Hydrated Magnesium Carbonate Research Articles

Exploring Mechanisms of Hydration and Carbonation of MgO and Mg(OH)2 in Reactive Magnesium Oxide-Based Cements.

Reactive magnesium oxide (MgO)-based cement (RMC) can play a key role in carbon capture processes. However, knowledge on the driving forces that control the degree of carbonation and hydration and rate of reactions in this system remains limited. In this work, density functional theory-based simulations are used to investigate the physical nature of the reactions taking place during the fabrication of RMCs under ambient conditions. Parametric indicators such as adsorption energies, charge transfer, electron localization function, adsorption/dissociation energy barriers, and the mechanisms of interaction of H2O and CO2 molecules with MgO and brucite (Mg(OH)2) clusters are considered. The following hydration and carbonation interactions relevant to RMCs are evaluated: (i) carbonation of MgO, (ii) hydration of MgO, carbonation of hydrated MgO, (iii) carbonation of Mg(OH)2, (iv) hydration of Mg(OH)2, and (v) hydration of carbonated Mg(OH)2. A comparison of the energy barriers and reaction pathways of these mechanisms shows that the carbonation of MgO is hindered by the presence of H2O molecules, while the carbonation of Mg(OH)2 is hindered by the formation of initial carbonate and hydrate layers as well as presence of excessed H2O molecules. To compare these finding to bulk mineral surfaces, the interactions of the CO2 and H2O molecules with the MgO(001) and Mg(OH)2 (001) surfaces are studied. Therefore, this work presents deep insights into the physical nature of the reactions and the mechanisms involved in hydrated magnesium carbonates production that can be beneficial for its development.

Management of solid waste marble powder: improving quality of sodium chloride obtained from sulphate-rich lake/subsoil brines with simultaneous recovery of high-purity gypsum and magnesium carbonate hydrate.

Marble industry worldwide produces large amount of non-degradable marble dust powder (MDP) waste during mining and processing stages. MDP mainly comprises of CaCO3 with small amounts of Mg, Fe or Si in various forms. In India, mainly in Rajasthan state, marble is quarried in huge amounts and MDP thus produced is collected improperly and dumped at any abandoned land or identified disposal sites. On the other hand, the composition of sub soil/lake brines of Rajasthan is typical in nature as it does not have much Ca2+ and Mg2+ impurities but contains higher levels of SO42-. Therefore, the common salt (NaCl) produced from such brines is contaminated with Na2SO4 (8-30 wt%) depending upon SO42- concentration in the brine. Such a salt produced is suitable neither for edible purpose nor for industrial usage. Herein, we have reacted MDP with HCl, and the resulting solution (CaCl2 and MgCl2 slurry) is used in stoichiometric ratio of Ca2+ to SO42- in brines to produce high-purity NaCl and gypsum (CaSO4·2H2O) via fractional crystallization. Remaining magnesium-containing solution was reacted with Na2CO3 to prepare high purity magnesium carbonate hydrate. Purity of crystallized NaCl, CaSO4·2H2O and MgCO3·6H2O has been ascertained through analytical and spectral methods (TGA, FTIR, P-XRD). Field emission scanning electron microscopy was used to elucidate morphology of crystals. The method reported for improving purity of NaCl along with CaSO4·2H2O and MgCO3·6H2O production from sulphate-rich brines is simple and economic, and allows management of MDP generated in huge amounts, which poses problems of disposal.

High-performance Reactive Magnesium Cement Incorporating Hollow Natural Fiber and Silica Sand

Global warming caused by CO2 emissions makes reactive magnesium cement (RMC) increasingly attractive due to its ability to sequester CO2, however, the diffusion of CO2 in RMC is severely limited by the dense hydrated magnesium carbonates (HMCs) formed on the outer layer. This work utilizes hollow natural fiber (e.g., sisal fiber) to facilitate the diffusion of CO2 into the deep part of the RMC specimen. Combining with adding silica sand as a filling agent, the mechanical strength can be enhanced from 42.4 MPa of the control group to 92.6 MPa of the specimen with 2 vol.% sisal fiber, this is attributed to that the addition of sisal fiber significantly enhances the carbonation depth. FTIR and XPS results further prove that the addition of 2 vol.% or more sisal fiber can improve the carbonation degree by over 200%, leading to a sharp reduction of CO2 emission from 37 kg/(m3>MPa) of the control group to 12.1 kg/(m3∘MPa) of the specimen with 2 vol.% sisal fiber. Therefore, adding hollow natural fiber and silica sand to RMC can be a promising approach to make RMC stronger and more sustainable.

