Metal Leaching Research Articles

Stabilization of waste foundry sand with alkali-activated binder: Mechanical behavior, microstructure and leaching

This study evaluates the stabilization of waste foundry sand (WFS) using an alkali-activated binder (AAB) produced from rice husk ash, hydrated eggshell lime, and sodium hydroxide. Mechanical properties, leaching behavior, and microstructure were assessed. The material’s durability was investigated, and the impact of wetting-drying cycles on mechanical strength and metal leaching was analyzed. The stabilized WFS fulfilled the requirements for unconfined compressive strength (qu) and accumulated loss of mass (ALM), making it suitable for use in pavement layers. Wetting-drying cycles did not significantly affect strength, and leached metal concentrations remained below toxic limits.

Assessing the complexation of dissolved organic matter with heavy metals (Cu2+, Pb2+) in leachate from an old Japanese landfill site using fluorescence quenching.

Dissolved organic matter (DOM) in landfill leachate impacts the toxicity, bioavailability, and migration of heavy metals. The present study investigated the complexation of heavy metals (Cu2+ and Pb2+) with DOM from two landfill leachate samples, representing an old landfill site containing incineration residues and incombustible waste. The logarithms of the stability constant (log KM) and percentage of complexed fluorophores were calculated using both the Ryan-Weber non-linear model and the modified Stern-Volmer model, yielding good agreement. The log KM values (at pH = 6.0 ± 0.1) calculated using both methods for the two sampling points were 5.02-5.13 and 4.85-5.11 for Cu2+-DOM complexation, and 5.01-5.13 and 4.46-4.87 for Pb2+-DOM complexation, respectively. Log KM was slightly higher for binding of DOM with Cu2+ than Pb2+, and the quenching degree was stronger for complexation with Cu2+ (28.5-30.6% and 38.0-45.9%) than Pb2+ (6.5-7.1% and 10.0-15.4%) in both leachate samples. While log KM values were similar, differences in the contributions of functional groups and molecular composition led to varying degrees of quenching. This study reveals the potential for heavy metal binding by DOM in landfill leachate with a unique solid waste composition and emphasizes variations in fluorescence quenching between Cu2+ and Pb2+ despite similar log KM levels. These findings may be useful for assessing heavy metal behavior in landfill leachate and its impacts on the surrounding environment.

The Effect of CaO in the Immobilization of Cd2+ and Pb2+ in Fly Ash-Based Geopolymer

The use of geopolymers for the solidification/stabilization (S/S) of municipal solid waste incineration fly ash (MSWI FA) is promising because the Cao in MSWI FA can provide an alkaline environment to facilitate geopolymer reactions and help to form the gel phase in the solidified body. This study investigated the role of CaO in MSWI FA in immobilizing common heavy metals, especially Cd2+ and Pb2+. Tests were performed to evaluate the effect of CaO on the unconfined compressive strength (UCS) of the polymer and the leaching of heavy metals. The findings revealed that as the CaO content increased, the UCS of the geopolymer samples also rose, reaching a maximum 28-day UCS of 24.8 MPa at a CaO content of 31.5%. Additionally, higher CaO levels resulted in lower leaching concentrations of heavy metals in the stabilized material. When the CaO level is 32%, the levels of heavy metals that leach out are very low, with Pb2+ at 0. 02 mg/L and Cd2+ at 0. 01 mg/L, achieving a stabilization rate of over 93.6% for these ions. Moreover, the geopolymer’s characteristics were analyzed by XRD, FTIR, and SEM, and the immobilization mechanisms of Cd2+ and Pb2+ were identified as gelation, physical encapsulation, and chemical substitution.

