CaCO3 Crystals Research Articles

Innovative application of green surfactants as eco-friendly scale inhibitors in industrial water systems.

Scale deposition poses significant challenges in various industrial utilities, necessitating the development of eco-friendly scale inhibitors in line with environmental regulations. This study investigates the potential of two natural surfactants, Casein and Rhamnolipid, as innovative inhibitors for calcium carbonate (CaCO3) scale formation, offering an alternative to traditional water treatment chemicals. The anti-scaling characteristics of these two green surfactants were performed using conductivity and electrochemical impedance spectroscopy (EIS) techniques. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to analyze the morphology of CaCO3 crystals and understand the structural changes induced by surfactant interaction. The results revealed that Rhamnolipids significantly outperform Casein in suppressing scale formation, attributed to the adsorption of their multiple functional groups onto scale microcrystals. This adsorption modifies the crystal structure and inhibits further growth. Computational studies were employed to investigate the inhibition mechanism of these surfactants. The spatial and electrical configurations of optimal molecular structures are also analyzed using the Density Functional Theory (DFT) approach. Monte Carlo simulations on the CaCO3 (104) surface demonstrated that Rhamnolipids exhibit superior inhibition compared to Casein, as evidenced by their higher adsorption energy, indicating a more stable binding to the surface. Overall, this research highlights the potential of these natural surfactants as sustainable scale inhibitors, particularly in industries such as food and pharmaceuticals, thereby contributing to environmentally friendly water treatment solutions.

Isolation and selection of spore-forming bacilli with potential for self-healing of concrete

The self-healing of concrete through the use of bacteria is an ecological, sustainable, and environmentally friendly method that can replace time-consuming and costly repairs. The aim of this research was to isolate and select spore-forming bacilli with potential for concrete self-healing. Soil samples from the limestone mines of Simbal, Trujillo, La Libertad, Peru were used. These samples were processed to primarily isolate spore-forming bacteria. The self-healing potential of these bacteria was evaluated through their ability to produce the urease enzyme, grow at an alkaline pH, and produce calcium carbonate crystals in a culture medium with urea and CaCl2 at pH 8.0. The produced crystals were visualized with scanning electron microscopy and their calcium content was confirmed through EDS analysis. The isolated bacteria were identified by 16 S rRNA gene amplification by PCR as Bacillus sp and Streptomyces sp. It was observed that Bacillus sp. produces CaCO3 crystals with vaterite morphology, while Streptomyces sp. produces rhombohedral calcite crystals. It is concluded that the isolated bacteria have the potential to be used in concrete self-healing processes.

Influence of ultra-fine pozzolanic materials on the self-healing capabilities of ultra-high performance concrete under carbonation conditioning

This work studies the autogenous self-healing of ultra-high performance concrete (UHPC) incorporating two ultra-fine pozzolanic materials, silica fume (USF) and ultra-fine fly ash (UFFA), under carbonation conditioning. Both ultra-fine pozzolanic materials stimulate the healing of cracks by promoting the secondary hydration of the cement matrix. USF and UFFA form healing products primarily consisting of C-S-H and ettringite, respectively, and the latter product closes the cracks more effectively. Under carbonation conditioning, UFFA accelerates CaCO3 formation with residual uncarbonated ettringites as the structural skeleton, improving the impermeability recovery. USF generates silica gel as a bonding layer between the CaCO3 crystals and the cement matrix after decalcification, which induces more multi-dimensional cracking upon regenerated structures under flexural reloading, thereby enhancing the mechanical property restoration of UHPC. UFFA-modified UHPC is ideal for applications requiring high impermeability, whereas USF-incorporated UHPC is better suited for scenarios with high load-bearing demands.