The transition from a closed to an open lake in the Pannonian Basin System (Croatia) during the Miocene Climatic Optimum: Sedimentological evidence of Early Miocene regional aridity

In the area of the North Croatian Basin, as the south-western part of the Pannonian Basin System, a lake that was characterized by mainly dolomite deposition evolved in the late Early Miocene. The dolomites precipitated directly from the water body, and are associated with tuffites and marls, together with minerals such as analcime, hydrous Ca-bearing magnesium carbonate, and natrolite. This indicates deposition in a shallow, hydrologically closed lake of highly alkaline waters controlled by an arid climate in the first stage of its evolution. The second evolutionary stage is represented by the intercalation of sandstones as a result of gravity flows, and dolomites that reflect changes of hydrologically open and closed lacustrine environments controlled by the frequent alternation of humid and arid climates. The third stage, that probably commenced in the Middle Miocene, indicates the formation of a long-lived, hydrologically mostly open lake, characterized by deposition of siliciclastics by gravity flows. The whole lacustrine depositional sequence coincides with the Miocene Climatic Optimum generally characterized by hot and warm, and humid climates. However, the evolution of the closed lake that is correlative with similar lakes in northern Bosnia and central Serbia, indicates the existence of an arid zone in the region that was confined by areas characterized by a more humid climate in the late Early Miocene.

On the carbonation of brucite: Effects of Mg-acetate on the precipitation of hydrated magnesium carbonates in aqueous environment

The role of organic ligands on the formation of hydrated magnesium carbonates (HMCs) has been remaining unclear. This work reports insights into the effects of Mg-acetate on the carbonation of brucite including the kinetics of reaction, the precipitation of different HMCs, and reaction mechanisms. We found that the organic ligand increases the kinetics of brucite's carbonation and alter the formation and conversion of HMCs. A relatively unknown phase (i.e., giorgiosite) precipitates in the presence of Mg-acetate with nanowire morphology. With the presence of acetate ligand, nucleation sites formed after the breakdown of Mg-acetate complexes and be replaced by the Mg–CO3 bonds. These sites act as a sink for Mg2+ to grow crystals and prevent the passivation layer of HMCs on brucite's surface. Findings reported here can enable an approach to steer pore solution chemistry in the HMC-based binder for better reaction degree, durability, and mechanical properties.

Biomimetic mineralization and characterization of hierarchically structured hydrated magnesium carbonates: The effects of sodium alginate

Recently, CO2 mineralization involving magnesium salt provides a feasible way for carbon sequestration. The produced hydrated magnesium carbonates (HMCs) can be used as functional materials and will bring huge economic benefits. Inspired by the mineralization in biological organisms, the indirect CO2 mineralization process involving NH4HCO3-MgCl2 in the presence of sodium alginate (SA) was systematically investigated. XRD, SEM, FTIR, TG and XPS were used to characterize the crystal phase, morphology, structure and surface of HMCs. By the regulation of temperature, HMCs with a complex hierarchical structure were successfully synthesized, i.e., sea urchin-like nesquehonite assembled by nanorods and 3D spiderweb-like hydromagnesite assembled by nanosheets. The presence of SA inhibits the phase transition from nesquehonite to hydromagnesite, and the inhibitory effect increases as the concentration of SA increases. By decreasing the molar ratio of Mg2+/HCO3−, the shape of nesquehonite particle changes from a sphere to an ellipsoid or a gourd. The spherical structure of nesquehonite is destroyed in a weak alkaline solution and the crystalline product is flower-like hydromagnesite in a strong alkaline solution. The decomposition process of HMCs is composed of dehydration (or dehydration and dehydroxylation) stage and decarbonation stage. XPS results for nesquehonite and hydromagnesite are quite different due to their different surface structure. This study will provide insights into the preparation of hierarchically structured HMCs by indirect CO2 mineralization and promote added values of HMCs by biomimetic mineralization method.

