HDEHP Research Articles

Comediating Adsorption and Electron Transfer via Dual‐Active Site Catalyst Construction for Improving the Treatment of Extraction Wastewater

Solvent extraction is widely applied, while extraction wastewater treatment remains a huge challenge because of the stability of extractants. Heterogeneous Fenton‐like catalysis is a promising method, but the short half‐life of hydroxyl radicals (•OH) generated by hydrogen peroxide (H2O2) activation results in unsatisfactory •OH utilization and organics removal. Herein, an efficient strategy for treating extraction wastewater based on comediating adsorption and electron transfer by fluorine and nitrogen co‐doped carbon (FNC) catalyst with dual‐active site was developed. Specially, N sites adsorb organics and F sites activate H2O2, shortening the migration distance of •OH. Theoretical calculation and di(2‐ethylhexyl) phosphoric acid (D2EHPA) extraction wastewater degradation experiment showed that F site with electron acquisition can transfer electrons provided by electron‐rich D2EHPA enriched at N sites to H2O2, facilitating the continuous generation of •OH through lowering the energy barrier for H2O2 activation. As a result, 96.49% D2EHPA in simulated wastewater and 90.26% total organic carbon in real extraction wastewater were removed. Moreover, FNC catalyst exhibited excellent reusability and ionic adaptability, and can be extended to the removal of various extractants. The proposed dual‐active site catalyst provides an effective strategy for Fenton‐like reaction to treat refractory extraction wastewater, promoting sustainable development of solvent extraction industry.

Comediating Adsorption and Electron Transfer via Dual-Active Site Catalyst Construction for Improving the Treatment of Extraction Wastewater.

Solvent extraction is widely applied, while extraction wastewater treatment remains a hugechallengebecause of the stability of extractants.Heterogeneous Fenton-like catalysis is a promising method, but the short half-life of hydroxyl radicals (•OH)generated by hydrogen peroxide (H2O2)activation results in unsatisfactory •OH utilization and organics removal.Herein, an efficient strategy for treating extraction wastewater based on comediating adsorption and electron transfer by fluorine and nitrogen co-doped carbon (FNC) catalyst with dual-active site was developed. Specially, N sites adsorb organics andFsites activateH2O2, shortening the migration distanceof •OH. Theoretical calculation and di(2-ethylhexyl) phosphoric acid (D2EHPA)extraction wastewater degradation experimentshowed that F sitewith electron acquisition can transfer electrons provided by electron-rich D2EHPA enriched at N sites toH2O2,facilitating the continuous generation of •OH through lowering the energy barrier for H2O2activation.As a result, 96.49% D2EHPA in simulated wastewaterand 90.26% total organic carbonin realextraction wastewaterwere removed. Moreover, FNC catalystexhibited excellent reusability and ionic adaptability, and can be extended to the removal of various extractants. The proposed dual-active site catalyst providesan effective strategyforFenton-likereactiontotreatrefractory extraction wastewater, promotingsustainable development of solvent extraction industry.

Removal of Impurities from Nickel and Cobalt in Mixed Hydroxide Precipitate with Solvent Extraction Using Di(2-Ethylhexyl) Phosphoric Acid

ABSTRACT This study investigates the removal of major impurities, namely Fe, Al, Zn, and Mn, in a solution produced by sulfuric acid leaching of mixed hydroxide precipitate from the Ni and Co via solvent extraction using di(2-ethylhexyl) phosphoric acid (D2EHPA). The results of extraction experiments showed that the extracted Ni, Co, Fe, Al, Zn, Mn, and Mg increased as the equilibrium pH, D2EHPA concentration, and O/A ratio increased. The optimum extraction condition was achieved at a pH of 3.5, a 20% (v/v) D2EHPA concentration, and an O/A ratio of 1, with a complete (>99.9%) extraction of Al, Fe, Zn, and 97.33% Mn with co-extracted Ni and Co of 22.32% and 29.13%, respectively, in a single extraction stage. Complete Mn removal can be achieved in two extraction stages. Co-extracted Ni and Co can be scrubbed out using a mild sulfuric acid solution at a pH of 1.2 with only less than 2% of the Al, Fe, Zn, and Mn co-scrubbed. McCabe-Thiele diagrams of the scrubbing processes were constructed, and the results showed that Ni and Co can be scrubbed out using a mild acidic solution at a pH of 1.2, O/A ratio of 1, and temperature of 40°C for 10 min of mixing. Zn and Mn can be stripped completely using 0.5 M sulfuric acid solution at an O/A of 1 and temperature of 40°C for 10 min of mixing, while Fe and Al remained unstripped. Fe and Al can subsequently be stripped via reductive stripping.

