Hydrated Magnesium Carbonate Research Articles

Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks

Magnesium carbonate minerals produced by reaction of H2O–CO2 with ultramafic rocks occur in a wide range of paragenetic and tectonic settings and can thus provide insights into a variety of geologic processes, including (1) deposition of ore-grade, massive-vein cryptocrystalline magnesite; (2) formation of hydrous magnesium carbonates in weathering environments; and (3) metamorphic carbonate alteration of ultramafic rocks. However, the application of traditional geochemical and isotopic methods to infer temperatures of mineralization, the nature of mineralizing fluids, and the mechanisms controlling the transformation of dissolved CO2 into magnesium carbonates in these settings is difficult because the fluids are usually not preserved. Clumped-isotope compositions of magnesium carbonates provide a means to determine primary mineralization or (re)equilibration temperature, which permits the reconstruction of geologic processes that govern magnesium carbonate formation. We first provide an evaluation of the acid fractionation correction for magnesium carbonates using synthetic magnesite and hydromagnesite, along with natural metamorphic magnesite and low-temperature hydromagnesite precipitated within a mine adit. We show that the acid fractionation correction for magnesium carbonates is virtually indistinguishable from other carbonate acid fractionation corrections given current mass spectrometer resolution and error. In addition, we employ carbonate clumped-isotope thermometry on natural magnesium carbonates from various geologic environments and tectonic settings. Cryptocrystalline magnesite vein deposits from California (Red Mountain magnesite mine), Austria (Kraubath locality), Turkey (Tutluca mine, Eskişehir district) and Iran (Derakht-Senjed deposit) exhibit broadly uniform Δ47 compositions that yield apparent clumped-isotope temperatures that average 23.7±5.0°C. Based on oxygen isotope thermometry, these clumped-isotope temperatures suggest mineralization at shallow crustal depths in the presence of meteoric water. Hydrous magnesium carbonates from a 400-km latitudinal transect along the serpentinized-peridotite bodies of the California Coast Ranges record clumped-isotope temperatures between 14.2 and 22.7±2.8°C, in agreement with historical maximum temperatures during the rainy season for California. Talc–carbonate alteration of ultramafic rocks in Greenland (Isua Supracrustal Belt) and Vermont (Ludlow) yields clumped-isotope alteration temperatures of magnesite and dolomite between 326 and 490°C, broadly consistent with paragenesis and thermodynamic analysis for CO2 metasomatism of ultramafic rocks. These metamorphic carbonates extend the applicability of clumped-isotope thermometry to high-temperature magnesium carbonate systems and indicate equilibrium blocking temperatures for magnesite of ∼490°C. Our study demonstrates the applicability of the clumped isotope approach to provide information on the formation of magnesium carbonates as ore resources, surface records of climate, and metamorphic assemblages.

Recovery of magnesium from Uyuni salar brine as hydrated magnesium carbonate

Uyuni salar (Bolivia), the largest resource of lithium (Li) in the world not only contains a high level of Li but also ~1.3% w/w magnesium (Mg) in strong NaCl brines. The recovery of Mg is therefore essential as the resources represent high value of Mg by-products if recovered. High purity hydrated magnesium carbonate (HMC as dypingite or hydromagnesite) could be recovered from the Uyuni salar brines as an easy-saleable product. The precipitation process used for this recovery relies on the selective removal of Ca by adding excess oxalic acid at an oxalate/Ca molar ratio of 6.6:1. The excess oxalate has to be subsequently removed as Mg oxalate by adjusting the pH to pH 4–7. HMC products of 97.3–99.6% purity could be produced as a result (equivalent to 25.3–25.9% Mg in the product compared to a theoretical value of 25.99% Mg for hydromagnesite). Without removing Mg oxalate, products could only reach 23.3–24.3% Mg. The light HMC (hydromagnesite) product could be precipitated at ambient conditions as long as the drying was set at >65°C. Precipitation at >55°C also yields more crystalline hydromagnesite compared to those obtained at lower temperatures. The light HMC product has a heat adsorbing capacity (endothermic) of 1123–1196J/g dry product. The product has a sheet-like structure and is easily filtered, compared to magnesium hydroxide.

