Separation Of Metals Research Articles

Coupling electrokinetic technique with hydrothermal carbonization for phosphorus-enriched hydrochar production and heavy metal separation from sewage sludge

Hydrothermal carbonization is a promising treatment technology for wet organic solid wastes, due to its energy-efficient production of functionalized carbonaceous materials. However, the usage of sewage sludge (SS) derived hydrochar as phosphorus (P) fertilizer for agricultural soil is inhibited by the presence of heavy metals (HMs). Appropriate HM removal technology is required prior to its land application. In this study, an innovative FeCl3-assisted electrokinetic technique coupling with hydrothermal carbonization (FEK–HTC) is proposed to produce SS hydrochars with reduced HM content and increased P-retention. FEK–HTC treatment showed synergistic effects in terms of P retention and HM content reduction (56–64 % for Ni, Cu, and Zn). Furthermore, the toxicity of the remaining HMs was dramatically reduced, e.g., by 39.35 % in the case of Zn. Additionally, FEK–HTC transformed P species in hydrochars into highly bio-available form. Electrokinetic treatment resulted in decreased pH values of SS feedstock and promoted the solubilization and erosion of Ca-associated P, resulting in higher non-apatite inorganic phosphorus contents (12.47 to 23.19 mg·g−1) compared to hydrochars from untreated sludge. The P migration patterns during the FEK-HTC treatment were assessed based on the combined result of chemical extraction, 31P NMR, X-ray absorption near edge structure (XANES), and diffusive gradients in thin film (DGT). DGT analysis showed that the addition of treated hydrochars greatly increased the available P content in the soil. The results provide new insights into applying FEK-HTC technique for SS management.

Sequential separation of critical metals from lithium-ion batteries based on deep eutectic solvent and electrodeposition

The rise and development of electric vehicles have brought much attention to the recycling of lithium-ion batteries (LIBs). However, the recovery of critical metals from LiNixCoyMn1−x−yO2 (NCM) is a challenge, especially for the nickel and cobalt, which have similar chemical properties. Here, a novel ternary deep eutectic solvent (DES) composed of choline chloride, ethylene glycol, and tartaric acid was proposed. Our protocol of DES synthesis, nickel separation, and leaching of cobalt and manganese were integrated into one step, which significantly simplified the recovery process. The crystallization occurring during DES leaching was subjected to detailed investigation. The lithium, nickel, and cobalt were sequentially separated as Li2CO3, NiO, and Co(OH)2 by anterior formic acid leaching and posterior electrodeposition. After electrodeposition, DES was reused. This work provides new ideas for the sequential separation of critical metals from NCM and has great application prospects.

A trifecta membrane modified by multifunctional superhydrophilic coating for Oil/Water separation and simultaneous absorption of dyes and heavy metal

Adsorption and separation are the most important chemical engineering processes for wastewater treatment. Exerting microfiltration membranes as the central separation technology and decorating them with absorption property, forming absorptive membranes, result in the separation and purification of diverse wastewaters in an energy-efficient manner. Herein, a versatile polyanionic coating with superhydrophilicity/underwater superoleophobicity, superior anti-oil-fouling, and efficient charges is acquired through mussel-inspired co-deposition, followed by b-PEI functionalization, N-alkylation, and anionization. Thanks to the superhydrophilicity/underwater superoleophobicity, the as-prepared microfiltration membrane achieves selective separation of oil/water emulsions. Meanwhile, the functional membranes exhibited excellent selective and efficient adsorption capacity for organic dyes and heavy metal ions due to the abundant surface charges. Interestingly, benefiting from superhydrophilicity and considerable surface charges, the as-designed microfiltration membrane can realize selective and efficient simultaneous adsorption and separation of wastewaters with complicated components, including oil/water emulsions, organic dyes, and heavy metal ions by the concept of “achieving three things at one stroke”. Such a versatile and feasible strategy could pave a new path for constructing multifunctional membranes for complex wastewater treatment and purification.