Recovery and direct carbonation of brucite from desalination reject brine for use as a construction material

This study investigated the direct carbonation of brucite recovered from reject brine of desalination plants and its mechanical property development as part of an assessment for its potential use as a construction material. Brucite nano-powder was synthesized from reject brine through chemical precipitation with calcium oxide (CaO). Formation of brucite with nano-platelet-like structures was observed. Compacted pellets produced with the brucite precipitates and exposed to 20% carbon dioxide (CO2) attained a 4-fold increase in the compressive strength (~30 MPa) within one day relative to those cured under the ambient condition. Thermogravimetry and morphological analyses of fragments extracted from the carbonated pellets revealed the formation of amorphous hydrated magnesium carbonates, which contributed to the matrix densification and strength gain. The findings confirm that brucite can be synthesized from reject brine with low-cost and energy-effective procedures and has the capability to sequester CO2, making it a promising and sustainable material for the construction industry.

Recycling carbonated reactive magnesium cement (RMC) as a building material

This study assessed the recyclability of reactive magnesium cement (RMC). To simulate the condition of construction waste recovery, a carbonated RMC-based paste was ground and used as a replacement for fresh RMC at 20 and 40 wt%. Both paste and mortar specimens were prepared and subjected to carbonation under 20% CO2, 80% RH, and 30 °C. Calorimetry data revealed that the main hydration peaks were delayed. The cumulative heat flow values were reduced, attributable to an increase in pore solution pH and physical barrier created by amorphous phases, which were confirmed by the appearance of broad peaks coinciding with those of hydromagnesite. Under carbonation, the peaks became more apparent due to the transformation of the phases into crystalline hydromagnesite. At 20 wt% replacement, the composite incorporated with the recycled RMC attained an improved strength performance due to more formation of the amorphous phases and hydrated magnesium carbonates (HMCs) from brucite.

Effect of hydrated magnesium carbonate grown in situ on the property of MgO-activated reactive SiO2 mortars

The effects of carbonation on the strength and microstructural evolution of MgO-activated reactive SiO2 (M-A-R-S) mortars under different conditions have been investigated. M-A-R-S mortars with a binder-to-silica sand ratio of 50% were prepared by light-calcined MgO and silica fume (SF) under accelerated carbonation at 20% CO2 condition for different periods. Carbonation significantly increases the compressive strength of M-A-R-S mortars. The specimens cured for 28 days in air and placed to accelerated carbonation for ∼14 days achieved the highest strength of ∼83 MPa and the lowest porosity of 13.5%. The increased strength and density resulted from the formation of the hydrated magnesium carbonate (i.e. nesquehonite (MgCO3·3H2O) with a needle/column-like morphology. However, it was also found that continuous carbonation for longer periods (e.g. 28 days), associated with excessive carbonated phase(s) formed, caused micro-cracking and a reduction in compressive strength.

Mechanical and microstructural changes in reactive magnesium oxide cement-based concrete mixes subjected to high temperatures

This study investigated the mechanical, microstructural, and chemical changes in reactive MgO cement-based concrete cured under ambient and accelerated carbonation conditions, followed by exposure to high temperatures. The compressive strength of the ambient-cured samples increased from 10 to 30 MPa when subjected to up to 200 °C, induced by increased hydration of the remaining MgO. The accelerated formation of brucite at 50 °C also enhanced the compressive strength of the carbonated samples (58 vs. 65 MPa). A relatively stable performance (~56 MPa) was observed at temperatures ranging between 100 and 300 °C for the carbonated samples, associated with additional formation of brucite and transition of nesquehonite and hydromagnesite to artinite. The hydrated magnesium carbonates (HMCs) forming around brucite acted as barriers and delayed its dehydroxylation. The decomposition of brucite and HMCs at 400 °C caused a porous microstructure and a low residual strength (5–8 MPa) in both the ambient-cured and carbonated samples.

Syntheses of Nanostructured Magnesium Carbonate Powders with Mesoporous Structures from Carbon Dioxide

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.

Effect of calcination temperature on the light burned MgO matrix and its physical properties

ABSTRACT Light-burned MgO cement has a lower calcination temperature than ordinary Portland cement. It has been widely studied as a measure to reduce carbon dioxide because of its property of absorbing carbon dioxide during curing. This study investigated the effects of calcination temperature on the physical properties of light hydrated magnesium carbonate and calcined MgO hydrated in moisture and CO2 at 25 °C and 60 °C. The crystal size of light-burned MgO increased with increasing calcination temperature, and carbonates were formed through carbonation curing. Further, nesquehonite and hydromagnesite were formed in the 25CC and 60CC specimens, respectively, and the carbonate formation reduced with increasing crystal size. The highest compressive strength of 3.5 MPa was obtained for the 25CC specimen in which nesquehonite was formed; however, hydromagnesite exhibited better CO2 sequestration capacity.

