Recovery Of Critical Raw Materials Research Articles

Low-Temperature Carbothermic Reduction for Recycling LiCoO2 for the Recovery of Critical Raw Materials: The Role of Cellulose

Low-Temperature Carbothermic Reduction for Recycling LiCoO₂ for the Recovery of Critical Raw Materials: The Role of Cellulose

(Invited) Solvometallurgy as a Sustainable Approach for Lithium-Ion Batteries Recycling

Lithium-Ion Batteries, LIBs, are the core devices that made possible the diffusion of portable consumer electronics and, more recently, the booming of the electric vehicle market. [1] Their ubiquitous use and diffusion led to the well-known and urgent problem of spent LIBs management. Indeed, spent LIBs represent a complex and hazardous kind of waste for which specific regulation, disposal, and recycling routes are still missing. At the same time the continuous and growing production of LIBs involves the mandatory use of specific elements such as Li, Co, Ni, Cu, Al that are considered strategic or critical raw materials due to their limited availability, high costs, monopoly, and geological distribution. [2] The development of efficient and sustainable procedures for recycling of spent LIBs is the answer to these two main challenges as in enable to properly manage the LIBs waste and allow for the recovery of critical raw materials. While at industrial scale the high temperature pyrometallurgy and hydrometallurgy are the methods in use today, in the very last years, many approaches have been explored at research level, among them low temperature pyrometallurgy, soft hydrometallurgy, solvometallurgy, bioleaching. [3] Among them, the solvometallurgical approach exploiting Deep Eutectic Solvents (DESs) as leaching agents is particularly appealing thank to some specific features such as the low volatility, low flammability, low costs, ease of preparation combined with high leaching efficiencies.DESs are mixture of based on the presence of a hydrogen bond donors and acceptors forming a eutectic mixture at ambient temperature; although their first conceptualization is recent, several compositions have been already appeared in literature for this specific application. [4] At the same time, a rationalization of the role of the mixture components and a specific design of the composition, tailored for the application in LIBs recycling is still missing. We here present the results of our work on the development of new DESs compositions enabling the close-loop recycling of different spent cathodes. The DES compositions have been designed considering the overall recycling process, the effect of the DES compositions in terms of hydrogen bond donors and acceptors has been evaluated and rationalized through a preliminary chemical-physical characterization through thermal, NMR, FTIR, viscosity analysis. The leaching of the most common cathode has been optimized against the dominant parameters (temperature, treatment duration, cathode-to-DES ratio) opening the ways for two possibilities: the recovery of critical raw materials and the direct resynthesis of new cathodes. All the steps and products have been fully characterized with a multi-technique approach including structural and chemical investigation through the electrochemical testing of the re-synthetized materials. Finally, these two options have been assessed through LCA analysis, being able to provide an overview of the global sustainability of the proposed processes.[1] Ji et al., Chem Soc. Rev. (2023) doi 10.1039/d3cs00254c[2] Global Supply Chains of EV Batteries report, International Energy Agency[3] Yasa et al. J. En. Stor. 73 (2023) 109073[4] Padwal et al. Adv. En. Sus. Res. 3 (2022) 2100133

The Application of Atomic Spectroscopy Techniques in the Recovery of Critical Raw Materials from Industrial Waste Streams, Part II

This month’s column is Part 2 of a contribution from my daughter Glenna, who recently completed her PhD studies in Environmental Science from the University of Copenhagen in Denmark. Her article explores the current landscape of global critical raw materials (CRM) trends in research and the applications of atomic spectroscopy (AS), including inductively coupled plasma–mass spectrometry (ICP-MS), inductively coupled plasma–optical emission spectrometry (ICP-OES), and X-ray analytical techniques in their identification of diverse industrial and environmental media, which have been essential in method validation and quantification of CRMs in complex matrices presenting high risks of interference. Some important examples to be presented include rare earth elements (REEs) in water leaching purification (WLP) residues that co-occur with radioactive materials; REEs and other metals in acid mine drainage (AMD) environments; REEs in coal combustion (fly ash) residues; arsenic (As) from groundwater treatment sediment; and platinum-group elements (PGEs) from sewage sludge. The article also classifies the different techniques in use at each stage of the CRM recovery train, investigates present challenges to each analytical method, and discusses the problem-solving tools used.

