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• Scrapped PV panels are recovered comprehensively. • Leaching efficiency of Ag is over 96% by HNO 3. • The impurities in solar cells are removed efficiently. • Cu strips are purified and recovered by replacement reaction. • The proposed method for PV panels recycling is profitable. The increasing scrapped Si-based photovoltaic (PV) panels has become an urgent problem, and their disposal is essential for resources utilization and environment issues. This paper proposes a comprehensive process for recycling of discarded silicon-based PV panels economically, environmentally, and efficiently. Based on the thermal properties of ethylene vinyl acetate (EVA), they are removed from the discarded PV panels at 600 °C with heating rate of 5 °C/min and maintain for one hour. The glass, solar cells, and copper strips were separated after heat treatment. Simultaneously, the solar cells were crushed into powder. Nitric acid was used to recover silver from the solar cell powder, while most of the metal impurities such as Mg, Ti and Al, were removed as well. The leaching efficiency of silver was over 96 % under the optimized conditions: HNO 3 of 4.0 mol/L, liquid-to-solid ratio of 10:1, temperature of 50 °C for 80 min. Regarding the copper strips, they were sequentially treated with 0.5 mol/L CH 3 COOH and NaOH solution to remove the oxides of Pb and Sn on their surface. Subsequently, they were placed into the solution of 1.0 mol/L CuSO 4 with pH of 2 ∼ 3 to eliminate Pb and Sn. This article provides significant reference for the recycling of Si-based PV panels. [ABSTRACT FROM AUTHOR]

[Display omitted] • The advances in recycling LiFePO 4 have been reviewed. • Direct regeneration technologies of LiFePO 4 are discussed. • Hydrometallurgical leaching methods of LiFePO 4 are outlined. • Challenges and future directions for LiFePO 4 recycling are proposed. LiFePO 4 batteries have become one of the most promising batteries due to their excellent electrochemical performances, long life cycle, safety, and abundant mineral resources. As a result, the demand and scraped LiFePO 4 batteries increased dramatically in recent years. The recycling of waste LiFePO 4 batteries has raised great attention with the consideration of environmental issues and resources conservation. To date, there are massive literatures on the recycling of LiFePO 4 batteries aiming at providing an effective, economic and environmentally sustainable approach. Consequently, this review sorts out and analyzes the current advances in recycling LiFePO 4 from spent lithium batteries with the purpose of promoting the improvement of their recycling. Based on the damage degree of LiFePO 4 materials, direction regeneration and hydrometallurgical leaching are the main recycling processes. The direction regeneration of LiFePO 4 routes including high temperature solid regeneration, hydro/solvent thermal regeneration and electrochemical lithiation are discussed in detail. Inorganic or organic acid leaching, mechanically activated leaching and other leaching methods are reviewed as well. Finally, by comparing the various recycling technologies, the challenges are outlines and future directions for promoting the recycling effectiveness are proposed. [ABSTRACT FROM AUTHOR]

Platinum group metals (PGMs) are strategic metals. Auto-exhaust catalysts are their main application fields. The recovery of PGMs from spent auto-exhaust catalysts has remarkable economic value and strategic significance. Aiming at the problems of ferrosilicon generation for Fe capturing and subsequent oxygen blowing to remove iron with high energy consumption and heat release, a technology of Fe–Sn synergistic capturing PGMs was proposed. Taking full the advantage of the lower melting point of Fe–Sn alloy (<1200 °C) and its unique affinity for PGMs, the PGMs were captured at approximate 1400 °C with Fe–Sn as the collector. In experiment, 500 g of spent auto-exhaust catalysts were employed to minimize error and approximate industrial production. The mechanism of Fe–Sn synergistic capturing PGMs was elucidated. The generation of Fe–Sn-PGMs alloy lowered the activity of [PGMs] in the system, accelerated the reduction of the PGMs oxides and promoted the alloying of [PGMs]. Therefore, Fe–Sn synergistic capturing PGMs was realized. The inability of Si to enter the alloy phase was confirmed by theoretical calculations, avoiding the generation of ferrosilicon. The effects of basicity, CaF 2 , m (Fe)/ m (Sn) and the amount of collector on capturing PGMs were optimized. Under the optimized conditions (basicity R = 1.1, spent auto-exhaust catalysts 70 wt%, CaO 30 wt%, B 2 O 3 10 wt%, CaF 2 7 wt%, m (Fe)/ m (Sn) = 1/1 and the collector 15 wt%), the content of PGMs in the slag phase was 2.46 g/t. It is feasible to remove Fe and Sn by oxidation to achieve the purpose of PGMs enrichment. This technology offers guidance on the safe, environmentally sound, and efficient disposal of spent auto-exhaust catalysts, promoting the sustainable development of PGMs. [Display omitted] [ABSTRACT FROM AUTHOR]

