Search Results (17)

Addressing the significant pressure for carbon emission reduction in the cement industry, the development of novel cement materials capable of achieving “in situ carbon sequestration” has become an important research focus. This study introduces nesquehonite (MgCO₃·3H₂O, NQ) as a functional admixture into the Portland cement system, systematically investigating its effects on the cement hydration process, the evolution of hydration products, and its carbon sequestration efficiency. Through designed penetration resistance tests and hydration tests with a high water-to-solid ratio, this research utilized X-ray diffraction analysis to determine the phase composition and content of hydration products at different ages. This was combined with scanning electron microscopy to observe microstructural evolution and Nano Measure software 1.2.5 for ettringite crystal size measurement, analyzing the impact of NQ on the early hydration process of P.I cement. The results indicate that the incorporation of NQ significantly alters the early hydration of P.I cement. The Mg²⁺ and CO₃²⁻ ions released upon its dissolution interact with Ca²⁺ and OH⁻ in the pore solution, effectively promoting the early precipitation of carbon sequestration products such as calcium carbonate and minor magnesium-containing carbonates. The addition of 10% NQ hindered the crystallization of Ca(OH)₂ before 6 h but promoted its formation after 24 h. Mechanical property tests revealed that a sample with an optimal 3% NQ dosage not only increased the paste’s penetration resistance but also enhanced the compressive strength of the 1-day hardened sample by 8.37% compared to the plain sample, without a decrease and even a slight increase at 28 days. This enhancement is closely related to the microstructural strengthening effect induced by the carbonation products. This study confirms the feasibility of using NQ to steer the cement hydration pathway towards a low-carbon direction, revealing its dual functionality in regulating hydration and sequestering carbon within cement-based materials. The findings provide a new theoretical basis and technical pathway for developing high-performance, low-carbon cement. Full article

This study evaluated the ability of microalgae to produce carbonate minerals through CO₂ uptake, in comparison with abiotic, direct chemical synthesis through CO₂ absorption. A freshwater microalga (Synechococcus elongatus) isolated from garden soil in East Anglia, UK, was cultivated under laboratory conditions with CO₂ injection to generate a bicarbonate-rich aqueous solution, in which Fe²⁺, Mg²⁺, and Ca²⁺ ions were added to facilitate carbonate formation. Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analyses revealed distinct morphologies and mineral types. The algae-based process precipitated calcite, siderite, magnesite, and dolomite, whereas the abiotic process yielded, respectively, calcite, siderite, high-Mg calcite and nesquehonite. Biogenic minerals were finer and more morphologically diverse than their abiotically formed counterparts. The results indicated that microalgae produced 0.21 mol/L of calcium carbonate, compared to 0.51 mol/L obtained through abiotic CO₂ sequestration, and a comparable yield of about 0.25 mol/L reported for Sporosarcina pasteurii-induced precipitation. Acid resistance tests showed that algae-induced minerals had similar or improved resistance to acidic conditions compared to minerals formed through abiotic CO₂ consumption. Overall, despite slower kinetics, algae-induced carbonate precipitation offers advantages for soil stabilization by biocementation in the context of environmental sustainability, climate change mitigation and circular economy. Full article

The result of a complex mineralogical study of the first discovery of the rare hydrated magnesium carbonate minerals of Nesquehonite and Dypingite in the Obnazhennaya kimberlite pipe (of the Yakutian kimberlite province) is presented. The methods of X-ray phase analysis, electronic microscopy, and Raman spectroscopy have established that the main minerals of the samples found in the form of white crust on a small area of rock outcrop of kimberlite breccia are hydrated carbonates: Nesquehonite is MgCO₃•3H₂O, Dypingite is Mg₅(CO₃)₄(OH)₂•5H₂O. The formation of Dypingite over Nesquehonite was shown using Raman imaging for the first time. Nesquehonite is represented as aggregates consisting of chaotically oriented prismatic crystals or kidney-shaped formations. Dypingite in the examined samples appears less frequently as rose-shaped aggregates formed from lamellar crystals. It is assumed that the formation of rare carbonates of the Obnazhennaya kimberlite pipe is mainly the result of the weathering of silicates, formation of mineralized solutions, and their subsequent crystallization, including the capture of CO₂ from the air. Full article