Transformation of amorphous calcium carbonate into monohydrocalcite in aqueous solution: a biomimetic mineralization study

Monohydrocalcite (MHC, CaCO 3 · H 2 O) is a thermodynamically metastable phase relative to calcite and aragonite in aqueous solution. Although MHC occurs broadly in organisms, little information about its biogenic origin is available. In this paper, a series of amorphous calcium carbonates (ACCs) with different Mg 2+ contents were first synthesized in the presence of polyaspartic acid (PASP), and the phase transformations of the PASP-regulated Mg-ACCs (PASP-Mg-ACCs) were then studied under different medium conditions. The structure, morphology and composition of the precursor PASP-Mg-ACCs and transformation products were investigated by using a wide range of techniques, including XRD, FT-IR, FESEM, TG-DTA, 13 C NMR and ICP-AES. Our results show that PASP-Mg-ACC with 24.71 mol% Mg 2+ can be transformed into MHC, without formation of hydromagnesite or other hydrated magnesium carbonates, whereas the PASP-Mg-ACCs with 2+ resulted in magnesian calcite and aragonite. Time-course transition experiments unveiled that the transformation from PASP-Mg-ACCs to crystalline phases proceeds through the dissolution of the initial precursor PASP-Mg-ACCs and the subsequent crystallization of the secondary mineral phases. The formation of different secondary minerals depends not only on the Mg 2+ but also on the PASP content in precursor PASP-Mg-ACCs. Because of the exclusive formation of MHC from PASP-Mg-ACC under current biomimetic conditions, biomacromolecule-regulated Mg-ACC may act as the transient precursor and be responsible for the biogenesis of MHC. The current results contribute to the elucidation of the biogenic origin and role of MHC in nature.

Reply to the discussion of the papers “Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements” and “Enhancing the carbonation of MgO cement porous blocks through improved curing conditions”, by S.A. Walling and J.L. Provis

This paper is a reply to the discussion by S.A. Walling and J.L. Provis on our papers “Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements” and “Enhancing the carbonation of MgO cement porous blocks through improved curing conditions”. Walling and Provis discuss the assignment of X-ray diffraction patterns, the use of acid digestion to quantify the degree of carbonation, the interpretation of thermal analysis data, and the stability of hydrated magnesium carbonates. In this reply, we confirm the conclusions made in the two papers based on the combined evidence of microstructural and mechanical performance results.

A discussion of the papers “Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements” and “Enhancing the carbonation of MgO cement porous blocks through improved curing conditions”, by C. Unluer & A. Al-Tabbaa

This paper is a discussion of two recent papers by Unluer & Al-Tabbaa which analysed accelerated carbonation of reactive MgO blocks. We suggest that the authors have incorrectly analysed key data, leading to overstated claims of MgO carbonation. Based on the reassignment of their X-ray diffraction data, it is proposed that little MgO carbonation occurred in the samples discussed in those papers, with CaCO3 instead forming during accelerated carbonation. We also draw attention to the thermodynamic instability of nesquehonite under ambient conditions, which calls into question the long-term stability of these binders.

The continuous re-equilibration of carbon isotope compositions of hydrous Mg carbonates in the presence of cyanobacteria

The hydrous magnesium carbonate minerals dypingite (Mg5(CO3)4(OH)2·5H2O) and nesquehonite (MgCO3·3H2O) were precipitated in the presence and absence of Gloeocapsa sp. and Synechococcus sp. cyanobacteria in batch reactors. The Δ13Cmineral–DIC is similar in both biotic and abiotic systems. Stable carbon isotope analyses of the precipitated minerals and co-existing fluids indicated that the δ13C values of the precipitated carbonates co-vary over time with the δ13CDIC of the fluid phase, even after the precipitation of the carbonate is complete. This observation indicates the continuous isotopic exchange between the carbonates and the fluid, a process that efficiently resets the original δ13C values of the solids. Therefore although cyanobacterial-induced Mg carbonates are 10±5‰ enriched in 13C compared to inorganic carbonates, the δ13C values of natural hydrous Mg carbonates may reflect post precipitation processes and may not be reliable for paleo-environmental reconstructions.

