Closed-loop Recycling Process Research Articles

A tandem approach for precipitant-free highly selective recovery of valuable metals from end-of-life lithium-ion batteries using a green deep eutectic solvent

Recently, recycling lithium-ion batteries (LIBs) waste and the efficient recovery of valuable metals has become crucial for the circular economy. Deep eutectic solvents (DESs) have shown immense potential for metal extraction from end-of-life (EoL) LIBs. However, a complicated subsequent separation process is required due to the non-selectivity of the DES components for metal. Herein, we propose a tandem precipitant-free hydrometallurgical process for the selective recovery of Li and other valuable metals (Ni, Co, Mn) from EoL LIBs using a green DES. The process parameters, viz., reaction temperature (T), time (t), pulp density (S/L), and molar ratio (MR) of ethylene glycol to tartaric acid, were optimized via the statistical optimization technique of response surface methodology. The results revealed maximum extraction efficiencies of 99.2±0.5%, 96.1±1.4%, 95.2±1.2%, and 97.8±1.5% for Li, Ni, Co, and Mn, respectively, under the optimized process conditions of T = 118 °C, t = 17 min, S/L = 42 g/L, and MR = 3:1. The kinetic study showed that interfacial reaction governed the extraction process. A plausible mechanism depicting the role of DES constituents in synergistically facilitating the extraction reaction was elucidated. Moreover, Li and other metals (Ni, Co, and Mn) were selectively separated and recovered with an overall efficiency of ∼99%. The reusability of the recovered metal products and the DES were also assessed for a closed-loop recycling process. At the outset, the proposed process paves the way for a greener alternative for recycling valuable metals from EoL LIBs rather than conventional acid-based leaching processes.

Cascadic degradation of selected polyolefin grades in a simulated closed-loop recycling process

AbstractReintroducing recycled plastics into production processes can lead to irreversible degradation and changes in their properties, thereby limiting their recycling potential to a finite number of loops. This study investigates the impact of process-induced degradation resulting from multiple reprocessing cycles on specific material properties and aims to establish structure–property relationships. Four different polyolefins, including two polypropylenes, high-density polyethylene, and low-density polyethylene, were selected for the study. The materials underwent extrusion, pelletizing, injection molding, and milling before being reintroduced into the reprocessing cycle. This sequence of processing steps was repeated six times on each material. Various characterization techniques, including high-temperature gel permeation chromatography, melt mass flow rate, parallel-plate rheology, differential scanning calorimetry, gas chromatography–mass spectrometry, and optical defect control system, were performed to evaluate the molecular structure, rheological behavior, thermal stability, and the resulting contaminants and defects after each reprocessing step. The reprocessing of polypropylene resulted in a gradual decrease in the average molecular weights accompanied by a shift to lower viscosities and higher melt mass flow rates, whereas the polyethylene grades showed the opposite trend with a less pronounced effect in high-density polyethylene. The volatile organic compounds rose in polypropylene and sank in polyethylene after reprocessing. Additionally, all four materials exhibited an increase in degradation-related defects based on optical defect analysis. Graphical abstract

Utilization of lithium sulphate electrodialysis for closed-loop LIB recycling: Experimental study and process simulation

The hydrometallurgical recycling of spent lithium-ion batteries (LIBs) frequently relies on sodium hydroxide and sodium carbonate. This process generates a sodium-enriched solution, requiring treatment prior to safe discharge. This study focuses on a closed-loop recycling process for spent Lithium Nickel Manganese Cobalt Oxide (NMC) cathode material, eliminating sodium ions from conventional hydrometallurgical methods and regenerating acid and precipitant from disposal slurry. It employs lithium hydroxide (LiOH) as the precipitating reagent, while lithium recovery is conducted employing electrodialysis (ED) to regenerate LiOH and sulfuric acid (H2SO4) from the lithium sulfate solution. A part of the LiOH and H2SO4 reagents are subsequently used for the leaching and precipitation steps, creating a closed-loop recycling process. An experimental setup was developed to study the leaching, impurity removal, and metal extraction processes. The closed-loop recycling process was further investigated by simulation of this process. This involved the development of the ED module in both continuous and batch configurations using the Aspen Custom Modeler. This ED module is incorporated into Aspen Plus to integrate with the recycling process under experimental operational conditions. The minimal deviations of 3.34% and 2.38% within the precipitation and co-precipitation processes indicated the accuracy and validity of this work. Utilizing multiple batch-mode ED cells yields a 25% higher recovery of LiOH solution compared to continuous ED cells in the same operation conditions, i.e., employing 48 cells for 96 min under a current density of 1100 A·m−2. Furthermore, increasing the leaching temperature by 60°C yields a 53% increase in lithium leaching efficiency.

