Extraction of Valuable Metals and Preparation of Mesoporous Materials from Circulating Fluidized Bed-Derived Fly Ash via an Acid–Alkali-Based Alternate Method

Ma, Zhibin; Zhang, Xueli; Guo, Yanxia; Cheng, Fangqin

doi:10.1021/acsomega.0c04737

Cited by 24 publications

(3 citation statements)

References 29 publications

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“…Thus, to reduce the amount of sodalite in the solid residue, the preliminary acid extraction of the soluble Al before desilication is suggested [28]. The use of the acid-alkali-acid leaching method was reported by [29,30]. However, such methods have numerous washing steps, and the inevitable neutralization of the acid and alkali cannot be avoided.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Coal Fly Ash Desilication Using Atmospheric NaOH Leaching with Simultaneous Magnetic Separation

Shoppert,

Valeev,

Loginova

et al. 2023

Metals

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Coal fly ash (CFA) is a technogenic waste formed during coal combustion in thermal power plants (TPPs). The extraction of valuable components from CFA is complicated by the presence of a large amount of amorphous glassy mass and iron. Herein, a novel method of CFA desilication with complete extraction of the amorphous glassy mass without desilication product (DSP) precipitation and simultaneous magnetic fraction recovery in one stage is presented. The Fe recovery in the magnetic fraction using the proposed method was significantly improved from 52% to 68%. After conventional wet magnetic separation, followed by the proposed method for desilication and magnetic fraction separation, the Fe recovery was increased to 73.8%. Because of the absence of DSP precipitation, the Na2O content in the solid residue after desilication was lower than 1 wt.%. The simultaneous desilication and magnetic separation of magnetite was achieved by installing a belt of permanent magnets on the outer surface of the reactor, where the CFA was leached by the highly concentrated NaOH solution. The effects of different parameters on the extraction of Si, Al, and Fe from the raw CFA were elucidated by varying the liquid-to-solid ratio (L:S ratio) from 5 to 10, the temperature from 100 to 120 °C, the leaching time from 10 to 30 min, and the particle size from −50 µm to −73 µm. The optimal leaching parameters were determined to be temperature = 110 °C, L:S ratio = 7.5, and leaching time = 20 min. The extraction of Si and Fe under these conditions was higher than 66 and 73%, respectively. The Al extraction was lower than 10%. The solid residue of NaOH leaching and the magnetic fraction were examined by X-ray diffraction, X-ray fluorescence spectrometry, vibrating sample magnetometry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller, and laser diffraction analyses.

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Section: Introductionmentioning

confidence: 99%

Enhanced Coal Fly Ash Desilication Using Atmospheric NaOH Leaching with Simultaneous Magnetic Separation

Shoppert,

Valeev,

Loginova

et al. 2023

Metals

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“…However, using the conventional desilication method at the low L:S ratio, the Si extraction at the preliminary alkaline desilication stage does not exceed 60%; as much as ≈12-14 wt. % Na 2 O was found in the solid residue after desilication [40]. This is because a part of alumina in the CFA is contained in an amorphous glassy mass that readily dissolves and leads to DSP precipitation.…”

Section: Introductionmentioning

confidence: 99%

Kinetics Study of Al Extraction from Desilicated Coal Fly Ash by NaOH at Atmospheric Pressure

2021

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The most promising source of alumina in the 21st century is the coal fly ash (CFA) waste of coal-fired thermal plants. The methods of alumina extraction from CFA are often based on the pressure alkaline or acid leaching or preliminary roasting with different additives followed by water leaching. The efficiency of the alumina extraction from CFA under atmospheric pressure leaching is low due to the high content of acid-insoluble alumina phase mullite (3Al2O3·2SiO2). This research for the first time shows the possibility of mullite leaching under atmospheric pressure after preliminary desilication using high liquid to solid ratios (L:S ratio) and Na2O concentration. The analysis of the desilicated CFA (DCFA) chemical and phase composition before and after leaching has been carried out by inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray diffraction (XRD). The morphology and elemental composition of solid product particles has been carried out by scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). An automated neural network and a shrinking core model (SCM) were used to evaluate experimental data. The Al extraction efficiency from DCFA has been more than 84% at T = 120 °C, leaching time 60 min, the L/S ratio > 20, and concentration of Na2O—400 g L−1. The kinetics analysis by SCM has shown that the surface chemical reaction controls the leaching process rate at T < 110 °C, and, at T > 110 °C after 15 min of leaching, the process is limited by diffusion through the product layer, which can be represented by titanium compounds. According to the SEM-EDX analysis of the solid residue, the magnetite spheres and mullite acicular particles were the main phases that remained after NaOH leaching. The spheric agglomerates of mullite particles with non-porous surface have also been found.

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“…This allows a more effective release of the metal atoms from the SiO 4 tetrahedrons [ 22 ]. Therefore, some studies [ 23 , 24 , 25 ] of hydrometallurgical alkaline explored approaches to removal silica from CFA. It is worth mentioning that there were indisputable benefits for the alkali-calcination step form shortening the time for zeolitisation and reducing the inclusion of amorphous-crystalline textures, thereby helping to purify the zeolite crystal phase [ 26 , 27 , 28 ].…”

Section: Introductionmentioning

confidence: 99%

Study on the Overall Reaction Pathways and Structural Transformations during Decomposition of Coal Fly Ash in the Process of Alkali-Calcination

et al. 2021

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In this research, phase transformation and the role of NaOH on the structure of coal fly ash (CFA) during an alkali-calcination process were identified by a combination of X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) and deconvolution analysis. The variation in the different functional groups and structural parameters of the raw and post-alkali calcinated CFA were analysed by deconvolution of the FTIR results, conducted with a Gaussian approach. The results, firstly, provide a deep insight into the functional groups in CFA. In CFA systems, the vibration signals of Q0, Q1, Q2 and Q3 were detected and the dominant structural units associated with Si tetrahedron groups were isolated to Q3 and Q2. Deconvolution analysis of the band from 400 to 1400 cm−1 showed that the added NaOH resulted in an increase in Q1 at the cost of Q3 and Q2 and the degree of reaction of the CFA was, therefore, decreased. Concurrently, it was established that the changes in the Gaussian peak component were related to the calcination temperature and time that allowed us to tailor the model of the structural decomposition of CFA.

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Extraction of Valuable Metals and Preparation of Mesoporous Materials from Circulating Fluidized Bed-Derived Fly Ash via an Acid–Alkali-Based Alternate Method

Cited by 24 publications

References 29 publications

Enhanced Coal Fly Ash Desilication Using Atmospheric NaOH Leaching with Simultaneous Magnetic Separation

Enhanced Coal Fly Ash Desilication Using Atmospheric NaOH Leaching with Simultaneous Magnetic Separation

Kinetics Study of Al Extraction from Desilicated Coal Fly Ash by NaOH at Atmospheric Pressure

Study on the Overall Reaction Pathways and Structural Transformations during Decomposition of Coal Fly Ash in the Process of Alkali-Calcination

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