Electronic waste (e-waste) is one of the fastest growing and most valuable waste. In industry, the final disposal of e-waste is usually through copper smelting and followed by electro-refining. Compared to the conventional copper anode slime, the anode slime from e-waste smelting is much more valuable and complicated. The major components are gold, silver, tin, lead and antimony. In this paper, an integrated process has been put forward to recycle these metals. To decrease the dissolution of impurities and enhance gold recovery rate, NaClO 3 -NaCl-H 2 SO 4 solution was chosen as leaching agent for gold recovery. The concentration of Cl − and H + can be controlled by the leaching system. After selective extraction of gold and silver, the residue mainly consists of PbSO 4 , SnO 2 and Sb 2 O 5 . Then PbSO 4 was dissolved and removed in HCl-NaCl-CaCl 2 solution at 95 °C. SnO 2 and Sb 2 O 5 were transformed into soluble materials via alkali smelting with NaOH. The Na 2 SnO 3 was recovered by washing, evaporation and crystallization. The insoluble matter, mainly containing NaSbO 3 , was leached by the HCl-NaCl solution, followed by hydrolysis and aging. The results showed that, under the optimum conditions, the direct recovery ratio of Au, Pb, Sn, and Sb was 98.1%, 99.1%, 92.3% and 97.1%, respectively. Moreover, the wastewater was reused as much as possible. This integrated process is highly efficient and environmental conservation. [ABSTRACT FROM AUTHOR]

New development and technological innovations make electrical and electronic equipment (EEE) more functional by using an increasing number of metals, particularly the critical metals (e.g. rare and precious metals) with specialized properties. As millions of people in emerging economies adopt a modern lifestyle, the demand for critical metals is soaring. However, the increasing demand causes the crisis of their supply because of their simple deficiency in the Earth’s crust or geopolitical constraints which might create political issues for their supply. This paper focuses on the sustainable supply of typical critical metals (indium, rare earth elements (REEs), lithium, cobalt and precious metals) through recycling waste electrical and electronic equipment (WEEE). To illuminate this issue, the production, consumption, expected future demand, current recycling situation of critical metals, WEEE management and their recycling have been reviewed. We find that the demand of indium, REEs, lithium and cobalt in EEE will continuously increasing, while precious metals are decreasing because of new substitutions with less or even without precious metals. Although the generation of WEEE in 2014 was about 41.9 million tons (Mt), just about 15% (6.5 Mt) was treated environmentally. The inefficient collection of WEEE is the main obstacle to relieving the supply risk of critical metals. Furthermore, due to the widespread use in low concentrations, such as indium, their recycling is not just technological problem, but economic feasibility is. Finally, relevant recommendations are point out to address these issues. [ABSTRACT FROM AUTHOR]

Waste electrical and electronic equipment (WEEE) has been one of the fastest growing waste streams worldwide. Effective and efficient management and treatment of WEEE has become a global problem. As one of the world’s largest electronic products manufacturing and consumption countries, China plays a key role in the material life cycle of electrical and electronic equipment. Over the past 20 years, China has made a great effort to improve WEEE recycling. Centered on the legal, recycling and technical systems, this paper reviews the progresses of WEEE recycling in China. An integrated recycling system is proposed to realize WEEE high recycling rate for future WEEE recycling. [ABSTRACT FROM AUTHOR]

