Hydrated Magnesium Carbonate Research Articles

Forsterite [Mg2SiO4)] Carbonation in Wet Supercritical CO2: An in Situ High-Pressure X-ray Diffraction Study

Mechanisms controlling mineral stabilities in contact with injected supercritical fluids containing water are relatively unknown. In this paper, we discuss carbonation reactions occurring with forsterite (Mg(2)SiO(4)) exposed to variably wet supercritical CO(2) (scCO(2)). Transformation reactions were tracked by in situ high-pressure X-ray diffraction in the presence of scCO(2) containing dissolved water. Under modest pressures (90 bar) and temperatures (50 °C), scCO(2) saturated with water converted >70 wt % forsterite to a hydrated magnesium carbonate, nesquehonite (MgCO(3) · 3H(2)O), and magnesite (MgCO(3)) after 72 h. However, comparable tests with scCO(2) at only partial water saturation showed a faster carbonation rate but significantly less nesquehonite formation and no evidence of the anhydrous form (MgCO(3)). The presence and properties of a thin water film, observed by in situ infrared (IR) spectroscopy and with isotopically labeled oxygen ((18)O), appears to be critical for this silicate mineral to carbonate in low water environments. The carbonation products formed demonstrated by temperature and water-content dependence highlights the importance of these kinds of studies to enable better predictions of the long-term fate of geologically stored CO(2).

Using Mg Isotopes to Trace Cyanobacterially Mediated Magnesium Carbonate Precipitation in Alkaline Lakes

This study assesses the potential use of Mg isotopes to trace Mg carbonate precipitation in natural waters. Salda Lake (SW Turkey) was chosen for this study because it is one of the few modern environments where hydrous Mg carbonates are the dominant precipitating minerals. Stromatolites, consisting mainly of hydromagnesite, are abundant in this lake. The Mg isotope composition of incoming streams, groundwaters, lake waters, stromatolites, and hydromagnesite-rich sediments were measured. Because Salda Lake is located in a closed basin, mass balance requires that the Mg isotopic offset between Lake Salda water and precipitated hydromagnesite be comparable to the corresponding offset between Salda Lake and its water inputs. This is consistent with observations; a δ26Mg offset of 0.8–1.4 ‰ is observed between Salda Lake water and it is the incoming streams and groundwaters, and precipitated hydromagnesite has a δ26Mg 0.9–1.1 ‰ more negative than its corresponding fluid phase. This isotopic offset also matches closely that measured in the laboratory during both biotic and abiotic hydrous Mg carbonate precipitation by cyanobacteria (Mavromatis, V., Pearce, C., Shirokova, L. S., Bundeleva, I. A., Pokrovsky, O. S., Benezeth, P. and Oelkers, E.H.: Magnesium isotope fractionation during inorganic and cyanobacteria-induced hydrous magnesium carbonate precipitation, Geochim. Cosmochim. Acta, 2012a. 76, 161–174). Batch reactor experiments performed in the presence of Salda Lake cyanobacteria and stromatolites resulted in the precipitation of dypingite (Mg5(CO3)4(OH)2·5(H2O)) and hydromagnesite (Mg5(CO3)4(OH)2·4H2O) with morphological features similar to those of natural samples. Concurrent abiotic control experiments did not exhibit carbonate precipitation demonstrating the critical role of cyanobacteria in the precipitation process.

In Situ Infrared Spectroscopic Study of Brucite Carbonation in Dry to Water-Saturated Supercritical Carbon Dioxide

In geologic carbon sequestration, whereas part of the injected carbon dioxide will dissolve into host brine, some will remain as neat to water saturated supercritical CO(2) (scCO(2)) near the well bore and at the caprock, especially in the short term life cycle of the sequestration site. Little is known about the reactivity of minerals with scCO(2) containing variable concentrations of water. In this study, we used high-pressure infrared spectroscopy to examine the carbonation of brucite (Mg(OH)(2)) in situ over a 24 h reaction period with scCO(2) containing water concentrations between 0% and 100% saturation, at temperatures of 35, 50, and 70 °C, and at a pressure of 100 bar. Little or no detectable carbonation was observed when brucite was reacted with neat scCO(2). Higher water concentrations and higher temperatures led to greater brucite carbonation rates and larger extents of conversion to magnesium carbonate products. The only observed carbonation product at 35 °C was nesquehonite (MgCO(3)·3H(2)O). Mixtures of nesquehonite and magnesite (MgCO(3)) were detected at 50 °C, but magnesite was more prevalent with increasing water concentration. Both an amorphous hydrated magnesium carbonate solid and magnesite were detected at 70 °C, but magnesite predominated with increasing water concentration. The identity of the magnesium carbonate products appears strongly linked to magnesium water exchange kinetics through temperature and water availability effects.

