Synergistic strategy of solute environment and phase control of Pb-based anodes to solve the activity-stability trade-off

The contradiction between the activity and stability of metal anodes exists extensively, especially in acid electrooxidation under industrial-level current density. Although the anode modification enhanced the initial activity of anodes, its long-term activity is limited by anode slime accumulation. Herein, a synergistic strategy, coupling the solute environment with the phase control of anodes, is proposed to achieve the trade-off between activity and stability of Pb-based anodes in concentrated sulfuric acid electrolysis. Non-exogenous Mn2+ motivated a series of positive behaviours of reactive-oxygen-species capture, anode reconstruction and corrosion-dependent activity alleviation. The synergistic effects, which are crystal phase-dependent, mainly benefit from the continuous self-healing ability of the specific crystal phase of MnO2 on the anodes by the coexisted Mn2+. Compared with Mn2+/α-MnO2, Mn2+/γ-MnO2 exhibited outperformed activity and stability in boosting oxygen evolution reaction (OER) and reducing hazardous pollutants, which resulted from the energy difference in the rate-determining step of OER and in the selectivity priority of Mn2+/MnO2 oxidation pathway. Interestingly, the pre-coated γ-MnO2 on the anode also presents excellent inheritance, guaranteeing the unchanged crystal phase of MnO2 and the high performance in ultra-low hazardous slime generation in subsequent Mn2+ oxidation. The sustainability of Mn2+/γ-MnO2 was proved in the operating hydrometallurgy conditions on Pb-based anodes. This strategy offers a promising approach for this common issue in electrooxidation-related areas.

Can e-waste recycling provide a solution to the scarcity of rare earth metals? An overview of e-waste recycling methods

Recycling e-waste is seen as a sustainable alternative to compensate for the limited natural rare earth elements (REEs) resources and the difficulty of accessing these resources. Recycling facilitates the recovery of valuable products and minimizes emissions during their transportation. Numerous studies have been reported on e-waste recycling using various techniques, including thermo-, hydro- and biometallurgical approaches. However, each approach still has technical, economic, social, or environmental limitations. This review highlights the potential of recycling e-waste, including outlining the current unutilized potential of REE recycling from different e-waste components. An in-depth analysis of e-waste generation on a global scale and Australian scenario, along with various hazardous impacts on ecosystem and human health, is reported. In addition, a comprehensive summary of various metal recovery processes and their merits and demerits is also presented. Lifecycle analysis for recovering REEs from e-waste indicate a positive environmental impact when compared to REEs produced from virgin sources. In addition, recovering REEs form secondary sources eliminated ca. 1.5 times radioactive waste, as seen in production from primary sources scenario. The review outcome demonstrates the increasing potential of REE recycling to overcome critical challenges, including issues over supply security and localized dependency.

Risk assessment and strontium isotopic tracing of potentially toxic metals in creek sediments around a uranium mine, China

The contamination of creek sediments near industrially nuclear dominated site presents significant environmental challenges, particularly in identifying and quantifying potentially toxic metal (loid)s (PTMs). This study aims to measure the extent of contamination and apportion related sources for nine PTMs in alpine creek sediments near a typical uranium tailing dam from China, including strontium (Sr), rubidium (Rb), manganese (Mn), lithium (Li), nickel (Ni), copper (Cu), vanadium (V), cadmium (Cd), zinc (Zn), using multivariate statistical approach and Sr isotopic compositions. The results show varying degrees of contamination in the sediments for some PTMs, i.e., Sr (16.1-39.6 mg/kg), Rb (171-675 mg/kg), Mn (224-2520 mg/kg), Li (11.6-78.8 mg/kg), Cd (0.31-1.38 mg/kg), and Zn (37.1-176 mg/kg). Multivariate statistical analyses indicate that Sr, Rb, Li, and Mn originated from the uranium tailing dam, while Cd and Zn were associated with abandoned agricultural activities, and Ni, Cu, and V were primarily linked to natural bedrock weathering. The Sr isotope fingerprint technique further suggests that 48.22-73.84% of Sr and associated PTMs in the sediments potentially derived from the uranium tailing dam. The combined use of multivariate statistical analysis and Sr isotopic fingerprint technique in alpine creek sediments enables more reliable insights into PTMs-induced pollution scenarios. The findings also offer unique perspectives for understanding and managing aqueous environments impacted by nuclear activities.

Sustainable technologies for the recycling and upcycling of precious metals from e-waste

E-waste is the fastest growing solid waste in the world. Each year, over 50 million tonnes of e-waste are produced, with its rate increasing by 3-5 % annually. Currently, only 17 % of e-waste is properly recycled, leaving the majority managed unsustainably, thereby causing detrimental environmental and economic effects. Cleaner e-waste management technologies are essential to address this urgent and rapidly expanding issue. Precious metals within e-waste significantly contribute to recycling revenues. In this paper, we review state-of-the-art technologies for sustainable recycling and upcycling of these metals from e-waste, including cleaner extractive metallurgy, solution purification technologies, and direct synthesis of green nanomaterials. We also discuss the potential impacts and constraints of these technologies and provide recommendations for improving and implementing both existing and prospective technologies.

Effect of inorganic anions on hydrothermal removal of impurities Fe/Al from Cu-bearing polymetallic leachate

Hydrometallurgy recycling of heavy metals from electroplating sludge is of hot spot in recent decades. Such recycling was tedious in the separation of impure Fe/Al prior to heavy metals from acid leachate after sludge dissolution. Herein, a facile hydrothermal route was developed to separate Fe/Al from Cu-bearing leachate. The results showed that when the leachate was directly hydrothermally treated at 160 °C in the presence of nitrate and ethanol, Al/Cu were stable in the leachate, but nearly 100% Fe was removed as hematite nanoparticles. With the addition of chloridion, the removal efficiencies of Fe/Al/Cu did not change apparently, but the corresponding precipitate was akageneite, not hematite. By replacing chloridion with sulfate, nearly 100% Fe and 98.6% Al were separated as natrojarosite/natroalunite block, while the Cu loss was only 1.7%. However, with the supplementary of phosphate, the Fe/Al removal achieved nearly 100%, but the Cu removal also achieved by 92.6%. The thermodynamic analysis showed that Cu was precipitated rapidly via the phosphate/Cu oxyhydroxide route by adding phosphate but removed slightly via the coordination route on the Fe/Al precipitates with the addition of nitrate, chloridion, and sulfate. In summary, Fe was effectively separated as hematite, akageneite, natrojarosite, and phosphate halite, in the presence of nitrate, chloridion, sulfate, and phosphate, separately. But the removal of Al as natroalunite and AlPO4 only started by adding sulfate and phosphate, respectively. Such results enabled a short hydrometallurgy process to effectively recycle heavy metals from electroplating sludge.

Hydrometallurgical assessment of oxides of Nb, Ta, Th and U from Ethiopian tantalite ore

Tantalite ore is the main source of the metals niobium (Nb) and tantalum (Ta). Today, the needs for these economic and irreplaceable Nb, and Ta metals are becoming imperative for the technological world, to meet the demand, a lot of research is needed to ore reserves, extraction methodology and simplified refining processes should be in plethora. This study focuses on the Ethiopian tantalite ore located south of the Neoproterozoic Adola belt of the rare element Kenticha pegmatite deposit (global source of tantalite). Successive beneficiation of pegmatite ore results in a highest dissolution of 60.83 wt% of Ta2O5 with 4.58 wt% of Nb2O5 including the removal of U, Th, Ti, Fe and Si, resulting in a percentage low weight, which allows transporting ore concentrates. The concentrated ore is leached with a mixture of binary acids HF and H2SO4 with 6:1 ratio at temperatures from 100 to 400 °C. The filtered solution was extracted with MIBK then, precipitated with ammonium solution. The hydrometallurgy of Nb and Ta oxides is affected by leaching temperature and the presence of radioactive oxides of U and Th. Elemental analysis and surface topography were studied using SEM/EDS, revealing the highest percentage composition of Nb and Ta oxides at 200 °C of leaching temperature. Comparatively, the compositions of U and Th showed higher amounts at the leaching temperatures of 150 and 200 °C, and when the temperature reached about 350 and 400 °C, the percentage composition of U and Th became very low, the economic metals Nb and Ta were completely leached. The stability of the precipitated samples was analyzed using TGA-DTA and found to be thermally stable, and not contain significant moisture at each temperature studied. Studies for recovery of Ta, Nb, U and Th from Kenticha tantalite are required.

