Rare earths separation from fluorescent lamp wastes using ionic liquids as extractant agents

An eco-friendly and high-yield extraction of rare earth from the leaching solution of ion adsorbed minerals

Ion-adsorbed rare earth minerals are rich in medium and heavy rare earth (RE), which are important strategic resources. In this article, a novel approach for the extraction of RE from ion adsorbed minerals was developed. Through a comprehensive assessment of their extraction and separation performance, the hydrophobic deep eutectic solvents (HDES) with a composition of trioctylphosphine oxide (TOPO): dodecanol (LA): 2-thiophenoyltrifluoroacetone (HTTA) = 1:1:1 was determined as the optimal configuration. Under optimized conditions, only RE were extracted by the HDES, while Al, Ca, Mg were not extracted at all. The HDES based extraction obviated the need for diluent such as kerosene, eliminating the generation of impurity removal residues. The RE in the stripping solution could be successfully enriched by saponified lauric acid, achieving an impressive precipitation rate of 99.7%. The RE precipitate underwent further enrichment, resulting in a RE concentration of 176 g/L (REO = 210 g/L). Unlike industrial precipitants such as oxalic acid and ammonium bicarbonate, lauric acid can be effectively recycled, thereby avoiding a large amount of wastewater and carbon dioxide emissions. The obtained RE solution product exhibits high yield and purity, this study provides an eco-friendly and high-yield approach for extracting RE.

An insight into REEs recovery from spent fluorescent lamps: Evaluation of the affinity of an NH4-13X zeolite towards Ce, La, Eu and Y

The constantly increasing demand of Rare Earth Elements (REEs) made them to be part of the so-called "critical elements" indispensable for the energy transition. The monopoly of only a few countries, the so-called balance problem between demand and natural abundance, and the need to limit the environmental costs of their mining, stress the necessity of a recycling policy of these elements. Different methods have been tested for REEs recovery. Despite the well-known ion-exchange properties of zeolites, just few preliminary works investigated their application for REEs separation and recycle. In this work we present a double ion exchange experiment on a NH4-13X zeolite, aimed at the recovery of different REEs from solutions mimicking the composition of liquors obtained from the leaching of spent fluorescent lamps. The results showed that the zeolite was able to exchange all the REEs tested, but the exchange capacity was different: despite Y being the more concentrated REE in the solutions, the cation exchange was lower than less concentrated ones (16 atoms p.u.c. vs 21 atoms for Ce and La solutions), suggesting a possible selectivity. In order to recover REEs from the zeolite, a second exchange with an ammonium solution was performed. The analyses of the zeolites show that almost all of Ce and Eu remain in the zeolite, while nearly half of La and Y are released. This, once again, suggests a possible selective release of REEs and open the possibility for a recovery process in which Rare Earths can be effectively separated.

Enhancement of Cerium Sorption onto Urea-Functionalized Magnetite Chitosan Microparticles by Sorbent Sulfonation—Application to Ore Leachate

The recovery of strategic metals such as rare earth elements (REEs) requires the development of new sorbents with high sorption capacities and selectivity. The bi-functionality of sorbents showed a remarkable capacity for the enhancement of binding properties. This work compares the sorption properties of magnetic chitosan (MC, prepared by dispersion of hydrothermally precipitated magnetite microparticles (synthesized through Fe(II)/Fe(III) precursors) into chitosan solution and crosslinking with glutaraldehyde) with those of the urea derivative (MC-UR) and its sulfonated derivative (MC-UR/S) for cerium (as an example of REEs). The sorbents were characterized by FTIR, TGA, elemental analysis, SEM-EDX, TEM, VSM, and titration. In a second step, the effect of pH (optimum at pH 5), the uptake kinetics (fitted by the pseudo-first-order rate equation), the sorption isotherms (modeled by the Langmuir equation) are investigated. The successive modifications of magnetic chitosan increases the maximum sorption capacity from 0.28 to 0.845 and 1.25 mmol Ce g−1 (MC, MC-UR, and MC-UR/S, respectively). The bi-functionalization strongly increases the selectivity of the sorbent for Ce(III) through multi-component equimolar solutions (especially at pH 4). The functionalization notably increases the stability at recycling (for at least 5 cycles), using 0.2 M HCl for the complete desorption of cerium from the loaded sorbent. The bi-functionalized sorbent was successfully tested for the recovery of cerium from pre-treated acidic leachates, recovered from low-grade cerium-bearing Egyptian ore.

