Magnesium Silica Research Articles

Optimization of magnesium silica aerogel production and evaluation as a food additive: a comparative study of water glass and bio-based sodium silicate source as a precursor

Optimization of magnesium silica aerogel production and evaluation as a food additive: a comparative study of water glass and bio-based sodium silicate source as a precursor

Clarification of red grape juice by amine-functionalized magnesium silica aerogel

The clarification conditions and the selection of the clarification agent are pivotal in eliminating the haze components from red grape juice (RGJ) while minimizing the loss of functional color components. In this context, we synthesized a water glass-based APTES functionalized magnesium silica aerogel (MSA-NH3) incorporating 61.44 molecules/nm2 of amine groups, resulting in a positively charged zeta potential value of 33.9 mV (pH 3.4) for clarification of RGJ by targeting negatively charged polyphenols. The optimum clarification conditions using MSA-NH3 were determined as 0.18 g MSA-NH3/L RGJ, 20 °C, and 60 min through the application of Box-Behnken design. Under these conditions, MSA-NH3 exhibited excellent adsorption of haze components (3.61 NTU), outperforming the commercial bentonite-gelatine combination (BGC) (5.45 NTU). Furthermore, it exhibited greater efficacy in preserving anthocyanins while adsorbing browning components. MSA-NH3 has a high potential to serve as a functional alternative clarification agent in the beverage industry due to its promising clarification performance.

Core–shell structured magnesia–silica as a next generation catalyst for one-step ethanol-to-butadiene Lebedev process

Over 70 years, silica–magnesia catalyst prepared by wet-kneading method has been a benchmark for one-step ethanol-to-butadiene Lebedev process. Recent studies showed that wet-kneading provides an environment for the concomitant dissolution and cross-deposition of silicon and magnesium subunits, which can lead to the formation of not only the beneficial sites (Si on MgO), but also the detrimental ones (Mg on SiO2) for the Lebedev process. The use of conventional silica sources to formulate the silica–magnesia catalysts should be revisited, as they will be eventually dissolved and redispersed on MgO and the remaining SiO2 particles would be used for the formation of detrimental sites. In this regard, we demonstrated core–shell structured MgO–SiO2 catalysts as a second generation of Lebedev catalyst, where the Si subunits were selectively deposited on the MgO nanoparticles as surface magnesium silicates. Compared to the conventional wet-kneaded silica–magnesia catalyst system, we could reduce the amount of Si source by ∼40 times with the enhanced catalytic performance towards butadiene.

Author Correction: Origin of active sites on silica–magnesia catalysts and control of reactive environment in the one-step ethanol-to-butadiene process

Author Correction: Origin of active sites on silica–magnesia catalysts and control of reactive environment in the one-step ethanol-to-butadiene process

The Effect of SiC on the Phase Composition and Structure of Mixed Slag

In order to investigate the influence of SiC on the composition and structure of mixed slag (blast-furnace slag: steel slag = 1:9), the chemical composition, equilibrium-phase composition, and microscopic morphological characteristics and elemental distribution in the microscopic region of the SiC-reagent-tempered slag samples were analyzed by X-ray diffractometer (XRD), FactSage7.1 thermodynamic analysis software, scanning electron microscope, and energy spectrum analyzer. It was found that the main physical phases of the tempered slag samples were magnesia–silica–calcite (Ca3Mg(SiO4)2, C3MS2), calcium–aluminum yellow feldspar (Ca2Al2SiO7, C2AS), C2S, and iron alloy. Theoretical calculations suggest that the experimental temperature should be higher than 1500 °C to facilitate the combination of P5+ with Fe and Mn in the liquid phase to form an alloy, reduce the P5+ content in the tempered slag, and create conditions for the self-powdering of the conditioned slag. The doping of the SiC reagent can increase the liquid phase line temperature and reduce the binary basicity in the liquid phase; the liquid phase line temperatures were 1150 °C, 1200 °C, and 1300 °C and the basicities in the liquid phase were 4.68, 4.13, and 3.10 for the doping amounts of 3%, 4%, and 5% of the SiC reagent, respectively. The mixed slag doped with 4% SiC reagent achieves self-powdering and reduction of ferroalloys during the air-cooling and cooling processes, realizing the purpose of “resource utilization” of blast-furnace slag and steel slag.