Chemically recyclable polyolefin-like multiblock polymers.

Polyolefins are the most important and largest volume plastics produced. Unfortunately, the enormous use of plastics and lack of effective disposal or recycling options have created a plastic waste catastrophe. In this work, we report an approach to create chemically recyclable polyolefin-like materials with diverse mechanical properties through the construction of multiblock polymers from hard and soft oligomeric building blocks synthesized with ruthenium-mediated ring-opening metathesis polymerization of cyclooctenes. The multiblock polymers exhibit broad mechanical properties, spanning elastomers to plastomers to thermoplastics, while integrating a high melting transition temperature (Tm) and low glass transition temperature (Tg), making them suitable for use across diverse applications (Tm as high as 128°C and Tg as low as -60°C). After use, the different plastics can be combined and efficiently deconstructed back to the fundamental hard and soft building blocks for separation and repolymerization to realize a closed-loop recycling process.

Recycling of NCA cathode material from end-of-life LiBs via Glycerol-triacetate solvent -based separation

Currently, a challenging task for recycling both spent lithium-ion batteries and cathode scrap is the separation of cathode materials from the current collector. A promising and efficient recovery method is to use an organic solvent to dissolve the organic polyvinylidene difluoride (PVDF) binder to recover both cathode materials and aluminum foil. However, the use of toxic solvents hinders its practical application in recycling the large amounts of cathode scrap generated during the manufacturing process. The proposed solvent-based separation process uses glycerol triacetate, a bio-derived green solvent. This study investigates a closed-loop recovery process that recovers cathode materials, including Al foil and PVDF binder, from cathode scrap. Using the glycerol triacetate solvent, a closed-loop recycling process was developed. The glycerol triacetate separation process provides a sustainable platform for the recovery and reuse of electrodes, thereby contributing to battery recycling efforts.

An all-natural, bioinspired, biodegradable electrical insulating composite based on lignocellulose and mica tailings

The rapid development of modern electrical engineering puts forward urgent demand for high-performance electrical insulating materials. In this study, inspired by the layered structure of natural nacre, we present a novel biomimetic composite insulating film (referred to as M/C film) that is derived from agricultural waste corncobs and industrial waste mica tailings through a sol-gel-film transformation process. The novel insulating film has excellent tensile strength (94 MPa), high dielectric strength (68 kV mm−1), low dielectric loss, good heat resistance (T0 = 235 °C), and excellent UV shielding properties. Meanwhile, the M/C film presents environmental impacts much lower than those petrochemical-based plastic film as it can be 100 % recycled in a closed-loop recycling process and easily biodegraded in the environment (lignocellulose goes back to the carbon cycle and the mica return to the geological cycle). It is a potential alternative for petrochemical plastics and provides a possible way to utilize agricultural waste and mica tailings.

