Novel silica-based adsorbent layer-by-layer modified with polyhexamethylene guanidine and Arsenazo reagents for solid-phase extraction of lanthanides from lignites and products of their processing

Iron nanoparticles synthesized using Euphorbia cochinchinensis leaf extracts exhibited highly selective recovery of rare earth elements from mining wastewater: Exploring the origin of high selectivity

Iron nanoparticles synthesized using Euphorbia cochinchinensis leaf extracts (Ec-FeNPs) showed high selectivity for rare earth elements (REEs) recovery from mining wastewater. REEs recovery efficiencies were > 90 %, with distribution coefficients ranging from 2483.9 to 37500 mL/g, which were consistently much higher than non-REEs (15.0 - 234.8 mL/g). Moreover, even after 5 consecutive reuse cycles, Ec-FeNPs effectively adsorbed > 60 % of REEs. Application of advanced characterization techniques found that the high selectivity of Ec-FeNPs for REEs was mainly due to the biomolecules present in the Ec extract. During the synthesis of FeNPs, these biomolecules are modified on the surface of Ec-FeNPs, giving Ec-FeNPs an enhanced ability to separate REEs from non-REEs. The biomolecule capping layer, which is modified on the surface of Ec-FeNPs, constitutes a primary source of high selectivity. LC-MS identified amino acids, carbohydrates, and organic acids as the major biomolecule categories in the capping layer. Density functional theory (DFT) confirmed that the biomolecule capping layer of Ec-FeNPs had the strongest interaction with REEs; an association confirmed by Spearman's correlation analysis. The adsorption mechanism of REEs by Ec-FeNPs mainly involved a combination of ion exchange, electrostatic adsorption, and surface complexation. Overall, the novel findings reported here provide new perspectives for the design of absorbents with highly selective recovery of REEs from mining wastewater.

Biosorption of Neodymium (Nd) from Aqueous Solutions Using Spirulina platensis sp. Strains

Rare earth elements such as neodymium (Nd) are important elements used mainly in developing new technologies. Although they are found in low concentrations in nature, they can be obtained by extracting solid samples such as phosphogypsum. Among the techniques, adsorption has been used successfully with several adsorbent materials. In this work, two strains of Spirulina platensis (LEB-18 and LEB-52) were employed as biosorbents for efficiently removing the Nd element from the aqueous media. Biosorption tests were carried out in a batch system, and the results of the biosorption kinetics showed that for both materials, the biosorption of Nd was better described by the Avrami model. Moreover, it could be considered that 80 min would be necessary to attain the equilibrium of Nd(III) using both biosorbents. The result of the biosorption isotherms showed that for both strains, the best-fitted model was the Liu model, having a maximum biosorption capacity of 72.5 mg g−1 for LEB-18 and 48.2 mg g−1 for LEB-52 at a temperature of 298 K. Thermodynamics of adsorption showed that for both LEB-18 and LEB-52 the process was favorable (∆G° < 0) and exothermic (∆H° −23.2 for LEB-18 and ∆H° −19.9 for LEB-52). Finally, both strains were suitable to uptake Nd, and the better result of LEB-18 could be attributed to the high amount of P and S groups in this biomass. Based on the results, a mechanism of electrostatic attraction of Nd3+ and phosphate and sulfate groups of both strains of Spirulina platensis was proposed.