A systematic investigation was carried out for the selective extraction and recovery of vanadium from a citric acid-mediated leach liquor of spent catalyst using a mixture of Aliquat 336 and 2-Octanol. Prior to extraction, iron was efficiently removed at pHe 4.0 via slaked lime precipitation. Extraction equilibrium studies indicated that vanadium was predominantly extracted as the [VO(C6H5O7)] 2- anionic complex by Tricarpyl methyl Ammonium Chloride (Aliquat 336). The association of 2 mol of aliquat 336 was confirmed from the slope analysis method with extraction of vanadium from citrate media as [ (CH 3 R 3 N) 2 ] VO(C6H5O7) ] (org) . Vanadium extraction was quantitative under conditions of pH 6.0 ensuring no co-extraction of magnesium. Extraction isotherm examined using 0.6 M Aliquat 336 + 10% (v/v) 2-octanol at A: O = 8:1 in two stages leading to attaining 5 folds enrichment of vanadium during extraction. FTIR analysis confirmed the successful coordination of vanadium in the organic phase. Stripping of vanadium using NaOH at an aqueous-to-organic (A:O) ratio of 1:5 yielded a concentrated strip solution containing 47.2 g/L vanadium, representing almost eightfold enrichment compared to the initial leachate. Final precipitation and calcination of the strip solution produced high-purity V2O5, confirmed by XRD analysis. This study demonstrates a clean, efficient, and environmentally benign method for the selective recovery of vanadium from spent catalyst leachates using ionic liquid-based solvent extraction.

This study presents an environmentally sustainable approach for recovering rare earth elements (REEs) from NdFeB permanent magnet waste using eco-friendly organic acids as alternatives to conventional mineral acids. The NdFeB magnet sample was leached with different organic acids, such as acetic, ascorbic, citric, malic, lactic, and tartaric acids; among them, ascorbic acid exhibits the highest selectivity toward REEs over iron. Under the optimized conditions: 0.5 mol/L ascorbic acid, 6 h leaching time, 10 g/L solid-to-liquid ratio, 600 r/min agitation speed, and 30 °C temperature, complete dissolution of REEs is achieved through a two-stage leaching process, while iron dissolution is limited to 17.7%. Kinetic analysis indicates that the leaching of REEs and Fe follows the diffusion-controlled mechanism. Following leaching, solvent extraction was employed for the selective removal of REEs from the leach solution using various organophosphorus extractants, including PC 88A, Cyanex 572, and Cyanex 272. Among the tested extractants, PC 88A shows the highest extraction efficiency. The McCabe-Thiele plot indicates that neodymium is efficiently recovered in two extraction stages with organic to aqueous phase ratio of 1:1. Counter-current test confirms this, leaving only 16.7 mg/L of Nd in the raffinate. REEs were subsequently stripped from the metal-loaded organic phase using 0.5 mol/L oxalic acid, resulting in 99.8% precipitation of REEs as their oxalate. The oxalate precipitates were thermally treated to obtain high-purity mixed rare earth oxides, confirming the effectiveness of the integrated leaching, extraction, and recovery approach for sustainable REE recycling from NdFeB magnet waste.

The development of stable and efficient non-noble-metal electrocatalysts for the oxygen evolution reaction (OER) remains a major challenge due to the intrinsically sluggish four-electron transfer and O-O bond formation kinetics. Herein, we report for the first time a novel OER electrocatalyst derived from natural polymetallic nodules (PMNs). The catalyst was synthesized through a facile co-precipitation strategy followed by calcination and electrochemical activation via cyclic voltammetry (CV). The resulting material, denoted as CV-activated PMNs on a nickel substrate (NS), exhibits a hierarchically textured nanostructure that enhances electronic conductivity and exposes abundant catalytic sites, thereby facilitating efficient OER activity. The catalyst demonstrates excellent performance in alkaline electrolyte, delivering a low overpotential of 193 mV at 10 mA cm- 2 together with a favourable Tafel slope of 56 mV dec- 1. The CV-activated PMNs require a cell voltage of only 1.42 V to achieve 10 mA cm- 2 in 1 M KOH. In addition, the catalyst exhibits remarkable long-term electrochemical durability, highlighting its structural stability during continuous operation. These findings demonstrate that polymetallic nodules can serve as sustainable and earth-abundant precursors for the development of efficient OER electrocatalysts for clean energy conversion technologies.

