Insight to the cesium entrapment by natural shale: implications to geological disposal of nuclear waste

ABSTRACT

The knowledge of radionuclides sorption behavior of various site-specific heterogeneous geosystems is essential for developing different clean-up strategies and predicting the radiological risks for long term. The present study is aimed at understanding the mineralogical and textural characteristics of natural shale rock (sampled from Kachchh Basin of Gujarat, India) and its correlation with cesium (Cs) sorption behavior. The modal mineralogical composition, textural attributes, petrophysical properties, surface functionalities and morphology of shale were evaluated. Clay minerals (smectite, kaolinite and illite) constitute more than 40% of the shale along with the major component- quartz. A comprehensive Cs batch sorption study performed at varying experimental parameters demonstrated that the maximum Cs retention of shale was 34.80 ± 2.85 mg g⁻¹ in the studied concentration range. Sorption equilibrium data agreed well with Freundlich isotherm, highlighting the heterogeneity of shale. Variation in solution pH (in the range of 6–10) during sorption demonstrated the buffering of solution in near neutral range indicating the role of cations (available in the interlayers of clay minerals) in Cs uptake. Alternatively, the presence of illite mineral in the shale with known frayed edge sites contributed to the irreversibility of sorption event. The present studies illustrate the potential of shale as host rock for its application in nuclear waste management.

KEYWORDS:

• Cesium
• shale rock
• clay minerals
• batch sorption
• Cs retention capacity Freundlich isotherm

Acknowledgments

The authors would like to thank Dr. A.K. Tyagi, Director, Chemistry Group, BARC and Dr. C.N. Patra, Head, Analytical Chemistry Division, BARC for their encouragement and constant support. Thanks are also due to Ms. M. V. Pimple for AAS analysis, Dr. Naina Raje for Thermal analysis and Ms. Sudeshna Saha for SEM analysis. RS acknowledge the financial support in form of fellowship from the said BRNS project. UKB and RS highly appreciated the infrastructural and administrative support provided by PDEU to conduct the research work funded by BRNS.

Disclosure statement

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

Author contributions

The manuscript was written through contributions of all authors. HP, RS and UKB collected the shale sample. HP, UKB and PS conceptualized the research plan, decided the methodology and supervised the research. HP and RS performed the experiments. DS carried out the SANS analysis. SDK supervised the research and provided useful suggestions. HP and RS drafted the manuscript. HP, UKB and PS revised the manuscript. All authors have given approval to the final version of the manuscript.

Additional information

Funding

This work was supported by Board of Research in Nuclear Sciences (BRNS), Department of Atomic Energy (DAE) with Project sanction No. (58/14/4/2020-BRNS/37058).