Review on the gentle hydrometallurgical treatment of WPCBs: Sustainable and selective gradient process for multiple valuable metals recovery

The metal resource crisis and the inherent need for a low-carbon circular economy have driven the rapid development of e-waste recycling technology. High-value waste printed circuit boards (WPCBs) are an essential component of e-waste. However, WPCBs are considered hazardous to the ecosystem due to the presence of heavy metals and brominated organic polymers. Therefore, achieving the recycling of metals in WPCBs is not only a strategic requirement for building a green ecological civilization but also an essential guarantee for achieving a safe supply of mineral resources. This review systematically analyzes the hydrometallurgical technology of metals in WPCBs in recent years. Firstly, the different unit operations of pretreatment in the hydrometallurgical process, which contain disassembly, crushing, and pre-enrichment, were analyzed. Secondly, environmentally friendly hydrometallurgical leaching systems and high-value product regeneration technologies used in recent years to recover metals from WPCBs were evaluated. The leaching techniques, including cyanidation, halide, thiourea, and thiosulfate for precious metals, and inorganic acid, organic acid, and other leaching methods for base metals such as copper and nickel in WPCBs, were outlined, and the leaching performance and greenness of each leaching system were summarized and analyzed. Eventually, based on the advantages of each leaching system and the differences in chemical properties of metals in WPCBs, an integrated and multi-gradient green process for the recovery of WPCBs was proposed, which provides a sustainable pathway for the recovery of metals in WPCBs. This paper provides a reference for realizing the gradient hydrometallurgical recovery of metals from WPCBs to promote the recycling metal resources.

Co-recovery of Mn and Fe from pyrolusite and copper slag with hydrometallurgy process: Kinetics and leaching mechanisms

With the shortage of high-quality raw materials and increasingly strict environmental regulations, the recovery of metals from copper slag and pyrolusite has become a research hotspot. A novel method for simultaneously extracting Mn and Fe from pyrolusite and copper slag has been proposed. Under the optimal conditions (Copper slag / Pyrolusite = 2, H2SO4 = 2 M, liquid-solid ratio = 10, T = 90 ℃, holding time = 60 min), the leaching efficiencies of Mn and Fe can reach 98.28% and 99.04%, respectively. In addition, the treated residue containing 60.04 wt% SiO2 can be used as a raw building material. Through chemical kinetics and mineralogical transformation analyses, Fe2SiO4 in copper slag decomposes to release Fe2+, which can reduce and leach Mn from pyrolusite. The unreacted shrinkage nuclear reaction model under the control of the surface chemical reaction is the most suitable model to describe the process, and when the apparent activation energy is 35.50 kJ/mol, the apparent rate equation is: [Formula: see text].

Recovery technologies for indium, gallium, and germanium from end-of-life products (electronic waste) - A review

Advanced high-tech applications for communication, renewable energy, and display, heavily rely on technology critical elements (TCEs) such as indium, gallium, and germanium. Ensuring their sustainable supply is a pressing concern due to their high economic value and supply risks in the European Union. Recovering these elements from end-of-life (EoL) products (electronic waste: e-waste) offers a potential solution to address TCEs shortages. The review highlights recent advances in pre-treatment and hydrometallurgical and biohydrometallurgical methods for indium, gallium, and germanium recovery from EoL products, including spent liquid crystal displays (LCDs), light emitting diodes (LEDs), photovoltaics (PVs), and optical fibers (OFs). Leaching methods, including strong mineral and organic acids, and bioleaching, achieve over 95% indium recovery from spent LCDs. Recovery methods emphasize solvent extraction, chemical precipitation, and cementation. However, challenges persist in separating indium from other non-target elements like Al, Fe, Zn, and Sn. Promising purification involves solid-phase extraction, electrochemical separation, and supercritical fluid extraction. Gallium recovery from spent GaN and GaAs LEDs achieves 99% yield via leaching with HCl after annealing and HNO3, respectively. Sustainable gallium purification techniques include solvent extraction, ionic liquid extraction, and nanofiltration. Indium and gallium recovery from spent CIGS PVs achieves over 90% extraction yields via H2SO4 with citric acid-H2O2 and alkali. Although bioleaching is slower than chemical leaching (several days versus several hours), indirect bioleaching shows potential, achieving 70% gallium extraction yield. Solvent extraction and electrolysis exhibit promise for pure gallium recovery. HF or alkali roasting leaches germanium with a high yield of 98% from spent OFs. Solvent extraction achieves over 90% germanium recovery with minimal silicon co-extraction. Solid-phase extraction offers selective germanium recovery. Advancements in optimizing and implementing these e-waste recovery protocols will enhance the circularity of these TCEs.

Evaluation of the effect of physical and chemical factors in the recovery of Cu, Pb and Fe from waste PCB through acid leaching

Electronic waste recycling is a strategy that contributes to implement a circular economy model which include reuse, component and raw material recovery and minimum final deposition. Given the importance of reincorporating the components of electronic devices into the productive chain and a correct recovery for some hazardous metals such as lead contained in such residues. This study is focused on the effect of maximum available content (MAC) of metal, sulfuric acid initial concentration, agitation velocity, and oxidising agent on the recovery of copper, lead and iron from electronic waste through acid leaching. A solid-state characterization before and after treatment and electrochemical analysis was carried out to analyse MCA effects and surface chemistry. It was found that sub-millimetric particles show a better available extraction percentage in case of copper and iron, being opposite for lead. Presence of hydrogen peroxide enhance the extraction efficiency, however, this cause iron and lead precipitation, therefore it is inefficient for metals recovery as well as for reagent consumption. The presence of calcium salts reacts producing gypsum, which reduces the extraction yield of copper at particle size below 250 μm.

Comprehensive treatments of aluminum dross in China: A critical review

Aluminum is an important lightweight and high-value metal that is widely used in the transportation, construction, and military industries. China is the largest producer of Al in the world, and vast quantities of Al dross (ash) are generated and stored every year. Aluminum dross contains fluoride and heavy metals, and easily reacts with water and acid to produce stimulating, toxic, and explosive gases. Owing to a lack of developed technologies, most of this dross cannot be safely treated, resulting in a waste of resources and serious environmental and ecological risks. This review briefly describes the distribution and proportions of bauxite deposits in China, the Al extraction process, and the hazardous solid waste that is generated. It also discusses the comprehensive treatments for Al dross, including the hydrometallurgy and pyrometallurgy recovery processes, and reuse of Al, Al2O3, SiO2, and chloride salts as a summarized comparison of their advantages and disadvantages. In particular, this review focuses on the efforts to analyze the relationship between existing processes and the attempts to establish a comprehensive technology to treat Al dross. Additionally, areas for future research are suggested, which may provide new ideas for the closed-loop treatment of Al dross.

Hydrometallurgical recovery of silver and gold from waste printed circuit boards and treatment of the wastewater in a biofilm reactor: An integrated pilot application

A hydrometallurgical process for the recovery of gold and silver from waste printed circuit boards (PCBs) was experimentally verified and tested at pilot scale. The process comprises four sequential leaching stages; the first two based on HCl, correspond to base metals (e.g. Sn, Cu) removal, while the third is based on HNO3 for Ag leaching and the final on aqua regia for Au leaching. After base metals leaching, the solid residue, enriched in silver and gold about 5 times, contained silver almost quantitively as insoluble AgCl and significant losses (Ag loss <8%) were avoided. The necessary reduction of Ag in the solid phase was achieved with a solution of 0.5 M N2H4 and 3 M NaOH, at 80 °C and S/L ratio 10%. Leaching of silver by 4 M HNO3 was followed by its recovery from nitrate solution by 0.08 Μ N2H4 at ambient temperature with an efficiency of 83%. Gold was leached by aqua regia and quantitively recovered by 0.13 M N2H4 at ambient temperature. Wastewater resulting from the process, rich in nitrate (5 g/L) and chloride (50 g/L), was treated by an effective and novel biological denitrification system tolerating metals at ppm level, to comply with zero nitrate and residual metals discharge guidelines. The overall process requires low reagents and energy input and has zero discharge for liquid effluents. The scheme is appropriate to be applied at local small to medium industrial units, complying with decentralized circular economy principles for metal recovery from electronic waste.