Novel closed-loop recovery of light rare earth elements, as their oxides, from end-of-life mobile phone speakers using [Hbet][Tf2N

The use of rare earth elements (REEs) in many applications has proliferated in recent years. Growing demand for these elements, driven by global economic growth, a shift towards green technologies and the monopoly of their production by China, has led to their instability and shortage. The drive to source REEs from alternative secondary sources is imperative. Here, End-of-Life Mobile Phones (EoL-MPs), which represent a resource-rich stream for critical metals in general, and, specifically REEs, are used as feedstock. Exploiting the thermomorphic properties of the IL system, [Hbet][Tf2N]:H2O, the effects of time, water content and temperature for optimal leaching are determined in binary (Nd2O3-Pr2O3) and ternary (Nd2O3-Pr2O3-Fe2O3) systems, with the IL showing strong selectivity for oxides of light REEs. A complete hydrometallurgical process for the recovery of REEs, as oxides, from as-received EoL-MP speakers is developed involving pre-treatment, leaching, precipitation, and calcination, using the IL, [Hbet][Tf2N], as leaching agent. Each step was optimised to convert embedded REEs into their oxides to permit their full recovery. This novel closed-loop recycling process offers high selectivity for light REEs, utilising mild conditions, permitting the reuse of the IL up to five cycles, generating little waste and recovering the light REEs (Nd and Pr) with ≥ 90% efficiency and purity of product of ≥ 98%. Moreover, other highly valuable heavy REEs (Dy and Tb) are retained in the residue offering potential for their recovery. The proposed process provides a sustainable and efficient approach to close the gap between their supply and demand for these critical materials.

Low-carbon footprint approach to produce recycled compacted concrete

Achieving a closed-loop recycling process with low CO2 emissions remains a challenge for the concrete industry. To improve the recycling of concrete debris, a powder compaction process for concrete waste was designed to obtain recycled compacted concrete (hereinafter referred to as compact) and thermal treatment was proposed to be utilized to improve its strength. However, non-specific investigations of treatment parameters, like-treatment temperature, and duration, do still exist, and the required high production pressure (100 MPa) is impracticable. Therefore, this study aims to evaluate the effectiveness of two novel treatments on compact in improving its strength and reducing its carbon footprint. First, the heat treatment process used in a previous study [1] was expanded by varying immersion durations and treatment temperatures. Second, autoclaving was employed to obtain a stronger compact with different treatment settings. Additionally, in both treatment processes, the efficacy of low production pressure (<100 MPa) was evaluated. For this, eighteen different concrete wastes, having different industrial wastes, like-fly ash, slag, were collected, crushed, and powdered to produce compacts. The treated compacts were characterized based on both compressive strength and carbon footprint to compare the environmental performance of a compact prepared via thermal treatments in the production phase. The test results revealed that increasing water immersion duration (to 48 h) during the heat treatment process improved the compact strength to up to 48 MPa, and autoclaving at higher temperatures (at 220 °C) resulted in a compact strength of up to 98 MPa. Additionally, a strength of 30 MPa was attained even at a low production pressure (10 MPa) after autoclaving. The estimated CO2 emissions of the compact production process developed in this study were as low as 70.6 kg/m3 of compact. At the present stage of the study, it can be deduced that the compact manufactured possesses potential for implementation in various non-structural applications, including the production of pavement blocks and bricks, with lower CO2 emissions.

Sustainable regeneration of high-performance LiCoO2 from completely failed lithium-ion batteries

Utilising the solid-state synthesis method is an easy and effective way to recycle spent lithium-ion batteries. However, verifying its direct repair effects on completely exhausting cathode materials is necessary. In this work, the optimal conditions for direct repair of completely failed cathode materials by solid-state synthesis are explored. The discharge capacity of spent LiCoO2 cathode material is recovered from 21.7 mAh g−1 to 138.9 mAh g−1 under the optimal regeneration conditions of 850 °C and n(Li)/n(Co) ratio of 1:1. The regenerated materials show excellent electrochemical performance, even greater than the commercial LiCoO2. In addition, based on the whole closed-loop recycling process, the economic and environmental effects of various recycling techniques and raw materials used in the battery production process are assessed, confirming the superior economic and environmental feasibility of direct regeneration method.

Literature Review on Power Battery Echelon Reuse and Recycling from a Circular Economy Perspective.

