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An advanced analytical assessment of rare earth element concentration, distribution, speciation, crystallography and solid-state chemistry in fly ash
DOI:
10.1016/j.sab.2020.105950
Authors:
Ilemona C.
Okeme
(University of Bristol)
,
Peter G.
Martin
(University of Bristol)
,
Christopher
Jones
(University of Bristol)
,
Richard A.
Crane
(University of Exeter)
,
Theophilus I.
Ojonimi
(University of Jos)
,
Konstantin
Ignatyev
(Diamond Light Source)
,
Thomas B.
Scott
(University of Bristol)
Co-authored by industrial partner:
No
Type:
Journal Paper
Journal:
Spectrochimica Acta Part B: Atomic Spectroscopy
State:
Published (Approved)
Published:
August 2020
Diamond Proposal Number(s):
22876
Abstract: Fly ash represents a promising alternative source of rare earth elements (REE). However, information on REE containing mineral phases and their association with other fly ash components, vital for REE recovery from fly ash, is currently lacking. Herein, the mass fraction, distribution, crystallography and solid-state chemistry of REE, U and Th in Nigerian simulated fly ash samples were characterised using a range of laboratory and synchrotron x-ray based analytical techniques to underpin future extraction methodologies. Inductively coupled plasma mass spectrometry following full-acid digest of forty-five samples revealed recoverable average total REE content which ranged between 442 mgkg−1and 625 mgkg−1, comprising over 30 wt% of the critical REE Nd, Eu, Tb, Dy, Y and Er. These REE within the fly ash samples were found to be most frequently associated with discrete monazite, xenotime and Y-bearing zircon mineral particles, with the former the most detected, which could be beneficiated through gravity separation. Analysis of monazite particles isolated from the composite samples through a complimentary suite of analytical synchrotron radiation techniques revealed a core-shell pattern, with the shell rich in colocalised Ce, Nd and La, and the core enrich in both U and Th. Ce in monazite was found to exist in a mixed trivalent and tetravalent oxidation state, with the monazite structure amorphized due to the high temperature combustion process. Such results demonstrate the strong co-association and physical distribution of REE, U and Th within monazite in fly ash; knowledge of which can subsequently be used to optimise or develop a more selective, cost-effective and environmentally friendly solvent extraction methodology, by targeting the strongly colocalised and surface bound REE in fly ash monazite particles.
Journal Keywords: Nigeria; Fly ash; Rare earth elements; Monazite; Synchrotron radiation
Subject Areas:
Earth Science,
Chemistry,
Materials
Instruments:
I18-Microfocus Spectroscopy
Added On:
19/08/2020 08:33
Discipline Tags:
Earth Sciences & Environment
Mineralogy
Chemistry
Materials Science
Inorganic Chemistry
Technical Tags:
Diffraction
Imaging
Spectroscopy
X-ray Fluorescence (XRF)
X-ray Absorption Spectroscopy (XAS)
X-ray Absorption Near Edge Structure (XANES)