Formation Of CaCO3 Crystals Research Articles

Ureolytic bacteria-assisted recycling of waste concrete fines

This study investigates the potential of microbially-induced calcite precipitation (MICP) in converting waste concrete fines (WCF), an underutilized byproduct generated during the crushing of old concrete, into construction material. WCF samples treated with Sporosarcina pasteurii DSM 33 for periods ranging from 14 to 90 days exhibited up to an 11% increase in CaCO3 content, compared to a control group treated with a saline solution. The formation of CaCO3 crystals also resulted in a 15% reduction in porosity and, most importantly, enhanced the integrity of the WCF conglomerates, reaching 20% of the stiffness of autoclaved aerated concrete. These results suggest that MICP could be used for the valorization of WCF, aligning with sustainability and circular economy goals.

Revisiting the carbonation of recycled concrete fine: A pH-cycle carbonation method

Recycled concrete fine (RCF) has been demonstrated as a promising CO2 absorbent owing to its high-calcium and high-alkali contents. For the high-efficiency utilization of bubbled CO2 for the carbonation of RCF, this paper revisits the carbonation process by proposing a pH-cycle carbonation method. The carbonation of RCF was suspended when the pH of RCF suspension dropped to 7, and the subsequent carbonation was started when the pH reached constant values. The effect of the pH-cycle carbonation method on the performance of RCF-added mortars was investigated by preparing mortars using RCF suspension with different carbonation cycles. Experimental results showed that RCF spontaneously dissolved and released Ca2+ to the suspension during the intervals of carbonation cycles, which could save some CO2 that should be spent on attacking RCF in continuous carbonation approaches. In this method, the CO2 sequestration potential of RCF is approaching depletion by the bubble of 7 min CO2. The carbonation of RCF enabled the formation of CaCO3 crystals and nano-silica, leading to accelerated hydration of cement and refined pore structure of RCF-added mortars. The 28d compressive strength of RCF-added mortars was increased by 10.27–12.57% when RCF was subjected to different carbonation cycles. The two cycles of carbonation for RCF could be the optimal one.

Insights in MICP dynamics in urease-positive Staphylococcus sp. H6 and Sporosarcina pasteurii bacterium

Microbially induced calcite precipitation (MICP) is an efficient and eco-friendly technique that has attracted significant interest for resolving various problems in the soil (erosion, improving structural integrity and water retention, etc.), remediation of heavy metals, production of self-healing concrete or restoration of different concrete structures. The success of most common MICP methods depends on microorganisms degrading urea which leads to the formation of CaCO3 crystals. While Sporosarcina pasteurii is a well-known microorganism for MICP, other soil abundant microorganisms, such as Staphylococcus bacteria have not been thoroughly studied for its efficiency in bioconsolidation though MICP is a very important proccess which can ensure soil quality and health. This study aimed to analyze MICP process at the surface level in Sporosarcina pasteurii and a newly screened Staphylococcus sp. H6 bacterium as well as show the possibility of this new microorganism to perform MICP. It was observed that Staphylococcus sp. H6 culture precipitated 157.35 ± 3.3 mM of Ca2+ ions from 200 mM, compared to 176 ± 4.8 mM precipitated by S. pasteurii. The bioconsolidation of sand particles was confirmed by Raman spectroscopy and XRD analysis, which indicated the formation of CaCO3 crystals for both Staphylococcus sp. H6 and S. pasteurii cells. The water-flow test suggested a significant reduction in water permeability in bioconsolidated sand samples for both Staphylococcus sp. H6 and S. pasteurii. Notably, this study provides the first evidence that CaCO3 precipitation occurs on the surface of Staphylococcus and S. pasteurii cells within the initial 15–30 min after exposure to the biocementation solution. Furthermore, Atomic force microscopy (AFM) indicated rapid changes in cell roughness, with bacterial cells becoming completely coated with CaCO3 crystals after 90 min incubation with a biocementation solution. To our knowledge, this is the first time where atomic force microscopy was used to visualize the dynamic of MICP on cell surface.

