % dietary carbon, with average compositions of 28-56 %, standing in contrast to contents <10 % in other biogenic carbonate minerals. Results also indicate ichthyocarbonate contains 5.5-40.4 % total organic carbon. When scaled to the median revised global production of ichthyocarbonate, an additional 0.08 to 1.61 Pg C yr-1 can potentially be added to estimates of fish contributions to the biological pump, significantly increasing marine fish contributions to total surface carbon export. Our integration of geochemical and physiological analyses identifies an overlooked link between carbonate production and the biological pump. Since ichthyocarbonate production is anticipated to increase with climate change scenarios, due to ocean warming and acidification, these results emphasize the importance of quantitative understanding of the multifaceted role of marine fish in the global carbon cycle.

Green and effective remediation of heavy metals contaminated water using CaCO3 vaterite synthesized through biomineralization

Heavy metal pollution has attracted significant attention due to its persistent presence in aquatic environments. A novel vaterite-based calcium carbonate adsorbent, named biogenic CaCO3, was synthesized utilizing a microbially induced carbonate precipitation (MICP) method to remediate heavy metal-contaminated water. The maximum Cd2+ removal capacity of biogenic CaCO3 was 1074.04 mg Cd2+/g CaCO3 with a high Cd2+ removal efficiency greater than 90% (initial Cd2+ concentration 400 mg/L). Furthermore, the biogenic CaCO₃ vaterite, induced by microbial-induced calcium carbonate precipitation (MICP) process, demonstrated a prolonged phase transformation to calcite and enhanced stability. This resulted in a sustained high effectiveness (greater than 96%) following six consecutive recycling tests. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the semi-stable vaterite type of biogenic CaCO3 spontaneously underwent dissolution and recrystallization to form thermodynamic stable calcite in aquatic environments. However, the presence of Cd2+ leads to the transformation of vaterite into CdCO3 rather than undergoing direct converting to calcite. This transformation is attributed to the relatively low solubility of CdCO3 compared to calcite. Meanwhile, the biogenic CaCO3 proved to be an efficient and viable method for the removal of Pb2+, Cu2+, Zn2+, Co2+, Ni2+ and Mn2+ from water samples, surpassing the performance of previously reported adsorbents. Overall, the efficient and promising adsorbent demonstrates potential for practical in situ remediation of heavy metals-contaminated water.

Mobility, speciation of cadmium, and bacterial community composition along soil depths during microbial carbonate precipitation under simulated acid rain

An overexploitation of earth resources results in acid deposition in soil, which adversely impacts soil ecosystems and biodiversity and affects conventional heavy metal remediation using immobilization. A series of column experiments was conducted in this study to compare the cadmium (Cd) retention stability through biotic and abiotic carbonate precipitation impacted by simulated acid rain (SAR), to build a comprehensive understanding of cadmium speciation and distribution along soil depth and to elucidate the biogeochemical bacteria-soil-heavy metal interfaces. The strain of Sporosarcina pasteurii DSM 33 was used to trigger the biotic carbonate precipitation and cultivated throughout the 60-day column incubation. Results of soil pH, electrical conductivity (EC), and quantitative CdCO3/CaCO3 analysis concluded that the combination of biotic and abiotic soil treatment could reinforce soil buffering capacity as a strong defense mechanism against acid rain disturbance. Up to 1.8 ± 0.04 U/mg urease enzyme activity was observed in combination soil from day 10, confirming the sustained effect of urease-mediated microbial carbonate precipitation. Cadmium speciation and distribution analyses provided new insights into the dual stimulation of carbonate-bound and Fe/Mn-bound phases of cadmium immobilization under microbially induced carbonate precipitation (MICP). As confirmed by the microbial community analysis, outsourcing urea triggered diverse microbial metabolic responses, notably carbonate precipitation and dissimilatory iron metabolism, in both oxygen-rich topsoil and oxygen-depleted subsurface layers. The overall investigation suggests the feasibility of applying MICP for soil Cd remediation under harsh environments and stratagem by selecting microbial functionality to overcome environmental challenges.

Porites' coral calcifying fluid chemistry regulation under normal- and low-pH seawater conditions in Palau Archipelago: Impacts on growth properties

Ongoing ocean acidification is known to be a major threat to tropical coral reefs. To date, only few studies have evaluated the impacts of natural long-term exposure to low-pH seawater on the chemical regulation and growth of reef-building corals. This work investigated the different responses of the massive Porites coral living at normal (pHsw ~ 8.03) and naturally low-pH (pHsw ~ 7.85) seawater conditions at Palau over the last decades. Our results show that both Porites colonies maintained similar carbonate properties (pHcf, [CO32-]cf, DICcf, and Ωcf) within their calcifying fluid since 1972. However, the Porites skeleton of the more acidified conditions revealed a significantly lower density (~ 1.21 ± 0.09 g·cm-3) than the skeleton from the open-ocean site (~ 1.41 ± 0.07 g·cm-3). Overall, both Porites colonies exerted a strong biological control to maintain stable calcifying fluid carbonate chemistry that favored the calcification process, especially under low-pH conditions. However, the decline in skeletal density observed at low pH provides critical insights into Porites vulnerability to future global change.

Potential use of two Serratia strains for cadmium remediation based on microbiologically induced carbonate precipitation and their cadmium resistance

Cadmium (Cd) presence and bioavailability in soils is a serious concern for cocoa producers. Cocoa plants can bioaccumulate Cd that can reach humans through the food chain, thus posing a threat to human health, as Cd is a highly toxic metal. Currently, microbiologically induced carbonate precipitation (MICP) by the ureolytic path has been proposed as an effective technique for Cd remediation. In this work, the Cd remediation potential and Cd resistance of two ureolytic bacteria, Serratia sp. strains 4.1a and 5b, were evaluated. The growth of both Serratia strains was inhibited at 4 mM Cd(II) in the culture medium, which is far higher than the Cd content that can be found in the soils targeted for remediation. Regarding removal efficiency, for an initial concentration of 0.15 mM Cd(II) in liquid medium, the maximum removal percentages for Serratia sp. 4.1.a and 5b were 99.3% and 99.57%, respectively. Their precipitates produced during Cd removal were identified as calcite by X-ray diffraction. Energy dispersive X-ray spectroscopy analysis showed that a portion of Cd was immobilized in this matrix. Finally, the presence of a partial gene from the czc operon, involved in Cd resistance, was observed in Serratia sp. 5b. The expression of this gene was found to be unaffected by the presence of Cd(II), and upregulated in the presence of urea. This work is one of the few to report the use of bacterial strains of the Serratia genus for Cd remediation by MICP, and apparently the first one to report differential expression of a Cd resistance gene due to the presence of urea.

Properties and mechanisms of steel slag strengthening microbial cementation of cyanide tailings

The advantages of microbial induced carbonate precipitation (MICP) as bio-cementation technology for tailings-solidification are under extensive investigation. In order to improve performance of bio-cementation, many strengthening materials were applied to the bio-cementation of tailings. Steel slag (SS) is a kind of industrial solid waste, its chemical composition and mineral composition are similar to cement, and it has a certain application prospect as an auxiliary cementing material. In this study, the properties and mechanism of SS strengthening MICP cementation of cyanide tailings (CT) were investigated. The results showed that Sporosarcina pasteurii growth is not inhibited by SS, and Sporosarcina pasteurii can promote the hydration reaction of SS, providing a suitable alkaline environment and Ca2+, promoting the production of more CaCO3 in the MICP process. When 200 mL of CT leachate was added 1.4 g SS (200-400 mesh), the adsorption of Cu, Pb, Zn, Cd, total cyanide (T-CN), and free cyanide (F-CN) reached 48.05%, 44.28%, 36.25%, 16.67%, 79.05%, and 67.20%, respectively. The maximum unconfined compressive strength（UCS） of the cemented body (with 5%, 150 mesh SS) was 1.97 MPa, which was 3.396 times as high as that without SS. The cemented body with the addition of SS (5%, 150 mesh) contained more carbonate bound Cu (2.75%), Pb (4.89%), Zn (5.37%), and Cd (5.75%), and less exchangeable Cu (3.65%), Pb (6.85%), Zn (2.27%), and Cd (4.42%) than that without SS. In summary, the addition of SS improved the UCS of cemented bodies and the stability of heavy metals and cyanide, reduced the environmental risks existing in the process of CT storage. Meanwhile, it also provides new ideas for resource utilization of industrial solid waste SS and improvement of mine filling materials.

