Method For Recovery Of Metals Research Articles

Assessing metal extraction from metalliferous waste: A study using deep eutectic solvents and chelating agents vs. ethylenediaminetetraacetic acid

Conventional methods of metal recovery involving solvents have raised environmental concerns. To address these concerns and promote sustainable resource recovery, we explored the use of deep eutectic solvents (DES) and chelating agents (CA) as more environmentally friendly alternatives. Goethite and blast oxide slag dust (BOS-D) from heap piles at their respective sites and characterised via ICP-MS. The greatest extraction of critical metals was from goethite, removing 38% of all metals compared to 21% from the blast oxide slag. Among the tested CA, nitrilotriacetic acid (NTA) was the most effective, while for DES, choline chloride ethylene glycol (ChCl-EG) demonstrated superior performance in extracting metals from both blast oxide slag dust and goethite. The study further highlighted the selectivity for transition metals and metalloids was influenced by the carboxyl groups of DES. Alkaline metals and rare earth lanthanides extractions were favoured with DES due to improved mass transfer and increased denticity, respectively. In comparison to ethylenediaminetetraacetic acid (EDTA), typically used for metal extraction, CA and DES showed comparable extraction efficiency for Fe, Cu, Pb, Li, Al, Mn, and Ni. Using these greener chelators and solvents for metal extraction show significant promise in enhancing the sustainability of solvometallurgy. Additional conditions e.g., temperature and agitation combined with a cascading leaching process could further enhance metal extraction potential.

Speciation of toxic metals in metal finishing filter cake by X-ray absorption spectroscopy

The speciation of Cr, Zn, Cu and Pb in two metal finishing filter cakes (TX and ST) was investigated by X-ray absorption spectroscopy (XAS) complemented by X-ray fluorescence (XRF) and X-ray diffraction (XRD). XRF showed that concentrations of Cr, Zn, Cu and Pb were 1.4%, 0.19%, 0.20% and 0.01%, respectively, in TX, and 12.6%, 3.3%, 1.3% and 0.21% in ST. No crystalline phases were detected in TX by XRD whereas ST was dominated by calcite. Cr and Fe K edge XAS showed Cr to be trivalent and octahedrally coordinated, co-precipitated with Fe as CrxFe1-x-(oxy)hydroxides in both filter cakes. Zn, P and Ca K edge XAS showed that 2ZnCO3∙3Zn(OH)2 and Zn3(PO4)2 were the dominant zinc-containing phases, with combined tetrahedral and octahedral coordination; Zn phases were slightly more crystalline in TX than ST. Pb L3 edge X-ray absorption near edge spectroscopy (XANES) found that Pb was likely adsorbed on amorphous SiO2. Cu, Si and S K edge XAS showed that all Cu was divalent, and the dominant copper phases were found to be Cu2Cl(OH)3, Cu(OH)2 and CuSO4·5H2O for ST, whereas Cu appeared to adsorb to amorphous SiO2 for TX, which contained much less Pb. Cr is thus immobilized in the filter cakes in a phase with low solubility at environmentally feasible pH values, whereas Zn, Cu and Pb could be released when the pH decreases below 8 or above 11. These findings are significant for the development of waste management regulations and/or metal recovery methods (e.g., hydro/pyrometallurgy).

Recent chemical methods for metals recovery from printed circuit boards: A review