Iron-cobalt loading carbon nitride bimetallic catalyst activates peroxymonosulfate for bisphenol A degradation

In order to reduce metal leaching loss and carbon emissions, an active Peroxymonosulfate (PMS) catalyst (Fe/Co–CN) was prepared using a one-step thermal polycondensation method for the efficient treatment of wastewater containing bisphenol A (BPA). Fe/Co–CN has a low metal leaching (＜1 mg/L) and has good catalytic degradation performance for BPA. The degradation efficiency was 90.7% in 5 min and ∼100% in 10 min, which is much higher than single metal-loaded Fe–CN (77.2%) and Co–CN (73.2%). Nonradical species dominated by 1O2 and high-valent species were the main reactive oxygen species that degraded BPA in the Fe/Co–CN/PMS system. By strictly controlling the energy consumption during the synthesis and application of Fe/Co–CN, lower carbon emissions have been achieved than most catalysts reported. This achievement is of great significance for applying advanced oxidation methods to treat organic micro-pollutants and provides reference for the calculation of PMS catalysts carbon emissions.

Enhanced oil recovery and mitigating challenges in sandstone oil reservoirs employing EDTA chelating agent/ seawater flooding

While low salinity water (LSW) holds promise for improving oil recovery, its implementation is comparatively costly due to the substantial volumes of fresh water required to dilute seawater (SW). Additionally, concerns arise regarding potential issues related to LSW, including fines migration in sandstone reservoirs and scale formation in carbonate reservoirs. Chelating agents can be introduced into undiluted SW to bind with metal ions, thereby lowering its salinity. This approach mimics the behavior of LSW injection while overcoming associated challenges. This study involves measuring oil/injected solution interfacial tension (IFT), evaluating sandstone surface wettability alteration, along with conducting different sand pack flooding scenarios using Ethylenediaminetetraacetic acid (EDTA) chelating agent. The aim was to comprehend the EDTA oil recovery mechanisms and determine the optimal concentration of EDTA that minimizes chemical consumption while maximizing oil recovery. The findings indicated that incorporating 5 wt% EDTA into SW significantly reduced IFT from 29.52 mN/m to 4.75 mN/m, making the oil nearly miscible in the solution. Moreover, wettability tests confirmed that a minimum EDTA concentration of 5 wt% is required to shift wettability from oil-wet to strongly water-wet conditions. Sand pack flooding experiments, on the other hand, further demonstrated that this optimized fluid system can potentially recover an additional 16.1 % of oil following SW flooding. Finally, inductively coupled plasma (ICP) analysis revealed a notable increase in metal ion concentration during EDTA flooding, indicating enhanced leaching of metals from the sandstone surface and improved wettability characteristics.

Improving the Carbonation of Steel Slags Through Concurrent Wet Milling

This work studies mineral carbonation of steel slags with the aim to reduce the amount of slag that is landfilled. Besides permanently storing carbon dioxide (CO2), carbonating the slags can improve their quality for use in beneficial applications and reduces the leaching of harmful heavy metals. In order to intensify the mineral carbonation process, mechanical activation is used to improve both the carbonation kinetics and yield. The milling is performed in a planetary ball mill which allows for high-intensity grinding, resulting in a fast reduction of the particle size and quick amorphization and disturbance of the crystal structure, allowing high reaction rates to be achieved. The effects of the three main processing parameters of a planetary ball mill—bead-to-powder ratio R\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$R$$\\end{document}, bead size D\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D$$\\end{document} and milling speed S\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$S$$\\end{document}—are investigated. Under optimal conditions, more than 50% of the maximum CO2 uptake is achieved in only 6 min, representing a very significant improvement over regular slurry carbonation. Quantitative XRD allows to identify the reactivity of the different crystalline phases present in the slag under different milling conditions. With the help of a mass balance, the formation of an inert outer layer consisting of silica (SiO2) is confirmed. This explains both the shell diffusion mechanism controlling the carbonation reaction and the total conversion being limited to 50–60%.Graphical

Introducing and Boosting Oxygen Vacancies within CoMn2O4 by Loading on Planar Clay Minerals for Efficient Peroxymonosulfate Activation.

