Showing papers on "Sodium silicate published in 2017"

Characterisation of One-Part Geopolymer Binders Made from Fly Ash

Abstract: The kinetics of one-part “just add water” geopolymerisation reaction is studied in the system of fly ash as an aluminosilicate precursor and solid sodium silicate as alkali activator. The rates of the release of Si and Al nutrients from source materials can significantly affect their availability for reaction and their extent of participation in geopolymer gel structure. The crystalline phases that usually appear in fly ash geopolymers are missing in the one-part mix binders studied here, and by increasing the Si/Al ratio the amount of Si contribution in the final geopolymer gel is decreased. The sample with lower water content sees the participation of more Si in both stages of gel formation. Adjusting the composition of raw materials can improve the mechanical properties of the final one-part mix binder. Reasonable mechanical strength with the maximum strength of 65 MPa is achieved.

Combination formation in the reinforcement of metakaolin geopolymers with quartz sand

Abstract: Although quartz sand is widely used as filler material in construction, a few studies investigated the incorporation of quartz sand in geopolymers. To study the incorporation of quartz sand in the reinforcement of metakaolin geopolymer not only fills this gap, but also gives a clue on using non-calcinated aluminosilicates (e.g., mine tailings) in the synthesis of geopolymers. In the presence of sodium silicate, metakaolin geopolymers were synthesized with quartz sand of various size ranges as filler material. XRD, FTIR, SEM and NMR characterizations on the geopolymers indicate the dissolution, precipitation, and the formation of combination on quartz particles that associates them into the geopolymeric gel, so as to reinforce the mechanical strength of geopolymers. The compressive strength of metakaolin geopolymers with only silicate, silicate plus quartz sand and silicate plus rutile sand is 31.2, 52.2 and 41.5 MPa, respectively. In geopolymer with silicate and quartz sand, a decreasing Si/Al ratio as increasing distance from the quartz particle is observed through an energy dispersive X-ray (EDX) mapping. The SEM images and NMR spectra suggest that the formed combination is of several micrometers with main species of polysialates (-Si-O-) such as Q4(2Al), Q4(1Al).

Synthesis of glycerol carbonate from glycerol and dimethyl carbonate catalyzed by calcined silicates

Abstract: Several anhydrous silicates were prepared by calcination at 400 °C and utilized as solid base catalyst for synthesizing glycerol carbonate (GC) by transesterification of glycerol with dimethyl carbonate (DMC) Among them, calcined sodium silicate showed the best catalytic activity with glycerol conversion of 977% Then, a series of sodium silicates calcined at different temperatures were characterized using TGA, Hammett indicator method, BET, XRD, FT-IR and FESEM Effect of calcination temperature on their catalytic ability was carefully investigated, followed by a reaction optimization study The basicity of sodium silicates calcined at different temperatures highly depended on calcination temperature; their catalytic ability was affected by their total basicity rather than by their BET surface area; and the increased amount of strong basic sites resulted in the formation of by-product which decreased the GC yield and GC selectivity Sodium silicate calcined at 200 °C (Na 2 SiO 3 -200), which had the intermediate total basicity and relative low amount of strong basic sites, incurred the highest GC yield The highest catalytic performance of Na 2 SiO 3 -200 was achieved under the condition that the 4:1 molar ratio of DMC to glycerol was reacted at 75 °C for 25 h This catalyst could be reused five times without noticeable drop in catalytic activity

One-pot synthesis of highly efficient MgO for the removal of Congo red in aqueous solution

Abstract: Magnesium oxide (MgO) has been demonstrated to be a promising candidate for the treatment of toxic dyes in wastewater due to its unique characteristics (e.g., high isoelectric point, nontoxicity and cost-effectiveness). However, it is still a great challenge to fabricate highly efficient MgO for toxic dyes through facile synthetic strategies. Herein, a porous rod-like MgO with extremely high adsorption capacity for Congo red dye (3236 mg g−1) has been presented through a facile precipitation reaction between Mg2+ and CO32− in the presence of a trace amount of sodium silicate. After systematically investigating the experimental parameters, the results exhibited that the performance of the resulting MgO was very sensitive to the amount of sodium silicate in the reaction, stirring time and calcination temperature, and its adsorption capacity was closely related to the surface base properties rather than the specific surface areas of MgO. The adsorption process of Congo red on the as-synthesized product obeyed the pseudo-second-order rate equation and the Langmuir adsorption model. It is expected that the developed method will provide a facile route to gram level production of highly efficient MgO for handling toxic dyes in industrial wastewater.

