The Behaviour of Rare Earth Elements from South African Coal Fly Ash during Enrichment Processes: Wet, Magnetic Separation and Zeolitisation

Abstract

Rare earth elements (REEs) are essential raw materials in a variety of industries including clean energy technologies such as electric vehicles and wind turbines. This places an ever-increasing demand on global rare earth element production. Coal fly ash (CFA) possesses appreciable levels of REEs. CFA, a waste by-product of coal combustion, is therefore a readily available source of REEs that does not require mining. CFA valorisation to zeolites has been achieved via various synthesis pathways. This study aimed to evaluate one such pathway by monitoring how REEs partition during CFA processing by the wet, magnetic separation process and zeolitisation. South African CFA was subjected to wet, magnetic separation and subsequent zeolitisation of the nonmagnetic fraction (NMF); solid products were characterised by XRD, SEM, XRF and LA-ICP-MS. The wet, magnetic separation process resulted in the partitioning of a specific set of transition metals (such as Fe, Mn, Cr, V, Ni, Zn, Cu, Co and Mo) into the magnetic fraction (MF) of CFA, while REEs partitioned into the NMF with a total REE content of 530.2 ppm; thus, the matrix elements of CFA were extracted with ease. Zeolitisation resulted in a solid zeolite product (hydroxysodalite) with a total REE content of 537.6 ppm. The process of zeolitisation also resulted in the selective enrichment of Ce (259.1 ppm) into the solid zeolite product (hydroxysodalite), while other REEs were largely partitioned into the liquid phase. CFA valorisation by wet, magnetic separation and zeolitisation therefore allowed for the partitioning of REEs into various extraction products while recovering the matrix elements of CFA such as Fe, Si and Al. The findings of this study highlight the geopolitical importance of REEs in terms of the development of alternative processes for REE recovery from waste and alternative sources, which may potentially give countries that employ and develop the technology a key advantage in the production of REEs for the global market.

Systematic Search Using the Proknow-C Method for the Characterization of Atmospheric Particulate Matter Using the Materials Science Techniques XRD, FTIR, XRF, and Raman Spectroscopy

“…The filter can be analyzed from WDXRF, EDXRF 3D-EDXRF, and EDXRF [69,120,121]. This last filter, due to its portability, is suitable for use in indoor studies to assess air quality in the workplace, which suggests a great advantage [70,[122][123][124]. In recent decades, XRF has become a powerful and inexpensive analytical technique that enables multi-elemental analysis of a wide variety of samples, mainly in the solid state.…”

The Recycling of Coal Fly Ash: A Review on Sustainable Developments and Economic Considerations

“…Strzałkowska (2021) [115] proposed that the magnetic fraction can further be investigated as a potential catalyst in wastewater treatment. In the extraction of rare earth elements, magnetic separation is also used to concentrate the REEs [116]. The non-magnetic fraction, which is enriched with aluminium and silica, can further be utilized in the building and construction industry [117], used for zeolite synthesis [116], or processed for the metallurgical recovery of alumina and REEs [116,118,119].…”

Validation of microwave acid digestion, diffusive gradients in thin-film preconcentration and inductively coupled plasma optical emission spectrometry methodology for the determination of REEs in natural zeolites

“…6 REEs have also been used as ngerprints in geological, food authentication and environmental studies over the past decade. 2,[7][8][9][10] Most REEs are found in different mineral deposits, oen at extremely low concentrations. 6,10,11 REEs may occur in clay mineral deposits formed by the weathering of igneous or granitic rocks.…”