Bacteria-induced internal carbonation of reactive magnesia cement

With lower calcination temperature, reactive magnesia cement (RMC) can be a potential alternative to the Portland cement. However, RMC concrete requires accelerated carbonation curing from external sources which greatly hinder the wider applications of RMC. This study proposed a bacteria-based method for the strength gain of RMC through internal carbonation. Sporosarcina pasteurii, urea, and yeast extract were used as a carbonation agent for internal carbonation of RMC pastes. Results showed that the flowability of the fresh bio-RMC paste increased by 20% while the initial setting time remained unchanged. Besides serving as the CO2 provider, urea can also function as superplasticizer to reduce the water demand of the bio-RMC pastes. The resulting bio-RMC pastes showed a continuous strength gain with time, demonstrating the feasibility of bacteria-induced internal carbonation of RMC. Microstructure analysis revealed abundant formation of hydrated magnesium carbonates in the bio-RMC pastes, which is responsible for the strength gain of the bio-RMC pastes.

Rare hydrated magnesium carbonate minerals of the kimberlite pipe Obnazhennaya, The Yakutian Kimberlite Province

The first discovery of hydrated magnesium carbonates, dypingite and nesquehonite, in the kimberlite pipe Obnazhennaya of the Kuoyka field, the Yakutian kimberlite province is described. The pipe is composed of kimberlite breccia with abundant diverse xenoliths of practically intact mantle rocks. Olivine in phenocrysts and mantle rock is generally intact. The main body of the rock is carbonate-serpentine. Nesquehonite and dypingite are rare minerals and have first been observed in relation to kimberlites. The minerals were found in the bedrock outcrop of the Obnazhennaya pipe as white crusts up to 5 mm thick scattered over an area of a few tens of square meters. To identify and study the crusts we used the following methods: powder X-ray diffraction, electron microscopy, and Raman scattering spectroscopy. A comprehensive study suggests that the main minerals of these epigenetic formations are hydrated carbonates: nesquehonite MgCO3□3H2O and dypingite Mg5(CO3)4(OH)2□5H2O. Also, Raman scattering spectroscopy revealed a small proportion of hydromagnesite Mg5(CO3)4(OH)2□4H2O. Hydrated magnesium carbonate minerals we found make a significant contribution to the collection of kimberlites. They are epigenetic in nature, with their origin being related to weathering of silicates, in particular serpentine. Mechanisms of carbonate formation appear to be close to that suggested by Wilson et. al., 2009, with CO2 being trapped from the atmosphere to form nesquehonite. In the case of the Obnazhennaya pipe, mineral solutions form when rainwater filters through the talus at the top of the outcrop. They are enriched in Mg from minerals and trap CO2 from the atmosphere. After filtering, solutions reach the vertical wall of kimberlite breccia where modern precipitation of nesquehonite upon evaporation occurs. Further, dypingite and hydromagnesite form via decomposition of nesquehonite. A lip extending over the rock wall significantly contributes to the development and stability of nesquehonite and dypingite aggregates. Crusts of nesquehonite and dypingite are not found on rock outcrops without lips at the top. Thus, despite the fact that intrusion of the kimberlite pipe occurred during the Jurassic (Zaitsev, Smelov, 2010), formation of nesquehonite and dypingite in association with kimberlite rocks continues in the modern time due to favorable environmental factors, first of all, a unique natural outcrop of kimberlite.

Enhancing the performance of MgO-activated slag-fly ash mixes by accelerated carbonation

This study focused on the development of reactive MgO (RM) activated-GGBS binders containing fly ash (FA). Performance of these binders was aimed to be improved by enhancing the hydration of RM and dissolution of GGBS and FA via high temperature pre-curing (HTPC); and conversion of unreacted phases into carbonates via carbonation. Spherical FA particles mitigated inter-particle surface frictions and improved flow. Although the use of HTPC accelerated the hydration of MgO, rapid precipitation of brucite hindered the dissolution of GGBS and FA and formation of associated hydration products. Transformation of RM into hydrated magnesium carbonates (HMCs) under carbonation led to significant improvements in sample performance via the pore filling effect and binding strength provided by HMCs, despite the degradation of ettringite and C-(A)-S-H during carbonation. Inclusion of 12 % FA resulted in comparable strengths to the control sample, highlighting the feasibility of incorporating FA within RM activated-GGBS samples without compromising performance.