Iron removal and valuable metal recovery from spent lithium-ion batteries (LIBs) using solvent extraction after bioleaching

Our study investigated the feasibility of solvent extraction for the separation of impurities, specifically aluminum (Al), copper (Cu), and iron (Fe) from simulated leachate with similar composition to real pregnant leach solution (PLS) obtained after the bioleaching of spent lithium-ion batteries (LIBs). The Fe2+ in the Fe-rich PLS was oxidized to Fe3+ by addition of H2O2. Subsequently, Fe3+, Al3+, Cu2+, and Mn2+ were extracted at pH 4.0 using 20 % di-(2-ethylhexyl) phosphoric acid (D2EHPA) as the extractant. At this pH, 99.99 % of Al3+ and Fe3+, 93 % of Cu2+, and 83 % of Mn2+ were successfully extracted. Co-extracted Co2+ was recovered through a two-stages scrubbing process, where it was replaced with Mn2+ using a MnSO4 solution at an O/A ratio of 1:1. Finally, Al3+, Cu2+, and Mn2+ were stripped with 5 M H2SO4, and 99 % Fe3+ was separated by stripping with 100 % aqua regia. Our study presents an approach for effectively separating valuable metals and impurities, particularly Fe, by optimizing the extraction, scrubbing, and stripping stages of solvent extraction for PLS treatment. Moreover, this study emphasizes the need for further research on the pre-separation of Fe and the development of novel extractants and solvents to enhance the treatment of Fe-rich PLS after bioleaching.

Ion-selective electrode based on polyurethane-immobilized di-(2-ethyl hexyl) phosphoric acid for low-concentration aqueous Pb2+ detection and quantification

This study used a polyurethane (PU)-based ion selective electrode (ISE) immobilized with di-(2-ethyl hexyl) phosphoric acid (D2EHPA) to detect and quantify Pb2+ ions at low concentrations (10−10 to 10−1 M) in aqueous solution. PU, synthesized from castor oil (Ricinus communis L.), was utilized as the ISE membrane matrix. The ISE demonstrated a sensitivity of 26.24 ± 0.12 mV/decade, a detection limit of 1.44 × 10−7 M, and a response time of 10 s. We maintained the measurement stability for up to six days of storage.The results of Pb2+ quantification produced by ISE were compared with the results using atomic absorption spectroscopy (AAS), indicating similar Pb2+ concentrations in both artificial and real wastewater samples (calculated t-value < theoretical t-value). Therefore, this ISE is suitable for detecting trace levels of Pb2+ and quantifying them with high accuracy.

The use of organophosphorus extractants as a component of hydrophobic deep eutectic solvents (HDES) for the processing of spent lithium‑iron phosphate batteries

Hydrometallurgical processes for managing industrial waste have attracted significant attention due to tightening global standards on toxic emissions. Among these processes, the use of non-volatile hydrophobic deep eutectic solvents (HDESs) has emerged as a promising approach to optimising extraction processes. In this study, HDESs incorporating tributyl phosphate (TBP) and di(2-ethylhexyl)phosphoric acid (D2EHPA) were investigated in the context of the extraction and separation of elements found in lithium‑iron phosphate batteries, including lithium, aluminium, iron and copper. The physical properties of the HDESs, such as density, viscosity and refractive index, were characterized and the interactions between their components were analysed using infrared spectroscopy. Considering the different classes of extractants represented by D2EHPA and TBP, extraction efficiency for target metals was evaluated across a range of hydrochloric acid concentrations (1–10 mol/L). Optimal conditions for re-extraction (stripping) were identified for extractant regeneration and the production of individual metal ion solutions. Results demonstrated that Fe3+ ions could be extracted with an efficiency exceeding 99% across the majority of acidity levels, while Al3+ ions exhibited similar efficiency from a pH of 1.4. In contrast, Cu2+ ions showed limited extraction (<5%) at lower pH values but the level of extraction increased to 50% at pH 1.9 and above. Leveraging these findings, a sequential extraction scheme is proposed for Al3+, Cu2+, Fe3+ and Li+ from their mixture, based on a gradual reduction in solution acidity.