Directed precipitation of hydrated and anhydrous magnesium carbonates for carbon storage.

Magnesite is the most desirable phase within the magnesium carbonate family for carbon storage for a number of reasons: magnesium efficiency, omission of additional crystal waters and thermodynamic stability. For large-scale carbonation to be a viable industrial process, magnesite precipitation must be made to occur rapidly and reliably. Unfortunately, the formation of metastable hydrated magnesium carbonate phases (e.g. MgCO3·3H2O and Mg5(CO3)4(OH)2·4H2O) interferes with the production of anhydrous magnesite under a variety of reaction conditions because magnesite crystals are slower to both nucleate and grow compared to the hydrated carbonate phases. Furthermore, the reaction conditions required for the formation of each magnesium carbonate phases have not been well understood with conflicting literature data. In this study, the effects of both magnesite (MgCO3) and inert (Al2O3) seed particles on the precipitation of magnesium carbonates from a Mg(OH)2 slurry were explored. It was interesting that MgCO3 seeding was shown to accelerate anhydrous magnesite growth at temperatures (80-150 °C), where it would normally not form in short time scale. Since the specific surface areas of MgCO3 and Al2O3 seeding particles were similar, this phenomenon was due to the difference in the surface chemistry of two seeding particles. By providing a template with similar chemistry for the growth of magnesite, the precipitation of anhydrous magnesite was demonstrated. The effect of temperature on seeded carbonation was also investigated. A comparison with published MgCO3 precipitation rate laws indicated that the precipitation of magnesite was limited by either CO2 adsorption from the gas phase or the dissolution rate of Mg(OH)2.

Process optimization for mineral carbonation in aqueous phase

Carbon dioxide sequestration by a pH-swing carbonation process was considered in this work. A multi-step aqueous process is described for the fractional precipitation of magnesium carbonate and other minerals in an aqueous system at room temperature and atmospheric pressure. With the aim to achieve higher purity and deliver more valuable mineral products, the process was split into four steps. The first step consists of Mg leaching from the magnesium silicate in a stirred vessel using 1M HCl at 80°C, followed by a three step precipitation in reactors in sequence to remove Fe(OH)3, then Fe(OH)2 and other divalent ions, and finally MgCO3 nucleation and growth. Hydrated magnesium carbonate [MgCO3∙3H2O, nesquehonite] crystals were confirmed using X-ray diffraction (XRD) as final products. The optimal pH of precipitation reactors based on the maximum solid purity and production was determined by carrying out detailed mass balance. The maximum productivity and highest purity for nesquehonite were found to be dependent on pH values for the two last steps. The results also demonstrated that the process is optimized at pH9 and 10 for the second and third step of precipitation, respectively. The highest carbonation efficiency expressed as the conversion of Mg ions to magnesium carbonate reached 82.5 wt %. The maximum magnesium content in the final product was 99.21 wt % of MgO when the second precipitation reactor pH was equal to 9. This experimental study demonstrates that carbon dioxide sequestration requires at least 3.74 times the weight of ore to provide the Mg for mineral production. This confirms the possibility to use this process route for CO2 mitigation.

Solid products characterization in a multi-step mineralization process

In this paper, we describe a carbon dioxide mineralization process and its associated solid products. These solid products include amorphous silica, iron hydroxides and magnesium carbonates. These products were subjected to various characterization tests, and the results are published here. It was found that the iron hydroxides from this process can have different crystalline properties, and their formation depended very much on the pH of the reaction conditions. Different forms of magnesium carbonate were also obtained, and the type of carbonate precipitated was found to be dependent on the carbonation temperature. Hydromagnesite was obtained mainly at low temperatures, while dypingite was obtained at higher temperatures. Near ambient conditions, nesquehonite was the predominant form of magnesium carbonate obtained. The process mass balance shows that 3.1 tonne of hydrated magnesium carbonate with 99.82 wt% purity is obtained for each tonne of CO2 sequestrated. And for each tonne of carbon dioxide sequestrated, about 3.74 tonnes of mineral ore are needed as a source of magnesium.