Evaluation of sodium content and sodium hydroxide molarity on compressive strength of alkali activated low-calcium fly ash

Abstract: Activation of low calcium fly ash is investigated using activating solutions of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3). The oxide ratio of Na2O relative to the total reactive silica in the activated mix provides consistent results in achieving the highest ultimate strength. The total reactive silica used for calculating the ratio consists of the reactive silica contributed by fly ash and the silica from the activating solution. There is an increase in the ultimate compressive strength on increasing the total sodium content relative to the total reactive silica content in the activated system. Increasing the sodium content beyond a certain limit does not provide additional gain in the ultimate compressive strength. The ratio of total reactive SiO2 to Na2O in the activated system equal to 4.72 is shown to provide the highest compressive strength and there is no further increase in the ultimate strength on increasing the sodium content. A N-A-S-H type gel with reaction products containing Si, Al and Na, is formed in the activated system. The ultimate strength achieved is directly related to the reaction product content in the system and is dependent on the extent of glassy phase dissolution from fly ash. The extent of glassy phase dissolution and the quantity of reaction product formed in the system increases with an increase in the molarity of NaOH, which also contributes to an increase in the sodium content in the activating solution. The decrease in the unreacted glassy phase content of fly ash is sensitive to temperature at a lower molarity of NaOH. The Al/Na ratio in the reaction product approaches a value of 0.9 on increasing the sodium content in the activated system. The Si/Al ratio in the reaction product varies within a range of 2.3–2.8.

Hydrothermal Synthesis of Mesoporous Silica MCM-41 Using Commercial Sodium Silicate

Abstract: In this work, ordered mesoporous silica MCM-41 was pre- pared by hydrothermal synthesis using industrial-grade sodium silicate (Na2SiO3) as silica source, hexadecyltrimethyl-ammonium bromide (CTAB) as template agent and ethyl acetate as pH regulator. The in- fluence of CTAB/SiO2 molar ratio, reaction time, aging temperature, and co-surfactant type on the structural and morphological properties of the obtained silica was studied. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption-de- sorption isotherms. Ordered mesoporous MCM-41 silica was obtained at 80 °C by using a range of CTAB/SiO2 molar ratio from 0.35 to 0.71 and reaction times up to 72 h and isopropanol (i-PrOH) as co- surfactant.

Alkali Activation of Ladle Slag from Steel-Making Process

Abstract: Ladle slag, currently an under-utilized crystalline metallurgical residue, was studied for use as a precursor for alkali activation. An activating solution containing sodium silicate and potassium hydroxide was used in activating the slag with varying compositional ratios in order to optimize the compressive strength. Ladle slag is commonly regarded as having limited reaction with alkalis, and in previous studies, it has been therefore mixed with reactive precursors, such as metakaolin. However, based on our results, ladle slag shows potential as a sole precursor for alkali-activated binders. X-ray diffractometry reveals that the major minerals in the ladle slag were identified to be γ-dicalcium silicate and mayenite. After alkali activation, the major reaction product was a silicate hydrate according to DRIFT analysis–sodium-substituted calcium aluminosilicate hydrate gel, C–(N)–A–S–H. XRD analysis supports the hypothesis by revealing an amorphous “halo” in the alkali-activated slag. The unconfined compressive strength of the optimized alkali-activated ladle slag paste specimen was 65 MPa at 28 days.

Fabrication of superhydrophobic filter paper and foam for oil–water separation based on silica nanoparticles from sodium silicate

Abstract: We demonstrate the synthesis of hydrophobic silica nanoparticles from sodium silicate and their application in separation of the oil–water mixture. For this, hydrophobic silica nanoparticles of size 35 ± 8 nm were initially synthesized by sol–gel method using sodium silicate and trimethylchlorosilane, and further deposited on commercially available filter paper and polyurethane foam by dip coating technique. The coating cycles were optimized for filter paper to ensure that fibers of the filter paper have been completely covered with hydrophobic silica nanoparticles to provide an ideal porous superhydrophobic/superoleophilic framework for gravity based separation of oil–water mixtures. It was confirmed by water contact angle of ~155° and sliding angle <5°. Whereas the superhydrophobic polyurethane foam was utilized for collection of oil from oil–water mixtures via absorption. The capability of these materials to separate oil from water was tested against the mixtures of water with n-hexane, gasoline, diesel, kerosene oil and engine oil. Moreover, the produced particles can also be used for fabrication of semi-transparent superhydrophobic surfaces.

