Size-Selective Separation of Rare Earth Elements Using Functionalized Mesoporous Silica Materials

Abstract

The separation and preconcentration of rare earth elements (REEs) from mineral concentrates in an economically and environmentally sustainable manner are difficult tasks due to their similar physicochemical properties. Herein, a series of tetradentate phenylenedioxy diamide (PDDA) ligands were synthesized and grafted on large-pore three-dimensional KIT-6 mesoporous silica. In solid-phase extraction, the hybrid sorbents enable a size-selective separation of REEs on the basis of the bite angles of the ligands. In particular, smaller REE3+ ions are preferentially extracted by KIT-6-1,2-PDDA, whereas light REEs with larger ionic radius are favored by KIT-6-1,3-PDDA. The exposure of bauxite residue digestion solution containing REEs as well as a number of types of competitive ions (including Th and U) to the sorbents results in selective recovery of target REEs. The possibility of regenerating the mesoporous sorbents through a simple loading–stripping–regeneration process is demonstrated over up to five cycles with no significant loss in REE extraction capacity, suggesting adequate chemical and structural stability of the new sorbent materials.

Bridging Hydrometallurgy and Biochemistry: A Protein-Based Process for Recovery and Separation of Rare Earth Elements

“…Solid–liquid extraction, whereby chemical ligands with high REE affinity are covalently anchored onto solid support resin, provides an effective means to achieve REE recovery from complex feedstock leachates. , Here, REEs are selectively adsorbed to the resin until the column is saturated, at which point a stripping solution is applied to elute the REE concentrate. This process offers several advantages relative to liquid–liquid extraction, ,− including faster phase separation between the solid adsorbent and REE-bearing solution and high stability for reuse . However, most of the solid-phase adsorbents employed for REE separation are based on existing chemical ligands, which limits the intra-REE separation potential of the process …”

Microbe-Encapsulated Silica Gel Biosorbents for Selective Extraction of Scandium from Coal Byproducts

“…High Th adsorption capacity has been observed previously for A. nicotianae and other Gram-positive bacteria as well as other silica-based adsorbents. − For example, silica monoliths with/without diglycolamide functionalization coextracted Sc, Fe­(III), and Th from bauxite leachate . Th removal from REE mixtures can be achieved through a cocrystallization process using selenite and will be tested in our future investigation.…”

Critical Rare Earth Element Recovery from Coal Ash Using Microsphere Flower Carbon

“…The leeched NIST 1633c solution resulted in extractions of Na (17%), Ca (13%), Al (24%), Si (41%), Fe (17%), Sc (73%), La (59%), Ce (74%), Pr (73%), Eu (74%), Gd (72%), and Tb (75%). In comparison to another real-world sample, rare earth and impurity elements were extracted from bauxite residue samples using grafted ligands on mesoporous silica (KIT-6-1,3-PDDA) and resulted in extraction efficiencies of approximately Na (42%), Ca (39%), Al (28%), Si (66%), Fe (47%), Sc (78%), La (72%), Ce (82%), Pr (∼80%), Eu (38%), Gd (38%), and Tb (37%) …”

“…In comparison to another real-world sample, rare earth and impurity elements were extracted from bauxite residue samples using grafted ligands on mesoporous silica (KIT-6-1,3-PDDA) and resulted in extraction efficiencies of approximately Na (42%), Ca (39%), Al (28%), Si (66%), Fe (47%), Sc (78%), La (72%), Ce (82%), Pr (∼80%), Eu (38%), Gd (38%), and Tb (37%). 51 REEs and thorium were best extracted at a pH of 4.80 using MFC-O, while uranium was best extracted at pH 3.36 (Figure S14). Figure S15 is a simplified plot showing only Sm, Th, and U extraction k d at pH 3.36, 3.94, and 4.80, as all REEs show a trend similar to samarium(with an exception of Sc).…”