Ab Initio Thermodynamic Model for Magnesium Carbonates and Hydrates

An ab initio thermodynamic framework for predicting properties of hydrated magnesium carbonate minerals has been developed using density-functional theory linked to macroscopic thermodynamics through the experimental chemical potentials for MgO, water, and CO2. Including semiempirical dispersion via the Grimme method and small corrections to the generalized gradient approximation of Perdew, Burke, and Ernzerhof for the heat of formation yields a model with quantitative agreement for the benchmark minerals brucite, magnesite, nesquehonite, and hydromagnesite. The model shows how small differences in experimental conditions determine whether nesquehonite, hydromagnesite, or magnesite is the result of laboratory synthesis from carbonation of brucite, and what transformations are expected to occur on geological time scales. Because of the reliance on parameter-free first-principles methods, the model is reliably extensible to experimental conditions not readily accessible to experiment and to any mineral composition for which the structure is known or can be hypothesized, including structures containing defects, substitutions, or transitional structures during solid state transformations induced by temperature changes or processes such as water, CO2, or O2 diffusion. Demonstrated applications of the ab initio thermodynamic framework include an independent means to evaluate differences in thermodynamic data for lansfordite, predicting the properties of Mg analogues of Ca-based hydrated carbonates monohydrocalcite and ikaite, which have not been observed in nature, and an estimation of the thermodynamics of barringtonite from the stoichiometry and a single experimental observation.

A CCS Mineralization Process: Investigation of the Production of Magnesium Carbonates from Magnesium Chloride Solution

Abstract Carbon Capture and Storage (CCS) is considered as a promising technology to remediate the severe carbon dioxide release in the atmosphere. Mineralization in the storage process has several advantages, and its products can be used as low carbon footprint construction materials –magnesium oxide (MgO) cement. It is thought as a good replacement of traditional Portland Cement (PC) from both technical and environmental perspectives. In this study, MgO was obtained by mixing pure magnesium chloride and CO2 under alkaline condition, to produce hydrated magnesium carbonates as the intermediate product; and then calcined into the final one. This part of research presented in the paper mainly focused on the first stage of carbonation process, and investigated the importance of the pH effect, while other reaction parameters were fixed during the reaction. Filtrates and precipitates were then analysed by ICP and XRD respectively, and the results showed pH>9 has good performance in precipitation, and all the sediments formed in a short time are irrelevant to pH.

Impact of hydrated magnesium carbonate additives on the carbonation of reactive MgO cements

Reactive magnesia (MgO) cements have emerged as a potentially more sustainable and technically superior alternative to Portland cement due to their lower production temperature and ability to sequester significant quantities of CO2. Porous blocks containing MgO were found to achieve higher strength values than PC blocks. A number of variables are investigated to achieve maximum carbonation and associated high strengths. This paper focuses on the impact of four different hydrated magnesium carbonates (HMCs) as cement replacements of either 20 or 50%. Accelerated carbonation (20°C, 70–90% RH, 20% CO2) is compared with natural curing (20°C, 60–70% RH, ambient CO2). SEM, TG/DTA, XRD, and HCl acid digestion are utilized to provide a thorough understanding of the performance of MgO-cement porous blocks. The presence of HMCs resulted in the formation of larger size carbonation products with a different morphology than those in the control mix, leading to significantly enhanced carbonation and strength.

Atenolol characterization in solid formulations available in Brazilian market

Atenolol is the most used drug in Brazil to hypertension treatment. Two crystal structures are known for this molecule: a racemic form (R,S)-atenolol and a pure form S-atenolol. The racemic form is found in commercial tablets. X-ray powder diffraction (XRD) is an adequate tool to study crystalline structures including drugs. Using the Rietveld Method with XRD data it is possible to quantify the crystalline structures existing in the raw material. Other methods like Le Bail and Pawley can be used to the profile fit and phases identification. For this work we analyzed three tablets of atenolol, two generics and the reference (materials were purchased from a drugstore at the city of Araraquara). These tablets were analyzed by Rietveld, Le Bail and Pawley methods. All tablets exhibited the racemic mixture API (R,S)-atenolol. Some crystalline excipients could be characterized: magnesium carbonate hydrate, lactose monohydrate and talc. The conclusion is that the three methods can be efficiently used to characterize the three atenolol tablets.