Chelator-impregnated polydimethylsiloxane beads for the separation of medical radionuclides

Chelator-impregnated resins have been studied earlier for the chemical separation of elements in aqueous solutions, but issues with their chemical stability have limited their use in the separation of (medical) radionuclides from their respective irradiated targets. We developed a polydimethylsiloxane (PDMS)-based chelator-impregnated resin that showed a high chemical stability against leaching. Several different chelators were tested in this study. After impregnation of the PDMS beads with the di-2-ethylhexylphosphoric acid (D2EHPA) chelator, an in-flow separation study with various radionuclides (Y-90, La-140, and Ac-225) was conducted. These three radionuclides have potential use in nuclear medicine and a production route through irradiation of Sr-, Ba-, and Ra-targets respectively, necessitating their chemical separation. The D2EHPA-impregnated beads achieved high adsorption efficiencies of 99.89% ± 0.14%, 99.50% ± 0.10%, and 98.51% ± 0.25%, for Y-90, La-140, and Ac-225, respectively, while co-adsorption of minor amounts (<3%) of the targets were reported. These results, together with the high chemical stability of the PDMS-based resin, highlight the potential of chelator-impregnated resins in the rapidly growing field of (medical) radionuclide production.

Effect of Plasticizer Type on Polymer Inclusion Membranes Properties and Performance for Zinc Separation

AbstractThe goal of the present study is to evaluate the effect of plasticizer in PIMs properties and performance for zinc separation. Membranes were prepared by casting a solution containing poly (vinyl chloride) (PVC) as base polymer, di (2‐ethylhexyl) phosphoric acid (D2EHPA) as carrier, and 2‐nitrophenyl octyl ether (NPOE) or tris (2‐butoxyethyl) phosphate (TBEP) as plasticizers. The newly developed PIMs transported practically all ZnII ions from a feed phase at pH 5 to a 1 M H2SO4 stripping phase. The results showed that the transport flux and its efficiency depend on the chemical nature of the plasticizer. It can be perceived that NPOE (with dielectric constant of 23.1) produced the highest transport flux of zinc (J0=1.62±0.05 10−5 mol m−2 s−1). The single ion transport of zinc was significantly higher than the binary and ternary mixtures. In ternary solution, the transport efficiency for metal ions was in the order of ZnII&gt;CuII&gt;NiII. The transport efficiency of the PVC/NPOE/D2EHPA membrane remained constant until the seventh use. The findings of this work will allow the invention of advanced separation technology ensuring the sustainability of metal resources.

Optimization of rare earth magnet recovery processes using oxalic acid in precipitation stripping: Insights from experimental investigation and statistical analysis

Recycling the valuable metals found in spent permanent magnets (REPMs) poses a significant global challenge for the future. This study examines the efficiency of back extraction of rare earth elements (REEs) by oxalic acid solution from di-(2-ethylhexyl) phosphoric acid (D2EHPA) in recycling REPMs. To evaluate the efficiency of this process, several experiments were carried out using designed BOX-Behnken methodology to investigate the effects of various operational and chemical parameters, including stripping solution to loaded organic phase volume ratio (in the range of 1.0–2.0), oxalic acid concentration (ranging from 0.25 to 0.75 M), the stirring rate (ranged between 150 and 350 rpm), and stripping time (ranging from 15 to 45 min) on the REEs recovery and the purity of final production. Analysis of variance was applied to rigorously examine the results statistically. The results showed that more than 85 % of light and 80 % of heavy REEs can be recovered under optimal conditions. Moreover, the final product contained 43.5 % REEs and approximately 0.1 % iron. The stripping experiment using phosphoric acid as the reagent demonstrated ∼57 % light and ∼4 % heavy REEs recovery. Additionally, the recyclability of the organic phase showed its effective reuse for up to four cycles. This study underscores significant progress in the selective recovery of rare earth elements through a relatively straightforward process consuming mild reagents.