Developing new energy vehicles (NEVs) is necessary to grow the low-carbon vehicle industry. Many concentrated end-of-life (EoL) power batteries will cause large-scale environmental pollution and safety accidents when the time comes to replace the first generation of batteries if improper recycling and disposal methods are utilized. Significant negative externalities will result for the environment and other economic entities. When recycling EoL power batteries, some countries need to solve problems about lower recycling rates, unclear division of echelon utilization scenarios, and incomplete recycling systems. Therefore, this paper first analyzes representative countries' power battery recycling policies and finds out the reasons for the low recycling rate in some countries. It is also found that echelon utilization is the critical link to EoL power battery recycling. Secondly, this paper summarizes the existing recycling models and systems to form a complete closed-loop recycling process from the two stages of consumer recycling and corporate disposal of batteries. The policies and recycling technologies are highly concerned with echelon utilization, but few studies focus on analyzing application scenarios of echelon utilization. Therefore, this paper combines cases to delineate the echelon utilization scenarios clearly. Based on this, the 4R EoL power battery recycling system is proposed, which improves the existing recycling system and can recycle EoL power batteries efficiently. Finally, this paper analyzes the existing policy problems and existing technical challenges. Based on the actual situation and future development trends, we propose development suggestions from the government, enterprises, and consumers to achieve the maximum reused of EoL power batteries.

Scalable Production of Biodegradable, Recyclable, Sustainable Cellulose-Mineral Foams via Coordination Interaction Assisted Ambient Drying.

Heavy reliance on petrochemical-based plastic foams in both industry and society has led to severe plastic pollution (the so-called "white pollution"). In this work, we develop a biodegradable, recyclable, and sustainable cellulose/bentonite (Cel/BT) foam material directly from resource-abundant natural materials (i.e., lignocellulosic biomass and minerals) via ambient drying. The strong resistance to the capillary force-driven structural collapse of the preformed three-dimensional (3D) network during the ambient drying process can be ascribed to the purpose-designed cellulose-bentonite coordination interaction, which provides a practical way for the locally scalable production of foam materials with designed shapes without complex processing and intensive energy consumption. Benefiting from the strong cellulose-bentonite coordination interaction, the Cel/BT foam material demonstrates high mechanical strength and outstanding thermal stability, outperforming commercial plastic polystyrene foam. Furthermore, the Cel/BT foam presents environmental impacts much lower than those of petrochemical-based plastic foams as it can be 100% recycled in a closed-loop recycling process and easily biodegraded in the environment (natural cellulose goes back to the carbon cycle, and bentonite minerals return to the geological cycle). This study demonstrates an energy-efficient ambient drying approach for the local and scalable production of an all-natural cellulose/bentonite foam for sustainable packaging, buildings, and beyond, presenting great potential in response to "white pollution" and resource shortage.

A closed-loop recycling process for carbon fiber-reinforced polymer waste using thermally activated oxide semiconductors: Carbon fiber recycling, characterization and life cycle assessment

The objective of this study is to investigate the properties of recycled carbon fiber (rCF) and its environmental impact, with a specific focus on the energy consumption of the recycling process based on the use of thermally activated oxide semiconductors (TASC). The mechanical and surface properties of rCF obtained under the optimal process parameters were characterized. The life cycle assessment method was used to evaluate the environmental impact of a closed-loop recycling process for carbon fiber-reinforced polymer (CFRP) waste using TASC. The results indicated that the decomposition rate of resin was 95.5 %, and no carbonaceous solid was generated. The gaseous produced of the recycling process were mainly CO2 and H2O, and no liquid products were produced. The surface oxidation degree of rCF was relatively slight. COOH was generated on the surface of rCF, which was conducive to improving the interfacial adhesion viscosity with resin. The monofilament tensile strength of rCF was maintained above 97 %. Compared with landfill and incineration, CFRP waste recycling using TASC can make global warming potential, acidification potential and eutrophication potential reduced by 28 %, 32 %, and 25 %, respectively. Ozone layer depletion potential, human toxicity potential and terrestrial ecotoxicity potential in disposing CFRP waste using TASC were 30 %, 21 % and 41 % of that using pyrolysis, respectively. The energy consumption in carbon fiber recycling by TASC was only 23 % of that in virgin carbon fiber manufacturing. TASC is found to be a promising potential strategy for managing CFRP waste.