Carbonating magnesia for soil stabilization

This paper investigates the potential for carbonating reactive magnesia (MgO) to serve as a more sustainable soil stabilization method by providing rapid and significant strength development of the stabilized soil through absorbing substantial quantities of CO2. Gaseous CO2was forced through laboratory-prepared reactive MgO-treated soil samples in a triaxial cell set-up, and their resulting mechanical and microstructural properties were investigated using unconfined compressive strength, X-ray diffraction, and scanning electron microscopy. The results showed that adequately carbonated MgO-treated soils could, in a few hours, reach a similar strength range to corresponding 28 day Portland cement (PC)-stabilized soils. Hydrated magnesium carbonates, namely nesquehonite and hydromagnesite–dypingite, were the main products of the carbonated MgO in the soil, and were responsible for the significant strength development.

Characterization of light and heavy hydrated magnesium carbonates using thermal analysis

Upon heating, hydrated magnesium carbonates (HMCs) undergo a continuous sequence of decomposition reactions. This study aims to investigate the thermal decomposition of various commercially produced HMCs classified as light and heavy, highlight their differences, and provide an insight into their compositions in accordance with the results obtained from thermal analysis and microstructure studies. An understanding of the chemical compositions and microstructures, and a better knowledge of the reactions that take place during the decomposition of HMCs were achieved through the use of SEM, XRD, and TG/differential thermal analysis (DTA). The quantification of their CO2 contents was provided by TG and dissolving the samples in HCl acid. Results show that variations exist within the microstructure and decomposition patterns of the two groups of HMCs, which do not exactly fit into the fixed stoichiometry of the known HMCs in the MgO–CO2–H2O system. The occurrence of an exothermic DTA peak was only observed for the heavy HMCs, which was attributed to their high CO2 contents and the relatively delayed decomposition pattern.

Preliminary Laboratory-Scale Model Auger Installation and Testing of Carbonated Soil-MgO Columns

Abstract This paper presents details of the installation and performance of carbonated soil-MgO columns using a laboratory-scale model auger setup. MgO grout was mixed with the soil using the auger and the columns were then carbonated with gaseous CO2 introduced in two different ways: one using auger mixing and the other through a perforated plastic tube system inserted into the treated column. The performance of the columns in terms of unconfined compressive strength (UCS), stiffness, strain at failure and microstructure (using X-ray diffraction and scanning electron microscopy) showed that the soil-MgO columns were carbonated very quickly (in under 1 h) and yielded relatively high strength values, of 2.4–9.4 MPa, which on average were five times that of corresponding 28-day ambient cured uncarbonated columns. This confirmed, together with observations of dense microstructure and hydrated magnesium carbonates, that a good degree of carbonation had taken place. The results also showed that the carbonation method and period have a significant effect on the resulting performance, with the carbonation through the perforated pipe producing the best results.

Atmospheric corrosion of two field-exposed AZ31B magnesium alloys with different grain size

A fine-grained AZ31B alloy and a commonly hot-extruded AZ31B alloy with coarser grains were exposed to marine and urban environments for 1year, and the atmospheric corrosion behavior of the AZ31B alloys was investigated. The fine-grained AZ31B alloy displays slightly higher corrosion resistance than the commonly hot-extruded AZ31B, particularly in urban environment. Magnesium carbonate hydrate and hydromagnesite are principal corrosion products of the two AZ31B alloys in both marine and urban environments. Besides, it is found that Al–Mn intermetallic particles have little influence on the atmospheric corrosion of the AZ31B alloys.

