Recovery Of Critical Materials Research Articles

Clay-polymer hybrid hydrogels in the vanguard of technological innovations for bioremediation, metal biorecovery, and diverse applications.

Polymeric hydrogels are among the most studied materials due to their exceptional properties for many applications. In addition to organic and inorganic-based hydrogels, "hybrid hydrogels" have been gaining significant relevance in recent years due to their enhanced mechanical properties and a broader range of functionalities while maintaining good biocompatibility. In this sense, the addition of micro- and nanoscale clay particles seems promising for improving the physical, chemical, and biological properties of hydrogels. Nanoclays can contribute to the physical cross-linking of polymers, enhancing their mechanical strength and their swelling and biocompatibility properties. Nowadays, they are being investigated for their potential use in a wide range of applications, including medicine, industry, and environmental decontamination. The use of microorganisms for the decontamination of environments impacted by toxic compounds, known as bioremediation, represents one of the most promising approaches to address global pollution. The immobilization of microorganisms in polymeric hydrogel matrices is an attractive procedure that can offer several advantages, such as improving the preservation of cellular integrity, and facilitating cell separation, recovery, and transport. Cell immobilization also facilitates the biorecovery of critical materials from wastes within the framework of the circular economy. The present work aims to present an up-to-date overview on the different "hybrid hydrogels" used to date for bioremediation of toxic metals and recovery of critical materials, among other applications, highlighting possible drawbacks and gaps in research. This will provide the latest trends and advancements in the field and contribute to search for effective bioremediation strategies and critical materials recovery technologies.

Organic acid-assisted vapor phase reduction for high-dense defects of retired graphite for high-performance lithium-ion batteries

Recycling and reusing anode graphite from spent lithium-ion batteries are now essential strategies to achieve green sustainability and clean-energy storage. However, viable and affordable regeneration methods of anode have become a significant obstacle for the recovery procedure. Hydrometallurgy has shown efficiency and sustainability in the recovery of critical materials from LIBs, and heat treatment is confirmed to be required to reconstruct the structure of graphite. In this study, oxalic acid is used as the leaching agent and subsequent heat treatment is conducted to repair the graphite structure. The leaching results showed that oxalic acid has a higher leaching rate of lithium ions (96.10%). Interestingly, CO2 or CO-diffusion from oxalic acid thermal decomposition can be controlled rationally by nanoconfined structures in spent graphite, resulting in carbon defects. Electrochemical performance test results reveal that the recovered graphite exhibits improved specific capacity and stability, retaining 356.45 mAh g−1 at 0.1C after 300 cycles and a coulombic efficiency of over 97%. Its performance is comparable to that of artificial graphite and superior to most reported acid-leaching-based recycled graphite. Thus, the outcomes point to a viable technique for recovering and reusing spent graphite anode.

Removal of impurity Metals as Phosphates from Lithium-ion Battery leachates

Recovery of critical materials from end-of life (EOL) lithium-ion batteries (LIB) is gaining interest as demands for materials grows. Hydrometallurgical processes start with an intermediate product known as black mass which contains critical materials of interest (Co, Ni, Li, and graphite) as well as impurities such as Cu, Al, and Fe. These impurities are deleterious to downstream separation processes, as well as impact functionality of the final products. These impurities effectively compete with most solvent extraction (SX) and metal recovery processes to diminish the overall yields of the desired materials. In this work, a process flowsheet is presented where a previously reported electrochemical leaching (ECL) process is followed by selective precipitation using diammonium hydrogen phosphate (DAP) to remove Cu, Al, and Fe from LIB leachate solutions. The electrochemical leach process removes Cu and produces a pH-adjusted leachate, ca. pH 2, without requiring an extra Cu extraction step. The addition of the precipitant DAP to leachate by slightly adjusting the pH to 3–4 at 45 °C, precipitates 95–99% of Al and Fe as their phosphates and the leachate retains >95% of Co, Ni and Li. After the filtration of phosphate impurities, the solution is ready for further processing, such as SX. As an unexpected result from the leachate processing, 20–30% of the Ni and Co co-crystalize as the double salt after cooling to room temperature, which could provide a shorter route to their recovery.

