Experimental Study on the Characteristics of Activated Coal Gangue and Coal Gangue-Based Geopolymer

Zhang, Weiqing; Dong, Chaowei; Huang, Peng; Sun, Qiang; Li, Meng; Chai, Jinxiang

doi:10.3390/en13102504

Cited by 56 publications

(27 citation statements)

References 42 publications

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“…The activation effect is related to the modulus of sodium silicate (modulus is the ratio of SiO 2 to Na 2 O) and the dosage of alkali. The modulus of a sodium silicate excited geopolymer is usually about 1 [ 12 ], and the mixing ratio of the alkali activator is about 20%. The modulus of liquid sodium silicate sold on the market is above 2.25, and too high a modulus of sodium silicate is not conducive to the excitation of geopolymer, so the modulus needs to be reduced.…”

Section: Methodsmentioning

confidence: 99%

“…However, geopolymers that only use coal gangue as raw materials have low compressive strength and cannot meet the high compressive strength requirements of engineering [ 10 ]. Therefore, coal gangue is often combined with other industrial solid wastes such as steel slag, blast furnace slag, and fly ash to produce geopolymers [ 11 , 12 , 13 , 14 ]. Blast furnace slag (BFS) is another solid waste byproduct when pig iron is smelted in the blast furnace at 1400–1600 °C.…”

Section: Introductionmentioning

confidence: 99%

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Compressive and Flexural Properties of Ultra-Fine Coal Gangue-Based Geopolymer Gels and Microscopic Mechanism Analysis

Yang

Zhang

Lin

2022

Gels

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Geopolymer gel that possesses advantageous features of fast setting, high strength, and good durability is increasingly used in civil engineering, including rapid retrofit projects, roadway, and other construction projects. Furthermore, geopolymer gel is also a green and economical material as it derives from solid wastes. In this study, activators with different sodium silicate modulus and alkali content were used to activate ultrafine coal gangue and slag powder to prepare coal-gangue-based geopolymers with high strength. To study the influence of slag powder content, sodium silicate modulus, and alkali activator content on strength, a two-stage design was adopted. In the first stage, the orthogonal test with three factors and four levels (10–40% slag, 0.4–1.0 modulus, 16–22%) was used to obtain the influence of each factor on the strength and select the design range of the specimen mix ratio with higher strength. In the second stage, based on the orthogonal experiment, the scope was narrowed to continue to find the optimal excitation scheme and the relationship between the influencing factors and strength. Further, mineral compositional, microstructural, functional group and elemental analyses were performed using X-ray diffraction technique, IR infrared diffraction, electron microscope observation and energy spectrum analysis to elucidate the mechanisms of the strength development. The results show that the factors affecting the geopolymer’s strength were in the order of slag content > alkali content > modulus. The optimum dosage of alkali activator was 18–20%, and the sodium silicate modulus was 0.6–0.8, and the compressive and flexural strength could reach above 40 MPa and 5.9 MPa, respectively. The compressive strength and modulus were in a parabolic relationship. Three types of cementing gels (N-A-S-H, C-A-S-H, and C-N-A-S-H) that were characterized with dense structure and high strength were identified from coal gangue and slag powder after alkali excitation.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Compressive and Flexural Properties of Ultra-Fine Coal Gangue-Based Geopolymer Gels and Microscopic Mechanism Analysis

Yang

Zhang

Lin

2022

Gels

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“…As a solid waste, coal gangue is often piled in the open field, which can contaminate the surrounding environment, e.g., dust, toxic gas, heavy metal leaching, and acidic pollution [ 9 , 10 , 11 ]. Coal gangue contains a large amount of silica and alumina is a desirable raw material that can be used to produce geopolymer gel [ 12 , 13 , 14 , 15 ]. The use of coal gangue in the production of geopolymers can effectively solve the problem of environmental pollution.…”

Section: Introductionmentioning

confidence: 99%

“…Calcination belongs to thermal activation, and the reactivity of raw materials is increased by calcination. For raw coal gangue, its reactivity is relatively weak; however, this can be enhanced after high temperature treatment [ 13 , 18 ]. Research shows that calcination at a temperature of 700 °C for 2 h would transform coal gangue into amorphous metakaolin with strong activity [ 19 ].…”

Section: Introductionmentioning

confidence: 99%

Microstructure Analysis and Effects of Single and Mixed Activators on Setting Time and Strength of Coal Gangue-Based Geopolymers