CoMn2O4 (CMO) has been recognized as an effective peroxymonosulfate (PMS) activator; however, it still shows disadvantages such as limited reactive sites and metal leakage. Herein, an effective and environmentally friendly composite catalyst, CMO/Kln, was synthesized by anchoring CMO on kaolinite (Kln), a natural clay mineral with a special lamellar structure, to activate peroxymonosulfate (PMS) for the degradation of residue pharmaceuticals in water. The abundant hydroxyl groups located on the surface of Kln helped induce rich oxygen vacancies (OVs) into composite CMO/Kln, which not only acted as additional active sites but also accelerated working efficiency. In addition, compared with bare CMO, CMO/Kln showed lower crystallinity, and the adoption of the Kln substrate contributed to its structural stability with lower metal leaching after three rounds of reaction. The universal applicability of CMO/Kln was also verified by using three other pharmaceuticals as probes. This work shed light on the adoption of natural clay minerals in modifying CMO catalysts with promoted catalytic activity for the efficient and eco-friendly remediation of pharmaceuticals in wastewater.

LaCoO3/Graphene Catalysts As a Novel Catalyst for Peroxymonosulfate Activation to Degrade Aquatic Organic Pollutants: A Singlet Oxygen-Dominated Nonradical Pathway

Trace organic pollutants including pharmaceuticals, industrial chemicals, pesticides, and personal care items pose considerable risks to the environment and human health due to their enduring nature, toxicity, and tendency to accumulate in biological systems [1,2]. In addressing this, sulfate radical-based advanced oxidation processes have emerged as highly promising advanced oxidation process methods for water and wastewater treatment in the past decade. Recently, transition metal-based perovskites like LaCoO3 nanoparticles have gained attention in sulfate radical-based advanced oxidation processes due to their structural and compositional flexibility, strong electronic conductivity, and ability to create oxygen vacancies [3]. However, their practical application is hindered by metal leaching during wastewater treatment. Additionally, the robust and scalable synthesis of stable perovskite-based catalysts with large surface areas is crucial for their practical implementation in wastewater treatment but has been rarely achieved so far.In this study, we developed a cost-effective and scalable approach to produce novel LaCoO3/graphene nanocomposites for eliminating organic pollutants from wastewater. These newly developed catalysts demonstrated outstanding catalytic degradation (> 99%) of diclofenac, metoprolol, carbamazepine, and bisphenol A at a high concentration (40 mg/l) in less than 10 minutes in the peroxymonosulfate activation system, with a respective mineralization of 57%, 55%, 61%, and 62%. This improved performance compared to LaCoO3 nanoparticles is attributed to the nanocomposite's abundant oxygen vacancies, synergistic effects between LaCoO3 and graphene, and its larger surface area. More importantly, the LaCoO3/graphene nanocomposites showed good catalytic performance over a broad range of pH (from 3 to 11) and exhibited excellent reusability with consistent catalytic activity. Moreover, their catalytic efficacy remained largely unaffected in samples of drinking water and tap water, presenting high resistance to co-existing ions and NOM, proving the potential of LaCoO3/graphene materials for practical application in real wastewater treatment systems.The fabrication of LaCoO3/graphene composites effectively prevents cobalt leaching and increases the content of Co2+ in the structure, resulting in significantly higher catalytic activity than that of pure LaCoO3. Experiments involving radical quenching and electron paramagnetic resonance revealed the involvement of both radical (SO4 •–, •OH and O2 •–) and non-radical pathways (1O2) in pollutant degradation, with the 1O2 radical playing a predominant role in the oxidation of the pollutant. The relative contributions of •OH, SO4 •–, and 1O2/O2 •– were determined to be 13.4%, 32.6%, and 54% for bisphenol A removal, respectively. Overall, our findings demonstrate the potential utilization of the LaCoO3/graphene system for peroxymonosulfate activation in environmental remediation. REFERENCES: [1] A. Asghar, M. Hammad, K. Kerpen, F. Niemann, A.K. Al-Kamal, D. Segets, H. Wiggers, T.C. Schmidt, Ozonation of carbamazepine in the presence of sulfur-dopped graphene: Effect of process parameters and formation of main transformation products, Sci. Total Environ. 864 (2023) 161079. https://doi.org/https://doi.org/10.1016/j.scitotenv.2022.161079.[2] M. Hammad, P. Fortugno, S. Hardt, C. Kim, S. Salamon, T.C. Schmidt, H. Wende, C. Schulz, H. Wiggers, Large-scale synthesis of iron oxide/graphene hybrid materials as highly efficient photo-Fenton catalyst for water remediation, Environ. Technol. Innov. 21 (2021) 101239. https://doi.org/https://doi.org/10.1016/j.eti.2020.101239.[3] M. Hammad, B. Alkan, A.K. Al-kamal, C. Kim, M.Y. Ali, S. Angel, H.T.A. Wiedemann, D. Klippert, T.C. Schmidt, C.W.M. Kay, H. Wiggers, Enhanced heterogeneous activation of peroxymonosulfate by Ruddlesden-Popper-type La2CoO4+δ nanoparticles for bisphenol A degradation, Chem. Eng. J. 429 (2022) 131447. https://doi.org/https://doi.org/10.1016/j.cej.2021.131447.

