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In electroplating sludge, iron (Fe) and aluminum (Al) are common impurities that need to be separated before recycling valuable heavy metals. However, the traditional Fe/Al separation process often leads to significant losses of heavy metals. To address this issue, a new approach was developed to sequentially separate Fe/Al and recycle chromium (Cr) and nickel (Ni) from real electroplating sludge. The sludge contained 4.5% Cr, 1.2% Al, 1.1% Ni, and 14.6% Fe. Initially, the sludge was completely dissolved in a mixture of hydrochloric and nitric acids. The resulting acid solution was then heated to 160 °C for 10 h with the addition of saccharose. This hydrothermal treatment led to the hydrolysis and crystallization of 98.3% of Fe, 31.8% of Cr, 1.1% of Al, and 4.9% of Ni, forming akaganeite-bearing particles. It was observed that the excessive amount of saccharose also improved the removal of Cr, Al, and Ni, but decreased the removal of Fe. After the hydrothermal treatment, the remaining supernatant was adjusted to different pH levels (1.9, 2.9, and 4.5, respectively), and then Al, Cr, and Ni were stepwise extracted using di-(2-ethylhexyl) phosphate acid (P204). The recycling efficiencies achieved were 97.4% for Al, 61.2% for Cr, and 89.3% for Ni. This approach provides a promising method for the stepwise separation of Fe/Al and the recycling of heavy metals from electroplating sludge. [Display omitted] • Electroplating sludge was recycled into akaganeite and Al/Cr/Ni crystals. • Hydrothermal treatment removed Fe/Cr with minimal Al/Ni loss compared to pH adjustment. • Approximately 98% Fe and 32% Cr were removed as akaganeite-bearing aggregates. • Sequential extraction of Al, Cr, and Ni was performed by using P204. [ABSTRACT FROM AUTHOR]

The rapid proliferation of electronic waste (e-waste), including waste printed circuit boards (WPCBs), has exerted immense pressure on the environment. The recovery of precious metals from WPCBs not only serves as an effective means of alleviating this environmental burden but also generates economic value. This review focuses on bioleaching, an environmentally friendly method for extracting precious metals from WPCBs. Under various conditions, this method has achieved leaching rates of 30%–73% for Au and 33.8%–90% for Ag. However, there is a relative scarcity of studies on the bioleaching of precious metals from WPCBs. In this paper, we provide an overview of the current status of bioleaching for precious metals from WPCBs and describe the underlying mechanisms. We also briefly outline the influence of various process factors on leaching efficiency. While this review underscores the considerable potential of bioleaching in WPCBs applications, certain limitations hinder the engineering-scale application of the technology. Consequently, this paper describes the current enhanced processes for enhancing leaching efficiency. Overall, this review can serve as a valuable reference for future research endeavors, ultimately promoting the widespread utilization of bioleaching for the recovery of precious metals from WPCBs. [Display omitted] • Bioleaching is found to be green and effective method to recycle precious metals from PCBs. • Two-step-bioleaching and spent medium bioleaching facilitate the leaching efficiency of Au and Ag. • Factors affecting bioleaching of PCBs and bioleaching mechanism are discussed. • A number of studies have focused on enhancing the effectiveness of bioleaching precious metals from PCBs. [ABSTRACT FROM AUTHOR]

