Process optimization for acidic leaching of rare earth elements (REE) from waste electrical and electronic equipment (WEEE)

Recycled Rare Earth Ions From E-Waste In Borogermanate Glasses For Magneto-Optical Applications

Magneto-optical borogermanate glasses were developed by incorporating electro-electronic waste recovered from fluorescent lamps. Glasses with a composition of (41GeO₂-25B₂O₃-4Al₂O₃-10Na₂O-20BaO)-x%wst, (x=0, 10, 20, 30, and 50 wt% of waste) were prepared. The final chemical composition was determined, and the glasses were characterized through thermal, structural, morphological, optical, and magneto-optical analyses. The addition of lamp waste to the glass matrix did not induce crystallization and stable glass materials were obtained, as confirmed by thermal analysis. Raman spectroscopy has shown that the addition of different amounts of waste into the vitreous matrix induces structural rearrangements as evidenced by the vibration bands of non-bridging B-O- bonds. Regarding optical properties, the transmittance of the glasses slightly decreased with waste incorporation. Photoluminescence showed electronic transitions attributed to the Tb3+ and Eu3+ ions and non-radiative energy transfer from the host to both Ln3+ ions and between them was observed. Finally, a Verdet constant value of -40.9 rad. T-1 m-1 at 632.8 nm was obtained, highlighting the potential of these sustainable glasses as Faraday rotators.

Selective leaching of rare earths, base metals and precious metals from used smartphones

Discarded smartphones represent a valuable source of rare earths (REE), base metals and precious metals. This study focussed on the optimisation of three-stage selective leaching conditions for REE, copper and precious metals (Au and Ag), respectively, contained in printed circuit boards (PCBs) found in end-of-life smartphones. The effects of several leaching conditions, such as sulphuric acid and thiourea concentrations, were investigated using a statistical approach based on a design of experiments using Box-Behnken methodology. Optimum leaching efficiencies were achieved when PCB powder was contacted (solid concentration of 100 g/L) with (1) a 0.2 M H2SO4 solution for 30 min at a temperature of 20°C for REEs; (2) a 1 M H2SO4 solution with 67 g H2O2/L for 180 min at 80°C for Cu and (3) a solution of 42 g thiourea/L in 0.1 M H2SO4 and 9 g Fe2(SO4)3/L for 120 min at 20°C for Au and Ag. Using these optimal conditions, a complete leaching procedure included an REE solubilisation step and a base metal leaching step, both repeated twice, and a precious metal leaching step. This procedure solubilised 91% of the REE, 100% of the copper, 98% of the gold and 87% of the silver contained in the PCB powder during their respective leaching stages.

Rare Earth Element Extraction from Ionic Rare Earth Ores by Two Typical Acidogenic Microorganisms, Aspergillus niger and Acidithiobacillus ferrooxidans

Ionic rare earth ore (IREO) has a high abundance of medium and heavy rare earth elements (REEs), making it a vital strategic resource for China. In this work, two typical microorganisms, Aspergillus niger and Acidithiobacillus ferrooxidans, were used to study the interaction mechanism during the bioleaching of IREO under acidic conditions. The results revealed some differences in the interaction and leaching effects of A. niger and A. ferrooxidans on ionic rare earth minerals. A. niger mainly forms rare earth complexes with rare earth ions in IREO by secreting metabolites such as organic acids, thereby promoting the release of REEs, and it has a strong adsorption capacity for Yb. A. ferrooxidans promotes the release of REEs from rare earth minerals, primarily through iron-sulfur oxidation. The differential expression of metabolic genes (e.g., gpmL, FabF, FASN) associated with major metabolite secretion indicates their correlation with the leaching process. The above results reveal the role of the typical acid-producing microorganisms A. niger and A. ferrooxidans and their metabolites in the leaching of IREO, which is valuable for understanding the interaction mechanisms between microorganisms and IREO under acidic conditions.