Synthesis and evaluation of an environmentally friendly phosphorus-free and nitrogen-free polymer as a scale and corrosion inhibitor

Polyepoxysuccinic acid (PESA) was modified by glycidyl (Gly) to obtain a phosphate-free and nitrogen-free polymer (Gly-PESA), and its scale and corrosion inhibition properties were studied.The effects of Gly-PESA concentration, calcium ion concentration and temperature to scale inhibition performance were studied by static scale inhibition method. The corrosion inhibition performance of Gly-PESA was studied by static weight-loss method. The morphology and structure of calcium scale and steel surface were characterized by spectroscopic and microscopic methods. The scale inhibition efficiency of Gly-PESA for CaCO3 and CaSO4 was 98.06% and 92.6%, respectively. Under the same experimental conditions, the scale inhibition effect of Gly-PESA was obviously better than that of PESA. Gly-PESA could effectively inhibit the growth of CaCO3 and CaSO4 crystals and cause their crystal lattice distortion or crystal dispersion. The corrosion inhibition efficiency of Gly-PESA for carbon steel was 78.17%. The adsorption of Gly-PESA on the surface of the steel test piece followed Langmuir adsorption isotherm, and formed a protective film, which increased the corrosion resistance of the steel test piece, thus effectively protecting the steel test piece. Therefore, Gly-PESA was a green scale and corrosion inhibitor, which solved the problem of environmental pollution.

Enhancing mechanical properties of carbonated steel slag through surfactant-assisted CaCO3 crystallization

This study investigates the enhancement of mechanical properties in carbonated steel slag through surfactant-assisted CaCO3 crystallization. Sodium dodecyl benzene sulfonate (SDBS) was employed at various concentrations (0.1–0.4 mol/L) and temperatures (20–60 °C) to modulate the carbonation process. Optimal performance was achieved with 0.2 mol/L SDBS at 40 °C, resulting in a maximum CO2 uptake of 8.51 % and a compressive strength of 62.89 MPa, 81.66 % higher than unmodified steel slag. Characterization techniques confirmed the formation of crystalline calcite, vaterite, and aragonite, contributing to improved microstructure and strength. SDBS micelles act as templates for CaCO3 nucleation and growth, with low concentrations facilitating carbonation and high concentrations inhibiting it. This research offers new insights into surfactant-assisted crystallization for enhancing carbonated steel slag properties, paving the way for high-performance, eco-friendly building materials from industrial waste.

In Situ Monitoring the Nucleation and Growth of Nanoscale CaCO3 at the Oil-Water Interface.

Interfaces can actively control the nucleation kinetics, orientations, and polymorphs of calcium carbonate (CaCO3). Prior studies have revealed that CaCO3 formation can be affected by the interplay between chemical functional moieties on solid-liquid or air-liquid interfaces as well as CaCO3's precursors and facets. Yet little is known about the roles of a liquid-liquid interface, specifically an oil-liquid interface, in directing CaCO3 mineralization which are common in natural and engineered systems. Here, by using in situ X-ray scattering techniques to locate a meniscus formed between water and a representative oil, isooctane, we successfully monitored CaCO3 formation at the pliable isooctane-water interface and systematically investigated the pivotal roles of the interface in the formation of CaCO3 (i.e., particle size, its spatial distribution with respect to the interface, and its mineral phase). Different from bulk solution, ∼5 nm CaCO3 nanoparticles form at the isooctane-water interface. They stably exist for a long time (36 h), which can result from interface-stabilized dehydrated prenucleation clusters of CaCO3. There is a clear tendency for enhanced amounts and faster crystallization of CaCO3 at locations closer to isooctane, which is attributed to a higher pH and an easier dehydration environment created by the interface and oil. Our study provides insights into CaCO3 nucleation at an oil-water interface, which can deepen our understanding of pliable interfaces interacting with CaCO3 and benefit mineral scaling control during energy-related subsurface operation.

Study on the effect of particles in oilfield produced water on the deposition process of CaCO3