Separation of Lithium over Magnesium, Sodium, and Calcium By Electrodialysis Using Commercial Membranes

Lithium is considered a critical raw material worldwide due to the growing market for electric vehicles. Due to the risk of supply interruption in the short and medium term, alternative sources of lithium are being explored for battery supply. Among these, salt-lake brines have become a key supply because their abundance represents about 59% of lithium resources 1. A secondary source in the medium term is the recycling of spent Li-ion batteries by hydrometallurgical processes 2,3. Together, recovering lithium from brine and recycling can supply the demand for transport electrification. Conventional lithium extraction techniques from both brine and battery recycling face the challenge of selective separation over contaminants and low extraction efficiencies 4,5.As an alternative, electrodialysis (ED) is an important selective separation technique with high selectivity, productivity, and less consumption of chemical reagents under energy consumption. This electrochemical membrane separation process uses an electric field inducing anion and cation transport across alternating anion and cation exchange membranes. While standard electrodialysis can be used to desalinate water and generate more concentrated brine), selective electrodialysis processes that up-concentrate a specific ion from a mixed salt solution are less developed. Our goal with this work is to evaluate the effect of common ions on lithium separation by ED using three different commercial membranes. The experiments were carried out in a 4-chamber reactor where the feed solutions consisted of equimolar chloride salts of lithium and either nickel (representing battery recycling), magnesium, sodium, or calcium (representing brine). Anolyte, receiving, and catholyte chambers (Figure 1) contained 1.0 M H2SO4.Here, we present the results in terms of cation permselectivity, productivity, and energy consumption using three different commercial membranes for the cation exchange membrane in the ED setup: a standard cation exchange membrane (CXM-200), a monovalent cation exchange membrane (CXP-S) and a nanofiltration membrane (NF-90). The performance of each membrane was tested under varying applied current densities to assess the impact of operating conditions on ion transport. Results have demonstrated monovalent cationic membranes are strongly selective for lithium over magnesium and nickel, achieving selectivity of 43 and 57, respectively. The increase in current density from 2.8mA/cm² to 11.5mA/cm² also increased the fluxes of lithium and co-ions by the monovalent membrane, consequently decreasing the selectivity from 56.7 to 2.4. In addition, nickel precipitates in the feed chamber as the current density increases from 2.8mA/cm² to 5.7mA/cm². We then translate these results into a process model for upscaling the ED reactor, considering the species transport rate through the reactor chambers and selectivity for lithium. Keywords: battery recycling; brine; electrochemical membrane separation; critical raw materials.Figure 1: ED reactor used for lithium selective separation by commercial membranes References (1) Fuentealba, D.; Flores-Fernández, C.; Troncoso, E.; Estay, H. Technological Tendencies for Lithium Production from Salt Lake Brines: Progress and Research Gaps to Move towards More Sustainable Processes. Resources Policy 2023, 83 (January). https://doi.org/10.1016/j.resourpol.2023.103572.(2) Guimarães, L. F.; Botelho Junior, A. B.; Espinosa, D. C. R. Sulfuric Acid Leaching of Metals from Waste Li-Ion Batteries without Using Reducing Agent. Miner Eng 2022, 183 (May), 107597. https://doi.org/10.1016/j.mineng.2022.107597.(3) Martins, L. S.; Rovani, S.; Botelho Junior, A. B.; Romano Espinosa, D. C. Sustainable Approach for Critical Metals Recovery through Hydrometallurgical Processing of Spent Batteries Using Organic Acids. Ind Eng Chem Res 2023. https://doi.org/10.1021/acs.iecr.3c03048.(4) Asadi Dalini, E.; Karimi, G.; Zandevakili, S. Treatment of Valuable Metals from Leaching Solution of Spent Lithium-Ion Batteries. Miner Eng 2021, 173 (September), 107226. https://doi.org/10.1016/j.mineng.2021.107226.(5) Xu, S.; Song, J.; Bi, Q.; Chen, Q.; Zhang, W. M.; Qian, Z.; Zhang, L.; Xu, S.; Tang, N.; He, T. Extraction of Lithium from Chinese Salt-Lake Brines by Membranes: Design and Practice. J Memb Sci 2021, 635 (May), 119441. https://doi.org/10.1016/j.memsci.2021.119441. Figure 1