Life cycle analysis on sequential recovery of copper and gold from waste printed circuit boards

Informal recycling activities of waste printed circuit boards, such as pyrolysis and landfilling, cause severe environmental harm to society. Pyrolysis of resin and polymer fraction leads to the generation of toxic effluents, and landfilling causes the leaching of heavy metals into the groundwater. A sustainable and eco-friendly way to recover base and precious elements will be an economically attractive option. Current research studied the cradle-to-gate environmental impacts of the sequential recovery of copper and gold through delamination, leaching, solvent extraction, electrowinning and cementation from waste printed circuit boards with the help of life cycle assessment.GaBi software was utilized to assess environmental impacts such as global warming, abiotic depletion (fossil), acidification potential and human toxicity potential during the process. Inventory data was collected by conducting several experiments and from optimizing parameters for recycling and separating 4.53 g of copper and 2.25 mg of gold from 16 g of component-free waste printed circuit boards. Results indicate that the chemical pre-treatment or delamination process for separating metal clads from the non-metallic fraction is primarily involved in the impact category. The higher impact during delamination is due to electricity consumption. The proposed study also corroborates the industrial viability of recycling valuable metals from waste printed circuit boards to minimize the environmental impacts. The outcomes of this work could be beneficial in creating the environmental guiding principle for WPCBs recycling plants.

Catalytic recovery of metals from end-of-life polycrystalline silicon photovoltaic cells: Experimental insights into silver recovery

A steady increase in end-of-life (EoL) polycrystalline silicon photovoltaic (c-Si PV) panels is necessitating the development of recycling technologies to guarantee sustainable environmental management and a circular economy. Herein, we propose a comprehensive EoL c-Si PV recycling strategy with an emphasis on selective silver (Ag) recovery. Primarily, a combination of physical and thermal treatment led to the isolation of PV cell fraction from the EoL PV module. Thereafter, a less-toxic, sulphuric acid-hydrogen peroxide (1 M H2SO4- H2O2 1% (v/v %)) lixiviant was used for Ag leaching at 70 °C. A novel catalytic process using platinum-embedded activated carbon (Pt/AC) was used with only hydrogen gas and air to recover selectively and concentrate the Ag+ from the synthetic PV cells leachate. Finally, pure metallic silver (Ag > 99.0 %) was obtained by the conventional electrowinning process. This study also proposes an explicit recovery process for Al, Cu, and Si. In addition, the Pt/AC catalytic process could efficiently recover Cu from the PV cells, similar to Ag. Following the complete recovery of Ag and Cu through Pt/AC, there is sufficient scope to isolate other metals like Al and Pb leaving behind crude Si wafers. Hence, the as-proposed recycling and metal recovery process is a newer approach benefiting industrial implementation.

An assessment of the strategies for the energy-critical elements necessary for the development of sustainable energy sources

There have been several strategies developed to increase the diversified supply of energy so that it can meet all of the future demands for energy. As a result, to ensure a healthy and sustainable energy future, it is imperative to warrant reliable and diverse energy supply sources if the "green energy economy" is to be realized. The purpose of developing and deploying clean energy technologies is to improve our overall energy security, reduce our carbon footprint, and ensure that the generation of energy is secure and reliable in the future, making sure that we can spur economic growth in the future. In this paper, advancements in alternative sources of energy sustainability and strategies will be examined to ensure there will be enough fuel to supply all the future demands for energy. Several emerging clean energy technologies rely heavily on the availability of materials that exhibit unique properties that are necessary for their development. This paper examines the roles that rare earth and other energy-critical materials play in securing a clean energy economy and the development of clean energy economies in general. For the development of these technologies to be successful and sustainable, a number of these energy-critical materials are at risk of becoming unavailable. This is due to their limited availability, disruptions in supply, and a lack of suitable resources for their development. An action plan focusing on producing energy-critical materials in energy-efficient ways is discussed as part of an initiative to advance the development of clean and sustainable energy.

Recovery of residual metals from jarosite waste using chemical and biochemical processes to achieve sustainability: A state-of-the-art review

Jarosite is a residue that is generated as a by-product during zinc extraction, and it consists of various types of heavy metal (loid)s such as arsenic, cadmium, chromium, iron, lead, mercury and silver. Due to the huge jarosite turn-over rate, and less efficient and expensive residual metal extraction processes, the zinc-producing industries dispose this waste in landfills. However, the leachate generated from such landfills contains a high concentration of heavy metal (loid)s that could contaminate the nearby water resources and cause environmental concern and human health risk. Various thermo-chemical and biological processes have been developed for the recovery of heavy metals from such waste. In this review, we have discussed all those pyrometallurgical, hydrometallurgical, and biological. Those studies were critically reviewed and compared on the basis of their techno-economic differences. The review indicated that these processes have their own benefits and drawbacks such as overall yield, economic and technical constraints, and the need for more than one process to mobilize multiple metal ions from jarosite. Also, in this review, the residual metal extraction processes from jarosite waste have been linked with the relevant UN Sustainable Development Goals (SDGs), which can be useful for a better approach to sustainable development.

Hybrid leaching of tantalum and other valuable metals from tantalum capacitor waste

We propose a novel integrated model for the recovery of tantalum from tantalum-rich waste using a combination of hydrometallurgical and bio-metallurgical processes. To this end, leaching experiments with heterotrophs (Pseudomonas putida, Bacillus subtilis and Penicillium simplicissimum) were carried out. The heterotrophic fungal strain leached manganese with an efficiency of 98%; however, no tantalum was detected in the leachate. An unidentified species did mobilise 16% tantalum in 28 days in an experiment with non-sterile tantalum capacitor scrap. Attempts to cultivate isolate and identify these species failed. The results of a range of leaching trials resulted in an effective strategy for Ta recovery. A bulk sample of homogenised Ta capacitor scrap was first subjected to microbial leaching using Penicillium simplicissimum, which solubilised manganese and base metals. The residue was subjected to the second leach using 4 M HNO₃. This effectively solubilised silver and other impurities. The residue collected after the second leach was pure tantalum in concentrated form. The hybrid model produced derives from observations from previous independent studies and shows that we can effectively recover tantalum along with silver and manganese in an efficient and environmentally friendly manner from tantalum capacitor scrap.

A mechanochemical method for one-step leaching of metals from spent LIBs

A one-step system based on mechanochemical activation and the use of grape skins (GS) was proposed to recover metals from lithium-ion batteries (LIBs) cathode waste. The effects of the ball-milling (BM) speed, BM time, and quantity of added GS on the metal leaching rate were explored. The spent lithium cobalt oxide (LCO) and its leaching residue before and after mechanochemistry were characterized by SEM, BET, PSD, XRD, FT-IR, and XPS analysis. Our study shows that mechanochemistry promotes the leaching efficiency of metals from LIBs battery cathode waste by changing the cathode material properties (that is, reducing the LCO particle size (12.126 μm ∼ 0.0928 μm), increasing the specific surface area (0.123 m²/g ∼ 15.957 m²/g), enhancing the hydrophilicity and surface free energy (57.44 mN/m² ∼ 66.18 mN/m²), promoting the generation of mesoporous structures, refining grains, disrupting the crystal structure, and increasing the microscopic strain, while deflecting the binding energy of the metal ions). A green, efficient and environmentally friendly process for the harmless and resource-friendly treatment of spent LIBs has been developed in this study.