Oyster reefs' control of carbonate chemistry-Implications for oyster reef restoration in estuaries subject to coastal ocean acidification

Globally, oyster reef restoration is one of the most widely applied coastal restoration interventions. While reefs are focal points of processes tightly linked to the carbonate system such as shell formation and respiration, how these processes alter reef carbonate chemistry relative to the surrounding seawater is unclear. Moreover, coastal systems are increasingly impacted by coastal acidification, which may affect reef carbonate chemistry. Here, we characterized the growth of multiple constructed reefs as well as summer variations in pH and carbonate chemistry of reef-influenced seawater (in the middle of reefs) and ambient seawater (at locations ~50 m outside of reefs) to determine how reef chemistry was altered by the reef community and, in turn, impacts resident oysters. High frequency monitoring across three subtidal constructed reefs revealed reductions of daily mean and minimum pH (by 0.05-0.07 and 0.07-0.12 units, respectively) in seawater overlying reefs relative to ambient seawater (p < .0001). The proportion of pH measurements below 7.5, a threshold shown to negatively impact post-larval oysters, were 1.8×-5.2× higher in reef seawater relative to ambient seawater. Most reef seawater samples (83%) were reduced in total alkalinity relative to ambient seawater samples, suggesting community calcification was a key driver of modified carbonate chemistry. The net metabolic influence of the reef community resulted in reductions of CaCO3 saturation state in 78% of discrete samples, and juvenile oysters placed on reefs exhibited slower shell growth (p < .05) compared to oysters placed outside of reefs. While differences in survival were not detected, reef oysters may benefit from enhanced survival or recruitment at the cost of slowed growth rates. Nevertheless, subtidal restored reef communities modified seawater carbonate chemistry in ways that likely increased oyster vulnerability to acidification, suggesting that carbonate chemistry dynamics warrant consideration when determining site suitability for oyster restoration, particularly under continued climate change.

A Novel Spectrophotometric Method for Determination of Percarbonate by Using N, N-Diethyl-P-Phenylenediamine as an Indicator and Its Application in Activated Percarbonate Degradation of Ibuprofen

Sodium percarbonate (SPC) concentration can be determined spectrophotometrically by using N, N-diethyl-p-phenylenediamine (DPD) as an indicator for the first time. The ultraviolet-visible spectrophotometry absorbance of DPD•+ measured at 551 nm was used to indicate SPC concentration. The method had good linearity (R2 = 0.9995) under the optimized experimental conditions (pH value = 3.50, DPD = 4 mM, Fe2+ = 0.5 mM, and t = 4 min) when the concentration of SPC was in the range of 0-50 μM. The blank spiked recovery of SPC was 95-105%. The detection limit and quantitative limit were 0.7-1.0 μM and 2.5-3.3 μM, respectively. The absorbance values of DPD•+ remained stable within 4-20 min. The method was tolerant to natural water matrix and low concentration of hydroxylamine (<0.8 mM). The reaction stoichiometric efficiency of SPC-based advanced oxidation processes in the degradation of ibuprofen was assessed by the utilization rate of SPC. The DPD and the wastewater from the reaction were non-toxic to Escherichia coli. Therefore, the novel Fe2+/SPC-DPD spectrophotometry proposed in this work can be used for accurate and safe measurement of SPC in water.

Anion elements incorporation into corals skeletons: Experimental approach for biomineralization and paleo-proxies

The elemental composition of coral skeletons provides important information for palaeoceanographic reconstructions and coral biomineralization. Partition of anions and their stable isotopes in coral skeleton enables the reconstruction of past seawater carbonate chemistry, paleo-CO2, and past climates. Here, we investigated the partition of B, S, As, Br, I, and Mo into the skeletons of two corals, Acropora cervicornis and Pocillopora damicornis, as a function of calcium and carbonate concentrations.* Anion-to-calcium ratio in the corals (An/CaCoral) were correlated with the equivalent ratios in the culturing seawater (An/CO32-SW). Negative intercepts of these relationships suggest a higher CO32- concentration in the coral extracellular calcifying fluid (ECF) relative to seawater, from which the skeleton precipitates. The enrichment factor of CO32- at the ECF was 2.5 for A. cervicornis and 1.9 for P. damicornis, consistent with their relative calcification rates. The CO32-ECF concentrations thus calculated are similar to those proposed by previous studies based on B/Ca coupled with δ11B, as well as by direct measurements using microsensors and fluorescent dyes. Rayleigh fractionation modeling demonstrates a uniform Ca utilization at various CaSW concentrations, providing further evidence that coral calcification occurs directly from a semiclosed seawater reservoir as reported previously. The partition coefficients reported in this study for B, S, As, Br, I, and Mo open up wide possibilities for past ocean chemistry reconstructions based on Br having long residence time (~160 Ma) in the ocean. Other elements like S, Mo, B, as well as pCO2 may also be calculated based on these elements in fossil coral.

Resilience of Emiliania huxleyi to future changes in subantarctic waters

Lower pH and elevated temperature alter phytoplankton growth and biomass in short-term incubations, but longer-term responses and adaptation potential are less well-studied. To determine the future of the coccolithophore Emiliania huxleyi, a mixed genotype culture from subantarctic water was incubated for 720 days under present-day temperature and pH, and also projected future conditions by the year 2100. The future population exhibited a higher growth rate relative to present-day cells transferred to future conditions after 309 days, indicating adaptation or genotype selection; this was reflected by an increase in optimum growth temperature of ~2.5°C by the end of the experiment. Following transfer to opposing conditions in short-term cross-over incubations, cell volume responded rapidly, within eight generations, confirming trait plasticity. The changes in growth rate and cell volume were larger than reported in previous single stressor relationships and incubations, suggesting synergistic or additive effects of combined elevated temperature and lower pH and highlighting the importance of long-term multiple stressor experiments. At the end of the incubation there were no significant differences in cellular composition (particulate organic content and chlorophyll a), or primary production between present-day and future populations. Conversely, two independent methods showed a 50% decrease in both particulate inorganic carbon and calcification rate, consistent with the decrease in cell volume, in the future population. The observed plasticity and adaptive capacity of E. huxleyi indicate resilience to future conditions in subantarctic waters, although changes in cell volume and carbonate may alter grazing loss and cell ballast, so influencing carbon export to the deep ocean.

Biopolymer-assisted enzyme-induced carbonate precipitation for immobilizing Cu ions in aqueous solution and loess

Wastewater, discharged in copper (Cu) mining and smelting, usually contains a large amount of Cu2+. Immobilizing Cu2+ in aqueous solution and soils is deemed crucial in preventing its migration into surrounding environments. In recent years, the enzyme-induced carbonate precipitation (EICP) has been widely applied to Cu immobilization. However, the effect of Cu2+ toxicity denatures and even inactivates the urease. In the present work, the biopolymer-assisted EICP technology was proposed. The inherent mechanism affecting Cu immobilization was explored through a series of test tube experiments and soil column tests. Results indicated that 4 g/L chitosan may not correspond to a higher immobilization efficiency because it depends as well on surrounding pH conditions. The use of Ca2+ not only played a role in further protecting urease and regulating the environmental pH but also reduced the potential for Cu2+ to migrate into nearby environments when malachite and azurite minerals are wrapped by calcite minerals. The species of carbonate precipitation that are recognized in the numerical simulation and microscopic analysis supported the above claim. On the other hand, UC1 (urease and chitosan colloid) and UC2 (urea and calcium source) grouting reduced the effect of Cu2+ toxicity by transforming the exchangeable state-Cu into the carbonate combination state-Cu. The side effect, induced by 4 g/L chitosan, promoted the copper-ammonia complex formation in the shallow ground, while the acidic environments in the deep ground prevented Cu2+ from coordinating with soil minerals. These badly degraded the immobilization efficiency. The Raman spectroscopy and XRD test results tallied with the above results. The findings shed light on the potential of applying the biopolymer-assisted EICP technology to immobilizing Cu ions in water bodies and sites.