Shortfall in the supply of metals critical for transition to the low carbon economy necessitates extraction from low-grade ores and wastes. This requires new flowsheet development where the operating parameters of each unit operation must be optimized. This approach is experiment intensive with a large gestation period. To accelerate flowsheet development for sustainable metal extractionMetal extraction, a conceptual framework of Metal ExtractionMetal extraction InformaticsInformatics (MEI) has been proposed. MEI combines some aspects of material informaticsInformatics and multi-objective optimizationOptimization. Three objective functions have been used: process efficiency, operating costs, and environmental impactEnvironmental impact. A case study of the leachingLeaching of copperCopper from waste printed circuit boards has been modelled to illustrate the MEI framework.

The increasing demand for rare earth elements (REEs) in advanced technological applications, combined with the limited availability of primary resources, has intensified efforts to recover REEs from secondary sources. Spent NdFeB magnets, commonly found in hard disk drives (HDDs), represent a rich and promising source, containing approximately 30% of REEs. This study focuses on the comparative leaching studies between roasted and unroasted NdFeB magnet samples using HCl as lixiviant. Leaching experiments were systematically conducted to evaluate the influence of key process parameters: acid concentration, temperature, and leaching duration on the recovery of valuable metals. The unroasted sample achieved 99.9% REEs recovery; however, high iron dissolution indicated poor selectivity. In comparison, the roasted sample demonstrated higher selectivity, with recoveries of 96.9% for Dy, 95.4% for Pr, and 93.2% for Nd, while iron dissolution was limited. Leaching kinetic analysis of roasted magnet powder indicated that rare earth leaching kinetics followed a mixed control mechanism, with the activation energy calculated as 39.35 kJ/mol within the temperature range of 30-60 degrees C.

The widespread use of neodymium-iron-boron (NdFeB) magnets has raised concerns about the environmental impact of their disposal, prompting the need for sustainable recycling strategies. Traditional solvents used in recycling are toxic and flammable, making them risky to use. Ionic liquids are safer and greener options with low vapor pressure, high stability, and less flammability. This study introduces an eco-friendly recycling approach utilizing the [P66614][Cy272] ionic liquid to selectively extract iron and recover rare earth elements (REEs) from the leach liquor of waste NdFeB magnets. Pre-treatment processes enhanced metal concentration before leaching, including demagnetization, grinding, and screening. Optimal leaching conditions: 2 mol L-1 HCl, 80 degrees C, 10 g L-1 pulp density, and 90 minutes, resulted in complete leaching of REEs (Dy, Pr, Nd), iron, and boron. Using 0.01 mol L-1 [P66614][Cy272] ionic liquid, 100% of the iron was removed from the leach liquor with minimal co-extraction of REEs (similar to 4%). Precipitation of iron leading to Fe2O3 (hematite) after calcination and is verified through XRD and SEM-EDS analyses. The ionic liquid also enabled 81.1% recovery of HCl from the leach liquor, reducing neutralization needs and operational costs. Subsequent REEs separation using 0.01 mol L-1 [P66614][Cy272] ionic liquid demonstrated high selectivity, achieving separation factors of 18.55 (Dy/Pr) and 15.52 (Dy/Nd) at pH 2.03. Dy(iii) was successfully separated from NdFeB leach solutions using counter-current extraction, leaving 6.0 mg L-1 in the raffinate, requiring two extraction stages at a 2 : 3 organic-to-aqueous phase (O/A) ratio. The reusability of the ionic liquid further enabled a sustainable, closed-loop recycling process. This approach highlights the potential for integrating ionic liquids into green technologies for NdFeB magnet recycling, ensuring resource recovery while minimizing environmental impact.