In crude oil production, scale deposition significantly reduces production output and elevates operational costs, posing a severe threat to production safety. While chemical methods have been extensively explored for the scaling and inhibition of inorganic salts, the inorganic scaling triggered by solid particle scaling in complex oilfield water has largely been overlooked. This study involves the introduction of particles into a supersaturated CaCO3 solution, utilizing static scale inhibition and conductivity techniques to examine their influence on the scaling process and crystallization rate. It is evident that solid particles expedite the deposition process of CaCO3. Moreover, the deposition rate of CaCO3 is influenced by factors such as the solid particle content, particle size, and stirring speed. It is noteworthy that the presence of solid particles solely impacts the formation rate of CaCO3 crystals, without altering the total deposition. Specifically, under conditions of 70°C, 250/min stirring speed, and 0.08% SiO2 addition, the deposition rate of CaCO3 is enhanced by 13.5%. The nucleus growth rate constant increases from 11.10 × 10-3min-1 to 14.52 × 10-3min-1 and the crystal growth rate constant increases from 3.02 × 10-3min-1 to 3.36 × 10-3min-1 at most. Observations made through scanning electron microscopy (SEM) and polarized light microscopy reveal that scaling occurs predominantly on the added solid particles in later stages, indicating that solid particles in supersaturated solutions serve as crystal nuclei, inducing the growth of CaCO3 crystals and thus accelerating scaling. This research provides valuable insights for the study of scaling in complex water environments.

Microscale insights into enzyme-induced carbonate precipitation in rock-based microfluidic chips

Biomineralisation technology shows promise for sealing subsurface fractures, but understanding its microscale mechanisms in real rock fractures remains incomplete. In this study, a microfluidic chip incorporating real rock slices was utilised to conduct enzymatically induced carbonate precipitation (EICP) experiments using a one-phase continuous injection strategy. Real-time observations revealed grey flocs forming and clustering into aggregates susceptible to transport by flow. Calcium carbonate (CaCO3) crystals that formed on rock and polydimethylsiloxane surfaces effectively filled and bridged fractures, leading to a significant pressure drop. Rough surfaces can provide additional sites for solute attachment and heterogeneous nucleation of calcium carbonate. High velocities and small apertures generally promoted floc formation and reduced crystal growth. Precipitation content gradually increased with a decreasing rate. Lower estimated precipitation efficiency was obtained in smaller, high-flow fractures. Precipitates on rock interfaces induced eddies and significant pressure drops within narrow pore throats. Crystal growth displayed a two-stage development: an initial increase followed by a decrease, varying across different facets (the surfaces or orientations of the growing crystals). Growth competition will occur when two or more neighbouring crystals come into contact with diverse grain orientations. The findings provide valuable microscale insights into microscale processes governing EICP within real rock fractures, contributing to evaluation of its efficacy in subsurface fracture sealing applications.

Use of rise husks to improve the efficiency of MICP-based soil improvement technique

Biogrouting has been identified as the best alternative approach for the conventional cement and chemical grouts. Among the various types of biogrouting techniques, microbial induced carbonate precipitation (MICP) has been recently recognized as a promising pathway for producing biogrout material, hence densifying the weak soils. In MICP, calcium carbonate (CaCO3) biocement is produced through biochemical reactions induced by the urease enzyme. The efficiency and productivity of MICP can be further improved by introducing various additives, including fibers, organic polymers, powders, waste materials, etc. In this research, rice husk was sustainably incorporated into the MICP process, and (i) the effect of the rice husk content, (ii) the concentration of the cementation solution and (iii) the treatment time on the unconfined compressive strength (UCS) of the sandy soil were investigated at the laboratory-scale. Cementation solutions with higher concentrations exhibited a higher UCS values than solutions with lower concentrations. Interestingly, the content of rice husk had a marked influence on the UCS, and the optimum rice husk content was 15%. Compared to that of the control sample (0% rice husk), a threefold greater UCS was obtained for 15% of the rice husk content sample. The outcomes further suggested that longer treatment with lower concentration of cementation solution was the best combination for achieving effective cementation within the sand matrix. Rice husk acted as the template for CaCO3 crystals to nucleate while promoting the efficient formation of CaCO3, indicating that the rice husk is an excellent additive to improve the efficiency of the MICP biocementation in a sustainable way.

