Virus-Based Separation of Rare Earth Elements.

The utilization of biomaterials for the separation of rare earth elements (REEs) has attracted considerable interest due to their inherent advantages, including diverse molecular structures for selective binding and the use of eco-friendly materials for sustainable systems. We present a pioneering methodology for developing a safe virus to selectively bind REEs and facilitate their release through pH modulation. We engineered the major coat protein of M13 bacteriophage (phage) to incorporate a lanthanide-binding peptide. The engineered lanthanide-binding phage (LBPh), presenting ∼3300 copies of the peptide, serves as an effective biological template for REE separation. Our findings demonstrate the LBPh's preferential binding for heavy REEs over light REEs. Moreover, the LBPh exhibits remarkable robustness with excellent recyclability and stability across multiple cycles of separations. This study underscores the potential of genetically integrating virus templates with selective binding motifs for REE separation, offering a promising avenue for environmentally friendly and energy-efficient separation processes.

Precision Engineering of 2D Protein Layers as Chelating Biogenic Scaffolds for Selective Recovery of Rare-Earth Elements.

Rare-earth elements, which include the lanthanide series, are key components of many clean energy technologies, including wind turbines and photovoltaics. Because most of these 4f metals are at high risk of supply chain disruption, the development of new recovery technologies is necessary to avoid future shortages, which may impact renewable energy production. This paper reports the synthesis of a non-natural biogenic material as a potential platform for bioinspired lanthanide extraction. The biogenic material takes advantage of the atomically precise structure of a 2D crystalline protein lattice with the high lanthanide binding affinity of hydroxypyridinonate chelators. Luminescence titration data demonstrated that the engineered protein layers have affinities for all tested lanthanides in the micromolar-range (dissociation constants) and a higher binding affinity for the lanthanide ions with a smaller ionic radius. Furthermore, competitive titrations confirmed the higher selectivity (up to several orders of magnitude) of the biogenic material for lanthanides compared to other cations commonly found in f-element sources. Lastly, the functionalized protein layers could be reused in several cycles by desorbing the bound metal with citrate solutions. Taken together, these results highlight biogenic materials as promising bioadsorption platforms for the selective binding of lanthanides, with potential applications in the recovery of these critical elements from waste.

Biohydrometallurgy for Rare Earth Elements Recovery from Industrial Wastes.

Biohydrometallurgy recovers metals through microbially mediated processes and has been traditionally applied for the extraction of base metals from low-grade sulfidic ores. New investigations explore its potential for other types of critical resources, such as rare earth elements. In recent times, the interest in rare earth elements (REEs) is growing due to of their applications in novel technologies and green economy. The use of biohydrometallurgy for extracting resources from waste streams is also gaining attention to support innovative mining and promote a circular economy. The increase in wastes containing REEs turns them into a valuable alternative source. Most REE ores and industrial residues do not contain sulfides, and bioleaching processes use autotrophic or heterotrophic microorganisms to generate acids that dissolve the metals. This review gathers information towards the recycling of REE-bearing wastes (fluorescent lamp powder, spent cracking catalysts, e-wastes, etc.) using a more sustainable and environmentally friendly technology that reduces the impact on the environment.

A short critique on biomining technology for critical materials.

Being around for several decades, there is a vast amount of academic research on biomining, and yet it contributes less to the mining industry compared to other conventional technologies. This critique briefly comments on the current status of biomining research, enumerates a number of primary challenges, and elaborates on some kinetically-oriented strategies and bottom-up policies to sustain biomining with focus on critical material extraction and rare earth elements (REEs). Finally, we present some edge cutting developments which may promote new potentials in biomining.

Recent Materials Developed for Dispersive Solid Phase Extraction.

Solid phase extraction (SPE) is an analytical procedure developed with the purpose of separating a target analyte from a complex sample matrix prior to quantitative or qualitative determination. The purpose of such treatment is twofold: elimination of matrix constituents that could interfere with the detection process or even damage analytical equipment as well as enriching the analyte in the sample so that it is readily available for detection. Dispersive solid phase extraction (dSPE) is a recent development of the standard SPE technique that is attracting growing attention due to its remarkable simplicity, short extraction time and low requirement for solvent expenditure, accompanied by high effectiveness and wide applicability. This review aims to thoroughly survey recently conducted analytical studies focusing on methods utilizing novel, interesting nanomaterials as dSPE sorbents, as well as known materials that have been only recently successfully applied in dSPE techniques, and evaluate their performance and suitability based on comparison with previously reported analytical procedures.

Direct Recovery of the Rare Earth Elements Using a Silk Displaying a Metal-Recognizing Peptide.