As a robust photocatalyst, Bi4O5I2 have has attracted significant scientific interest owing to its narrow bandgap energy, escalated electronic properties and high stability. Nonetheless, the unfavourable band structure and higher recombination of excitons have restricted its diversified photocatalytic applications. In this context, binary heterojunction construction using Bi4O5I2 could be considered an effective strategy for spatial charge carrier separation across the hetero-interface, leading to an enhanced activity. In this study, we have prepared Bi4O5I2/g-C3N4 Z-scheme hetero-structures via a wet impregnation strategy that preserves the spherical structure of Bi4O5I2. The phase purity, chemical bonding, morphology and microstructure of the composite were confirmed using XRD, FTIR, SEM, TEM and HRTEM studies. The formation of robust 3D-2D contact junction triggers the charge separation and migration at the hetero-interface. Furthermore, the Z-scheme charge transfer dynamics helps to retain the redox ability of the excitons. As a result, The Bi4O5I2/g-C3N4 heterojunction composite exhibited 84.6% of tetracycline degradation within 60 min that is 1.8 and 2.7 folds higher than pristine Bi4O5I2 and g-C3N4, respectively. The findings of this study have major implications for building highly effective heterojunctions for upgraded photocatalytic applications.

The SmCo5 magnet alloy is a powerful magnet used in defence, aerospace, and automotive transmissions. While shaping to form different magnets, a lot of scraps are produced. These wastes offer a sustainable way to recover the critical metals, Sm and Co, reducing reliance on primary raw materials. This study investigates the recovery of Sm and Co from SmCo5 magnet alloy scrap using solvometallurgical techniques, which utilise organic solvents for metal extraction while minimising water usage compared to traditional methods. Various organophosphorus extractants were tested as lixiviant, with the solvoleaching efficiency order D2EHPA > PC 88 A > Cyanex 572 > Cyanex 272, reflecting their decreasing acidity and influence on metal dissolution. The optimal solvoleaching conditions: 2 mol/L D2EHPA concentration, 80 degrees C temperature, 8 h leaching time, 400 rpm agitation speed, and 10 g/L pulp density resulted in near-complete recovery of samarium and cobalt. Samarium and cobalt were effectively separated from strip leach liquor using the sodium sulfate double salt precipitation method. Samarium was recovered as NaSm(SO4)(2)nH(2)O with a precipitation efficiency of 99.9 % under optimised conditions: 80 degrees C temperature, 90 min reaction time, Na2SO4:Sm molar ratio of 4:1, and pH 1.25. Cobalt in the residual solution was precipitated as cobalt oxalate with an efficiency of 99.7 % at 60 degrees C temperature, 60 min reaction time, and 1.25:1 oxalate to cobalt molar ratio. The precipitated cobalt oxalate was calcined at 450 degrees C, forming cobalt oxide (Co3O4). This study demonstrates solvometallurgical method as high-yield, sustainable solution for efficient SmCo5 magnet recycling with minimal environmental impact.

2D–2D GCN/O v –ZFO direct Z-scheme heterojunctions for photocatalytic MO degradation and H 2 production.