Self-healing capacity of ultra-rapid-hardening fiber-reinforced cementitious composites under tension

This study investigates the self-healing capacity of ultra-rapid-hardening fiber-reinforced cementitious composites. For this purpose, polyethylene (PE) fibers with three different lengths (6, 9, and 12 mm) were incorporated with different volume fractions of 1.0, 1.5, and 2.0%. All test series were pre-damaged with 0.5 and 1.0% pre-strains and re-tested after 30 wet-dry healing cycles. The fiber reinforcing index was proportional to the tensile performance regardless of the pre-strain and the length of the PE fiber was more dominant than the volume fraction. The case in which self-healing occurred most appropriately was for specimens that incorporated 2% of medium-length (9 mm) fibers. Thirty wet-dry cycles improved the tensile strength by up to 47.5% compared to the conventional one, while the strain capacity was reduced, resulting in a recovery ratio of only 74.5%. The energy absorption capacity was sufficiently recovered to be comparable to that of the control specimen and excellent strain-hardening behavior was obtained with a sufficient number of additional microcracks. Microcracks with widths of less than 50 μm were filled significantly with the formation of CaCO3 crystals, which was verified by scanning electron microscopy and energy dispersive X-ray spectroscopy.

A novel approach for the development of sustainable hybridized geopolymer mortar from waste printed circuit boards

Printed circuit boards (PCB) contain metallic and non-metallic fractions (NMF) that are hazardous and toxic when disposed of in a landfill. This paper emphasizes the feasibility of using NMF reclaimed from waste PCB's as a replacement to fly ash (FA) and metakaolin (MK) in a geopolymer mortar. Geopolymer mortar mixes were prepared with five FA-MK replacement ratios of 100-0, 90-10, 80-20, 70-30 and 60-40 and for each mix FA was also replaced with NMF by 5%, 10%, 15%, and 20%. The compressive strength and microstructures of geopolymer mortar were investigated and it was found that the addition of NMF enhanced the compressive strength. Maximum strength gain was found with 30% of MK and 15% of NMF in FA. The pozzolanic action of alumino-silicates was studied through SEM and XRD which reflected the formation of C-S-H gel with a dense geopolymer matrix along with the formation of CaCO3 crystals resulting in strength gain. The experimental studies provide a practical and sustainable recycling approach for the use of NMF in geopolymers for the construction industry.

Additives: Their Influence on the Humidity- and Pressure-Induced Crystallization of Amorphous CaCO3

Nature possesses a unique control over the formation of CaCO3 crystals that imparts fascinating mechanical properties to many CaCO3-based biomaterials. This high level of control is, at least in pa...

Formation and Inhibition of Calcium Carbonate Crystals under Cathodic Polarization Conditions

The formation of CaCO3 crystals on the cathode surface and the scale-inhibition performance of scale inhibitor 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) on the cathode surface were studied by methods of solution analysis, gravimetric analysis, SEM, FTIR, and XRD techniques. They were then compared with the results of the formation and suppression of CaCO3 crystals in aqueous solution. PBTCA had a good solution-scale-inhibition performance and good lattice-distortion effects on CaCO3 crystals in solution, which could change the CaCO3 from calcite to vaterite and aragonite crystals. The solution-scale-inhibition efficiency exceeded 97% when the PBTCA concentration reached 8 mg/L. Under cathodic polarization conditions, the surface-scale-inhibition efficiency of the cathode and solution-scale-inhibition efficiency near the cathode surface both exceed 97% at polarization potential of −1V. The addition of PBTCA significantly reduced the amount of CaCO3 crystals formed on the cathode surface and had good surface and solution-scale-inhibition effect. However, the lattice-distortion effect of PBTCA on CaCO3 crystals disappeared on the cathode surface, and the resulting CaCO3 contained only calcite crystals. The high-scale-inhibition effect of PBTCA under cathodic polarization was mainly due to the inhibition of the formation of calcium carbonate crystals by PBTCA, and not because of the lattice distortion of CaCO3 crystals.

