Calcined Magnesite Research Articles

Recovery of struvite for organic production: Mineral-based magnesium supplementation and pH elevation

Phosphate in wastewater can be recovered in the form of struvite crystals for use as slow-release fertilizer. Currently, struvite recovery often requires supplementing magnesium ions and raising pH with chemicals, making the recovered struvite unfavorable for organic production. In an effort for cleaner production, this study developed a versatile approach employing two mineral products in variable combinations for optimal supplementation of magnesium and elevation of pH. Magnesite, a mineral of MgCO3, was ground and calcined without use of any catalysts. The magnesite calcined under the optimum conditions (800 °C for 30 min) can be dissolved in near-neutral filtrate of sludge digestate to supplement magnesium and raise pH for effective struvite formation. The OMRI-listed Epsom salts (MgSO4∙7H2O), mineral-based water-soluble commercial products, can be used to supplement magnesium without changing pH of alkaline wastewater. Six-hour batch operation of an air-lift crystallizer removed 85.7% and 94.7% of phosphate in hydrolyzed human urine when magnesium was amended to 1.2 × molar concentration of phosphate with calcined magnesite and an OMRI-listed Epsom salt, respectively. More than 98% of phosphate was removed from filtrate of sludge digestate in 3-h batch operation using calcined magnesite to raise pH to 8.5 and the Epsom salt for further magnesium supplementation. Struvite accounted for 85.7%, 90.5%, and 81.5% of the crystals recovered from urine with calcined magnesite, urine with Epsom salt, and filtrate with both mineral products, respectively. The material and energy costs of this green process were estimated to be $0.16/kg struvite from urine with calcined magnesite, $1.37/kg struvite from urine with Epsom salt, and $0.94/kg struvite from filtrate with both mineral products. This study proved the technical and economic feasibility of chemical-free magnesium supplementation and pH elevation, making the recovered struvite potentially certifiable for organic production.

Evaluation of the technical properties of reactive-MgO cements produced by solar calcination of magnesite in a fluidized bed reactor

Magnesium oxide (MgO)-based cements display very interesting technical properties and environmentally-friendly features. The novel idea investigated in this study is to synthesize MgO cements, using as raw material natural magnesite calcined in fluidized bed heated by concentrated solar energy. Calcination was performed in a lab-scale system equipped with a concentrated solar simulator, operated under different process conditions. The most reactive MgO was mixed with 3% by weight of MgCO3 (nucleation agent) and four different solutions containing magnesium acetate or chloride. The binders were hydrated in air or 20% CO2 atmosphere (accelerated carbonation conditions) until 28 days. X-ray diffraction, differential-thermal and mercury intrusion porosimetry analyses, and compressive mechanical strength tests, were performed on the hydrated systems. Solar calcination produced a highly reactive MgO. The performance of the cement pastes improved at higher curing times, and when using magnesium acetate as hydration agent, as also witnessed by the application of a kinetic model. Accelerated carbonation conditions further enhanced the mechanical properties of the cements thanks to the formation of nesquehonite, allowing to reach a mechanical strength comparable to that of ordinary Portland cements class 32.5. The achieved outcomes encourage the production of low-CO2 magnesite cements from solar calcined magnesite, boosting the green aspect of the entire process.

Investigation into the possibility of intensifying the sintering of pure magnesia raw materials

The influence of additives of different nature on grinding, compressibility and sintering of calcined magnesite was investigated. It was found that the investigated recycled additives, when introduced in the amount of up to 0,5 wt. %, do not significantly change the grain composition of calcined periclase after grinding, do not effect the compressibility of powders, do not change their chemical and phase composition after firing up to the temperature of 1870 оC. An additive based on dust-like waste of titanium production enables increasing the density of the obtained briquette by 1,0‒3,5 % or reducing the briquette firing temperature by 50‒100 °С.