Designing low-carbon cement-free binders for stabilization/solidification of MSWI fly ash

Low-carbon and high-efficiency binder is desirable for sustainable treatment of municipal solid waste incineration fly ash (MSWI FA). In this study, CaO or MgO was used to activate ground granulated blast furnace slag (GGBS) to form calcium silicate hydrate and magnesium silica hydrate gel for stabilization/solidification of hazardous MSWI FA. Experimental results showed that potential toxic elements (PTEs), such as Pb and Zn, significantly inhibited the formation of reaction products in CaO-GGBS system due to the complexation between Ca(OH)2 and PTEs, whereas PTEs only had insignificant inhibition on transformation from MgO to Mg(OH)2 in MgO-GGBS system, resulting in lower leachabilities of PTEs and higher mechanical strengths. Stabilization/solidification experiments demonstrated that MSWI FA (70 wt%) could be recycled by MgO-GGBS binder (30 wt%) into blocks with desirable 28-day compressive strengths (3.9 MPa) and PTEs immobilization efficiencies (99.8% for Zn and 99.7% for Pb). This work provides mechanistic insights on the immobilization mechanisms of PTEs in CaO/MgO-GGBS systems and suggests a promising MgO-GGBS binder for low-carbon treatment of MSWI FA.

Origin of active sites on silica–magnesia catalysts and control of reactive environment in the one-step ethanol-to-butadiene process

Origin of active sites on silica–magnesia catalysts and control of reactive environment in the one-step ethanol-to-butadiene process

Magnesium silica gel crystallized in the cell lumen of Chinese fir to construct porous structure for filtering toxic fumes

Magnesium silica gel crystallized in the cell lumen of Chinese fir to construct porous structure for filtering toxic fumes

Expansion of Nanosized MgSiO3/Chitosan Nanocomposite Structural and Spectroscopic for Loading Velosef by Nanomaterial Intervention

The aim of this study is to investigate the effect of different doses of Velosef in magnesium silica/chitosan nanocomposite in terms of structural, morphology, optical properties, and bioactivity. Loading Velosef in fine-sized magnesium silica/chitosan is an efficient engineering approach for drug delivery. The sol-gel process was used to prepare magnesium silica fine-sized before being blended into chitosan matrix, which acts as a potential morphogenetic biomaterial. The Velosef/magnesium silica/chitosan nanocomposites were characterized by XRD, TEM, SEM, FTIR, UV-absorption, and antimicrobial studies. The XRD was characteristic the crystallinity degree of the MgO-SiO2/chitosan/Velosef nanocomposites with a three maximum peaks at 26.37°, 33.34o, 36.9°. FTIR results indicated the structural change occurred with the Velosef sol-gel polymerization process. UV-absorbance reveals that the MgO-SiO2/chitosan nanocomposite appeared a high performance for loading Velosef at two absorption bands at 253 and 347 nm. The MgO-SiO2/Chitosan/Velosef nanocomposites showed considerable antimicrobial activity in opposition to the tested representative microorganisms. The maximum antimicrobial activity was obtained with MgO-SiO2/Chitosan against both Escherichia coli and Candida albicans (37 mm), while the minimum antimicrobial activity (30 mm) was recorded against B. mycoides and E. coli with control.

