Due to the rapid expanding of plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs) and electric vehicles (EVs), the projectfed demand for lithium-ion batteries (LIBs) is huge and ...might result in supply risks for natural lithium-containing reserves. After the service life, spent LIBs continuously accumulate in the market, and they are excellent secondary resources for lithium recovery. To alleviate resource shortage and to decrease potential environmental pollution caused by improper solid waste disposal, recycling of spent LIBs is motivated world widely in recent years. Previous studies have usually focused on the recovery of cobalt and nickel, which create high economic benefit. Recovery of lithium, however, has not been highlighted. In this article, state-of-the-art on spent LIBs recycling is discussed with emphasis on lithium recovery. In addition to understanding underlying mechanisms and physiochemistry features of various recycling methods, the possibility for industrial realization of each method is also evaluated. The complex processing steps limit the industrial implementation of hydrometallurgy-dominant methods, which usually reclaim lithium in the last step, resulting in a poor recovery efficiency of lithium. The pyrometallurgy-dominant approach is readily to scale up but lithium is lost in the slag phase. Therefore, the mild recycling (cleaner production) methods are recommended for future study since they take advantages of traditional pyrometallurgy and hydrometallurgy, and could decrease treatment temperature as well as acid/alkaline usage.
Display omitted
•More efforts are appealed to recycle electrolyte with respect to lithium recovery.•Lithium is usually the last metal to recycle in hydrometallurgical methods.•Pyrometallurgical methods should decrease lithium lost and energy consumption.•External field assisted pyro combined with hydro methods are promising.
Heterogeneous catalytic ozonation (HCO) processes have been widely studied for water purification. The reaction mechanisms of these processes are very complicated because of the simultaneous ...involvement of gas, solid, and liquid phases. Although typical reaction mechanisms have been established for HCO, some of them are only appropriate for specific systems. The divergence and deficiency in mechanisms hinders the development of novel active catalysts. This critical review compares the various existing mechanisms and categorizes the catalytic oxidation of HCO into radical-based oxidation and nonradical oxidation processes with an in-depth discussion. The catalytic active sites and adsorption behaviors of O3 molecules on the catalyst surface are regarded as the key clues for further elucidating the O3 activation processes, evolution of reactive oxygen species (ROS) or organic oxidation pathways. Moreover, the detection methods of the ROS produced in both types of oxidations and their roles in the destruction of organics are reviewed with discussion of some specific problems among them, including the scavengers selection, experiment results analysis as well as some questionable conclusions. Finally, alternative strategies for the systematic investigation of the HCO mechanism and the prospects for future studies are envisaged.
Human activities contribute greatly to heavy metal pollution in soils. Concentrations of 15 metal elements were detected in 105 soil samples collected from a typical rural-industrial town in southern ...Jiangsu, China. Among them, 7 heavy metals—lead, copper, zinc, arsenic, chromium, cadmium, and nickel—were considered in the health risk assessment for residents via soil inhalation, dermal contact, and/or direct/indirect ingestion. Their potential sources were quantitatively apportioned by positive matrix factorization using the data set of all metal elements, in combination with geostatistical analysis, land use investigation, and industrial composition analysis. Furthermore, the health risks imposed by sources of heavy metal in soil were estimated for the first time. The results indicated that Cr, Cu, Cd, Pb, Ni, and Co accumulated in the soil, attaining a mild pollution level. The total hazard index values were 3.62 and 6.11, and the total cancer risks were 9.78 × 10−4 and 4.03 × 10−4 for adults and children, respectively. That is, both non-carcinogenic and carcinogenic risks posed by soil metals were above acceptable levels. Cr and As require special attention because the health risks of Cr and As individually exceeded the acceptable levels. The ingestion of homegrown produce was predominantly responsible for the high risks. The potential sources were apportioned as: a) waste incineration and textile/dyeing industries (28.3%), b) natural sources (45.4%), c) traffic emissions (5.3%), and d) electroplating industries and livestock/poultry breeding (21.0%). Health risks of four sources accounted for 23.5%, 32.7%, 7.4%, and 36.4% of the total risk, respectively.
•Soil heavy metals caused unacceptable health risks, mainly through homegrown food.•Arsenic and chromium were the predominant hazardous elements.•Waste incineration, textile/dyeing industries were the main anthropogenic inputs.•Electroplating and livestock/poultry industries produced the highest health risks.
Recycling of spent lithium-ion batteries (LIBs) has attracted significant attention in recent years due to the increasing demand for corresponding critical metals/materials and growing pressure on ...the environmental impact of solid waste disposal. A range of investigations have been carried out for recycling spent LIBs to obtain either battery materials or individual compounds. For the effective recovery of materials to be enhanced, physical pretreatment is usually applied to obtain different streams of waste materials ensuring efficient separation for further processing. Subsequently, a metallurgical process is used to extract metals or separate impurities from a specific waste stream so that the recycled materials or compounds can be further prepared by incorporating principles of materials engineering. In this review, the current status of spent LIB recycling is summarized in light of the whole recycling process, especially focusing on the hydrometallurgy. In addition to understanding different hydrometallurgical technologies including acidic leaching, alkaline leaching, chemical precipitation, and solvent extraction, the existing challenges for process optimization during the recycling are critically analyzed. Moreover, the energy consumption of different processes is evaluated and discussed. It is expected that this research could provide a guideline for improving spent LIB recycling, and this topic can be further stimulated for industrial realization.
