Rare earth elements and radioactive elements in black sands from the Konkan and Malabar coasts of India

ABSTRACT

The objective of the present work is to demonstrate the ability of the laser-induced breakdown spectroscopy (LIBS) technique for quick detection and quantification of rare earth elements (REEs) and radioactive elements in the black sands at selected locations of the Konkan coast (Goa) and Malabar coast (Kerala) in India. Several REEs such as Ce, Nd, Sm, Dy, Ho, Tm, Gd, and Th have been detected in the LIBS spectra. Calibration-free LIBS method has been used to calculate the concentration of REEs and radioactive elements. The experimental result shows that the concentration of REEs such as Sm, Dy, Ho, and radioactive element Th is maximum in the sands collected from Thiruvananthapuram (Kerala) beach and minimum in the Baga (Goa) beach. The reliability of the results (qualitative and quantitative) obtained by the LIBS method has been examined by other spectroscopic techniques like XRF and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and found to be in close agreement. The multivariate approach (principal component analysis) has been applied to discern the samples based on their spectral data. Photoacoustic spectroscopy and XRD technique are used to detect compounds/minerals of REEs. The relative hardness, degree of crystallinity (DOC), and crystallite size have been calculated.

KEYWORDS:

• Black sand
• REEs
• radioactive element
• Konkan and Malabar coasts
• LIBS
• XRF
• XRD
• ICP-MS
• Hardness
• DOC

Acknowledgments

One of the authors, V.K. Shukla is thankful to the University Grants Commission (UGC) for providing D. Phil. Fellowship. The XRF spectroscopy was carried out with the Raja Ramanna Centre for Advanced Technology (RRCAT) in Indore, Madhya Pradesh. The authors thank the technical staff of BL-16 beamline for their generous assistance. Dr. M.K. Tiwari, senior scientist and in-charge of BL-16 beamline of Indus-2 facility, is gratefully acknowledged for fruitful discussions, suggestions, and encouragement.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All the data reported in the paper are presented in the main text. Any other data will be provided on request.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.