Inorganic CaCO3 Research Articles

In-situ stabilized lipase in calcium carbonate microparticles for activation in solvent-free transesterification for biodiesel production

Biodiesel serves as a crucial biofuel alternative to petroleum-based diesel fuels, achieved through enzymatic transesterification of oil substrates. This study aims to investigate stabilized lipase (LP) within calcium carbonate (CaCO3) microparticles as a catalyst for solvent-free transesterification in biodiesel synthesis. The specific hydrolysis activity of the in-situ immobilized LP was 66% of that of free LP. However, the specific transesterification activity of immobilized LP in the solvent-free phase for biodiesel production was 2.29 times higher than that of free LP. These results suggest that the interfacial activation of LP molecules is facilitated by the inorganic CaCO3 environment. The immobilized LP demonstrated higher biodiesel production levels with superior stability compared to free LP, particularly regarding methanol molar ratio and temperature. To the best of our knowledge, there are no previous reports on the in-situ immobilization of LP in a CaCO3 carrier without any crosslinker as an interfacial-activated biocatalyst for biodiesel production.

Study and characterization of paper bookbindings from 16 to 18th stored in the Marciana National Library (Venice)

Paper bookbindings have been disregarded for centuries by scholars since they were only considered temporary covering materials for manuscripts and books. Recently, there is a willingness to reconsider these bindings and to evaluate their role. Thanks to the collaboration with the Marciana National Library in Venice, which stores an impressive collection of 849 detached bindings, the current research provides a chemical-physical elucidation about the composition and the manufacture of paper bookbindings realized between the 16th and the eighteenth century in the Venetian area. A selection of bookbindings was analysed by the means of complementary methods (thickness measurements, Attenuated Total Reflection—Fourier-Transform Infrared Spectroscopy (ATR-FTIR), Pyrolysis–Gas Chromatography–Mass Spectrometry (Py-GC–MS) and X-Ray Fluorescence (XRF)). Data evidence the presence of cellulose as the main component of paper pulp; hemicellulose and lignin were identified too, probably related to the presence of linen/hemp rags in the paper production. Gelatine was detected muck likely related to paper sizing; among inorganic additives CaCO3 was found in all samples. The presence of waxy material may be due to past undocumented conservation treatments.

A study of biodegradation, water uptake and thickness swelling of animal fibers reinforced unsaturated polyester resin composites

The ever-increasing quantities of trash produced by the poultry and tannery industries, particularly chicken feathers, cow hairs, and waste leather fibers, pose serious challenges to maintaining a pristine natural environment. In this research, the polymer composites were produced by combining 2, 5, 7, 10, 12, and 15 % (by weight) recycled chicken feather fibers (CFF), cow hair fibers (CHF), and leather fibers (LF) with inorganic materials ZnO, Al2O3, CaCO3, and unsaturated polyester resin (UPR) through a hand lay-up process. After cleaning, a portion of the fibers was subjected to a two-hour soak in 0.20 M KOH at 50 °C, followed by five hours of drying at 60 °C, and the remaining half was not attended. This study successfully reduced environmentally hazardous waste from the poultry and tannery industries. The biodegradation of composites was compared in weather, water, brine, soil and compost over a period of 90 days at 25 °C, suggesting that the composites have potential in a variety of settings. Degradation rates varied among the composites, and the leather fibre-UPR composites (LR + UPR + Al2O3) showed the fastest degradation rate under all media and were especially degraded highest percentages (17.8 %) when buried in compost. Degradation percentages in compost media for (CHF + UPR + Al2O3), (CFF + UPR + Al2O3) and (CHF + CFF + UPR + Al2O3)) composites are 16.3 %, 14.8 %, and 13.5, respectively. The helical structure of the composites disintegrated in thermogravimetric analysis (TGA), losing its chain-linkage skeleton and peptide fiber bridges, and dissolving keratin and collagen into carbon dioxide (CO2), hydrogen sulfide (H2S), and hydrogen cyanide (HCN). The results of the water uptake and thickness swelling study for up to 15 days due to water absorption can have positive effects on the mechanical properties of the composite material and found 8.8 % water uptake and 15.8 % thickness swelling both for (LR + UPR + Al2O3) composite.