Smelting dust is a toxic waste produced in metal-mineral pyrometallurgical processes. To eliminate or reduce the adverse environmental impacts of smelting dust, valuable components need to be selectively separated from the toxic components present in the waste. This paper reviews the chemical composition, phase composition and particle size distribution characteristics of smelting dust, and the results show that smelting dust has excellent physicochemical characteristics for recovering valuable metals. The process flow, critical factors, development status, advantages and disadvantages of traditional technologies such as pyrometallurgy, hydrometallurgy and biometallurgy were discussed in depth. Conventional treatment methods typically prioritize separating and reclaiming specific elements with high concentrations. However, these methods face challenges such as excessive chemical usage and limited selectivity, which can hinder the sustainable utilization of smelting dust. With the increasing scarcity of resources and strict environmental requirements, a single treatment process can hardly fulfil the demand, and a physical field-enhanced technology for releasing and separating valuable metals is proposed. Through analysing the effect of electric field, microwave and ultrasound on recovering valuable metals from smelting dust, the enhancement mechanism of physical field on the extraction process was clarified. This paper aimed to provide reference for the resource utilization of smelting dust. [Display omitted] • Valuable metal recovery from smelting dust is a sustainable management method. • Critical information on valuable metal recycling is provided. • Conventional/unconventional metal recovery processes are analysed in detail. • A multi-physical field enhanced metal release and separation technique is proposed. [ABSTRACT FROM AUTHOR]

Abstract Recycling of process wastes will be in future an essential step to meet the demands for valuable metals of a growing market. Depending on their particle sizes incineration slags are already used to recover metals but particle size fractions below 4 mm are still difficult to recycle. Therefore, different particle size fractions (mesh size 2 and 4 mm, high energy grinded) of dry discharged slags were used for bioleaching with and without the pure cultures Acidithiobacillus ferrooxidans or Leptospirillum ferrooxidans or a mixture of Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans in batch cultures. Regarding Al, Cr, Cu, Ni, Mn and the rare earth elements Ce, La and Er, bioleaching was significantly more successful with iron oxidizing bacteria compared to abiotic controls. Metal mobilization for Al, Cu, Mn, Cr and Er with bacteria was between 70 and 100% and for Ce, Ni and La around 50% almost after 7 days, making an industrial application for the high concentrated metals like Al and Cu feasible. In addition to the recovery of valuable metals, a reduction in cost of landfilling was identified. After treatment of the slag with the microorganisms, concentrations of harmful substances in the residues could be reduced and thus a classification in lower safety levels regarding the LAGA or EU regulations was calculated. Highlights • Recycling potential of dry discharged slags by bacteria was demonstrated. • Elimination of pollutants was possible by bioleaching. • A. ferrooxidans achieved highest leaching efficiencies for Al, Cu and Ni. • Up to 100% of the rare earths were leached by L. ferrooxidans. [ABSTRACT FROM AUTHOR]

Steel slag is a major by-product of the steel industry and a potential resource of technology critical elements. For this study, a basic oxygen furnace (BOF) steel slag was tested for bacterial leaching and recovery of aluminium (Al), chromium (Cr), and vanadium (V). Mixed acidophilic bacteria were adapted to the steel slag up to 5% (w/v). In the batch tests, Al, Cr, and V were bioleached significantly more from steel slag than in control treatments. No statistical difference was observed arising from the duration of the leaching (3 vs 6 d) in the batch tests. Al and Cr concentrations in the leachate were higher for the smaller particle size of the steel slag (<75 μm), but no difference was observed for V. In the column tests, no statistical difference was found for pH, Al, Cr and V between the live culture (one-step bioleaching) and the supernatant (two-step bioleaching). The results show that the culture supernatant can be effectively used in an upscaled industrial application for metal recovery. If bioleaching is used in the 170–250 million tonnes of steel slag produced per year globally, significant recoveries of metals (100% of Al, 84% of Cr and 8% of V) can be achieved, depending on the slag composition. The removal and recovery percentages of metals from the leachate with Amberlite ® IRA-400 are relatively modest (<67% and <5%, respectively), due to the high concentration of competing ions (SO 4 2− , PO 4 3− ) in the culture medium. Other ion exchange resins can be better suited for the leachate or methods such as selective precipitation could improve the performance of the resin. Further research is needed to minimise interference and maximise metal recovery. [ABSTRACT FROM AUTHOR]