Yang

Zhang

Lin

2022

Gels

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Geopolymer is a green non-metallic material with high strength and favorable properties in resistance to corrosion, fire, and high temperature, which makes it a potential substitute for Portland cement. The existing studies have primarily focused on the preparation of geopolymers using silico-alumina materials such as fly ash, red mud, metakaolin, volcanic ash, and blast furnace slag to develop geopolymers. This study explores the potential of using ultrafine calcined coal gangue and ground granulated blast furnace slag to develop a new geopolymer with the activation of a single activator (sodium hydroxide) or mixed activator (sodium hydroxide, liquid sodium silicate, and desulfurization gypsum). The setting time and strength of the geopolymers were investigated, followed by the mineral, functional groups, microstructure, and elements analyses using X-ray diffraction, Fourier transform infrared diffraction, scanning electron microscope, and energy dispersive spectrometer to elucidate the effect of different activators on geopolymers. The results showed that the optimum molarity of NaOH single activator was 2 mol/L, the initial setting time and final setting time were 37 min and 47 min, respectively, and the compressive and flexural strengths at 28 days were 23.2 MPa and 7.5 MPa. The optimal mixing ratio of the mixed activator was 6% desulfurization gypsum, 0.6 Na2SiO3 modulus, and 16% SS activator; the initial setting time and final setting time were 100 min and 325 min, respectively, and the compressive and flexural strengths at 28 days were 40.1 MPa and 7.8 MPa. The coal gangue geopolymers were mainly C–A–S–H, N–A-S-H, and C–N–A–S–H gels. The mixed activator tended to yield higher strengths than the single activator, the reason is that the hydration reaction was violent and produced more gels. Meanwhile, the relation between setting time and activator and the relation between strength and activator were also obtained, which provide theoretical support for predicting the setting time of coal gangue base polymer and the ratio of alkali activator for geopolymers with a certain strength.

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“…Coal gangue is the main solid waste generated during coal mining and washing, accounting for about 10-25% of total coal production [1][2][3][4]. With the progress of coal mining activities, coal gangue accumulates in large quantities; it has become one of the largest industrial residues [5,6].…”

Section: Introductionmentioning

confidence: 99%

Adsorption and Desorption of Coal Gangue toward Available Phosphorus through Calcium-Modification with Different pH

Min

Jiang

et al. 2022

Minerals

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The chemical reaction between calcium ions (Ca2+) and phosphate in the soil is the main way to maintain the availability of soil phosphorus. Thus, we believe stimulating coal gangue with Ca2+ solution would be an effective way to improve its adsorption and desorption capacity toward phosphate. In order to explore the effects of different pH of Ca2+ solution on the modified effect of coal gangue, we conducted mechanical grinding (<1 mm), high temperature calcination (800 °C), and the stimulation of Ca2+ solution with different pH (2, 7, 13), to prepare acidic calcium-modified coal gangue (Ac-CG) (Ac-CG, acidic calcium-modified coal gangue; Ne-CG, neutral calcium-modified coal gangue; Al-CG, alkali calcium-modified coal gangue; RCG, raw coal gangue), neutral calcium-modified coal gangue (Ne-CG), and alkali calcium-modified coal gangue (Al-CG); raw coal gangue (RCG) was regarded as the control. The results indicated that Al-CG had better phosphate adsorption (3.599 mg g−1); this favorable adsorption performance of Al-CG was related to the formation of hydrated calcium silicate gel and ettringite, which provided more Ca2+, Al3+, and hydroxyl groups, and a larger specific surface area (9.497 m2 g−1). Moreover, Al-CG not only held more phosphate but also maintained its availability longer for plants. It is suggested that stimulating coal gangue with Ca2+ solution under alkaline conditions is a perfect way to enhance its adsorption and desorption capacity toward phosphate; the Al-CG we prepared could be used as filling material and soil conditioner in the reclamation area.

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Experimental Study on the Characteristics of Activated Coal Gangue and Coal Gangue-Based Geopolymer

Cited by 56 publications

References 42 publications

Compressive and Flexural Properties of Ultra-Fine Coal Gangue-Based Geopolymer Gels and Microscopic Mechanism Analysis

Compressive and Flexural Properties of Ultra-Fine Coal Gangue-Based Geopolymer Gels and Microscopic Mechanism Analysis

Microstructure Analysis and Effects of Single and Mixed Activators on Setting Time and Strength of Coal Gangue-Based Geopolymers

Adsorption and Desorption of Coal Gangue toward Available Phosphorus through Calcium-Modification with Different pH

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