A facile template free solution approach for the synthesis of dypingite nanowires and subsequent decomposition to nanoporous MgO nanowires with excellent arsenate adsorption properties

In this paper, one-dimensional (1-D) dypingite (hydrated magnesium carbonate hydroxide, Mg5(CO3)4(OH)2·5H2O) nanowires with several hundreds micrometers in length were synthesized at 100 °C by a simple solution method without using any template or catalyst for the first time. A plausible diffusion growth model for the growth of the dypingite nanowires was proposed. The influences of the magnesium ion concentrations and the magnesium sources on the structures of the products were also studied. The as-synthesized nanowires were an excellent precursor for the fabrication of 1-D nanoporous magnesium oxide (MgO) nanowires via a simple thermal transformation process. Room temperature photoluminescence studies suggest that the nanoporous MgO nanowires show a strong ultraviolet emission and a weak blue emission. The adsorption properties of the porous MgO nanowires were investigated for As(V) removal. A high As(V) adsorption capacity of 384.6 mg g−1 was realized, which was resulted from the reaction between the As(V) species and MgO in aqueous solution.

Effect of H2O on Mg(OH)2 carbonation pathways for combined CO2 capture and storage

Mg-bearing sorbents, derived from silicate minerals and industrial wastes, can act as combined carbon capture and storage media in various energy conversion systems. Mg(OH)2 carbonation in the slurry phase occurs spontaneously and recent results show improved gas–solid carbonation with comparable materials in the presence of H2O vapor; however, the reaction mechanism is still poorly understood at high temperature and pressure conditions. This study investigated the pathways of H2O enhanced Mg(OH)2 carbonation at elevated temperatures and CO2 pressures (up to 673K and 1.52MPa) in the presence of steam and in the slurry phase. For a given reaction temperature, carbonation conversion showed dramatic increase with increasing H2O loading. Comprehensive solid analyses via thermogravimetric analysis, X-ray diffraction, and UV-Raman allowed for qualitative and quantitative compositional characterization of reacted solids. The results suggest that a hydrated environment facilitates the formation of intermediate hydrated magnesium carbonate species. The hydrated carbonates form relatively quickly and can transform into anhydrous carbonates while subjected to greater H2O loading, higher temperature, and/or longer reaction time.

Formation condition of monohydrocalcite from CaCl2–MgCl2–Na2CO3 solutions

Monohydrocalcite (MHC: CaCO3·H2O) is a rare mineral in geological settings. Its rare occurrence indicates that MHC forms in unique environmental conditions in nature. Both laboratory studies and natural observations have indicated that the formation of MHC requires magnesium in the solution in spite of the incompatibility of magnesium into the MHC structure. In this study, systematic syntheses from CaCl2–MgCl2–Na2CO3 solutions were conducted to elucidate MHC formation conditions and to clarify the role of magnesium in MHC formation.For this study, MHC was formed from mixing solutions of which the ratio of the total carbonate to calcium was higher than 1 in the presence of a certain amount of magnesium. The pH of the reacted solutions after the MHC formation was 9.8–11.0. The solid-phase magnesium contents in the formed precipitates were widely varied. MHC exhibits low crystallinity and small particle size when the ratio of magnesium to calcium in the solid was higher than 0.4. After MHC formation, ion activity products of the reacted solutions with respect to MgCO3·xH2O stoichiometry took almost constant values. The ion activity products were significantly higher than the solubility product of anhydrous MgCO3, but they were close to the solubility of nesquehonite, which indicates that MHC formation of requires paragenesis of the hydrous magnesium carbonate. To produce the hydrous magnesium carbonate simultaneously with MHC, the initial solution must contain magnesium and more CO32- than Ca2+, which is consistent with the formation conditions of MHC from the initial solution compositions.Magnesium ion possesses a high hydration energy. The hydrous magnesium carbonates surrounding MHC probably play a protective role for MHC in preventing its dehydration to anhydrous calcium carbonate. The solution chemistries of saline lakes of which the MHC formation was observed in nature are also at equilibrium or are oversaturated with respect to hydrous magnesium carbonates and MHC. Rare occurrences of MHC in nature are explainable by the paragenesis requirements of hydrous magnesium carbonates and by the metastability of MHC.