Investigation of the hydrogen evolution phenomenon on CaCO3 precipitation in artificial seawater

Precipitation of CaCO3, as the most important part of scales, causes a serious problem in industrial equipment such as pipelines and desalination plants. The effect of the hydrogen evolution phenomenon on the electrochemical precipitation was studied through varying different factors including cathodic potential (CP), bicarbonate concentration, and solution temperature. The application of CP from −0.8 VSCE to −1.2 VSCE, an increase in bicarbonate concentration and temperature elevation from 25 °C to 45 °C led to the increase of scaling time (ts) and residual current density (ir). In all cases, it was indisputably found that the hydrogen evolution phenomenon had a predominant effect on the calcium carbonate precipitation. The surface analyses by means of scanning electron microscopy (SEM) showed formation of crystals in two defined forms of calcite and aragonite. Moreover, the energy dispersive spectroscopy (EDS) technique confirmed the formation of CaCO3 crystals.

Heterogeneous growth of calcite at aragonite {001}- and vaterite {001}-melt interfaces: A molecular dynamics simulation study

Crystal growth at the interface between a calcium carbonate (CaCO3) crystal and its melt at a high temperature of 1500K is investigated by means of a molecular dynamics simulation. The simulation is performed for the interfaces of a calcite {104} plane, aragonite {001}, {100}, and {010} planes, and vaterite {001}, {110}, and {100} planes. The growth from a pure melt and that from a melt containing Mg2+ are examined. Calcite growth occurs on the calcite {104} plane, aragonite growth occurs on the aragonite {100}, and {010} planes, and vaterite growth occurs on the vaterite {110} and {100} planes. However, the heterogeneous growth of calcite occurs on the {001} plane of aragonite and vaterite, irrespective of the presence of Mg2+. The results advance our understanding of geological processes that occur at high temperature, such as the formation of CaCO3 crystals from carbonatite magma and the formation of marble. Moreover, the results provide useful information for the control of CaCO3 crystal formation in material design.

Real-time monitoring of calcification process by Sporosarcina pasteurii biofilm

Sporosarcina pasteurii is known to produce calcite or biocement in the presence of urea and Ca(2+). Herein, we report the use of novel ultramicrosensors such as pH, Ca(2+), and redox sensors, along with a scanning electrochemical microscope (SECM), to monitor a real-time, bacteria-mediated urea hydrolysis process and subsequent changes in morphology due to CaCO3 precipitation. We report that the surface pH of a live biofilm changed rapidly from 7.4 to 9.2 within 2 min, whereas similar fast depletion (10 min) of Ca(2+) was observed from 85 mM to 10 mM in the presence of a high urea (10 g L(-1)) brine solution at 23 °C. Both the pH and the Ca(2+) concentration profiles were extended up to 600 μm from the biofilm surface, whereas the bulk chemical composition of the brine solution remained constant over the entire 4 h of SECM experiments. In addition, we observed a change in biofilm surface morphology and an increase in overall biofilm height of 50 μm after 4 h of precipitation. Electron microscopy confirmed the changes in surface morphology and formation of CaCO3 crystals. Development of the Ca(2+) profile took 10 min, whereas that of the pH profile took 2 min. This finding indicates that the initial urea hydrolysis process is fast and limited by urease or number of bacteria, whereas later CaCO3 formation and growth of crystals is a slow chemical process. The ultramicrosensors and approaches employed here are capable of accurately characterizing bioremediation on temporal and spatial scales pertinent to the microbial communities and the processes they mediate.

Hydrogen peroxide as a crystal growth modifier of CaCO3

Using exclusively H2O2 as an additive, facile morphology control over CaCO3 crystal aggregation was realized readily by changing the concentrations of H2O2 and the pH values of the crystallization system. The ionization of H2O2 to [H–O–O]− and [O–O]2− and the generated gas molecules played significant roles in modifying the crystal morphologies. Based on the CaCO3 particles morphology through different aging times, a mechanism about the formation of CaCO3 crystals in the presence of H2O2 was proposed.