The natural magnesite efficacy on arsenic extraction from water and alkaline influence on metal release in water

Arsenic (As) removal studies were carried out through batch experiments to investigate the performance of the locally available calcined magnesite mineral rocks from Tanzania. Natural water from a stream source in Tanzania and the prepared synthetic water at the laboratory were used for the studies. Parameters such as initial As concentration, calcined magnesite dosage, contact time and pH were evaluated for As removal using an overhead rea×2 shaker. Arsenic concentration was reduced from 5.3 to 1.1 mg/L As(V) at 180 min when 0.5 g/L calcined magnesite was applied to a synthetic water sample, whereas the concentration of 117 μg/L As(V) and 5.2 μg/L As(III) was reduced to below 0.1 μg/L in natural water. An increase in calcined magnesite dosage resulted in increased As removal up to below 0.01 mg/L. The calcined magnesite raised the pH of the water sample from 6.8 to 10 when the applied dosage increased between 0.002 g/L and 0.05 g/L. The pH was constant at around 10 even when the amount of 0.05 g/L was added 2000 times. Despite the high pH, the amount of magnesium released in water was low. The calcination of magnesite at 500 °C increased surface area by 4 times as compared to the natural magnesite and X-ray diffraction showed presence of MgCO3 phase as the dominant phase at this temperature. The reaction kinetics of As removal on 0.5 g/L calcined magnesite fitted with the pseudo-second-order (R2 = 0.96). Reaction isotherm was strongly fitted with Freundlich isotherm (R2 = 0.98). Linear regression and artificial intelligence neural network showed the As removal was influenced by both contact time and pH. Arsenic can be removed from As water using calcined magnesite and will be suitable for water treatment around gold mining areas.

Investigation of calcined magnesite sintering

The composition and properties of two types of calcined magnesium oxide powders, differing in chemical composition, are investigated. The difference in chemical and phase composition determines the different behavior of powders during firing, which is smoothed only at a temperature of more than 1850 °C. The microstructure of the obtained briquettes differs in the amount of glass phase, the type and size of pores, as well as the size and quality of the crystals of the periclase. From the studied powders of decarbonized magnesium oxide without sintering additives, a briquette with an apparent density of at least 3,35 g/cm3 required to obtain high-quality products can be obtained only at a firing temperature of at least 1850 °C with an exposure at the final firing temperature of at least 2 hours. Ill. 2. Ref. 14. Tab. 4.

Performance of geopolymer concrete activated by sodium silicate and silica fume activator

This study examined the properties (strength, workability and crack) of geopolymer concrete activated by sodium silicate and silica fume activator. Sodium silicate and sodium hydroxide (NaOH) are commonly activators used to make geological polymer composite. However, they will cause the decline of the performance of geopolymer concrete when it is prone to polymerization in the surrounding of alkaline. Silica fume can improve the workability and strength of geopolymer concrete. The Pearson correlation coefficient and experiment is used to study the performance of geopolymer concrete with sodium silicate and silica fume activator. The influence of two kinds of activators on the slump of geopolymers with different mix ratios was analyzed by Pearson correlation coefficient. The relative coefficient of mineral powder decreased from 0.785 to 0.409. The absolute relative coefficient of calcined magnesite decreased from 0.829 to 0.156. The correlation between slag, calcined magnesite and slump changed from significant to insignificant. The analysis shows that the slump of geopolymers with silica fume activator are less affected by mineral powder and calcined magnesite than that of sodium silicate activator. Geopolymer concrete have more stable performance with silica fume activator. The geopolymer concrete excited by silica fume activator compared with the sodium silicate activator, the cracks and internal porosities on the surface of the specimens are less. The compressive strength and crack of geopolymer concrete excited by silica fume activator reached 43.36 MPa and 0.095 mm, respectively, at 20 ℃ ± 2 ℃ and more than 95% humidity. It shows good early strength and less cracks. The experimental mix proportions are optimized to conduct the complex the equilibrium of physical and chemical reactions and to reinforce the mechanical property of geopolymer concrete with silicate fume activator.