Numerical modeling of electromagnetic field spatiotemporal evolution to evaluate the effects on calcium carbonate crystallization

Calcium carbonate (CaCO3) scaling is a significant impediment to water systems. Electromagnetic field (EMF) treatment is a promising approach to control scaling owing to its simplicity and low or no energy requirements. However, the underlying mechanisms by which EMF impacts CaCO3 crystallization remain unclear due to the challenges in measuring the EMFs in feed solutions and the lack of a fundamental understanding of the applied EMFs and the observed physicochemical phenomena. To fill this knowledge gap, a high-fidelity COMSOL model was first developed to simulate EMFs in bulk solutions for three alternating current-induced EMF devices with different configurations and properties. These were then integrated with experimental data to unveil the underlying mechanism by which applied EMFs alter the physicochemical processes. The study revealed that even low-strength EMFs (e.g., electric fields <0.15 V/m and magnetic fields <0.03 mT) promoted CaCO3 precipitation in bulk solutions. The electric fields created by these EMF devices resulted in higher Lorentz force compared to their induced magnetic fields. The methodology of this study offers the capability to predict the effectiveness of different EMF devices in facilitating crystallization processes, and these mechanistic insights lay the foundation for the smart design of EMF devices for diverse water treatment applications.

Effect of sticky rice on the strength and permeability of bio-cemented sand

Microbially induced carbonate precipitation (MICP) is an eco-friendly soil improvement technique. However, this method still has some drawbacks, such as low conversion efficiency of CaCO3 crystallization, insufficient strength for certain applications, and requiring multiple treatments. Previous studies have reported that sticky rice can regulate CaCO3 crystals (i.e., chemical CaCO3) in the sticky rice-lime mortar, showing potential for improving the bio-cementation. Therefore, this study explored the possibility of using sticky rice to enhance the biocementation effect. Tests were carried out to assess the strength and permeability of bio-cemented sand with the inclusion of sticky rice. The results indicated that sticky rice may regulate the type and size of bio-CaCO3 crystals, and the use of an appropriate amount of sticky rice as additive could increase the strength of sand columns by regulating CaCO3 crystallization. Polyhedral calcites may be more favourable for the increasing strength than some vaterites with a hollow spherical structure. The combination of MICP and sticky rice can significantly decrease the coefficient of permeability to a value that was much lower than that by using sticky rice and MICP alone. Bio-CaCO3 immobilized the sticky rice on one end on sand particles, and the reticulated structure of sticky rice divided large pores into small pores, which may be the important cause of the decrease in permeability coefficient. Finally, this study proposed that the MICP with the sticky rice as an additive may enhance the MICP effect and prevent the surface erosion of coarse-grained sand slopes.

Effect of acid type on biomineralization of soil using crude soybean urease solution

The one-phase-low-pH method is a simple, efficient, and user-friendly biogrouting technique that can effectively improve the biomineralization of enzyme-induced carbonate precipitation (EICP) using free urease enzyme. One of the most significant advantages of this method is its capacity to effectively delay calcium carbonate (CaCO3) precipitation by reducing the pH of the solution through the addition of acid. This prevents bioclogging during the biogrouting process and improves the biomineralization effect. However, the biomineralization of the one-phase-low-pH based EICP method may be influenced by the specific acid used. To investigate the impact of acid type on the one-phase-low-pH EICP method using crude soybean urease solution (CSUS), four types of acids, including hydrochloric acid (HCl), nitric acid (HNO3), acetic acid (CH3COOH), and lactic acid (C3H6O3), were used to adjust the pH of CSUS. A series of macroscopic and microscopic experiments were conducted to evaluate the effect of acid type on the one-phase-low-pH EICP method. The results indicate that the acid has an inhibition on the urease activity (UA) of CSUS. Among the acids tested, HNO3 exhibits the most pronounced inhibitory effect on the UA of CSUS, followed by HCl, and the least pronounced inhibitory effect for CH3COOH and C3H6O3 under the same pH conditions. Meanwhile, CH3COOH and C3H6O3 could provide a longer delay duration of CaCO3 precipitation than HNO3 and HCl. Therefore, the one-phase-low-pH EICP method based on CH3COOH and C3H6O3 can significantly improve the effective biocementation depth compared to that based on HNO3 and HCl. Nevertheless, the different types of acids appear to have no obvious effect on the polymorph and crystalline of the precipitated CaCO3 crystals.