Armoring of MgO by a Passivation Layer Impedes Direct Air Capture of CO2

It has been proposed to use magnesium oxide (MgO) to separate carbon dioxide directly from the atmosphere at the gigaton level. We show experimental results on MgO single crystals reacting with the atmosphere for longer (decades) and shorter (days to months) periods with the goal of gauging reaction rates. Here, we find a substantial slowdown of an initially fast reaction as a result of mineral armoring by reaction products (surface passivation). In short-term experiments, we observe fast hydroxylation, carbonation, and formation of amorphous hydrated magnesium carbonate at early stages, leading to the formation of crystalline hydrated Mg carbonates. The preferential location of Mg carbonates along the atomic steps on the crystal surface of MgO indicates the importance of the reactive site density for carbonation kinetics. The analysis of 27-year-old single-crystal MgO samples demonstrates that the thickness of the reacted layer is limited to ∼1.5 μm on average, which is thinner than expected and indicates surface passivation. Thus, if MgO is to be employed for direct air capture of CO2, surface passivation must be circumvented.

Stromatolite-like Structures Within Microbially Laminated Sandstones of the Paleoarchean Moodies Group, Barberton Greenstone Belt, South Africa

We report abundant small calcareous mounds associated with fossilized kerogenous microbial mats in tidal-facies sandstones of the predominantly siliciclastic Moodies Group (ca. 3.22 Ga) of the Barberton Greenstone Belt (BGB), South Africa and Eswatini. Most of the bulbous, internally microlaminated mounds are several centimeters in diameter and formed at the sediment-water interface contemporaneously with sedimentation. They originally consisted of Fe-Mg-Mn carbonate, which is now largely silicified; subtle internal compositional laminations are composed of organic matter and sericite. Their presence for >6 km along strike, their restriction to the inferred photic zone, and the internal structure suggest that mineral precipitation was induced by photosynthetic microorganisms. Similar calcareous mounds in this unit also occur within and on top of fluid-escape conduits, suggesting that carbonate precipitation may either have occurred abiogenically or involved chemotrophic metabolism(s) utilizing the oxidation of organic matter, methane, or hydrogen, the latter possibly generated by serpentinization of underlying ultramafic rocks. Alternatively or additionally, carbonate may have precipitated abiotically where heated subsurface fluids, sourced by the intrusion of a major Moodies-age sill, reached the tidal flats. In summary, precipitation mechanisms may have been variable; the calcareous mounds may represent "hybrid carbonates" that may have originated from the small-scale overlap of bioinduced and abiotic processes in space and time. Significantly, the widespread occurrence of these stromatolite-like structures in a fully siliciclastic, high-energy tidal setting broadens search criteria in the search for life on Mars while their possible hybrid origin challenges our ability to unambiguously identify a biogenic component.

Plight of CORMs: The unreliability of four commercially available CO-releasing molecules, CORM-2, CORM-3, CORM-A1, and CORM-401, in studying CO biology

Carbon monoxide (CO) is an endogenously produced gaseous signaling molecule with demonstrated pharmacological effects. In studying CO biology, three delivery forms have been used: CO gas, CO in solution, and CO donors of various types. Among the CO donors, four carbonyl complexes with either a transition metal ion or borane (BH3) (termed CO-releasing molecules or CORMs) have played the most prominent roles appearing in over 650 publications. These are CORM-2, CORM-3, CORM-A1, and CORM-401. Intriguingly, there have been unique biology findings that were only observed with these CORMs, but not CO gas; yet these properties were often attributed to CO, raising puzzling questions as to why CO source would make such a fundamental difference in terms of CO biology. Recent years have seen a large number of reports of chemical reactivity (e.g., catalase-like activity, reaction with thiol, and reduction of NAD(P)+) and demonstrated CO-independent biological activity for these four CORMs. Further, CORM-A1 releases CO in an idiosyncratic fashion; CO release from CORM-401 is strongly influenced or even dependent on reaction with an oxidant and/or a nucleophile; CORM-2 mostly releases CO2, not CO, after a water-gas shift reaction except in the presence of a strong nucleophile; and CORM-3 does not release CO except in the presence of a strong nucleophile. All these beg the question as to what constitutes an appropriate CO donor for studying CO biology. This review critically summarizes literature findings related to these aspects, with the aim of helping result interpretation when using these CORMs and development of essential criteria for an appropriate donor for studying CO biology.

Fungal biorecovery of cerium as oxalate and carbonate biominerals

Cerium is the most sought-after rare earth element (REE) for application in high-tech electronic devices and versatile nanomaterials. In this research, biomass-free spent culture media of Aspergillus niger and Neurospora crassa containing precipitant ligands (oxalate, carbonate) were investigated for their potential application in biorecovery of Ce from solution. Precipitation occurred after Ce3+ was mixed with biomass-free spent culture media and >99% Ce was recovered from media of both organisms. SEM showed that biogenic crystals with distinctive morphologies were formed in the biomass-free spent medium of A. niger. Irregularly-shaped nanoparticles with varying sizes ranging from 0.5 to 2 μm and amorphous biominerals were formed after mixing the carbonate-laden N. crassa supernatant, resulting from ureolysis of supplied urea, with Ce3+. Both biominerals contained Ce as the sole metal, and X-ray diffraction (XRD) and thermogravimetric analyses identified the biominerals resulting from the biomass-free A. niger and N. crassa spent media as cerium oxalate decahydrate [Ce2(C2O4)3·10H2O] and cerium carbonate [Ce2(CO3)3·8H2O], respectively. Thermal decomposition experiments showed that the biogenic Ce oxalates and carbonates could be subsequently transformed into ceria (CeO2). FTIR confirmed that both amorphous and nanoscale Ce carbonates contained carbonate (CO32-) groups. FTIR-multivariate analysis could classify the biominerals into three groups according to different Ce concentrations and showed that Ce carbonate biominerals of higher purity were produced when precipitated at higher Ce3+ concentrations. This work provides new understanding of fungal biotransformations of soluble REE species and their biorecovery using biomass-free fungal culture systems and indicates the potential of using recovered REE as precursors for the biosynthesis of novel nanomaterials.

Carbonate-induced enhancement of phenols degradation in CuS/peroxymonosulfate system: A clear correlation between this enhancement and electronic effects of phenols substituents

This study investigated the enhancement effects of dissolved carbonates on the peroxymonosulfate-based advanced oxidation process with CuS as a catalyst. It was found that the added CO₃^2- increased both the catalytic activity and the stability of the catalyst. Under optimized reaction conditions in the presence of CO₃^2-, the degradation removal of 4-methylphenol (4-MP) within 2 min reached 100%, and this was maintained in consecutive multi-cycle experiments. The degradation rate constant of 4-MP was 2.159 min^-1, being 685% greater than that in the absence of CO₃^2- (0.315 min^-1). The comparison of dominated active species and 4-MP degradation pathways in both CO₃^2--free and CO₃^2--containing systems suggested that more CO₃•^-/¹O₂ was produced in the case of CO₃^2-deducing an electron transfer medium, which tending to react with electron-rich moieties. Meanwhile, Characterization by X-ray photoelectron spectroscopic and cyclic voltammetry measurement verified CO₃^2- enabled the effective reduction of Cu²⁺ to Cu⁺. By investigating the degradation of 11 phenolics with different substituents, the dependence of degradation kinetic rate constant of the phenolics on their chemical structures indicated that there was a good linear relationship between the Hammett constants σ_p of the aromatic phenolics and the logarithm of k in the CO₃^2--containing system. This work provides a new strategy for efficient removal of electron-rich moieties under the driving of carbonate being widely present in actual water bodies.