Microstructures and strengths of microporous MgO–Al2O3 ceramics from Al(OH)3 and calcined magnesite

AbstractSeven microporous MgO–Al2O3 ceramics with an Al2O3 content of 15–90 wt% were prepared using Al(OH)3 and calcined magnesite as raw materials. A wet mixing process was employed during sample preparation to transform the calcined magnesite with a larger particle size to smaller Mg(OH)2 particles. The in situ decomposition synthesis method and the Kirkendall effect were utilized to produce and control the pore structure of the microporous MgO–Al2O3 ceramics. There were two kinds of pores in the microporous MgO–Al2O3 ceramics. The first one resulted from the in situ decomposition of Al(OH)3 and Mg(OH)2 particles, which were small and equally distributed. Another one originated from the position of the Mg(OH)2 particles due to the Kirkendall effect caused by MgO diffusion. They were similar in size to the Mg(OH)2 pseudomorph particles. Simultaneously, the Al2O3 content affected the packing behavior and the spinel formation, which changed the characteristics of the pores and necks among the particles. These mechanisms also affected the strengths of the microporous MgO–Al2O3 ceramics. Thus, when the Al2O3 content was 45–90 wt%, the microporous MgO–Al2O3 ceramics had a high compressive strength (10.0–18.3 MPa) and apparent porosity (52.2%–58.4%).

Interactive removal of bacterial and viral particles during transport through low-cost filtering materials.

Pathogen filtration is critically important for water sanitation. However, it is a big challenge to balance removal efficiency and filtering material cost. In this study, we quantified the removal processes of a bacterial strain Escherichia coli 652T7 and a model bacteriophage MS2 (ATCC 15597-B1) during their transport through columns containing iron filings (IF), calcined magnesite (CM), natural ore limestone (OL) or corn stalk biochar (BC) under saturated flow conditions. Experimental results showed that 99.98, 79.55, 63.79, and 62.59% of injected E. coli 652T7 and 98.78, 92.26, 68.79, and 69.82% of injected MS2 were removed by IF, CM, OL, and BC, respectively. The differences in removal percentage were attributed to the disparities of the microorganisms and filtering materials in surface function groups, surface charges, and surface morphology. Transport modeling with advection-dispersion equation (ADE) and interaction energy calculation with extended Derjaguin, Landau, Verwey, and Overbeek (XDLVO) model indicated that E. coli 652T7 and MS2 were mostly removed via irreversible attachment. In IF columns, E. coli 652T7 promoted the transport of MS2 but not vice versa. In CM columns, MS2 facilitated the transport of E. coli 652T7 and vice versa at a less extent. Such changes were a combined result of attachment site competition, steric effect, and mechanical straining. We found that the sum of the removal percentages of the two microorganisms in their respective transport experiments were similar to those calculated from their co-transport experiments. This result suggests that the removals were mainly limited by the attachment sites in the filtering materials.

Environmental application of engineering magnesite slag for phosphate adsorption from wastewater.

Herein, magnesite slags (MS), which remain after sulfuric acid extraction from light burnt magnesite in the magnesite industry, were used as phosphate adsorbents in wastewater. The MS were calcined under 700°C to enhance phosphate adsorption. The calcined magnesite slags (CMS) were characterized by nitrogen adsorption-desorption isotherm, X-ray diffraction, and scanning electron microscopy. A series of batch adsorption experiments were carried out to test the phosphate adsorption capacity of CMS. The results showed that the calcific treatment promoted the conversion from Mg, Ca, Fe, etc. compound to metal oxide of the MS. The generated metal oxide particles resulted in 237.4mg/g increase in the phosphate adsorption capacity. The phosphate adsorption isotherm of CMS fitted the Langmuir model better, and the maximum adsorption capacity of CMS was 526mg/g. The adsorption kinetics of phosphate on CMS can be described by the pseudo-second-order model. The phosphate removal efficiency was greater than 98% in 300mg/L phosphate solution. Mechanism investigation results indicated that phosphate was adsorbed by CMS through MgO protonation, electrostatic attraction, Mg-P complexation, and ligand exchange. The results obtained in this work demonstrate that the CMS is a potential effective adsorbent for removal and reutilization phosphate from P-contaminated water, due to it can be employed as a fertilizer after phosphate adsorption.