2D-2D heterostructured photocatalysts with direct Z-scheme charge dynamics have garnered immense research interest recently owing to their enlarged hetero-interface, which facilitates the separation and migration of photo-induced charge carriers. Although 2D g-C3N4 (GCN) and 2D ZnFe2O4 (ZFO) based photocatalysts have been extensively investigated, the design and performance of GCN/oxygen vacancy-rich ZFO (GCN/Ov-ZFO) 2D-2D heterojunction photocatalysts with Z-scheme charge transfer dynamics remained unexplored. Herein, we reported that the thermal condensation of dicyandiamide (DCDA) with ZFO nanosheets at 550 degrees C for 5 hours resulted in the formation of GCN/Ov-ZFO 2D-2D heterojunctions. Triethanolamine (TEA) acted as both a complexing agent and a soft template during the synthesis of ZFO nanosheets. Scavenging experiments, XPS results and band-edge potential calculations revealed the formation of a direct Z-scheme charge transfer dynamics. GCN/Ov-ZFO2 displayed a maximum MO degradation efficiency of 99.54% which is 3.7 and 1.8 times higher than that of pristine ZFO and GCN, respectively. It also demonstrated elevated photocatalytic H2 production of 735.4 mu mol g-1 h-1, surpassing those of pristine ZFO and GCN by factors of 8.5 and 3.6, respectively. The augmented performance of GCN/Ov-ZFO2 might be attributed to maximized charge separation, extended visible light absorption, improved surface properties and strong redox ability resulting from the combined effect of the 2D-2D heterointerface, introduction of Ovs, and the direct Z-scheme heterojunction.

This study explores the extraction of Nd(III) from synthetic solutions using the ionic liquid [P66614] [Cy272]. Key extraction parameters, including the effect of phase contact time, initial pH, salting-out agents, extractant concentration, and temperature, were systematically optimized. Results revealed that a phase contact time of 15 min, an initial pH of 2.14, and 0.2 mol center dot L-1 NaCl as a salting-out agent and extractant concentration of 0.015 mol center dot L-1 [P66614][Cy272], achieved maximum extraction efficiency of 99.7%. Thermodynamic analysis confirmed the process is to be exothermic, spontaneous, and entropydriven, highlighting the strong complexation between Nd(III) and the ionic liquid [P66614][Cy272]. Stripping tests revealed that using 0.1 mol center dot L-1 H2SO4, achieved complete recovery (100%) of Nd(III) from the loaded-organic phase. These findings underscore the potential of [P66614][Cy272] ionic liquid as a green, efficient alternative to conventional extractants, providing high efficiency and reduced environmental impact. This research advances hydrometallurgical recycling of REEs, particularly from end-of-life NdFeB magnets, supporting sustainable resource recovery and addressing global supply challenges for critical materials.

Presently huge operation costs arising from aeration and high electron donor requirements accompanied by low metal recovery rates are some impediments to the large-scale application of bioleaching for low-grade ores. The current study investigates key parameters for scaling up anoxic bioleaching, which overcomes some of the above shortcomings, on polymetallic manganese nodules using soil-based manganese-reducing bacterial consortia in a stirred bioreactor. Operating conditions such as carbon source concentration and pulp density were optimized. Parameters like pH, oxidation-reduction potential (ORP), and microbial growth were monitored in the bioreactor in both stirred and non-stirred conditions. The Mn(IV) reduction and dissolution in the bioreactor was 27 (+/- 2.8)% over 30 days, which significantly enhanced to 43 (+/- 1.5)% and 42 (+/- 0.35)% in the presence of humic acid and anthraquinone sulfonic acid, respectively, in 15 days. A maximum dissolution of 21 (+/- 4.1)% Cu, 10 (+/- 3.0)% Ni, 18 (+/- 4.7)% Co and 7 (+/- 3.9)% Fe were also obtained with 100 mu M humic acid from the agitated bioreactor in 15 days. The corresponding specific glucose consumption rate per unit mass of ore was found to be 27 mg g-1 day-1, which is 10 times lower than the rates reported previously for aerobic bioleaching methods. The investigation shows that mild agitation can significantly improve the anoxic bioleaching, especially with added electron shuttles, to enable better ore-bacteria interaction and prevent ore compaction during scale-up. The pH and ORP of the system point toward a reductive dissolution of Mn by the organisms.