Smelting activity by its very nature produces large amounts of metal-bearing waste, often called metallurgical slag(s). In the past, industry used to dispose of these waste products at dumping sites without the appropriate environmental oversight. Once there, ongoing biogeochemical processes affect the stability of the slags and cause the release of metallic contaminants. Rather than viewing metallurgical slags as waste, however, such deposits should be viewed as secondary metal resources. Metal bioleaching is a “green” treatment route for metallurgical slags, currently being studied under laboratory conditions. Metal-laden leachates obtained at the bioleaching stage have to be subjected to further recovery operations in order to obtain metal(s) of interest to achieve the highest levels of purity possible. This perspective paper considers the feasibility of the reuse of base-metal slags as secondary metal resources. Special focus is given to current laboratory bioleaching approaches and associated processing obstacles. Further directions of research for development of more efficient methods for waste slag treatment are also highlighted. The optimized procedure for slag treatment is defined as the result of this review and should include following steps: i) slag characterization (chemical and phase composition and buffering capacity) following the choice of initial pH, ii) the choice of particle size, iii) the choice of the liquid-to-solid ratio, iv) the choice of microorganisms, v) the choice of optimal nutrient supply (growth medium composition). An optimal combination of all these parameters will lead to efficient extraction and generation of metal-free solid residue. [ABSTRACT FROM AUTHOR]

The massive spent lithium-ion batteries (LIBs) need to be recycled due to their increasing decommission in recent years. This paper aims to propose an effective process that uses self-supplied reductant roasting and acid leaching to recover Lithium, Nickle, Cobalt and Manganese from spent LIBs. In the absence of external carbon resources, the waste membrane from spent LIBs was used as the reductant in the self-supplied reductant roasting. A thermodynamic analysis was conducted to judge the possible reduction reaction between the cathode material and waste membrane. Then, the effects of roasting temperature, roasting time and membrane dosage on the crystal structure and phase transformation of roasting products were investigated and optimized. After the roasting process, the valence state of metals in the cathode material decreased and the structure became loose and porous. Moreover, the layer structure of the cathode material was transformed into groups of Li 2 CO 3 , Ni, Co, NiO, CoO and MnO. Further, the reduction effect of cathode powders under each roasting condition was verified under the same leaching conditions. After leaching for 30 min, the leaching efficiencies of Li, Ni, Co and Mn were over 99% under the optimum roasting conditions. Finally, economic assessments proved that the proposed process is profitable. The whole process demonstrates an effective and positive way for recycling spent LIBs and making full use of their waste membrane, which promotes resource recovery and environmental protection. [Display omitted] • The possible reaction between cathode powders and the waste membrane is obtained. • Li 2 CO 3 , Ni, Co, NiO, CoO and MnO are formed by self-supplied reductant roasting. • The leaching efficiencies are over 99% for Li, Ni, Co and Mn for 30 min. • A method of making use of the waste membrane in spent LIBs is proposed. [ABSTRACT FROM AUTHOR]

Electronic waste (e-waste) is the world's fastest-growing type of waste, with lighting accounting for 9% of the total. Light-emitting diodes (LEDs) are composed of the most concentrated critical elements (Ag and Au) and recovery of these metals could generate economic benefits and reduce the burdens of environmental pollution; nevertheless, the absence of information about their composition currently presents a challenge in recycling these metals with minimal prospects for recovery. This study assessed the distribution and variation of elemental concentrations of 16 different elements in three generations of LEDs (12 different LED units): sub-mounted-device (SMD #10), chip-on-board (COB #1), and positive-intrinsic-negative (PIN #1). The SMD LEDs contained a considerable amount of Au with a median average concentration of 1204 mg/kg (ranging from 323 − 3687 mg/kg), which was similar to that of COB (1550 mg/kg), but higher than that of PIN LED (175 mg/kg). Based on the total threshold limiting concentration (TTLC), the Cu levels (605,823 mg/kg) in the SMD package exceeded the regulatory limits (2500 mg/kg). Concentrations of the hazardous elements Cr (29 mg/kg), Pb (12 mg/kg), Cd (0.1 mg/kg), and As (1 mg/kg) in the LED packages were within the regulatory limits. To recycle precious metals and other technological metals, a well-organized and dedicated optimized assessment of the value of metals is required especially in accordance with the concept of criticality and recyclability. Two factors, i.e., a high resource index (RI) and technology index (TI), suggest the importance of waste to the economy and has a significant potential for recycling with less processing burdens. Present findings indicated that the COB and a few of the studied SMD LEDs (3020, 4014, 5630, and 7020), exhibit high criticality and recyclability. For the RI and TI index, the contribution of metals such as Cu, Fe, Al, and Au were dominant. These findings can serve as a reference for the development of a viable approach for the recycling and recovery of targeted metals from LED e-waste. • The study assessed the concentrations of various metals in three generations of LEDs. • High amount of Au was found in SMD LEDs (1204 mg/kg) and COB LED (1550 mg/kg). • The Cu in SMD LEDs (605,823 mg/kg) exceeded the regulatory limit. • Hazardous elements (Cr, Pb, As, Cd) in LEDs were below the regulatory limit. • COB and a few SMD LEDs exhibit high criticality and recyclability. [ABSTRACT FROM AUTHOR]