Application of slags for the production of resource‐efficient paving stones

AbstractIn a recent research project under the lead of the Fraunhofer Institute for Building Physics IBP, gravel and sand within a mixture of paving stones were replaced with LD converter slag and blast furnace slag for 50 wt. % and 100 wt. % to produce resource‐efficient concrete components. For this purpose, first, the dry processing of the slags including metal separation and crushing was carried out. In the next step, the particle size distributions of slags using sieve analysis were determined. Finally, the mix designs were set based on the optimum combination of different size fractions of slags. This combination was determined in a way to lead to an almost identical grading curve as that of the original formulation. Splitting tensile strengths of the obtained samples were measured after 14 days of curing under a humidity of 95%. Several paving stone specimens containing slags showed higher splitting tensile strengths than that of the reference sample. Similar results were observed for industrially produced paving stones which demonstrates the successful transfer of the laboratory mixes to the industrial plant.

Pre-treatment for the separation of actinide and noble metals from high-level radioactive waste to improve the vitrification process and performance

Pre-treatment for the separation of actinide and noble metals from high-level radioactive waste to improve the vitrification process and performance

Designing Low-Cost, Green, and Recyclable Deep Eutectic Solvents for Selective Separation and Recovery of Valuable Metals from Spent Li-Ion Batteries

Designing Low-Cost, Green, and Recyclable Deep Eutectic Solvents for Selective Separation and Recovery of Valuable Metals from Spent Li-Ion Batteries

Carbothermal treatment of municipal solid waste incineration fly ash: Purification and valuable elements extraction

Thermal separation of heavy metals from municipal solid waste incineration fly ash (MSWI FA) is a promising approach for both fly ash purification and heavy metal recovery. However, its commercial viability is hindered by excessive energy consumption. In this study, we introduce carbothermal reduction for MSWI FA treatment as an innovative strategy to enhance heavy metal volatilization and reduce the required heating temperature. By incorporating carbon (FA/Carbon = 1:0.2), the volatilization fractions of Pb, Cd and Zn reached 96.5 %, 100 %, and 63.9 %, respectively, when subjected to 900 °C for 2 h. Remarkably, these volatilization amount surpassed the volatilization fractions attained when raw fly ash (RFA) was independently calcined at 1000 °C for 2 h: Pb (90.2 %), Cd (92.9 %) and Zn (30.2 %). Conversely, Cu volatilization was impeded by carbon inclusion. Comparable trends were shown in washing fly ash (WFA). Notably, concentrated carbothermal reduction led to substantial concentrations of Pb (2.5–7.1 %) and Zn (4.9–20.7 %), rendering them amenable for recycling through metallurgical routes. Intriguingly, higher carbon content (FA/Carbon = 1:0.3) hindered rather than enhanced heavy metal volatilization from RFA. We found that condensation of NaCl and KCl occurred in carbon pores, causing the formation of molten eutectic which trapped the heavy metals at high temperatures. Therefore, more carbon showed more enhancement of heavy metal volatilization from WFA which was free of NaCl and KCl. Ultimately, two comprehensive pathways for the resourceful utilization of fly ash based on carbon thermal reduction were proposed and compared. This study demonstrates carbothermal reduction as an effective approach for simultaneous purification and metal recovery of MSWI FA, exhibiting promising potential for industrial application.

Sequential Recovery of Critical Metals from Leached Liquor of Processed Spent Lithium-Ion Batteries

The processing and extraction of critical metals from black mass is important to battery recycling. Separation and recovery of critical metals (Co, Ni, Li, and Mn) from other metal impurities must yield purified metal salts, while avoiding substantial losses of critical metals. Solvent extraction in batch experiments were conducted using mixed metal sulphates obtained from the leach liquor obtained from spent and shredded lithium-ion batteries. Selective extraction of Mn2+, Fe3+, Al3+ and Cu2+ from simulated and real leached mixed metals solution was carried out using di-2-ethylhexylphophoric acid (D2EPHA) and Cyanex-272 at varying pH. Further experiments with the preferred extractant (D2EPHA) were performed under different conditions: changing the concentration of extractant, organic to aqueous ratio, and varying the diluents. At optimum conditions (40% v/v D2EPHA in kerosene, pH 2.5, O:A = 1:1, 25 °C, and 20 min), 85% Mn2+, 98% Al3+, 100% Fe3+, and 43% Cu2+ were extracted with losses of only trace amounts (<5.0%) of Co2+, Ni2+, and Li+. The order of extraction efficiency for the diluents was found to be kerosene > Exxal-10 >>> dichloromethane (CH2Cl2) > toluene. Four stages of stripping of metals loaded on D2EPHA were performed as co-extracted metal impurities were selectively stripped, and a purified MnSO4 solution was produced. Spent extractant was regenerated after Fe3+ and Al3+ were completely stripped using 1.0 M oxalic acid (C2H2O4).