Influence of Waste Plastic Aggregate and Water-Repellent Additive on the Properties of Lightweight Magnesium Oxychloride Cement Composite

The aim of the present study is to improve the thermal and hygric performance of magnesium oxychloride (MOC) cement composites by the incorporation of waste plastic-based aggregate and the use of the inner and surface hydrophobic agents. The crushed waste expanded polypropylene particles were used as a full replacement of natural silica sand. The aggregate properties were evaluated in terms of their physical and thermal parameters. The caustic calcined magnesite was studied by SEM, XRF, and XRD spectroscopy. The MOC cement composites were characterized by SEM/EDS, XRD, and FT-IR spectroscopy and measurement of their structural properties, strength parameters, thermal conductivity, and volumetric heat capacity. Assessment of water- and water vapor transport properties was also conducted. The results show significantly improved thermal parameters of MOC cement composite containing expanded polypropylene (EPP) as aggregate and indicate high efficiency of surface hydrophobic agent (impregnation) as a barrier against the transport of liquid and gaseous moisture. The resulting lightweight EPP-MOC cement composite with improved thermal insulation function and suitable mechanical properties can be used to produce thermal insulation floors, ceilings, or wall panels reducing the operational energy demand of buildings.

The determination of the optimum conditions upon the leaching performance of calcined magnesite

The aim of the study is to examine the reaction of calcined magnesite in the citric acid media, and after that it is determination of optimal conditions about the leaching performance of calcined magnesite by an experimental plan of Taguchi Statistical Method with L16 (45). The parameters such as particle size, reaction temperature, acid concentration, solid–liquid ratio and reaction period are tested. In this work, the optimal combination of the parameters that achieves robustness against noise factors is found as: 50 °C, 45 min, -319 μm, 0.125 g/mL, and 2M, respectively. Extraction efficiency of the magnesium from calcined magnesite is 98.86 %.

Production of Mg-Li alloys by aluminothermic vacuum reduction

Mg?Li alloys are the lightest metallic construction materials and one of the most representative light alloys. The process of producing Mg?Li alloys by vacuum aluminothermic reduction, using magnesite and lithium carbonate as raw materials, was studied. The influence of reduction parameters on the extents of reduction of MgO and Li2O was investigated. The results show that Mg?Li alloys can be produced by vacuum aluminothermic reduction using calcined magnesite and lithium carbonate. MgO was relatively easier to reduce by aluminum than Li2O. Almost all MgO was reduced to Mg and more than 96% of Li2O was reduced to Li. The main phase in the reduction slag was Li2O?5Al2O3. The reaction mechanism was discussed. Vacuum aluminothermic reduction can be considered as a highly efficient and environmental friendly method for producing Mg?Li alloys.

Phosphorus recovery from wastewater using light calcined magnesite, effects of alkalinity and organic acids

To solve the problem of phosphorus pollution and resource crisis, phosphorus recovery by struvite crystallization has become a focus of research in recent years. In municipal wastewater, insufficient magnesium content and relatively low pH can be a limitation for struvite formation. A commercial magnesium source, light calcined magnesite (LCM), was used in this study for phosphorus recovery from wastewater without an adjustment of pH. Bench-scale jar test experiments were conducted to study the kinetics of phosphate removal by LCM. The effects of LCM dosage, initial phosphate concentration, carbonate alkalinity and organic acid content on the removal of phosphate was evaluated. Hydrolyzation of LCM released hydroxyl ions (OH−) during the reaction, increasing the solution pH from 7.63 to 8.62. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the composition and morphology of formed precipitates. At an LCM dosage of 200 mg/L, 84.5% of phosphate was removed mainly through the formation of struvite. Increased alkalinity and organic acid concentration in the solution inhibited struvite formation, and higher alkalinity promoted the formation of coarse crystal surfaces. Abundant global reserves of the magnesite ore resource reveal LCM may be a viable and cost-effective source of magnesium and hydroxyl reagent for phosphorus recovery from wastewater.