Examination of the use of binderless zeolite blend as backfill materials to enhance CO2 adsorption in coal mine working face

The release and accumulation of CO2 in the working face of the coal mine is a major safety concern and requires an effective means to avoid the incidence of the mine. This present study therefore sought to develop a self-CO2 adsorbing backfill (SCAB) material to remove CO2 from the working environment, and simultaneously mitigate the movements of the surrounding rock layers. SCAB was formulated using coal mine solid waste activated with an alkali activator, and binderless 4 A zeolite was embedded in the backfill body. The total CO2 adsorption capacity was investigated using a CO2 flow-through method under ambient pressure and temperature conditions. The adsorption plateau was found in stages II and III respecting the predetermined curing time and zeolite contents. The maximum adsorption capacity was 143.8 mg-CO2/g-SCAB, resulting in an increase of up to 82 % in UCS compared to reference samples. The underlying mechanism was discovered in morphological analyses.1) The well distribution of zeolite in the SCAB body provided as diffusive pathways and adsorption sites for CO2 after standard curing. 2) The adsorbed CO2 underwent a desorption stage when the CO2 concentration decreased and reacted to the cementitious matrix of the SCAB body. 3) More CaCO3 crystals were generated and filled in the micro spaces of the SCAB body, which contributed to an increase in compressive strength. This study developed an effective approach to remove CO2 gas from the working face of the coal mine during backfilling. Adsorbed CO2 improved the strength of the material, provided as a novel multi-function backfill mining for sustainable green coal mining technology.

Seeding improves the strength of bio-tiles grown with microbially induced calcium carbonate precipitation

Bio-tiles are a biobased alternative to conventional tiles that utilise a promising technology called microbially induced calcium carbonate (CaCO3) precipitation (MICP). This technology has low energy requirements and also sequesters carbon. Bio-tiles have been made in previous work using a submersion method, however, the process required additives such as 0.3 M magnesium chloride to achieve bio-tiles that meet international standards. The current study aimed to improve the bio-tile strength properties with CaCO3 crystal seeding and a pumping method instead of the use of magnesium that also increases ionic strength. With this technique, cementation solution containing the required calcium and urea for the MICP reaction was pumped through a sealed mould in a series of programmed treatments. The highest concentration of ureolytic Sporosarcina pasteurii with an effective urease activity of 40 mmol NH4-N/L·min was found to be most beneficial to the breaking strength of the bio-tiles, as were the shortest retention times of 1 h between treatments. Seeding with CaCO3 crystals offered significant benefit to the MICP process. Pre-seeding of the geotextiles was explored and the mass of seeds initially present on the geotextiles was found to have a direct improvement on the breaking strength of 21–82 %, increasing with seed loading.The highest CaCO3 seed loading tested of 0.072 g seeds/cm2 geotextile resulted in bio-tiles with a breaking strength of 940 ± 92 N and a modulus of rupture of 16.4 ± 1.7 N/mm2, meeting international targets for extruded tiles with 6–10 % water absorption. When a seed loading of 0.021 g/cm2 was used instead, bio-tiles meeting targets for tiles with a water absorption of >10 % were produced at 628 ± 18 N and 10.5 ± 1.1 N/mm2.

Synergistic effect of CaCO3 particles and porous carbon towards the removal of Zn2+ ions in aqueous solutions

This work describes the preparation of an adsorbent containing CaCO3 particles dispersed in activated carbon and its use for the removal of Zn2+ ions from aqueous solutions. The combination of the large porosity of the activated carbon support with the easy ion exchange occurring at the surface of the carbonate particles led to the achievement of fast adsorption kinetics and excellent ion removal capacity for the composite adsorbent. The material was synthesized by wet impregnation of the porous carbon support with an aqueous solution of Ca(NO3)2, followed by evaporation of the solvent with subsequent heat treatment in an inert atmosphere. X-ray diffraction results demonstrated the presence of CaCO3 crystals in the material, but with broad and low intensity diffraction peaks, corresponding to an average crystallite size of 20 nm; solid-state 13C NMR spectroscopy confirmed the presence of this phase by means of the identification of the signal relative to the 13C nuclei of the CO32− group at ∼170 ppm. The carbon-based adsorbent containing the CaCO3 particles showed excellent ability to remove Zn2+ ions from aqueous solutions, with essentially all ions removed after 30 min of contact time. In addition, the kinetic analysis data were properly fitted using the pseudo-second order model, pointing to the occurrence of chemisorption as the rate limiting of the process. The equilibrium adsorption isotherms were correctly described by the Langmuir model, indicating that the adsorption takes place with the formation of a monolayer on the adsorbent surface. The results evidenced a synergistic effect of the porous carbon and the CaCO3 particles regarding the Zn2+ ions removal, with a fast adsorption kinetics at the initial stage of adsorption attributed to the high availability of the dispersed CaCO3 particles on the carbon surface.