A facile strategy for reclaiming discarded graphite and harnessing the rate capabilities of graphite anodes

Graphite negative electrodes are unbeaten hitherto in lithium-ion batteries (LiBs) due to their unique chemical and physical properties. Thus, the increasing scarcity of graphite resources makes smart recycling or repurposing of discarded graphite particularly imperative. However, the current recycling techniques still need to be improved upon with urgency. Herein a facile and efficient hydrometallurgical process is reported to effectively regenerate aged (39.5 %, 75 % state-of-health, SOH) scrapped graphite (SG) from end-of-life lithium-ion batteries. Ultimately, the first cycle reversible capacity of SG1 (SOH = 39.5 %) improved from 266 mAh/g to 337 mAh/g while 330 mAh/g (98 %) remain after 100 cycles at 0.5 C. The reversible capacity for the first cycle of SG2 (SOH = 75 %) boosted from 335 mAh/g to 366 mAh/g with the capacity retention of 99.3 % after 100 cycles at 0.5 C, which is comparable with the benchmark commercial graphite. The regenerated graphites RG1 and RG2 exhibit excellent output characteristics even increasing the rate up to 4 C. This is the best rate level reported in the literature to date. Finally, the diffusion coefficient of Li ions during deintercalation and intercalation in the regenerated graphites have been measured by galvanostatic intermittent titration technique (GITT), determining values 2 orders-of-magnitude higher than that of the spent counterparts. Taking advantage of the synergistic effect of acid leaching and heat treatment, this strategy provides a simple and up-scalable method to recycle graphitic anodes.

E-waste recycled materials as efficient catalysts for renewable energy technologies and better environmental sustainability

Waste from electrical and electronic equipment exponentially increased due to the innovation and the ever-increasing demand for electronic products in our life. The quantities of electronic waste (e-waste) produced are expected to reach 44.4 million metric tons over the next five years. Consequently, the global market for electronics recycling is expected to reach $65.8 billion by 2026. However, electronic waste management in developing countries is not appropriately handled, as only 17.4% has been collected and recycled. The inadequate electronic waste treatment causes significant environmental and health issues and a systematic depletion of natural resources in secondary material recycling and extracting valuable materials. Electronic waste contains numerous valuable materials that can be recovered and reused to create renewable energy technologies to overcome the shortage of raw materials and the adverse effects of using non-renewable energy resources. Several approaches were devoted to mitigate the impact of climate change. The cooperate social responsibilities supported integrating informal collection and recycling agencies into a well-structured management program. Moreover, the emission reductions resulting from recycling and proper management systems significantly impact climate change solutions. This emission reduction will create a channel in carbon market mechanisms by trading the CO2 emission reductions. This review provides an up-to-date overview and discussion of the different categories of electronic waste, the recycling methods, and the use of high recycled value-added (HAV) materials from various e-waste components in green renewable energy technologies.

E-waste management, treatment options and the impact of heavy metal extraction from e-waste on human health: Scenario in Vietnam and other countries

Ho Chi Minh (HCM) City is the most important urban region of Vietnam, Southeast Asia. In recent times, the quantity of electronic waste (e-waste) has been growing by several thousand tonnes every year. In this research, some of the existing and developing technologies being employed for the recycling of e-waste have been reviewed. Accordingly, the paper has been divided into three sections namely, e-waste treatment technologies in Ho Chi Minh City, the effect of heavy metals on human health and the extraction of metals from e-waste using pyrolysis, hydrometallurgy, bioleaching, mechanical, and air classifier methods, respectively. The extraction of precious metals and heavy metals such as Cd, Cr, Pb, Hg, Cu, Se, and Zn from e-waste can be hazardous to human health. For example, lead causes hazards to the central and peripheral nervous systems, blood system and kidneys; copper causes liver damage; chronic exposure to cadmium ends up causing lung cancer and kidney damage, and mercury can cause brain damage. Thus, this study examines the key findings of many research and review articles published in the field of e-waste management and the health impacts of metal pollution.

Conversion of Lithium Chloride into Lithium Hydroxide by Solvent Extraction

A hydrometallurgical process is described for conversion of an aqueous solution of lithium chloride into an aqueous solution of lithium hydroxide via a chloride/hydroxide anion exchange reaction by solvent extraction. The organic phase comprises a quaternary ammonium chloride and a hydrophobic phenol in a diluent. The best results were observed for a mixture of the quaternary ammonium chloride Aliquat 336 and 2,6-di-tert-butylphenol (1:1 molar ratio) in the aliphatic diluent Shellsol D70. The solvent extraction process involves two steps. In the first step, the organic phase is contacted with an aqueous sodium hydroxide solution. The phenol is deprotonated, and a chloride ion is simultaneously transferred to the aqueous phase, leading to in situ formation of a quaternary ammonium phenolate in the organic phase. The organic phase, comprising the quaternary ammonium phenolate, is contacted in the second step with an aqueous lithium chloride solution. This contact converts the phenolate into the corresponding phenol by protonation with water extracted to the organic phase, followed by a transfer of hydroxide ions to the aqueous phase and chloride ions to the organic phase. As a result, the aqueous lithium chloride solution is transformed into a lithium hydroxide solution. The process has been demonstrated in continuous counter-current mode in mixer-settlers. Solid battery-grade lithium hydroxide monohydrate was obtained from the aqueous solution by crystallization or by antisolvent precipitation with isopropanol. The process consumes no chemicals other than sodium hydroxide. No waste is generated, with the exception of an aqueous sodium chloride solution.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40831-022-00629-2.

Development of a novel chelation-based recycling strategy for the efficient decontamination of hazardous petroleum refinery spent catalysts

The conventional hydrometallurgical methods for recycling refinery spent hydroprocessing catalysts are ineffective in simultaneously removing all metals (Ni, V, and Mo) in a single-stage operation. In this study, a novel octadentate chelating agent, diethylenetriaminepentaacetic acid (DTPA-C₁₄H₂₃N₃O₁₀), has been proposed for the first time to remove toxic metals (Ni, V, and Mo) in a single stage of operation from an industrial spent atmospheric residue desulfurization (ARDS) catalysts. It was discovered that the efficient formation of metal-DTPA complexes was attained under the optimum experimental conditions (60 °C, stirring - 150 rpm, S/L ration (w/v) of 2.5%, 7.5% DTPA, and medium pH-9) that resulted in the high removal of Mo (83.6%), V (81.3%) and Ni (64.1%) from the spent ARDS catalyst. Kinetic studies suggest that the leaching process followed a semi-empirical Avrami equation (R² > 0.92), which predicted that the diffusion control reaction controlled the leaching. Species distribution and ecological risk analysis of the remaining metals in the insoluble residue (mostly Al₂O₃) indicated that the potential bioavailability of the remaining metals (except Ni) was significantly decreased, and residue poses a low ecological and contamination risk (individual contamination factor <1). Furthermore, the textural properties of the residue (BET surface area-103 m²/g and pore volume- 0.49 ml/g) were dramatically improved, suggesting that fresh hydroprocessing catalyst support can be synthesized using the leached residue. Compared to the conventional processes, the proposed chelating process is highly selective, closed-loop, and achieved high metal recovery in a single-stage operation while decreasing the environmental risks of the hazardous spent catalysts.

Enhancement of leaching copper by organic agents from waste printed circuit boards in a sulfuric acid solution

Leaching copper from waste printed circuit boards (WPCBs) by hydrometallurgy has always been a hot research topic. At atmospheric pressure, hydrogen peroxide (H₂O₂) was used as an oxidant to study the leaching behavior of copper from WPCBs in sulfuric acid (H₂SO₄) solution with ethylene glycol (EG). To elucidate the leaching mechanism of copper from WPCBs, the effect of various parameters on the leaching performance with or without EG was investigated. The results showed that the copper leaching process from WPCBs in the presence of EG was found to conform to the ash diffusion-controlled shrinking core model according to the kinetic curve and a activation energy of 18.38 kJ/mol. Moreover, the presence of EG strengthened the stability of H₂O_2, improved dispersity and increased electrical activity of WPCBs, which enhanced the leaching of copper from WPCBs in the high leaching temperature (>323.15 K). As a result, apart from the fact that the optimal leaching concentration of H₂O₂ was reduced by the addition of EG, the improved copper leaching efficiency from WPCBs was achieved by the addition of EG, as demonstrated by a maximum copper leaching efficiency of 98.01% and a maximum loss rate of 29.68%. Besides, the mineralogical and morphological properties of leaching residue validated the leaching results. Based on this, our findings confirmed the enhanced leaching performance of copper from WPCBs by EG, which benefited for the efficient recovery of copper from WPCBs.