Experimental study and hybrid optimization of material extrusion process parameters for enhancement of fracture resistance of biodegradable nanocomposites

Among the additive manufacturing processes, the material extrusion (ME) is the most popular and affordable technique in production of a wide range of products, from prototypes to the final products, for different industrial sectors. The most popular raw material in this process is the biodegradable polylactic acid (PLA) polymer that offers ease of production in relatively low price and wide applications in synthesis of medical proteases. However, the mechanical strength of fabricated samples and their resistance against the fracture loadings, which are critical for components synthesized for medical applications, are strongly dependent on the ME process parameters and the composition of the base material. Therefore, this study is aimed to address both the strengthening mechanisms of inorganic CaCO3 nanoadditives in the PLA matrix and the influence of ME process parameters on the fracture resistance of fabricated samples. To this aim, the PLA/CaCO3 nanocomposite filaments have been produced by mix-blending/extrusion technique and were employed to fabricate tensile and fracture test samples in ME process under different sets of parameters, including printing speed, layer thickness, filling ratio and printing pattern, determined by Taguchi L27 orthogonal array. The fracture experiments were conducted on a uniaxial tensile test machine using a specially designed fixture that makes the application of mixed-mode loading on fracture samples possible. The results of fracture toughness of specimens were employed as input data to model the response of fabricated samples and to determine the ME parameter levels and nanoparticle concentrations for maximum fracture resistance of fabricated samples based on a hybrid algorithm of artificial neural network and ant colony optimization (ANN/ACO). Differential scanning calorimetry was used to characterize the thermal features (i.e. glass transition, crystallization and melting temperatures) as well as the degree of crystallization of ME samples. Scanning electron microscopy of fracture surfaces were employed to study the influence of ME parameters and CaCO3 nanoadditives on the characteristics of fracture of 3D printed specimens under various modes of loading. Overall, the results showed that the effects of ME parameters on the fracture behavior of 3D printed samples are highly interconnected and, in the case of a semicrystalline polymer, are highly dependent on the physical characteristics of the fabrication process, including the heat transfer and crystallization rate of the matrix.

Enhanced thermal conductivity and photothermal effect of microencapsulated n-octadecane phase change material with calcium carbonate-polydopamine hierarchical shell for solar energy storage

The development of microencapsulated phase change materials with excellent photothermal conversion and storage performances is significant for solar energy utilization. Herein, a kind of the novel n-octadecane microcapsules with calcium carbonate-polydopamine (CaCO3-PDA) hierarchical shell was fabricated through a simple one-pot synthetic strategy. The n-octadecane droplets were firstly encapsulated into inorganic CaCO3 shell in the SDBS-templating emulsion, and subsequently the formed n-octadecane microcapsules were further modified by adhesive PDA. The resultant composite microcapsules displayed a regular and compact spherical morphology with a well-defined core-shell microstructure, and the light-absorption PDA coating uniformly deposited onto the CaCO3 shell surface. The phase change microcapsules possessed a satisfactory latent heat storage capability of more than 140 J g−1 and a favorable energy storage efficiency of about 60%. Owing to the existence of CaCO3 shell, the as-prepared n-octadecane microcapsules achieved a remarkable enhancement in the thermal conductivity compared to pristine n-octadecane. With the surface modification of PDA, the composite microcapsules demonstrated not only superior thermal stability and phase change reliability but also improved photothermal effect. Moreover, the microcapsules exhibited stable photothermal conversion and storage performances under the cycling sunlight irradiation. Therefore, the developed composite n-octadecane microcapsules in this work present a promising prospect in the field of solar-to-thermal energy utilization and storage.

