Encountering Unprecedented Phase Transformation of Bentonite and Evaluating Its Extraction Efficiency To Sequester ReO ₄ ^– (Surrogate of TcO ₄ ^– ) from a Simulated Radwaste Solution

Herein, we report an experimental investigation unraveling the thermal behavior of raw bentonite using in situ high-temperature X-ray diffraction, illustrating partial phase transformation which is not reported elsewhere to the best of our knowledge. The Le-Bail fit to the diffraction pattern, along with the surface morphology study, substantiates the partially formed phase to be zeolite-A. Despite the transformation, raw bentonite exhibited the highest porosimetry parameters at ambient temperature, and thus, it was directly employed for the extraction of perrhenate (ReO4–) ions, which are surrogates for radioactive pertechnetate (99TcO4–) ions, without any surface modification. The adsorption data fitted well with the Langmuir isotherm model (R2 = 0.978), estimating a maximum sorption capacity of 293 mg g–1 at pH ∼ 7, surpassing most minerals reported earlier. The XPS and FT-IR spectra validate the speciation of adsorbed rhenium. This work also paves the way for the extraction of 99TcO4– and other toxic anions.