Platinum group metals (PGMs) are regarded as strategic metals due to high melting point, corrosion resistance and catalytic activity. They are widely employed in renewable energy, petrochemical industry, vehicles and pharmaceutical engineering. However, the supply and demand of PGMs are facing challenges stemming from rarity and unequal distribution across the globe. This review aims to delve into the supply-demand of PGMs to elucidate primary applications and pinpoint current or projected shortfalls in the supply chain. The future demand for PGMs indicates a significant increase, particularly within the hydrogen sector. It is anticipated that Pt and Ir consumption in fuel cell vehicles and proton exchange membrane electrolysis will reach 143 tons and 38 tons by 2050, respectively. Production of PGMs is far from meeting demand. Sustainable development strategies, including recycling, substitution and innovative technologies, are proposed to address this contradiction. Recycling serves as a strategy to increase PGMs supply. Nevertheless, recycled PGMs accounted for approximately 26 %. Substitution represents a pathway to decrease the PGMs contents in products. The Pt load in fuel cells declined from 1.0 g kW−1 in the 1990s to 0.3 g kW−1 nowadays. Innovative technologies can mitigate the PGMs demand. Electric vehicles, solid oxide fuel cells and electrolysis cells provide promising alternatives for PGMs intensive industry. Ultimately, key future development directions for PGMs are outlined. The emphasis should lie on enhancing PGMs recovery efficiencies and intensifying research into catalytic mechanisms. Notably, ensuring the secure supply of PGMs will facilitate the advancement of renewable and sustainable energy. [Display omitted] • The supply and demand for PGMs is serious imbalance. • The demand for PGMs is forecasted, especially hydrogen industry. • PGMs sustainable strategies include recycle, substitution, innovative technologies. • Challenges and suggestions for PGMs sustainable development are raised. [ABSTRACT FROM AUTHOR]

The secondary production of platinum group metals (PGMs) occupies a 30% proportion of the global supply. The iron-capturing recycling technology produces Fe-PGMs alloy, of which PGMs need further enrichment for purification. We applied electrolytic refining method on Fe-PGMs alloy for separating PGMs from iron. Fe-PGMs alloy and titanium plates are used as anode and cathode. The main electrolyte is ferrous sulfate. During electrolysis, iron is electrolytically migrated to the cathode and electrodeposited, while PGMs settle to form anode slime. An appropriate parameters range for electrolysis is potential (0.5–0.8 V), concentration of Fe2+ (1.0–1.5 mol/L), temperature (60–80 °C), pH (3.0–3.5). The impurities like carbon and phosphorous can promote the dissolution of iron in the early electrolysis by expanding the coverage of reaction intermediates adsorbed on the anode surface but will hinder the dissolution and enrichment if forming a film layer. After electrolysis at 0.7 V constant voltage, PGMs were separated from the iron matrix and enriched in the anode slime (85–90%) and residual anode (10–15%). The recovery efficiency reached nearly 100%. Pure iron was prepared on the cathode and the electrolytic liquid can be reused. This electrolytic enrichment process has lower energy consumption, less wastewater, and higher recovery efficiency. • Specific properties of Fe-PGMs alloys were detected. • Appropriate process parameters for electrolysis were determined. • The recovery efficiency of PGMs was nearly 100% by electrorefining. • Enrichment concentration of PGMs was increased by 10 times. • Electrolytic refining consumes lower energy with less wastewater. [ABSTRACT FROM AUTHOR]