Extraction Strategies from Black Alloy Leachate: A Comparative Study of Solvent Extractants

Recycling spent lithium-ion batteries (LIBs) is crucial to prevent environmental pollution and recover valuable metals. Traditional methods for recycling spent LIBs include hydrometallurgy and pyrometallurgy. Among these methods, solvent extraction can selectively extract valuable metals in spent LIB leachate. Meanwhile, spent LIBs that underwent pyrometallurgical treatment generate a so-called ‘black alloy’ of Ni, Co, Cu, and so on. These elements in the black alloy need to be separated by solvent extraction and there have been few studies on extracting valuable metals from black alloy. Therefore, it is necessary to examine the extraction behavior of elements in black alloy and optimize the solvent extraction process to recover valuable metals. In this paper, four types of organic extractants are used to extract metals from simulated black alloy leachate: di-(2ethylhexyl) phosphoric acid (D2EHPA), bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex272), 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A), and neodecanoic acid (Versatic acid 10). Based on the pH isotherms, D2EHPA would be the most reasonable for Mn extraction and impurity removal. Cyanex 272 would be more suitable for Co separation than PC88A, and Versatic acid 10 is preferred for Cu extraction over other metals. In conclusion, the optimal combination of extractants is suggested for the recovery of valuable metals.

Online separation of critical rare earth elements from end-of-life permanent magnets using micro polymer inclusion beads (µPIBs)

A column filled with micro polymer inclusion beads (µPIBs) was developed and investigated for the first time. The µPIBs were composed of 60 wt% di-(2-ethyl-hexyl) phosphoric acid (D2EHPA) and 40 wt% poly(vinyl chloride) (PVC) and the column was used for the separation of ions of rare earth elements (REEs) from synthetic solutions and the digest of end-of-life (EOL) rare earth permanent magnets (REPMs). This µPIB packed column was successfully applied to separating La3+ from Gd3+, as representatives of the light and middle REEs, previously achieved by us using a polymer inclusion membrane (PIM) containing the same chemical components as the µPIBs used in this study. The results obtained demonstrated the feasibility of the µPIBs packed in a column for light and middle REE ion separation similarly to their PIM counterpart. The separation potential of the µPIB packed column was further demonstrated by the selective recovery of Nd3+ and Dy3+ from an EOL REPM digest in 2 M sulfuric acid which also contained Fe3+, Co2+, and Ni2+. Nd3+ and Dy3+ could be selectively extracted from the diluted to 0.03 M sulfuric acid digest after the addition of ascorbic acid which reduced Fe3+ to Fe2+. Nd3+ and Dy3+ were separated via selective back-extraction from the µPIB-column using 0.3 and 2 M sulfuric acid receiving solutions, respectively. Thermogravimetric analysis of the µPIBs, before and after application in the µPIB-column, indicated negligible D2EHPA loss after six processing cycles. Thus, these results demonstrated the strong potential of the proposed µPIB-column method for the sustainable recovery of REEs from electronic waste such as REPMs.