The Application of Atomic Spectroscopy Techniques in the Recovery of Critical Raw Materials from Industrial Waste Streams, Part I

This month’s column is a contribution from my daughter Glenna, who recently completed her PhD studies in environmental science from the University of Copenhagen in Denmark. Her article explores the current landscape of global critical raw materials (CRM) trends in research and the applications of atomic spectroscopy (AS), including inductively coupled plasma–mass spectrometry (ICP–MS), inductively coupled plasma–optical emission spectrometry (ICP–OES), and X-ray analytical techniques in their identification of diverse industrial and environmental media, which have been essential in method validation and quantification of CRMs in complex matrices presenting high risks of interference. Some important examples that are presented include rare earth elements (REE) in water leaching purification (WLP) residues that co-occur with radio- active materials, REEs and other metals in acid mine drainage (AMD) environments, REEs in coal combustion (fly ash) residues, arsenic (As) from groundwater treatment sediment, and platinum-group elements (PGE) from sewage sludge. In addition, the article classifies the different techniques in use at each stage of the CRM recovery train, investigate present challenges to each analytical method, and discuss the problem-solving tools used.

Techno-economic evaluation of antimony and bismuth upcycling from pyrometallurgical copper wastes

The recovery of critical raw materials (CRMs) is important to reduce the supply risk disruption and the dependency on third-countries within the European Union (EU). The present study evaluates the techno-economic implications of antimony (Sb) and bismuth (Bi) recovery from the process stream produced in the polishing stages of the copper electrorefining circuit. The upcycling process was based on the selective precipitation of Sb and Bi from the concentrated hydrochloric acid (HCl) (up to 5–6 M) process stream containing high arsenic (As) concentrations. Four different scenarios were included in the evaluation, in which Sb and Bi were recovered as Sb4O5Cl2(s)/Sb2O3(s) and BiOCl(s)/Bi2O3(s), respectively. The results showed that implementing Bi and Sb upcycling configurations in the copper metallurgical facilities was economically feasible when recovering BiOCl(s)/Sb4O5Cl2(s) and BiOCl(s)/Sb2O3(s) from the eluate stream. Sb recovery was the most cost-intensive process in all the configurations evaluated due to the high chemical requirements needed to neutralize the free HCl excess. The consumption of chemicals represented the most important cost contributor, since high amounts of chemicals are needed for the selective Sb and Bi precipitation. The sensitivity analysis illustrated that recovering these CRMs was economically attractive for all the configurations when achieving Sb and Bi prices above 8.5 and 9.5 €/kg, respectively. Under these CRM prices, the payback period and internal rate of return for the different scenarios range from 4 to 19 years and from 6 to 28 %, respectively. This output highlights that future increase in CRM prices can be an important driver to implement Sb and Bi recovery schemes. Overall, the results of this study highlight the economic potential of implementing Sb and Bi recovery schemes in copper metallurgical plants to align with the ambitious circular economy objectives established by the EU.

Perspective on the use of methanogens in lithium recovery from brines.

Methanogenic archaea stand out as multipurpose biocatalysts for different applications in wide-ranging industrial sectors due to their crucial role in the methane (CH4) cycle and ubiquity in natural environments. The increasing demand for raw materials required by the manufacturing sector (i.e., metals-, concrete-, chemicals-, plastic- and lubricants-based industries) represents a milestone for the global economy and one of the main sources of CO2 emissions. Recovery of critical raw materials (CRMs) from byproducts generated along their supply chain, rather than massive mining operations for mineral extraction and metal smelting, represents a sustainable choice. Demand for lithium (Li), included among CRMs in 2023, grew by 17.1% in the last decades, mostly due to its application in rechargeable lithium-ion batteries. In addition to mineral deposits, the natural resources of Li comprise water, ranging from low Li concentrations (seawater and freshwater) to higher ones (salt lakes and artificial brines). Brines from water desalination can be high in Li content which can be recovered. However, biological brine treatment is not a popular methodology. The methanogenic community has already demonstrated its ability to recover several CRMs which are not essential to their metabolism. Here, we attempt to interconnect the well-established biomethanation process with Li recovery from brines, by analyzing the methanogenic species which may be suitable to grow in brine-like environments and the corresponding mechanism of recovery. Moreover, key factors which should be considered to establish the techno-economic feasibility of this process are here discussed.