Effect of sodium hydroxide and sodium silicate solutions on strengths of alkali activated high calcium fly ash containing Portland cement

Abstract: In this paper, the mechanical performance of fly ash and Portland cement geopolymer activated with sodium hydroxide and sodium silicate solutions was studied. The Geopolymer Mortars (GM) were made from high calcium Fly Ash (FA) and ordinary Portland Cement (PC) with FA:PC weight ratios of 100:0, 95:5, 90:10, 85:15, and 80:20. The GMs were activated with three combinations of sodium Hydroxide Solution (SH) and sodium Silicate Solution (SS) viz., SH, SH+SS (SH:SS=2) and SS. For all mixes, 10 molar SH, alkali activator liquid/solid binder ratio of 0.60 and curing at ambient temperature of 25oC were used. The result indicated that the compressive and shear bond strengths of GM depended on the alkali activators used and the amount of PC. The use of SH and SHSS resulted in the formation of additional Calcium Silicate Hydrate (CSH) which coexisted with sodium aluminosilicate hydrate (NASH) gel. Whereas, the use of SS resulted in NASH gel with only a small amount of CSH. The increasing of PC content enhanced the compressive and shear bond strengths of GMs due to the formation of additional CSH. The 15% PC mixed with SHSS gave the optimum compressive and shear bond strengths.

Fresh properties and compressive strength of high calcium alkali activated fly ash mortar

Abstract: This paper reports the fresh properties and compressive strength of high calcium alkali-activated fly ash (AAFA) mortar. Two different sources of class C fly ash, with different chemical compositions were used to prepare alkali-activated mortar mixtures. Four different sodium silicate to sodium hydroxide (SS/SH) ratios of 0.5, 1.0, 1.5, and 2.5 were used as alkaline activators with a constant sodium hydroxide concentration of 10 M. Two curing regimes were also applied, oven curing at 70 °C for 24 h, and ambient curing at 23 ± 2 °C. The rest time, i.e., the time between casting the mortar cubes and starting the oven curing was 2 h. The results revealed that the setting time, and workability of mortar decreased with increasing the alkali to fly ash ratio, and decreasing the water to fly ash ratio. The optimum sodium silicate to sodium hydroxide ratio was 1.0, which showed the highest compressive strength and setting time. An increase of sodium silicate to sodium hydroxide ratio to 2.5 led to a significant reduction in the setting time, and workability of mortar. The 7-day compressive strength of the mortar approached 20.80 MPa for ambient cured regime and 41.10 for oven cured regime.

The combined effect of lead ion and sodium silicate in the flotation separation of scheelite from calcite

Abstract: Flotation separation of scheelite from calcite is difficult because of the existence of the same cation in the minerals and similar physicochemical characteristics. Many studies have been performed to determine the selective depressants for calcite, but the separation of scheelite from calcite is still a big problem. In this article, the flotation separation of scheelite from calcite has been studied by flotation tests. The results show that benzohydroxamic acid has weak collecting ability to both scheelite and calcite. Lead ions can activate the flotation of scheelite and calcite, but the flotation separation of scheelite from calcite can’t be realized. The depressant saline sodium silicate (mixture of sodium silicate and lead ions) has selective depression effect on calcite and the optimum ratio of sodium silicate to lead ions is 3:1. The use of saline sodium silicate as a depressant can achieve the flotation separation of scheelite from calcite. The zeta potential results and adsorption studies...

Comparison of strength and durability characteristics of a geopolymer produced from fly ash, ground glass fiber and glass powder

Abstract: Strength and durability characteristics of geopolymers produced using three precursors, consisting of fly ash, Ground Glass Fiber (GGF), and glass-powder were studied. Combinations of sodium hydroxide and sodium silicate were used as the activator solutions, and the effect of different sodium and silica content of the activators on the workability and compressive strength of geopolymers was investigated. The parameters used in this study were the mass ratio of Na2O-to-binder (for sodium content), and SiO2-to-Na2O of the activator (for silica content). Geopolymer mixtures that achieved the highest compressive strength from each precursor were assessed for their resistance to alkali-silica reaction and compared against the performance of portland cement mixtures. Test results revealed that GGF and fly ash-based geopolymers performed better than glass-powder-based geopolymer mixtures. The resistance of GGF-based and fly ash-based geopolymers to alkali-silica reaction was superior to that of portland cement mixtures, while glass-powder-based geopolymer showed inferior performance.