Synthesis of a green ALG@KLN adsorbent for high-efficient recovery of rare earth elements from aqueous solution

The increasing consumption of rare earth elements (REEs) and disposal of REE-containing wastes pose a threat to resources and environment. Hence, it is important to achieve efficient REEs recovery while use eco-friendly methods. Herein, natural kaolinite is loaded on alginate hydrogel to prepare ALG@KLN composites via a facile one-step cross-link reaction without any hazardous chemicals. The characterizations of ALG@KLN, adsorption isotherms, adsorption kinetics, and desorption were investigated by SEM-EDS, XPS, FT-IR, and Zeta-potential. The maximum adsorption capacity of Gd (Ⅲ), Y (Ⅲ), Ho (Ⅲ), and Nd (Ⅲ) reached 74.40, 84.48, 85.18, and 75.17 mg/g, respectively. The adsorption kinetics and isotherm were well fitted to pseudo-second-order model and Langmuir model, respectively. The ∼2 mm diameter ALG@KLN can be easily collected and reused. The presence of Na+, Mg2+, and Al3+ has a minor effect on the adsorption of REEs. The adsorption mechanism is mainly via the chemical chelation of oxygen-containing functional groups and electrostatic interaction on negatively charged surface of ALG@KLN. In addition, the cost of ALG@KLN is as low as ∼0.041 USD/gram. This work greatly contributes to the development of economical and eco-friendly REE adsorbents, which plays an important role in sustainable development.