Tuning the Charge and Hydrophobicity of Graphene Oxide Membranes by Functionalization with Ionic Liquids at Epoxide Sites.

Functionalization of graphene oxide (GO) membranes is generally achieved using carboxyl groups as binding sites for ligands. Herein, by taking advantage of the ability of imidazolium-based ionic liquids (ILs) to undergo an epoxide ring-opening reaction, a new approach of GO modification was established, in which ILs were bonded to the abundant epoxides on GO without sacrificing the carboxyl groups. Computational methods confirmed this unique configuration of ILs on GO, which enabled the dispersion of IL/GO flakes in water for facile casting into laminate membranes. Compared with neat GO, the ILs in IL/GO membranes served as spacers that substantially reduced the multi-valent cation mobility, simultaneously facilitated ion desolvation, and increased the water flux across the membrane. Our studies found that the higher separation efficiency of IL/GO membranes may be attributed to the synergistic modification of the hydrophobicity and surface charge. Specifically, the protonated nitrogen of the imidazolium cations altered the surface charge of GO, thereby generating electrostatic repulsion that enhanced the selectivity of cation rejection. On the other hand, the increased length of the alkyl chains bound to the imidazolium rings was found to increase the hydrophobicity of GO, which, in turn, aided the fine-tuning of the water desolvation/transport dynamics at the GO/IL interface to achieve a high water flux. Additionally, the water retention was reduced on the hydrophobic planes, which inhibited GO swelling during aqueous separations. Molecular dynamics simulations revealed increased water diffusivity when ILs were intercalated within GO layers. We establish that without requiring a high energy input, functionalization of GO membranes with ILs may be a promising approach to achieve efficient ion separation and critical material recovery.

Sorption of rare-earth elements onto a ligand-associated media for pH-dependent extraction and recovery of critical materials

Toward recovering rare-earth elements, we prepared a solid-phase media that binds and elutes metals for extraction and enrichment. We report the synthesis and methodology for a solid-phase media that exhibits pH-dependent binding of aqueous rare-earth elements. The media shows pH-dependent binding of NdIII and retains efficiency over at least six cycles of binding and elution. Mixed solutions of rare-earth elements demonstrated a preference for mid and heavy rare-earth elements based on thermodynamic binding preferences of the ligand, and selectivity for rare-earth elements over iron and aluminum were observed with coal fly ash leachate. We expect this new recovery method to be a significant step towards aqueous-based extraction and enrichment of critically important rare-earth elements.

Enabling sustainable critical materials for battery storage through efficient recycling and improved design: A perspective

Abstract

Assessment of priorities in critical material recovery from Waste Electrical and Electronic Equipment

A major problem in developing environmental management systems for assessing recovery priorities for high added-value materials such as critical metals from wastes is that the input data required are contained in a variety of databases compiled for different purposes with different levels of content and accuracy. To deal with decision-making priorities for environmental issues where uncertainties and inconsistencies are inherent in input data sources a Multi-Criteria Decision Analysis (MCDA) approach using an Analytic Hierarchy Process (AHP) to determine weights and fuzzy numbers to account for input data uncertainties is developed and is illustrated for determination of critical metal recovery priorities from Waste Electrical and Electronic Equipment (WEEE) in Europe. A spreadsheet programme with many user-friendly input and output features is developed to aid data-handling and the calculations required in the MCDA approach. Where data uncertainties exist, weighted input parameters for the critical metals are determined by an absolute judgement panel of key stakeholders and include data on: recovery potential, geographical supply concentration and stability, end use substitution, future metal demand and economic importance in key industrial sectors. Sensitivity analyses can be carried out on results of recovery priority outputs by simple numerical variation of input parameters and/or by the use of specialist input decision panels representing stakeholder groups with differing priorities, and the results suggest that recovery priorities in the European situation should concentrate on gallium, indium and germanium. The spreadsheet-MCDA program set up in developing the methodology for criticality has wide general application in environmental decision-making analysis particularly where uncertainties exist in the input data required.