Construction of a multi-scale microporous structure in EVA matrix toward passive cooling roofs

Global warming has brought tremendous attention to developing passive cooling materials. Due to the high performance of solar reflection, heat insulation and infrared radiation, constructing porous structures in polymeric matrix has emerged as a promising technique to fabricate passive cooling materials. This work herein demonstrated a multi-scale microporous structure in ethylene-vinyl acetate copolymer (EVA) matrix via chemical foaming and chemical etching. It was found that pore size and shape depended upon the addition and removal of inorganic particles CaCO3. In chemical foaming system, by reflecting 76.9% NIR light and transmitting heat through the atmosphere in the long-wave infrared, the cellular EVA/CaCO3 composites (40% porosity, 13.84 μm avg. pore size)-covered device exhibited a final temperature of 31.6 °C after solar simulation for 1 h with the intensity of ∼594 W/m2. To further enhance the cooling effect, the CaCO3 particles in cellular EVA/CaCO3 composites were removed via 20% HCl solution etching to minimize the pore structure. Higher heat insulation with thermal conductivity of 0.148 Wm−1K−1 accompanied by 65.5% NIR irradiance and 0.84 thermal emittance made the excellent cooling property with a final temperature of 30.6 °C (lower than all EVA/CaCO3 composites-covered device) realize after chemical etching. Furthermore, the prepared porous EVA materials possessed good tensile properties and are of potential value in the field of passively cooled roofs.

A hybrid ANN/PSO optimization of material composition and process parameters for enhancement of mechanical characteristics of 3D-printed sample

PurposeThis paper aims to study the effects of inorganic CaCO3 nanoadditives in the polylactic acid (PLA) matrix and fused filament fabrication (FFF) process parameters on the mechanical characteristics of 3D-printed components.Design/methodology/approachThe PLA filaments containing different levels of CaCO3 nanoparticles have been produced by mix-blending/extrusion process and were used to fabricate tensile and three-point bending test samples in FFF process under various sets of printing speed (PS), layer thickness (LT), filling ratio (FR) and printing pattern (PP) under a Taguchi L27 orthogonal array design. The quantified values of mechanical characteristics of 3D-printed samples in the uniaxial and the three-point bending experiments were modeled and optimized using a hybrid neural network/particle swarm optimization algorithm. The results of this hybrid scheme were used to specify the FFF process parameters and the concentration of nanoadditive in the matrix that result in the maximum mechanical properties of fabricated samples, individually and also in an accumulative response scheme. Diffraction scanning calorimetry (DSC) tests were conducted on a number of samples and the results were used to interpret the variations observed in the response variables of fabricated components against the FFF parameters and concentration of CaCO3 nanoadditives.FindingsThe results of optimization in an accumulative scheme showed that the samples of linear PP, fabricated at high PS, low LT and at 100% FR, while containing 0.64% of CaCO3 nanoadditives in the matrix, would possess the highest mechanical characteristics of 3D-printed PLA components.Originality/valueFFF is a widely accepted additive manufacturing technique in production of different samples, from prototypes to the final products, in various sectors of industry. The incorporation of chopped fibers and nanoparticles has been introduced recently in a few articles to improve the mechanical characteristics of produced components in FFF technique. However, the effectiveness of such practice is strongly dependent on the extrusion parameters and composition of polymer matrix.

A new strategy for simultaneous photoluminescence and thermal energy storage/release: Microencapsulated phase change materials via nano-Y2O3 modified PW@CaCO3

A multifunctional microencapsulated phase change material (PW@CaCO3/Y2O3) with both photoluminescence and thermal energy storage/release properties has been prepared by in situ polymerization. The material is based on the phase change material paraffin wax (PW) as its core, and the highly thermally conductive inorganic material CaCO3 is selected as the shell material to which a nano-Y2O3 material is attached. Five samples with different amounts of nano-Y2O3 incorporated in the shell are prepared. The microscopic morphology, chemical composition, crystal structure, thermal energy storage properties, thermal conductivity, thermal stability, as well as fluorescence spectra and intensities of the samples are experimentally measured and compared. The luminescence properties of nano-Y2O3 and the light enhancement phenomenon of microencapsulated phase change materials are also analyzed. The thermal properties are investigated, and it is found that the PC-Y3 sample (i.e., the mass ratio of PW:CaCO3:nano-Y2O3 is 100:100:3.0) exhibits the best thermal performance among the five samples with a melting enthalpy of (87.5 ± 2.5) J/g, an encapsulation efficiency of (61.9 ± 1.2)%, a thermal energy storage efficiency of (62.1 ± 1.5)%, an average specific heat capacity of (1.38 ± 0.21) kJ/(kg K) in solid phase (10–20 °C) and (1.46 ± 0.02) kJ/(kg K) in liquid phase (70–80 °C), and a thermal conductivity of (1.55 ± 0.01) W/(m K) in solid phase that is six times that of the solid PW. A study of the optical properties revealed that the microcapsules emitted blue light at an excitation wavelength of 290.0 ± 2.2 nm. The fluorescence intensity appeared to be enhanced with the addition of nano-Y2O3. This microencapsulated phase change material has potential applications in areas where synchronization of fluorescence and thermal modulation is required; for example, some specific fluorescent sensors that are very sensitive to heat should operate at a fixed low temperature.

