Spectroscopic evaluation of clay-assisted extraction of rare earth elements from alkali-roasted and acid-leached Amba Dongar carbonatite: an integrated geochemical and mineralogical approach

An integrated clay-assisted extraction framework was developed to recover rare earth elements (REEs) from alkali-roasted and acid-leached Amba Dongar carbonatite, Gujarat, India. Mineralogical, geochemical, and spectroscopic analyses were combined to clarify REE mobilization, coordination, and adsorption mechanisms within natural clay matrices. Kaolinite, montmorillonite, bentonite, and attapulgite were evaluated as sustainable adsorbents for REE uptake from hydrochloric acid leachates. ICP-MS analyses revealed total REE concentrations ranging from 3993 to 20,010 mg/kg in the raw carbonatite, dominated by Ce, La, and Nd. Structural characterization using XRD, FTIR, and Raman spectroscopy confirmed crystallinity and functional group variability, linking lattice flexibility and hydroxyl functionality to adsorption behavior. UV – Visible spectra exhibited absorption bands between 212 and 359 nm associated with Ce3+, Sm3+, Pr3+, Tb3+, Nd3+, and Eu3+, while fluorescence emissions between 200 and 520 nm identified Ce3+, Yb2+/3+, Eu2+, and Er3+, validating REE coordination environments and oxidation states. Montmorillonite and bentonite showed the highest relative REE uptake under the investigated conditions, whereas kaolinite and attapulgite displayed more selective sorption governed by surface functional groups. Overall, the integrated process provides a mineralogically guided and environmentally benign pathway for REE recovery.