Hydrothermal Synthesis of Silicoaluminophosphate with AEL Structure Using a Residue of Fluorescent Lamps as Starting Material

Silicoaluminophosphate molecular sieves of SAPO-11 type (AEL structure) were synthesized by the hydrothermal method, from the residue of a fluorescent lamp as a source or Si, Al, and P in the presence of water and di-propyamine (DPA) as an organic template. To adjust the P₂O₅/SiO₂ and Si/Al and ratios, specific amounts of silica, alumina, or alumina hydroxide and orthophosphoric acid were added to obtain a gel with molar chemical composition 1.0 Al₂O₃:1.0 P₂O₅:1.2 DPA:0.3 SiO₂:120 H₂O. The syntheses were carried out at a temperature of 473 K at crystallization times of 24, 48, and 72 h. The fluorescent lamp residue and the obtained samples were characterized by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and BET surface area analysis using nitrogen adsorption isotherms. The presence of fluorapatite was detected as the main crystalline phase in the residue, jointly with considered amounts of silica, alumina, and phosphorus in oxide forms. The SAPO-11 prepared using aluminum hydroxide as Al source, P₂O₅/SiO₂ molar ratio of 3.6 and Si/Al ratio of 0.14, at crystallization time of 72 h, achieves a yield of 75% with a surface area of 113 m²/g, showing that the residue from a fluorescent lamp is an alternative source for development of new materials based on Si, Al, and P.

Synthesis of a New Phosphonate-Based Sorbent and Characterization of Its Interactions with Lanthanum (III) and Terbium (III)

High-tech applications require increasing amounts of rare earth elements (REE). Their recovery from low-grade minerals and their recycling from secondary sources (as waste materials) are of critical importance. There is increasing attention paid to the development of new sorbents for REE recovery from dilute solutions. A new generation of composite sorbents based on brown algal biomass (alginate) and polyethylenimine (PEI) was recently developed (ALPEI hydrogel beads). The phosphorylation of the beads strongly improves the affinity of the sorbents for REEs (such as La and Tb): by 4.5 to 6.9 times compared with raw beads. The synthesis procedure (epicholorhydrin-activation, phosphorylation and de-esterification) is investigated by XPS and FTIR for characterizing the grafting route but also for interpreting the binding mechanism (contribution of N-bearing from PEI, O-bearing from alginate and P-bearing groups). Metal ions can be readily eluted using an acidic calcium chloride solution, which regenerates the sorbent: the FTIR spectra are hardly changed after five successive cycles of sorption and desorption. The materials are also characterized by elemental, textural and thermogravimetric analyses. The phosphorylation of ALPEI beads by this new method opens promising perspectives for the recovery of these strategic metals from mild acid solutions (i.e., pH ~ 4).

Phosphorylation of Guar Gum/Magnetite/Chitosan Nanocomposites for Uranium (VI) Sorption and Antibacterial Applications

The development of new materials is needed to address the environmental challenges of wastewater treatment. The phosphorylation of guar gum combined with its association to chitosan allows preparing an efficient sorbent for the removal of U(VI) from slightly acidic solutions. The incorporation of magnetite nanoparticles enhances solid/liquid. Functional groups are characterized by FTIR spectroscopy while textural properties are qualified by N2 adsorption. The optimum pH is close to 4 (deprotonation of amine and phosphonate groups). Uptake kinetics are fast (60 min of contact), fitted by a pseudo-first order rate equation. Maximum sorption capacities are close to 1.28 and 1.16 mmol U g-1 (non-magnetic and magnetic, respectively), while the sorption isotherms are fitted by Langmuir equation. Uranyl desorption (using 0.2 M HCl solutions) is achieved within 20-30 min; the sorbents can be recycled for at least five cycles (5-6% loss in sorption performance, complete desorption). In multi-component solutions, the sorbents show marked preference for U(VI) and Nd(III) over alkali-earth metals and Si(IV). The zone of exclusion method shows that magnetic sorbent has antibacterial effects against both Gram+ and Gram- bacteria, contrary to non-magnetic material (only Gram+ bacteria). The magnetic composite is highly promising as antimicrobial support and for recovery of valuable metals.