Effect of particles on the induction time of calcium carbonate in synthetic SWRO concentrate

Particles, which are naturally present in seawater, have been reported to affect the formation of CaCO3 crystals. In this study the effect of foreign particles on induction time was explored. Induction time was monitored using a highly sensitive pH meter mounted in an air-tight glass reactor. Experimental work was performed with synthetic seawater prepared using ultra-pure water with a composition equivalent to 50% recovery SWRO concentrate (based on the composition of seawater from the Gulf of Oman). The prepared synthetic solutions were filtered through filters having different pore sizes namely 0.22 μm; 0. μm and 100kD (≈0.03 μm). In addition, glass beads of diameter 20–30 nm were added in volumes of (1; 0.5 and 0.1 ml) to synthetic seawater to yield an increase in glass/water contact area of 123%, 16% and 1% compared to the total reactor glass area in contact with the synthetic water. Different mixing speeds were applied namely 10; 50; 150 and 300 rpm to investigate the effect of mixing on experimenta...

Biological synthesis of calcite crystals using Scindapsus aureum petioles

We report a novel strategy for the biological synthesis of calcite crystals using the petioles of the plant Scindapsus aureum. The resultant calcite crystals were characterized by scanning electron microscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray powder diffractometry, and electron diffraction. The biomolecules of S. aureum petioles were confirmed by UV–Vis and FT-IR analysis. The results showed that the spherical or rhombohedral calcite crystals were obtained in the cells of S. aureum petioles. Biomimetic synthesis of calcium carbonate (CaCO3) in aqueous solution containing extracts of S. aureum petioles was also performed to investigate the soluble biomolecules’ influence on crystal growth of CaCO3. It was found that twinborn spherical calcite crystals were formed, suggesting that the soluble biomolecules of S. aureum play a crucial role in directing the formation of calcite spherical particles. The possible mechanism of formation of CaCO3 crystals using S. aureum is also discussed; the biomolecules of S. aureum may induce and control the nucleation and growth of CaCO3 crystals.

Influence of N,O-carboxymethyl chitosan on the properties of octadecanoic acid/octadecylamine monolayers and the fractal structure of calcium carbonate

The properties of octadecanoic acid-otctadecylamine monolayers and growth of calcium carbonate (CaCO3) induced by the monolayers on the surface of supersaturated CaCO3 solution with N,O-carboxymethyl chitosan (CMC) are studied. The results suggest that CMC is either adsorbed on or inserted into the monolayers, as is confirmed by π-A, dπ/dA-A, and π-t isotherms. The adsorption of CMC changes the properties of the monolayers, a process that results in the transformation of the shape of CaCO3 particles from crystal-like into the fractal pattern beneath the monolayers. Different fractal morphologies, such as butterfly and wicker branches consisting of hollow ellipsoidal, solid ellipsoidal, and spherical particles, correspondingly, are observed; these morphologies depend on the CMC concentration in the subphase. The dimensions of fractal patterns are determined. The mechanisms of the formation of CaCO3 crystals and fractal structures are discussed.

Precursor structures in the crystallization/precipitation processes of CaCO3 and control of particle formation by polyelectrolytes

The formation of CaCO3 is usually discussed within the classical picture of crystallization, i.e. assuming that the formation of CaCO3 crystals proceeds via nucleation and growth. This may be true for the case of low supersaturation. In this work it is shown that the formation process is far more complex at high supersaturation, i.e. during precipitation. New insight into the mechanisms of precipitation is obtained by analyzing structure formation with a time resolution down to the millisecond range from the initiation of the reaction. The techniques used are scanning electron microscopy, electron diffraction, X-ray microscopy and cryo-transmission electron microscopy combined with a special quenching technique. It is seen that upon mixing CaCl2 and Na2CO3 solutions (0.01 M) first an emulsion-like structure forms. This structure decomposes to CaCO3-nanoparticles. These nanoparticles aggregate to form vaterite spheres of some micrometers in diameter. The spheres transform via dissolution and recrystallization to calcite rhombohedra. Once a suitable amount of additive, in our case polycarboxylic acid, is present during the precipitation the nanoparticles are stabilized against compact aggregation; instead they form flocs. This stabilization is either of a temporary nature if the amount of polymer is insufficient to cover the surface of the nanoparticles formed or more long lived if there is enough polymeric material present. By means of Ca-activity measurements it can be shown that the polymers are partially incorporated into the forming crystals.

