Recovery of rare earth elements present in mobile phone magnets with the use of organic acids

Currently, the recovery of materials from secondary sources is increasingly necessary because of the scarcity of materials. Significant amounts of rare earth elements (REE) are found in permanent neodymium-iron-boron (NdFeB) magnets, used in various electrical and electronic equipments, such as mobile phones. However, the estimated recycling rate for REEs is only 1%. Hydrometallurgical routes are the most commonly used for REE recovery from secondary sources. This route usually uses inorganic acids, which are expensive and toxic. Thus, in this work the leaching efficiency of organic acids (acetic and citric) in leaching the REE (neodymium and praseodymium) present in magnets of obsolete or defective mobile phones was evaluated. Different concentrations of acids, solid/liquid relations, times and leaching techniques (microwave, ultrasound and conventional) are also evaluated. The results indicate that acetic and citric acids have the potential to leach Nd and Pr. Microwave leaching was the most effective method, compared to ultrasound and conventional methods. In microwaves, citric acid at 0.5 M (ratio s/l 1/100) leached 57% of Nd and 58% of Pr. Acetic acid at 0.5 M (s/l ratio—1/100) leached 48% of Nd and 65% of Pr, in 15 min. Furthermore, both citric acid and acetic acid also leached high percentages of iron (51% and 72%, respectively)

Recovery and Recycling of Valuable Metals

Metals have always played a significant role in human life, and the current global growth and prosperity are directly dependent on these materials. With the rapidly growing global demand for metals, their extraction from natural minerals (as their primary sources) has been enhanced, causing a significant reduction in the grade and quality of the ores in ore deposits and leading to the production of huge amounts of waste, which requires management. In light of this, new proposals to develop more advanced metal recovery technologies from minerals are needed. Additionally, the huge quantity of waste generated through all steps of metal production is known to be a source of environmental pollution, while its valorization can create value via recycling metals or even though use in the production of other valuable materials. Such waste valorization is also in line with the United Nations’ Sustainable Development Goals (SDGs), as well as the implementation of the Paris Agreement. In this regard, the recycling of end-user products in order to reproduce valuable metals can also create significant value and reduce mining activities, and thus, their harmful consequences worldwide. Therefore, research and development in the state-of-the-art technologies for the recovery and recycling of metals are absolutely necessary. The aim of this Special Issue was to collect a range of articles on different aspects of valuable metal recovery and recycling from primary and secondary sources, as well as to decipher all new methods, processes, and knowledge in valuable metal production. We hope that this open access Special Issue will provide a great opportunity to demonstrate the work of researchers working in this area all around the world and help to provide new ideas for researchers who are working in the areas of hydrometallurgy, mineral processing, and waste recycling and valorization

Tyre4REEcyle Recovery of Rare Earth Elements from NdFeB Magnets by Using Porous Carbons Produced from Rubber of Spent Tyres