In-Depth Understanding of Hardmetal Corrosion Performance Reveals a Path to the Electrochemical Demolition of Scrap

Recycling of hardmetal scrap is strategic for critical raw materials recovery. Available recycling processes are polluting and have a large carbon footprint. Attempts to exploit controlled corrosion failed in industrial practice, owing to self-limiting processes. We revisit the corrosion route, in view of gaining the fundamental knowledge enabling high-throughput recovery. We selected the worst-case approach of highly corrosion-resistant CoNiWC-based hardmetal grades and neutral aqueous electrolyte at room temperature. Systematic electrochemical measurements, UV–Vis spectroscopy and SEM microscopy disclosed that, even though there is no hope to overcome the self-limiting corrosion rate, nevertheless, by exploiting the mechanical action of anodic O2 evolution acting precisely at the interface between the residual active material and the corrosion film, the latter can be efficiently removed, periodically reactivating the hardmetal corrosion in a way that results in an ultra-high scrap destruction rate, of interest for real-life industrial processes.

Critical Raw Materials recovery potential from Spanish mine wastes: A national-scale preliminary assessment

In Spain, due to its important mining past, there are many abandoned mine waste facilities. This study evaluates the potential of Spanish mine wastes for the recovery of critical and strategic raw materials and other elements of economic relevance. For this purpose, 20 mine waste facilities have been selected in different parts of Spain based on criteria such as tonnage, element content or metal market price. Surface samples were taken at the facilities, considered representative of these, for subsequent granulometric, mineralogical and chemical analysis. The grain size data were obtained by standard sieving (ASTM 5000), while the mineralogy was obtained by X-ray Diffraction (XRD). For chemical characterization, Wavelength Dispersion X-ray Fluorescence Spectrometry (WDXRF) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used to analyze 38 chemical elements (Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Br, Rb, Sr, Y, Zr, Nb, Mo, Ag, Cd, Sn, Sb, I, Cs, Ba, La, Ce, Nd, Sm, Hf, Ta, W, Tl, Pb, Bi, Th and U), many of them included in the European Union’s list of Critical Raw Materials (CRMs). In addition, leachate data from mine wastes in the Iberian Pyritic Belt were analyzed to assess their bioleaching potential. The calculated enrichment factors (EF) indicate that some critical elements, as well as others with strategic and economic interest, are highly enriched in the wastes, including Sb, Bi, As, Pb, Cu, Ag, Zn, Cd, Sn, Se and Th. The most promising facilities with the highest recovery potential are located in the historic Riotinto and Tharsis mines (both in Huelva, Iberian Pyrite Belt) and the Rubiais mine in Lugo, whose tailings could contribute up to 3.2 billion dollars gross, according to the current market metal prices. This paper aims to provide a first step to promote mine waste recycling and circular mining in Spain, an initiative that would also help to mitigate the environmental damage derived from abandoned mine wastes.

Uncaptured mercury lost to the environment from waste electrical and electronic equipment (WEEE) in scrap metal and municipal wastes