Recycling printed circuit boards (PCBs) in the e-waste stream is essential for ecological protection and metal recycling for a circular economy. Efficient metal recovery from PCBs is highly dependent on the determination of the optimum combination of inputs in the recycling process. In this study, optimization and predictive modelling of the bio-Fenton process were performed employing the response surface methodology (RSM) and the artificial intelligence (AI) models for efficient enzymatic metal bioleaching from discarded cellphone PCBs. The Box-Behnken design (BBD) of RSM was chosen as the design matrix. Further, two AI models, i.e., support vector machine (SVM) and artificial neural network (ANN) were employed to predict complex metal bioleaching process. Experiments were performed based on variations of four input process parameters, namely, glucose oxidase (GOx) content (100–1000 U/L), Fe2+ content (10–50 mM), PCB pulp density (1–10 g/L), and shaking speed (150–450 rpm). Results revealed that the maximum simultaneous enzymatic metal extraction of 100% Cu, 70% Ni, 40% Pb, and 100% Zn was attained at the optimized conditions: GOx content: 300 U/L, Fe2+ content: 10 mM, pulp density: 1 g/L, and shaking speed: 335 rpm. A comparative analysis of the AI models suggested that the ANN-based model predicting more accurate results than the SVM-based model with coefficient of determination values > 0.99 for all the targeted metals. The FTIR analysis confirmed the partial disintegration of PCB polymeric base by OH radicals (OH•), which helped in liberating and exposing the embedded metals to the bio-Fenton solution. Further, the oxidation of metals by ferric ions produced from GOx-mediated oxidation of ferrous ions ensued efficient enzymatic metal bioleaching. Selective metal recovery of >99% was obtained by the chemical precipitation of bioleachate. [Display omitted] • Enzymatic metal bioleaching from PCB was optimized and predicted by RSM and AI models. • BBD-RSM models for metal bioleaching were statistically significant (P < 0.05) by ANOVA. • AI models showed ANN predicting enzymatic metal extraction more accurately than SVM. • FTIR and TGA confirmed polymer degradation by OH.• aided efficient metal bioleaching. • Metal precipitation upon bio-Fenton process as integrated approach for PCB recycling. [ABSTRACT FROM AUTHOR]

