On the characterization and leaching of rare earths from a coal fly ash of Indian origin

ABSTRACT

Fly Ash from a lignite coal-based power plant was spotted in southern India to contain economic concentration of total Rare Earth Elements (TREE) in the order of 2100 mg/kg, of which 20% are heavier rare earth elements (HREE). Optical microscopy revealed that the portion of Lighter rare earth elements (LREE) occurs in the form of Zircon and Monazite minerals. Direct leaching of the fly ash yielded differential solubilization LREE(50%) and HREE(90%), equivalent to 60% recovery of TREE, under the optimum conditions: Sulfuric acid (1.5 M initial concentration), 20% solids (by wt.), Room Temperature (25°C), 5 h contact time.

KEYWORDS:

• Rare earth elements (REE)
• Indian coal fly ash
• leaching

Highlights

• Mapping of Rare Earth Elements in Indian coal fly ashes.

• Characterization of coal fly ash is carried out by Scanning electron microscopy and Sequential Chemical Extraction.

• Leaching process developed for recovery Rare Earth Elements from fly ash using sulfuric acid.

• About 90% of Heavier Rare Earth Elements could be leached under optimum conditions.

Acknowledgements

The authors thank their colleagues in Atomic Minerals Directorate for Exploration and Research (AMD) for various analyses including X-ray Fluorescence, X-ray Diffraction, and Chemical analysis of the fly ash samples. They express gratitude to the authorities of thermal power plants at Neyveli, Gujarat, Ramagundam, Singareni, Farakka and Manuguru for permitting the collection of fly ash samples. The authors are also grateful to the Director, Materials Group for the kind encouragement for investigations undertaken.