AbstractAs the volume of e-waste continues to rise, it is crucial to sustainably manage printed circuit boards (PCBs) and their valuable metal components. PCBs are ubiquitous in modern society, powering a variety of electronic devices. The metal resource crisis and the imperative for a low-carbon circular economy have accelerated the development of e-waste recycling technology. High-value discarded PCBs represent a vital component of e-waste. However, discarded PCBs are deemed hazardous to the ecosystem due to the presence of heavy metals and brominated organic polymers. Thus, recycling metals from discarded PCBs is not only a strategic necessity for fostering a green ecological civilisation but also a crucial guarantee for ensuring a safe supply of mineral resources. This comprehensive review gives the profound details of PCBs, and the performance of and advances in the latest chemical metal recovery methods. Reviewing the latest metal recovery processes, we explored the application of diverse leaching agents, including ionic liquids (ILs), deep eutectic solvents (DESs), organic acids and amino acids. These solvents were assessed in terms of their recovery efficiencies, and most of them demonstrated excellent leaching performance. The role of optimising leaching parameters such as concentration, oxidants, pH, particle size, solid-to-liquid ratios (S/L), temperature, and contact time is underscored, offering insights into achieving sustainable PCB recycling practices. Most of these recent leaching methods successfully extracted base metals (Cu, Fe, Zn, Sn, etc.), as well as precious metals (Au and Ag), achieving leaching efficiencies exceeding 90.0%. Interestingly, their effectiveness can compete with that of traditional hydrometallurgical methods.

An overview of metals extraction and recovery from industrial wastewater sludge

AbstractIndustrial wastewater sludge is one of the vital sources of metals, including heavy metals, valuable metals, and precise metals. Apart from metals' necessity and economic value, some are toxic and harmful to the environment. This review explores the technologies currently applied for extracting and recovering heavy metals from industrial wastewater sludge. The technologies have been explained, and the merits and demerits of methods, as reported in past investigations, have been highlighted. The salient findings of this review are that the hydrometallurgical processes using acid leaching (H2SO4, HNO3, HCl, etc.) have been considered for the metal extraction process. Metal dissolution, concentration/purification, and recovery are the main stages of hydrometallurgical processes. The selection of successive metal recovery methods depends on the concentration of metals and chemical characteristics of industrial wastewater sludge. Different metal purification and concentrations were reported, including adsorption, ion exchange solvent extraction, and so forth, while precipitation and electrodeposition were mainly applied for metal recovery from industrial wastewater sludge. In this review, the cost and economic viability of the metal recovery process are also evaluated by previous reported studies. This review may be considered a valuable source of information for environmentally friendly and cost‐effective methods for metal recovery from industrial wastewater sludge.

Architecting an Open-Source IIoT Framework for Real-Time Control and Monitoring in the Bioleaching Industry

Electronic waste (e-waste) contains toxic elements causing an important impact on environmental and human health. However, the presence of valuable metals, such as copper or gold, among others, make recycling a necessity for obtaining an alternative source of raw materials. Conventional metal recovery methods are environmentally unsound, prompting the exploration of greener alternatives like bioleaching, which utilizes the activity of microorganisms for a more sustainable recovery. However, the mechanisms involved in the process and the conditions to optimize the metabolic paths are still not completely known. Monitorization and automatization of the different stages composing the global process are crucial for advancing in the implementation of this novel technology at an industrial scale. For the first time, an open-source industrial IoT system is designed to enhance and regulate bioleaching by implementing real-time monitoring and control within the plant’s infrastructure. This system includes an Android app that displays real-time plant data from sensors and a robust server featuring a flexible application programming interface (API) for future applications. The app caters to specific needs such as remote sensor reading, actuator control, and real-time bioleaching alerts, ensuring secure access and proactive event management. By utilizing collected data, it minimizes downtime, equipment failures, and supply chain disruptions. The server maintains seamless communication with the plant controller, enabling efficient pump activation and sensor data transmission. A telegram bot demonstrates the API’s flexibility by forwarding plant alerts to users. During validation with concurrent remote user access, the application demonstrated its ability to prevent irreversible plant failures through an advanced alarm system. Ultimately, this IIoT system amplifies plant performance, safety, and efficiency by optimizing processes and decision-making capabilities. It emerges as a pivotal open-source tool, securing remote oversight and management of large-scale bioleaching plants, promising adaptability for future enhancements.