Reactive Transport Modeling of Natural Carbon Sequestration in Ultramafic Mine Tailings

Atmospheric CO2 is naturally sequestered in ultramafic mine tailings as a result of the weathering of serpentine minerals [Mg3Si2O5(OH)4] and brucite [Mg(OH)2], and subsequent mineralization of CO2 in hydrated magnesium carbonate minerals, such as hydromagnesite [Mg5(CO3)4(OH)2·4H2O]. Understanding the CO2 trapping mechanisms is key to evaluating the capacity of such tailings for carbon sequestration. Natural CO2 sequestration in subaerially exposed ultramafic tailings at a mine site near Mount Keith, Australia is assessed with a process‐based reactive transport model. The model formulation includes unsaturated flow, equations accounting for energy balance and vapor diffusion, fully coupled with solute transport, gas diffusion, and geochemical reactions. Atmospheric boundary conditions accounting for the effect of climate variations are also included. Kinetic dissolution of serpentine, dissolution‐precipitation of brucite and primary carbonates—calcite (CaCO3), dolomite [MgCa(CO3)2], magnesite (MgCO3), as well as the formation of hydromagnesite, halite (NaCl), gypsum (CaSO4·2H2O), blödite [Na2Mg(SO4)2·4H2O], and epsomite [MgSO4·7H2O]—are considered. Simulation results are consistent with field observations and mineralogical data from tailings that weathered for 10 yr. Precipitation of hydromagnesite is both predicted and observed, and is mainly controlled by the dissolution of serpentine (the source of Mg) and equilibrium with CO2 ingressing from the atmosphere. The predicted rate for CO2 entrapment in these tailings ranges between 0.6 and 1 kg m−2 yr−1. However, modeling results suggest that this rate is sensitive to CO2 ingress through the mineral waste and may be enhanced by several mechanisms, including atmospheric pumping.

Reducing dust exposure in indoor climbing gyms

As users of indoor climbing gyms are exposed to high concentrations (PM(10) up to 4000 μg m(-3); PM(2.5) up to 500 μg m(-3)) of hydrated magnesium carbonate hydroxide (magnesia alba), reduction strategies have to be developed. In the present paper, the influence of the use of different kinds of magnesia alba on dust concentrations is investigated. Mass concentrations, number concentrations and size distributions of particles in indoor climbing gyms were determined with an optical particle counter, a synchronized, hybrid ambient real-time particulate monitor and an electrical aerosol spectrometer. PM(10) obtained with these three different techniques generally agreed within 25%. Seven different situations of magnesia alba usage were studied under controlled climbing activities. The use of a suspension of magnesia alba in ethanol (liquid chalk) leads to similar low mass concentrations as the prohibition of magnesia alba. Thus, liquid chalk appears to be a low-budget option to reduce dust concentrations. Magnesia alba pressed into blocks, used as powder or sieved to 2-4 mm diameter, does not lead to significant reduction of the dust concentrations. The same is true for chalk balls (powder enclosed in a sack of porous mesh material). The promotion of this kind of magnesia alba as a means of exposure reduction (as seen in many climbing gyms) is not supported by our results. Particle number concentrations are not influenced by the different kinds of magnesia alba used. The particle size distributions show that the use of magnesia alba predominantly leads to emission of particles with diameters above 1 μm.