Biogenic apatite in carbonate concretions with and without fossils investigated in situ by micro-Raman spectroscopy

Micro-Raman spectra of concretions with and without fossils were measured in a nondestructive manner. The band position and full width at half maximum height (FWHM) of ν1-PO43- of apatite in the concretions were analyzed to investigate the origin of apatite. The analyzed concretions were derived from the Kita-ama Formation of the Izumi Group, Japan. The micro-Raman analysis showed that the apatites in the concretions were divided into two groups: Group W (wide FWHM group) and Group N (narrow FWHM group). The apatite belonging to Group W is suggested to be biogenic apatite originating from the soft body tissues of organisms because the Sr content is high and the FWHM is similar to that of apatite in bones and teeth of present-day animals. The other apatite belonging to Group N is considered affected by the diagenetic process because of its narrow FWHM and F substitution. These features of both groups were observed regardless of the presence of fossils or absence of fossils in the concretions. This Raman spectroscopic study suggests that the apatite at the time of concretion formation belonged to Group W but was changed to Group N by the substitution of F during the diagenesis process.

Effect of Clay Minerals on Carbonate Precipitation Induced by Cyanobacterium Synechococcus sp

Carbonate precipitation induced by cyanobacteria is an important factor in lacustrine fine-grained carbonate rock genesis. As key components of these rocks, clay minerals play an important role in aggregating cyanobacteria. However, the formation mechanism of fine-grained carbonate under the effect of clay minerals is unclear. In this study, we investigated carbonate precipitation by Synechococcus cells under the influence of clay minerals. The results showed that clay minerals can accelerate Synechococcus aggregation, and the aggregation rate of the kaolinite group was significantly higher than that of montmorillonite. The aggregate size and Synechococcus cell content increased with an increase in clay minerals, resulting in increasing organic matter and carboxyl content in the aggregates. Due to the high affinity between carboxyl and Ca2+, the presence of Synechococcus sp. could improve the Mg/Ca molar ratio in the microenvironment of aggregates, which is conducive to aragonite precipitation. Thus, aragonite 5 to 10 μm in size precipitated when Synechococcus and clay minerals coexisted, whereas low-magnesium calcite (15 to 60 μm) was the main carbonate only in the presence of Synechococcus. This study provides important insights into the mechanisms of microbial-induced carbonate precipitation under the effect of clay minerals, which might offer theoretical support for the genesis of fine-grained lacustrine carbonate. IMPORTANCE The biogenesis of lacustrine fine-grained carbonates is of great significance to the exploitation of shale oil. Clay minerals are an important component of lacustrine fine-grained sedimentary rocks, which is conductive to the aggregation and settlement of cyanobacteria. We investigated the precipitation of carbonate induced by Synechococcus sp. with the addition of kaolinite and montmorillonite. The pH and calcium carbonate saturation of the environment increased under the effect of cyanobacteria photosynthesis. The aggregation of cyanobacteria cells increased the Mg/Ca molar ratio of the microenvironment, creating a favorable condition for the precipitation of aragonite, which was similar in size to the micritic calcite of fine-grained sedimentary rocks. This study provides theoretical support for the genesis of fine-grained carbonates.

Natural siderite derivatives activated peroxydisulfate toward oxidation of organic contaminant: A green soil remediation strategy

Natural siderite (FeCO₃), simulated synthetic siderite and nZVI/FeCO₃ composite were used as green and easily available iron-based catalysts in peroxydisulfate activation for remediating 2-chlorophenol as the target contaminant and this technique can effectively degrade organic pollutants in the soil. The key reaction parameters such as catalysts dosage, oxidant concentration and pH, were investigated to evaluate the catalytic performance of different materials in catalytic systems. The buffering property of natural soil conduced satisfactory degradation performance in a wide pH range (3-10). Both the main non-radical of ¹O₂ and free radicals of SO₄^·- and OH^· were evidenced by quenching experiment and electron paramagnetic resonance. The reduction of nZVI on FFC surface not only has the advantage for electronic transfer to promote the circulation of Fe(III) to Fe(II), but also can directly dechlorinate. Furthermore, the intermediates were comprehensively analyzed by GC-MS and a potential removal mechanism of three oxidant system for 2-CP soil degradation was obtained. Briefly, this research provides a new perspective for organic contaminate soil treatment using natural siderite or simulated synthetic siderite as efficient and environmental catalytic material.

A re-examination of the mechanism of whiting events: A new role for diatoms in Fayetteville Green Lake (New York, USA)

Whiting events-the episodic precipitation of fine-grained suspended calcium carbonates in the water column-have been documented across a variety of marine and lacustrine environments. Whitings likely are a major source of carbonate muds, a constituent of limestones, and important archives for geochemical proxies of Earth history. While several biological and physical mechanisms have been proposed to explain the onset of these precipitation events, no consensus has been reached thus far. Fayetteville Green Lake (New York, USA) is a meromictic lake that experiences annual whitings. Materials suspended in the water column collected through the whiting season were characterized using scanning electron microscopy and scanning transmission X-ray microscopy. Whitings in Fayetteville Green Lake are initiated in the spring within the top few meters of the water column, by precipitation of fine amorphous calcium carbonate (ACC) phases nucleating on microbial cells, as well as on abundant extracellular polymeric substances (EPS) frequently associated with centric diatoms. Whiting particles found in the summer consist of 5-7 μm calcite grains forming aggregates with diatoms and EPS. Simple calculations demonstrate that calcite particles continuously grow over several days, then sink quickly through the water column. In the late summer, partial calcium carbonate dissolution is observed deeper in the water column. Settling whiting particles, however, reach the bottom of the lake, where they form a major constituent of the sediment, along with diatom frustules. The role of diatoms and associated EPS acting as nucleation surfaces for calcium carbonates is described for the first time here as a potential mechanism participating in whitings at Fayetteville Green Lake. This mechanism may have been largely overlooked in other whiting events in modern and ancient environments.

Spatial pH variability of coral reef flats of Kiritimati Island, Kiribati

Ocean acidification poses a threat to carbonate-dominated marine systems, such as tropical coral reefs, as it impacts the ability of organisms to calcify. For assessing the susceptibility of coral reef flats to open ocean acidification it is crucial to better understand the dynamics between the carbonate chemistry of open ocean waters flowing onto coral reef flats and the ecological and hydrodynamic processes that locally modify seawater conditions. In this study, variations in seawater pH and temperature were measured along cross-reef flat transects in high resolution (∼0.3 m) and complemented by surveys of the benthic community composition and reef flat bathymetry. Results represent a snapshot in time and suggest that reef flat hydrodynamic processes determine spatial pH modifications, with little influence of variations in benthic community composition. As mean reef flat pH largely equals ocean conditions, ocean acidification has had and will have an unhampered impact on narrow fringing reef flats.

Evaluation of the kinetics of direct aqueous mineral carbonation of wood combustion ash using modified shrinking core models

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.

Immobilizing of lead and copper using chitosan-assisted enzyme-induced carbonate precipitation

Enzyme-induced carbonate precipitation (EICP) is considered as an environmentally friendly method for immobilizing heavy metals (HMs). The fundamental of the EICP method is to catalyze urea hydrolysis using the urease, discharging CO₃^2- and NH₄⁺. CO₃^2- helps to form carbonates that immobilize HMs afterwards. However, HMs can depress urease activity and reduce the degree of urea hydrolysis. Herein, the potential of applying the chitosan-assisted EICP method to Pb and Cu immobilization was explored. The chitosan addition elevated the degree of urea hydrolysis when subjected to the effect of Cu²⁺ toxicity where the protective effect, flocculation and adsorption, and the formation of precipitation, play parts in improving the Cu immobilization efficiency. The use of chitosan addition, however, also causes the side effect (copper-ammonia complex formation). Two calcium source additions, CaCl₂ and Ca(CH₃COO)₂, intervened in the test tube experiments not only to prevent pH from raising to values where Cu²⁺ complexes with NH₃ but also to separate the urease enzyme and Cu²⁺ from each other with the repulsion of charges. The FTIR spectra indicate that the chitosan addition adsorbs Cu²⁺ through its surface hydroxyl and carboxyl groups, while the SEM images distinguish who the mineral are nucleating with. The findings shed light on the potential of applying the chitosan-assisted EICP method to remedy lead- and copper-rich water bodies.