Rare earth elements (RE) are indispensable metallic resources in the production of advanced materials; hence, a cost- and energy-effective recovery process is required to meet the rapidly increasing RE demand. Here, we propose an artificial RE recovery approach that uses a functional silk displaying a RE-recognizing peptide. Using the piggyBac system, we constructed a transgenic silkworm in which one or two copies of the gene coding for the RE-recognizing peptide (Lamp1) was fused with that of the fibroin L (FibL) protein. The purified FibL-Lamp1 fusion protein from the transgenic silkworm was able to recognize dysprosium (Dy3+), a RE, under physiological conditions. This method can also be used with silk from which sericin has been removed. Furthermore, the Dy-recovery ability of this silk was significantly improved by crushing the silk. Our simple approach is expected to facilitate the direct recovery of RE from an actual mixed solution of metal ions, such as seawater and industrial wastewater, under mild conditions without additional energy input.

Biosorption as green technology for the recovery and separation of rare earth elements.

Rare earth elements (REE) have great demand for sustainable energy and the high-end technology sector. The high similarity of REE owing to the nature of their electronic configurations increases the difficulty and costs of the development of chemical processes for their separation and recovery. In this way, the development of green technologies is highly relevant for replacing conventional unit operations of extractive metallurgy, viz. precipitation, liquid-liquid and solid-liquid extraction, and ion-exchange. Biosorption is a physicochemical and metabolically-independent biological process based on a variety of mechanisms including absorption, adsorption, ion-exchange, surface complexation and precipitation that represents a biotechnological cost-effective innovative way for the recovery of REE from aqueous solutions. This mini-review provides an overview and current scenario of biosorption technologies existing to recover REE, seeking to address the possibilities of using a green technology approach for wastewater treatment, as well as for the recovery of these high valued elements in the REE production chain.

Biological leaching of rare earth elements.

The distinctive physico-chemical features of rare earth elements (REEs) have led to an increase in demand by the global market due to their multiple uses in industrial, medical and agricultural implementations. However, the scarcity of REEs and the harsh eco-unfriendly leaching processes from primary sources beside obliviousness to their recycling from secondary sources, together with the geopolitical situation, have created the need to develop a more sustainable mining strategy. Therefore, there is a growing interest in bio-hydrometallurgy, which may contribute to the scavenging of these strategic elements from low-grade resources in an environmentally friendly and economically feasible way as with copper and gold. Several prokaryotes and eukaryotes show the ability to leach REEs, however, the success in employing these microorganisms or their products in this process relays on several biotic and abiotic factors. This review focuses on the differences made by microorganisms in REEs leaching and fundamentally explains microbes-REEs interaction.

Recovery of Rare Earth Elements from Wastewater Towards a Circular Economy.

The use of rare earth elements is a growing trend in diverse industrial activities, leading to the need for eco-friendly approaches to their efficient recovery and reuse. The aim of this work is the development of an environmentally friendly and competitive technology for the recovery of those elements from wastewater. Kinetic and equilibria batch assays were performed with zeolite, with and without bacterial biofilm, to entrap rare earth ions from aqueous solution. Continuous assays were also performed in column setups. Over 90% removal of lanthanum and cerium was achieved using zeolite as sorbent, with and without biofilm, decreasing to 70% and 80%, respectively, when suspended Bacillus cereus was used. Desorption from the zeolite reached over 60%, regardless of the tested conditions. When in continuous flow in columns, the removal yield was similar for all of the rare earth elements tested. Lanthanum and cerium were the elements most easily removed by all tested sorbents when tested in single- or multi-solute solutions, in batch and column assays. Rare earth removal from wastewater in open setups is possible, as well as their recovery by desorption processes, allowing a continuous mode of operation.

Bioleaching of metals from WEEE shredding dust.

A bioleaching process developed in two separate steps was investigated for the recovery of base metals, precious metals and rare earth elements from dusts generated by Waste Electrical and Electronic Equipment (WEEE) shredding. In the first step, base metals were almost completely leached from the dust in 8 days by Acidithiobacillus thiooxidans (DSM 9463) that lowered the pH of the leaching solution from 3.5 to 1.0. During this step, cerium, europium and neodymium were mobilized at high percentages (>99%), whereas lanthanum and yttrium reached an extraction yield of 80%. In the second step, the cyanide producing Pseudomonas putida WSC361 mobilized 48% of gold within 3 h from the A. thiooxidans leached shredding dust. This work demonstrated the potential application of biohydrometallurgy for resource recovery from WEEE shredding dust, destined to landfill disposal, and its effectiveness in the extraction of valuable substances, including elements at high supply risk as rare earths.