Mechanochemical processing of serpentine with ammonium salts under ambient conditions for CO2 mineralization

This paper assesses the suitability of mechanochemistry as a convenient low-energy processing option in CO2 mineralization. Whereas some success has been reported in milling alkaline earth-containing minerals under gaseous CO2, this work focuses instead on a purely solid-state approach towards two key objectives: (a) Mg extraction from serpentine using ammonium bisulfate; and (b) direct or indirect CO2 sequestration using ammonium bicarbonate in a natural extension of its role as “CO2 carrier” in the chilled ammonia scrubbing process. In Mg extraction work, dry milling of serpentine with ammonium bisulfate gave respectable yields (>60% Mg) as boussingaultite [(NH4)2Mg(SO4)2·6H2O] in 2 to 4 h. In CO2 sequestration, dry milling anhydrous magnesium sulfate with ammonium bicarbonate yielded only mixed sulfate products. Carbonation of the heptahydrate, epsomite, was found to proceed via ammonium magnesium carbonate hydrate [(NH4)2Mg(CO3)2·4H2O], which dissolves incongruently to yield nesquehonite [MgCO3·3H2O]. The modest conversion (∼30%) is probably due to equipartition of Mg into the double sulfate co-product. A similar route is followed in magnesia and brucite, in which the existence of an amorphous native carbonate precursor to nesquehonite in the same molar ratio (Mg : CO2 = 1) was inferred from inconsistency in the XRD intensities. This was largely responsible for the high carbonation yields in the unwashed products, ∼70% and ∼85% in MgO and Mg(OH)2, respectively, as confirmed by TG-FTIR. The same intermediate is probably formed in serpentine, but it is apparently soluble in the aqueous mineral environment. When the unwashed product is subjected to mild thermal consolidation, stable hydromagnesite [Mg5(CO3)4(OH)2·4H2O] is formed in ∼20% yield after milling for 16 h. Possible identities for the amorphous precursor are briefly considered.

Magnesium isotope fractionation during hydrous magnesium carbonate precipitation with and without cyanobacteria

The hydrous magnesium carbonates, nesquehonite (MgCO 3·3H 2O) and dypingite (Mg 5(CO 3) 4(OH) 2·5(H 2O)), were precipitated at 25 °C in batch reactors from aqueous solutions containing 0.05 M NaHCO 3 and 0.025 M MgCl 2 and in the presence and absence of live photosynthesizing Gloeocapsa sp. cyanobacteria. Experiments were performed under a variety of conditions; the reactive fluid/bacteria/mineral suspensions were continuously stirred, and/or air bubbled in most experiments, and exposed to various durations of light exposure. Bulk precipitation rates are not affected by the presence of bacteria although the solution pH and the degree of fluid supersaturation with respect to magnesium carbonates increase due to photosynthesis. Lighter Mg isotopes are preferentially incorporated into the precipitated solids in all experiments. Mg isotope fractionation between the mineral and fluid in the abiotic experiments is identical, within uncertainty, to that measured in cyanobacteria-bearing experiments; measured δ 26Mg ranges from −1.54‰ to −1.16‰ in all experiments. Mg isotope fractionation is also found to be independent of reactive solution pH and Mg, CO 3 2−, and biomass concentrations. Taken together, these observations suggest that Gloeocapsa sp. cyanobacterium does not appreciably affect magnesium isotope fractionation between aqueous fluid and hydrous magnesium carbonates.

Study on Synthesis of Nesquehonite Whiskers

Thermal composition of low temperature water is taken as way in the text, with the MgSO4•7H2O and NH4HCO3being raw materials to make nesquehonite whiskers, further talking about the concentration of the reactant, reactive temperatures, mixing speed, solution pH and the quantity of additive addition etc. factors impacting whiskers synthetic of magnesium carbonate hydrate by controlling the growth environment. On this foundation ,finally drop MgSO4solutions by 2.45 mL/min at 50oC by 0.5 mol/L. Join 0.5% KH2PO4obtain slender perfectly straight, smooth surface and average length-diameter ratio of 34 crystal whiskers, carrying out the control to the crystal whiskers facial look and optimized performance for 247 μm and average diameter for 7.2 μm and on the average long diameter comparing.