Insight into adsorption of Pb(II) with wild resistant bacteria TJ6 immobilized on biochar composite: Roles of bacterial cell and biochar

Microbial immobilization is a new strategy for bio-remediation of heavy metals. However, information regarding immobilization of wild resistant bacteria onto biochar for heavy metal separation is limited. This study proposed the use of wild-resistant bacteria TJ6 in combination with biochar produced from agricultural waste (BC-TJ6) for Pb removal and investigated the associated mechanisms using Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Compared with the theoretical adsorption capacity according to the linear combination calculating by the mass ratio and adsorption capacity of individual component in the composite material, the actual adsorption capacity of BC-TJ6 for Pb(II) was increased by 73.54%. Specifically, the bridge between the bacteria and biochar of Pb(II) may explain the higher observed adsorption capacity of BC-TJ6 compared to theoretical values. EDS analysis based on electron micrograph showed that Pb(II) adsorbed onto TJ6 strain was 0.48%, while that onto biochar component was 0.14%. It indicated that the resistant bacteria contributed more to the adsorption of Pb(II) in BC-TJ6 composites. The FT-IR analysis suggested that the amide, carboxyl, and hydroxyl groups on the surface of the composite were involved in the adsorption of Pb(II). Further, XPS analysis demonstrated that Pb-O (42.12%) and Pb-OOC (27.6%) were the main Pb-molecular structures bound to the surface of the composite. This study is significant for improving the understanding of biochar-wild resistant bacterial combinations for heavy metal adsorption, and can provide guidance for the use of biochar-microbial remediation of heavy metal pollution.

Green and efficient coordination of Ti(IV) with bisamide solvent

Titanium(Ti) is known as a strategic metal due to its excellent physical and chemical properties. Ti based materials are widely used in many fields, such as aerospace, biomedical, and photovoltaic materials. Since the metal smelting industry is often accompanied by high pollution, deep eutectic solvent, as a new type of environmentally friendly solvent, is gradually being widely used in the field of metal separation and purification. Through the transformation from non-ionic organic deep eutectic solvents (DESs-5) to inorganic deep eutectic solvents (DESs-M), the efficient coordination of Ti(IV) in acidic chloride medium was achieved. Under the optimal condition, over 95% of Ti(IV) in aqueous solution can be coordinated into DESs in a single stage, which can be used for the separation and purification of Ti(IV). The formation mechanism of DESs-5 was revealed by the quantum chemistry method and the lowest energy mechanism in the conversion reaction process was revealed by frontier molecular orbital (FMO) theory. The thermodynamic and kinetic processes of the conversion reaction were analyzed, which provided important research data for the construction of DESs-based Ti(IV) separation and purification system.

Reduction and reconstruction of vanadium-containing steel slag at high temperature

The effective recovery of metallic iron and vanadium from steel slag and ensuring the gelling properties of the residual slag after metal separation are crucial for their high-value-added utilisation. In this study, we established suitable process conditions for high-temperature reduction and reconstruction using the Si/Al ratio as an adjustment parameter and employing rice husk ash, SiO2, and Al2O3 as the adjustment materials. The influence of the reconstructed steel slag composition and structure on the iron reduction rate and vanadium migration was investigated. Additionally, we tested the compressive strength of the cement slurry at different times to compare the gelling performance of the tailings after iron reduction from the Vanadium-containing steel slag.The results showed that the high-temperature reduction method effectively reduced metallic iron and vanadium in the steel slag. The iron reduction rate reached as high as 98.53%, and inert components such as the CaO-FeO-MgO-MnO solid solution (RO) phase, C2F, and Fe3O4 in the original steel slag could be effectively reconstructed to form a glass-phase structure with certain gelling properties. Moreover, the content of the glass phase remained stable above 90%. For the same temperature, the liquid viscosity of the reconstructed steel slag increased, and after cooling, the glass-phase content decreased with decreasing Si/Al ratio. This resulted in an increase in the amount of crystalline-phase minerals such as Ca3Mg(SiO4)2, Ca2Al2SiO7, and C2S. The iron reduction rate generally exhibited a downward trend, and the change in the vanadium content was consistent with the iron reduction rate. Following the reduction and reconstruction of iron separation, the gelling properties of the vanadium-containing steel slag improved, with a 28-day strength that was 64.26% higher than that of the original steel slag.