Biotechnological Approaches for Metal Recovery from Electronic Wastes

The disposal of electronic waste (EW) in open landfills has caused several toxic environmental effects. The harmful metallic components released in the environment due to deposition of EW act as hazards for living systems. EW management has been widely studied in recent days across the world. Though, several processes are implemented in extraction, recycling and recovery of heavy metals from the EW, most of them are not effective in recovering the precious metals. Various chemical processes are executed for efficient extraction of precious metals from e-wastes. Though the techniques are easy to process and rapid, however, the chemical leaching also has detrimental environmental consequences. Biological approaches, on the other hand, solves the purpose for efficient and environmentally friendly recovery of precious metals. Thus, both resource recovery as well as remediation can be targeted simultaneously. Biotechnological methods offer sustainable and efficient solutions for metal recovery from electronic wastes, presenting a viable alternative to traditional methods. Continued advancements in this field hold significant promise for addressing the growing e-waste challenge.

A review of greener approaches for rare earth elements recovery from mineral wastes

The use of rare earth elements (REE) in many various fields, including high-tech products, increases the demand for these materials day by day. The production of REE from primary sources has expanded in response to increasing demand; however, due to its limited, a more sustainable supply is also started to offer for the REE demand by using secondary sources. The most commonly used metallurgical method for REE recovery is hydrometallurgical processes. However, it has some disadvantages, like pyrometallurgical methods. In the review, studies of the environmental impacts of REE production from primary sources and life cycle assessments of products containing REE were investigated. According to the results, it has been seen that those studies in the literature in which hydrometallurgical methods have changed to more environmentally friendly approaches have begun to increase. In this review, mine wastes, which are secondary sources, were defined, conventional methods of recovery of rare earth elements were discussed, greener approaches to the recovery of REE from these sources were comprehensively examined and studies in the literature were evaluated. Furthermore, it was stated that there are limited studies on green approaches and REE recovery from mineral wastes and that this field is developing with an emphasis on the current outlook and future perspectives.

Rare Earth and Platinum Group Elements In Sub-Saharan Africa and Global Health: The Dark Side of the Burgeoning of Technology

Despite steady progress in the development and promotion of the circular economy as a model, an overwhelming proportion of technological devices discarded by the Global North still finds its way to the Global South, where technology-related environmental health problems start from the predation of resources and continue all the way to recycling and disposal. We reviewed literature on TCEs in sub-Saharan Africa (SSA), focussing on: the sources and levels of environmental pollution; the extent of human exposure to these substances; their role in the aetiology of human diseases; their effects on the environment. Our review shows that even minor and often neglected technology-critical elements (TCEs), like rare earth elements (REEs) and platinum group elements (PGEs), reveal the environmental damage and detrimental health effects caused by the massive mining of raw materials, exacerbated by improper disposal of e-waste (from dumping to improper recycling and open burning). We draw attention of local research on knowledge gaps such as workable safer methods for TCE recovery from end-of-life products, secondary materials and e-waste, environmental bioremediation and human detoxification. The technical and political shortcomings in the management of TCEs in SSA is all the more alarming against the background of unfavourable determinants of health and a resulting higher susceptibility to diseases, especially among children who work in mines and e-waste recycling sites or who reside in dumping sites.This paper demonstrates, for the first time, that the role of unjust North-South dynamics is evident even in the environmental levels of minor trace elements and that the premise underlying attempts to solve the problem of e-waste dumped in Africa through recycling and disposal technology is in fact misleading. The influx of foreign electrical and electronic equipments should be controlled and limited by clearly defining what is a 'useful' second-hand device and what is e-waste; risks arising from device components or processing by-products should be managed differently, and scientific uncertainty and One Health thinking should be incorporated in risk assessment.

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.

Generation estimation and metals recycling potentials evaluation of retired mobile phones in Korea

The goal of this work is to evaluate generation and metals recycling potentials of retired mobile phones in Korea. The generation estimation is conducted with the sales&new method and statistic data, such as sales of mobile phones and amount of the subscribers. The result shows that there are 17.99 million of mobile phones retired in 2022, compared 13.12 million in 2001. Accordingly, the deduced lifetime has minimum and maximum values in 2003 and 2020, which are 2.02 and 4.33 years, compared with 4.16 years in 2022 and 2.21 years in 2001. The deduced lifetime trends to increase with the increased values of subscribers and the fluctuated values of sales. The crosscheck testifies to the veracity of the result in comparison with the actual condition. The amount and dynamic of critical metals are also calculated with the content and amount of retired mobile phones.