The management and prevention of environmental risks associated with spent telecommunications printed circuit boards (STPCBs) is a concerning issue worldwide. Recycling might be proposed as a proper method to overcome this issue. Despite knowing that, choosing a sustainable method is challenging because of STPCBs complexity. This problem was overcome by analyzing STPCBs using different analytical methods and metal speciation. Understanding these data is essential in selection strategies to maximize selective recycling of metals and to minimize environmental impact. This research focused on characterizing STPCBs based on their structural, morphological, physiochemical, surface, and thermal properties. The accurate measurement of metal contents, indicating 187,900 mg kg−1 Cu, 22,540 mg kg−1 Pb, 1320 mg kg−1 Ag, and 205 mg kg−1 Au elements, plus other base metals, revealed a remarkable potential value in STPCBs. The results of structural analyses indicated that the powder has a crystalline structure and consists of Cu, Sn and Pb phases as well as different functional groups. In addition, after evaluating the zeta potential of the sample, the isoelectric pH of the sample was observed to be 5.6, which indicates that the powder particles have a negative surface in an environment with a pH higher than this value. Further, the metal speciation via sequential extraction procedure was performed, which showed that a unique harsh recycling strategy is required due to the stable structure of STPCBs. According to the results of this analysis, the global contamination factor (GCF) value was 83.48, which indicates STPCBs have a high degree of contamination. Leaching tests and environmental criteria were also conducted on this waste. The findings suggest that STPCBs needs pretreatments before landfilling to lower the concentration of toxic metals. Also, waste extraction test was the most aggressive procedure to assess mobility. Achieving this information is considered an essential step to choosing the most efficient recycling methods that minimize environmental impact while maximizing selective recycling of metals. [Display omitted] • The comprehensive characterization of STPCBs was assessed. • STPCBs were found to contain a significant amount of metallic content. • Fractionation of metals revealed that most metals were in residual fractions. • RAC, CF, GCF, and IR were used to assess environmental risk. • A leaching test showed that STPCBS must not be disposed of in landfills. [ABSTRACT FROM AUTHOR]

Rapid surge in electronic waste (e-waste) and its unscientific handling has an adverse impact on humans and the environment. Waste printed circuit board (WPCB), an integrated component of e-waste, has a high metallic content that includes both toxic and precious metals. Therefore, metal recovery is essential not just to avoid environmental degradation but also for economic growth. The current literature analysis focuses on one such eco-friendly approach, known as fungal biotechnology, for extracting metals from WPCBs. Among diverse bioleaching agents, fungi have shown promising metal extraction efficiency (Al: 65–96%; Co: 45–90%; Cu: 34–100%; Ni: 8–95%; Mn: 70–95%; Pb: 27–95%; Zn: 54–99%) and the ability to work in a wide pH range. However, in terms of metal recovery from WPCBs, fungal bioleaching has been less explored. This review, thus, assesses the fungal biotechnology for metal extraction from WPCBs and discusses the associated mechanism and kinetics involved. Different process parameters affecting the fungal bioleaching have also been discussed briefly. The review highlights that, while this process has enough potential, some associated drawbacks hinder its practical applicability on an industrial scale. Lastly, some suggestions for scaling up and reducing the cost of the process have been made, which need to be addressed. [Display omitted] • Fungal bioleaching for urban mining of metals from WPCBs comprehensively reviewed. • Fungal biotechnology has emerged as a green alternative for WPCB recycling. • Process efficacy for base and precious metal extraction varies in the range of 8–100%. • Diffusion and chemical reaction govern the kinetics of fungal bioleaching of metals. • Reactor set-up with agro-industrial wastes as carbon source can scale-up the process. [ABSTRACT FROM AUTHOR]

E-wastes being potential sources of numerous valuable metals are promoted to undergo recycling and recovery under the umbrella of urban mining and circular economy. Thus, the present study provides a critical review of the technological details of different metal recycling processes, pre-treatment methods, and the advancements made in these techniques. Critical evaluation of different metal recovery techniques has also been presented based on the available life cycle assessment (LCA), techno-economic, and industrial-scale studies. The study revealed that the integrated metal recovery techniques serve better in terms of recovery efficiency and environmental performance than any single recovery technique. Also, scaling up of biometallurgical, electrochemical, and super critical fluid extraction methods needs to be promoted due to their better environmental performances. [Display omitted] • Different metal extraction & recovery techniques from e-wastes have been reviewed. • Critical evaluation of different extraction & recovery methods has been done. • Novel techniques and other sustainable methods have been discussed in depth. • Research gaps in this area have been identified. • Scope for integrated and other metal recovery techniques has been identified. [ABSTRACT FROM AUTHOR]