Immobilization of Cd2+ and Pb2+ by biomineralization of the carbonate mineralized bacterial consortium JZ1

Microbially induced carbonate precipitation (MICP) has been proven to effectively immobilize Cd²⁺ and Pb²⁺ using a single bacterium. However, there is an urgent need for studies of Cd²⁺ and Pb²⁺ immobilized by a bacterial consortium. In this study, a stable consortium designated JZ1 was isolated from soil that was contaminated with cadmium and lead, and the dominant genus Sporosarcina (99.1%) was found to have carbonate mineralization function. The results showed that 91.52% and 99.38% of Cd²⁺ and Pb²⁺ were mineralized by the consortium JZ1 with 5 g/L CaCl₂ at an initial concentration of 5 mg/L Cd²⁺ and 150 mg/L Pb²⁺, respectively. The bioprecipitates were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Moreover, the kinetic studies indicated that the urea hydrolysis reaction fit well with the Michaelis-Menten equation, and the kinetic parameters K_m and V_max were estimated to be 38.69 mM and 58.98 mM/h, respectively. When the concentration of urea increased from 0.1 to 0.3 M, the mineralization rate increased by 1.58-fold. This study can provide a novel microbial resource for the biomineralization of Cd and Pb in soil and water environments.

Carbon dioxide sequestration of iron ore mining waste under low-reaction condition of a direct mineral carbonation process

Mining waste that is rich in iron-, calcium- and magnesium-bearing minerals can be a potential feedstock for sequestering CO₂ by mineral carbonation. This study highlights the utilization of iron ore mining waste in sequestering CO₂ under low-reaction condition of a mineral carbonation process. Alkaline iron mining waste was used as feedstock for aqueous mineral carbonation and was subjected to mineralogical, chemical, and thermal analyses. A carbonation experiment was performed at ambient CO₂ pressure, temperature of 80 °C at 1-h exposure time under the influence of pH (8-12) and particle size (< 38-75 µm). The mine waste contains Fe-oxides of magnetite and hematite, Ca-silicates of anorthite and wollastonite and Ca-Mg-silicates of diopside, which corresponds to 72.62% (Fe₂O₃), 5.82% (CaO), and 2.74% (MgO). Fe and Ca carbonation efficiencies were increased when particle size was reduced to < 38 µm and pH increased to 12. Multi-stage mineral transformation was observed from thermogravimetric analysis between temperature of 30 and 1000 °C. Derivative mass losses of carbonated products were assigned to four stages between 30-150 °C (dehydration), 150-350 °C (iron dehydroxylation), 350-700 °C (Fe carbonate decomposition), and 700-1000 °C (Ca carbonate decomposition). Peaks of mass losses were attributed to ferric iron reduction to magnetite between 662 and 670 °C, siderite decarbonization between 485 and 513 °C, aragonite decarbonization between 753 and 767 °C, and calcite decarbonization between 798 and 943 °C. A 48% higher carbonation rate was observed in carbonated products compared to raw sample. Production of carbonates was evidenced from XRD analysis showing the presence of siderite, aragonite, calcite, and traces of Fe carbonates, and about 33.13-49.81 g CO₂/kg of waste has been sequestered from the process. Therefore, it has been shown that iron mining waste can be a feasible feedstock for mineral carbonation in view of waste restoration and CO₂ emission reduction.

Accelerated and natural carbonation of a municipal solid waste incineration (MSWI) fly ash mixture: Basic strategies for higher carbon dioxide sequestration and reliable mass quantification

The carbonation of alkaline wastes is an interesting research field that may offer opportunities for CO₂ reduction. However, the literature is mainly devoted to studying different waste sequestration capabilities, with lame attention to the reliability of the data about CO₂ reduction, or to the possibilities to increase the amount of absorbed CO₂. In this work, for the first time, the limitation of some methods used in literature to quantify the amount of sequestered CO₂ is presented, and the advantages of using suitable XRD strategies to evaluate the crystalline calcium carbonate phases are demonstrated. In addition, a zero-waste approach, aiming to stabilize the waste by coupling the use of by-products and the possibility to obtain CO₂ sequestration, was considered. In particular, for the first time, the paper investigates the differences in natural and accelerated carbonation (NC and AC) mechanisms, occurring when municipal solid waste incineration (MSWI) fly ash is stabilized by using the bottom ash with the same origin, and other by-products. The stabilization mechanism was attributed to pozzolanic reactions with the formation of calcium silicate hydrates or calcium aluminate hydrate phases that can react with CO₂ to produce calcium carbonate phases. The work shows that during the AC, crystalline calcium carbonate was quickly formed by the reaction of Ca(OH)₂ and CaClOH with CO₂. On the contrary, in NC, carbonation occurred due to reactions also with the amorphous Ca. The sequestration capability of this technology, involving the mixing of waste and by-products, is up to 165 gCO₂/Kg MSWI FA, which is higher than the literature data.

Advanced oxidation processes for water purification using percarbonate: Insights into oxidation mechanisms, challenges, and enhancing strategies

Percarbonate (SPC) has drawn considerable attention due to its merits in the safety of handling and transport, stability, and price as well as environmental friendliness, which has been extensively applied in advanced oxidation processes (AOPs) for water decontamination. Nevertheless, comprehensive information on the application of SPC-AOPs for the treatment of organic compounds in aquatic media is scarce. Hence, the focus of this review is to shed light on the mechanisms of reactive oxygen species (ROS) evolution in typical SPC-AOPs (i.e., Fenton-like oxidation, photo-assisted oxidation, and discharge plasma-involved oxidation processes). These SPC-AOPs enable the formation of multiple reactive species like hydroxyl radical (^•OH), superoxide radical (O₂^•-), singlet oxygen (¹O₂), carbonate radicals (CO₃^•-), and peroxymonocarbonate (HCO₄^-), which together or solely contribute to the degradation of target pollutants. Simultaneously, the potential challenges in practical applications of SPC-AOPs are systematically discussed, which include the influence of water quality parameters, cost-effectiveness, available active sites, feasible activation approaches, and ecotoxicity. Subsequently, enhancing strategies to improve the feasibility of SPC-AOPs in the practical implementation are tentatively proposed, which can be achieved by introducing reducing and chelating agents, developing novel activation approaches, designing multiple integrated oxidation processes, as well as alleviating the toxicity after SPC-AOPs treatment. Accordingly, future perspectives and research gaps in SPC-AOPs are elucidated. This review will hopefully offer valuable viewpoints and promote the future development of SPC-AOPs for actual water purification.

Converting industrial waste into a value-added cement material through ambient pressure carbonation

Converting industrial wastes into value-added building products in an environmental management strategy is a challenging yet vital component of the industrial process. Steel slag (SS), an industrial waste by-product from the steel-making process, is typically disposed of in landfill which consumes land resources and pollutes the environment. This paper explores the possibility of a closed-loop system to convert steel slag into a cement material through carbonation activation, thereby significantly reducing the amount of steel slag waste sent to landfills across Canada. The production of this cementing material can occur next to the steel mill, utilizing steel slag and carbon dioxide collected on-site to fabricate carbon-negative products. To save energy and allow production to be feasible on an industrial scale, ambient pressure (AP) carbonation is developed to reduce carbon emissions while improving their performance. High pressure (HP) carbonation curing and normal hydration (NH) references were also implemented at the same time to justify the application of AP carbonation in reducing CO₂ emission. The results of this study found AP carbonation-activated SS compacts have comparable CO₂ uptake (about 7.5 tons CO₂/100 tons slag) and mechanically compressive strength values as those subjected to HP carbonation, suggesting that AP could be used to replace HP in carbonation curing to ensure a lower energy input. Additionally, AP seemed to possess as effective carbonation as HP. The studies investigated by multiple techniques including X-ray diffractometer (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopic analysis, and scanning electron microscopy (SEM) aim to identify the microstructure development of carbonated SS paste to assess carbonation results. Developed with life cycle assessment (LCA), environmental impact evaluation shows that AP presents a smaller global warming potential (GWP) value than HP. The comparable CO₂ sequestration, satisfactory engineering properties, enhanced microstructure and lesser environmental impact in AP carbonation confirm the feasibility of replacing high pressure with extremely low pressure to cure concrete products. The use of AP carbonation for cement material created using steel slag reduces carbon emissions, energy usage, and natural resource consumption.

