Extraction of alumina from coal fly ash using an acid leach-sinter-acid leach technique

Shemi, A.; Ndlovu, Sehliselo; Sibanda, Vusumuzi; Dyk, L. Van

doi:10.1016/j.hydromet.2015.08.023

Cited by 73 publications

(39 citation statements)

References 15 publications

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“…In this process, leaching is achieved by proton attack whereby the hydronium ion displaces the metal cation from the ash particle matrix (Eq. 3), rendering the metal soluble [9] Increasing the liquid:solid ratio increases the solubility of CaSO 4 in acid, thus exposing the underlying aluminum to the acid for further dissolution. Their findings confirmed earlier results by Seidel and Zimmels [13] who also achieved poor alumina extraction at low acid concentration.…”

Section: Direct Acid Leachingmentioning

confidence: 99%

“…Shemi [9] conveniently categorized the processing of CFA using the acid route into two groups: direct and indirect leaching. In direct leaching, there is no prior treatment of the CFA before contacting with the acid, whereas indirect leaching involves prior interventions meant to make the alumina more responsive to acid leaching.…”

Section: Direct Acid Leachingmentioning

confidence: 99%

“…In direct leaching, there is no prior treatment of the CFA before contacting with the acid, whereas indirect leaching involves prior interventions meant to make the alumina more responsive to acid leaching. While the amorphous phase is reactive and soluble in inorganic acids, the mullite phase is refractory and unresponsive to acid leaching under conditions of low acid concentration [9,14,15,23]. Unfortunately, in typical CFA, it is the mullite phase which contains a larger proportion of the total alumina.…”

Section: Direct Acid Leachingmentioning

confidence: 99%

“…Amenability of CFA to different forms of leaching for aluminum recovery has been successfully demonstrated in concept by a number of workers including sulfuric acid leaching [21,22,9], nitric acid leaching [10], alternate alkaline (other than NaOH) leaching [11], and bioleaching [12,13].…”

Section: Introductionmentioning

confidence: 99%

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Towards the Utilization of Fly Ash as a Feedstock for Smelter Grade Alumina Production: A Review of the Developments

Sibanda

Ndlovu

Dombo

et al. 2016

J. Sustain. Metall.

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The major commercial technology for the production of smelter grade alumina has conventionally been the Bayer process which converts bauxite ore, an aluminum containing ore which typically contains about 50 % Al 2 O 3 , into smelter grade alumina that contains over 99.0 % Al 2 O 3 . Another potential source of aluminum that is receiving renewed attention is coal fly ash (CFA), which is a by-product of coal combustion during electricity generation in power stations. Most coal fly ash found around the world contain typically between 25 and 35 % Al 2 O 3 , which is substantial to make CFA a potential alternative source of alumina. There has been some considerable research effort, in the last two decades, aimed at extracting aluminum from this semi-waste product. Much emphasis from the different workers has been on the leaching of the contained aluminum, while the purification and recovery of alumina from the liquor solution has received less attention. Notwithstanding that several patents on the processes to recover alumina from CFA exist, limited commercialisation of the processes has been reported. This paper seeks to review and discuss the hydrometallurgical extraction processes that have been formulated and tested by different workers and then assesses the available opportunities and the way forward on the prospects of commercially extracting alumina and other valuable components from this abundant resource.

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Section: Direct Acid Leachingmentioning

confidence: 99%

Section: Direct Acid Leachingmentioning

confidence: 99%

Section: Direct Acid Leachingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Towards the Utilization of Fly Ash as a Feedstock for Smelter Grade Alumina Production: A Review of the Developments

Sibanda

Ndlovu

Dombo

et al. 2016

J. Sustain. Metall.

Self Cite

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“…Previously, aluminum has been recovered from CFA using hydrometallurgy techniques such as solvent extraction [13], acid leaching [14][15][16][17][18], alkaline leaching [19][20][21], and acid/alkali combination methods [22]. The CFA may be pre-processed before leaching using auxiliary reinforcement methods, such as lime stone sintering [6], soda lime sintering [23], and ammonium sulfate sintering [14,24].…”

Section: Introductionmentioning

confidence: 99%

An Efficient Approach for Lithium and Aluminum Recovery from Coal Fly Ash by Pre-Desilication and Intensified Acid Leaching Processes

Qin

Kang

et al. 2017

Metals

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A novel technique was developed for the recovery of lithium and aluminum from coal fly ash using a combination of pre-desilication and an intensified acid leaching process. The main components of the high-aluminum fly ash were found to be Al 2 O 3 and SiO 2 , and the Al/Si ratio increased from 1.0 to 1.5 after desiliconization. The lithium content of the coal fly ash met national recycling standards. The optimal acid leaching conditions, under which the leaching efficiencies of lithium and aluminum were 82.23% and 76.72%, respectively, were as follows: 6 mol/L HCl, 1:20 solid to liquid ratio, 120 • C and 4 h. During the hydrochloric acid pressure leaching process, spherical particles of desilicated fly ash were decomposed into flakes. Part of the mullite phase was dissolved, and most of the glass phase leached into the liquor. The generation of the silicates hindered lithium transport, which decreased the leaching rate of lithium. This work suggests that the preprocessing is a promising option for effective recovery of high-aluminum and fly ash-associated lithium.

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Bisurfactant‐assisted preparation of amorphous silica from fly ash

Liu

Cheng

2016

Asia-Pacific J Chem Eng

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Amorphous silica (white carbon black) has been prepared via a one‐step hydrochloride acidification of fly ash with the assistance of cetyl‐trimethylammonium bromide (CTAB) and polyethylene glycol (PEG). The effects of surfactant types and their concentration on the properties of amorphous silica have been investigated by X‐ray diffraction (XRD), particle size analysis and dibutyl phthalate (DBP) absorption value measurement. The results show that both the dispersity and hydrophobicity of the prepared silica modified by the mixed surfactants of CTAB and PEG are better than those modified by either CTAB or PEG individually. The particle size and DBP absorption value of the silica products are 3.2 µm and 3.11 cm3 · g−1 at the optimized CTAB concentration of 9 × 10−4 mol · L−1 and PEG dosage of 0.5 wt%, respectively. Consequently, the filtration time for the obtained silica is shortened as little as 3 min. It is worth mentioning that the purity of the products has been improved with the aid of the mixed surfactants. Copyright © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

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Extraction of alumina from coal fly ash using an acid leach-sinter-acid leach technique

Cited by 73 publications

References 15 publications

Towards the Utilization of Fly Ash as a Feedstock for Smelter Grade Alumina Production: A Review of the Developments

Towards the Utilization of Fly Ash as a Feedstock for Smelter Grade Alumina Production: A Review of the Developments

An Efficient Approach for Lithium and Aluminum Recovery from Coal Fly Ash by Pre-Desilication and Intensified Acid Leaching Processes

Bisurfactant‐assisted preparation of amorphous silica from fly ash

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