This study aimed to investigate the structure and shape of carbonate crystals induced through microbial activity and carbon dioxide reactions in the sand. The strength of sandy soil treated with carbonate minerals was subsequently determined using unconfined compression strength (UCS) tests. Sporoscarcina pasteurii bacteria were used to produce an aqueous solution of free carbonate ions (CO₃²⁻) under laboratory circumstances called microbial-induced carbonate precipitation (MICP). In CO₂-induced carbonate precipitation (CICP), carbon dioxide was added to a sodium hydroxide solution to form free carbonate ions (CO₃²⁻). Different carbonate mineral compositions were then provided by adding Fe²⁺, Mg²⁺, and Ca²⁺ ions to carbonate ions (CO₃²⁻). In the MICP and CICP procedures, the results of scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) revealed a distinct morphology of any type of carbonate minerals. Vaterite (CaCO₃), siderite (FeCO₃), nesquehonite (MgCO₃(H₂O)₃), and dolomite (CaMg(CO₃)₂ were produced in MICP. Calcite (CaCO₃), siderite (FeCO₃), nesquehonite (MgCO₃(H₂O)₃), and high-Mg calcite (Ca-Mg(CO₃)) were produced in CICP. According to UCS data, siderite and high-Mg calcite/dolomite had more effectiveness in increasing soil strength (63–72 kPa). The soils treated with nesquehonite had the lowest strength value (25–29 kPa). Mineral-treated soils in CICP showed a slightly higher UCS strength than MICP, which could be attributable to greater particle size and interlocking. This research focused on studying the mineralogical properties of precipitated carbonate minerals by CICP and MICP methods to suggest a promising environmental method for soil reinforcement. Full article

Reactive magnesia cement is considered an eco-efficient binder due to its low synthesis temperature and CO₂ absorption properties. However, the hydration of pure MgO–H₂O mixtures cannot produce strong Mg(OH)₂ pastes. In this study, nesquehonite (Nes, MgCO₃·3H₂O) was added to the MgO–H₂O system to improve its strength properties, and its hydration products and pore structure were analyzed. The experimental results showed that the hydration product changed from small plate-like Mg(OH)₂ crystals to interlaced sheet-like crystals after the addition of a small amount of Nes. The porosity increased from 36.3% to 64.6%, and the total pore surface area increased from 4.6 to 118.5 m²/g. At the same time, most of the pores decreased in size from the micron scale to the nanometer scale, which indicated that Nes had a positive effect on improving the pore structure and enhancing the compressive strength. Combined with an X-ray diffractometer (XRD), a Fourier transform infrared spectrometer (FTIR), and a simultaneous thermal analyzer (TG/DSC), the hydration product of the sample after Nes addition could be described as xMgCO₃·Mg(OH)₂·yH₂O. When Nes was added at 7.87 and 14.35 wt%, the x-values in the chemical formula of the hydration products were 0.025 and 0.048, respectively. These small x-values resulted in lattice and property parameters of the hydration products that were similar to those of Mg(OH)₂. Full article

Magnesium oxide (MgO) has been investigated as a wet mineral carbonation adsorbent due to its relatively low adsorption and regeneration temperatures. The carbon dioxide (CO₂) capture efficiency can be enhanced by applying external force on the MgO slurry during wet carbonation. In this study, two aerosol-processed MgO nanoparticles were tested with a commercial MgO one to investigate the external force effect on the wet carbonation performance at room temperature. The MgO nano-adsorbents were carbonated and sampled every 2 h up to 12 h through forced and non-forced wet carbonations. Hydrated magnesium carbonates (nesquehonite, artinite and hydromagnesite) were formed with magnesite through both wet carbonations. The analyzed results for the time-dependent chemical compositions and physical shapes of the carbonation products consistently showed the enhancement of wet carbonation by the external force, which was at least 4 h faster than the non-forced carbonation. In addition, the CO₂ adsorption was enhanced by the forced carbonation, resulting in a higher amount of CO₂ being adsorbed by MgO nanoparticles than the non-forced carbonation, unless the carbonation processes were completed. The adsorbed amount of CO₂ was between the maximum theoretical amounts of CO₂ adsorbed by nesquehonite and hydromagnesite. Full article

MgO/Mg(OH)₂-based materials have been intensively explored for CO₂ adsorption due to their high theoretical but low practical CO₂ capture efficiency. Our previous study on the effect of H₂O wetting on CO₂ adsorption in MgO/Mg(OH)₂ nanostructures found that the presence of H₂O molecules significantly increases (decreases) CO₂ adsorption on the MgO (Mg(OH)₂) surface. Furthermore, the magneto-water-wetting technique is used to improve the CO₂ capture efficiency of various nanofluids by increasing the mass transfer efficiency of nanobeads. However, the influence of magneto-wetting to the CO₂ adsorption at nanobead surfaces remains unknown. The effect of magneto-water-wetting on CO₂ adsorption on MgO/Mg(OH)₂ nanocomposites was investigated experimentally in this study. Contrary to popular belief, magneto-water-wetting does not always increase CO₂ adsorption; in fact, if Mg(OH)₂ dominates in the nanocomposite, it can actually decrease CO₂ adsorption. As a result of our structural research, we hypothesized that the creation of a thin H₂O layer between nanograins prevents CO₂ from flowing through, hence slowing down CO₂ adsorption during the carbon-hydration aging process. Finally, the magneto-water-wetting technique can be used to control the carbon-hydration process and uncover both novel insights and discoveries of CO₂ capture from air at room temperature to guide the design and development of ferrofluid devices for biomedical and energy applications. Full article