Direct recovery of Zn from wasted alkaline batteries through selective anode's separation

In the present study, a leaner process for recovering zinc from spent alkaline batteries is studied at a laboratory scale. Such process is part of a diagram, under development, that aims at maximizing the value of all the battery components while reducing the costs of treatment and the environmental footprint involved in recycling this waste. It starts by a physical and selective pre-treatment stage that separates the anode from the remaining components followed by neutral leaching (three washing cycles at room temperature, S/L ratio of 1/5 (w/v), magnetic stirring for 15 min and settling during 45 min), acid leaching of the washed solid (4 mol/L of sulphuric acid, S/L ratio of 1/3 (w/v), 120 min at room temperature under magnetic stirring) and, finally, electrowinning of zinc from the pregnant leach solution (100 mA/cm², 120 min under slow magnetic stirring). By leaching the anode alone, it is possible to obtain a solution rich in zinc (86 g/L), with very low concentration of other metals (<0.08 g/L). Such solution was adequate for zinc electrowinning, allowing an average recovery rate of 58%, without applying any purification stages, at the same time regenerating sulphuric acid for its recirculation. In conclusion, the results demonstrate that a more specific physical pre-treatment stage is highly desirable to recycle spent alkaline batteries in order to reduce the number of stages involved and the overall complexity, thus, reducing the costs involved and the potential environmental impacts, while maintaining high recovery rates of zinc.

Removal of chlorine from zinc sulfate solution: a review

During zinc hydrometallurgy process, the chloride ions in the materials go into the leaching solution, which have abominable effects on equipment, electrowinning, and environment. So, it is necessary to remove chloride ions from zinc sulfate solution. The present review outlines the current research of removal methods of chlorine by holistically highlighting the advantages and mechanisms. The main techniques used to remove chloride ions from zinc sulfate solution are also discussed in detail. Among the methods, the precipitation method using copper slag to remove chlorine is widely used and the chlorine removal rate is up to 98%. In addition, the combination of electrochemistry and nanofiltration technology can form a closed-loop production process with less waste output and near-zero emissions. In addition, the challenges and possible future directions of chlorine removal from zinc sulfate solutions are also delineated.

Recycling of cathode material from spent lithium-ion batteries: Challenges and future perspectives

The intrinsic advancement of lithium-ion batteries (LIBs) for application in electric vehicles (EVs), portable electronic devices, and energy-storage devices has led to an increase in the number of spent LIBs. Spent LIBs contain hazardous metals (such as Li, Co, Ni, and Mn), toxic and corrosive electrolytes, metal casting, and polymer binders that pose a serious threat to the environment and human health. Additionally, spent LIBs may serve as an economic source for transition metals, which could be applied to redesigning under a closed-circuit recycling process. Thus, the development of environmentally benign, low cost, and efficient processes for recycling of LIBs for a sustainable future has attracted worldwide attention. Therefore, herein, we introduce the concept of LIBs and review state-of-art technologies for metal recycling processes. Moreover, we emphasize on LIB pretreatment approaches, metal extraction, and pyrometallurgical, hydrometallurgical, and biometallurgical approaches. Direct recycling technologies combined with the profitable and sustainable cathode healing technology have significant potential for the recycling of LIBs without decomposition into substituent elements or precipitation; hence, these technologies can be industrially adopted for EV batteries. Finally, commercial technological developments, existing challenges, and suggestions are presented for the development of effective, environmentally friendly recycling technology for the future.

Simple, green organic acid-based hydrometallurgy for waste-to-energy storage devices: Recovery of NiMnCoC2O4 as an electrode material for pseudocapacitor from spent LiNiMnCoO2 batteries

A simple, green approach to recover NiMnCoC₂O₄ as an electrode material for high-performance pseudocapacitors from spent LiNiMnCoO₂ (NMC) batteries is proposed. Four strategic metals (Li, Ni, Co, and Mn) were leached from spent NMC batteries using several organic acids as model green leachants. Among the various candidates of green leaching agents, 2 M citric acid and 5 wt% glucose were selected as the leachant and reductant, respectively. Microwave irradiation was conducted during the leaching step to maximize the performance of the leaching rate and efficiency. The leaching efficiencies within 0.5 h for Ni(II), Li(I), Mn(II), and Co(II) were 90.7 ± 1.6%, 98.3 ± 2.4%, 94.9 ± 4.3%, and 95.6 ± 1.4%, respectively, and were thus as efficient as using aqua regia leaching. After the leaching process, divalent metal ions, that is, Ni(II), Co(II), and Mn(II), were immediately separated at room temperature using oxalic acid. The recovered samples were not further treated and used directly for energy storage applications. The recovered NiMnCoC₂O₄⋅nH₂O has been demonstrated as a promising electrode for pseudocapacitors, providing a specific capacitance of 1641 F/g, good rate-retention capability (80% of low-current capacitance), and good cycle stability over 4000 charge-discharge cycles.

Comprehensive Review on Metallurgical Upgradation Processes of Nickel Sulfide Ores

With the vigorously growing demand of the steel industry, corrosion resistance alloys, clean energy industries, and a variety of engineered infrastructure or technology, high-grade nickel ores are being exhausted gradually in the world. This review outlines metallurgical processes for nickel production from various nickel sulfide ores resources, particularly focusing on recent developments in metallurgical processes to identify potential trends and technical requirements in nickel metallurgy. The main methods have been extensively reviewed for nickel extraction from nickel sulfide ores which maybe are potentially applicable to provide new ideas for smelting technology innovation of nickel and even other similar metals. The main metallurgical methods include pyrometallurgical and hydrometallurgy, containing smelting, leaching, and purification. The advantages and disadvantages of each typical process have been analyzed and compared in this review, and a special emphasis is put forth. Biological metallurgy is highly selective for recovery of nickel and the most promising method recommended for future research and development. Moreover, ion exchange offers useful method for extraction and purification of nickel. In addition, many of the typical new methods involved are also introduced in this article.

Graphical Abstract

Recycling chains for lithium-ion batteries: A critical examination of current challenges, opportunities and process dependencies

Lithium-ion batteries (LIBs) show high energy densities and are therefore used in a wide range of applications: from portable electronics to stationary energy storage systems and traction batteries used for e-mobility. Considering the projected increase in global demand for this energy storage technology, driven primarily by growth in e-vehicles, and looking at the criticality of some raw materials used in LIBs, the need for an efficient recycling strategy emerges. In this study, current state-of-the-art technologies for LIB recycling are reviewed and future opportunities and challenges, in particular to recover critical raw materials such as lithium or cobalt, are derived. Special attention is paid to the interrelationships between mechanical or thermal pre-treatment and hydro- or pyrometallurgical post-treatment processes. Thus, the unique approach of the article is to link processes beyond individual stages within the recycling chain. It was shown that influencing the physicochemical properties of intermediate products can lead to reduced recycling rates or even the exclusion of certain process options at the end of the recycling chain. More efforts are needed to improve information and data sharing on the exact composition of feedstock for recycling as well as on the processing history of intermediates to enable closed loop LIB recycling. The technical understanding of the interrelationships between different process combinations, such as pyrolytic or mechanical pre-treatment for LIB deactivation and metal separation, respectively, followed by hydrometallurgical treatment, is of crucial importance to increase recovery rates of cathodic metals such as cobalt, nickel, and lithium, but also of other battery components.

Selective separation and recovery of lithium, nickel, MnO2, and Co2O3 from LiNi0.5Mn0.3Co0.2O2 in spent battery

The recovery of valuable metals from the LiNi_0·5Mn_0·3Co_0·2O₂ in spent batteries deserves more attention. We report a series of feasible procedures to selectively recover the four metals (Li, Ni, Mn, and Co) using a combination of hydrometallurgical and pyrometallurgyical processes. Firstly, oxalic acid is used to dissolve Li and precipitate the other three metals in oxalate forms. It is found that under the optimal condition, about 98% of the Li is dissolved, and on average 93% of the other three metals are transformed to precipitated oxalates. The oxalates are then transformed to NiO·Mn₂O₃·Co₃O₄ by being calcinated at 723 K under atmospheric environment. The selective recovery of NiO·Mn₂O₃·Co₃O₄ can be achieved by using H₂SO₄ under three different conditions. The first step is to use H₂SO₄ to selectively dissolve CoO from the Co₃O₄. Then the combination of H₂SO₄ and ultrasound is adopted to dissolve NiO, during which the ultrasound destroys the surficial oxide film on the NiO. Afterwards, the Mn₂O₃ is transformed to MnO₂ and Mn²⁺ in heated H₂SO₄. The Co, Ni and Mn ions are dissolved in a sequence, which facilitates their separation and recovery. As the main components of the final residual solids, Co₂O₃ and MnO₂ present in distinctly different sizes and shapes, which are beneficial for their separation and direct usage.