Trash to Treasure: Recovery of Trace Platinum from Industrial Process Solutions

Concerns about metal scarcity are becoming more prevalent due to the depletion of the world’s natural resources and increased demand of metal productions. Therefore, more efficient and innovative methods for metal recovery are required. Among the traditional hydrometallurgical methods [1], the electrochemical recovery of metals - like electrowinning - provide a state-of-the-art basis for sustainable metals recovery through the use of renewable electricity. In electrowinning, the metals are recovered by electrodeposition from concentrated and purified leaching solutions. Nevertheless, the process solutions in the final stages of hydrometallurgical or pyro-hydrometallurgical operations still contain precious metals Ag, Au, and platinum group metals at very low concentrations (< mg L-1 or < μg L-1). For example, platinum - a critical element in photocatalysts for the hydrogen economy, electronics and medical applications – can also be recovered from such trace concentrations to prevent both material loss and to provide additional value. Recently, electrodeposition and redox replacement (EDRR) - method has been applied for selective precious metal recovery from lower-grade raw materials-hydrometallurgical process solutions [2]. During EDRR, a sacrificial metal with less nobility is first deposited through electrodeposition, then the precious metal is recovered onto the electrode surface through RR reaction, driven by the difference in reduction potentials between the two metals. EDRR can be tailored through operational parameter selection, thereby allowing an optimized purity of recovered metals and even controllable preparation of metal coatings, nanoparticles, high-value-added functional surfaces (photocatalyst, corrosion resistant) directly from industrial process solutions [2].In the course of previous studies, it has been observed that metal reduction may also occur via aqueous reduction close to the electrode surface [3]. If actual electrodeposition of sacrificial species into metallic form is not indispensable before the metal recovery in the RR step, process with lower energy consumption and higher purity end-product may be realized via aqueous reduction (EAR). In the current study, multivalent iron was selected as reductive species during EAR-process to recover dissolved platinum. Specifically, dissolved Fe(III) in chloride-based media is first electrochemically reduced to a lower oxidation state Fe(II), then in the RR step, the produced aqueous Fe(II) species serve as reductant to trigger the consequent deposition of Pt on the electrode. As a result, the EAR method succeeded in recovering platinum on the electrode. Chloride concentration was shown to have a substantial impact on the platinum recovery, in terms of both recovery efficiency and structure of deposits, which is suggested to be derived from the Fe and Pt complexation in chloride-based media. The recovery of Pt based on EAR also varies with EAR process parameters, e.g., the applied potential and time to reduce Fe(III), or RR time. The influence of other species (concentrations) and the pH in solution were systematically studied as well, further paving the way to apply EAR method in other metal recovery system. Acknowledgements This work was supported by the Academy of Finland project EARMetal (LC, KY, ML: 339979 and LC, KY, JV: 342080). The RawMatTERS Finland Infrastructure (RAMI) funded by the Academy of Finland and based at Aalto University is also acknowledged. Reference [1] M.E. Wadsworth, J.D. Miller, Hydrometallurgical Processes. In: H.Y. Sohn, M.E. Wadsworth (Eds), Rate Processes of Extractive Metallurgy, Springer, Boston, 1979. https://doi.org/10.1007/978-1-4684-9117-3_4[2] L. Cui, K. Yliniemi, J. Vapaavuori, M. Lundström,Recent developments of electrodeposition-redox replacement in metal recovery and functional materials: A review, Chem Eng J. (2023). https://doi.org/10.1016/j.cej.2023.142737 [3] I. Korolev, S. Spathariotis, K. Yliniemi, B.P. Wilson, A.P. Abbott, M. Lundström, Mechanism of selective gold extraction from multi-metal chloride solutions by electrodeposition-redox replacement, Green Chem. 22 (2020) 3615–3625. https://doi.org/10.1039/D0GC00985G