Electrofiltration-Enabled Nitrate Reduction Reactivity of Carbon Nanotube Electrified Membrane for Drinking Water Treatment

Electrocatalytic nitrate reduction could enable nitrate removal in drinking water without generating concentrated waste streams. However, current processes heavily rely upon metal catalysts with high activity to achieve sufficient nitrate removal, which increases treatment costs and can inevitably lead to leaching of metals into treated water. In this study, we elucidate how electrified filtration enables sufficient nitrate conversion to meet drinking water standards in metal-free defective CNTs by tunable matching of mass transport and reaction timescales. The metal-free carbon nanotube (CNT)-based electrified membrane (EM) was employed as a porous flow-through cathode to decrease the diffusion boundary layer. Computational fluid dynamics simulations revealed that the flow-through mode mitigates diffusion limitations to enhance overall reaction activity, as compared to the conventional flow-by mode at the same flow rate. Additionally, the nitrate reduction rate could be tuned by controlling the nitrate advection rate using permeate flux (0 to 60 L h-1 m-2). A maximum removal efficiency of 86.9% was reached when the mass transport rate matched the reaction rate across a range of applied potentials. Furthermore, defects in CNTs were identified as the catalytic active sites. We employed density functional theory and molecular dynamics simulations to gain insight into CNT defect-catalyzed nitrate reduction under electrofiltration. Finally, the long-term stability, tolerance of environmental interferences, and sufficient nitrate removal and N2 selectivity to meet drinking water standards were demonstrated in synthetic surface water, suggesting that the CNT-EM and flow-through reactor may provide a promising solution for decentralized nitrate destruction in drinking water.