Mercury is a persistent toxic substance and once in the environment it can be transformed by bacteria into methylmercury which bioaccumulates in food chains. Prevention of mercury releases are key to protecting human health. Alternatives to mercury in products are now available and further phase-outs are underway as the Minamata Convention progresses toward its aims. In the European Union, mercury is a priority substance for safe removal from WEEE collected and treated. Despite mercury phase outs, WEEE items will continue to necessitate mercury depollution for many years to come. Capture of mercury-added product waste and their replacement products at source protects health, the environment and progresses the circular economy in terms of job creation and critical raw materials recovery. This paper presents an analysis of mercury-containing WEEE observed in scrap metal sites and kerbside waste collection in Ireland, these items did not undergo depollution and so the mercury contained within is lost to the environment. Mercury-added products found in metal scrap included desktop PCs, laptops, screens, LCD, LED and plasma screens and monitors, and assorted fluorescent and special lamps. It is estimated that a minimum of 17.89 kgs of mercury was released to the environment in 2018 due to inappropriate WEEE management from demolition, renovation, and home maintenance activities. Whilst the impact of the Restriction of Hazardous Substances Directive in reducing mercury content in products is undoubtably positive, mercury emissions due to historic WEEE, professional WEEE, and batteries are not fully understood. The key loss of mercury was due to inappropriate gas discharge lamp handling at scrap metal sites and in municipal wastes. Protecting local environments from exposure and ensuring the safe recovery of mercury should be prioritised. The findings of this research highlight an urgent need to develop indicators of mercury-added product stocks and flows to optimise hazardous waste management in support of the circular economy. Improved material flow analysis with respect to mercury-added products are necessary for more accurate estimates in national inventories, thereby aiding global efforts to eliminate anthropogenic mercury releases especially from secondary release sources.

Increasing recovery opportunities of metal(loid)s from municipal solid waste via landfill leachate recirculation

The recovery of 12 critical raw materials (CRM) from municipal solid wastes (MSW) via leachate recirculation was evaluated using a 4 L semi-pilot scale column percolation. The results showed that the recovery of the metal(loid)s was mainly influenced by order of importance: pH > organic content > type of metal(loid)s > age of the waste > redox potential. Among the CRM, Cd and Ni were the most mobile elements, while As and Cr were the least mobile. A comparison of leachate from the leachate recirculated columns before and after the initiation of recirculation indicates an increase in the concentrations of certain CRM and metalloids. The first recirculation cycle supported achieving 100 % recovery. CRM and metalloids in leachate can be recovered; however, the concentrations of CRM and metalloids are usually below 1 mg/L. In this regard, leachate recirculation may enhance the increasing concentration of CRM in landfill leachate. For example, after first recirculation cycle, Ni concentration increased from 0.05 mg/L to 0.11 mg/L. The results obtained from this study can develop further methodologies for the potential recovery of CRM and help foster further research into overcoming limitations for recovering CRM in landfill leachate.

A Digital Product Passport for Critical Raw Materials Reuse and Recycling

The reuse and recycling of critical raw materials is limited, as waste electrical and electronic recycling focuses on base and precious metals, and device component reuse is in its infancy. To help to address this issue this paper provides the conceptual design of a Digital Product Passport based circular supply management system. To enable the recovery of critical raw materials at component and material levels for reuse and recycling. The works include an assessment of existing critical raw materials information management and an information needs identification survey, with 10 manufacturers, producer responsibility organisations, collectors and recyclers. The needs were used to generate 14 key product information management processes and exchanges that when implemented form a Digital Product Passport based circular supply management system. Information managed via a physical-digital linkage through individual product tags includes product registrations, materials declarations, life cycle status updates, the sorting of products at collection points based on critical raw material contents, and flagging of products for critical raw materials component extraction. A dataspace-based IT systems architecture is proposed for the implementation of the supply management system taking into account global and European information standards. Finally, key challenges to implement such an IT architecture are discussed.

Challenges and Opportunities for the Recovery of Critical Raw Materials from Electronic Waste: The Spanish Perspective

The path toward energy transition requires many metals, some of which are scarce in nature or their supply is controlled by a few countries. The European and Spanish situations are particularly vulnerable because of the scarcity of crucial geological mineral resources, especially those known as critical. In this context, the recovery of metals from waste electric and electronic equipment (WEEE) presents an important opportunity to partly alleviate this situation because this region produces most of the WEEE per capita. In this study, 43 different categories of EEE placed in the Spanish market between 2016 and 2021 were assessed, considering the composition of up to 57 elements, with 34 being critical. The results show the great opportunities for urban mining: 1.4 million tons of metals valued at USD 2.43 billion, representing 80% of the mass and 25% of the price of the primary extraction in Spain during that period. In addition, 20,000 tons corresponded to critical metals. However, the short life of EEE and the low traceability and low recovery of metals, especially critical and precious (94% and 87% of their values are lost, respectively), make it necessary to overcome major challenges to develop a new industry capable of moving toward a deeper circular economy.