Concomitant Leaching and Electrochemical Extraction of Rare Earth Elements from Monazite.

Rare earth elements (REEs) have become increasingly important in modern day technologies. Unfortunately, their recycling is currently limited, and the conventional technologies for their extraction and purification are exceedingly energy and chemical intensive. New sustainable technologies for REE extraction from both primary and secondary resources would be extremely beneficial. This research investigated a two-stage recovery strategy focused on the recovery of neodymium (Nd) and lanthanum (La) from monazite ore that combines microbially based leaching (using citric acid and spent fungal supernatant) with electrochemical extraction. Pretreating the phosphate-based monazite rock (via roasting) dramatically increased the microbial REE leaching efficiency. Batch experiments demonstrated the effective and continued leaching of REEs by recycled citric acid, with up to 392 mg of Nd L-1 and 281 mg of La L-1 leached during seven consecutive 24 h cycles. Neodymium was further extracted in the catholyte of a three-compartment electrochemical system, with up to 880 mg of Nd L-1 achieved within 4 days (at 40 A m-2). Meanwhile, the radioactive element thorium and counterions phosphate and citrate were separated effectively from the REEs in the anolyte, favoring REE extraction and allowing sustainable reuse of the leaching agent. This study shows a promising technology that is suitable for primary ores and can further be optimized for secondary resources.

Bioadsorption of Rare Earth Elements through Cell Surface Display of Lanthanide Binding Tags.

With the increasing demand for rare earth elements (REEs) in many emerging clean energy technologies, there is an urgent need for the development of new approaches for efficient REE extraction and recovery. As a step toward this goal, we genetically engineered the aerobic bacterium Caulobacter crescentus for REE adsorption through high-density cell surface display of lanthanide binding tags (LBTs) on its S-layer. The LBT-displayed strains exhibited enhanced adsorption of REEs compared to cells lacking LBT, high specificity for REEs, and an adsorption preference for REEs with small atomic radii. Adsorbed Tb(3+) could be effectively recovered using citrate, consistent with thermodynamic speciation calculations that predicted strong complexation of Tb(3+) by citrate. No reduction in Tb(3+) adsorption capacity was observed following citrate elution, enabling consecutive adsorption/desorption cycles. The LBT-displayed strain was effective for extracting REEs from the acid leachate of core samples collected at a prospective rare earth mine. Our collective results demonstrate a rapid, efficient, and reversible process for REE adsorption with potential industrial application for REE enrichment and separation.

Selective Extraction of Rare Earth Elements from Permanent Magnet Scraps with Membrane Solvent Extraction.

The rare earth elements (REEs) such as neodymium, praseodymium, and dysprosium were successfully recovered from commercial NdFeB magnets and industrial scrap magnets via membrane assisted solvent extraction (MSX). A hollow fiber membrane system was evaluated to extract REEs in a single step with the feed and strip solutions circulating continuously through the MSX system. The effects of several experimental variables on REE extraction such as flow rate, concentration of REEs in the feed solution, membrane configuration, and composition of acids were investigated with the MSX system. A multimembrane module configuration with REEs dissolved in aqueous nitric acid solutions showed high selectivity for REE extraction with no coextraction of non-REEs, whereas the use of aqueous hydrochloric acid solution resulted in coextraction of non-REEs due to the formation of chloroanions of non-REEs. The REE oxides were recovered from the strip solution through precipitation, drying, and annealing steps. The resulting REE oxides were characterized with XRD, SEM-EDX, and ICP-OES, demonstrating that the membrane assisted solvent extraction is capable of selectively recovering pure REEs from the industrial scrap magnets.

Tracking the Flow of Resources in Electronic Waste - The Case of End-of-Life Computer Hard Disk Drives.

Recovery of resources, in particular, metals, from waste flows is widely seen as a prioritized option to reduce their potential supply constraints in the future. The current waste electrical and electronic equipment (WEEE) treatment system is more focused on bulk metals, where the recycling rate of specialty metals, such as rare earths, is negligible compared to their increasing use in modern products, such as electronics. This study investigates the challenges in recovering these resources in the existing WEEE treatment system. It is illustrated by following the material flows of resources in a conventional WEEE treatment plant in Denmark. Computer hard disk drives (HDDs) containing neodymium-iron-boron (NdFeB) magnets were selected as the case product for this experiment. The resulting output fractions were tracked until their final treatment in order to estimate the recovery potential of rare earth elements (REEs) and other resources contained in HDDs. The results further show that out of the 244 kg of HDDs treated, 212 kg comprising mainly of aluminum and steel can be finally recovered from the metallurgic process. The results further demonstrate the complete loss of REEs in the existing shredding-based WEEE treatment processes. Dismantling and separate processing of NdFeB magnets from their end-use products can be a more preferred option over shredding. However, it remains a technological and logistic challenge for the existing system.