Metal extraction by the use of deep eutectic solvent (DES) is also called as “Solvatometallurgy” i.e. metal extraction from minerals and secondaries by using DES as prime solvent. Solvatometallurgical extraction is highly futuristic in the study as it involves nontoxic and ecofriendly solvents and comparatively more economic process flowsheet using lower water content. In this study, Cu was extracted from two different resources Cu spent catalyst and Cu concentrate by using DES. The DES mixture was obtained by mixing Choline Chloride (Quaternary Ammonium salt) with ethylene glycol (EG) at 80 °C. The leaching reaction takes place with the as obtained DES in a glass reactor. Elemental analyses of the leach liquor were carried out with an Atomic Absorption Spectrophotometer after it reacted with aqua regia to break metal-ligand complex so that metal ion will be perfectly detected by the instrument. The maximum extraction of Cu was 81.6 and 99.9 pct in 72 hour for Cu catalyst and 24 hour for Cu concentrate. Parametric variations were performed such as variation of time, temperature, ratio of EG:Choline chloride and pulp density to obtain the optimized condition for the leaching reaction. The extracted Cu from DES is taken into an aqueous system via solvent extraction with LIX. DEHPHA and Na-DEHPHA. Here the solvent extraction is organic vs organic but they are separated easily because of their density difference. The stripping of 63.63 pct was recorded for 10 pct LIX-84 and the stripping of 66.6 pct was reported for 10 pct H2SO4. The advantage of DES extraction is that it is selective towards the metal of interest and generates no effluent or sludge thus making the downstream simple and cost effective. Efforts are given to establish the reaction mechanism of the DES and the Cu containing solid phases like Cu concentrate and spent catalyst sample with the help of the result analyses of NIR and NMR. One reaction mechanism is also proposed schematically to represent the reaction mechanism.

The threats posed by heavy metal ions and antibiotics present in natural aqueous environments have been a serious cause of concern across the globe. The synchronous elimination of these contaminants through visible light responsive semiconductor mediated photocatalysis is a suitable strategy to solve this problem. However, designing proficient photocatalysts for the said purpose is a crucial task. Herein, hierarchical 3D/2D architectures of Bi4O5I2/g-C3N4 p-n type direct Z-scheme heterojunction photocatalysts (BOCNs) were fabricated by a two-step solvothermal-calcination approach. The characterisation of BOCNs by XRD, FTIR, XPS, SEM, TEM, HRTEM, LSV and MS techniques corroborated the robust heterojunction formation between Bi4O5I2 and g-C3N4. The presence of g-C3N4 and application of high treatment temperature (400 degrees C) assisted the formation of BiOC bond which is responsible for the development of an intimate interfacial interaction in BOCN. The heterostructured photocatalyst (BOCN3) demonstrated higher rate constant (k(Cr(VI)/synchronous)) of 0.068 min(-1) for Cr(VI) detoxification and that (k(TCH/synchronous)) of 0.075 min(-1) for TCH degradation synchronously with respect to the reported values. The determined rate constants are about 1.8 folds greater than those were observed in isolated systems. The expedited photocatalytic activity can be ascribed to its wide visible light response, minimum charge recombination rate and increased redox ability. These are resulted from the synergistic effect of hierarchical 3D/2D architecture construction, existence of strong BiOC interfacial bond, p-n heterojunction formation and prevalence of direct Z-scheme charge transfer principle. The synchronous elimination of Cr(VI) and TCH over BOCN3 up to the fifth consecutive cycle without any appreciable change in photoactivity signified its enhanced stability and reusability. The plausible mechanism for the spectacular photocatalytic performance of BOCN3 was proposed.

This piece of work aims to study the extraction behavior of light and heavy rare earth elements, which are often found in permanent magnets, using a mixture of tri-octyl amine and bis-(2,4,4-trimethylpentyl) phosphinic acid from a chloride medium. The study showed that the extraction efficiency of Dy(III) is more than that of Nd(III) and Pr(III). Benzene proved to be an effective diluent. Increasing the pH of the aqueous phase improved the extraction percentages, with maximum extractions of 98.4% for Dy(III), 61.2% for Nd(III), and 58.3% for Pr(III) at pH 5.04 using 0.1 mol/L of each extractant. Adding sodium chloride enhanced the extraction efficiency due to the salting-out effect. The extraction mechanism has been proposed based on the slope analysis and FTIR data. From thermodynamic variables, the process was found to be exothermic. The simulated leach liquor of NdFeB magnets showed the highest separation factors of 67.7 (Dy/Pr) and 56.9 (Dy/Nd) at pH 2.05 with 0.25 mol/L extractants. The counter-current study showed that 4.15 mg/L Dy(III) was left behind in the raffinate indicating 97.4% removal of Dy(III) in two stages at unity phase ratio. Testing with actual leach liquor from hard disk magnets revealed a preference for iron extraction, which impeded REE extraction.

