Search

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]

Impurity accumulation within the aluminum scrap cycle results in downgrading and challenges the sustainability recycling. Aerospace-grade aluminum alloys demand stringent compositional standards and minimal impurity content, establishing the theoretical and technological underpinnings of their recycling as a blueprint for advancing high-quality aluminum recycling. Drawing on the concept of aluminum energy flow, this study posits that the minimal Gibbs free energy differential between the raw materials and the final product inherently contributes to the advantages of recycled aluminum, including its lower energy requirements and abbreviated processing cycle. The assessment of energy flow and market demand indicates that the aluminum cycle should prioritize grade-maintaining, subsequently downgrading, and ultimately upgrading. Downgrading leads to an unsustainable cycle of aluminum resources. Thus, this paper elucidates the principle of system integration including dismantling, sorting, decoating, impurity element elimination, melt purification, and solid-state electrolysis. It further encapsulates the localized shortcomings of prevailing recycling technologies and proffers suggestions for global optimization. Ultimately, the merits and constraints of solid-state electrolysis technology are delineated, and a composite upcycling system predicated on galvanic cell and electrolysis is proposed, anticipated to facilitate sustainable upgrading of aluminum scraps. This paper introduces an innovative perspective on the energy flow principles within the scrap cycle process, conducts a systematic review of the inherent mechanisms governing aluminum recycling, and identifies theoretical and technological challenges to be addressed in future research. [Display omitted] • Principles of energy flow in the aluminum cycle. • Integration principle for aerospace aluminum scraps upgrade cycle. • Aircraft aluminum alloy recycling theory and experiment. • Theory and data on deep purification of recycled aluminum alloy melts. • Upgrading system consisting of galvanic cell and electrolysis. [ABSTRACT FROM AUTHOR]

Spent hydrogenation catalysts are strategic resources due to the high contents of Ni, Mo, and V. These metals were reduced and enriched as NiMoV alloy through pyrometallurgical smelting. However, it is a technical bottleneck for the separation of Ni, Mo and V from the polymetallic alloy. Hence, this paper proposed the atmospheric oxidation leaching of NiMoV alloy and separation of Ni, Mo and V through solvent extraction. The mixed solution of HCl and HNO 3 was employed as the leaching reagent for the dissolution of the alloy. The leaching efficiencies of Ni, Mo and V were all exceed 99.5% under the optimal conditions: c(HCl) of 3.0 mol/L, c(HNO 3) of 2.5 mol/L, S/L of 1:10 (g/mL), temperature of 95 °C for 3.0 h. N235 was used as the extractant for the synergistic extraction of V and Mo, while TBP and sulfonated kerosene was used as modifier and diluent. The extraction efficiencies of V and Mo were 99.2% and 99.9% under three-stage extraction of the following conditions: pH of 1.2, c(N235) of 25 vol%, and O/A of 1:1. It was found that only 0.01% Ni and 9.7% Fe entered the organic phase and can be removed by washing, which showed excellent selectivity for V and Mo. Then, based on the principle of ion exchange, H 2 SO 4 and NH 3 ·H 2 O were used to selectively strip V and Mo. Finally, V 2 O 5 , MoO 3 and Ni(OH) 2 were obtained after precipitation and calcination. [Display omitted] • The atmospheric oxidation leaching of NiMoV alloy was realized. • The solvent extraction presented excellent selectivity for V and Mo. • The mechanism of extraction and selective stripping of V and Mo was analyzed. • The high-value products V 2 O 5 , MoO 3 and Ni(OH) 2 were obtained. [ABSTRACT FROM AUTHOR]

• 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]

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]

In this study, fast-heating (300 °C/s) was applied to achieve the intercritical annealing of a cold-rolled quenching and partitioning (Q&P) steel with a wide range of soaking temperature (770–850 °C) and soaking time (0–120 s) for austenitization. The dilatometry and microstructural analysis revealed that in contrast to the conventional heating rate (5 °C/s), a fast-heating rate led to an accelerated transformation and grain refinement of the prior austenite in the Q&P samples. The microstructures of the Q&P treated samples subjected to different intercritical annealing conditions were studied in detail by various material characterization techniques including electron microscopy, electron probe micro-analysis, and X-ray diffraction. The working hardening behavior and the mechanical stability of the retained austenite were discussed on the basis of the typical stress-strain curves. The statistics of the ultimate tensile strength vs. total elongation of each sample under the orthogonal annealing conditions suggest that, for the investigated steel, the fast-heating process improved the strength with approximately 90 MPa on average within the elongation ranged from 17 to 27%. [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]