Calcined magnesite as an adsorbent for cationic and anionic dyes: characterization, adsorption parameters, isotherms and kinetics study

The ability of calcined magnesite for Methylene Blue (MB), Direct Red 81 (DR81), Methyl Orange (MO) and Crystal Violet (CV) dye removal was evaluated in this study. The experiments were designed to test the hypothesis that alkaline earth carbonates can remove dyes from water through a combination of sorption and coagulative reactions involving Mg2+. To achieve that, several operational factors like residence time, dosage, adsorbent concentration and temperature were appraised. The batch study proved that calcined magnesite is effective in the treatment of MB, DR81, CV and MO contaminated water and moreover it performed well in terms of color removal. The adsorption equilibrium data were analysed by the Langmuir, Freundlich, Dubinin–Radushkevich and Temkin isotherm models, and the Dubinin–Radushkevich and Temkin models were found to be the most appropriate fit to MB and MO dyes respectively. The adsorption kinetics process primarily followed the Elovich and Pseudo-second order model, a possible indication that chemisorption was the rate limiting step during the dye uptake process. With the adsorption–desorption cycle repeated four times, the calcined magnesite regeneration efficiency for DR81 and MO loaded dyes remained very high. According to the results of this study, it can be concluded that calcined magnesite can be used effectively for the adsorption of MB, DR81, CV and MO from wastewater.

Utilisation of light calcined magnesite tailings to compensate the autogenous shrinkage of steam-cured cement paste

Calcined magnesia in a designed formulation was prepared with magnesite tailings below 1100°C to compensate for the autogenous shrinkage of steam-cured Portland cement and fly ash pastes with low water/binder ratios. The morphology and hydration properties of the light calcined magnesite tailings (LCM) were studied by field-emission source scanning electron microscopy (FESEM) and isothermal calorimetry. The hydration of magnesium oxide in paste and the microstructure of the paste were determined by thermogravimetric and differential thermal analysis, mercury intrusion porosimetry, FESEM and backscattered SEM. The results show that the hydration activity of LCM can be easily designed by regulating the calcining temperature. Both early age (7 d) and later age (90 d) autogenous shrinkage of steam-cured cement paste could be partially compensated when adding 4 wt% LCM prepared at 850°C (M85), probably due to the locally restrained continued slow hydration of magnesium oxide in M85.

Kinetics and mechanism of vacuum isothermal reduction of magnesia by aluminium

The kinetics and mechanism of vacuum isothermal reduction of calcined magnesite by Al were studied in the present paper. The results showed that the aluminothermic reduction process was divided into two stages. The apparent activation energy values of the two stages were determined to be 144.4 and 235.3 kJ mol−1, respectively. The phase MgAl2O4 was formed in the first stage. In the second stage, the intermediate phase Mg0.4Al2.4O4 was formed and the phase Al2O3 was obtained from the further reduction of Mg0.4Al2.4O4. The diffusion of molten aluminium is the rate-determining step of the reduction process. The out diffusion of magnesium vapour has some effect on the reduction ratio at the briquetting pressure between 60 and 120 MPa, but it is not the major rate-limiting step.Dans cet article, on a étudié la cinétique et le mécanisme de réduction isotherme sous vacuum de la magnésite calcinée par l’Al. Les résultats ont montré que le procédé de réduction aluminothermique était divisé en deux étapes. On a déterminé les valeurs d’énergie d’activation apparente des deux étapes à 144.4 et 235.3 kJ/mol, respectivement. La phase de MgAl2O4 était formée dans la première étape. La phase intermédiaire de Mg0.4Al2.4O4 était formée dans la seconde étape et l’on a ensuite obtenu la phase d’Al2O3 par réduction additionnelle du Mg0.4Al2.4O4. La diffusion de l’aluminium fondu est l’étape cinétiquement déterminante du procédé de réduction. La diffusion vers l’extérieur de la vapeur de magnésium a un certain effet sur le taux de réduction à la pression de briquetage entre 60 et 120 MPa, mais il ne s’agit pas de l’étape majeure cinétiquement limitante.