Selective lithium extraction and regeneration of LiCoO2 cathode materials from the spent lithium-ion battery

Due to the mounting pressure to mitigate environmental pollution and guarantee the sustainability of the battery metals, the recycling of spent lithium-ion batteries (LIBs) has become a crucial issue in recent years. Numerous studies have focused on utilizing high temperatures or strong acid/alkali to reduce the spent active cathode material to a low valence state, which exacerbates recycling and post-treatment costs. Herein, a low-temperature roasting process followed by a water leaching strategy is developed to recycle and regenerate LiCoO2 cathode material from spent LiCoO2 batteries. The spent LiCoO2 is roasted with glucose (C6H12O6) as a reagent to attain reduction of the cathode material into water-soluble Li salt (Li2O and Li2CO3) and water-insoluble (Co and CoO). The proposed method utilizes moderate roasting temperature and water as the only leaching reagent, which effectively reduces energy and chemical consumption. Li and Co recovery rates are 97 % and 99 %, respectively, under the optimal conditions of 1 h roasting at 550 °C followed by 30 min water leaching using a solid–liquid ratio of 50 g/L. The recovered Li-rich solution and Co-rich residue can be easily converted to Li2CO3 and Co3O4, respectively, which are the precursors for regenerating the LiCoO2 cathode material. The regenerated LiCoO2 exhibits superior cycling stability with 87 % capacity retention after 800 cycles at 4.4 V. This developed closed-loop recycling process has lower recycling costs, is eco-friendly and efficient, and thus could potentially promote the sustainable long-run development of the LIBs industry.

Is Closed-Loop Recycling of Lithium-Ion Batteries Feasible ?

Rechargeable Li-ion batteries have been developed and marketed over the past 30 years and are used today in different fields like electric vehicles, portable electronics, etc. In a few years, the development of this technology has been exponential, and it has quickly imposed on the energy storage market. However, it is important to note that this technology is very dependent on metals (Co, Ni, Cu, Al, Li ...). These metals are rare, expensive and non-renewable. In addition, they are unevenly distributed in the earth's crust and their production is often very polluting. Thus, the massive use of this technology is creating an imbalance between the needs for metals and the existing primary resources, leading irrevocably to environmental and economic problems.Recycling this waste is therefore essential to both limit the overexploitation of primary metal resources and reduce their ecological impact.In terms of batteries recycling, two main families of processes can be distinguished. The first, known as pyrometallurgy, is based on the high-temperature treatment of waste. In contrast, hydrometallurgical processes are processes with significantly lower energy costs, as these processes are carried out at near ambient temperatures. The principle is to dissolve metals in their ionic form. Toxic acids (and their mixtures) are very often used, but other methods are possible (bases, complexing agents, oxidants). Once in solution, the metals can be recovered in the form of salts, hydroxides or in their metallic form by conventional chemical processes (precipitation, crystallization, etc.) or electrochemical processes (electro-deposition). Several separation / purification steps are sometimes necessary. Relatively few studies have looked at closed-loop recycling, i.e. the resynthesis and reuse of recycled materials in batteries.Thus, the objective of this project is to test the feasibility of closed-loop recycling of cathode materials from Li-ion batteries based on the use of innovative and less toxic recycling routes, and to verify the electrochemical performance of recycled materials at the end of the recycling process.To build this green cycle, the present study has been carried out using both model cathode materials (LCO, NMC) and real cathodes from spent drone batteries, that have been discharged, opened and dismantled in a glove box. All materials have, of course, been characterised (X-ray diffraction, SEM) and the present metals content has been quantified (wet digestion followed by AAS analyses) in order to be able to establish reliable material balances at the end of the recycling process.The developed closed-loop recycling process was composed of three subsequent steps:1) The cathode materials recovered have been leached in a deep eutectic solvent medium (DES) composed of ethylene glycol – choline chloride mixture, replacing the concentrated acids traditionally used. DES is a new class of green solvents, that is, non-harmful to human health and the environment compared to conventional organic solvents. They consist of a mixture of products (solids) which, at a given ratio, become liquid (eutectic), and which have the combined properties of the different constituents of the mixture.2) Synthesis of recycling active material from the DES media by precipitation and calcination.3) Assembly of button cells, followed by electrochemical tests and batteries post-mortem analyses (X-ray diffraction, SEM) have been carried-out at the last step.Composite electrodes made of recycled active materials, polymer binder and carbon have been formulated and assembled into button cells with a Li counter-electrode and a conventional separator (e.g. Celgard impregnated with liquid electrolyte). The prepared batteries were then recycled by electrochemical methods coupled with impedance measurements. The aging of the cells was carried out through one hundred charge / discharge cycles and a specified «fast charging» test developed in our laboratory, allowing to calculate the lithium diffusion coefficient in the cathode material.The results have shown that the recycling of metals has been successfully carried out using a deep eutectic solvent (DES), in a closed-loop manner. The leaching protocol have been optimized at the optimum conditions: ChCl: EG (1:2) with 0.8 mol.L-1 of HCl, with a ratio(wt.) S/L of 1/50, heated to 87.5 °C, for 2 h. After being completely dissolved, the metals have been then recovered from the DES by precipitation, calcined and reused as active materials. Using this method, the DES solvent has also been recovered and reused in a closed-loop without suffering any damage. This work has also shown that the recovered battery materials can be reused into the battery manufacturing cycle without changing their electrochemical performance. Indeed, this process allowed to obtain a homogeneous powder with a morphology similar to the initial materials (particle size <1 μm), presenting good capacities (154 mAh.g-1). Figure 1