Thermokinetic analysis of the MgO surface carbonation process in the presence of water vapor

Experiments were performed on magnesium oxide, using water vapor with N 2 or CO 2 as carrier gases, between room temperature and 70 °C, in order to elucidate its thermal stability. Initial experiments were performed with water vapor in the presence of N 2 to elucidate the different physicochemical processes produced by water vapor exclusively, as N 2 is an inert gas. These results showed that water is only adsorbed on the MgO surface. On the other hand, when CO 2 was used as carrier gas the MgO reactivity changed, producing hydrated magnesium carbonate, due to the CO 2 absorption. On the basis of these results and the fact that under dry conditions CO 2 is not absorbed on MgO at T < 70 °C, a possible MgO–H 2O–CO 2 reaction mechanism is proposed, where MgO microstructural parameters play a significant role during the CO 2 absorption.

Plutonium behaviour in nuclear fuel storage pond effluents

Corrosion of the cladding of spent Magnox nuclear fuel elements in water-filled storage ponds has produced a settled layer of fine particulate sludge (corroded Magnox sludge; CMS). CMS is believed to be predominantly composed of brucite (Mg(OH)2), and is contaminated with fragments of spent fuel, together with the associated Pu and fission products. For safe management of the ponds and eventual removal of the sludge as part of pond decommissioning, a comprehensive understanding of sludge chemistry is required. Brucite can sequester Pu from solution and, given that brucite can also form colloidal species in solution, this interaction may enhance Pu mobility within the ponds. To assess the likely effect on Pu mobility, we have measured the affinity of ‘dissolved’ 239Pu for a CMS simulant using a series of ultrafiltration experiments. The experiments were performed using a model Magnox storage pond liquor containing Pu, a CMS simulant, sodium carbonate, polyelectrolyte, and silica. Solution pH was controlled by the addition of sodium hydroxide, perchloric acid, and carbon dioxide gas to mimic storage pond and effluent treatment plant conditions. Multivariate analysis of the results was used to identify which parameters influenced Pu filterability. The presence of carbonate ions (0.03 M) had the largest effect on the system, allowing the majority of Pu to pass the filter. Addition of polyelectrolyte (0.35 ppm) produced a significant increase in Pu retention, even in the presence of carbonate and absence of CMS. The presence of CMS, even at only 3 ppm, increased Pu filterability, which was enhanced at higher pH. Over the pH range 7–11, Pu was generally better retained at higher pH. A 3-way interaction (the presence of CMS and polyelectrolyte at pH 11) affecting Pu filterability was also identified. The presence of silica (at 1 ppm) in the model system did not influence Pu filterability. Additional filtration experiments indicated a strong positive correlation between CMS concentration and Pu filter retention. This interaction was pH dependent, with more Pu filtered at pH 11.5 than at pH 10.8. Increased Pu filtration at high pH may reflect an increase in negatively charged surface species on the CMS particulate, and increased sorption of Pu although the precipitation of more CMS particulate at higher pH could also contribute. The pH dependence of Pu association with brucite is potentially an important control of Pu mobility within storage pond systems. The exact composition of the authentic pond sludge is unknown although it probably comprises mainly brucite, with smaller amounts of hydrous magnesium carbonate. Characterisation of the CMS simulant, synthesised from inactive Magnox swarf, showed the particulate to be primarily composed of platy brucite crystals, with a smaller but significant quantity of acicular artinite crystals.

Synthesis of crystalline layered double hydroxides: Precipitation by using urea hydrolysis and subsequent hydrothermal reactions in aqueous solutions

The urea method is frequently used for synthesis of highly crystalline layered double hydroxides (LDHs). However, in the Mg–Al system, Mg/Al ratios in products have been often found to be smaller than those of starting solutions. In this study, we emphasized monitoring of Mg/Al ratios to investigate the process of LDH formation, while setting the Mg/Al ratio of the starting solutions at 2. LDHs were synthesized by using the urea hydrolysis reaction under hydrothermal conditions. From a starting solution with high metal ion concentration (0.5 M), by-products formed when Mg/Al ratios of products reached about 2; these by-products were most likely hydrated magnesium carbonate hydroxide phases (HM). In contrast, from a low metal ion concentration starting solution (0.01 M), a boehmite-like by-product was detected at an early stage of product formation, but prolonged reaction time or increasing temperature led to product conversion to the LDH phase. Particle size was mainly influenced by metal ion concentration. However, in this study, formation of HM by-products from relatively high metal ion concentration starting solution could not be avoided in one step. Therefore, in order to convert the products to pure LDH phase, product containing HM was reacted hydrothermally in various solutions, yielding almost pure LDH phase. The size of relatively large platelets remained almost the same as that before the hydrothermal reactions, but some or many small broken pieces were present in products after the hydrothermal reactions. Moreover, Mg/Al ratio slightly increased when Na 2CO 3 or NaOH solution was used; with NaOH solution, (00 l) reflections split.