The disposal of biomass enriched with heavy metals (HMs) limits the application of phytoextraction. This study investigated the feasibility of obtaining K-rich fertilizer with low risk of HMs and biochar with good application prospect by extracting Napier grass biochar using 15% HNO 3 and separating HMs from the filtrate using 40% KOH. In this study, Napier grass biochar produced at 500 °C showed better potential for utilization owing to its relatively low HM contents, high nutrient contents, and high yield. In fact, 61.26% Cd, 84.22% Zn, and more K were extracted from biochar when the pH was adjusted to 1 using 15% HNO 3. Then, Cd and Zn could be almost separated from the filtrate by adjusting the pH to 10 or more by adding 40% KOH. The Cd content in the biochar was reduced from a low risk level to a no-risk level, and the Zn content in the biochar was reduced from a medium risk level to a low risk level when the pH was adjusted to 1 and 2 by adding 15% HNO 3. The adsorption capacity of biochar to dyes was enhanced when the pH was adjusted to 1 using 15% HNO 3. The cation exchange mechanism endows the biochar with better potential for reuse (for methylene blue). This work provides a safe, efficient, and maneuverable resource allocation method. [Display omitted] • Napier grass biochar produced at 500 °C has good potential in resource utilization. • ●HNO 3 can realize simultaneous extraction and modification of Napier grass biochar. • ●KOH can precipitate heavy metals in the leach liquor and supplement K element. • ● q m of MB and KNR on modified biochar reached 101.13 and 13.23 mg g−1, respectively. • ●The cation exchange mechanism endows the biochar with better potential for reuse. [ABSTRACT FROM AUTHOR]

The reuse and recycling of industrial solid wastes such as scrap metal is supported and encouraged both internationally and domestically, especially when such wastes can be used as substitutes for raw material. However, scrap metal processing facilities, such as mini-mills, have been identified as a source of mercury (Hg) emissions in the United States. This research aims to better define some of the key issues related to the source and nature of mercury in the scrap metal waste stream. Overall, it is difficult to pinpoint the key mercury sources feeding into scrap metal recycling facilities, quantify their associated mercury concentrations, or determine which chemical forms are most significant. Potential sources of mercury in scrap metal include mercury switches from discarded vehicles, electronic-based scrap from household appliances and related industrial systems, and Hg-impacted scrap metal from the oil and gas industry. The form of mercury associated with scrap metal varies and depends on the source type. The specific amount of mercury that can be adsorbed and retained by steel appears to be a function of both metallurgical and environmental factors. In general, the longer the steel is in contact with a fluid or condensate that contains measurable concentrations of elemental mercury, the greater the potential for mercury accumulation in that steel. Most mercury compounds are thermally unstable at elevated temperatures (i.e., above 350 °C). As such, the mercury associated with impacted scrap is expected to be volatilized out of the metal when it is heated during processing (e.g., shredding or torch cutting) or melted in a furnace. This release of fugitive gas (Hg vapor) and particulates, as well as Hg-impacted bag-house dust and control filters, could potentially pose an occupational exposure risk to workers at a scrap metal processing facility. Thus, identifying and characterizing the key sources of Hg-impacted scrap, and understanding the nature and extent of associated releases, represent a practical research need that is essential for improving the environmental management of Hg-impacted scrap and assessing measures to protect workers from potential health and safety hazards that might be posed by mercury and Hg-impacted scrap. [ABSTRACT FROM AUTHOR]