A simple model for predicting the hydraulic conductivity of MICP-treated sand.

In this research paper, we introduce a novel and sustainable approach for forecasting the hydraulic conductivity of sand layers subjected to microbial-induced carbonate precipitation (MICP) to mitigate the diffusion of toxic pollutants. The proposed model uniquely integrates the impact of varying CaCO3 contents on the void ratio and estimates the average particle size of CaCO3 crystals through scanning electron microscopy (SEM) analysis. By incorporating these parameters into the K-C equation, a simplified predictive model is formulated for assessing the hydraulic conductivity of MICP-treated sand layers. The model's effectiveness is validated through comparison with experimental data and alternative models. The outcomes demonstrate a substantial reduction in hydraulic conductivity, with a decrease ranging between 93 and 97% in the initial assessment and a decrease between 67 and 92% in the follow-up assessment, both at 10% CaCO3 content. Notably, the hydraulic conductivity shows an initial sharp decrease followed by stabilization. These findings provide valuable insights into improving the prediction of hydraulic conductivity in MICP-treated sand layers, promoting a sustainable method for preventing pollution dispersion.

Experimental study on improving the performance of imitation earthen site soil in carbon dioxide environment

This study aims to explore the performance of lime-treated soil for repairing the lime soil of the earthen city wall of Kaifeng and to standardize the construction technology of lime-treated soil. The research comprehensively considered factors such as carbonation time, lime particle size, aging conditions, and lime content, and conducted various tests and analyses including triaxial mechanical properties, surface crack analysis, particle size distribution, pH measurement, composition analysis, and electron microscopy on different samples. The results indicate that the significant effect of high-concentration CO2 carbonation enhances the chemical reactions of lime soil, and an appropriate carbonation process can strengthen the bonding and density between soil particles. Under the maintenance condition of 5 % CO2, with increasing carbonation time, the crack ratio, average crack length, and average crack width of the samples decreased. Cohesion and internal friction angle of the samples exhibited an initial increase followed by a decrease, while shear strength of the samples increased by 22.93 %–75.09 %. The lime particle size has a critical impact on the formation of cracks in lime soil. With increasing lime particle size, the crack ratio, average crack length, and average crack width of the samples increased. Cohesion and internal friction angle of the samples gradually increased with increasing lime content. The increase in crack ratio, average crack length, and average crack width during natural curing of lime-treated soil samples was proportional to the lime content. Appropriate carbonation time, smaller lime particle size, and curing conditions with 5 % CO2 contribute to improving the particle size distribution of lime-treated soil samples, reducing surface cracks, and enhancing performance. However, prolonged carbonation may lead to larger lime particle size, resulting in rough and loose particles, disorganized arrangement of CaCO3 crystals, and the inability to form a cross-linked network skeleton, causing a reduction in shear strength of the samples. These research findings provide important theoretical basis and construction technology guidance for the application of lime-treated soil combined with CO2 carbonation in repairing earthen city walls.

Influence of Different Ions on Pulse Electrodeposition of CaCO3 Scales in the Simulated Seawater.