Development of a MgO-metakaolin binder system

The relatively high cost and limited availability of the constituent materials, are among the factors which limit the adoption of the magnesium silica hydrate (M-S-H) binder system in practice. Furthermore, the fresh and hardened properties of M-S-H binder systems vary significantly with the proportion of MgO and amorphous silica available for the hydration. In this paper, we demonstrate the application of metakaolin (Mk), a highly reactive aluminosilicate, to replace silica fume to develop a M-S-H-based binder system. To investigate the effects of component proportions on the workability, through variations in the required amount of super plasticizer, and compressive strength of the M-S-H-based mortar, a response surface methodology (RSM) is used where a series of mortar samples were prepared based on a central composite experimental design. The response surface model thus developed allowed optimization of the proportions of the mortar ingredients for a target set of workability and compressive strength. The model illustrates the highest sensitivity of water to cementitious material (w/cm) ratio for both workability and strength while revealing minor sensitivities to the other two variables of MgO/Mk ratio, and fine aggregate content. The mineralogical composition of the hydrated paste was investigated through FTIR and X-Ray diffraction and revealed the formation of a hydrotalcite-like phase along with the M-S-H gel.

The Importance of Thermal Treatment on Wet-Kneaded Silica-Magnesia Catalyst and Lebedev Ethanol-to-Butadiene Process.

The Lebedev process, in which ethanol is catalytically converted into 1,3-butadiene, is an alternative process for the production of this commodity chemical. Silica–magnesia (SiO2–MgO) is a benchmark catalyst for the Lebedev process. Among the different preparation methods, the SiO2–MgO catalysts prepared by wet-kneading typically perform best owing to the surface magnesium silicates formed during wet-kneading. Although the thermal treatment is of pivotal importance as a last step in the catalyst preparation, the effect of the calcination temperature of the wet-kneaded SiO2–MgO on the Lebedev process has not been clarified yet. Here, we prepared and characterized in detail a series of wet-kneaded SiO2–MgO catalysts using varying calcination temperatures. We find that the thermal treatment largely influences the type of magnesium silicates, which have different catalytic properties. Our results suggest that the structurally ill-defined amorphous magnesium silicates and lizardite are responsible for the production of ethylene. Further, we argue that forsterite, which has been conventionally considered detrimental for the formation of ethylene, favors the formation of butadiene, especially when combined with stevensite.

Study of the silica–magnesia relationship in silicate slags on electrical conductivity at high temperature

Slags are metallurgical aggregates with beneficial minerals and in some processes, they constitute the most abundant mass of the operation and for this reason their control is necessary. These materials have physicochemical behaviors that serve to model the process variables. A particular condition of silicate slags in processes for obtaining some ferroalloys is that there are relationships between compounds that allow predicting the behavior of other variables, these relationships are maintained during production. This study aims to know the electrical behavior of a slag so that the data will contribute to have an additional control in the operation of an electric arc furnace. An alumina content of up to 50% was gradually added to one sample and the other was remelted on three occasions, for all cases the electrical conductivity was determined at a temperature between 1400 °C and 1600 °C. For the electrical resistance value, a Miller 400 type resistivity measurement advice was used, and the temperature was achieved by melting the samples in a high-frequency induction furnace with a collapsible silicon carbide crucible, lined with high-grade refractory alumina. Analysis of the electrical conductivity data for silicate slags made it possible to demonstrate that they are proportional to the values of the major oxides of the slag in their silica-magnesia ratio.

Optimization Aging Parameters of Mg Silica Aerogel Using Box-Behnken Approach

The main objective of the present study was to investigate the application of Box–Behnken design which is a type of optimization design of response surface methodology (RSM) to predict and optimize some aging condition of magnesium silica aerogel (MSA) for improving surface properties such as surface area, pore volume and pore size. Brunauer-Emmett-Teller (BET), Barrett-Joyner-Halenda (BJH), Fourier Transform Infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) techniques, tap density method and helium pycnometer were used to characterize aerogels. The operating conditions were optimized as a function of the molar ratio of Mg:Si (0.35, 0.50 and 0.65), aging time (24 h, 60 h and 96 h) and aging temperature (50 oC, 70 oC and 90 oC). Lack of fit test indicates that the quadratic regression model was significant with the high coefficients of determination values for all three properties. Optimized aging factors for synthesis MSA with high BET surface area, high BJH pore volume and average BJH pore size were found to be 0.5 Mg:Si molar ratio, 79.62 oC and 61.51 h, respectively. Under these conditions, magnesium silica aerogels have great properties: 734 m2.g-1 BET surface area, 0.41 cm3.g-1 BJH pore volume and 4.91 nm BJH pore size, 0.12 g.cm−3 density and 95 % porosity. Box-Behnken is useful optimization tool for production of nanoporous magnesium silica aerogel.

