Exploring rare earth elements in coalmine overburden: nanoscale insights from FESEM, TEM and XPS analysis

Area of Science:

• Geochemistry
• Economic Geology
• Materials Science

Background:

• Rare earth elements and yttrium (REY) are critical for advanced technologies and economic growth.
• Coal and its by-products are potential sources of REY, but coal mine overburden (OB) remains largely unexplored.
• The Makum coalfield in India's Northeastern Region (NER) is examined for REY potential.

Purpose of the Study:

• To investigate the existence, distribution, and depositional conditions of REY in coal and coal mine OB.
• To analyze the geochemical behavior and potential commercial viability of REY in the study area.
• To assess the suitability of OB as a future source for REY recovery.

Main Methods:

• Analysis of REY content in coal and OB samples from the Makum coalfield.
• Utilizing advanced analytical techniques including nanoscale morphology, Field Emission Scanning Electron Microscopy (FE-SEM), and High-Resolution Transmission Electron Microscopy (HR-TEM).
• Evaluation of geochemical indicators such as light (LREY) to heavy (HREY) ratio, and anomalies of Europium (δEu), Cerium (δCe), and Gadolinium (δGd).

Main Results:

• Coal and coal mine OB samples from the Makum coalfield are identified as promising sources of REY.
• The average REY concentration is 167.66 mg kg^-1, with a mean LREY to HREY ratio of 37.67.
• Significant Europium (δEu = 3.20), Cerium (δCe = 0.71), and Gadolinium (δGd = 5.30) anomalies were observed, indicating specific depositional conditions.

Conclusions:

• The coal-forming conditions (slightly oxidizing, highly reducing, M-type enrichment) are favorable for REY preservation.
• The absence of anaerobic microbial activity aided in preserving organic matter and REY.
• Coal mine OB and coal deposits in the Makum coalfield represent a viable opportunity for future REY exploration and recovery.