This thesis explores the recovery of rare earth elements, specifically Neodymium and Dysprosium, from NdFeB magnets through adsorption using porous carbon materials derived from spent tyre rubber. The increasing disposal of end-of-life tyres and the scarcity of rare earth elements in technological applications present significant environmental and economic challenges. By utilizing tyre pyrolysis, this research converts waste into valuable porous carbons that serve as effective adsorbents for rare earth elements recovery. Porous carbons were produced via pyrolysis of spent tyre rubber, followed by physical activation of the resulting chars. These materials were characterized and tested for their adsorption capacity toward rare earth elements under both batch and dynamic conditions. Single-component and competitive adsorption studies were conducted to evaluate the interactions between Neodymium and Dysprosium ions. In addition, real magnet leachates were utilized to simulate real-world applications of these materials. The findings revealed substantial adsorption capacities for both rare earth elements, with physically activated chars exhibiting superior performance, attributable to their enhanced properties. Beyond rare earth elements recovery, the rare earth-loaded porous carbons were assessed for their catalytic activity in photocatalytic hydrogen production. The successful incorporation of rare earth elements and porous carbons derived from spent tyre rubber as catalysts in hydrogen evolution further closed the waste valorisation loop, demonstrating the dual functionality of the materials. This thesis provides a novel approach to the circular economy by addressing two waste streams - spent tyre rubber and electronic waste - while developing sustainable materials for critical raw material recovery. The findings highlight the potential of this process for industrial applications and contribute to the advancement of green chemistry and sustainable engineering in resource recovery.Esta tese explora a recuperação de elementos de terras raras, especificamente neodímio e disprósio, a partir de magnetos NdFeB através da adsorção utilizando materiais de carbono poroso derivados de borracha de pneus usados. A crescente quantidade de pneus em fim de vida e a escassez de elementos de terras raras disponíveis para aplicações tecnológicas representam desafios ambientais e económicos significativos. Ao utilizar a pirólise de pneus, esta investigação converte os resíduos em materiais de carbono porosos que servem como adsorventes para a recuperação de elementos de terras raras. Os materiais de carbono porosos foram produzidos através da pirólise de borracha de pneus usados, seguida da ativação física dos materiais resultantes. Estes materiais foram caracterizados e testados quanto à sua capacidade de adsorção de terras raras em condições dinâmicas e em batch. Foram realizados estudos de adsorção mono-componente e de adsorção competitiva de forma a avaliar as interações entre os iões de neodímio e disprósio. Posteriormente, foram utilizados lixiviados de ímanes reais para simular aplicações reais destes materiais. Os resultados revelaram capacidades de adsorção substanciais para ambas as terras raras, com os carvões ativados a exibirem um desempenho superior. Além da recuperação de terras raras, os carvões porosos carregados com terras raras foram avaliados quanto à sua atividade catalítica para a produção de hidrogénio. A incorporação de terras raras e de carbonos porosos derivados da borracha de pneus como catalisadores em reações de evolução de hidrogénio fecha o ciclo de valorização dos resíduos, demonstrando a dupla funcionalidade dos materiais. Esta tese fornece uma abordagem nova à economia circular, tratando dois fluxos de resíduos - borracha de pneus usada e resíduos eletrónicos - ao mesmo tempo que desenvolve materiais sustentáveis para a recuperação de matérias-primas críticas. Os resultados destacam o potencial deste processo para aplicações industriais e contribuem para o avanço da química verde e da engenharia sustentável na recuperação de recursos

A toolbox for improved recycling of critical metals and materials in low-carbon technologies

The shift towards renewable energy sources combined with other factors, such as population increase, digitalisation, and a need to decrease carbon footprint, leads to increasing metal consumption. To meet this growing demand and avoid accumulation of waste in landfills, efficient recycling methods are needed. Current pyrometallurgical and hydrometallurgical methods achieve complete digestion of end-of-life materials using high temperatures and high consumption of chemicals, respectively. These methods can be applied to recover critical metals from end-of-life materials but suffer from inherent limitations when it comes to complex end-of-life materials made of interpenetrated layers of metals, inorganics and organics. This critical review describes a set of chemical and physical tools for improved recovery of metals from various waste streams, with a strong focus on the renewable energy sector (wind turbines, solar cells) as well as lithium-ion batteries and catalysts for hydrogen production. These tools target weaknesses at the interfaces between different layers to liberate the valuable metals. Physical methods used for size reduction and separation, ultrasound to process brittle materials, hydrogen decrepitation, selective dissolution and bio-metallurgical methods to process metals are among those reviewed. Management of inorganic and organic fractions is also emphasised, with pyrolysis and solvolysis to process organics and ways to recycle these materials. Limitations and future directions are discussed, providing a comprehensive guide to improve recycling of metals with versatile tools.</p

Current Trends and Perspectives in the Application of Polymeric Materials for Wastewater Treatment

Water is indispensable to the functioning of most known life forms, and good water quality is essential to human health, social and economic development, and ecosystem functioning. Nonetheless, population growth has been leading to the degradation and depletion of fresh water resources. Under these circumstances, ensuring sufficient and safe water supplies for everyone is one of the Sustainable Development Goals (SDGs) set by the United Nations General Assembly in 2015 for the year 2030. For this goal to be achieved, the development and implementation of appropriate and efficient wastewater treatments that allow us to reduce water pollution is a major challenge.In view of the relevant contribution that polymers and polymeric materials may have in the conservation of the aquatic environment, namely by their application in wastewater treatment, original research and review papers on “Current trends and perspectives in the application of polymeric materials for wastewater treatment” were here brought together. For sure, this set of papers will be helpful and inspiring for readers interested in this topic