Towards mine tailings valorization: Recovery of critical materials from Chilean mine tailings

The mining industry produces large volumes of mine tailings – a mix of crushed rocks and process effluents from the processing of mineral ores. Mine tailings are a major environmental issue due to implications related to their handling and storage. Depending on the mined ore and the process used, it may be possible to recover valuable elements from mine tailings, among them critical raw materials (CRMs) like rare earths, vanadium, and antimony.The aim of this study was to investigate the techno-economic feasibility of producing critical raw materials from mine tailings. Data from 477 Chilean tailings facilities were analyzed and used in the techno-economic assessment of the valorization of mine tailings in the form of CRMs recovery. A review of applicable technologies was performed to identify suitable technologies for mine tailings processing. To assess the economic feasibility of CRMs production, net present value (NPV) was calculated using the discounted cash flow (DCF) method. Sensitivity analysis and design of experiments were performed to analyze the influence of independent variables on NPV. Two options were assessed, rare earth oxides (REOs) production and vanadium pentoxide (V2O5) production. The results show that it is possible to produce V2O5 with an NPV of 76 million US$. In the case of REOs, NPV is positive but rather low, which indicates that the investment is risky. Sensitivity analysis and the ANOVA run using the design of experiments indicated that the NPV of REOs is highly sensitive to the price of REOs and to the discount rate.

Electro-Assisted Recycling of Lithium Ion Batteries

The fast growth of the electric vehicle (EV) market is generating increasing anxiety regarding the sources and availability of minerals required to meet with a growing demand for lithium ion batteries (LIBs). Critical elements (lithium, cobalt, and graphite) are crucial to sustain the manufacturing of a growing EV market as well as thriving wireless demand. However, the geographical concentration of mining and refining of cobalt and graphite constitute a supply chain risk for the global production of LIBs. This is driving technical development, which in turn, is leading to a dynamic change in battery chemistry. Lithium sources are more diverse in nature and geographical distribution, and current lithium reserves are enough to cover projected scenarios within the next twenty years. Nevertheless, the main question is whether the extraction technologies can keep up with the pace of market growth for EV. Interest in LIBs recycling is surging as a path to a circular battery economy and supply chain stabilization for critical materials on LIBs. Industrial processes for the recycling of LIBs are already operating around the world. However, these processes are almost exclusively focused on the recovery of Co, Ni and Mn from battery cathodes as the most valuable metals in the LIBs. Hydrometallurgical processes have been proposed for a comprehensive recovery that includes lithium and graphite, but the high operating costs and intensive chemical consumption do not support a cost-effective recovery of Li at industrial level. To target this issue, an electro-assisted reduction technology, based on the use of electrons as green reagent, has been proposed for the extraction and recovery of critical materials from LIBs. Through this process, high extraction efficiencies (>98%) can be achieved at solid to liquid ratios up to 120 g/L and in a peroxide free environment. The process is suitable to different battery chemistries and allows for the recovery of graphite as bi-product. A description of the process, as well as a flowsheet, that describes a comprehensive recovery for different value streams will be discussed.

Recovery of critical materials from mine tailings: A comparative study of the solvent extraction of rare earths using acidic, solvating and mixed extractant systems

Our society heavily depends on the availability of raw materials. Technology metals such as rare earth elements (REEs) are vital in many applications. Because their virgin mining and production is constrained by a multitude of factors, future exploitation of secondary sources is strongly considered. Tailings from past and present mining activities are important sources of REEs and other critical raw materials, e.g., tungsten and phosphate. The possibility of processing such tailings was thoroughly investigated in the ENVIREE European Project (2015–2018). In this paper, we assess the use of solvent extraction to recover REEs from tailings originating from New Kankberg (Sweden) and Covas (Portugal). Extraction of REEs from common mineral acid solutions was carried out using solvating (Cyanex 923 and TODGA) and acidic extractants (DEHPA and Cyanex 572). Extraction was studied in the presence of high amounts of phosphate, iron and copper in solution. This was to identify bottlenecks in the separation process and ways to mitigate them. While copper and phosphate didn't pose significant issues, iron was co-extracted with the REEs in several systems, e.g., DEHPA – sulfuric acid. Co-extraction was reduced by using a blended DEHPA – Cyanex 923 organic phase. At the same time, the extraction efficiency of REEs improved. Control of the contact time between the aqueous and organic phase, and selective stripping were also used to effectively mitigate the extraction of iron.