Biological calcium carbonate enhanced the ability of biochar to passivate antimony and lead in soil.

The mechanism of immobilization of heavy metals in the soil using biochar has been studied extensively. However, the decomposition of biochar by biological and abiotic factors can reactivate the immobilized heavy metals in soil. Previous research showed that the addition of biological calcium carbonate (bio-CaCO3) can significantly increase the stability of biochar. However, the influence of bio-CaCO3 on the ability of biochar to immobilize heavy metals remains unclear. Therefore, this study evaluated the effect of bio-CaCO3 on the use of biochar to immobilize the cationic heavy metal lead and the anionic heavy metal antimony. The addition of bio-CaCO3 not only significantly improved the passivation ability of Pb and Sb but also reduced their migration in the soil. Mechanistic studies have shown that the reasons for the enhanced ability of biochar to immobilize heavy metals can be summarized in three aspects. First, the introduced inorganic component CaCO3 can precipitate and exchange ions with lead and antimony. Second, the N element in the organic component of bio-CaCO3 underwent polycondensation with the organic carbon in biochar to form pyridine N and pyrrole N structures, which can form a strong complex with lead and antimony. Pyridine N complexes more strongly than pyrrole N. Third, bio-CaCO3 increased the degree of aromatization and the surface π-electron density of biochar, which enhanced the ability of biochar to adsorb heavy metals. This study will provide a new concept for the application of biochar as an amendment to remediate heavy metals in the soil.

Improvement in the thermal conductivity and stability of rare-earth metal oxide nanofluids using the stabilizing action of nano CaCO3 in comparison with the stabilizing action of sodium dodecyl sulphate

The stabilizing action of inorganic CaCO3 nanoparticles to increase the thermal conductivity of nanofluids containing nanoparticles of yttrium oxide (Y2O3), zirconium oxide (ZrO2), and yttria-stabilized zirconia (YSZ) prepared from their respective micron size metal oxide precursor through gel combustion method is reported in this work. The nanoparticles obtained through the gel-combustion method after calcination yield nano-size rare earth metal oxide particles. The morphology and composition of the constituents’ nanoparticles thus prepared were explored through XRD, FESEM with EDX, and elemental mapping analysis to confirm the purity and the particle sizes. Thermal conductivities of the nanofluids prepared using the above-mentioned nanoparticles were found to be superior to that of the base fluid, but their stabilities were lesser. Commercially available stabilizers like sodium dodecyl sulphate (SDS) were used to improve the stability but their addition reduces the thermal conductivity of the nanofluids. The nano-CaCO3 particle as a stabilizer provides better stability than SDS was reported. The stability of all the nanofluids was evaluated through the results obtained from zeta potential measurements and the mixture with the highest stability was evaluated. Based on the visual inspection and through UV–vis spectral measurements, the settling ability of the nanoparticles present in the nanofluid was also evaluated. Remarkably, Y2O3 + CaCO3 suspended nanofluid exhibits a commendable thermal conductivity of 29.18 % higher than the base fluid. Such fluids possessing higher stability with good thermal conductivity can be effectively utilized in heat exchanger applications.

Can element chemical impurities in aragonitic shells of marine bivalves serve as proxies for environmental variability?