Raw data of silver extraction from sodium-silver jarosite using three different lixiviants in alkaline medium

This article presents the raw data of silver concentration ([Ag]) obtained as a function of time (t) from silver leaching experiments, which were conducted using a synthetic sodium-silver jarosite and different complexing agents: thiosulfate, thiocyanate, and cyanide. Leaching experiments were performed under different conditions of temperature, pH and lixiviant concentration. The data refer to the article “Silver leaching from jarosite-type compounds using cyanide and non-cyanide lixiviants: a kinetic approach” (Islas et al., 2021), in which they were used to determine the leaching kinetics of jarosite-type compounds. The datasets were obtained experimentally from batch experiments. Concentration of silver, [Ag], was determined in each experiment as a function of time by atomic absorption spectroscopy. The information presented in this article can be useful for engineering students interested in mineral processing; particularly, for the calculation of kinetic parameters of silver leaching process. The data could also help in the formulation, implementation, or optimization of strategies for extraction of valuable metals from residues generated by the hydrometallurgical industry.

Performance of a double-slope solar still for the concentration of lithium rich brines with concomitant fresh water recovery

Lithium recovery from brines has become a hot topic. The current evaporitic technology is slow, and serious environmental concern has been raised regarding the large volumes of water used, relating both to brine concentration through evaporation, and intensive pumping of fresh water needed in the fine chemical processing to produce high purity lithium carbonate. In this work, an experimental and theoretical analysis of brine desalination using a double-slope Solar Still was carried out. The Solar Still was installed right next to an existing lithium mining facility in northwest Argentina, and was tested with native high salinity lithium rich brine for a continuous year under the typical weather conditions of lithium deposits: high altitude, large thermal amplitude between day and night, strong winds, and high solar radiation. The performance of the solar still as an evaporator was compared with that of a PAN evaporimeter class A, and correlated to experimentally determined weather parameters. While the performance of the Solar Still for brine concentration was below that of open air evaporation, the Solar Still allowed for the production of an average of 2 L day^-1 m^-2 of distilled water, in marked contrast with current practice. Numerical simulations allowed us to quantify heat exchanges in both the Solar Still and the open air system.

Method of developing Thermo-Kinetic diagrams: The Cu-H2O-acetate and the Cu-H2O systems

A method to develop thermo-kinetic (TK) diagrams for the Cu-H2O-acetate and Cu-H2O systems is described. Conventional Eh-pH diagrams, also known as Pourbaix diagrams, are developed based on the thermodynamic stability of component species, typically in aqueous media. TK diagrams are an improvement on Eh-pH diagrams as they also describe the kinetics of electrochemical processes. These diagrams are developed by using data from linear scan voltammetry of Cu rotating disk electrodes exposed to aqueous media of different pH. By applying the same procedure, the TK diagrams can be developed for other metals or mineral systems exposed to aqueous media containing ligands. To ensure reproducibility and reconstruction of the TK diagrams for other metal/mineral/electrolyte systems, some important experimental considerations are highlighted in this study. These TK diagrams are useful to evaluate the corrosion of metals, the leaching performance of minerals and to predict the suitable conditions for metal recycling processes. Briefly, this article explains:•Important experimental considerations that could affect the kinetics of electrochemical processes.•A method to construct TK diagrams with examples of the Cu-H2O-acetate and Cu-H2O systems.•With overlaid Eh-pH diagrams, TK diagrams explain both the thermodynamic stability of component species and the kinetics of the electrochemical processes.

Using of leaching reactant obtained from mill scale in hydrometallurgical copper extraction

This study, which covered a set of leaching processes at a few stages, investigated the inclusion of iron found in mill scale, which is a waste of the iron-steel industry, in the solution as FeCl_x=2,3 in the presence of HCl and the conditions of using this solution with an oxidizing character in extraction of metals from chalcopyrite concentrate. Mill scale was treated with HCl, and an FeCl_x solution was obtained at a 100% Fe solubility and 83.43% Fe³⁺ conversion rate in the conditions of 60 min, 105 °C, 7 M HCl, and 1/10 solid-liquid ratio. This solution that was obtained was later used in copper extraction from a chalcopyrite concentrate. In the optimum conditions (120 min of leaching time, 105 °C of leaching temperature, 1/25 solid-liquid ratio, 400 rpm stirring speed), 95.04% of the copper was taken into the solution. In the leaching experiment in a medium containing mill scale + chalcopyrite and HCl at the same time, under the optimum conditions (120 min of leaching time, 105 °C of leaching temperature, 7 M HCl concentration, 1 g chalcopyrite concentrate, 1/25 solid-liquid ratio, 5 g mill scale, 400 rpm stirring speed), approximately 96% of copper was taken into the solution.

Electronic waste generation, recycling and resource recovery: Technological perspectives and trends

The growing population and increased disposal of end-of-life (EoL) electrical and electronic products have caused serious concerns to the environment and human health. Electronic waste (e-waste) is a growing problem because the quantity and the rate at which it is generated has increased exponentially in the last 5 years. The rapid changes or upgradation in technologies, IT requirements for working or learning from home during COVID-19, manufacturers releasing new electronic gadgets and devices that serves the consumers comfort and a declension in services has contributed to an increase in the e-waste or waste of electrical and electronic equipment (WEEE) generation rates. The current status of e-waste generation, handling procedures and regulatory directives in USA, EU, China, India, Vietnam and Gulf Cooperation Council (GCC) countries are presented in this review. The recent developments in e-waste recycling methods/recovery of base and precious metals, the advantages and limitations of hydrometallurgy, pyrometallurgy, biohydrometallurgy and pyrolysis are discussed. Considering the impediments in the present technologies, the extraction of valuable resources, i.e. precious metals, from e-waste using suitable biocatalysts shows promising applications. This review also stresses on the research needs to assess the economic effects of involving different unit operations/process industries for resource recovery, reuse and recycling.

Treatment of copper converter slag with deep eutectic solvent as green chemical

Industrial copper slag is among the most important wastes to be evaluated in terms of containing valuable metals and the amount of waste approaching 30 million tons per year. Therefore, in this study, it was aimed to propose a feasible route for copper and zinc recovery from copper converter slag (CCS) by using choline chloride (ChCl) based deep eutectic solvent which is applied on this type of slag for the first time. During the leaching experiments with the pure ChCl-2urea mixture, temperature (25-95 °C), leaching duration (2-72 h), and pulp density (1/10-1/40 g/mL) were selected as the parameters to be investigated for Cu and Zn extraction. After the experimental results, the optimized conditions for the ChCl-2urea leaching process, which gave 89.9% Cu and 65.3% Zn extraction was found at 48 h, 95 °C, 1/20 g/mL pulp density with 600 rpm stirring speed. It is noted that the iron dissolution ratio is very low (max. 4.7%) under the selected conditions. At the end of the iron cementation stage, the total recovery efficiency as a pure metallic copper was 63%. The calculated activation energy for the dissolution of the copper and zinc from CCS is 8.86 kJ mol^-1 and 14.48 kJ mol^-1, respectively.