In the circulating water system of coastal power plants, various kinds of ions have a great influence on the formation and growth of CaCO3 scales. This paper focuses on investigating the influence of existing ions on the pulse electrodeposition behaviors of CaCO3 scales. Different concentrations of ions, such as Fe3+, Mg2+, PO43- and SiO32-, are introduced to simulate the actual seawater environment, and their influence on the CaCO3 scale deposition behaviors is assessed by linear sweep voltammetry, chronoamperometry, and electrochemical impedance spectroscopy tests. The surface coverage of the CaCO3 scale layer is evaluated through the residual current density and polarization resistance values, while the crystal structure and surface compactness of the layer are confirmed by the scanning electron microscope and X-ray diffractometer tests. Results indicate that high concentrations of Mg2+, Fe3+, and PO43- ions have the most significant inhibitory effect on the pulse electrodeposition of CaCO3 scales, among which the inhibition effect of Mg2+ ions is mainly reflected in the change of crystal morphology of CaCO3, that is, the crystallization growth process is inhibited. The inhibition effect of PO43- ions is mainly reflected in the gradually reduced coverage and density of CaCO3 crystals on the electrode surface, suggesting that the crystallization nucleation process is inhibited, while Fe3+ ions have a certain inhibition effect on both the crystallization nucleation and growth processes. Furthermore, lower concentrations of SiO32- ions also display a significant inhibition effect on the crystallization nucleation and growth process, and the inhibition effect weakens with increased concentration. This study provides a theoretical basis for exploring the removal of ions in the industrial water softening field.

The Effect of Volcanic Stone and Metakaolin on the Compressive Properties of Ultrahigh-Performance Concrete Cubes

Over the past few decades, ultrahigh-performance concrete (UHPC) has been widely studied and applied because of its outstanding mechanical properties, such as its high strength and notable durability. However, because of its high cost and easy shrinkage cracking during early pouring in mass concrete construction, to reduce the cost of UHPC and reduce the cracks caused by early pouring, volcanic stone was used as a new type of UHPC coarse aggregate, while metakaolin (MK) was added to the system at the same time, and then two parameters, namely the volcanic rock particle size group and the MK dispersion ratio, were set. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric (TG) microanalysis methods were used to reveal the influence of changes in the material microstructure, phase composition, material composition and crystallinity of the mineral composition on the compressive properties of the UHPC cubes. The results show that the mechanical “lock-in effect” of the structure formed by the volcanic rock holes and mortar can effectively improve the shear resistance of the UHPC–volcanic rock interface, and the compressive strength of the UHPC cubes increases with the volcanic stone’s particle size. When the MK dispersion ratio is less than 4%, the cube compressive strength of the UHPC and the contents of CaCO3 crystals, C-S-H gel and travertine in the UHPC increase with an increasing MK dispersion ratio. At an age of 28 days, compared with the addition of 1% MK, the addition of 4% MK increases the production of C-S-H gel and travertine in the UHPC matrix by 24.82%. When the MK dispersion ratio is 4%, the crystallinity values of the C-S-H gel, travertine and limestone in the UHPC are greater. Adding MK at a 4% dispersion ratio can promote the crystallization of limestone into a large amount of calcite, which can increase the strength of UHPC. On the one hand, the addition of volcanic coarse aggregate results in the retention of more free water and bound water; on the other hand, it also makes it difficult to crystallize CaCO3. The combined action of MK at a 4% dispersion ratio and volcanic rock significantly inhibits CaCO3 crystallization.

Potentiometric titration study of CaCO3 scaling control with non-water soluble polyetherimide and sulfonated polyetherimide films

Automatic potentiometric titration (APT) is a chemical analysis method to study the crystallization of CaCO3 in solution. We demonstrate how APT is also valuable for studying CaCO3 crystallization using water-insoluble polymer films, ideal for studying surfaces exposed to Ca2+ and CO32− ions with the capacity to remove Ca2+ and/or susceptible to scale formation, equipment surfaces, ion exchange surfaces or desalination membranes, etc. Polyetherimide (PEI) and sulfonated polyetherimide (SPEI) films were prepared by solvent casting technique, and their surface studied using FESEM, XPS, Z potential, and contact angle. APT assays were performed with polymer films, using a carbonate buffer (pH 9), dosed with CaCl2, and monitoring free Ca2+. The APT curves with PEI showed no significant difference compared to the control, while the presence of SPEI film affected the kinetics of CaCO3 formation. This was evidenced by changes in the slope and peak maximum of the APT curves. FTIR, XRD, and FESEM of the polymeric films and the CaCO3 after the APT assays showed control over the types of CaCO3 polymorphs. We show that the SPEI film is a good candidate to delay the formation of CaCO3 in water, through the adsorption of Ca2+ ions and the adsorption of pre-nucleation clusters of CaCO3.