Cesium extraction from an alkali-free solution using a 4-tert-butyl-2-(α-methylbenzyl) phenol–di-(2-ethylhexyl) phosphoric acid synergistic system: A conceptual process flowsheet for separating cesium salt from salt-lake brine

Cesium is an important strategic resource, and solvent extraction is the most frequently used technology for its extraction from various minerals and brines. However, this common method faces operational and cost problems owing to large alkali consumption. A synergistic extraction system consisting of 4-tert-butyl-2-(α-methylbenzyl) phenol (t-BAMBP) and di-(2-ethylhexyl) phosphoric acid (D2EHPA) was designed and used to extract Cs+ from an alkali-free solution. The effects of variables such as: (i) pH, (ii) concentration of t-BAMBP and D2EHPA, (iii) temperature, (iv) Cs+ concentration, and (v) coexisting cations, on the Cs+ extraction performance of the synergistic system were investigated. The most suitable organic phase composition was 1.0 mol/L t-BAMBP and 0.1 mol/L D2EHPA in kerosene, and the synergistic coefficient was up to 57 at 25 °C and an organic/aqueous phase volume ratio of 1/1. The extraction sequence of cations using the t-BAMBP–D2EHPA synergistic system followed the descending order Cs+ > Rb+ > Ca2+ > K+ > Li+ > Mg2+ > Na+. The chemical formula of the extracted species was determined as [CsA(HA)(ROH)2] using the slope method. The Cs+ extraction process is an exothermic reaction with an enthalpy (ΔHo) of −55.3 kJ mol−1, confirmed by the thermodynamic study. After three-stage countercurrent extraction, the extraction efficiency of Cs+ was 92.6%, demonstrating excellent selectivity from coexisting cations. The t-BAMBP–D2EHPA synergistic system showed outstanding economic and environmental advantages and a good application prospect to develop a conceptual process flowsheet for extraction with this system and stripping with HCl to separate cesium salt from salt-lake brine.

Efficient separation and comprehensive recovery of rare earth, bismuth and iron by one-step extraction and two-step stripping

A route was proposed to separate bismuth, iron, and rare earth elements from a solution containing nickel and magnesium through one-step extraction and two-step stripping. Firstly, saponified di-(2-ethylhexyl) phosphoric acid (D2EHPA) was used as the extractant to separate target elements. RE(III), Bi(III), and Fe(III) could be separated from Ni(II) and Mg(II), with extraction efficiencies of more than 99 %. Secondly, RE(III), Bi(III), and Fe(III) were stripped selectively by nitric acid and oxalic acid, respectively. Subsequently, the iron present in the oxalic acid stripping solution was treated under UV irradiation for 15 min to recover oxalic acid and obtain the ferrous oxalate product. The stripping efficiencies of RE(III), Bi(III), and Fe(III) were up to 100 % for four-stage countercurrent stripping, and the recovery rates of RE(III) and Bi(III) were 97.3 % and 99.2 %. The purities of nitrate rare earth enrichment solution, bismuth oxalate and ferrous oxalate were 99.7 %, 98.4 % and 99.5 %, respectively. In addition, the extraction dynamic demonstrated that the double salt precipitation was not observed during the extraction when the extraction time exceeded 7 min and the extraction mechanism was analyzed using the slope method. This process shortens steps, and is more efficient to separate RE(III), Bi(III), and Fe(III) from the mixed solution containing Ni(II) and Mg(II), which has a prospective industrial application.

PVDF-HFP-based polymer inclusion membrane functionalized with D2EHPA for the selective extraction of bismuth(III) from sulfate media

This study is the first application of a PVDF-HFP-based polymer inclusion membrane incorporating the poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and di(2-ethylhexyl)phosphoric acid (D2EHPA) as the base polymer and extractant for the extraction of bismuth(III), respectively. It is demonstrated that the PIM comprised of 60 wt% PVDF-HFP and 40 wt% D2EHPA is the most effective in the extraction of bismuth(III) from feed solution containing 20 mg L−1 bismuth(III) and 0.2 mol L−1 sulfate adjusted to pH 1.4. The extracted bismuth(III) ions are back-extracted quantitatively to the receiving solution containing 1 mol L−1 sulfuric acid. The stoichiometry experiments reveal that the Bi: D2EHPA ratio in the bismuth(III) extracted complex is 1:6, and D2EHPA is dimer. Moreover, it is shown that the studied PIM has high selectivity in the extraction of bismuth(III) over other interfering ions such as Mo(VI), Cr(III), Al(III), Fe(III), Ni(II), Zn(II), Cd(II), Co(II), Cu(II), and Mn(II). The interference of Fe(III) is also eliminated by masking with fluoride, leading finally to a nearly pure extraction of bismuth(III).