Effect of pulverized fuel ash, ground granulated blast-furnace slag and CO2 curing on performance of magnesium oxysulfate cement

This paper aims to investigate the influence of pulverized fuel ash (PFA) and ground granulated blast-furnace slag (GGBS) on compressive strength and water resistance of magnesium oxysulfate (MOS) cement with and without CO2 curing treatment. Hydration products and microstructure of typical samples were also evaluated using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential thermal analysis-thermogravimetry (DTA-TG), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) facilities. The results showed that compressive strength of MOS cement was decreased by the addition of PFA or GGBS. The CO2 curing resulted in a negative effect on compressive strength of MOS cement other than Portland cements. The decreased compressive strength of MOS cement induced by CO2 curing can be alleviated by incorporation of suitable dosages of PFA or GGBS. Both PFA and GGBS behaved an improvement on the water resistance of MOS due to the formation of magnesium silica hydrate gel (M-S-H gel). Therefore, the coupling effect of PFA or GGBS as partial substitution of magnesium oxide (MgO) and CO2 curing treatment provides a potential method to manufacture MOS cement with higher durability and lower environmental impact.

Development of magnesium-silicate-hydrate (M-S-H) cement with rice husk ash

Rice husk ash (RHA) is a waste material obtained from the combustion of rice hulls. The properties of RHA, such as its crystallinity and reactivity, depend on the combustion conditions. This study investigated the use of RHA as a silica source in MgOSiO2 samples. Two different RHA sources (crystalline and amorphous) were used in comparison to microsilica (MS), which is commonly used in MgOSiO2 formulations to form magnesium silica hydrate (M-S-H). Isothermal calorimetry and pH measurements were used to analyze the progress of hydration. In addition to compressive strength measurements, microstructural analysis was performed via XRD, TG/DTG, FTIR and FESEM. Samples containing amorphous RHA as the silica source achieved the highest compressive strengths at early ages (34 MPa at 7 days), whereas those containing MS revealed the highest strengths in the long term (47 MPa at 56 days). This was in line with the faster dissolution rate of amorphous RHA in comparison to MS, as observed in pH measurements. The formation of M-S-H was clearly observed in all samples containing amorphous RHA and/or MS. The use of crystalline RHA led to low strengths, which was provided by brucite in the absence of M-S-H. Combination of amorphous RHA with MgO resulted in M-S-H formation, which was accompanied with a notable mechanical performance. Utilization of amorphous RHA in MgO systems could not only lead to strength gain, but also bring environmental and economic benefits.

Effect of Dissolved Silica on Immobilization of Boron by Magnesium Oxide

The effect of silica on the immobilization reaction of boron by magnesium oxide was investigated by laboratory experiments. In the absence of silica, due to dissolution of the magnesium oxide, boron was removed from solutions by the precipitation of multiple magnesium borates. In the presence of silica, magnesium silica hydrate (M-S-H) was formed as a secondary mineral, which takes up boron. Here 11B magic-angle spinning nuclear magnetic resonance (MAS-NMR) and Fourier transform infrared spectrometer (FT-IR) data show that a part of the boron would be incorporated into M-S-H structures by isomorphic substitution of silicon. Another experiment where magnesium oxide and amorphous silica were reacted beforehand and boron was added later showed that the shorter the reaction time of the preceding reaction, the higher the sorption ratio of boron. That is, boron was incorporated into the M-S-H mainly by coprecipitation. The experiments in the study here show that the sorption of boron in the presence of silica is mainly due to the incorporation of boron during the formation of the M-S-H structure, which suggests that boron would not readily leach out, and that stable immobilization of boron can be expected.