Graphitic carbon nitride (g-C 3 N 4) can be used to degrade organic pollutants in wastewater owing to its excellent chemical stability, tunable band structure, and visible light (VL) responsiveness. Nevertheless, the application of pristine g-C 3 N 4 is significantly hindered by its low specific surface area, unsatisfactory VL utilization (<460 nm), high exciton binding energy (E b ≈ 0.2 eV), and low photoinduced carrier separation. Development of strategies to overcome these limitations and improve the degradation efficiency has attracted considerable attention. Considering the principles of photoexcitation, this paper describes two unique photoexcitation processes, the carrier and exciton processes, of which the strong exciton effect of g-C 3 N 4 has not been extensively discussed in prior reviews. In addition, we comparatively present the latest progress and related mechanisms of the modification strategies such as morphology controlling, elemental doping, defect engineering, and heterojunction building employed in polluted water treatment are compared from the carrier and exciton perspectives. Finally, the unique characteristics, challenges, and future directions are discussed. This review presents research progress on the photoexcitation processes involved in g–C 3 N 4 –based materials, and proposes that the modification based on the exciton effect and direct verification of the transfer mechanism in the heterojunction can be potential areas of future investigations. [Display omitted] • Energy band theory and exciton effect related to photoexcitation mechanism were discussed. • Various modification strategies for enhancing the photocatalytic activity of g-C 3 N 4 are reviewed. • Construction of the Z-scheme system can improve photocatalytic activity. [ABSTRACT FROM AUTHOR]

Reclamation of spent catalysts for the efficient recovery of palladium (Pd) is gaining growing attention due to its scarcity and high supply risk. Currently Pd extraction from spent catalysts through an efficient, economical, and green method has remained a challenge. In this study, Fe3+ is utilized for leaching through oxidation of Pd in a mild condition. Before leaching, distillation was proposed to remove and recover the organics from spent catalysts. The effects of HCl concentration, Fe3+ concentration, NaCl concentration, leaching time, and temperature on the leaching efficiency of Pd were investigated to determine the optimum leaching conditions. The results show that Pd extraction and dissolution of Al2O3 increase with higher HCl concentration. The effect of NaCl on Pd leaching efficiency is significant at low acid concentration (2.0 mol/L HCl). The leaching efficiency was 99.5% for Pd under the following conditions: 2.0 mol/L HCl, 4.0 mol/L NaCl, and 0.67 mol/L Fe3+ at 80 °C for 90 min. The leaching kinetics fits best to the shrinking-core model of surface chemical reaction. The activation energy for the leaching of Pd was 47.6 kJ/mol. PdCl42− was selectively adsorbed by anion exchange resin. The filtrate containing adequate H+, Cl-, and Fe3+ was reused as leaching agent. Pd leaching efficiency was over 96% after five cycle times. This study provides an efficient process for recovery of Pd from spent catalysts. [ABSTRACT FROM AUTHOR]