Thermodynamic and kinetic studies of the MgCl2‐NH4Cl‐NH3‐H2O system for the production of high purity MgO from calcined low‐grade magnesite

To improve the overall sustainability of MgO‐based refractory production, a novel process to produce high purity MgO from calcined low‐grade magnesite in ammonium chloride solution was developed. The process was designed on the basis of the phase equilibria of the NH4Cl‐MgCl2‐NH3‐H2O system obtained using the Mixed Solvent Electrolyte model embedded in OLI software. The optimum calcination temperature of low‐grade magnesite was determined to be 650°C in terms of the conversion ratio of magnesium and calcium in the leaching experiments. An apparent activation energy of Mg extraction was 30.98 kJ/mol, which is slightly lower than that of Ca leaching. An empirical kinetic model of magnesium extraction was also developed to describe the effects of NH4Cl concentration, particle size of calcined magnesite, and solid‐to‐liquid ratio on the extent of extraction of magnesium. At leaching time of 10 min, the leachate with high Mg/Ca molar ratio was obtained. Then, MgO with a purity of 99.09% was produced through the decomposition of intermediate 4MgCO3·Mg(OH)2·4H2O. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1933–1946, 2015

Effect of Two Magnesium Fertilizers on Leaf Magnesium Concentration, Yield, and Quality of Potato and Sugar Beet

Twelve field experiments were conducted to study the impacts of calcined magnesite and Kieserite fertilizers on yield, quality and leaf concentrations of magnesium (Mg) in potatoes and sugar beet. The rate of Mg applied was 60 kg Mg ha−1, and the experiments were realized in six locations for both crop species. There were clear increases in leaf Mg concentration and yield of both crops resulting from application of Mg fertilizers. Mean increase in leaf Mg concentration and crop yield for both species were more pronounced with Kieserite than with calcined magnesite. Sugar concentrations of sugar beet and dry matter yield of potatoes were, however, influenced only slightly by the Mg fertilizers. It seems that superiority of Kieserite to calcined magnesite is related to higher Mg solubility of Kieserite. Use of Mg fertilizers with higher solubility helps to avoid the risk of Mg deficiency and subsequent losses in yield and economic returns.

Mechanism of extracting magenesium from mixture of calcined magnesite and calcined dolomite by vacuum aluminothermic reduction

The process of aluminothermic reduction of a mixture of calcined dolomite and calcined magnesite had been developed. The mechanism of the process was studied by SEM and EDS. The reduction process was divided into three stages: 0≤ηt/ηf≤0.43±0.06, 0.43±0.06≤ηt/ηf≤0.9±0.02 and 0.9±0.02≤ηt/ηf <1, where ηt and ηf are the reduction ratio at time t and the final reduction ratio obtained in the experiment at temperature T, respectively. The first stage included the direct reaction between calcined dolomite or calcined magnesite and Al with 12CaO·7Al2O3 and MgO·Al2O3 as products. The reaction rate depended on the chemical reaction. The CA phase was mainly produced in the second stage and the overall reaction rate was determined by both the diffusion of Ca2+ with molten Al and the chemical reaction. The CA2 phase was mainly produced in the third stage and the reaction process was controlled by the diffusion of Ca2+.

Characteristics of Calcined Magnesite and Its Application in Oxidized Pellet Production

Calcined magnesite is a binding additive and an MgO-bearing flux for pellets production. The effects of calcination temperature and time on the characteristics of calcined magnesite were investigated. Experimental results indicated that the best calcination condition was 850 °C and 1 h. Under this condition, the hydration activity of the calcined magnesite was 80. 56%, and the average diameter of crystal grain D, specific surface area S and the medium particle size D50 were 25. 4 nm, 45. 40 m2/g and 3. 41 μm, respectively. This kind of calcined magnesite was a good binding additive for pellets production. At the same proportion of calcined magnesite, the effects of activities of calcined magnesite on metallurgical properties of green pellet and indurated pellet showed that calcined magnesite with high activity could improve the dropping strength and compressive strength of green pellet and enhance the burst temperature of green pellet; however, the effects of activity on compressive strength, low-temperature reduction degradation index, reduction swelling index and reduction index of indurated pellet were not obvious.