Manganese recovery from industrial ore processing waste by means of leaching with sulfuric acid was the objective of this study. Experimental conditions were optimized by multivariate experimental design approaches. In order to study the factors affecting leaching, a screening step was used involving a full factorial design with central point for three variables in two levels (2 3 ). The three variables studied were leaching time, concentration of sulfuric acid and sample amount. The three factors screened were shown to be relevant and therefore a Doehlert design was applied to determine the best working conditions for leaching and to build the response surface. By applying the best leaching conditions, the concentrations of 12.80 and 13.64 %w/w of manganese for the global sample and for the fraction −44 + 37 μm, respectively, were found. Microbeads of chitosan were tested for removal of leachate acidity and recovering of soluble manganese. Manganese recovery from the leachate was 95.4%. Upon drying the leachate, a solid containing mostly manganese sulfate was obtained, showing that the proposed optimized method is efficient for manganese recovery from ore tailings. [ABSTRACT FROM AUTHOR]

Over the last few decades, a substantial amount of e-waste including waste printed circuit boards (WPCBs) has been produced and is accumulating worldwide. More recently, the rate of production has increased significantly, and this trend has raised some serious concerns regarding the need to develop viable recycling methods. The presence of other materials in the WPCBs, such as ceramics and polymers, and the multi-metal nature of WPCBs all contribute to the increased complexity of any recycling process. Among the viable techniques, pyrometallurgy, with the inherent ability to process the waste independent of its composition, is a promising candidate for both rapid and large-scale treatment. In the present study, firstly, the principles of the pyrometallurgical methods for WPCB recycling are discussed. Secondly, the different unit operations of thermochemical pretreatment including incineration, pyrolysis, and molten salt processing are reviewed. Thirdly, the smelting processes for the recovery of metals from WPCBs, as well as the issues surrounding slag formation and subsequent treatment are explained. Fourthly, alternative methods for the recovery of polymers and ceramics, in addition to metal recycling, are elucidated. Fifthly, emission control techniques and the potential for energy recovery are evaluated. [Display omitted] • Advantages of pretreatment of WPCBs for improved efficiency. • Proposed modification based on scientific principles to decrease the emissions. • Mechanistic insight into pyrolysis and molten salt methods. • Thorough discussion on the chemistry of the slag for improvement in the efficiency. • Advances and current trends in pyrometallurgical recycling of WPCBs. [ABSTRACT FROM AUTHOR]

While disposal bans of lithium-ion batteries are gaining in popularity, the infrastructure required to recycle these batteries has not yet fully emerged and the economic motivation for this type of recycling system has not yet been quantified comprehensively. This study combines economic modeling and fundamental material characterization methods to quantify economic trade-offs for lithium ion batteries at their end-of-life. Results show that as chemistries transition from lithium-cobalt based cathodes to less costly chemistries, battery recovery value decreases along with the initial value of the raw materials used. For example, manganese-spinel and iron phosphate cathode batteries have potential material values 73% and 79% less than cobalt cathode batteries, respectively. A majority of the potentially recoverable value resides in the base metals contained in the cathode; this increases disassembly cost and time as this is the last portion of the battery taken apart. A great deal of compositional variability exists, even within the same cathode chemistry, due to differences between manufacturers with coefficient of variation up to 37% for some base metals. Cathode changes over time will result in a heavily co-mingled waste stream, further complicating waste management and recycling processes. These results aim to inform disposal, collection, and take-back policies being proposed currently that affect waste management infrastructure as well as guide future deployment of novel recycling techniques. [Copyright &y& Elsevier]

The purpose of this study was to investigate the effect of extraction conditions (i.e., culture filtrate concentration, extraction temperature, and extraction time) on the removal of metals from chromated copper arsenate (CCA)-treated wood particles by using an unknown Polyporales sp. KUC8959. As the first research, a 20-run central composite design using response surface methodology was applied to optimize the system and construct the models, which predicted metal removal by bioleaching. The coefficients of determination of fitted models were 0.874–0.989, which indicated that the models can predict the metal removal yield accurately under various conditions. The Cu removal model suggested that the following conditions, culture filtrate concentration of 45.8%, extraction temperature of 34.2 °C, and extraction time of 20.6 h, were required for maximal removal of Cu (82.1%). The model predicted that extraction conditions of increased severity would result in complete removal of Cr and As from CCA-treated wood particles. In order to confirm actual metals removal efficiency, metals extraction was subsequently conducted under optimal bioleaching condition evaluated in this study. By applying the model, we demonstrated 83.9% Cu, 96.0% Cr, and 99.3% As removal from treated wood particles. [Copyright &y& Elsevier]

