Recovery of Critical Raw Materials from Industrial Wastes by Advanced Methods

Dear Colleagues,

Raw Materials (RMs) are crucial to the world economy. They form a strong industrial base, producing a broad range of goods and applications used in everyday life. Reliable and unhindered access to certain RMs is a growing concern within the EU and across the globe. To address this challenge, the European Commission has created a list of 30 critical raw materials (CRMs) for the EU, which is subject to a regular review and update. CRMs combine RMs of high importance to the EU economy and of high risk associated with their supply; moreover, they are closely linked to clean technologies.

The use as secondary RMs from marginal resources as industrial wastes, is of strategic importance for industrial production, due to their high concentration on valuable metals.

RMs (i.e. gold, silver, copper, zinc, manganese, nickel) and CRMs (i.e. platinum, indium, cobalt, vanadium, magnesium, antimony, niobium and  rare hearts), are essential for the application of emerging modern technologies and to preserve the environment from technological waste, avoiding the release of pollutants components.

The advancement of the innovative processes such as bio-hydrometallurgy, electrowinning, phytoremediation, bioprecipitation, compared with the conventional processes, are given by the lowest environmental impact and energy consumption, and by the greater degree of purity of the valuable metals obtained.

The economic value of the advanced methods for recovery of critical raw materials from industrial wastes, which is closely linked to the choice and optimization of the experimental parameters of the processes, is of great importance.

For publication in this Special Issue, those articles that contribute to the improvement of the of the above-mentioned methods considered.

I hope you accept this invitation, and help us to create a high-impact and high-quality Special Issue on "Recovery of Critical Raw Materials From Industrial Wastes by Advanced Methods".

Dr. Stefano Ubaldini
Guest Editor

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• critical raw materials
• strategic raw materials
• low-grade georesources
• heavy metals
• bio-hydrometallurgy
• electrowinning
• phytoremediation
• bioprecipitation
• industrial wastes
• WEEE

Title: Biotechnological tool for metal(loids) management with multiple approaches
Authors: Ana Rosa Castaño Gañan; Adalgisa Scotti; Vanesa Silvani; Andrea Juarez; Stefano Ubaldini
Affiliation: Bio Environmental Laboratory, International Center for Earth Sciences, National Atomic Energy Commission, San Rafael Mendoza 5600 (AS); Institute of Environmental Geology and Geoengineering, National Research Council of Italy, Research Area of Rome 1, Strada Provinciale 35d, n. 9, 00010 – Montelibretti (RM), Italy; Faculty of Exact and Natural Science, Institute of Biodiversity and Applied and Experimental Biology, National Scientific and Technical Research Council—University of Buenos Aires, Buenos Aires 1428, Argentina (V.S.); Faculty of Exact and Natural Science, University of Cuyo, Padre Contreras 1300, Mendoza, 5600, Argentina.
Abstract: Naturally or anthropically contaminated soils are presented as a challenge for implementing biotechnology for remediation, recovering Critical Raw Materials (CRMs) and Strategic Raw Materials (SRMs), and ensuring food security. The EU, in its document 32023R0915, establishes the maximum limits for As, Pb, Cd and Hg in foods. On the other hand, the EU’s 5th list of CRMs identified 34 elements that should be recovered within a circular economy model.Our objective was to find a biotechnological tool capable of decontaminating soils with heavy metal(loids), and/or phytostabilizing them to prevent their entry into the food chain, and recovering valuable chemical elements such as CRMs and SRMs.The experiment consisted of placing Baccharis salicifolia (Bs) plants, either inoculated or not with a mixture of arbuscular mycorrhizal fungi isolated from an Zn-Pb-Ag mine, into Bioreactors (BR) containing either non-contaminated (control) or contaminated soil with Cd, Ni and Cu, following a procedure detailed in Argentina Patent No. AR090183B1, and performed in a 2 x 2 factorial design. Also, the bioextractive potential of this biotechnological tool was estimated at a high Technological Readiness Level (TRL 6) using a vegetable depuration module (VDM).The highest aerial Bioaccumulation Coefficient in the BR was observed for Cd (68.62), followed by P (2.99), Ni (2,51) and Cu (0,18).Significant differences in bioaccumulation were found for all the elements under study when Bs plants were mycorrhized, as well as for the Translocation Factors.The proposed biotechnological tool composed of mycorrhizal Bs under patent procedure, scaled at TRL 6 showed a Bioextractive Potential of 1.16 g for Ni, 11.3 g for Cd, 3.05 g for Cu and 246.9 g for P performing a cycle of VDM/1m3 during 4 months. Finally, CRMs (Ni and P) and SRMs (Cu and Cd) could be recovered from biomass through hydrometallurgical processes within a circular economy concept.

Title: Leaching of Rare Earths from End-of-Life NdFeB Magnets by Citric Acid using Full Factorial Design, Response Surface Methodology, and Artificial Neural Network Analysis
Authors: Pietro Romano; Adriana Zuffranieri; Soroush Rahmati; Roshanak Adavodi; Francesco Ferella; Francesco Vegliò
Affiliation: Department of Industrial and Information Engineering and of Economics (DIIIE), Engineering Headquarters of Roio, University of L’Aquila, 67100 L’Aquila, Italy
Abstract: In recent years, the increasing demand and prices of Rare Earth Elements (REEs) and the supply risk (about 95% of these elements are supplied by China) have led the European Commission to consider REEs as critical raw materials. Developing and optimizing processes for recovering REEs from secondary sources such as NdFeB magnets is fundamental in this context. A novel method to recover REEs by leaching with citric acid and separating the rare earth elements using the solvent extraction method as the next step has been introduced. Therefore, this research investigates the leaching efficiency of REEs, Fe and B from NdFeB magnets. A full factorial design with 18 experimental setups was conducted to optimize the citric acid concentration (1-3 mol/L), leaching time (1-3 h), and solid-to-liquid ratio (5-10 %wt./vol.). Different optimizations (response surface methodology (RSM) and artificial neural network (ANN) analysis) are used to maximize the REEs leaching efficiency. RSM determined a maximum extraction yield of total rare earth elements (TREEs) of about 90% in the investigated experimental plan. The result is similar to ANN's (about 91%) but more accurate than RSM's. In fact, for the ANN, an overall R-value higher than 0.99 was obtained. This result means that the developed ANN can be used as an accurate model for estimating the leaching efficiencies of REEs from NdFeB magnets.

Title: Improving the hydrometallurgical recycling process of Li-ion batteries by blending LFP-NMC black masses
Authors: Francesca Pagnanelli; Pietro Altimari; Marco Colasanti; Jacopo Coletta; Ludovica D’Annibale; Alyssa Mancini; Pier Giorgio Schiavi
Affiliation: Department of Chemistry, Sapienza University of Rome (IT)
Abstract: The development of hydrometallurgical recycling processes for lithium ion batteries suffers from the heterogeneity of the electrode powders recovered through physical processes from end-of-life lithium ion batteries. The electrode masses (black masses) can have various contents of nickel, manganese and cobalt (NMC) but also the presence of other chemicals such as lithium iron phosphate (LFP). The work reports the results relating to the hydrometallurgical treatment of NMC and LFP mixed black masses with a view to developing flexible recycling processes, exploiting the reducing power of LFP and guaranteeing a composition of the leach liquor suitable for resynthesis processes of NMC precursors