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

Highly Ordered Supramolecular Assembled Networks Tailored by Bioinspired H-Bonding Confinement for Recyclable Ion-Transport Materials

An environmentally benign closed-loop process for the selective recovery of valuable metals from industrial end-of-life lithium-ion batteries

An efficient environmentally benign hydrometallurgical process using ethylenediamine tetraacetic acid (EDTA) as the chelating agent has been developed for the recovery of valuable metals viz., cobalt (Co), lithium (Li), and copper (Cu) from the industrial end-of-life (EoL) lithium-ion batteries (LIBs). The experimental process parameters such as EDTA concentration, temperature, solid to liquid ratio (pulp density), pH, and reaction time were optimized to achieve high metal recoveries. The experimental results revealed maximum recoveries of 93.5 ± 3.1%, 96.4 ± 2.9%, and 97.1 ± 2.4% for Co, Li, and Cu respectively, under the optimized process conditions of EDTA concentration = 0.8 M, T = 90 °C, pulp density = 50 g/L, pH = 10, and reaction time = 4 h. A shrinking core model-based kinetic investigation revealed that interfacial chemical reaction is the rate-controlling step and the apparent activation energies corresponding to Co, Li, and Cu were evaluated to be 51.9, 41.0, and 42.3 kJ mol−1, respectively. Moreover, a plausible mechanism was elucidated, highlighting the synergistic effect and the role of Cu in augmenting the extraction reaction. The chelating agent, EDTA, was also recovered during the reaction and reused for cyclic repeat tests. Finally, the recovered metals were selectively separated in the downstream process via the precipitation reactions to depict a closed-loop recycling process. The envisaged approach will pave the way for a sustainable green alternative to the acid-based leaching processes used for metal extraction from EoL LIBs.

A closed-loop recycling process for carbon fiber reinforced vinyl ester resin composite