Farklı İki Metal Grubun Geri Kazanımı İçin Gravite Ayırıcısı Tasarımı

This study, "Design of a Gravity Separator for the Recovery of Two Different Metal Groups", represents important research aiming to recover metals in a sustainable way and reduce the amount of waste. This study aims to separate metals according to their density differences. It is an effective method, especially for the separation of different metals such as copper and aluminum. Therefore, this study investigates how this technology can be used more efficiently.As a result of the literature review, existing gravity separation techniques were evaluated. This formed the basis for a new and novel gravity separator design based on existing knowledge. This design is designed to have a capacity of one ton per hour. This capacity demonstrates usability on an industrial scale. The designed separator aims to separate mixed copper and aluminum pieces and convert them into pure granule raw material.During the implementation phase, it was tested how this design would perform in the field. As a result of these tests, it is aimed to recover approximately 8760 tons of waste material annually. This makes a positive contribution to the environment by recycling large amounts of waste material. In conclusion, this study highlights an important method for sustainable recovery of metals. The effective use of gravity separation technology is of great importance in reducing the amount of waste and protecting natural resources. This study is an important step in highlighting sustainability and environmentally friendly practices.

Simple and environmentally friendly metal recovery from waste printed circuit boards by using deep eutectic solvents

Increased environmental awareness has necessitated the development of a simple and environmentally friendly method for metal recovery from waste printed circuit boards (WPCBs). Deep eutectic solvents (DESs) are environmentally friendly and non-aqueous lixiviants that can leach metal oxides to replace mineral acids. In this study, three choline chloride (ChCl)-based DESs were synthesized, using ethylene glycol, oxalic acid (OA), and glycolic acid (GA) as the hydrogen bond donors in the eutectic mixtures. The time-dependent leaching yields and saturated loading capacities of the DESs to typical metal oxides and Ag were evaluated. Considering the leaching performances, a simple and environmentally friendly method for metal recovery from WPCBs was established, based on two-stage DES leaching processes. The research object was the mixed metal powder collected from the mechanical processing of WPCBs. The results indicated that 90.35% of Zn, 87.47% of Pb, and 16.77% of Cu were removed from the mixed metal powder after calcination by leaching of the ChCl-GA DES and precipitation of the oxalic acid solution. When the residue was subjected to ChCl-OA DES leaching, Cu was recovered by diluting ChCl-OA DES with water. Specifically, 74.93% of Cu was separated in the form of CuC2O4·2H2O with a purity of >98 wt%. The Sn remaining in the aqueous solution was efficiently recovered by the addition of reduced Fe powder, and the recovery yield of Sn in the recovery product was 51.29%. Finally, the advantages of a simplified and environmentally friendly process framework, are highlighted by a comparison of the recovery strategy for WPCB proposed in this study with conventional pyro- and hydro-metallurgical approaches.

Bioleaching Techniques for Sustainable Recovery of Metals from Solid Matrices

This review paper explores the potential of bioleaching as a sustainable alternative for recovering metals from solid matrices. With over 12 billion tons of solid waste annually worldwide, bioleaching provides a promising opportunity to extract metals from solid waste, avoiding harmful chemical processes. It explains bacterial and fungal bioleaching techniques that extract copper, gold, zinc, and other metals from solid matrices. Fungal bioleaching effectively extracts a wide range of valuable metals, including nickel, vanadium, aluminium, molybdenum, cobalt, iron, manganese, silver, platinum, and palladium. The review highlights different solid matrices with metal contents that have the potential to be recovered by bioleaching, presenting promising bioprocess alternatives to current industrially available technologies for metal recovery. The optimal conditions for bioleaching, including pH, temperature, agitation–aeration, and pulp density are also discussed. The review shows that bioleaching has the potential to play a crucial role in the transition to a more sustainable and circular economy by providing an efficient, cost-effective, and environmentally friendly method for metal recovery from solid matrices.

Treatment of copper-containing leaching residue by sulfation roasting followed by acid/water leaching

This research investigates the extraction of copper from copper-containing leaching residue, which includes 33.45% of copper, 14.14% of iron, 23.87% of sulfur and trace amounts of silver and other elements. Roasting the copper-containing residue under air and oxygen flow convert sulfides into sulfate, followed by water and acid leaching to extract copper. The process parameters, including leaching temperature, sulfuric acid concentration, leaching time, solid-to liquid ratio, and agitation speed, were optimized for both water and acid leaching methods. Results showed that the maximum copper dissolution efficiency was 93.12% with water leaching, and 97.16% with acid leaching. Chemical analysis revealed that the water and acid leaching residue contained 48.13% and 31.64% of iron, respectively. This study provides valuable insights into the process optimization for copper extraction from copper-containing leaching residue, which can inform the development of more efficient and sustainable methods for metal recovery.