Conspectus Photocatalytic ozonation (light/O3/photocatalyst), an independent advanced oxidation process (AOP) proposed in 1996, has demonstrated over the past two decades its robust oxidation ...capacity and potential for practical wastewater treatment using sunlight and air (source of ozone). However, its development is restricted by two main issues: (i) a lack of breakthrough catalysts working under visible light (42–43% of sunlight in energy) as well as ambiguous property–activity relationships and (ii) unclear fundamental reasons underlying its high yield of hydroxyl radicals (•OH). In this Account, we summarize our substantial contributions to solving these issues, including (i) new-generation graphitic carbon nitride (g-C3N4) catalysts with excellent performance for photocatalytic ozonation under visible light, (ii) mechanisms of charge carrier transfer and reactive oxygen species (ROS) evolution, (iii) property–activity relationships, and (iv) chemical and working stabilities of g-C3N4 catalysts. On this basis, the principles/directions for future catalyst design/optimization are discussed, and a new concept of integrating solar photocatalytic ozonation with catalytic ozonation in one plant for continuous treatment of wastewater regardless of sunlight availability is proposed. The story starts from our finding that bulk/nanosheet/nanoporous g-C3N4 triggers a strong synergy between visible light (vis) and ozone, causing efficient mineralization of a wide variety of organic pollutants. Taking bulk g-C3N4 as an example, photocatalytic ozonation (vis/O3/g-C3N4) causes the mineralization of oxalic acid (a model pollutant) at a rate 95.8 times higher than the sum of photocatalytic oxidation (vis/O2/g-C3N4) and ozonation. To unravel this synergism, we developed a method based on in situ electron paramagnetic resonance (EPR) spectroscopy coupled with an online spin trapping technique for monitoring under realistic aqueous conditions the generation and transfer of photoinduced charge carriers and their reaction with dissolved O3/O2 to form ROS. The presence of only 2.1 mol % O3 in the inlet O2 gas stream can trap 1–2 times more conduction band electrons than pure O2 and shifts the reaction pathway from inefficient three-electron reduction of O2 (O2 → •O2 – → HO2 • → H2O2 → •OH) to more efficient one-electron reduction of O3 (O3 → •O3 – → HO3 • → •OH), thereby increasing the yield of •OH by a factor of 17. Next, we confirmed band structure as a decisive factor for catalytic performance and established a new concept for resolving this relationship, involving “the number of reactive charge carriers”. An optimum balance between the number and reducing ability of photoinduced electrons, which depends on the interplay between the band gap and the conduction band edge potential, is a key property for highly active g-C3N4 catalysts. Furthermore, we demonstrated that g-C3N4 is chemically stable toward O3 and •O2 – but that •OH can tear and oxidize its heptazine units to form cyameluric acid and further release nitrates into the aqueous environment. Fortunately, •OH usually attacks organic pollutants in wastewater in preference to g-C3N4, thus preserving the working stability of g-C3N4 and the steady operation of photocatalytic ozonation. This AOP, which serves as an in situ •OH manufacturer, would be of interest to a broad chemistry world since •OH radicals are active species not only for environmental applications but also for organic synthesis, polymerization, zeolite synthesis, and protein footprinting.
A closed-loop process to recover lithium carbonate from cathode scrap of lithium-ion battery (LIB) is developed. Lithium could be selectively leached into solution using formic acid while aluminum ...remained as the metallic form, and most of the other metals from the cathode scrap could be precipitated out. This phenomenon clearly demonstrates that formic acid can be used for lithium recovery from cathode scrap, as both leaching and separation reagent. By investigating the effects of different parameters including temperature, formic acid concentration, H2O2 amount, and solid to liquid ratio, the leaching rate of Li can reach 99.93% with minor Al loss into the solution. Subsequently, the leaching kinetics was evaluated and the controlling step as well as the apparent activation energy could be determined. After further separation of the remaining Ni, Co, and Mn from the leachate, Li2CO3 with the purity of 99.90% could be obtained. The final solution after lithium carbonate extraction can be further processed for sodium formate preparation, and Ni, Co, and Mn precipitates are ready for precursor preparation for cathode materials. As a result, the global recovery rates of Al, Li, Ni, Co, and Mn in this process were found to be 95.46%, 98.22%, 99.96%, 99.96%, and 99.95% respectively, achieving effective resources recycling from cathode scrap of spent LIB.