Carbon Dioxide Fixation within Mine Wastes of Ultramafic-Hosted Ore Deposits: Examples from the Clinton Creek and Cassiar Chrysotile Deposits, Canada

Abstract Carbon dioxide (CO2) is sequestered through the weathering and subsequent mineralization of the chrysotile mine tailings at Clinton Creek, Yukon Territory, and Cassiar, British Columbia, Canada. Accelerated weathering is attributed to a dramatic increase in surface area, which occurs during the milling of ore. We provide a detailed account of the natural process of carbon trapping and storage as it occurs at Clinton Creek and Cassiar, including mineralogy, modes of occurrence, methods of formation for carbonate alteration, light stable isotope geochemistry, and radiocarbon analysis. Powder X-ray diffraction data were used to identify weathering products as the hydrated magnesium carbonate minerals nesquehonite [MgCO3·3H2O], dypingite [Mg5(CO3)4 (OH)2·5H2O], hydromagnesite [Mg5(CO3)4(OH)2·4H2O], and less commonly lansfordite [MgCO3·5H2O]. Textural relationships suggest that carbonate precipitates formed in situ after milling and deposition of tailings. Samples of efflorescent nesquehonite are characterized by δ13C values between 6.52 and 14.36 per mil, δ18O values between 20.93 and 26.62 per mil, and F14C values (fraction of modern carbon) between 1.072 and 1.114, values which are consistent with temperature-dependent fractionation of modern atmospheric CO2 during mineralization. Samples of dypingite ± hydromagnesite collected from within 0.2 m of the tailings surface give δ13C values between −1.51 and +10.02 per mil, δ18O values between +17.53 and +28.40 per mil, and F14C values between 1.026 and 1.146, which suggests precipitation from modern atmospheric CO2 in a soil-like environment. Field observations and isotopic data suggest that hydrated magnesium carbonate minerals formed in two environments. Nesquehonite formed in an evaporative environment on the surface of tailings piles, and dypingite and hydromagnesite formed in the subsurface environment with characteristics similar to soil carbonate. In both cases, these minerals have been trapping and storing the greenhouse gas, CO2, directly from the atmosphere. Combined use of δ13C, δ18O, and F14C data has been applied effectively as a tool for verifying and monitoring sequestration of atmospheric CO2 within mine tailings. A number of other deposit types produce tailings suitable for CO2 sequestration, including Cu-Ni-PGE deposits, diamondiferous kimberlite pipes, and podiform chromite deposits. Our results suggest that conversion of about 10 wt percent of tailings to carbonate minerals could offset the greenhouse gas emissions from many ultramafic-hosted mining operations.

Raman and mid‐IR spectroscopic study of the magnesium carbonate minerals—brugnatellite and coalingite

AbstractTwo hydrated hydroxy magnesium carbonate minerals brugnatellite and coalingite with a hydrotalcite‐like structure were studied by Raman spectroscopy. Intense bands are observed at 1094 cm−1 for brugnatellite and at 1093 cm−1 for coalingite attributed to the CO32−ν1 symmetric stretching mode. Additional low intensity bands are observed at 1064 cm−1. The existence of two symmetric stretching modes is accounted for in terms of different anion structural arrangements. Very low intensity bands at 1377 and 1451 cm−1 are observed for brugnatellite, and the Raman spectrum of coalingite displays two bands at 1420 and 1465 cm−1 attributed to the (CO3)2−ν3 antisymmetric stretching modes. Very low intensity bands at 792 cm−1 for brugnatellite and 797 cm−1 for coalingite are assigned to the CO32− out‐of‐plane bend (ν2). X‐ray diffraction studies by other researchers have shown that these minerals are disordered. This is reflected in the difficulty of obtaining Raman spectra of reasonable quality and explains why the Raman spectra of these minerals have not been previously or sufficiently described. A comparison is made with the Raman spectra of other hydrated magnesium carbonate minerals. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Controllable Fabrication of Mesoporous MgO with Various Morphologies and Their Absorption Performance for Toxic Pollutants in Water