Fabrication of Thermo‐Responsive Hybrid Hydrogels by In‐Situ Mineralization and Self‐Assembly of Microgel Particles

AbstractSummary: An in‐situ mineralization process in the presence of thermo‐responsive microgels leads to the formation of well‐defined hybrid materials. Experimental data suggest that control of the mineralization process in the presence of the microgels offers the possibility to obtain sub‐micrometer‐sized hybrid particles or macroscopic hybrid hydrogels. The rapid formation of CaCO3 crystals in the microgel structure favors the preparation of the hybrid particles wherein inorganic crystals cover the shell layer of the microgel. The slow formation of CaCO3 crystals leads to the simultaneous self‐assembly of the microgel particles on the bottom of the reaction vessel, and the formation of a physical network. It has been demonstrated that hybrid hydrogel materials with different calcium carbonate contents and temperature‐dependent swelling‐deswelling properties can be prepared.Formation of a hybrid hydrogel by the vapor diffusion method.magnified imageFormation of a hybrid hydrogel by the vapor diffusion method.

Feasibility study of crystallization process for water softening in a pellet reactor

One of the undesirable characteristics of some groundwater sources is hardness, which has some adverse effects on water pipes, boilers and soap consumption. Therefore several treatment processes have been introduced to remove or reduce the hardness from hard waters. One of the new innovations in this regard is crystallization process. Hardness can be removed from hard waters by growth of calcium carbonate crystals in a fluidized bed reactor called pellet reactor. The design, setting up, starts up and reaching optimal condition for calcium carbonate crystallization process in a pellet reactor which has been initially seeded with sand as a crystal citation can be a successful solution for treatment of hard waters. The chemistry of pellet softening process is essentially the same as conventional softening process, instead of precipitation of calcium carbonate which does not have any useful consumption and must be removed once in a while some how, crystallization process in a fluidized bed reactor produces pure solid grain of calcite. These pellets can be used in some industries and are in fact an economic commodity. For this purpose a pilot was set up as a crystallization reactor and water with total hardness ranging from 150 up to 500 mg/l as CaCO3 was fed to the system with a flow rate of 24 l/hr. To remove hardness, caustic and soda, lime milk was fed to the system separately at first stage at then together. The formation of CaCO3 crystals on the surface of sands represented the reduction of hardness. An analysis is made for the characteristics of a softed water resulted from the use of caustic soda, lime milk or both as regent.

A crustacean Ca2+-binding protein with a glutamate-rich sequence promotes CaCO3 crystallization.

The DD4 mRNA of the penaeid prawn Penaeus japonicus was shown previously to be expressed in the epidermis adjacent to the exoskeleton specifically during the post-moult period, when calcification of the exoskeleton took place. The encoded protein possessed a Ca2+-binding site, suggesting its involvement in the calcification of the exoskeleton. In the present study, an additional ORF (open reading frame) of 289 amino acids was identified at the 5' end of the previous ORF. The newly identified part of the encoded protein included a region of approx. 120 amino acids that was highly rich in glutamate residues, and contained one or more Ca2+-binding sites. In an immunohistochemical study, signals were detected within calcified regions in the endocuticular layer of the exoskeleton. Bacterially expressed partial segments of the protein induced CaCO3 crystallization in vitro. Finally, a reverse transcription-PCR study showed that the expression was limited to an early part of the post-moult period, preceding significant calcification of the exoskeleton. These observations argue for the possibility that the encoded protein, renamed crustocalcin (CCN), promotes formation of CaCO3 crystals in the exoskeleton by inducing nucleation.