Formation Of Magnesium Carbonates Research Articles

Thermodynamic and Kinetic Study of Leaching Magnesia from Natural Magnesites by Carbon Dioxide

The applicability of carbon dioxide pressure leaching for the extraction of high purity magnesia from natural magnesites has been investigated. Factors which have influence on the magnesia recovery such as time, temperature, pressure, particle size and calcination temperature have been studied. Optimum values were determined: calcination temperature was in the range 650 – 750 0C, time of the calcination was approximately 5 – 3 hours; carbon dioxide partial pressure leaching for the extraction of magnesia was about 3 bar; particle size was between 0,2 – 0,6 mm. A kinetic study of carbonation of MgO has been investigated at leaching temperature from 00C to 50 0C. Two processes were observed: the formation of a magnesium bicarbonate solution and the precipitation of magnesium carbonate. Our research has determined that the concentration of impurities in magnesium carbonate is virtually no different from their concentration in natural magnesites. Apparently, the formation of magnesium carbonate proceeds without destruction of structure. So the extraction of high purity magnesia from natural magnesites by carbon dioxide is only possible using magnesium bicarbonate. It is necessary to optimize the translation process of magnesium in solution and the technology of extraction of pure MgO from it to generate high purity magnesium on an industrial scale.

Experimental investigations of the effects of acid gas (H2S / CO2 ) exposure under geological sequestration conditions

Abstract Acid gas (mixed CO 2 and H 2 S) injection into geological formations is increasingly used as a disposal option. For example, more than 40 acid gas injection projects are currently operating in Alberta, Canada . In contrast to pure CO 2 injection, there is little understanding of the possible effects of acid gases under geological sequestration conditions on exposed materials ranging from reactions with reservoir minerals to the stability of proppants injected to improve oil recovery to the possible failure of wellbore cements. The number of laboratory studies investigating effects of acid gas has been limited by safety concerns and the difficulty in preparing and maintaining single-phase H 2 S/ CO 2 mixtures under the experimental pressures and temperatures required. In an effort to address the lack of experimental data addressing the potential effects of acid gas injection, the Plains CO 2 Reduction Partnership (PCOR) in the United States has developed approaches using conventional syringe pumps (ISCO 260D pumps) and reactor vessels (Parr Instruments) to prepare and maintain H 2 S/ CO 2 mixtures under relevant sequestration conditions of temperature, pressure, and exposure to water and dissolved salts. Exposures up to several months can be conducted at temperatures and pressures up to 350 °C and 414 bar (6000 psi) using any desired H 2 S/ CO 2 mole ratio. Up to 16 individual samples racked in separate glass vials can be exposed at one time, and the use of separate glass vessels allows different salt brine concentrations to be evaluated. In addition to performing static exposure experiments, the pumps and vessels are sufficiently leakfree that reaction rates can be determined by monitoring mass flow at the pumps. Interestingly, this is much easier to perform for reactions with H 2 S than with CO 2 , because H 2 S is much less compressible and has lower Joule–Thompson heating/cooling effects than CO 2 . Thus, obtaining accurate values for the mass of CO 2 used during an experiment based on pump volume is much more difficult than for H 2 S, although controlling the pump cylinder temperature with a water jacket allows reasonable measurements to be made. These systems have been used to determine reaction rates of model systems, such as the formation of magnesium carbonate from magnesium silicate and the formation of pyrite from iron oxide (Fe 3 O 4 ). For example, the use of H 2 S (as measured at the pump) was steady at ca. 0.5 grams per day (for 18.6 grams of Fe 3 O 4 ) until the reaction was complete. The half-life of the reaction was 20 days, and the mass balance (0.54 moles H 2 S actual compared to 0.48 moles theoretical) was reasonable.

High CO2 Storage Capacity in Alkali‐Promoted Hydrotalcite‐Based Material: In Situ Detection of Reversible Formation of Magnesium Carbonate

Alkali-promoted hydrotalcite-based materials showed very high CO(2) storage capacity, exceeding 15 mmol g(-1) when the carbonation reaction was carried out at relatively high temperature (300-500 °C) and high partial pressure of steam and CO(2). In situ XRD experiments have allowed correlation of high CO(2) capacity to the transformation of magnesium oxide centres into magnesium carbonate in alkali-promoted hydrotalcite-based material. Moreover, it has been clearly shown that crystalline magnesium carbonate may be reversibly formed at temperatures above 300 °C in the presence of sufficient partial pressure of steam in the gas phase, conditions that are prevalent in pre-combustion CO(2) capture. The role of steam appears to be of utmost importance for the formation of the bulk carbonate phase and for its reversibility. It is proposed that a high partial pressure of steam keeps the magnesium oxide periclase phase sufficiently hydroxylated to allow magnesium carbonate formation if a relatively high partial pressure CO(2) is present in the gas phase.