In many biogenic and geogenic materials, ion impurities can provide serviceable proxies for environmental conditions. However, the element/Ca ratios of bivalve shells are notoriously challenging to interpret. Due to strong vital effects, nonclassical nucleation and growth mechanisms, and/or kinetic processes, the concentration of trace and minor elements in marine shells typically remains below values observed in inorganic CaCO3 precipitated from a solution resembling seawater chemistry but above those expected for thermodynamic equilibrium. The interpretation is further complicated by non-lattice bound and microstructure-specific element content. If environmental conditions were still encoded in the shells, they should result in statistically significantly reproducible element/Ca chronologies between contemporaneous specimens from the same site. Here, we tested this hypothesis and exemplarily studied seven elements in twelve modern specimens of Arctica islandica collected from four different localities in the North Atlantic (Faroe Islands, NE Iceland, Isle of Man, Gulf of Maine). Age-detrended chronologies of weighted annual B, Mg, Sr and Ba/Ca ratios (Al, Zn and Pb largely remained below detection limit) measured in the shells were reproducible between most specimens from the same site, supporting the hypothesis that the incorporation of these elements was at least partly controlled by environmental forcings. Notably, the agreement (explored with linear regression analyses and sign tests) between shell element/Ca ratios and environmental quantities was weaker than the agreement of respective element/Ca ratios between specimens suggesting that the available information on temperature, food and water chemistry did not properly reflect the in-situ conditions to which the bivalves were exposed or other extrinsic factors were at work. As in inorganic aragonite – but in contrast to thermodynamic expectations –, annual Sr/Ca, Mg/Ca and B/Ca ratios were negatively correlated to water temperature (up to 40% explained variability). The link between Ba/Ca and bulk phytoplankton often remained below the significance threshold, but was otherwise positive. Quantitative environmental reconstructions based on ion impurities in bivalve shells will remain challenging or impossible unless the chemistry of the parent solution (= extrapallial fluid) from which the shell actually formed is known, including temporal changes thereof. This information is crucial to compute representative partition coefficients required to calibrate transfer functions.

Heat-Resistant, Robust, and Hydrophilic Separators Based on Regenerated Cellulose for Advanced Supercapacitors.

Separators in supercapacitors (SCs) typically suffer from defects of low mechanical property, limited ion transport, and electrolyte wettability, and poor thermal stability, impeding the development of SCs. Herein, high-performance regenerated cellulose (RC) based separators are designed that are fabricated by effective hydrolytic etching of inorganic CaCO3 nanoparticles from a filled RC membrane. The as-prepared RC separator displays excellent comprehensive performances such as higher tensile strength (75.83MPa) and thermal stability (200°C), which is superior to commercial polypropylene-based separator (Celgard 2500) and sufficient to maintain their structural integrity even at temperatures in excess of 200°C. Benefiting from its hydrophilicity, high porosity, and outstanding electrolyte uptake rate (208.5%), the RC separator exhibits rapid transport and permeability of ions, which is 2.5× higher than that of the commercial nonwoven polypropylene separator (NKK -MPF30AC-100) validated by electrochemical tests in the 1.0m Na2 SO4 electrolyte. Results show that porous RC separator with unique advantages of superior electrolyte wettability, mechanical robustness, and high thermal stability, is a promising separator for SCs with high-performance and safety.

Microbial ecosystem responses to alkalinity enhancement in the North Atlantic Subtropical Gyre