Synergistic photocatalytic degradation of ciprofloxacin under natural sunlight using hot dip galvanization and medical incineration waste residues

To improve the photodegradation capacity, for the first time, a simple yet efficient photocatalyst was prepared by solely employing hot dip galvanization waste (GW) and fly ash (FA) disposed from medical waste incinerators. Impressively, the as-synthesized photocatalyst (GW-FA) in the ratio 3:1 displayed an outstanding ciprofloxacin degradation efficiency of 98.3% under natural sunlight within 60 min and possessed superior reusability. Herein, adjusting the amount of GW evidenced effective tuning of the electronic band structure and increased active sites. Detailed microscopic morphology, chemical structure, magnetic, and optical properties of GW-FA were studied by UV-DRS, FESEM-EDX, HRTEM, XRD, XPS, ESR, VSM, and AFM, which confirmed the successful fabrication of GW-FA and their outstanding ability to reduce the recombination rate. Besides, the effects of crucial experimental parameters (concentration, pH, and photocatalyst loading) on ciprofloxacin degradation were examined using RSM-BBD. Further, OH• was manifested to be the main active species for the photodegradation of ciprofloxacin. Eventually, GC-MS analysis was employed to deduce plausible photodegradation pathways, and ICP-AES analysis proved that the concentration of leached heavy metals was lower than that of the standard limits for irrigation water. This work establishes a new route for effectively reutilizing waste generated from medical waste incinerators and galvanization industries as a photocatalyst, which otherwise would be disposed in landfills.

Natural sea water and artificial sea water are not equivalent in plastic leachate contamination studies.

Plastic contamination is one of the concerns of our age. With more than 150 million tons of plastic floating in the oceans, and a further 8 million tons arriving to the water each year, in recent times the scientific community has been studying the effects these plastics have on sea life both in the field and with experimental approaches. Laboratory based studies have been using both natural sea water and artificial sea water for testing various aspects of plastic contamination, including the study of chemicals leached from the plastic particles to the water. We set out to test this equivalence, looking at the leaching of heavy metals form plastic particles. We obtained leachates of polyvinyl chloride plastic pre-production nurdles both in natural and artificial sea water and determined the elements in excess from untreated water by Inductively coupled plasma - optical emission spectrometry. We then used these different leachates to assess developmental success in the tunicate Ciona intestinalis by treating fertilised eggs through their development to hatched larvae. Here we report that chemical analysis of polyvinyl chloride plastic pre-production pellet leachates shows a different composition in natural and artificial sea water. We find that the zinc leaching from the plastic particles is up to five times higher in natural seawater than in artificial seawater, and this can have an effect in the toxicological studies derived. Indeed, we observe different effects in the development of C. intestinalis when using leachates in natural or artificial sea water. We also observe that not all artificial sea waters are suitable for studying the development of the tunicate C. intestinalis. Our results show that, at least in this case, both types of water are not equivalent to produce plastic leachaetes and suggest that precaution should be taken when conclusions are derived from results obtained in artificial sea water.

Investigation of the effect of re-refined engine oil bottom on asphalt mixture performance and ecological implications

ABSTRACT This study explores the use of re-refined engine oil bottom (REOB) as an alternative to bitumen in asphalt mixtures for flexible pavement structures. REOB is considered due to its low cost, availability, large production volume, and eco-friendliness. This paper investigates the effects of adding 5, 9, and 14 wt% of REOB to neat bitumen on the asphalt mixture’s characteristics, mechanical behaviour, and ecological implications. The findings reveal significant reductions in indirect tensile strength by up to 51%, moisture resistance by up to 17%, rutting resistance by up to 79%, and cracking resistance at intermediate and low temperatures, especially when 14 wt% of REOB is added. While the heavy metal concentrations in both bitumen and REOB exceed permissible limits, the leached metal concentrations from the asphalt mixture remain within the safe range. Despite the potential environmental benefits of using REOB, the economic evaluations suggest that incorporating REOB into asphalt mixtures slightly increases the construction cost. Therefore, careful economic consideration should be performed for each project.