New combination of pulsed light and iron (II) for carbonate radical production to enhanced degradation of bisphenol A: Parameter optimization and degradation pathway

Bisphenol A(BPA) is a common industrial chemical with significant adverse impacts on Environment and human health. The present work evaluates the efficacy of pulsed light (PL) and Fe²⁺ ions in activation of sodium percarbonate (SPC) to produce hydroxyl (OH^•) and carbonate (CO₃^•-) radicals for efficient degradation of BPA. The effects of operational parameters such as solution pH, SPC and Fe²⁺ dose as well as the mixture composition were analyzed and the decomposition pathway of BPA proposed. The BPA was successfully degraded at the initial concentration of 15.0 mg/L and optimized conditions by the PL/Fe²⁺/SPC process (99.67 ± 0.29%). A rapid reduction in the degradation of BPA was observed with increasing pH due to OH^• radicals quenching and also the precipitation of Fe²⁺. Under the optimized conditions, degradation of BPA by PL/Fe²⁺/SPC process was five-times faster than the individual process. The quenching experiments revealed that radical and non-radical pathways on BPA degradation was accomplished with OH^•, CO₃^•-, O₂^•-, and ¹O_2, while OH^• and CO₃^•- radicals (as a dominant radicals) have the contributions of 80.23% and 8.30%, respectively. Based on the detected byproducts, ring cleavage can be considered as the main transformation mechanism of BPA by the PL/Fe²⁺/SPC process.

Carbonate Minerals and Dissimilatory Iron-Reducing Organisms Trigger Synergistic Abiotic and Biotic Chain Reactions under Elevated CO2 Concentration

Increasing CO₂ emission has resulted in pressing climate and environmental issues. While abiotic and biotic processes mediating the fate of CO₂ have been studied separately, their interactions and combined effects have been poorly understood. To explore this knowledge gap, an iron-reducing organism, Orenia metallireducens, was cultured under 18 conditions that systematically varied in headspace CO₂ concentrations, ferric oxide loading, and dolomite (CaMg(CO₃)₂) availability. The results showed that abiotic and biotic processes interactively mediate CO₂ acidification and sequestration through "chain reactions", with pH being the dominant variable. Specifically, dolomite alleviated CO₂ stress on microbial activity, possibly via pH control that transforms the inhibitory CO₂ to the more benign bicarbonate species. The microbial iron reduction further impacted pH via the competition between proton (H⁺) consumption during iron reduction and H⁺ generation from oxidization of the organic substrate. Under Fe(III)-rich conditions, microbial iron reduction increased pH, driving dissolved CO₂ to form bicarbonate. Spectroscopic and microscopic analyses showed enhanced formation of siderite (FeCO₃) under elevated CO₂, supporting its incorporation into solids. The results of these CO₂-microbe-mineral experiments provide insights into the synergistic abiotic and biotic processes that alleviate CO₂ acidification and favor its sequestration, which can be instructive for practical applications (e.g., acidification remediation, CO₂ sequestration, and modeling of carbon flux).

Microbial-induced carbonate precipitation prevents Cd2+ migration through the soil profile

Cadmium (Cd)-containing wastewater has been used to irrigate agricultural land. However, long term usage has resulted in the accumulation of Cd in the soil systems, which can eventually leach into the aquifer, contaminating groundwater. Microbial-induced carbonate precipitation (MICP), an economical and effective method, was used to block the in situ migration of Cd²⁺ in the soil profile. The results of the laboratory experiments showed that the maximum Cd²⁺ adsorption capacity of the soil exposed to MICP (8.92 mg/g) was higher than that of soil without MICP (7.12 mg/g). The Thomas model provided a good fit for the Cd²⁺ migration process in soil exposed to MICP (R² > 0.96), and Cd²⁺ was trapped more effectively by soil exposed to MICP than by soil alone. Further testing showed that the Cd²⁺ retention time in the MICP soil column increased with increasing soil urea content and pH but decreased with increasing flow rate. Soil physico-chemical properties showed that the MICP process increased the soil particle size and Cd capacity and decreased the proportion of exchangeable Cd in the soil. Scanning electron microscopy and X-ray diffraction analyses confirmed the generation of CdCO₃ in the MICP soil column. The findings of this study indicate that MICP can be effectively used to immobilize Cd²⁺ and prevent its migration in the soil profile.

Study on the catalytic degradation of Acid Orange 7 and the potential mechanism by ferrous-percarbonate

Factors affecting the degradation of Acid Orange 7 (AO7) were evaluated and optimized when ferrous was used to catalyze percarbonate in the present study. The optimized conditions included the initial pH values ranging from 3 to 11 for AO7 solution, the initial level of AO7, sodium percarbonate (SPC), and Fe²⁺ . Some ions and natural organic materials, which commonly exist in natural water, were also tested to evaluate their potential impacts on the degradation of AO7. The degradation efficiency of AO7 was up to 95% under the optimized test conditions, where the ferrous/percarbonate/AO7 molar ratio was 15/10/1 in the 0.285 mmol/l AO7 aqueous solution. The presence of Cl^- , SO₄ ^2- , NO₃ ^- , Na⁺ , and Mg²⁺ did not affect the removal of AO7. The addition of HCO₃ ^- significantly inhibited its removal, even when the concentration of HCO₃ ^- was low to 0.6 mmol/l. A slight inhibition effect was observed when the added concentration of humic acid ranged from 0.5 to 5 mg/l, whereas the residue of AO7 was significantly enhanced when the level of humic acid was continually increased from 50 to 100 mg/l. Hydroxyl radicals (•OH) were the main reactive intermediates controlling the oxidation of AO7 in the present Fe²⁺ /SPC system. The produced intermediates through the degradation of AO7 were identified to include 2-coumaranone, 2-naphthol, phthalic acid, phthalimide, N-methylnaphthylamine, and 2-methylphenol. The proposed degradation pathways are consistent with the radical formation and the identified intermediates. PRACTITIONER POINTS: The ferrous/percarbonate system can remove 95% of AO7 under the optimized conditions. AO7 removal was inhibited by adding HCO₃ ^- and humic acid, but not affected by Cl^- , SO₄ ^2- , NO₃ ^- , Na⁺ , and Mg²⁺ . Hydroxylation, ring opening, and mineralization driven by the generated hydroxyl radicals were derived as the major processes for degrading AO7.

Facile Construction of Carboxyl-Functionalized Ionic Polymer towards Synergistic Catalytic Cycloaddition of Carbon Dioxide into Cyclic Carbonates

The development of bifunctional ionic polymers as heterogeneous catalysts for effective, cocatalyst- and metal-free cycloaddition of carbon dioxide into cyclic carbonates has attracted increasing attention. However, facile fabrication of such polymers having high numbers of ionic active sites, suitable types of hydrogen bond donors (HBDs), and controlled spatial positions of dual active sites remains a challenging task. Herein, imidazolium-based ionic polymers with hydroxyl/carboxyl groups and high ionic density were facilely prepared by a one-pot quaternization reaction. Catalytic evaluation demonstrated that the presence of HBDs (hydroxyl or carboxyl) could enhance the catalytic activities of ionic polymers significantly toward the CO₂ cycloaddition reaction. Among the prepared catalysts, carboxyl-functionalized ionic polymer (PIMBr-COOH) displayed the highest catalytic activity (94% yield) in the benchmark cycloaddition reaction of CO₂ and epichlorohydrin, which was higher than hydroxyl-functionalized ionic polymer (PIMBr-OH, 76% yield), and far exceeded ionic polymer without HBDs groups (PIMBr, 54% yield). Furthermore, PIMBr-COOH demonstrated good recyclability and wide substrate tolerance. Under ambient CO₂ pressure, a number of epoxides were smoothly cycloadded into cyclic carbonates. Additionally, density functional theory (DFT) calculation verified the formation of strong hydrogen bonds between epoxide and the HBDs of ionic polymers. Furthermore, a possible mechanism was proposed based on the synergistic effect between carboxyl and Br⁻ functionalities. Thus, a facile, one-pot synthetic strategy for the construction of bifunctional ionic polymers was developed for CO₂ fixation.