Rare earth elements recovery from secondary wastes by solid-state chlorination and selective organic leaching

Processing of end-of-life products (EoL) containing rare earth elements (REE) has gained increasing importance in recent years with the aim of avoiding supply risks. In addition, circular economy renders complete recirculation of technology metals mandatory. Fluorescent lamp wastes are an important source for REE recovery since they contain significant amounts, up to 55 wt%, of Y and Eu in red phosphors. For these purposes, solid-state chlorination (SSC) is an economically attractive alternative to wet acid leaching treatment, which profits from a considerable reduction of chemicals consumption and process costs. Chlorination takes place with dry HCl_(g) produced from thermal decomposition of NH₄Cl_(s), not only converting the REE content of the Hg-free phosphor waste into water soluble REE metal chlorides, but also avoiding the implications of aqueous complex chemistry of REE. To establish an industrial process viable on a commercial scale, the SSC process has been optimized by (i) using a design of experiment (DOE) varying temperature, residence time, and g_NH4Cl/g_solid ratio and (ii) improved leaching of the chlorinated metals with an organic mixture selective for REE. As a result, 95.7% of the Y and 92.2% of the Eu were selectively recovered at 295.9 °C, 67 min and a ratio of 1.27 g_NH4Cl/g_solid, followed by quantitative selective leaching of the REE. Owed to its low chemicals consumption and operation costs, the current process allows for valorizing lamp waste even when raw material prices are low.

Recovery of Neodymium (III) from Aqueous Phase by Chitosan-Manganese-Ferrite Magnetic Beads

Neodymium is a key rare-earth element applied to modern devices. The purpose of this study is the development of a hybrid biomaterial based on chitosan (CS) and manganese ferrite (MF) for the recovery of Nd(III) ions from the aqueous phase. The preparation of the beads was performed in two stages; first, MF particles were obtained by the assessment of three temperatures during the co-precipitation synthesis, and the best nano-MF crystallites were incorporated into CS to obtain the hybrid composite material (CS-MF). The materials were characterized by FTIR, XRD, magnetization measurements, and SEM-EDX. The adsorption experiments included pH study, equilibrium study, kinetics study, and sorption–desorption reusability tests. The results showed that for MF synthesis, 60 °C is an appropriate temperature to obtain MF crystals of ~30 nm with suitable magnetic properties. The final magnetic CS-MF beads perform maximum adsorption at pH 4 with a maximum adsorption capacity of 44.29 mg/g. Moreover, the material can be used for up to four adsorption–desorption cycles. The incorporation of MF improves the sorption capacity of the neat chitosan. Additionally, the magnetic properties enable its easy separation from aqueous solutions for further use. The material obtained represents an enhanced magnetic hybrid adsorbent that can be applied to recover Nd(III) from aqueous solutions.

Recovery of rare earth elements from coal fly ash by integrated physical separation and acid leaching

Coal fly ash (CFA) is one of the most promising secondary sources of rare earth elements and yttrium (REY). This research first studied the modes of occurrence of REY in CFA collected from a China's power generation plant which utilizes a coal feedstock with an elevated REY content. The fact that rare earth minerals remain in CFA and REY associate with metal oxides was proved by emission-scanning electron microscope with an energy-dispersive X-ray spectrometer. The technical feasibility of recovery of REY from CFA was then studied through conducting various physical separation methods followed by acid leaching. It was found that REY are concentrated in fine particle size, non-magnetic and middle density fractions. Using combined physical separation processes, the REY of CFA was enriched from 782 μg·g^-1to 1025 μg g^-1. The acid leaching process was optimized for various parameters via the Taguchi three-level experimental design. Upon optimization, the physical separation product was leached at the optimum condition and 79.85% leaching efficiency was obtained. Based on the obtained results, a conceptual process flowsheet was developed for recovery of REY from CFA. Such recovery maximizes REY resources utilization and enhances sustainability of CFA disposal.

Rare-earth elements in the circular economy: The case of yttrium

This paper discusses the economic rationale of recycling exhaustible raw materials and assesses how a circular economy perspective can improve the sustainable use of critical raw materials (CRMs). We use the case study of yttrium, a rare-earth element (REE) on the EU list of CRMs, given its widespread use in the electronics industry and the geopolitical concentration of its supply. Even if recycling REEs from waste electric and electronic equipment is a valid alternative to extraction from mines, as proposed by the circular economy paradigm, less than 1% of REEs used today are recycled. Nevertheless, studies on the economic benefits of recovery REEs are very limited. In this paper, we present the business case of an Italian recycling company, Relight Ltd., and its HydroWEEE project, to recycle REEs such as yttrium, from spent lamps. In environmental terms, recycling REEs has a much lower impact than their extraction from virgin source. In economic terms, it is profitable to recycle yttrium if its market price is above 14€/kg, and above 9.54€/kg taking in consideration the external costs of mining. Therefore, in 2012 and 2013, recycling was profitable thanks to the high price of yttrium, while between 2014 and 2016 recycling was not cost effective. In these cases, policymakers must incentivize recovery and recycling solutions with appropriate policies.