In addition to reducing carbon dioxide (CO2) emissions, actively removing CO2 from the atmosphere is widely considered necessary to keep global warming well below 2°C. Ocean Alkalinity Enhancement (OAE) describes a suite of such CO2 removal processes that all involve enhancing the buffering capacity of seawater. In theory, OAE both stores carbon and offsets ocean acidification. In practice, the response of the marine biogeochemical system to OAE must be demonstrably negligible, or at least manageable, before it can be deployed at scale. We tested the OAE response of two natural seawater mixed layer microbial communities in the North Atlantic Subtropical Gyre, one at the Western gyre boundary, and one in the middle of the gyre. We conducted 4-day microcosm incubation experiments at sea, spiked with three increasing amounts of alkaline sodium salts and a 13C-bicarbonate tracer at constant pCO2. We then measured a suite of dissolved and particulate parameters to constrain the chemical and biological response to these additions. Microbial communities demonstrated occasionally measurable, but mostly negligible, responses to alkalinity enhancement. Neither site showed a significant increase in biologically produced CaCO3, even at extreme alkalinity loadings of +2,000 μmol kg−1. At the gyre boundary, alkalinity enhancement did not significantly impact net primary production rates. In contrast, net primary production in the central gyre decreased by ~30% in response to alkalinity enhancement. The central gyre incubations demonstrated a shift toward smaller particle size classes, suggesting that OAE may impact community composition and/or aggregation/disaggregation processes. In terms of chemical effects, we identify equilibration of seawater pCO2, inorganic CaCO3 precipitation, and immediate effects during mixing of alkaline solutions with seawater, as important considerations for developing experimental OAE methodologies, and for practical OAE deployment. These initial results underscore the importance of performing more studies of OAE in diverse marine environments, and the need to investigate the coupling between OAE, inorganic processes, and microbial community composition.

A study on the effects of internal architecture on the mechanical properties and mixed-mode fracture behavior of 3D printed CaCO3/ABS nanocomposite samples

PurposeThe purpose of this study was to investigate the effects of CaCO3 nanoparticles on the mechanical properties, and mixed-mode fracture behavior of acrylonitrile butadiene styrene 3D printed samples with different internal architectures.Design/methodology/approachThe nanocomposite filaments have been fabricated by a melt-blending technique. The standard tensile, compact tension and special fracture test samples, named Arcan specimens, have been printed at constant extrusion parameters and at four different internal patterns. A special fixture was used to carry out the mixed-mode fracture tests of Arcan samples. Finite element analyses using the J-integral method were performed to calculate the fracture toughness of such samples. The fractographic observations were used to evaluate the mechanism of fracture at different concentrations of nanoparticles.FindingsThe addition of CaCO3 nanoparticles has resulted in a significant increase in the fracture loading of the samples, although this increase was not consistent for all the filling patterns, being more significant for samples with linear and triangular structures. According to the fractographic observations, the creation of uniformly distributed microvoids due to the blunting effect of nanoparticles and 3D stress state at the crack tip in the samples with linear and triangular structures justify the enhancement in the fracture loading by the addition of CaCO3 nanoparticles in the matrix.Originality/valueThere is a significant gap in the knowledge of the effects of different nanoparticles in the polymer samples produced by the fused filament fabrication process. One of such nanoparticles is an inorganic CaCO3 nanoparticle that has been frequently used as nanofillers to improve the thermomechanical properties of thermoplastic polymers. Here, experimental and numerical studies have been conducted to investigate the effects of such nanoadditives on the mechanical and fracture behavior of 3D printed samples.

Impacts of temperature on hydrophilicity/functionalities of char and evolution of bio-oil/gas in pyrolysis of pig manure

Pig manure is a carbonaceous waste and has a distinct composition with biomass and the pyrolysis products properties could also be different. In this study, particular attention was paid on the evolution of functionalities and the changes of hydrophobicity/hydrophilicity of char with an increase in temperature, as these surface properties determine the applications of char as support of catalyst or adsorbent. Our results demonstrated that both oxygen and nitrogen-containing organic species in manure were thermally unstable, decomposition of which initiated from 200 °C and proceeded to near completion at 600 °C. The substantial deoxygenation at 300–500 °C did not result in the proportional increase of carbon content of char, as the carbonization did not take place effectively. Instead, the excessive cracking of these organic species made the inorganic SiO2 and CaCO3 as the dominant species in the char formed at high temperatures. The abundant oxygen-containing functionalities in the char produced via pyrolysis below 300 °C could not be sufficiently exposed, leading to the high hydrophobicity of char. In comparison, the exposure of the inorganic species in the char produced at high pyrolysis temperature made char more hydrophilic, which, however, was not favorable for the dispersion of metallic nickel species in the Ni/char catalyst.