Enhanced Recovery of Zn from Carbonate-Type Mixed Oxidized Ore (CMO) by Combining Organic Acid Leaching with Mechanical Activation

With excessive consumption of sulfide ores, using low-grade Pb-Zn mixed ores to obtain Zn has attracted more attention. Acid leaching is an effective method for Zn recovery; however, a high concentration of inorganic acid brings severe environmental issues, including acidic wastewater, contaminated soil, etc. Compared with inorganic acid, organic acid showed lower acidity and toxicity. Herein, we applied an effective method for Zn recovery from carbonate-type Pb-Zn mixed ore (CMO), by combining organic acid leaching with mechanical activation. Among the organic acids applied (lactic, malonic, citric, amber, acetic, and tartaric one), lactic acid was selected for its high leaching efficiency. The optimum condition was identified via response surface methodology, with a lactic acid concentration of 1.15 mol/L, L/S ratio of 20, leaching time of 75 min, and temperature of 75 °C. The effect of mechanical activation on Zn leaching was further investigated. The leaching efficiency increased to 90.1% after mechanical activation, which was the highest leaching efficiency for organic acid leaching. Mineralogical characterization showed that the bulk minerals were milled into small particles while the proportion of amorphization increased. Such activation effects improved the acid-solubility of Zn speciation. This work provided a potential green method for metal recovery from low-grade sources.

Electrolyte circulation: Metal recovery from waste printed circuit boards of mobile phones by alkaline slurry electrolysis

Alkaline slurry electrolysis has been verified as an effective method for metal recovery from waste printed circuit boards (WPCBs). However, the electrolyte that remains after slurry electrolysis contains high concentrations of metal, which can cause pollution without suitable treatment. Most importantly, the metals in the electrolyte are not completely recovered, resulting in wasted resources and increased costs. Here, the feasibility of circulating this electrolyte and its effect on copper recovery, current efficiency, and purity, is discussed. We also describe in detail the migration and transformation of copper and other metals, such as nickel, zinc, and lead, during the preparation of high-purity cathode copper from mobile phone WPCBs (WPCB-MPs) using an ammonia-ammonium chloride slurry electrolysis system. Experimental results from 19 cycles of electrolyte reuse show that copper is mainly distributed in the cathode products, whereas other metals are mainly distributed in the electrolyte and anode residues. With an increase in the number of cycles, the concentration of other metals in the electrolyte gradually increased, showing metal enrichment. The current efficiency fluctuates but is usually >90%. In addition, the copper recovery rate and purity were essentially unaffected, being >99% and >99.9% for all 20 runs, respectively, and all the cathode copper foils were easily peeled off. This study demonstrated that electrolytes can be reused for metal recycling from WPCB-MPs by alkaline slurry electrolysis without decreasing Cu purity, Cu recovery rate, and current efficiency. Thus, this study provides a green and cost-effective process for recycling resources from e-waste.

Investigations into the closed-loop hydrometallurgical process for heavy metals removal and recovery from biosolids via mild acid pre-treatment

