Characterization of rare earth elements present in coal ash by sequential extraction

Area of Science:

• Geochemistry
• Environmental Science
• Materials Science

Background:

• Coal ash contains significant amounts of rare earth elements (REEs).
• Understanding REE binding in coal ash is crucial for efficient extraction and recycling.
• Limited knowledge exists on REE association with the coal ash matrix.

Purpose of the Study:

• To analyze the binding characteristics of REEs within coal ash using sequential extraction.
• To investigate REE recovery potential during a coal ash recycling process.
• To determine the optimal methods for REE extraction from coal ash.

Main Methods:

• Tessier sequential extraction to determine REE fraction distribution.
• BCR sequential extraction to further characterize REE binding.
• Analysis of REE recovery from wastewater during coal ash-derived zeolite synthesis.

Main Results:

• Coal ash contains substantial REEs (185.8 mg/kg in bottom ash, 179.2 mg/kg in fly ash).
• Approximately 85% of REEs are in the residual fraction (Tessier), and 60-70% (BCR), indicating strong binding.
• 46.3% of REEs can be recovered from wastewater during zeolite synthesis.

Conclusions:

• REEs are strongly bound within the mineral matrix of coal ash, necessitating aggressive extraction methods.
• Coal ash recycling processes offer a potential avenue for REE recovery from wastewater.
• Further research into efficient REE extraction techniques from the residual fraction is warranted.