Source-specific health risks of PM2.5-bound metals were analyzed for emission control by integrating source apportionment with health risk assessments of residents affected via inhalation pathways. A ...total of 218 daily PM2.5 samples were collected in 2016 in the central urban district of Beijing, China. Analyses showed that the mean annual concentrations of total heavy metals (THMs) and PM2.5 were 0.39 and 104.37 μg m−3, respectively. The heating season had significantly higher concentrations of THMs and PM2.5 (0.61, 134 μg m−3) than the non-heating season (0.27, 88.1 μg m−3) (p < 0.05). Among all metals, arsenic had the largest incremental cancer risk of 7.04 × 10−6. Six sources were identified by positive matrix factorization combined with conditional probability function and potential source contribution function analyses. The order of contribution to PM2.5-bound metal concentrations was resuspended dust (61.0%), traffic emission (16.3%), Cu-related industry (14.1%), coal combustion (3.7%), Cr-related industry (3.4%), and fuel oil combustion (1.6%). During the heating season, the contribution of coal combustion decreased slightly, which may have been due to the countermeasure of substituting coal for gas or electric heat in 2016. However, in terms of cancer risk contribution, coal combustion was the top contributor in both heating (3.5 × 10−6, 51.6%) and non-heating (2.7 × 10−6, 59.6%) seasons due to high attributable contents of the toxic metals, As, Cd and Pb. The Cr-related and Cu-related industries were the next controlled sources in the heating and non-heating seasons, respectively. Thus, these sources should receive priority in the development of control measures.
Display omitted
•Individual PM2.5-bound heavy metals have higher concentrations in heating season.•Arsenic had the largest cancer risk, exceeding the acceptable level (1 × 10−6).•Six identical sources with seasonal contribution order were found by PMF-CPF-PSCF.•Resuspended dust contributed the greatest mass concentration.•With the highest cancer risk, coal combustion should be the priority control objective.
Catalytic ozonation is a highly effective method in wastewater treatment, and MnO2 materials are widely recognized as active heterogeneous catalysts in this process. Many works reported the progress ...in active MnO2 synthesis, but the active phase is rarely systematically studied. In this paper, all six phases of MnO2 (α-, β-, δ-, γ-, λ- and ε-) were synthesized by facile methods. Their catalytic activities in ozonation of 4-nitrophenol (4-NP) were evaluated and correlated with the physicochemical properties obtained from X-ray Diffraction (XRD), transmission electron microscopy (TEM), physical adsorption and cyclic voltammetry (CV) analysis. α- MnO2 was found to be the most active catalyst in 4-NP degradation at neutral pH. MnO2 with low average oxidation state (AOS) showed stronger oxidation/reduction peaks in CV characterization, which benefited catalytic decomposition of ozone to generate active species. Superoxide radical was confirmed as the main oxidizing species, along with singlet oxygen and ozone molecule oxidation in bulk solution and little contribution of oxidation on the MnO2 surface. Mn2+ leaching happened during catalytic ozonation, but its catalytic role is negligible. This result may give rise to the preparation of new active MnO2 catalysts.
Display omitted
•Six phases of MnO2 were synthesized for catalytic ozonation.•α-MnO2 is more active than β-, δ-, γ-, λ- and ε-MnO2 materials.•Average oxidation state is the key factor determining their activities.•O2− oxidation in bulk solution is mainly responsible for nitrophenol degradation.
The rapid growth of lithium ion batteries (LIBs) for portable electronic devices and electric vehicles has resulted in an increased number of spent LIBs. Spent LIBs contain not only dangerous heavy ...metals but also toxic chemicals that pose a serious threat to ecosystems and human health. Therefore, a great deal of attention has been paid to the development of an efficient process to recycle spent LIBs for both economic aspects and environmental protection. In this paper, we review the state-of-the-art processes for metal recycling from spent LIBs, introduce the structure of a LIB, and summarize all available technologies that are used in different recovery processes. It is notable that metal extraction and pretreatment play important roles in the whole recovery process, based on one or more of the principles of pyrometallurgy, hydrometallurgy, biometallurgy, and so forth. By further comparing different recycling methods, existing challenges are identified and suggestions for improving the recycling effectiveness can be proposed.
Recovery of valuable metals from spent lithium-ion battery (LIB) is of both environmental and economic importance. Acidic leaching usually encounters issues of low selectivity or slow kinetics with ...considerable secondary waste generation during further purification. In this research, a closed-loop process with improved leaching selectivity for recycling of spent LiNixCoyMn1-x-yO2 battery using weak acidic leachant was demonstrated. To obtain optimal conditions of the leaching process, the effects of acid concentration, solid to liquid (S/L) ratio, temperature and reductant content were systematically investigated. Almost all Co, Li, Mn and Ni could be effectively recovered into the solution while Al remained in the residue as metallic form, after one-step leaching. The role of reductant during leaching was further evaluated which was found to be critical for the leaching kinetics. It is clear that the addition of reductant could alter the rate-controlling step of leaching from the ion diffusion in the residue layer to the surface chemical reactions. With high selectivity against impurities, this research proposed and verified a process to recover high purity Li2CO3 from the cathode scrap of LIBs, and more than 90% of the global recovery rate of valuable metals can be achieved.
Display omitted
•A selective leaching process for recycling spent lithium-ion battery was proposed.•Acetic acid leaches all metals out except Al whose leaching rate is only 2.36%.•The effect of reductant on the leaching kinetics was quantitatively evaluated.•The introduction of reductant alters the rate-controlling step of leaching process.•High purity of Li2CO3 is recovered with more than 90% of recovery rate for metals.
PDF