Tailoring a bio-based adsorbent for sequestration of late transition and rare earth elements

The demand for new renewable energy sources, improved energy storage and exhaust-free transportation requires the use of large quantities of rare earth (REE) and late transition (LTM, group 8-12) elements. In order to achieve sustainability in their use, an efficient green recycling technology is required. Here, an approach, a synthetic route and an evaluation of the designed bio-based material are reported. Cotton-derived nano cellulose particles were functionalized with a polyamino ligand, tris(2-aminoethyl) amine (TAEA), achieving ligand content of up to ca. 0.8 mmol g^-1. The morphology and structure of the produced adsorbent were revealed by PXRD, SEM-EDS, AFM and FTIR techniques. The adsorption capacity and kinetics of REE and LTM were investigated by conductometric photometric titrations, revealing quick uptake, high adsorption capacity and pronounced selectivity for LTM compared to REE. Molecular insights into the mode of action of the adsorbent were obtained via the investigation of the molecular structure of the Ni(II)-TAEA complex by an X-ray single crystal study. The bio-based adsorbent nanomaterial demonstrated in this work opens up a perspective for tailoring specific adsorbents in the sequestration of REE and LTM for their sustainable recycling.

Generation estimation and material flow analysis of retired mobile phones in China

The generation estimation of retired mobile phones is launched with the sales and new method using the revised sales data and amount of the subscribers. Several assumptions have been made due to the insufficient sources of the data. The sales data of legal mobile phones are calculated with the authoritative and continuous official data. The sales data of smuggled and counterfeit mobile phones in China are also estimated based on the behavior data collected from the questionnaires. The results of generation estimation show that there are 636.52 million mobile phones retired in 2020, compared with 14.44 million in 1999 and several negative values in 2000, 2001, and 2008. The annual total mass of retired mobile phones in China escalated with the contributions of both the increasing generation amount and constant mass of the single unit. There are 50,921.60 ton of mobile phones retired in 2020 compared with 1155.20 ton in 1999, while the peak is 58,131.20 ton in 2019. There are 26,066.80 ton of retired mobile phones are stockpiled in 2020, while 16,152.40 ton and 8702.40 ton of retired mobile phones are reused as a whole unit and recycled, respectively. In the retired mobile phones that are recycled, 4600.50 ton material is recovered and 1216.50 ton components are reused, while 2885.40 ton residues need final disposal. The amount and dynamic characteristics of metals in the retired mobile phones are also calculated. Based on the results, several policy implications are made to improve sustainable management system of retired mobile phones in China.

Enrichment and occurrence form of rare earth elements during coal and coal gangue combustion

Coal ash has emerged as an important alternative source for rare earth elements (REEs). The enrichment and occurrence form of REEs among coal combustion products are of great significance for both technical design and economic evaluation of recovering REEs from the coal ash. Here, the enrichment and occurrence form of REEs in the ash were investigated. Compared with ashes from muffle furnace, coal fly ash (CFA) from power plants involved higher enrichment ratio of REEs, which was explained by the fractionation of coal ashes to concentrate REEs in finer CFA, higher combustion temperature to vaporize more volatile elements, and longer residence time of fly ash to absorb REEs in the gas. In addition, CFA samples were analyzed by sequence chemical extraction procedure (SCEP) and scanning electron microscope with an energy dispersive spectrometer (SEM-EDX), which revealed the important role of aluminum in the occurrence form of REEs compared with Si in aluminosilicates of CFA. This conclusion was further confirmed by thermodynamic equilibrium calculation, which also agreed qualitatively with the observation that REEs mainly existed in the solid phase. Both experimental and computational results of this work provided insights to understand the distribution of REEs in CFA and optimize their extraction processes.