Biosolids contain heavy metals (HMs), restricting their beneficial reuse in agricultural land. However, these metals can be a valuable resource in many applications if recovered efficiently. Therefore, the removal and recovery of HMs and other limiting contaminants in biosolids without degrading the organic nutrients of the resulting treated biosolids demands holistic investigations. A closed-loop hydrometallurgical treatment process for metal removal and recovery from biosolids was developed in this study. Firstly, mild acid treatment using 3% v/v H2SO4 at 25 °C, 600 rpm for 30 min was performed in a 1 L continuous stirred tank reactor to extract common HMs (such as As, Cd, Co, Cr, Cu, Ni, Pb, and Zn) from biosolids into the aqueous phase. The effects of solids concentration and acid types on the HMs extraction efficiency were studied. Then, the primary acid leachate stream was continuously recycled for metal extraction from biosolids until the dissolved metals in the solution reached saturation concentration. After that, the dissolved metals were recovered in staged NaOH precipitation and adsorption. Low solids contents (<5% w/v) using mineral acids having pH <2 and oxidation-reduction potential (ORP) ∼500 mV (versus SHE) favoured HMs solubilisation from biosolids with an average extraction efficiency of 70%. The dissolution of ferric iron (Fe3+) by H2SO4 and subsequent in-situ formation of ferric sulfate enhanced the metal extraction strength of the spent leachate stream during recycling. However, the solids loading in each leaching process must be kept low to prevent ferric concentration build-up and precipitation as the leachate pH steadily increases above 2 during recycling. Amongst the metal recovery methods investigated, H2O2 oxidation prior to 2-stage NaOH precipitation had the highest efficiency with 75–95% HMs recovery. The clarified stream was used to neutralise the acidic treated biosolids to close the process loop. The complete process flowsheet was developed with mass balances, and the fate of nutrients (mainly C, N, and P) and major per- and polyfluoro alkyl substances (PFAS) were overviewed.

Comparison of synthetic rhamnolipids as chemical precipitants for Pb, La, and Mg

Identifying and exploiting cost-effective and green methods of metal recovery from natural and contaminated aqueous systems is widely recognized as necessary to supplement the supply of critical elements, decrease the environmental impacts associated with hardrock mining, and remediate metal-contaminated waters. This research examines a novel approach based on rhamnolipid-facilitated chemical precipitation of metals. Three techniques were assessed to remove the rhamnolipid:metal complex from solution: mixing only, and mixing following by filtration or centrifugation. Recent advances in the ability to synthetically produce rhamnolipid surfactants allowed investigation of a variety of rhamnolipid structures. Rhamnolipids differing in the length and number of hydrophobic tails were assessed to remove Pb, La, and Mg from single metal solutions. In general, removal increased with increased rhamnolipid hydrophobicity and with the addition of an active removal step (filtration or centrifugation). Filtration removed up to 96% of all metals while centrifugation removed up to 97% for Pb and La and 60% for Mg. Results suggest tailoring the rhamnolipid structure and removal methods may enable selective metal removal to achieve specific outcomes. Future studies in mixed-metal and real-world solutions will be needed to confirm the viability of these techniques in complex systems.

Interaction among Heavy Metals in Landfill Leachate and Their Effect on the Phytoremediation Process of Indian Marigold

Phytoremediation is considered an effective and economical method for metal recovery along with removing toxic chemicals from contaminated soil. The studies done so far concentrate on the factors responsible for uptake of a single heavy metal from the soil. However, in nature, pollutants are generally found as a mixture of various heavy metals. Furthermore, research related to phytoremediation of mixed contaminant sites such as landfills are focused on the selection of plants rather than heavy metal uptake pattern. Thus, it becomes important to understand how phytoremediation processes change in remediating a mixed pollutant with respect to removing single metal contamination. In the present study, the phytoremediation potential of Indian marigold is compared when the soil–metal concentration is individually spiked with Cd, Pb, Ni, and Cr salt solution against the remediation potential of marigold when the soil–metal concentration is spiked by landfill leachate (mixture of heavy metal) collected from the Gazipur landfill site, New Delhi, India. The result shows that the rate of metal accumulation is highly sensitive to metal concentration and metal interactions. When the soil–metal concentration is spiked with metal salts, their respective total uptake by marigold follows the order Cd > Pb > Cr > Ni with BCF > 1, TF > 2, and ECf > 1 for Cd and Cr making marigold a hyperaccumulator and with BCF < 1, TF > 2, and ECf < 1 showing an avoidance toward uptake of Pb and Ni. When the heavy metal accumulation pattern is studied for soil–metal concentration spiked by landfill leachate, the order of accumulation follows Cd > Cr > Pb > Ni with BCF > 1, TF > 2, and ECf > 1, and marigold is an accumulator for Cr. BCF > 1, TF < 2, and ECf < 1 stabilizes Cd and Pb add by leachate and there is no uptake of Ni after reaching a tolerance level of 555 µg/kg. The study is useful for understanding change in heavy metals uptake from heterogeneous sites for better landfill management.