Comparison of glass powder and pulverized fuel ash for improving the water resistance of magnesium oxychloride cement

The water resistance of magnesium oxychloride cement (MOC) incorporating glass powder (GP) and pulverized fuel ash (PFA) with and without CO2 curing was investigated in terms of the strength retention coefficient and the volume stability. The microstructure was studied using quantitative X-ray diffraction (QXRD), thermogravimetry (TG), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the effect of incorporating GP on the water resistance is much lower than that of PFA due to the lower pozzolanic activity of GP generating a lower amount of magnesium silica hydrate gel (M-S-H gel). The MOC incorporated with GP or PFA showed high water resistance after CO2 curing due to the higher quantity of amorphous gel that formed a much denser interlocking network.

Influence of Gel Aging Time on the Properties of Various Silica Aerogels Synthesized from Water Glass

In the present paper, water glass was used to synthesize silica aerogels and calcium magnesium silica aerogels. The present research was aimed to investigate the effect of gel aging time (1 and 24 hours) on the physical and surface properties of aerogels. Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, Fourier Transform Infrared spectroscopy and scanning electron microscopy techniques were used to characterize aerogels. Successful formation of nanopores (2.8-4.4 nm) was approved by N2 adsorption/desorption isotherms. The aerogels contained porous network structure with different surface areas (388.9-729.9 m2 g-1). Aging for longer times led to an ability to decrease the density of the aerogels. The bulk density was higher in silica aerogels than in calcium magnesium silica aerogels. The well-tailored network matrix with high BET surface area (729.9 m2 g-1) and low density (0.116 g cm-3) was achieved via 24 hours gel aging of calcium magnesium silica aerogel.

Ethanol to 1,3‐Butadiene Conversion by using ZrZn‐Containing MgO/SiO2 Systems Prepared by Co‐precipitation and Effect of Catalyst Acidity Modification

AbstractThe conversion of ethanol to 1,3‐butadiene (1,3‐BD) has been investigated over ZrO2‐ and ZnO‐containing magnesia silica oxides prepared by a co‐precipitation method at different Mg‐to‐Si molar ratios. The effect of reaction temperature and ethanol flow rate was investigated. The catalyst acidity was modified through the addition of alkali metals (Na, K and Li) to the final materials. Catalysts were characterised by nitrogen physisorption analysis, X‐ray diffraction, scanning electron microscopy with energy dispersive X‐ray, temperature‐programmed desorption of ammonia, infrared spectroscopy and 29Si/(7Li) NMR spectroscopy. The catalytic results showed that the controlled reduction of catalyst acidity allows ethanol dehydration to be suppressed, whilst increasing 1,3‐BD selectivity. The best catalytic performance achieved 72 mol % for the combined 1,3‐BD and acetaldehyde selectivity.

Role of Magnesium Silicates in Wet-Kneaded Silica–Magnesia Catalysts for the Lebedev Ethanol-to-Butadiene Process

Wet-kneading is a technique commonly used for the synthesis of SiO2–MgO catalysts for the Lebedev ethanol-to-butadiene process, with catalyst performance known to depend heavily on the preparation parameters used in this method. Here, the large influence of Mg precursor and MgO content on morphology, chemical structure (as determined by TEM(-EDX), FT-IR, XRD and solid-state 1H–29Si cross-polarized MAS NMR), and on catalyst performance is demonstrated. The Mg precursor used is found to influence the extent of magnesium silicate formation during wet-kneading, as estimated from TEM and FT-IR, which, in turn, was found to correlate with catalyst performance. Accordingly, the catalyst synthesized from a nanosized Mg(OH)2 precursor (SiO2–MgO (III)nano), showing the highest degree of chemical contact between the SiO2 and MgO components, gave the highest butadiene yield. Variation of the Mg/Si ratio in a series of SiO2–MgO (III)nano materials showed a volcano-type dependence of the butadiene yield on MgO content....