Herein, a novel and simple approach for directly growing nanowire-built nanofibrous ceramic foams with tunable hierarchical pores has been put forward, where silicon particles, Ludox® and carbon black are selected as the initial materials. Firstly, cellular green bodies were constructed by freeze casting method, and their oriented pores provided sufficient but designated space for the generation of nanowires during carbothermal reduction nitridation process, meanwhile ensured the adequate nitrogen supply. The prepared multi-laminate ceramic foams assembled by nanowires with low density of 0.40 g/cm3 exhibit excellent heat insulation performance with low thermal conductivity of W/(m·K) and outstanding dielectric properties with low dielectric constant of 2.35 at frequency of 10.0 GHz, which could be attributed to the hierarchical porous structure built by nanowires level by level, and they would have promising applications in the thermal insulators, absorptions, catalyst supports, filters for gas or liquid as well as wave-transparent materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • 1. Novel ultrathin porous N-GQDs/P-g-C 3 N 4 photocatalysts were prepared. • 2. Efficient exciton dissociation and charge transfer were obtained. • 3. The exciton and carrier behaviors in photocatalytic systems were revealed in detail. • 4. Expending visible-light response of g-C 3 N 4 upto near infra-red region. • 5. Directional regulation of ROS by changing the content of N-GQDs. Graphitic carbon nitride (g-C 3 N 4) is a promising candidate for solving energy and environmental problems. However, narrow photoresponse range, difficult exciton dissociation, and high charge recombination rate severely restrict its activity. Herein, a novel ultrathin porous N-GQDs/P-g-C 3 N 4 (PG-CNS) nanocomposite was fabricated by combining P-element doping, N-doped graphene quantum dots (N-GQDs) coupling, and morphology regulation strategies. The optimal sample (PG-CNS-0.2) was found to extend the photoresponse range over 780 nm due to the combination of midgap state induced by P-doping and excellent upconversion performance of N-GQDs, achieving a fuller utilization of solar energy. Photoluminescence and electrochemical tests confirmed that both exciton dissociation and charge transfer within PG-CNS-0.2 were dramatically enhanced, as reflected by a 3.0-fold increase in carrier density. This enhancement was attributed to reduced exciton binding energy resulting from P-doping, superior electron conduction ability of N-GQDs, as well as larger specific surface area and shorter migration paths provided by the 2D porous structure. Besides, the trapping experimental result indicated that targeted regulation of reactive oxygen species was achieved by changing the addition amount of N-GQDs, thereby enhancing the controllability of photocatalytic reactions. Compared with g-C 3 N 4 nanosheets (CNS), the H 2 production rate and tetracycline degradation rate of PG-CNS-0.2 under visible light were improved by 15.7 and 6.9 times, respectively. Meanwhile, the molecular oxygen activation ability of PG-CNS-0.2 was also significantly increased, as reflected by the generation of O 2 – and H 2 O 2 at concentrations 2.5 and 3.5 times higher than that of CNS, respectively. This work not only comprehensively reveals the exciton and carrier behaviors in g-C 3 N 4 -based reaction systems, but also provides a new strategy for designing low-cost, environmentally friendly, and efficient broad-spectrum responsive photocatalysts. [ABSTRACT FROM AUTHOR]

Municipal solid waste incinerated (MSWI) fly ash and pickling sludge contain heavy metals such as Cr, Pb, Ni, etc., which are harmful to the environment but also suitable to be the nucleating agents in glass-ceramics preparation. In this paper, MSWI fly ash, pickling sludge, and waste glass were melted at 1400 °C for 3 h, and the obtained parent glass was nucleated and crystallized at 800 °C for 0.5 h. Glass-ceramics was successfully prepared by the one-step process. The effects of the content of pickling sludge on crystalline properties of parent glass and the physicochemical properties of glass-ceramics have been systematically discussed. The gap between nucleation temperature (T n) and crystallization temperature (T c) can be narrowed with higher content of pickling sludge, which caused fracture of the glass network (Si-O) and generation of the nonbridging oxygen (NBO), promoting the formation of diopside phase. As a result, nucleation and crystallization can be finished at the same temperature, called one-step process. The sample PS22 with 22 wt% pickling sludge added performed the best crystallization ability for having the narrowest gap (ΔT = 177 °C) between T c and glass transition temperature (T g) and the highest ratio of NBO to total oxygen (T) (NBO/T = 1.72). The Vickers' hardness and bending resistance of the products are 13.11 GPa and 135.84 MPa, respectively. The glass-ceramics are composed of homogeneously distributed diopside, donathite-spinel and glass phase. The toxic heavy metals are effectively stabilized by glass-ceramics. This study provides insights into more efficient and cleaner utilization of MSWI fly ash, pickling sludge and waste glass as glass-ceramic materials. Image 1 • Glass-ceramics were made from MSWI fly ash and pickling sludge and waste glass. • Properties of glass-ceramics by one-step were satisfied with the industrial standard. • Pickling sludge is an efficient nucleating agent in terms of glass crystallization. • Pickling sludge depolymerizes the glass network and decreases the thermal stability. [ABSTRACT FROM AUTHOR]