We have developed a method of controllable synthesis of MgO with various morphologies by adjusting the composition and phase structure of magnesium carbonate hydrate (MCH). The phase structure of the MCH varied from monoclinic Mg5(CO3)4(OH)2(H2O)4 to hexagonal MgCO3 by changing the concentration of Mg2+ and HCO3−; the corresponding morphology of the MCH ranges from nanoflakes and flowerlike microspheres composed of nanoflakes to layer-like rhombohedra and microspheres composed of rhombohedra. After annealing, four kinds of mesoporous cubic MgO micronano structures were obtained with their original morphologies. Because of the high specific surface area, MgO mesoporous nanoflakes and flowerlike microsphers exhibited excellent absorption performance for common toxic heavy metal ions and organic pollutants and are expected to be a potential absorbent in wastewater treatment.

Dust exposure in indoor climbing halls

The use of hydrated magnesium carbonate hydroxide (magnesia alba) for drying the hands is a strong source for particulate matter in indoor climbing halls. Particle mass concentrations (PM10, PM2.5 and PM1) were measured with an optical particle counter in 9 indoor climbing halls and in 5 sports halls. Mean values for PM10 in indoor climbing halls are generally on the order of 200-500 microg m(-3). For periods of high activity, which last for several hours, PM10 values between 1000 and 4000 microg m(-3) were observed. PM(2.5) is on the order of 30-100 microg m(-3) and reaches values up to 500 microg m(-3), if many users are present. In sports halls, the mass concentrations are usually much lower (PM10 < 100 microg m(-3), PM2.5 < or = 20 microg m(-3)). However, for apparatus gymnastics (a sport in which magnesia alba is also used) similar dust concentrations as for indoor climbing were observed. The size distribution and the total particle number concentration (3.7 nm-10 microm electrical mobility diameter) were determined in one climbing hall by an electrical aerosol spectrometer. The highest number concentrations were between 8000 and 12 000 cm(-3), indicating that the use of magnesia alba is no strong source for ultrafine particles. Scanning electron microscopy and energy-dispersive X-ray microanalysis revealed that virtually all particles are hydrated magnesium carbonate hydroxide. In-situ experiments in an environmental scanning electron microscope showed that the particles do not dissolve at relative humidities up to 100%. Thus, it is concluded that solid particles of magnesia alba are airborne and have the potential to deposit in the human respiratory tract. The particle mass concentrations in indoor climbing halls are much higher than those reported for schools and reach, in many cases, levels which are observed for industrial occupations. The observed dust concentrations are below the current occupational exposure limits in Germany of 3 and 10 mg m(-3) for respirable and inhalable dust. However, the dust concentrations exceed the German guide lines for work places without use of hazardous substances. In addition, minimizing dust concentrations to technologically feasible values is required by the current German legislation. Therefore, substantial reduction of the dust concentration is required.

Surface fabrication of oxides via solution chemistry

A template- and catalyst-free strategy has been successfully designed to prepare MgO and hydrated magnesium carbonate hydroxide (Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O) nanosheets with different patterns (such as chrysalides- and rose-like morphology) on the substrate surface. Experimental results reveal that the temperature and substrate allow us to tune the morphology of patterns. Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O thermodynamically prefers to grow into the sheet-like crystal at the current solution growth environment, which has been successfully explained by using the chemical bonding theory. The predicted morphology can accord well with the current experimental results. The obtained MgO and its precursor Mg 5 (CO 3 ) 4 (OH) 2 ·4H 2 O with novel patterns might find enhanced applications in catalysis, refractory materials, plastics, fire retardants, and functional nanodevices.