New synthetic [LREE (LREE = La, Ce, Pr, Sm), Pb]-phosphate phases

Abstract Search for inexpensive and efficient methods of critical raw materials recovery is of great importance across the world due to growing demand for green technologies. Formation and detailed characterization of new Pb- and Light Rare Earth Elements (LREE)-containing phosphates, compared to already described Pb- or LREE-containing phosphates, was described in this work. These phases were precipitated at experimental conditions similar to these used in a newly proposed coprecipitation route for REE recovery from aqueous solutions. The formation of La, Ce, Pr and Sm phosphates from aqueous solutions proceeded differently in the presence of Pb than in its absence. No rhabdophane group minerals, (REE,Ca,Th)(PO4)·nH2O were formed, which were the product of crystallization in the absence of Pb, as evidenced by the PXRD analysis of the control LREE phosphates. Instead, a new, distinct phase was formed, which is neither a ‘phosphoschultenite’, PbHPO4, with La, Ce, Pr or Sm substitution nor a rhabdophane with Pb substitution. This showed that PbHPO4 structure did not accept isomorphic substitutions of LREE elements and rhabdophane structures are reluctant to accept Pb substitutions. At the same time, the formation of a hitherto unknown crystalline phase was found to be a mixed (LREE,Pb)-phosphate. A lower pH caused higher crystallinity of phases, as confirmed by SEM and PXRD. FTIR spectroscopy showed the hydrous nature of the obtained phases, which was additionally confirmed by thermal analysis. Decreasing pH of the reaction solution resulted in a higher crystalline water content. Moreover, La-bearing phases contained more chemically bound water than other phases. A combined EDS analysis and ICP-OES led to the chemical composition of new Pb phases with La, Ce, Pr and Sm that can be expressed as La2Pb3(PO4)4·3.5H2O, Ce2Pb3(PO4)4·3.3H2O, Pr2Pb3(PO4)4·3.1H2O and Sm2Pb3(PO4)4·3.3H2O, respectively. These results give a better understanding of potential novel recovery pathways of REE from phosphate mineral sources or wastes.

Specification and Classification of Pelletised Dried Sewage Sludge: Identifying Its Key Properties as a Renewable Material for Enabling Environmentally Non-Harmful Energy Utilisation

Renewable active sludge is a smart material for wastewater treatment and the protection of surface water bodies. The generated pellets (dried and pelletised dehydrated anaerobically stabilised excess sludge) are produced in a quantity of 31.4 ± 5.6 g dry matter (DM) per one Population equivalent (PE) calculated to COD (PECOD) in one day. As pellets are combustible material, their energy utilisation must reach the sustainable development goals (SDGs)—a bridge must be created between “treated sewage sludge as the tool to remove pollutants and nutrients from wastewater” and “preparation of the valuable material as a solid recovered fuel (SRF) that meets customer-specific requirements”. Technical Report CEN/TR 15508 and Technical Standard EN ISO 21640 set up methods for specifying and classifying pellets as an SRF. In the last eleven years (2010–2021), pellets’ net calorific value (NCV) is 13.0 ± 0.7 MJ kg−1 as received (ar). In 2021, the 80th percentile of the Hg/NCV ratio was 0.079 mg Hg MJ−1. In 2010–2021, the annual amount of Hg transferred to stakeholders reduced by 64.3% m/m—from 10.1 kg to 3.67 kg. The halogen contents of the pellets do not threaten corrosion to the incineration facility. Stable pellets’ energy potential and perspective ash composition for critical raw materials recovery qualify pellets as a specific waste stream and a renewable material for SRF production.