Hydrometallurgical recycling of EV lithium-ion batteries: Effects of incineration on the leaching efficiency of metals using sulfuric acid

The growing demand for lithium-ion batteries will result in an increasing flow of spent batteries, which must be recycled to prevent environmental and health problems, while helping to mitigate the raw materials dependence and risks of shortage and promoting a circular economy. Combining pyrometallurgical and hydrometallurgical recycling approaches has been the focus of recent studies, since it can bring many advantages. In this work, the effects of incineration on the leaching efficiency of metals from EV LIBs were evaluated. The thermal process was applied as a pre-treatment for the electrode material, aiming for carbothermic reduction of the valuable metals by the graphite contained in the waste. Leaching efficiencies above 70% were obtained for Li, Mn, Ni and Co after 60 min of leaching even when using 0.5 M sulfuric acid, which can be linked to the formation of more easily leachable compounds during the incineration process. When the incineration temperature was increased (600-700 °C), the intensity of graphite signals decreased and other oxides were identified, possibly due to the increase in oxidative conditions. Higher leaching efficiencies of Mn, Ni, Co, and Li were reached at lower temperatures of incineration (400-500 °C) and at higher leaching times, which could be related to the partial carbothermic reduction of the metals.

Harmless disposal and resource utilization for secondary aluminum dross: A review

Secondary aluminum dross (SAD) is solid waste of primary aluminum dross extracted aluminum, which contains approximately 40-60 wt% alumina, 10-30 wt% aluminum nitride (AlN), 5-15 wt% salts and other components. The salts include sodium chloride, potassium chloride and fluorine salts. SAD has dual attributes as resource and pollutant. SAD landfill disposal has the disadvantages of occupying land, wasting resources, a high cost and great environmental impact. SAD utilization methods are currently pyrometallurgy and hydrometallurgy. In pyrometallurgy, AlN is oxidized and the salts are evaporated at high temperature. After mixing, molding and calcination, firebricks and ceramics can be manufactured from SAD. In hydrometallurgy, AlN is hydrolyzed and salts are dissolved in water. After dissolving, filtrating, precipitating, washing and calcination, γ-Al₂O₃ can be prepared from SAD. Resource consumption and emission from both utilization methods were assessed. A ton of magnesium aluminum titanate based ceramics by pyrometallurgy consumes 1043 kg raw materials and releases 69 kg of waste gas, 4.17 t of waste water and no solid waste. A ton of γ-Al₂O₃ by hydrometallurgy consumes 3389 kg raw materials and releases 111 kg of waste gas, 12.98 t of waste water and 267 kg of solid waste. Therefore, the resource consumption and emission of SAD utilization by pyrometallurgy is lower than that by hydrometallurgy. We should focus on reducing the emission of the three wastes from pyrometallurgy. We are sure that SAD can be utilized for glass ceramics by pyrometallurgy. AlN and salts can be transformed into alumina and glass phases at high temperature with no emission. We should clarify mechanisms for SAD composition adjustment to lower the glass ceramics' melting point, AlN and salts transformed into alumina and glass phases respectively, and nucleation and crystal growth of glass ceramics at high temperature.

Advanced utilization of copper in waste printed circuit boards: Synthesis of nano-copper assisted by physical enrichment

The copper in the waste printed circuit boards (WPCBs) is cleanly recycled by physical methods and presented in the form of nano copper particles by hydrometallurgical, which provides environmental approach to the advanced utilization of metal copper. Copper in WPCBs was first pre-concentrated by gradient enrichment process including gravity separation, mechanical grinding and flotation. The leaching method was then used to dissolve copper from the flotation concentrate in ammoniacal/ammonium salt solutions. Subsequently, reduction treatment was conducted to synthesize nano-copper from leaching solution. The enrichment results of the clean physical separation process show that the grade of copper increased from 16.22% to -38.05% by gravity separation, and the grade of copper further increased to 72.62 % by flotation after dissociation, which avoids overgrinding of low value components. Copper nanoparticles can be prepared effectively, and the recovery of copper in the leaching process reaches 99 %. The particle size of copper nanoparticles obtained by ascorbic acid reduction is tens of nanometers, and the surface of copper nanoparticles is smooth and nearly spherical. The present study proposes an environmentally friendly process of preparing nano-copper from the copper in WPCBs.

Recycling of cathode from spent lithium iron phosphate batteries

We demonstrate the concept of fabricating new lithium ion batteries from recycled spent 18650 lithium ion batteries (LIB). LiFePO₄ cathode was extracted from these spent LIB using combined approach of pre-treatment, mechanical treatment and hydrometallurgical process wherein weak organic acids, such as methyl sulfonic acid (MSA) and p-toluene sulfonic acid (TSA), were employed for the first time for leaching at room temperature of metal ions instead of conventional strong acids. High leaching efficiencies (95%) were obtained for extraction of Li and Fe using these acids from black mass. Reuse of these extracted metal ions is also demonstrated by precipitating them and synthesizing LiFePO₄ cathode. Structural characterization showed the formation of single-phase LiFePO₄ and electrochemical evaluation of this cathode in a LiFePO₄/Li half-cell exhibited a capacity of 93 mA h/g and 80 mA h/g at 0.2C and 1C rate respectively with good cycle stability.

E-waste upcycling for the synthesis of plasmonic responsive gold nanoparticles

One of the current challenges in circular economy is the ability to transform waste into valuable products. In this work, waste of electrical and electronic equipment (WEEE) was used as a gold source to prepare stable gold nanoparticles (AuNP). The proposed methodology involves a series of physical and chemical separation steps, carefully designed according to the complex nature of the selected WEEE and the targeted product. In a first step, pins from microprocessors were separated by mechanical treatments, allowing to concentrate gold in a metallic fraction. A two-step hydrometallurgical method was subsequently performed, to obtain a Au (III) enriched solution. Such solution was used as a secondary raw material to obtain AuNP. For that purpose, a specific synthetic method was developed, adapted to the high acidity and ionic strength of the solution. Thanks to the use of two easily available reducing agents (sodium citrate and ascorbic acid) and a polymeric stabilizer (PVP), it was possible to obtain high purity AuNP presenting a mixture of well-defined spherical and triangular shapes. These AuNP were finally deposited onto glass substrates and present a sensitive response to refractive index changes in the environment, a necessary condition towards application in optical sensors. In summary, this upcycling case study demonstrates that e-waste can successfully replace primary raw materials to obtain highly valuable and useful nanomaterials. These results highlight the potential of urban mining as a sustainable and circular approach to the development of nanotechnologies.

Effective recycling of Cu from electroplating wastewater effluent via the combined Fenton oxidation and hydrometallurgy route

Heavy metals, which commonly occur in complex forms, are difficult to remove in alkali electroplating wastewater effluent, and their resource recycling is rarely reported. Here, a Cu-bearing alkali wastewater effluent was effectively treated through Fenton oxidation, and the generated Fenton sludge was recycled into highly pure tenorite and hematite particles. The effluent contained 1.51 mg/L Cu and was subjected to Fenton oxidation, pH adjustment and coagulation. Amongst the three methods, Fenton oxidation showed superior efficiency to Cu removal, and the residual Cu in the effluent was 0.06 mg/L, thereby meeting the discharge standard for electroplating wastewater. However, Cu removal achieved less than 20% after pH adjustment and coagulation. Cu-bearing sludge, which was generated through the Fenton process, was dissolved in a mixture of hydrochloric and nitric acids. The dissolved solution contained 1.92 g/L Cu and 73.6 g/L Fe impurity. Impure Fe (67.4%) was removed as hematite aggregates after the solution was directly treated via a hydrometallurgy route, whilst 99.2% Cu was kept. When 0.5 mL of methanol was introduced to the hydrometallurgy system, nearly 100% Fe was removed as hematite nanoparticles with 94.8% purity, whilst more than 98% Cu was kept. The residual Cu was 1.88 g/L and precipitated as a tenorite block with a CuO content of 91.1% by adjusting the treated solution to pH 9. This study presented an environment-friendly method for enriching Cu from electroplating wastewater effluent without generating any waste.

Comprehensive treatments of tungsten slags in China: A critical review

As a critical and strategic metal, tungsten is widely used in the fields of machinery, mining and military industry. With most of the tungsten resources reserves in the world, China is the largest producer and exporter of tungsten. This has resulted in the generation of a huge amount of tungsten slag (slag) stored in China. This slag always contains not only valuable elements, such as tungsten (W), scandium (Sc), tin (Sn), niobium (Nb) and tantalum (Ta), but also toxic elements, such as arsenic (As), lead (Pb), chromium (Cr) and mercury (Hg). Due to a lack of developed technologies, most of these slags cannot be treated safely, which results in a waste of resources and serious environmental and ecological risks. In this review we briefly describe the distribution and proportion of tungsten deposits in China, the tungsten extraction process and the properties of tungsten slag. We also mainly discuss the comprehensive treatments for the valuable and toxic slag, including the amounts of valuable metal elements that can be recovered and the stabilization of toxic elements. These aspects are summarized in a comparison of their advantages and disadvantages. In particular, we focus on the efforts to analyze the relationship between the existing processes and attempts to establish a comprehensive technology to treat tungsten slag and also suggest areas for future research.