Synthesis of Mg5 (CO3)4 (OH)2 • 4H2O with Flower-like Micro-structure and Its Catalytic Activity for Transesterification of Dimethyl Carbonate with Phenol

Abstract A novel flower-like hydrated magnesium carbonate hydroxide, Mg5 (CO3)4 (OH)2 • 4H2O, with micro-structure composed of individual thin nano-sheets was synthesized using a facile solution route without the use of template or organic surfactant. Reaction time has an important effect on the final morphology of the product. The micro-structure and morphology of Mg5 (CO3)4 (OH)2 • 4H2O were characterized by means of X-ray diffractometry (XRD), field-emission scanning electron microscopy (FE-SEM). Brunauer-Emmett-Teller (BET) surface areas of the samples were also measured. The probable formation mechanism of flower-like micro-structure was discussed. It was found that Mg5 (CO3)4 (OH)2 • 4H2O with flower-like micro-structure was a novel and efficient catalyst for the synthesis of diphenyl carbonate (DPC) by transesterification of dimethyl carbonate (DMC) with phenol.

Hydromagnesite and dypingite from the Northern Pennine Orefield, Northern England

SUMMARY The rare basic hydrated magnesium carbonate minerals hydromagnesite and dypingite are reported from low temperature hydrothermal Pb–Zn deposits in the Alston Block of the Northern Pennine Orefield. Both minerals occur as very late stage constituents of deposits rich in barium carbonates. Apparently similar though uncharacterized magnesium carbonates are noted in very small amounts from elsewhere in the orefield.

Verifying and quantifying carbon fixation in minerals from serpentine-rich mine tailings using the Rietveld method with X-ray powder diffraction data

Most carbon on Earth is bound within minerals, and increasing the uptake of atmospheric carbon dioxide into minerals may reduce the greenhouse gas content of the atmosphere. We document carbon disposal through the mineralization of mine tailings at Clinton Creek, Yukon Territory, and Cassiar, British Columbia. We confirm crystallographic binding of carbon in these tailings and quantify carbon dioxide uptake using quantitative phase analysis with the Rietveld method for X-ray powder diffraction data. Planar disorder in the structures of the kaolinite-serpentine group minerals makes Rietveld refinements of X-ray powder diffraction data for serpentinites problematic. Using structureless pattern fitting and with the addition of a known quantity of a well-crystallized material, the problem of structural disorder is overcome by considering the serpentine minerals as amorphous phases. We test the accuracy and precision of this refinement method using synthetic serpentine-rich mine tailings of known composition. Estimates of the abundance of hydrated magnesium carbonates in these tailings have a precision of approximately 5% relative for mineral species present in amounts greater than 10 wt%. Precise estimates of carbonate mineral content and crystallographically bound atmospheric CO 2 are made for samples of serpentine-rich tailings from Clinton Creek and Cassiar. Results for mine tailings are also compared to mineralogically similar samples from a carbonate playa at Atlin, British Columbia. The potential for decomposition of metastable hydrated magnesium carbonate phases to geologically stable magnesite may represent long-term stability of the products of mineral sequestration in mine tailings.

Temperature- and pH-Dependent Morphology and FT−IR Analysis of Magnesium Carbonate Hydrates

Various morphologies of magnesium carbonate hydrates have been synthesized by carefully adjusting the reaction temperature and pH value of the initial reaction solution in the precipitation process. At lower temperatures (from room temperature to 328 K) and lower pH values (variation with the reaction temperature), magnesium carbonate hydrates are prone to display needlelike morphology, and the axis diameter of the particles decreases with the increase of reaction temperature and pH value. With the further increase of the reaction temperature (333-368 K) and pH value, the sheetlike crystallites become the preferred morphology, and at higher temperatures and pH values, these crystallites tend to assemble into layerlike structures with diverse morphologies, such as spherical-like particles with rosette-like structure and cakelike particles built from sheetlike structure. Fourier transform infrared (FT-IR) spectra show that these various morphologies are closely related to their compositions. The needlelike magnesium carbonate hydrate has a formula of MgCO3.xH2O, in which the value x is greatly affected by the experimental conditions, whereas with the morphological transformation from needlelike to sheetlike structure, their corresponding compositions also change from MgCO3.xH2O to Mg5(CO3)4(OH)2.4H2O in the interval of 328-333 K.