Applied Tests to Select the Most Suitable Fungal Strain for the Recovery of Critical Raw Materials from Electronic Waste Powder

Electrical and electronic wastes (WEEEs) are a potential source of raw materials. The main challenge for scientists is to set up a reliable and eco-friendly process to recycle raw materials and precious elements from WEEEs. Today, we know that fungi could play an active role in green technologies aimed at recycling valuable elements. The bioaccumulation mechanism and bioleaching activity of filamentous fungal species have already been exploited fruitfully in extraction processes. However, not all fungal strains possess the same characteristics, and it is crucial to choose the right strains to use. In this work, we show a method to assess the precious elements’ recovery efficiency from WEEE using fungal strains. A CAS agar screening test for siderophore detection was carried out with three strains. The following plate accumulation test performed on a medium added with 120 ppm of electronic waste powder highlighted the differences in accumulation capability, growth rate, and biomass production. Among the elements in tested waste, yttrium, copper, and palladium show the highest bioconcentration factor. The results confirm the biotechnological potential of fungi to recover valuable elements at the bench scale, highlighting the importance of effective screening tests to assess the most efficient strain for each kind of waste.

Hydrothermally-assisted recovery of Yttria- stabilized zirconia (YSZ) from end-of-life solid oxide cells

Effective and scalable recycling strategies for the recovery of critical raw materials are yet to be validated for solid oxide cells (SOCs) technologies. The current study aimed at filling this gap by developing optimized recycling processes for the recovery of Yttria-stabilized Zirconia (YSZ) from End-of-Life (EoL) SOC components, in view of using the recovered ceramic phase in cell re-manufacturing. A multi-step procedure, including milling, hydrothermal treatment (HT), and acidic-assisted leaching of nickel from composite Ni-YSZ materials, has been implemented to obtain recovered YSZ powders with defined specifications, in terms of particle size distribution, specific surface area, and chemical purity. The overall optimized procedure includes a pre-milling step (6 h) of the EoL composite materials, and a hydrothermal (HT) treatment at 200 °C for 4 h to further disaggregate the sintered composite, followed by selective oxidative leaching of Ni2+ by HNO3 solution at 80 °C for 2 h. In particular, the intermediate HT step was assessed to play an essential role in promoting the disaggregation of the sintered powders, with a related increase of specific surface area (up to 13 m2 g−1) and the overall reduction of the primary particle aggregates. The acid-assisted leaching allowed to fully extract Nickel from the composite Ni-YSZ powders, with retention of YSZ crystallinity and negligible loss of Zr and Y, as revealed by ICP analysis on the recovered supernatants.The developed multi-step pathway offers a promising strategy to recover valuable YSZ materials for the re-manufacturing of SOCs components, with the aim to boost a circular economy approach in the field of fuel-cell and hydrogen (FCH) technologies.

Applicability of new sustainable and efficient alginate-based composites for critical raw materials recovery: General composites fabrication optimization and adsorption performance evaluation

Based on the 2020 list of raw materials for the EU, there are 30 critical minerals on the critical raw materials list, among which the rare earth elements group is placed. This study demonstrates a viable approach to the increasing possibility of the critical materials recovery through biosorption. The environmentally friendly biosorbents were prepared modifying calcium alginate with biochar and clinoptilolite. Firstly, the optimization procedure was applied for obtaining new biocomposites. After that the adsorption studies of La(III), Ce(III), Pr(III), and Nd(III) ions as a function of solution pH, biosorbent mass, interaction time, initial metal concentration, temperature, and competing ions presence were carried out using the batch mode. The kinetic studies were analyzed using the pseudo-first order, pseudo-second order, Weber and Morris intraparticle diffusion, Boyd as well as Dumwald-Wagner kinetic models. The experimental equilibrium data were fitted using the Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The thermodynamic functions, i.e. ΔG°, ΔH°, and ΔS° were also determined. Importantly, the biocomposite beads were readily regenerated using diluted mineral acids (exemplary 0.1 mol/dm3 HNO3) and moreover, the adsorption effectiveness was very satisfactory even after six adsorption–desorption cycles (97%). New biocomposites as potential sorbents were characterized with ATR/FT-IR and XPS spectroscopy, SEM, EDX, OM and AFM microscopy, nitrogen adsorption, TG/DTG, CHNS, XRD as well as the sieve analysis and pHpzc measurements. After the interactions of the alginate composites with La(III) ions, a possible sorption mechanism was analyzed by ATR/FT-IR, XPS, and EDX spectroscopy.