Semiconductor based photocatalysis is considered as an effective and sustainable approach for the efficient treatment of effluents containing organic dyes and pharmaceuticals. Herein, visible light responsive g-C3N4/ NiFe2O4 (CN/NF) composite photocatalysts were designed by sol-gel auto-combustion assisted calcination method using ethylene glycol (EG) as a chelating agent. Bidentate nature and lower molecular weight of EG favour slow hydrolysis of Ni2+ and Fe3+ ions followed by formation of homogenous gel phase which under auto-combustion produced NF precursors. Calcination of the mixture of dicyandiamide (DCDA) and predetermined amount of NF precursors at 550 °C for 4 h resulted in the formation of CN/NF nanocomposites in which NF nanoparticles are anchored on thick plates of porous CN. The construction of CN/NF S-scheme heterojunctions was established through XPS studies and scavenging tests. The 10CN/NF nanocomposite exhibited superior photocatalytic Rhodamine B (RhB) degradation efficiency (98.6 %) which is 2.7 and 3.1 folds superior than that of pure NF and CN respectively. Additionally, the photocatalytic performance of 10CN/NF for tetracycline hydrochloride (TCH) degradation was found to be 84.32 %. The degradation efficiency was around 1.75 and 2.6 times higher than that was observed for pristine NF and CN correspondingly. The current study will bring fresh insights into the synthesis of CN/NF heterojunctions with an S-scheme charge transfer channel for the efficient treatment of waste waters containing dyes and antibiotics.

Continuous countercurrent decantation (CCD) washing is an important unit operation employed mostly in hydrometallurgical, mining, and chemical process industries. In many of the hydrometallurgical processes CCD system is used in combination with leaching circuit. It is observed that while obtaining the number of CCD stages, water and material balance the work becomes very cumbersome and time consuming. In this work simple equations are developed to overcome the above complexity of CCD system. The equations developed were utilised to find the numbers of CCD stages, the solute concentrations at various stages, final solute concentration and wash solution requirement, etc. The unreacted solid passes through subsequent stages unhindered and rejected along with reject solute solution. The equilibrium model equations can be utilised for both combined and standalone CCD circuits. Case studies are included to check the validity of the model equations under different operating conditions. The work has been carried out specifically for hydrometallurgical operations where concentrated leach solution can be generated from very lean ore.

Tellurium is used in cadmium tellurium-based solar cells. Mercury cadmium telluride is used as a sensing material for thermal imaging devices. High-purity tellurium is used in alloys for electronic applications. It is one of the important raw materials for solar energy applications. It is used as an alloying element in the production of low-carbon steel and copper alloys. Tellurium catalysts are used chiefly for the oxidation of organic compounds and as vulcanizing/accelerating agents in the processing of rubber compounds. Even though several researchers tried to recover tellurium from different raw materials, there is no attempt to develop a process flow sheet to recover tellurium from waste anode slime having a high tellurium concentration. In this study, optimum conditions were developed to recover Te and Cu from anode slime with the composition Cu: 31.8%, Te: 24.7%, and As: 0.96%. The unit operations involved are leaching, purification, and electro winning. The optimum conditions for producing Te at a recovery of 90% are found to be roasting of anode slime at 450 °C without the addition of soda ash followed by leaching in 1 M NaOH at 10% pulp density for 2 h. The purity of Te metal achieved was up to 99.99%, which could provide a sustainable energy future. The major impurities of the tellurium are observed to be in the order: Se > Sb > As > Cu.