Phosphorous extraction and heavy metal separation from sewage sludge ash by two-compartment electrodialysis in an upscaled tube reactor

Two-compartment electrodialytic extraction (2C-ED) is a one-step process for the simultaneous phosphorous extraction and separation of heavy metals from sewage sludge ash (SSA). The process is driven by an applied electric DC field, which can be supplied from renewable sources. The proof-of-concept of the method was conducted in small laboratory cells; however, upscaling to a continuous 2C-ED process, which additionally can treat SSA suspensions at a low liquid-to-solid (L:S) ratio, requires a new design. This paper presents such a new design. In principle, ED consists of two compartments separated by a cation exchange membrane. One compartment contains a suspension of SSA in water and the anode. A cathode is placed in the other compartment. Electrolysis at the anode acidifies the suspension causing the dissolution of phosphorous and heavy metals. The heavy metals are separated from the suspension by electromigration into the catholyte, whereas the dissolved phosphorous remains in the dispersion solution. In the new design, the SSA was suspended in a tube-shaped reactor with the cation exchange membrane covering the outside. The reactor was placed in a container with the catholyte. Periodically turning off the reactor kept SSA in suspension even at a low L:S ratio without corners and pockets where the SSA otherwise tends to settle. Five 2C-ED experiments were conducted with 1.5 to 3 kg SSA at varying currents and durations. Up to 89% P was extracted. The extracted P was concentrated in the dispersion solution of the SSA suspension, where the obtained P-related concentrations of heavy metals were far below the limiting values for spreading on agricultural land. The experiments underlined that treating the SSA in a suspension with a low L:S ratio is advantageous. A comparison to previous laboratory experiments in small cells treating 50 g SSA shows a significantly more efficient use of the applied current in the new reactor setup. Thus, the new reactor design for 2C-ED fulfilled the set criteria for the operation and did additionally result in a higher efficiency than the laboratory setups, i.e., the design can be the first step towards an upscaling.

Glass phase extraction for one-step separation and recovery of strategic metals from spent hydrofining catalysts

Spent hydrofining/selective catalytic reduction catalysts generated during the production of ultra-low-sulfur/nitrogen fuel are considered to be hazardous wastes. Furthermore, the sustainable supply of critical metal resources such as molybdenum (Mo), tungsten (W), nickel (Ni) and vanadium (V), which are present in high concentrations in spent catalysts, is challenged by the climate emergency, ore depletion and inefficient technologies for separating metals. Here, glass phase extraction is proposed as a novel approach for simultaneously separating metals and obtaining recovered products from spent hydrofining catalysts in one step. By constructing a glass network structure that satisfied a stable coordination environment for the target metal ions, 99.82 % of the Mo6+ was “melt-melt” separated with the glass phase as Na2MoO4, while the extraction efficiencies of Ni2+ and Al3+ were >99.16 %. The separation factors βMo/Ni and βMo/Al were as high as 65812.95 and 71944.85, respectively. The obtained results verify this method as a valuable synthetic route for refractory metal salts and transition metal ion-doped glass–ceramic materials, enhancing the prospect of achieving full-component resource recovery from hazardous wastes.

One-step selective separation and efficient recovery of valuable metals from spent lithium batteries by phosphoric acid-based deep eutectic solvent

With more and more lithium-ion batteries (LIBs) being put into production and application, precious metals such as lithium and cobalt are scarce, so it is imminent to recover various strategic metal resources from spent LIBs. Meanwhile, the complex and difficult problem of separating and recovering metals from leaching solutions has been an urgent question that needs to be resolved. In this work, a phosphoric acid-based deep eutectic solvent (DES) was developed for extracting metals from spent LIBs and one-step selectively separating and efficiently recovering transition metal. The prepared DES shows excellent extraction performance for Li (100%) and Co (92.8%) at 100 °C. In addition, the extraction system can effectively separate and precipitate Co through its own components, avoiding the introduction of new precipitants and the destruction of the original composition structure of DES. This also contributes to the good cycle stability of the extraction system with excellent extraction performance for Li (94.3%) and Co (80.8%) after 5 cycles. This work proposes a green method for one-step selectively separating and recovering valuable metals from spent LIBs.