Integrative application of heavy metal-resistant bacteria, moringa extracts, and nano-silicon improves spinach yield and declines its contaminant contents on a heavy metal-contaminated soil.

Microorganism-related technologies are alternative and traditional methods of metal recovery or removal. We identified and described heavy metal-resistant bacteria isolated from polluted industrial soils collected from various sites at a depth of 0-200 mm. A total of 135 isolates were screened from polluted industrial soil. The three most abundant isolate strains resistant to heavy metals were selected: Paenibacillus jamilae DSM 13815T DSM (LA22), Bacillus subtilis ssp. spizizenii DSM 15029T DSM (MA3), and Pseudomonas aeruginosa A07_08_Pudu FLR (SN36). A test was conducted to evaluate the effect of (1) isolated heavy metal-resistant bacteria (soil application), (2) a foliar spray with silicon dioxide nanoparticles (Si-NPs), and (3) moringa leaf extract (MLE) on the production, antioxidant defense, and physio-biochemical characteristics of spinach grown on heavy metal-contaminated soil. Bacteria and MLE or Si-NPs have been applied in single or combined treatments. It was revealed that single or combined additions significantly increased plant height, shoot dry and fresh weight, leaf area, number of leaves in the plant, photosynthetic pigments content, total soluble sugars, free proline, membrane stability index, ascorbic acid, relative water content, α-tocopherol, glycine betaine, glutathione, and antioxidant enzyme activities (i.e., peroxidase, glutathione reductase, catalase, superoxide dismutase, and ascorbate peroxidase) compared with the control treatment. However, applying bacteria or foliar spray with MLE or Si-NPs significantly decreased the content of contaminants in plant leaves (e.g., Fe, Mn, Zn, Pb, Cd, Ni, and Cu), malondialdehyde, electrolyte leakage, superoxide radical , and hydrogen peroxide (H2O2). Integrative additions had a more significant effect than single applications. It was suggested in our study that the integrative addition of B. subtilis and MLE as a soil application and as a foliar spray, respectively, is a critical approach to increasing spinach plant performance and reducing its contaminant content under contaminated soil conditions.

Process and mechanism of strengthening chlorination cascade recovery of valuable metals from electroplating sludge

Electroplating sludge (ES) is a kind of man-made ore-rich hazardous waste with dual characteristics of resource and hazard. In this paper, through thermodynamic calculation and comparison of the chlorine supply capacity of different chlorinating agents, NH4Cl and CaCl2 are selected as the best synergistic chlorine donors, and FeSO4•7H2O is introduced as the green strengthening agent. The results show that the decomposition products SO2 and O2 of FeSO4•7H2O at approximately 700 °C can promote the decomposition of CaCl2 to Cl2 and transform sulfur into CaSO4. The enhanced chlorination system can prolong chlorination, and realize the efficient stepwise chlorination volatilization of Ni, Cu and Cr in ES by adjusting the temperature field. The mass ratios are controlled of M(ES): M(NH4Cl): M(CaCl2) = 10:12:3, M(CaCl2): M(FeSO4•7H2O) = 1:2, and roast at 1100 °C for 90 min, Cr, Ni and Cu recovery rates reach 31.23%, 93.86% and 98.75%, respectively. The content of metals such as nickel and copper in the roasted product is significantly reduced, and the leaching toxicity reaches the standard, which can be used as a secondary resource. The stepwise separation mechanism of Cr, Ni and Cu is further explored through XRD, thermodynamic analysis, XPS, etc. The Me–O and Me–S (Me = Ni, Cu, Cr, etc.) bonds in NiO, CuO and Cr2S3 are easily destroyed by active-[Cl] in HCl and Cl2 to combine to form CrCl3, NiCl2 and CuCl3, which are gradually volatilized in steps at 500 °C, 800 °C and 900 °C, respectively. This study proposed a new chlorination system and explored the stepwise chlorination volatilization process of multi-metal, which provided a new method for metal recovery from ES and polymetallic solid waste.