Simple Halogen-Free, Biobased Organic Salts Convert Glycidol to Glycerol Carbonate under Atmospheric CO2 Pressure

Glycerol carbonate (GC) has emerged as an attractive synthetic target due to various promising technological applications. Among several viable strategies to produce GC from CO₂ and glycerol and its derivatives, the cycloaddition of CO₂ to glycidol represents an atom-economic an efficient strategy that can proceed via a halide-free manifold through a proton-shuttling mechanism. Here, it was shown that the synthesis of GC can be promoted by bio-based and readily available organic salts leading to quantitative GC formation under atmospheric CO₂ pressure and moderate temperatures. Comparative and mechanistic experiments using sodium citrate as the most efficient catalyst highlighted the role of both hydrogen bond donor and weakly basic sites in the organic salt towards GC formation. The citrate salt was also used as a catalyst for the conversion of other epoxy alcohols. Importantly, the discovery that homogeneous organic salts catalyze the target reaction inspired us to use metal alginates as heterogeneous and recoverable bio-based catalysts for the same process.

Catalytic effect of cesium on the oxidation behavior of cation exchange resins in Li2CO3-Na2CO3-K2CO3 melt

After the treatment of liquid radioactive waste, there is a certain amount of Cs in the waste resin, and these Cs-doped resins are prone to volatilize during the thermal treatment process and cause radionuclide leakage. The molten salt oxidation (MSO) can effectively prevent the volatilization of toxic metal, especially the volatilization of Cs. Under nitrogen and air conditions, it is found that the oxidation behavior between Cs-doped and clean cation exchange resins (CERs) is quite different. In the presence of oxygen and molten carbonate salt, Cs₂CO₃ is generated by the destruction of functional groups in Cs-doped CERs. The Cs₂CO₃ in Na₂CO₃-K₂CO₃-Li₂CO₃ reacts with oxygen to form Li₂O₂, which reduces the content of S in residue from 26.33 to 13.38% in air conditions at 400 °C and promotes the generation of sulfate in the molten carbonate salt. The elements Cs and S in the Cs doped CERs spontaneously form thermally stable Cs₂SO₄ in the molten carbonate salt.

Carbonation of municipal solid waste gasification fly ash: Effects of pre-washing and treatment period on carbon capture and heavy metal immobilization

Carbon capture has become an important technology to mitigate ever-increasing CO₂ emissions worldwide, and alkali waste is a potential source of CO₂ capture material. Slagging-gasification is a novel technology for treating municipal solid waste (MSW), and the gasification fly ash (GFA) is the only solid residue that is not reused at present due to its high heavy metal content. GFA contains high amounts of Ca(OH)₂ and Ca(OH)Cl, making it protentional for CO₂ capture. In this study, GFA and washed gasification fly ash (WGFA) were treated with CO₂ for different treatment periods. Weight changes of samples were recorded to evaluate the efficiency of CO₂ capture. To assess the properties of treated GFA, pH value, leached heavy metal concentration, mineral composition, and microscopic morphology were studied. The results revealed that GFA and WGFA could adsorb 18.8% and 23.7% CO₂ of their weights, respectively. Carbonation could immobilize heavy metals including Pb, Zn, and Cu when a proper treatment period was applied. An excessive treatment period decreased the efficiency of heavy metal immobilization. Pre-washing is recommended as a pre-treatment method for GFA carbonation, which increased the efficiency to adsorb CO₂, improved the pH of carbonated GFA, and enhanced the effect to immobilize heavy metals.

Micro-dynamic process of cadmium removal by microbial induced carbonate precipitation

Microbially induced carbonate precipitation (MICP) is a technique used extensively to address heavy metal pollution but its micro-dynamic process remains rarely explored. In this study, A novel Cd-tolerant ureolytic bacterium DL-1 (Pseudochrobactrum sp.) was used to study the micro-dynamic process. With conditions optimized by response surface methodology, the removal efficiency of Cd²⁺ could achieve 99.89%. Three components were separated and characterized in the reaction mixture of Cd²⁺ removal by MICP. The quantitative-dynamic distribution of Cd²⁺ in different components was revealed. Five synergistic effects for Cd²⁺ removal were found, including co-precipitation, adsorption by precipitation, crystal precipitation on the cell surface, intracellular accumulation and extracellular chemisorption. Importantly, during Cd²⁺ removal by MICP, the phenomenon that crystalline nanoparticles adhere to the cell surface, but without any micrometer-sized precipitation encapsulated bacterial cells was observed. This indicated that the previously studied model of bacterial cells as nucleation sites for metal cation precipitation and crystal growth is oversimplified. Our findings provided valuable insights into the mechanism of heavy metals removal by MICP, and a more straightforward method for studying biomineralization-related dynamic process.

Removal of atmospheric CO2 by engineered soils in infrastructure projects

The use of crushed basic igneous rock and crushed concrete for enhanced rock weathering and to facilitate pedogenic carbonate precipitation provides a promising method of carbon sequestration. However, many of the controls on precipitation and subsequent effects on soil properties remain poorly understood. In this study, engineered soil plots, with different ratios of concrete or dolerite combined with sand, have been used to investigate relationships between sequestered inorganic carbon and geotechnical properties, over a two-year period. Cone penetration tests with porewater pressure measurements (CPTu) were conducted to determine changes in tip resistance and pore pressure. C and O isotope analysis was carried out to confirm the pedogenic origin of carbonate minerals. TIC analysis shows greater precipitation of pedogenic carbonate in plots containing concrete than those with dolerite, with the highest sequestration values of plots containing each material being equivalent to 33.7 t C ha^-1 yr^-1 and 17.5 t C ha^-1 yr^-1, respectively, calculated from extrapolation of results derived from the TIC analysis. TIC content showed reduction or remained unchanged for the top 0.1 m of soil; at a depth of 0.2 m however, for dolerite plots, a pattern of seasonal accumulation and loss of TIC emerged. CPTu tip resistance measurements showed that the presence of carbonates had no observable effect on penetration resistance, and in the case of porewater pressure measurements, carbonate precipitation does not change the permeability of the substrate, and so does not affect drainage. The results of this study indicate that both the addition of dolerite and concrete serve to enhance CO₂ removal in soils, that soil temperature appears to be a control on TIC precipitation, and that mineral carbonation in constructed soils does not lead to reduced drainage or an increased risk of flooding.

Efficient imidazolium ionic liquid as a tri-functional robust catalyst for chemical fixation of CO2 into cyclic carbonates

The recent increase in CO₂ levels has had an extensive impact on the environment; hence an effective catalyst for chemical CO₂ fixation into value-added products is demanded. This work demonstrates a simple approach towards the chemical fixation of CO₂ to cyclic carbonates without solvent, metal and additives using one-pot synthesized tri-functional-imidazolium bromide ionic liquid. Herein, synthesized tri-functional-imidazolium-based ionic liquids, namely 3-(2-hydroxyethyl)-1-vinyl-1H-imidazole-3-ium bromide ([VIMEtOH][Br] (24 and 72 h)), 3-(2-hydroxyethyl)-1-vinyl-1H-imidazole-3-ium hydroxyl ([VIMEtOH][OH]) and poly 3-(2-hydroxyethyl)-1-vinyl-1H-imidazole-3-ium bromide (poly [VIMEtOH][Br]), were used for the comprehensive investigation of chemical fixation of CO₂ into cyclic carbonates and their physiochemical properties. In case of [VIMEtOH][Br] ionic liquid, it displayed time-dependent synthesis dissolution in the reaction system. This study found that [VIMEtOH][Br]-72 ionic liquid is not dissolved in the reaction system. The effect on the catalytic efficiency of the presence of functional groups in ionic liquids such as N-vinyl (-CC-N), acidic proton of imidazolium (-C (2)-H) and hydroxyl (-OH) along with bromide anion and the reaction conditions are systematically investigated. For CO₂ fixation, 99.6% conversion of propylene oxide with an excellent selectivity of propylene carbonate (≥99%) over [VIMEtOH][Br]-72 catalyst (at 120 °C, 2 MPa, 2 h) was observed without co-catalyst, metal and solvent. Also, it demonstrated an excellent wide substrates scope of epoxide and all reactions were performed on gram-scalable, which are potential prospects for industrial use.