Ultrasonic pretreatment-solvent extraction process for separating zinc from pickling waste liquid

Solvent extraction is the most important method for non-ferrous metals extraction and separation. In this work, solvent extraction of zinc from pickling waste liquid is investigated by using di(l-methyl heptyl) methyl phosphate (P350) diluted in sulfonated kerosene. Introduction of ultrasonic enhanced reduction of Fe3+ in the pretreatment stage of pickling waste liquid. The effect of ultrasonic time on the reduction process of Fe3+ is studied. Compared with traditional restoration, the required time for reduction is greatly shortened. The functional relationship of organic phase composition, concentration of extractant, phase contacts time and phase ratio function in single-stage extraction is studied. When concentration of extractant is 25 %, phase ratio is 4:1, the contact time is 15 min and the single-stage extraction efficiency of Zn2+ can reach 80.8 %. The extraction efficiency of Zn2+ reaches 99 % through three-stage countercurrent recovery. When O/A is 1:2, 1.6 mol/L HCl is used as the stripping agent and the stripping efficiency of P350 can reach 90.4 %. In addition, extraction stoichiometry is determined by slope analysis and extraction mechanism is analyzed by FT-IR and mass spectrometry. Overall, this work provides a new solution in the extraction of zinc from pickling waste liquid.

Recent Advances in the Selective Transport and Recovery of Metal Ions using Polymer Inclusion Membranes

AbstractPolymer inclusion membranes (PIMs) have gained significant attention in the field of metal separation and recovery due to their high selectivity, long service life, high stability, flexible design and low cost. Over the past 10 years, interest around PIMs has increased considerably; hence, the number of research papers has grown exponentially. This review provides the preparation methods and composition of PIMs, presents an overview of studies on PIMs reported since 2012, and discusses the relationship between the physicochemical properties of different types of membrane components and the microstructure, selectivity, transport performance and stability of prepared PIMs. This review also elucidates the metal transport mechanism at the interface and interior of PIMs and summarizes the modification and separation intensification methods of PIMs. Additionally, the structure and stability of PIM relative to other liquid membranes are also discussed. Finally, the existing challenges and perspectives of PIMs in the field of metal separation and recovery are proposed and highlighted. Notably, the need for highly selective and low‐cost carriers, a deeper understanding of membrane microstructure and separation mechanisms, and strategies for promoting widespread adoption of polymer inclusion membrane‐electrodialysis technology deserve particular consideration, which are of guiding significance for accelerating the industrialization process of PIMs.

Selective Recovery of Copper from the Mixed Metals Leach Liquor of E-Waste Materials by Ion-Exchange: Batch and Column Study

Recovery of metals from e-waste forms a major focus of circular economy thinking and aligns well with the Sustainable Development Goals (SDG). While hydrometallurgical extraction from electronic printed circuit boards (PCBs) is well established, the separation of metals from the leach liquors, which are complex mixtures, remains a challenge. To achieve selective separation, ion exchange resins with chelating functional groups were employed in the present study. Batch and column studies for selective recovery of Cu2+ from a given mixed metals leach solution were conducted using Dowex M4195 resin, and both the adsorption isotherm and kinetics were studied. The process involves three major steps: selective recovery of Cu2+ by M4195 at low pH and elution with H2SO4; sorption of Ni2+ from the raffinate by Dowex M4195 at pH 2 and removal of Fe3+ from raffinate. The batch experimental results showed appreciable and selective recovery of copper (51.1%) at pH 0.7 and 40.0% Ni2+ was sorbed from raffinate at pH 2.0 with co-adsorption of Fe3+ as impurity. The batch adsorption data could be fitted with both Langmuir and Freundlich isotherms and exhibited pseudo-second-order kinetics. Column studies agreed with the Yoon–Nelson model and indicated that Cu2+ break-through time in the column decreased with an increase in flowrate from 3.0 to 10.0 min/mL and decreased in sorption capacity, while it was delayed with increased bed heights from 20 to 30 mm. Complete elution of Ni2+ was obtained with 2.0 M H2SO4 after selective elution of trace impurities with dilute HCl. Iron in the raffinate was removed via the addition of Ca (OH)2 at pH 4.0 leaving Zn-Al in the solution.

