Terbium Removal from Aqueous Solutions Using a In₂O₃ Nanoadsorbent and Arthrospira platensis Biomass

Terbium is a rare-earth element with critical importance for industry. Two adsorbents of different origin, In₂O₃ nanoparticles and the biological sorbent Arthrospira platensis, were applied for terbium removal from aqueous solutions. Several analytical techniques, including X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy, were employed to characterize the adsorbents. The effect of time, pH, and terbium concentration on the adsorption efficiency was evaluated. For both adsorbents, adsorption efficiency was shown to be dependent on the time of interaction and the pH of the solution. Maximum removal of terbium by Arthrospira platensis was attained at pH 3.0 and by In₂O₃ at pH 4.0-7.0, both after 3 min of interaction. Several equilibrium (Langmuir, Freundlich, and Temkin) and kinetics (pseudo-first order, pseudo-second order, and Elovich) models were applied to describe the adsorption. The maximum adsorption capacity was calculated from the Langmuir model as 212 mg/g for Arthrospira platensis and 94.7 mg/g for the In₂O₃ nanoadsorbent. The studied adsorbents can be regarded as potential candidates for terbium recovery from wastewater.