Calentamiento simultáneo microondas-radiación térmica

In this article we present the results of the simulation of a hybrid heat treatment methodology for materials, by using electromagnetic waves in the microwave range and the thermal power radiation of an electrical resistance. This resistance was placed in such a way that only half of the solid (a two-layers sphere) receives its energy. Then, it was controlled to produce a constant and uniform heat flow. In addition, for the present case, materials with different thermophysical properties were defined in each layer, which were considered to be invariant both with position and with temperature. The heat flow was considered constant over time. The temperature profiles for each layer showed variations in time and position, so it was observed that this simultaneous heating eases the adjustment of these profiles, according to the needs of thermal treatment. Thus, the advantage of hybrid heating was evidenced.En este artículo se presentan resultados de la simulación del tratamiento térmico híbrido de materiales, utilizando ondas electromagnéticas en el rango de las microondas y el calor por radiación térmica generado por una resistencia eléctrica. La resistencia se ubicó de tal forma que solo la mitad del sólido (una esfera de dos capas) recibe la energía generada por ésta. Además, la resistencia se controló de tal forma que generó energía térmica de forma uniforme y constante. Igualmente, se definieron materiales con propiedades termofísicas diferentes en cada capa, pero invariantes tanto con la posición como con la temperatura. El flujo de calor volumétrico se consideró constante con el tiempo. Los perfiles de temperatura para cada capa mostraron variaciones en el tiempo y la posición, observándose que el calentamiento simultáneo facilita la manipulación de estos perfiles, de acuerdo con las necesidades del tratamiento térmico. Así, se evidenció la ventaja de éste tipo de calentamiento híbrido

Hydrometallurgy

Hydrometallurgy, which involves the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual material, plays an integral role in the multi-billion dollar minerals processing industry. There are numerous hydrometallurgical process technologies used for recovering metals, such as: agglomeration; leaching; solvent extraction/ion exchange; metal recovery; and remediation of tailings/waste. Modern hydrometallurgical routes to extract metals from their ores are faced with a number of issues related to both the chemistry and engineering aspects of the processes involved. These issues include declining ore grade, variations in mineralogy across the deposits and geo-metallurgical locations of the ore site; which would influence the hydrometallurgical route chosen. The development of technologies to improve energy efficiency, water/resources consumption and waste remediation across the circuit is also an important factor to be considered. Therefore, there is an increasing need to develop novel solutions to these existing problems, to implement environmentally sustainable practices in the recovery of these valuable metals. Papers on recent advances, and review articles, particularly in regard to fundamental chemistry and the development of novel techniques and technologies in commercial processing of mineral commodities from their ores, are included in this Special Monograph on "Hydrometallurgy"

Scavengers, reagents, and catalysts supported on recyclable magnetic nanoparticles

In this work the immobilization of scavenging groups, reagents, chelating ligands, and catalysts on highly magnetic carbon-coated iron (Fe/C) or cobalt (Co/C) nanoparticles is described. To improve the dispersion stabilities of the nanoparticles and likewise the loading with functional groups, polymers are introduced by surface-initiated polymerization. Successful applications of these novel nanoparticles include the purification of intramolecular Mitsunobu cyclization reactions, the extraction of riboflavin (vitamin B2) from aqueous solutions by immobilized zinc(II)–cyclen complexes, and the preparation of a library of ureas and thioureas exclusively using magnetic scavengers and reagents. The extraordinary high magnetization of the metal core allows for rapid separation of the hybrid materials enabling convenient purification of the reaction mixtures by magnetic decantation. Additionally, the first controlled synthesis of transition-metal nanoparticles on the surface of Co/C nanobeads is described in detail. The synthesized Pd@Co/C nanoparticles are highly active in the hydrogenation of alkenes at atmospheric pressure