Extraction Equilibria in the Samarium Nitrate–Nitric Acid–Water–Di(2-ethylhexyl)phosphoric Acid–Organic Diluent System

Extraction Equilibria in the Samarium Nitrate–Nitric Acid–Water–Di(2-ethylhexyl)phosphoric Acid–Organic Diluent System

Preconcentrating extractive polymeric network in paper-based sensing of copper

The concept of using an extractive polymeric sensing network on a paper-based substrate for the pretreatment of samples in the colorimetric analysis of heavy metals is demonstrated with the determination of Cu2+ in aqueous samples. The newly developed paper-based device combines the advantages of both liquid–liquid extraction-based separation and the analytical capabilities of microfluidic paper-based analytical devices (μPADs). The preconcentrating extractive polymeric network composed of 53.5 wt% poly(vinyl chloride) (PVC), 45 wt% extractant (di-(2-ethylhexyl)phosphoric acid (D2EHPA)) and 1.5 wt% dye (1-(2′-pyridylazo)-2-naphthol (PAN)), coated on filter paper, shows good water-wicking properties, allowing the transmission of high sample volumes. This results in significant analyte preconcentration. The extractant (D2EHPA) selectively binds Fe3+ and Zn2+ which otherwise will compete with Cu2+ in its colour reaction with PAN at the chosen pH of 3.0. The device’s capacity to process higher sample volumes resulting in higher sensitivity is increased by the integration of several filter paper absorption layers. The optimized device is characterized by a limit of detection (LOD) for tap and environmental waters of 3.4 and 9.6 µg/L, respectively; stability of 51 days if stored in a refrigerator; and total analysis time (from sample insertion to colour detection) of less than 5 min.

Removal of Co(II) and various metal ions from the residue of the zinc plant through solvent extraction using both acid and neutral extractants

AbstractThe recovery of cobalt from secondary sources is a crucial issue in technology development, particularly for its numerous applications in various industries. Solvent extraction has proven an effective method for metallic ions separation from secondary sources. The main goal of this work was to study the separation of metals by solvent extraction technique from zinc plant leach waste. Initially, several extractants, including Cyanex 272, Cyanex 301, LIX 5640 H, Alamine 336, and tri‐n‐octylamine (TOA), were tested to treat the leach solution. It was discovered that the saponified extractant di‐(2‐ethylhexyl) phosphoric acid (D2EHPA) (10%) + tri‐n‐butyl phosphate (TBP) (10%) effectively eliminated interfering elements such as manganese, zinc, and iron, with extraction efficiencies of 95%, 98%, and 99.9%, respectively. To increase the concentration of cobalt in the purified solution, the cobalt recovery step was performed using various acids on the loaded organic phase. The best outcome was achieved using ammonium sulphate salt (1 M), which recovered about 50% of the cobalt present in the organic phase. The recovered cobalt was then subjected to the electrowinning process to produce cobalt metal of high purity. A cathodic current density of 100 A/m2 was determined to be the optimal current for the electrolyte solution. Lastly, scanning electron microscope (SEM) and X‐ray fluorescence (XRF) analyses were carried out to examine the structure and purity of the resulting metallic cobalt, which was found to have a purity of 99.5%.

In-syringe homogeneous liquid-phase microextraction followed by filtration-based phase separation for on-site extraction of chloroanilines from water samples.