Investigation on dual corrosion performance of magnesium-rich primer for aluminum alloys under salt spray test (ASTM B117) and natural exposure

Magnesium-rich primers perform very well on outdoor exposure and actual test conditions, yet fail rapidly in accelerated corrosion testing (salt spray test – ASTM B117). To investigate the behavioral dichotomy, Mg-rich primers exposed to salt spray testing and natural weathering were characterized at periodic intervals. The results revealed the presence of a thin and porous magnesium hydroxide layer in primers exposed to salt spray, and in natural exposure, a thicker, protective magnesium carbonate layer was detected and characterized. Samples exposed to atmospheric carbon dioxide exhibit excellent corrosion resistance but salt spray conditions are not conducive to facilitate magnesium carbonate formation.

Understanding corrosion via corrosion product characterization: I. Case study of the role of Mg alloying in Zn–Mg coating on steel

In the present work the corrosion inhibitive role of Mg in Zn–Mg coatings is considered for different stages of corrosion. Corrosion product characterization was carried out using XRD, IRRAS, MEB–FEG–EDS on technical Zn–Mg coatings after various exposure times in a standardized cyclic corrosion test. The results are compared with artificial corrosion products obtained by chemical and electrochemical synthesis. The importance of the ageing and the role of the atmospheric CO 2 on the nature and morphology of the corrosion products are discussed. The corrosion resistance of Zn–Mg alloy is correlated with the stabilization of simonkolleite against its transformation into smithsonite, hydrozincite, and zincite during ageing cycles in presence of CO 2. The stabilization appears to be due to the preferential formation of magnesium carbonates. Thermodynamic modeling and titrometric analysis demonstrate that Mg 2+ enhances simonkolleite during dry–wet cycling by (1) removing carbonate from the environment and thereby limiting of the transformation of simonkolleite into zincite, smithsonite, and hydrozincite and by (2) buffering the pH of the electrolyte around 10.2 due to the precipitation of Mg(OH) 2 preventing the dissolution of zinc based corrosion products into soluble hydroxide complexes.

Corrosion process of MgB 2 superconductor in a moisture atmosphere

The degradation behavior of polycrystalline magnesium diboride (MgB2) superconductor in a highly humid air has been investigated. The MgB2 samples with grain size around 10 μm were exposed to the action of dry carbon dioxide, to water-vapour-saturated air and to water vapour in a closed system. It has been shown that prolonged exposure to highly humid air completely destroys superconductivity. Infrared transmission spectroscopy analyses indicate that water simply acts as a catalyst for the formation of magnesium carbonate (MgCO3) and diboride oxide (B2O3) species, and the rate of degradation strongly depends on the water partial pressure in air. Microstructure analyses reveal that the degradation process was observed to initiate more likely at the surface and also at the grain boundaries of small MgB2 grains. Resistivity versus temperature measurements indicates that on exposure to humid air, the residual resistance ratio decreases and the material becomes insulator with prolonged exposure time. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Preparation and infrared study of magnesium borate gels with a wide composition range

Gels in the system χMgO · (1 − χ)B2O3 (0.42 ≤ χ ≤0.80) have been prepared by hydrolytic polycondensation of boron-butoxide with magnesium methoxide in alcoholic medium. The gels were heated at 400°C in order to obtain organic-free amorphous materials. The infrared spectra of these gels reveal the progressive modification of the borate network with increasing magnesium percentage. The X-ray diffraction patterns of the gels show that calcination at temperatures higher than 400°C leads to crystallization of the amorphous network. For the very high magnesium content glass (χ = 0.80), evidence for magnesium carbonate formation is detected.

Formation of Magnesium Carbonate by Reactive Crystallization

Formation of Magnesium Carbonate by Reactive Crystallization

A Preliminary Report on Magnesium Carbonate Formation in Glacial Lake Bonneville

A thin bed of unconsolidated dolomite occurs about a foot below the surface of the Great Salt Lake Desert west of Knolls, Utah. A date correlates with the onset of a drier climate and the desiccation of Lake Bonneville to the present Great Salt Lake. Shoreward, the dolomite zone is represented by a mixture of aragonite and a magnesite-like material, with an enlarged unit cell. Chemical-enrichment techniques have been utilized in obtaining minor-element abundance data.