Synthetic nesquehonite with a Mg(HCO₃)OH·2H₂O chemical formula is a solid product of CO₂ mineralization with cementitious properties. It constitutes an “MHCH” (magnesium hydroxy-carbonate hydrate) phase and, along with dypingite and hydromagnesite, is considered to be a promising permanent and safe solution for CO₂ storage with potential utilization as a supplementary material in “green” building materials. In this work, synthetic nesquehonite-based mortars were evaluated in terms of their compressive strengths. Nesquehonite was synthesized by CO₂ mineralization under ambient conditions (25 °C and 1 atm). A saturated Mg²⁺ solution was used at a pH of 9.3. The synthesized nesquehonite was subsequently studied by means of optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Impurity-free nesquehonite formed elongated fibers, often around a centerpiece, creating a rosette-like structure. The synthesized nesquehonite was mixed with reactive magnesia, natural pozzolan, standard aggregate sand and water to create a mortar. The mortar was cast into 5 × 5 × 5 silicone mold and cured in water for 28 days. A compressive strength of up to 22 MPa was achieved. An X-ray diffraction study of the cured mortars revealed the formation of brucite as the main hydration crystalline phase. Carbon dioxide mineralized nesquehonite is a very promising “green” building material with competitive properties that might prove to be an essential part of the circular economy industrial approach. Full article

In this work, we present the results of two synthesis approaches for mesoporous magnesium carbonates, that result in mineralization of carbon dioxide, producing carbonate materials without the use of cosolvents, which makes them more environmentally friendly. In one of our synthesis methods, we found that we could obtain nonequilibrium crystal structures, with acicular crystals branching bidirectionally from a denser core. Both Raman spectroscopy and X-ray diffraction showed these crystals to be a mixture of sulfate and hydrated carbonates. We attribute the nonequilibrium morphology to coprecipitation of two salts and short synthesis time (25 min). Other aqueous synthesis conditions produced mixtures of carbonates with different morphologies, which changed depending on drying temperature (40 or 100 °C). In addition to aqueous solution, we used supercritical carbon dioxide for synthesis, producing a hydrated magnesium carbonate, with a nesquehonite structure, according to X-ray diffraction. This second material has smaller pores (1.01 nm) and high surface area. Due to their high surface area, these materials could be used for adsorbents and capillary transport, in addition to their potential use for carbon capture and sequestration. Full article

In this paper, a simulations model of a seasonal thermal energy storage (TES) reactor integrated into a house heating system is presented. The water vapour chemisorbing reactor contains a composite material composed of silica gel and hydrated magnesium carbonate (nesquehonite, MgCO₃·3H₂O) that can be produced by a carbon capture and storage by mineralisation process. The performance of the TES to supply winter heat instead of electrical resistance heat is analysed. Dividing the reactor into a few units (connected in series) for better heat output and storage capacity as developed by the authors is compared to one unit or parallel unit solutions. The heating system components are an exhaust air heat pump, solar collectors and a heat recovery ventilation unit (HRV). The TES is used as heat source during colder periods, which implies improved efficiency and coefficient of performance (COP). Around 70% of electrical resistance heat, assisting an exhaust air heat pump during cold periods, can be substituted with heat from the TES according to the simulation model. Connecting three units in series will increase the usable storage capacity possibilities with by a 49% higher heat output. Full article