This study introduces a new in-syringe homogeneous liquid-phase microextraction method for the rapid on-site extraction of chloroanilines from water samples. Extraction was performed using a plastic syringe, eliminating the use of any electrical power source. Di-(2-ethylhexyl) phosphoric acid (DEHPA) served as the extractant. The process initially involved dissolving DEHPA in an alkaline solution to obtain a homogeneous solution. Subsequently, the sodium salt of DEHPA was precipitated by salting-out, and the resulting heterogeneous mixture was filtered using a syringe filter. The precipitate containing the analytes was then dissolved in methanol for analysis by high-performance liquid chromatography. Under optimal conditions, extraction recovery for chloroanilines ranged from 26% to 71%. Method linearity was evaluated within a concentration range of 1.0-100µg/L, resulting in coefficients of determination exceeding 0.9987 for all analytes. Method detection limits ranged from 0.28 to 0.41µg/L. Intra and inter-day precision values were below 9.5% and 10.8%, respectively. The developed method was applied to determine chloroanilines in real waters, yielding acceptable recoveries ranging from 80% to 109% for spiked tap, rain, and stream waters. Additionally, the method was successfully employed for on-site extraction of target contaminants, demonstrating no statistically significant differences compared to laboratory results.

Separation of heavy metals from dilute solutions using D2EHPA carrier fixed onto the outer surface of coaxially electrospun core-sheath fibers

In this study, porous membranes based on core-sheath fibers covered with fixed carriers were prepared by coaxial electrospinning for the separation of heavy metal ions from dilute solutions. Cellulose triacetate (CTA) and an extractant di(2-ethylhexyl)phosphoric acid (D2EHPA) were mixed to prepare a sheath-layer solution and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was adopted to prepare a core-layer solution for electrospinning. The morphological and textural properties as well as chemical composition of the fabricated core-sheath fibers were first analyzed to determine the optimal preparation conditions. The ability and selectivity of such fixed D2EHPA carriers were evaluated via the adsorption of Zn2+, Cu2+, and Ni2+ ions from dilute solutions. Dynamic tests revealed that the adsorption of metal ions on the core-sheath fibrous membrane made of 52 wt% PVDF-HFP, 18 wt% D2EHPA, and 30 wt% CTA (on a dry basis) reached equilibrium within 8 h. As expected, all adsorption isotherms at specific equilibrium pH values were well described by the Langmuir equation, ascribed to the chemical reaction nature between metal ions and D2EHPA carrier. The crossflow permeation-adsorption tests of a multi-metal solution in a total recycling mode revealed the adsorption selectivity of Zn2+ over Cu2+ and Ni2+, as observed in conventional liquid–liquid extraction. Four repeated adsorption-regeneration experiments revealed an adsorption efficiency beyond 95 % relative to the first route, demonstrating the satisfactory reusability and stability of the as-prepared core-sheath fibrous membranes for this purpose.

High-efficiency recovery of valuable metals from spent lithium-ion batteries: Optimization of SO2 pressure leaching and selective extraction of trace impurities

The recovery of valuable metals from spent lithium-ion batteries (LIBs) is crucial for environmental protection and resource optimization. In the traditional recovery process of spent LIBs, the leaching of high-valence metals has the problems of high cost and limited reagent utilization, and some valuable metals are lost in the subsequent purification process of the leaching solution. To reduce the cost of reagents, this study proposes the use of low-cost SO2 as a reagent combined with pressure leaching to efficiently recover high-valence metals from delithiated materials of spent LIBs, while selective solvent extraction is used to remove trace impurities in the leaching solution to avoid the loss of valuable metals. Experimental results demonstrated that by optimizing the conditions to 0.25 MPa SO2 partial pressure and 60 min reaction time at 70 °C, the leaching efficiencies for Ni, Co, and Mn reached 99.6%, 99.3%, and 99.6%, respectively. The kinetic study indicated that the leaching process was diffusion-controlled. Furthermore, the delithiated materials were used to completely utilize the residual SO2 in the solution to obtain a high concentration Ni–Co–Mn rich solution. Subsequently, Fe and Al impurities were deeply removed through a synergistic extraction of Di-2-ethylhexyl phosphoric acid (D2EHPA) and tributyl phosphate (TBP) without loss of valuable metals, achieving a high-purity Ni–Co–Mn solution. The process developed based on this work has the characteristics of environmental friendliness, high valuable metal recovery, and high product purity, providing a reference technical method for the synergistic treatment of waste SO2 flue gas with spent LIBs and the deep purification of impurities in spent LIBs.