Electrochemical routes for environmentally friendly recycling of rare-earth-based (Sm–Co) permanent magnets

The consumption of critical raw materials, especially those in permanent magnets of Nd–Fe–B and Sm–Co-type, has significantly grown in the past decade. With predictions on further electrification growing exponentially the demand for these materials will even increase. This implies that efforts in assuring sustainability must involve recycling from secondary resources. In recent years the electrochemical approaches in recycling have been extensively investigated and applied owing to their advantages of high efficiency and selectivity, easy operation, low energy consumption, and environmental friendliness. In this paper, we investigate the Sm2(Co,Fe,Cu,Zr)17 permanent magnet leaching process using the anodic oxidation to be paired with the metal deposition on the cathode. Linear sweep voltammetry was performed from − 0.15 to 1 V versus Pt quasi reference electrode that indicated current peaks that would correspond to some preferential leaching of the crystal phases contained in the magnet. The latter was confirmed using the SEM/EDXS analysis. The continuous leaching of the Sm2(Co,Fe,Cu,Zr)17 magnet was performed at a direct current density of 2, 4 and 8 mA cm−2 at the time period of 0–240, 240–480 and 480–720 min, respectively. The ICP-MS results confirmed the leaching of all the metals from the original Sm2(Co,Fe,Cu,Zr)17 permanent magnet. The concentration of Sm3+, Cu2+, Fe2+ and Zr2+ increases linearly along with the leaching time. Reversely the concentration of Co2+ decreases linearly due to its consumption by electrodeposition of Co, Fe and Cu on the cathode. The presented paired electrochemical process could serve as a starting point for the recycling and recovery of critical raw materials without any acid usage and waste generation.Graphical abstract

Progress on the Recovery of Critical Raw Materials

Progress on the Recovery of Critical Raw Materials

Rare Earths’ Recovery from Phosphogypsum: An Overview on Direct and Indirect Leaching Techniques

The need for rare earths elements (REEs) in high tech electrical and electronic based materials are vital. In the global economy, deposits of natural REEs are limited except for countries such as China, which has prompted current attempts to seek alternative resources of REEs. This increased the dependence on major secondary rare earth-bearing sources such as scrap alloy, battery waste, spent catalysts, fly ash, spent magnets, waste light-emitting diodes (LEDs), and phosphogypsum (PG) for a substantial recovery of REEs for use. Recycling of REEs from these alternative waste sources through hydrometallurgical processes is becoming a sustainable and viable approach due to the low energy consumption, low waste generation, few emissions, environmentally friendliness, and economically feasibility. Industrial wastes such as the PG generated from the production of phosphoric acid is a potential secondary resource of REEs that contains a total REE concentration of over 2000 mg/kg depending upon the phosphate ore from which it is generated. Due to trace concentration of REEs in the PG (normally < 0.1% wt.) and their tiny and complex occurrence as mineral phases the recovery process of REE from PG would be highly challenging in both technology and economy. Various physicochemical pre-treatments approaches have been used up to date to up-concentrate REEs from PG prior to their extraction. Methods such as carbonation, roasting, microwave heating, grinding or recrystallization have been widely used for this purpose. This present paper reviews recent literature on various techniques that are currently employed to up-concentrate REs from PG to provide preliminary insight into further critical raw materials recovery. In addition, the advantages and disadvantages of the different strategies are discussed as avenues for realization of REE recovery from PG at a larger scale. In all the different approaches, recrystallization of PG appears to show promising advantages due to both high REE recovery as well as the pure PG phase that can be obtained.