Recovery of rare earth elements from the sulfothermophilic red alga Galdieria sulphuraria using aqueous acid.

The demand for rare earth elements has increased dramatically in recent years because of their numerous industrial applications, and considerable research efforts have consequently been directed toward recycling these materials. The accumulation of metals in microorganisms is a low-cost and environmentally friendly method for the recovery of metals present in the environment at low levels. Numerous metals, including rare earth elements, can be readily dissolved in aqueous acid, but the efficiency of metal biosorption is usually decreased under the acidic conditions. In this report, we have investigated the use of the sulfothermophilic red alga Galdieria sulphuraria for the recovery of metals, with particular emphasis on the recovery of rare earth metals. Of the five different growth conditions investigated where G. sulphuraria could undergo an adaptation process, Nd(III), Dy(III), and Cu(II) were efficiently recovered from a solution containing a mixture of different metals under semi-anaerobic heterotrophic condition at a pH of 2.5. G. sulphuraria also recovered Nd(III), Dy(III), La(III), and Cu(II) with greater than 90% efficiency at a concentration of 0.5 ppm. The efficiency remained unchanged at pH values in the range of 1.5-2.5. Furthermore, at pH values in the range of 1.0-1.5, the lanthanoid ions were collected much more efficiently into the cell fractions than Cu(II) and therefore successfully separated from the Cu(II) dissolved in the aqueous acid. Microscope observation of the cells using alizarin red suggested that the metals were accumulating inside of the cells. Experiments using dead cells suggested that this phenomenon was a biological process involving specific activities within the cells.

Establishing carbon dots assisted high speed countercurrent chromatography and its application for efficient separation of rare earth element ions.

Rare earth elements with unique magnetic properties and optical properties, known as the 'industrial vitamin', has a very high commercial value. As a secondary resource of rare earth elements, low-concentration solution includes mixed rare earth ions, which need to realize efficient separation and recovery urgently. High speed countercurrent chromatography is suitable for the separation and purification of rare earth element ions due to its advantages of large loading, good tolerance to samples, and simple pretreatment. In this study, a carbon dots assisted high speed countercurrent chromatography method was designed and established, the carbon dots were applied to the mobile phase of high speed countercurrent chromatography for the first time. The low concentration of REEs solution was enriched, and the effective separation of La (III), Ce (III), Gd (III) and Er (III) was successfully achieved. The complete separation of La (III), Ce (III), Gd (III) and Er (III) was achieved with a solvent system of 0.05 mol L-1 P507 (PE), 0.05 mol L-1 HNO3, and 0.1 mol L-1 CDs2 carbon dots (1:1:0.01, v/v/v), the upper phase as stationary phase, the lower phase as mobile phase. Density functional theory result showed that the binding energy of REEs (III)-CDs2 was larger than that of REEs (III)-P507, so the affinity of CDs2 to REEs (III) was stronger than that of P507. Therefore, with the addition of CDs2, the ability of mobile phase to elute REEs from the stationary phase was enhanced, and the separation effect was improved.

Development and optimization of high-performance extraction chromatography method for separation of rare earth elements.

The effectiveness of commonly used extractants for chromatographic separation of rare earth elements (REEs) was compared. Columns loaded with similar molar concentrations of tributyl phosphate (TBP), di-(2-ethylhexyl) phosphoric acid (HDEHP), and N-Methyl-N, N, N-tri-octyl-ammonium chloride (Aliquat-336), with mineral acid as eluent were evaluated. Retention factors were determined, and separation efficiency was assessed based on the resolution data of the REEs acquired under the same elution conditions for each column. HDEHP demonstrated the best separation efficiency for the entire REE series (mean Rs = 2.76), followed by TBP (mean Rs = 1.52), while Aliquat-336 exhibited the lowest performance (mean Rs = 1.42). The HDEHP-coated column was then used to optimize the extraction chromatographic separation of the REEs. The primary challenge was to completely elute the heavy REEs (Tb - Lu) while maintaining adequate separation of the light REEs (La - Gd) within a reasonably short time. The stepwise gradient elution procedure improved the resolution between adjacent REEs, allowing the complete separation of the entire REE series within 25 minutes. Better separation efficiency for light REEs was achieved at higher column temperatures and a mobile phase flow rate of 1.5 mL/min in the tested domain of 20-60 °C, and 0.5-2.0 mL/min, respectively, resulting in plate heights (H) ranging from 0.011 to 0.027 mm.