Evaluating the performance of citric acid and maleic acid for mixed-acid leaching of critical metals from spent lithium-ion batteries

Evaluating the performance of citric acid and maleic acid for mixed-acid leaching of critical metals from spent lithium-ion batteries

Tetracycline degradation by peroxydisulfate activated with the composite material of biochar and cobalt-modified carbon nitride: Efficiency, stability, and degradation pathway

In recent years, non-homogeneous peroxydisulfate (PDS) activation for organic pollutant degradation has gained interest. Nonetheless, PDS activation using transition metal and carbon catalysts faces challenges such as metal leaching and inadequate catalytic performance. Herein, biochar-loaded cobalt-modified carbon nitride composite material (BC@CN-Co) was synthesized and employed as an activator for PDS activation. The outcomes suggested that the degradation efficiency of tetracycline (TC) could reach 82 % within 360 min under the optimized condition (TC = 5 mg/L, BC@CN-Co = 1 g/L, PDS = 2 mM, nature pH, T = 25℃), with corresponding apparent rate constant (Kobs) of 0.00375 min−1, which was approximately 5.5 and 2.0 times that of the biochar/PDS (0.00068 min−1) and cobalt-modified carbon nitride/PDS (0.00178 min−1) systems, respectively. BC@CN-Co exhibits excellent degradation of TC within a pH range of 3–7, with Cl-, NO3-, H2PO4-, and HA having little effect on TC degradation. Mechanistic experiments confirmed that the non-radical pathway mediated by singlet oxygen (1O2) and electron transfer plays an important role in TC degradation in the BC@CN-Co/PDS system. Furthermore, BC@CN-Co could efficiently reduce the leaching of Co ions to prevent metal pollution. This study provides an alternative PDS activator for the degradation of antibiotics in wastewater.

Mass balance and economic study of a treatment chain for nickel, cobalt and rare earth elements recovery from Ni-MH batteries

ABSTRACT The aim of this project is to develop and evaluate the economic performance of a complete process for recovering nickel, cobalt, and rare earths (REEs) from nickel metal hydride (Ni-MH) battery waste. The main elements contained in the battery powder are Ni (523 g/kg), La (58 g/kg), Co (39 g/kg), Zn (21 g/kg), Nd (19 g/kg), Sm (19 g/kg) and Ce (14 g/kg). Metal leaching was carried out with 2 M sulfuric acid, solubilising 100% of Ni, 93% of Co and 94% of REEs. Rare earths were precipitated with NaOH, then purified after resolubilization in nitric acid. Solvent extraction with bis(2-ethylhexyl) phosphoric acid (D2EHPA) followed by bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272) was used to separate Ni and Co. At the end of the process, REEs, nickel, and cobalt were recovered as oxides after precipitation as oxalates. The REE, nickel and cobalt oxides obtained have purities of 97.6%, 97.2% and 93.2% respectively. A techno-economic study was carried out using SuperPro Designer software. In this scenario, plant capacity was set at 1.0 t of used battery powder per hour for an operating period of 8 h/d and 250 days per year. The total investment was estimated at $26.9 million, with a payback period of 1.58 years. For a 15-year life, the net present value of this project is estimated at $95.9 million, with an interest rate of 7%. The internal rate of return is estimated at 46.1%, which is considered acceptable and economically viable.

Effect of in situ CO2 mixing of cement paste on the leachability of hexavalent chromium (Cr(VI))

In situ CO2 mixing technology is a potential technology for permanently sequestering CO2 during concrete manufacturing processes. Although it has been approved as a promising carbon capture and utilisation (CCU) method, its effect on the leachability of heavy metals from cementitious compounds has not yet been studied. This study focuses on the effect of in situ CO2 mixing of cement paste on the leaching of hexavalent chromium (Cr(VI)). The tank leaching test of the CO2 mixing cement specimen resulted in a Cr(VI) cumulative leaching of 0.614 mg/m2 in 28 d, which is ten times lower than that of the control mixing specimens. The results in thermogravimetric analysis indicated that a relatively significant amount of CrO42− is immobilised as CaCrO4 during the CO2-mixing, and a higher Cr–O extension is observed in the Fourier transform infrared spectra. Furthermore, a portion of the monocarboaluminate is inferred from microstructural analyses to incorporate CrO42− ions. These results demonstrate that in situ CO2 mixing is beneficial not only in reducing CO2 emissions, but also in controlling the leaching of toxic substances.