Kinetics and mechanisms of cyanobacterially induced precipitation of magnesium silicate

The biomineralization of CO₂ , in the form of carbonate minerals, is considered as one of the efficient solutions of atmospheric CO₂ removal, allowing stable and sustainable storage of this greenhouse gas. Cyanobacteria are among the most powerful microorganisms capable of precipitating carbonate minerals, both in the present and in the past. In the modern environments, high Si concentration during geoengineering biomineralization could occur due to dissolution of Mg-bearing primary silicates such as olivine. However, most of experimental studies aimed to understand the formation of these carbonates were performed in Si-poor solutions. Thus, experimental characterizations of the nature, rate, and stoichiometry of precipitated minerals in Si-rich solutions in the presence of bacteria are lacking. The present study attempted to reproduce, in controlled laboratory experiments, the processes of biomineralization in a carbonate- and Mg-bearing medium having high Si concentrations (2-4 mM, which is below the saturation with respect to amorphous silica). These experiments have been carried out in the presence of three contrasting cyanobacteria: Synechococcus sp., Chroococcidiopsis sp. and Aphanothece clathrata in order to characterize the rate of formation, stoichiometry and mineralogical nature of precipitates. The results demonstrated significant role of cyanobacteria in the precipitation of carbonate and silicate minerals by increasing the pH of the medium during photosynthesis. Magnesium precipitation rates measured between 50 and 150 h of reaction time ranged from 0.05 to 0.5 mmol h^-1 g_dry¹ and decreased (Synechococcus sp. and Chroococcidiopsis sp.) or increased (A. clathrata) with an increase in the Si:Mg ratio in solution. The abiotic instantaneous rates of Mg and Si removal from alkaline solutions were similar to those in the presence of cyanobacteria at the same pH value suggesting that photosynthetically induced pH rise was the main factor of mineral formation. The transmission electron microscopy (TEM) and spectroscopic observations and associated analyses identified an amorphous magnesium silicate together with hydrous Mg carbonates (hydromagnesite). The formation of carbonate solid phase at high Mg: Si ratios indicated the potential for the removal of inorganic carbon at pH > 10. The difference in the degree of C removal between different species was primarily linked to different degree of pH rise during photosynthesis. Taken together, the results obtained in this study allowed an efficient reproduction of combined magnesium hydroxo-carbonates and hydrous silicates precipitation under cyanobacterial activity, suitable for geoengineering of biologically controlled CO₂ sequestration in Si-Mg-carbonate-bearing solutions.

Controlling Gas Generation of Li-Ion Battery through Divinyl Sulfone Electrolyte Additive

The focus of mainstream lithium-ion battery (LIB) research is on increasing the battery’s capacity and performance; however, more effort should be invested in LIB safety for widespread use. One aspect of major concern for LIB cells is the gas generation phenomenon. Following conventional battery engineering practices with electrolyte additives, we examined the potential usage of electrolyte additives to address this specific issue and found a feasible candidate in divinyl sulfone (DVSF). We manufactured four identical battery cells and employed an electrolyte mixture with four different DVSF concentrations (0%, 0.5%, 1.0%, and 2.0%). By measuring the generated gas volume from each battery cell, we demonstrated the potential of DVSF additives as an effective approach for reducing the gas generation in LIB cells. We found that a DVSF concentration of only 1% was necessary to reduce the gas generation by approximately 50% while simultaneously experiencing a negligible impact on the cycle life. To better understand this effect on a molecular level, we examined possible electrochemical reactions through ab initio molecular dynamics (AIMD) based on the density functional theory (DFT). From the electrolyte mixture’s exposure to either an electrochemically reductive or an oxidative environment, we determined the reaction pathways for the generation of CO₂ gas and the mechanism by which DVSF additives effectively blocked the gas’s generation. The key reaction was merging DVSF with cyclic carbonates, such as FEC. Therefore, we concluded that DVSF additives could offer a relatively simplistic and effective approach for controlling the gas generation in lithium-ion batteries.

Impact of carbonation on leaching of constituents from a cementitious waste form for treatment of low activity waste at the DOE Hanford site

Carbonation can be a major aging process during disposal of alkaline cementitious waste forms and can impact constituent leaching by changes in material alkalinity, pore structure, and controlling mineral phases. The effect of carbonation on the leaching of major and trace constituents from Cast Stone, a cementitious waste form developed to treat high salt content low activity waste, was studied through a combination of leaching experiments and reactive transport simulations. Diffusive transport of constituents in the waste form was evaluated using reactive transport modeling of diffusion-controlled leaching test results and a geochemical speciation model derived from pH-dependent leaching. Comparisons between Cast Stone materials aged under nitrogen, air, and 2% carbon dioxide in nitrogen showed that carbonation impacts solubility, physical retention and observed diffusivity of major and trace constituents. Carbonation under 2% CO₂ decreased the diffusion-controlled leaching of chromium by two orders of magnitude. Modeling results suggest that carbonation may also decrease solubility of technetium while changes to microstructure by carbonation increases effective diffusivity of constituents in Cast Stone.

Numerical Simulation of S-Shaped Current–Voltage Curves Induced by Electron Traps in Inverted Organic Photovoltaics

Organic photovoltaics (OPVs) differ from their inorganic counterparts because of inevitable electronic disorders and structural heterogeneity. Charge carrier traps are inevitable in organic semiconductors. A common failure mechanism of OPVs is the development of an S-shaped current density–voltage characteristic (J-V curve). Herein, we focus on investigating the underlying physical mechanism of S-shaped deformation of J-V curve of the inverted organic photovoltaic devices with bulk-heterojunction, proven by experiments with the n-doped electron extraction layer and numerical simulations assuming electron traps (0.1 eV deeper) in the electron extraction layer. The numerical simulations are quite consistent with the experimental results. In addition, the open circuit voltage induced by S-kink is exemplified to be enhanced after removing the electron traps in the interlayer by introducing a dopant of cesium carbonate.

Rapid formation of mature microbialites in Lake Alchichica, Mexico

Microbialites are emblematic sedimentary rocks formed by phylogenetically and metabolically complex microbial communities thriving under specific physicochemical conditions. Most microbialites are photosynthesis-based ecosystems frequently formed by carbonates, thereby capturing inorganic carbon in the form of both, organic matter and mineral precipitates. However, little is known about the amount of sequestered carbon and the kinetics of the process, that is, microbialite growth rate. To assess microbialite growth rate and the influence of substrates on carbonate formation in Alchichica, an alkaline crater lake harbouring well-developed carbonate microbialites, we incubated in situ sterilized Nylon mesh, hydromagnesite and aragonite crystals, and bleached-coral aragonite for 2 years. We observed the rapid formation of nascent hydromagnesite and aragonite-containing microbialites on Nylon mesh, with an average growth rate of ~0.6 (and up to 1) mm year^-1 . By contrast, only thin (< 0.2 mm) biofilms developed on exposed hydromagnesite and aragonite crystals and bleached-coral aragonite, suggesting decoupled microbial colonization and biomineralization and/or potential interference of those mineral surfaces with new carbonate nucleation. Microbial communities associated with 2-year-old microbialites and biofilms were fully comparable to mature communities populating Lake Alchichica indigenous microbialites.