Metallurgical processes unveil the unexplored "sleeping mines" e- waste: a review

The aim of this review paper is to critically analyze the existing studies on waste electric and electronic equipment (WEEE), which is one of the most increasing solid waste streams. This complex solid waste stream has pushed many scientific communities to develop novel technologies with minimum ecological disturbance. Noteworthy amount of valuable metals makes e-waste to a core of "urban mining"; therefore, it warrants special attention. Present study is focused on all the basic conceptual knowledge of WEEE ranging from compositional analysis, global statistics of e-waste generation, and metallurgical processes applied for metals extraction from e-waste. This review critically analyses the existing studies to emphasize on the heterogeneity nature of e-waste, which has not been focused much in any of the existing review articles. Comprehensive analysis of conventional approaches such as pyrometallurgy and hydrometallurgy reveals that high costs and secondary pollution possibilities limit the industrial feasibilities of these processes. Therefore biohydrometallurgy, a green technology, has been attracting researchers to focus on this novel technique to implement it for metal extraction from WEEE.

Leaching efficiency and kinetics of the recovery of palladium and rhodium from a spent auto-catalyst in HCl/CuCl2 media

The recycling of scarce elements such as platinum-group metals is becoming crucial due to their growing importance in current and emerging applications. In this sense, the recovery of palladium and rhodium from a spent auto-catalyst by leaching in HCl/CuCl₂ media was studied, aiming at assessing the kinetic performance as well as the influence of some processing factors, and the behaviour of contaminant metals. Based on a kinetic model developed for the present case, the influence of temperature was evaluated and the corresponding values of activation energy were estimated as 60.1 ± 4.1 kJ mol^-1 for Pd and 44.3 ± 7.3 kJ mol^-1 for Rh, indicating the relevance of the chemical step rather than diffusion. This finding was corroborated by the non-significant influence of the stirring velocity. The reaction orders were estimated for each leaching reagent: for HCl, values of 2.1 ± 0.1 for Pd and 1.0 ± 0.3 for Rh were obtained; for Cu^2+, the obtained values were 0.42 ± 0.04 for Pd and 0.36 ± 0.06 for Rh. Without any significant loss of efficiency, solutions with higher metal concentrations were obtained using lower liquid/solid ratios, such as 5 L/kg. The main contaminant in solution was aluminum, and its leaching was found to be very dependent on the temperature and acid concentration.

Energy efficient electrodes for lithium-ion batteries: Recovered and processed from spent primary batteries

In an attempt to develop low cost, energy efficient and advanced electrode material for lithium-ion batteries (LIBs), waste-to-wealth derived as well as value added spent battery materials as potential alternatives assume paramount importance. By combining the low lithiation potential advantages, one can arrive at energy efficient electrodes bestowed with cost effective and eco-friendly benefits required for practical LIB applications. In the present study, Zn and Mn-salts along with C were successfully extracted from the spent zinc carbon batteries through a simple and efficient hydrometallurgy approach and decomposed thermally to obtain ZnMn₂O₄ at 350 °C for 12 h and 450 °C for 3 h. Further, C-ZnMn₂O₄ nanocomposites were prepared and demonstrated for appreciable electrochemical performance in LIB assembly. Our results show that C-ZnMn₂O₄ composites prepared at 350 °C and 450 °C demonstrate better performance than pristine ZnMn₂O₄ anode due to the improved electronic conductivity rendered by the added carbon obtained from spent primary battery. In particular, C-ZnMn₂O₄ at 350 °C @12 h exhibits appreciable electrochemical performance by showing a stable and higher capacity of 600 mAhg^-1 at a current density of 50 mAg^-1 in the voltage range of 0.01-3.0 V and qualifies it as a better performing cost-effective anode for LIBs.

A study on Zn recovery from other metals in the spent mixed batteries through a sequence of hydrometallurgical processes

A study on selective separation of Zn from a leaching solution by disposal batteries including various type batteries was carried out to understand the recovery behaviour of Zn in leaching solution. Selective recovery of Zn in leaching solution including Mn, Cd, Cu ion was difficult due to its similar physicochemical behaviour. Experiment results by present leaching solution with 279 µm undersize indicated that the best condition for leaching is 1 M H₂SO₄, 250 rpm, 5 vol.% H₂O₂ and 353 K and the leaching efficient of Zn, Co and Mn is approximately 97%, respectively. The exclusive extraction behaviour of Zn by using D2EHPA is indicated that the best conditions for solvent extraction are to be 0.6 M D2EHPA diluted with kerosene, 30% saponification, 298 K, 5-min contact time and three-stage countercurrent extraction, and the O/A ratio 1, respectively. Recovery of Zn was with approximately 99.7% selectively from Mn, Co, Ni, Cd and Li. After scrubbing 5 times by pH 2 modified solution and single stripping experiment by 1.5 M H₂SO₄, the solution including Zn of 9.0 g/L can be produced.

Interaction of H2O with (CuS)n, (Cu2S)n, and (ZnS)n small clusters (n = 1-4, 6): relation to the aggregation characteristics of metal sulfides at aqueous solutions

The interaction of H₂O onto small CuS, Cu₂S, and ZnS clusters was theoretically studied by Density Functional Theory computations to get insights into the aggregation characteristics of metal sulfides at aqueous solutions. The results show the charge-controlled interactions with polarized solvent molecules are favored on the ZnS clusters compared with CuS and Cu₂S clusters. Moreover, the chemical adsorption of H₂O molecules is energetically favored onto ZnS clusters with higher interaction energies of up to 35.4 kcal/mol compared with CuS and Cu₂S clusters (up to 31.3 kcal/mol), where the stability of H₂O adsorption decreases as the size of the clusters increases. However, thermochemical analysis shows that the adsorption of H₂O on copper sulfides is not a spontaneous process at room temperature. Additionally, the electrostatic energy of H₂O onto the Cu₂S and CuS clusters is lower than that associated with the H₂O-H₂O interactions, suggesting that copper precipitates prefer to bind between them at early stages of the precipitation process due to an unfavorable solvent-solute interaction. Dispersion forces play a relative key role in the interaction of water on copper sulfides, while for zinc sulfide clusters, the adsorption energy is slightly influenced by dispersion contributions. Accordingly, the aggregation of zinc sulfides in a water environment is expected to be lower compared with copper sulfides, and where the aggregation characteristics are not determined by the binding energy of the sulfides, but of the ability to interact with the solvent molecules. These statements were confirmed by experimental optical microscopy analysis and settling tests during precipitation processes in water. Therefore, this work allows proposing a simple strategy to study the aggregation characteristics of metal sulfides, which turns useful for use in hydrometallurgical applications.

Extraction of Li and Co from industrially produced Li-ion battery waste - Using the reductive power of waste itself

Industrially produced spent lithium-ion batteries (LIBs) waste contain not only strategic metals such as cobalt and lithium but also impurity elements like copper, aluminum and iron. The current work investigates the distribution of the metallic impurity elements in LIBs waste, and their influence on the acid dissolution of target active materials. The results demonstrate that the presence of these, naturally reductive, impurity elements (e.g. Cu, Al, and Fe) can substantially promote the dissolution of active materials. Through the addition of Cu and Al-rich larger size fractions, the extraction efficiencies of Co and Li increased up to over 99%, to leave a leach residue that is rich in graphite. By this method, the use of high cost reductants like hydrogen peroxide or ascorbic acid could be avoided. More importantly, additional Co and Li associated with the Cu and Al electrode materials could be also recovered. This novel approach contributes not only to improved reduction efficiency in LIBs waste leaching, but also to improved total recovery of Co and Li from LIBs waste, even from the larger particle size fractions, which are typically lost from circulation.