Hydroformylation of olefins over a novel active rhodium catalyst supported on a melamine–cyanuric acid co-crystal

Hydroformylation, or oxo synthesis, is one of the most important industrial petrochemical processes involving homogeneous catalysts. The development of efficient and stable phosphorus-free heterogeneous catalytic systems for this process is of great interest because it can solve the problem of separation and recycling of expensive metals and reduce the amount of phosphorus-containing waste. Macromolecular compounds containing triazine rings can be promising candidates for supports for the stabilization of metal nanoparticles and subsequent use in heterogeneous catalytic reactions. Herein, it was shown that the interaction of cyanuric chloride with melamine produces cyanuric acid–melamine (CAM) co-crystal, which was used as a support for stabilizing rhodium nanoparticles. The obtained catalyst (CAM/Rh) exhibits high activity and stability in the hydroformylation of olefins of various structures. After completion of the reaction, the catalyst is easily separated from the reaction mixture and can be used repeatedly with virtually no loss of activity.

Super concentrated HCl in a deep eutectic solvent as media for the integrated leaching and separation of metals from end-of-life lithium-ion batteries

Recycling spent lithium-ion batteries is vital to ensure the recovery of added-value resources and minimize environmental impact. Herein, an integrated and efficient process is developed for metal recovery from spent cathode powder combining both leaching and transition metal separation in one step. A hydrophobic deep eutectic solvent (DES) is proposed as a HCl super concentrator for the one-pot leaching of cathodes from spent lithium-ion batteries and simultaneous Ni(II) precipitation. The DES composed of decanoic acid and trioctylphosphine oxide can super concentrate HCl, 2.2-folds more than the aqueous limit of 37 wt%, whilst being thermally and chemically stable under leaching conditions up to 373 K. The proposed leaching process can quantitatively extract Co(II), Mn(II) and Cu(II) from spent cathodes of laptop batteries whilst only extracting 10 % of Ni(II). The latter could be easily recovered as NiCl2·2H2O with 99 % purity through the manipulation of the coordination environment afforded by the DES relative to aqueous media. Key leaching parameters were the HCl:metal molar ratio and temperature, both having a significant impact on the leaching efficiency and its selectivity. Metal recovery was accomplished after stripping of the loaded DES solution via a straightforward sequential precipitation process, with 99 % Co(II) and 98 % Mn(II) being precipitated with 95 % and 81 % purity, respectively. The reported system presents a better atom economy compared to other DES and conventional inorganic acids, providing a new mild approach for the simultaneous leaching and separation of metals from lithium-ion batteries.

Zwitterionic cyclodextrin membrane with uniform subnanometre pores for high-efficient heavy metal ions removal

Polymer nanofiltration (NF) membranes have been widely applied in the desalination, resource substances purification and separation, and wastewater treatment. Nevertheless, direct construction of subnanometre channel polymer membranes for achieving high-efficient metal ions separation is still challenging because of the complicated membrane preparation and difficultly manipulating the membrane pore-size in sub-nanometer. Herein, we exploited a novel subnanometre channel membrane with zwitterionic β-cyclodextrins (ZCDs) by interfacial polymerization. Wherein ZCDs act as building blocks with hydrophobic inner subnanometre cavities and hydrophilic outer rims, allowing for simultaneously improved water permeability and metal ions selectivity. By modulating the zwitterionic monomer grafting ratio of ZCDs and their loading content in the membrane, the ZCDM membrane exhibits high water permeance (J = 21.7 L m−2 h−1∙bar−1) and heavy metal ions rejection, e.g., RCr3+ = 99.8%, RFe3+ = 98.9%, respectively, these values outperform the state-of-the-art NF membranes. Moreover, the ZCDM membrane has good stability and anti-fouling/-bacterial properties, e.g., the water flux recovery ratio and anti-bacterial ratio is >97% and >99%, in the long-term running process. This work offers a feasible strategy for constructing polymer membranes with uniform subnanometre pore, and demonstrates their potential for the heavy metal separation and wastewater treatment.