In the world of construction, cement plays a vital role, but despite its reputation and affordable prices, the cement industry faces multiple challenges due to pollution and sustainability concerns. This study aimed to assess the possibility of utilizing carbonated kimberlite tailings, a waste product from diamond mining, as a partial cement substitute in the preparation of concrete bricks. This is a unique opportunity to help close the gap between fundamental research in mineral carbonation and its industrial implementation to generate commercial products. Kimberlite was subjected to a mild thin-film carbonation process in a CO₂ incubator at varying levels of CO₂ concentration (10 vol% and 20 vol% at ambient pressure), kimberlite paste moisture content (10 wt% to 20 wt%), and chamber temperature (35 and 50 °C). The formation of magnesium carbonates, in the form of nesquehonite and lansfordite, was verified by X-ray diffraction analysis, and total CO₂ uptake was quantified by thermal decomposition in furnace testing. Carbonated kimberlite tailings were then used to cast bricks. Replacement of cement between 10% and 20% were tested, with a constant water-to-binder ratio of 0.6:1, and a cementitious material-to-sand ratio of 1:3. Initial water absorption and 7- and 28-days compressive strength tests were carried out. The results obtained confirm the possibility of using carbonated kimberlite to replace cement partially, and highlight the benefits of carbonating the kimberlite for such application, and recommendations for future research are suggested. This study demonstrates the potential use of mining tailings to prototype the sequestration of CO₂ into sustainable building materials to positively impact the increasing demand for cement-based products. Full article

Na-Cu carbonates are relatively rare secondary minerals in weathering zones of ore deposits. Hereby we describe mineral composition and crystal chemistry of the most important secondary (Na)Cu minerals and their Na- and Mg-bearing associates forming rich paragenesis in Rudna IX mine. A non-bulky Ca-rich dripstone-like paragenesis from Lubin Główny mine is also characterized, using Powder X-Ray Diffraction, Rietveld, and Electron Microprobe methods. Light blue juangodoyite (3rd occurrence worldwide) and darker chalconatronite are the most important members of the Rudna IX paragenesis, being associated with malachite, aragonite (intergrown with hydromagnesite and northupite), and probably cornwallite. Most of the minerals are chemically close to their ideal composition, with minor Mg substitution in malachite. Cu chlorides are mainly represented by clinoatacamite and probably herbertsmithite. Additional, minor phases include trace Cu minerals langite, wroewolfeite, and a lavendulan-group mineral, and monohydrocalcite. Separate halite-rich encrustations are shown to be filled with eriochalcite, ktenasite, and kröhnkite. The most likely to be confirmed coexisting species include paratacamite, wooldridgeite/nesquehonite, johillerite, melanothallite, and kipushite. The Lubin paragenesis mainly comprises aragonite, gypsum, rapidcreekite, and monohydrocalcite, with trace vaterite. Blue colouration is mainly provided by a yet unspecified Ni-, Co-, Mg-, and Mn-bearing Cu-Zn-Ca arsenate mineral close to parnauite. Full article

In this work, a thermodynamic model of CO₂-H₂O-NaCl-MgCO₃ systems is developed. The new model is applicable for 0–200 °C, 1–1000 bar and halite concentration up to saturation. The Pitzer model is used to calculate aqueous species activity coefficients and the Peng–Robinson model is used to calculate fugacity coefficients of gaseous phase species. Non-linear equations of chemical potentials, mass conservation, and charge conservation are solved by successive substitution method to achieve phase existence, species molality, pH of water, etc., at equilibrium conditions. From the calculated results of CO₂-H₂O-NaCl-MgCO₃ systems with the new model, it can be concluded that (1) temperature effects are different for different MgCO₃ minerals; landfordite solubility increases with temperature; with temperature increasing, nesquehonite solubility decreases first and then increases at given pressure; (2) CO₂ dissolution in water can significantly enhance the dissolution of MgCO₃ minerals, while MgCO₃ influences on CO₂ solubility can be ignored; (3) MgCO₃ dissolution in water will buffer the pH reduction due to CO₂ dissolution. Full article

Removal of calcium and magnesium ions through biomineralization induced by bacteria has been proven to be an effective and environmentally friendly method to improve water quality, but the process and mechanism are far from fully understood. In this study, a newly isolated probiotic Bacillus licheniformis SRB2 (GenBank: KM884945.1) was used to induce the bio-precipitation of calcium and magnesium at various Mg/Ca molar ratios (0, 6, 8, 10, and 12) in medium with 30 g L⁻¹ sodium chloride. Due to the increasing pH and HCO₃⁻ and CO₃²⁻ concentrations caused by NH₃ and carbonic anhydrase, about 98% Ca²⁺ and 50% Mg²⁺ were precipitated in 12 days. The pathways of bio-precipitation include extracellular and intracellular processes. Biominerals with more negative δ¹³C values (−16‰ to −18‰) were formed including calcite, vaterite, monohydrocalcite, and nesquehonite with preferred orientation. The nucleation on extracellular polymeric substances was controlled by the negatively charged amino acids and organic functional groups. The intracellular amorphous inclusions containing calcium and magnesium also contributed to the bio-precipitation. This study reveals the process and mechanism of microbial desalination for the removal of calcium and magnesium, and provides some references to explain the formation of the nesquehonite and other carbonate minerals in a natural and ancient earth surface environment. Full article