The recovery of metals as high value powders and nanopowders from industrial wastewaters using potential-controlled electrolysis

The objective of the presented study was the recovery of Zn, Cr, Cu and Co in the form of powders and nanopowders from various types of industrial wastewaters. Powders and nanopowders as products of high added value find a wide applications in nanotechnology and material science and engineering. The metallic powders were obtained using potentiostatic electroreduction (potential-controlled electrolysis). The chosen method offers better control of the purity and structure of the products. The structure and size of crystallites depend on the value of electrolysis potentials and time, cathode material, concentrations of metal ions. In this investigation, the powders of different sizes ranging from 90 to 230 nm for Cr, 100–4000 nm for Zn, 25–100 nm for Co and 40–660 nm for Cu were deposited. The compositions, purity and size of the cathode deposits were confirmed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Presented metal recovery method is a promising technique for industrial application, given its simplicity, economic viability and environmental sustainability. It can be used on a wide range of solutions and help in reducing the problem of the growing amounts of industrial wastewater.

Life cycle assessment of a novel metal recovery method from co-processing of coal mine waste and low-grade printed circuit boards

A double waste stream problem arises from the increasing use of electrical and electronic equipment and their energy consumption: potentially toxic wastes from the equipment itself and potential acid mine drainage from the waste of the coal mines that provide the fuel to cover the energy demand. CEReS (Co-processing of Coal Mine & Electronic Wastes: Novel Resources for a Sustainable Future) is a novel method to co-process the coal mine and low-grade PCBs waste to reduce their environmental impacts while producing metals and other valuable products. The aim of this study is to investigate whether CEReS method is more environmentally friendly than the conventional practices of landfilling and incineration. Based on a Polish coal mine case study, our study found that the CEReS method could potentially eliminate the environmental impacts related to toxicity but increase the climate change impacts by ten times. A sensitivity analysis has shown that using a lower carbon electricity mix could reduce the climate change and fossil depletion impacts. It is also recommended to reduce water and energy requirements in some stages of the method.

Electronic waste and their leachates impact on human health and environment: Global ecological threat and management

Electronic waste is an important part of solid waste management around the world. Being a large part of the solid waste, e-waste contains numerous hazardous components in the form of halogenated compounds like polychlorinated biphenyls (PCBs), tetrabromobisphenol A (TBBPA), polybrominated biphenyl (PBB), etc. along with other toxic materials which cause an adverse impact on the plants, microbes and human beings. One of the major toxic components of e-waste are heavy metals (HMs) like As, Cr, Cd, Cu, and Hg, which needs to be handled carefully at the time of dismantling the e-wastes, being managed by informal sector in developing countries compounds the problem, also, the available disposal/treatment technologies of e-waste are inadequate, and they have a direct as well as indirect impact on human health and the environment. This review deals with the quantity of e-waste generated globally and how its different components affect important factors of the ecosystem like soil, plants, microbes, and animals, including humans. This review also deals the recovery of valuable metals using various methods. This review concludes that, there is a quintessential need to replace conventional traditional procedures with futuristic state of the art eco-friendly approaches to manage e-waste. • The e-waste production generation is expected to increase of 4%–5% annually worldwide. • Toxic effect of E-waste leachate to human health and environment is considered widely. • An environmental friendly methods have been expressed for E-wastes management. • Numerous methods for base and precious metals recovery from the e-waste are reviewed. • Biological method for recovery of metals from e-waste is most efficient and cost effective.