Anti-fouling performance investigation of micron-submicron hierarchical structure PVDF membranes in water-in-oil emulsion separation

Membrane technology was widely used in the field of oil-water separation. In the process of water-in-oil emulsion treatment, surface contamination of hydrophobic and lipophilic membranes was a difficult problem. Therefore, the effect of hydrophobic membrane surface micro-rough structure on oil-water separation performance and its anti-fouling behavior has been investigated as a major focus of current research. Superhydrophobic-superoleophilic polyvinylidene fluoride (PVDF) membranes with micron-submicron hierarchical structure were prepared by combining thermally induced phase separation (TIPS) with rolling embossing. The influence of the roller temperature on the structure and performance of the membrane were discussed. The best achieved superhydrophobicity with a high water contact angle (WCA) of 154.8° and rolling angle (SA) of 1.9°, which was similar with lotus-effect. Meanwhile, the N2 flux was 197 L m−2 s−1 and LEP was 4.08 bar. Besides, the tensile strength of PVDF membrane was 1.89 MPa. The embossed membrane showed good lipophilicity, and the residence time of kerosene on the membrane surface was only 0.14 s. PVDF membranes with lotus leaf effect showed excellent demulsification performance and high recyclability in water in oil emulsion. The oil flux and rejection rate were 1258 L m−2 h−1 and 99.14%, respectively. In the separation experiment of PVDF membranes in diesel emulsion containing inorganic pollutant CaCO3, the results showed that the anti-fouling effect of PVDF membranes by cross-flow filtration method was obviously better than that by dead-end filtration method. When the operating temperature and pressure were 0.1 MPa and 45 °C, respectively, embossed membrane showed relatively excellent separation performance in cross-flow filtration. This study provided some guidance for the anti-fouling performance of roughened surface superhydrophobic-superoelophilicity membrane in oil-water separation experiment.

Authigenic calcium carbonate precipitation in the “bathtub ring” around the anoxic Alum Shale Basin during the Furongian SPICE event (Baltic Basin, northern Poland)

ABSTRACT The precipitation of both biotic and abiotic calcium carbonate is of great importance in modern and ancient global biogeochemical cycles. In the present-day oceans, the widespread precipitation of inorganic CaCO3 on the seafloor or in the water column is possible only under extraordinary circumstances. By contrast, in the geological record, authigenic seafloor carbonate cements were widespread in the supersaturated, anoxic oceans of the Precambrian. Widespread authigenic carbonate precipitation ceased by the end of the Neoproterozoic as a consequence of global oceanic oxygenation: in the Phanerozoic, it occurred only during major anoxic events (for example, at the Permian/Triassic boundary) or in restricted, stagnant basins. Here, we present an anomalous record of CaCO3 precipitation from the Cambrian Alum Shale Basin of the Baltica palaeocontinent with Precambrian-like authigenic, seafloor encrusting, crystalline carbonates. The depositional environment of this well-recognized, cool-water, stagnant anoxic basin favoured local carbonate precipitation via the surplus generation of alkalinity in anoxic bottom waters. However, the correlation of the acme of authigenic carbonate formation with the onset and peak of the Steptoean Positive Carbon Isotope Excursion (SPICE) suggests a driver−trigger relation between the two phenomena. On a smaller scale, carbonate authigenic precipitation is manifested by a cement-supported texture of the limestone intercalations in the Alum Shale facies. Instantaneous calcification of the faunal remains, termed here the Snedronningen phenomenon, must have been of great importance in the formation of Orsten-type Konservat Lagerstätten.

Sodium incorporation into inorganic CaCO3 and implications for biogenic carbonates