Utilization of cow bone waste and calcium oxide for the solidification and stabilization of MSWI fly ash: Towards sustainable practices

The quest for sustainable waste management practices has catalysed the development of innovative approaches to transform waste into resourceful products. This study explores the effectiveness of cow bone waste and calcium oxide (CaO) as agents in the stabilization/solidification (S/S) process of Municipal Solid Waste Incineration (MSWI) fly ash derived from two distinct cities employing both grate-type and circulating fluidized bed incinerators in China. Employing a robust experimental framework, the research evaluated the stabilization efficacy for heavy metals, monitored the progression of pH, and quantified the compressive strength of the treated MSWI fly ash. Moreover, it conducted risk assessment and economic analyses. Incorporating CBW and CaO into the MSWI fly ash from grate-type incinerators significantly enhanced the Pb stabilization efficiency, achieving up to 99.7 % when adding 31 % CBW and 7 % CaO. This treatment resulted in the leaching of other heavy metals, which were also below the standard landfill limits. In the circulating fluidized bed incinerator fly ash, the leaching concentrations of heavy metals in the treated samples were reduced by up to 98.6 % for Cd and 64.4 % for Ni.Additionally, an increase in CaO content was found to substantially improve the compressive strength of the solidified samples across all tested curing periods (7, 14, and 28 days). The optimal compressive strength result, observed at 28 days, reached 1.2 MPa, compared to the raw fly ash, which exhibited only 0.77 MPa when adding just 9 % CaO. This highlights CaO's critical role in enhancing the mechanical integrity of the treated MSWI fly ash. The study concludes that strategically calibrated ratios of cow bone waste and CaO attenuate the environmental hazard presented by MSWI fly ash and bolster its mechanical attributes, thereby repurposing the waste into a viable material for construction.

Palladium fabricated on Fe3O4 as an organic-inorganic hybrid nanocatalyst for the Suzuki and Stille coupling reactions

The Fe3O4@L-Threonine-Pd complex, comprising palladium supported on modified Fe3O4 magnetic nanoparticles (MNPs), has been documented for its use in Stille and Suzuki coupling reactions. The catalyst's environmental friendliness was assessed through a range of techniques including vibrating sample magnetometry (VSM), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma (ICP), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), energy dispersive X-ray photoelectron spectroscopy (XPS), and X-ray spectroscopy (EDS). Using an external magnet, it is easy to separate nanoparticles from the mixture. The nanocatalyst underwent Metal leaching and heterogeneity testing using the ICP-OES technique, demonstrating its ability to be recovered and reused multiple times without a significant loss of catalytic efficiency or palladium leaching.

Engineering Single‐Atom Catalysts on Conjugated Porphyrin Polymer Photocatalysts via E‐Waste for Sustainable Photocatalysis

AbstractThis study presents a surface engineering strategy utilizing electronic waste (e‐waste) to incorporate single‐atom catalysts on conjugated polymers. Employing a conjugated porphyrin polymeric photocatalyst, gold single‐atom‐site catalysts are successfully introduced using the acidic metal leachates from e‐waste, where metal speciation and composition are regulated during the metal loading processes. The resulting photocatalyst with gold single atoms demonstrates a remarkable hydrogen peroxide (H2O2) selectivity of up to 97.56%, yielding a pure H2O2 solution at 73.3 µm h−1 under white LED illumination. The produced H2O2 is activated to •OH radicals on the same polymer with mixed gold and iron atoms, enabling a photo‐Fenton reaction and the complete degradation of toxic microcystin‐LR within 10 min under visible light. This study highlights the universal applicability of the metal mining strategy in various photoreactions. It is believed that this discovery pioneers sustainable photocatalysis, allowing the tuning of reactivity and selectivity on photocatalytic surfaces using metal waste.