Carbon fiber reinforced thermosetting polymer composites have been widely used in industrial fields, such as wind blades, aerospace and automobiles. However, it is extremely hard to degrade their waste due to the insoluble and infusible crosslinked networks. A solvothermal method is proposed to degrade carbon fiber reinforced vinyl ester resin composite (CF/VER) in this paper. The degradation reaction was conducted in a teflon-lined autoclave at 160 ℃ to 240 ℃ for 60 min to 180 min using isopropanol and acetone as solvents. NaOH or KOH were added to efficiently accelerate degradation process. Degradation ratio up to 99.96% was achieved. Furthermore, a multi-step degradation mechanism was put forward based on FT-IR and GC/MS analysis of degradation products. SEM, FT-IR, and XPS analysis of recycled carbon fibers (RFs) revealed that resin was nearly completely removed. Furthermore, contact angle measurement showed surface wettability of RFs was enhanced. XRD and Raman spectra further verified microstructure of RFs was not damaged drastically. Besides, reusing of degradation products and RFs was explored. Epoxy resin cured with degradation products exhibited excellent performances. Meanwhile, flexural strength tests and SEM images of fracture surfaces showed RFs reinforced epoxy resin composites had superior mechanical strength due to stronger interfaces between fibers and resin. Therefore, an efficient and closed-loop recycling process demonstrated in this manuscript provides a new pathway for degradation and reuse of CF/VER.

Closed-loop cobalt recycling from spent lithium-ion batteries based on a deep eutectic solvent (DES) with easy solvent recovery

Efficient recycling technology for the rapid growth of spent lithium-ion batteries (LIBs) is essential to tackle the resources and environmental crisis. Hydrometallurgical approach has attracted extensive research due to its potential to reduce the consumption of energy and threat to the environment. However, the simultaneous realization of green, efficient and closed-loop recycling is still challenging. Herein, we report a closed-loop and highly efficient approach to recycle lithium cobalt oxide from spent LIBs based on a choline chloride:oxalic acid (ChCl:OA) type deep eutectic solvent (DES). An ultrafast leaching process is observed at 180 °C for 10 s with no observable residues. The energy barrier during leaching is calculated to be 113.9 kJ/mol. Noteworthy, the solubility of cobalt ions can be reversibly tuned by simply adding/evaporating deionized water, thus avoiding the addition of precipitant and enabling the easy recovery of the leaching solvent for realizing a closed-loop recycling process. The simultaneous realization of high efficiency, green and closed-loop process is expected to push the DES into practical application for recycling the electrodes of LIBs.

Machine learning-aided engineering of hydrolases for PET depolymerization.

Plastic waste poses an ecological challenge1-3 and enzymatic degradation offers one, potentially green and scalable, route for polyesters waste recycling4. Poly(ethylene terephthalate) (PET) accounts for 12% of global solid waste5, and a circular carbon economy for PET is theoretically attainable through rapid enzymatic depolymerization followed by repolymerization or conversion/valorization into other products6-10. Application of PET hydrolases, however, has been hampered by their lack of robustness to pH and temperature ranges, slow reaction rates and inability to directly use untreated postconsumer plastics11. Here, we use a structure-based, machine learning algorithm to engineer a robust and active PET hydrolase. Our mutant and scaffold combination (FAST-PETase: functional, active, stable and tolerant PETase) contains five mutations compared to wild-type PETase (N233K/R224Q/S121E from prediction and D186H/R280A from scaffold) and shows superior PET-hydrolytic activity relative to both wild-type and engineered alternatives12 between 30 and 50 °C and a range of pH levels. We demonstrate that untreated, postconsumer-PET from 51 different thermoformed products can all be almost completely degraded by FAST-PETase in 1 week. FAST-PETase can also depolymerize untreated, amorphous portions of a commercial water bottle and an entire thermally pretreated water bottle at 50 ºC. Finally, we demonstrate a closed-loop PET recycling process by using FAST-PETase and resynthesizing PET from the recovered monomers. Collectively, our results demonstrate a viable route for enzymatic plastic recycling at the industrial scale.

Cover Feature: Low Carbon Footprint Recycling of Post‐Consumer PET Plastic with a Metagenomic Polyester Hydrolase (ChemSusChem 9/2022)

The Cover Feature shows the direct enzymatic degradation of post-consumer PET packaging by a novel metagenomic polyester hydrolase. The monomers can be recovered and used for the production of virgin PET, thereby achieving a closed-loop plastic recycling process with a low carbon footprint. More information can be found in the Full Paper by C. Sonnendecker et al.