The sodium content of biogenic carbonates shows potential as a palaeoceanographic proxy for salinity and/or calcium concentration but the incorporation of Na+ into inorganic and biogenic calcite is poorly understood. Taxonomic and conspecific variations in the sensitivity of carbonate Na/Ca to seawater Na+/Ca2+ and salinity point to a biological influence on Na+ partitioning and/or covariations with other environmental parameters. One major unknown of the biological control during calcification is the rate of mineral precipitation, which has a strong control on trace-element partitioning in inorganic carbonate systems. We conducted inorganic CaCO3 precipitation experiments where the effect of solution composition and crystal growth rate on Na+ uptake by carbonate crystals are independently assessed. Calcite crystals were precipitated at rates varying from 10−6.5 to 10−4.5 mol/m2/s, while faster growth rate than 10−4.5 mol/m2/s resulted in the coprecipitation of aragonite and vaterite. For a given crystal growth rate, calcite Na/Ca increases by 0.22% per % increase in solution (Na+)2/Ca2+ activity ratio. However, calcite Na/Ca increases up to fivefold per order of magnitude increase in crystal growth rate, suggesting crystal growth rate and precursor phases are likely dominant controls on marine carbonate Na/Ca. We use these results in the framework of the DePaolo (2011) model for trace element uptake by calcite to assess the origin of variable (Na/Ca)foraminifer sensitivities to [Ca2+]seawater and salinity. Last, maximum mineral growth rates are estimated for a range of marine carbonates based on known carbonate Na/Ca and the (Na+)2/Ca2+ activity ratio of seawater. Estimated rates vary from 10−5.6 (planktic foraminifers) to above 10−4 (sea urchins) mol/m2/s. Such high mineral growth rates imply high degrees of oversaturation with respect to calcite (10 to >100), supporting the idea that elemental partitioning and isotopic fractionation recorded in marine biogenic carbonates are controlled by kinetic rather than equilibrium exchanges.

Transition from horizontal expansion to vertical growth in the oyster prismatic layer

Biomimetic materials inspired by biominerals have substantial applications in various fields. The prismatic layer of bivalve molluscs has extraordinary flexibility compared to inorganic CaCO3. Previous studies showed that in the early stage, minerals expanded horizontally and formed prism domains as a Voronoi division, while the evolution of the mature prisms were thermodynamically driven, which was similar to grain growth. However, it was unclear how the two processes were correlated during shell formation. In this study, we used scanning electronic microscopy and laser confocal scanning microscopy to look into the microstructure of the columnar prismatic layer in the pearl oyster Pinctada fucata. The Dirichlet centers of the growing domains in mature prisms were calculated, and the corresponding Voronoi division was reconstructed. It was found that the domain pattern did not fit the Voronoi division, indicating the driving forces of the mature prisms evolution and the initiation stage were different. During the transition from horizontal expansion to vertical growth, the minerals broke through the inner periostracum and squeezed out the organic materials to the inter-prism space. Re-arrangement of the organic framework pattern was driven by elastic relaxation at the vertices, indicating the transition process was thermodynamically driven. Our study provided insights into shell growth in bivalves and pave the way to synthesize three-dimensional material biomimetically.

Characterisation and Traceability of Calcium Carbonate from the Seaweed Lithothamnium calcareum

Calcium carbonate (CaCO3) from the seaweed Lithothamnium calcareum is a suitable dietary supplement for the prevention of osteoporosis, due to its chemical composition. This study compared CaCO3 from L. calcareum to CaCO3 from oyster shell and inorganic minerals that are already used in the pharmaceutical industry. The Rietveld refinement of the XRD showed that the mineral fraction of L. calcareum is composed of aragonite (50.3 wt%), magnesian calcite (45.3 wt%), calcite (4.4 wt%), comin contrast to oyster shell and inorganic minerals, which contain only calcite. The morphology of L. calcareum carbonate particles is granular xenomorphic, which is distinct from the scalenohedral form of inorganic calcite and the fibrous and scale-like fragments of oyster shell. The crystal structures of aragonite and magnesian calcite, present in L. calcareum, have higher contents of oligoelements than the pure calcite in other materials. The isotopic composition (stable isotopes of carbon and oxygen) is heavy in the CaCO3 from L. calcareum (δ13C = 1.1‰; δ18O = −0.1‰) and oyster shell (δ13C = −4‰; δ18O = −2.8‰) in marked contrast to the much lighter isotopic composition of inorganic mineral CaCO3 (δ13C = −19.2‰; δ18O = −26.3‰). The differences indicated above were determined through principal component analysis, where the first and second principal components are sufficient for the clear distinction and traceability of CaCO3 sources.