Lignocellulosic wastes and chitosan composites applied to recover rare earth elements by liquid-solid separation

Tesi amb menció de Doctorat Internacional (English) Rare earths elements (REE) are crucial elements to the future of technology, particularly to the power generation and road transport. One of the most sustainable processes to recover rare earths is biosorption. In this work, two bio sorbent-based materials including lignocellulosic and chitosan were developed and evaluated as adsorbent materials for rare earths recovery. The lignocellulosic-based materials included three banana wastes (rachis, pseudosteam and peel) and a residue from saccharification process using banana rachis as starting material. While, the chitosan-based materials included a chitosan-ferric hydroxide composite beads, a chitosan-magnetic beads and a pickering emulsion formed by chitosan and Cyanex 923 (Cy923). The banana wastes were tested in its neat form. The results show that banana rachis was the best material compared with banana pseudosteam and peel, with about 100 mg/g of adsorption capacity for five critical rare earths (Nd, Eu, Y, Dy and Tb). The adsorption mechanism showed that the oxygen functionalities, particularly carboxylic groups causing the REE attachment to the material surface by electrostatic attraction. In addition, banana rachis performed very fast kinetics (8 min). A second material based on the residue of banana rachis after being saccharified by enzymatic hydrolysis with polyethylene glycol (BR-PEG) was evaluated in the recovering of Nd. BR-PEG material performs adsorption reaction in approximately 20 min and presented maximum adsorption capacity of 44.11 mg/g. The material was reused for five times during the adsorption-desorption cycles. Regarding to chitosan-based materials, chitosan-iron (ChiFer(III)) beads were obtained and applied to the Nd recovery from aqueous phase. The adsorption capacity of freeze-dried material was 13.8 mg/g at pH 4, which enhanced in around four times the adsorption capacity of neat chitosan of 3.54 mg/g. In addition, dynamic columns testing was successfully evaluated with synthetic Nd-B solutions confirmed the selectivity to Nd ions. The elution was carried out with excellent results using water at pH 3.5. A second material based on chitosan magnetic composite beads consisted in nanoparticles of manganese-ferrite (MnFe2O3) and chitosan were applied to the recovery of Nd from aqueous solutions. The adsorption experiments showed that composite beads perform the maximum adsorption at pH 4 with maximum adsorption capacity of 44.29 mg/