Rare Earth and Trace Metal Characteristics of Bentonite in the Rajmahal Hills

Ashok Kr. Jha1,Email

Raghvendra Thakur2

Sachin Verma3

Subhajit Sikdar4

1University Department of Chemistry, T.M.B.U., Bhagalpur, India.
2Atomic Minerals Directorate for Exploration and Research, Department of Atomic Energy, Bangalore, Karnataka, India.
3T.M.B.U., Bhagalpur, India
4Department of Chemistry, P.B.S. College, Banka, India.



Bentonite, a smectite group of minerals having 2:1 structure (i.e., one octahedral sheet sandwiched by two tetrahedral sheets), have been established as a potential remover of heavy metals, dyes and other toxic elements due to its high surface-area-to-volume ratio and cation exchange capacity. But rare earth metals have been found in traces due to the presence of a number of ores of uranium, tantalum, niobium, tungsten, and thorium. The monazite ore of thorium contains thorium, lanthanum, and cerium as deposits in metamorphic and granitic igneous rocks. These deposits give rise to the presence of rare earth metals along with Rajmahal bentonites. Analysis of the bentonite for trace metals by ICP-OES has revealed the presence of uranium < 22.53 ppm, thorium < 10 ppm, niobium < 99 ppm, tantalum < 93 ppm, beryllium < 10 ppm, tungsten < 10 ppm and chromium < 199 ppm. Major and minor oxides in the bentonite mineral are SiO2, Al2O3, Fe2O3, TiO2, MgO, CaO, Na2O and K2O. The maximum loss on ignition has been found to be 21.70%. Trace elements, e.g., niobium occur in rocks of volcanic origin along with formation of smectite group of clay minerals. The presence of radioactive elements, e.g., uranium and thorium can be explained due to the presence of mines of uranium and diffusion of natural fission products. Inductively coupled plasma-optical emission spectroscopy (ICP-OES), the latest and most accurate sophisticated method, has been employed for the analysis of trace metals.

Rare Earth and Trace Metal Characteristics of Bentonite in the Rajmahal Hills