Dataset Information

Green Approach for Rare Earth Element (REE) Recovery from Coal Fly Ash.

ABSTRACT: Due to the growing demands of rare earth elements (REEs) and the vulnerability of REEs to potential supply disruption, there have been increasing interests in recovering REEs from waste streams such as coal fly ash (CFA). Meanwhile, CFA as a large industrial waste stream in the United States (U.S.) poses significant environmental and economic burdens. Recovery of REEs from CFA is a promising solution to the REE scarcity issue and also brings opportunities for CFA management. This study demonstrates a green system for REE recovery from Class F and C CFA that consists of three modules: REE leaching using citrate, REE separation and concentration using oxalate, and zeolite synthesis using secondary wastes from Modules I and II. In Module I, ∼10 and 60% REEs were leached from the Class F and C CFA samples, respectively, using citrate at pH 4. In Module II, the addition of oxalate selectively precipitated and concentrated REEs from the leachate via the formation of weddellite (CaC₂O₄·2H₂O), while other trace metals remained in solution. In Module III, zeolite was synthesized using wastes from Modules I and II. This study is characterized by the successful recovery of REEs and upcycling of secondary wastes, which addresses both REE recovery and CFA management challenges.

SUBMITTER: Liu P

PROVIDER: S-EPMC10077585 | biostudies-literature | 2023 Apr

REPOSITORIES: biostudies-literature

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Green Approach for Rare Earth Element (REE) Recovery from Coal Fly Ash.

Liu Pan P Zhao Simin S Xie Nan N Yang Lufeng L Wang Qian Q Wen Yinghao Y Chen Hailong H Tang Yuanzhi Y

Environmental science & technology 20230321 13

Due to the growing demands of rare earth elements (REEs) and the vulnerability of REEs to potential supply disruption, there have been increasing interests in recovering REEs from waste streams such as coal fly ash (CFA). Meanwhile, CFA as a large industrial waste stream in the United States (U.S.) poses significant environmental and economic burdens. Recovery of REEs from CFA is a promising solution to the REE scarcity issue and also brings opportunities for CFA management. This study demonstra ...[more]

PMID: 36942728

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Project description:Geopolymers are inorganic polymers formed from the alkaline activation of amorphous alumino-silicate materials resulting in a three-dimensional polymeric network. As a class of materials, it is seen to have the potential of replacing ordinary Portland cement (OPC), which for more than a hundred years has been the binder of choice for structural and building applications. Geopolymers have emerged as a sustainable option vis-à-vis OPC for three reasons: (1) their technical properties are comparable if not better; (2) they can be produced from industrial wastes; and (3) within reasonable constraints, their production requires less energy and emits significantly less CO₂. In the Philippines, the use of coal ash, as the alumina- and silica- rich geopolymer precursor, is being considered as one of the options for sustainable management of coal ash generation from coal-fired power plants. However, most geopolymer mixes (and the prevalent blended OPC) use only coal fly ash. The coal bottom ash, having very few applications, remains relegated to dumpsites. Rice hull ash, from biomass-fired plants, is another silica-rich geopolymer precursor material from another significantly produced waste in the country with only minimal utilization. In this study, geopolymer samples were formed from the mixture of coal ash, using both coal fly ash (CFA) and coal bottom ash (CBA), and rice hull ash (RHA). The raw materials used for the geopolymerization process were characterized using X-ray fluorescence spectroscopy (XRF) for elemental and X-ray diffraction (XRD) for mineralogical composition. The raw materials' thermal stability and loss on ignition (LOI) were determined using thermogravimetric analysis (TGA) and reactivity via dissolution tests and inductively-coupled plasma mass spectrometry (ICP) analysis. The mechanical, thermal and microstructural properties of the geopolymers formed were analyzed using compression tests, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). Using a Scheffé-based mixture design, targeting applications with low thermal conductivity, light weight and moderate strength and allowing for a maximum of five percent by mass of rice hull ash in consideration of the waste utilization of all three components, it has been determined that an 85-10-5 by weight ratio of CFA-CBA-RHA activated with 80-20 by mass ratio of 12 M NaOH and sodium silicate (55% H₂O, modulus = 3) produced geopolymers with a compressive strength of 18.5 MPa, a volumetric weight of 1660 kg/m³ and a thermal conductivity of 0.457 W/m-°C at 28-day curing when pre-cured at 80 °C for 24 h. For this study, the estimates of embodied energy and CO₂ were all below 1.7 MJ/kg and 0.12 kg CO₂/kg, respectively.

Dataset Information

Green Approach for Rare Earth Element (REE) Recovery from Coal Fly Ash.

Publications

Green Approach for Rare Earth Element (REE) Recovery from Coal Fly Ash.

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