Influence of crack width on the stiffness recovery and self-healing of reactive magnesia-based binders under CO2-H2O conditioning

This study investigated the healing efficiency and phase formations in pre-cracked reactive magnesia-based binders under CO2/water conditioning. Pre-loaded samples with various crack widths were subjected to a healing regime involving 10% CO2 and water for 10 cycles. The recovery of samples was assessed by resonance frequency measurements and optical microscopy observations. A relationship between crack width and type of healing phases was established via microstructural analysis and carbonation depth measurements. All samples achieved a complete stiffness recovery after a few healing cycles. The healed cracks revealed a higher stiffness than the surrounding matrix under reloading. The recovery of sample stiffness was associated with the densification of sample microstructure via the formation of hydrated magnesium carbonates (HMCs). Depending on the crack width and depth, two different types of HMCs (nesquehonite and hydromagnesite) were observed within the healed cracks, whose formation was influenced by pH, determined by the diffusion of CO2.

Biocarbonation of reactive magnesia for soil improvement

This paper presents a new microbial technique for soil improvement through microbially induced carbonate precipitation (MICP) incorporating with reactive magnesia cement (RMC). Through a microbially induced carbonate precipitation (MICP) process, hydrated magnesium carbonates (HMCs) are produced due to biological carbonation of hydrated RMC, which then act as cementation agents to bind soil particles. The influence of several parameters including the RMC content, urea content, and water content on the MICP efficiency was investigated. The performance of the biocarbonated RMC-based sand samples was evaluated using unconfined compressive strength and permeability measurements. Microstructural analyses including scanning electron microscope, X-ray diffraction, and thermogravimetric analysis were also performed to understand the mechanisms behind the treatment. Biocarbonated RMC-based sand samples were compared with the biocement-treated samples using the conventional MICP method. The experimental results indicated the formation of different types of biocarbonation phases enabled by the carbonate ions produced by urea hydrolysis via microbial metabolism. These phases, identified as HMCs, have provided strong bonding to loose sand particles to increase its early strength. The HMCs also occupy the pores of sand matrix to reduce its permeability. The unconfined compressive strength gained at 28 days was up to 2.3 MPa, and the reduction in permeability was up to 1.8 × 10−7 m/s among the tests carried out. The obtained findings have demonstrated that the biocarbonation of reactive magnesia approach is effective for soil improvement.

Improving the carbonation resistance of Na2CO3-activated slag mixes via the use of reactive MgO and nucleation seeding

When exposed to carbonation, Na2CO3-activated slag (SCAS) concrete demonstrated 53% mass loss and 57% reduction in compressive strength due to the decalcification of C-(A)-S-H. Improvements in the carbonation resistance of SCAS mixes via the inclusion of hydromagnesite seeds (S) and reactive MgO (M) were reported in this study. The conversion of MgO into hydrated magnesium carbonates (HMCs) and the additional formation of hydrotalcite were observed in the presence of these additives. HMCs contributed to the binding network and limited the diffusion of CO2 into the sample. The decalcification of C-(A)-S-H was retarded via the absorption of CO2 in hydrotalcite, producing huntite. These changes in the reaction kinetics of samples involving M and S enabled the retention of hydration products and formation of additional carbonation products, leading to denser microstructures and ~40% increase in compressive strength after carbonation, which was ~10 times higher than the control sample (58 vs. 6 MPa).

Influence of CO2 concentration on the performance of MgO cement mixes

This paper investigated the influence of different CO2 concentrations on the microstructural and mechanical development of reactive MgO cement (RMC) concrete. Combination of various analyses revealed the enhancement of hydrated magnesium carbonate (HMC) phases with relatively superior micro-mechanical properties as the CO2 concentration increased from ambient (~0.04%) to accelerated (5–20%) levels. The higher CO2 diffusion within samples cured under 5–20% CO2 increased the compressive strength by ~5 times. While samples cured under 20% CO2 revealed high early strengths, the formation of a dense HMC layer on the sample exterior led to limitations on further CO2 diffusion. Use of 5% CO2 produced comparable strengths as 20% CO2 at 28 days, highlighting the potential of using lower concentrations. Samples cured under 10% CO2 revealed the best performance at 28 days, thereby defining this environment as the most favorable condition for the development of microstructural and mechanical properties of RMC concrete.

Simulations on Design and System Performance of Building Heating Boosted by Thermal Energy Storage (TES) with Magnesium Hydro Carbonates/Silica Gel

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.