Advanced gravity separation of ground electronic waste (e-waste) in a teeter-bed separator was investigated. It was established that the Floatex Density Separator (FDS) is a promising device for wet processing of e-waste to recover metal values physically. It was possible to enrich the metal content from 23% in the feed to 37% in the product in a single stage operation using the FDS with over 95% recovery of the metals. A two-stage processing scheme was developed that enriched the metal content further to 48.2%. The influence of the operating variables, namely, teeter water flow rate, bed pressure and feed rate were quantified. Low bed pressures and low teeter water rates produced higher mass yields with poorer product grades. On the contrary, a high bed pressure and high teeter water rate combination led to a lower mass yield but better product quality. A high feed rate introduced en-masse settling leading to higher yield but at a poorer product grade. For an FDS with 230 mm × 230 mm cross section and a height of 530 mm, the process condition with 6.6 lpm teeter water rate, 5.27 kPa bed pressure and 82 kg/hr feed rate maximized the yield for a target product grade of 37% metal in a single pass. [Copyright &y& Elsevier]

The purpose of this study was to combine the physical pretreatments of grinding, sieving, and magnetic-separation processes to reclaim iron-rich materials from the desulfurization slag, and to use the remainder for cement clinker production. The iron-rich materials can be separated out efficiently by grinding for 30 min and sieving with a 0.3 mm mesh. The non-magnetic fraction of the particles smaller than 0.3 mm was in the majority, and proved to be suitable for use as a cement raw material. The raw mixes prepared with a pretreated desulfurization slag had a relatively high reactivity, and the temperature at which alite forms was significantly reduced during the clinkerization process. The clinkers produced with 10% desulfurization slag had a high level of alite and good grindability. Generally, the improvements in clinkerization and clinker grindability are beneficial to energy conservation in cement manufacture. [Copyright &y& Elsevier]

Secondary lead smelters (SLS) represent an environmentally-challenging industry as they deal with toxic substances posing potential threats to both human and environmental health, consequently, they operate under strict government regulations. Such challenges have resulted in the significant reduction of SLS plants in the last three decades. In addition, the domestic recycling of lead has been on a steep decline in the past 10 years as the amount of lead recovered has remained virtually unchanged while consumption has increased. Therefore, one may wonder whether sustainable development can be achieved among SLS. The primary objective of this study was to determine whether a roadmap for sustainable development can be established for SLS. The following aims were established in support of the study objective: (1) to conduct a systematic review and an analysis of models of sustainable systems with a particular emphasis on SLS; (2) to document the challenges for the U.S. secondary lead smelting industry; and (3) to explore practices and concepts which act as vehicles for SLS on the road to sustainable development. An evidence-based methodology was adopted to achieve the study objective. A comprehensive electronic search was conducted to implement the aforementioned specific aims. Inclusion criteria were established to filter out irrelevant scientific papers and reports. The relevant articles were closely scrutinized and appraised to extract the required information and data for the possible development of a sustainable roadmap. The search process yielded a number of research articles which were utilized in the systematic review. Two types of models emerged: management/business and science/mathematical models. Although the management/business models explored actions to achieve sustainable growth in the industrial enterprise, science/mathematical models attempted to explain the sustainable behaviors and properties aiming at predominantly ecosystem management. As such, there are major disconnects between the science/mathematical and management/business models in terms of aims and goals. Therefore, there is an urgent need to integrate science and business models of sustainability for the industrial enterprises at large and environmentally-challenging industrial sectors in particular. In this paper, we offered examples of practices and concepts which can be used in charting a path towards sustainable development for secondary lead smelters particularly that the waste generated is much greater outside the industrial enterprise than inside. An environmentally-challenging industry such as secondary lead smelters requires a fresh look to chart a path towards sustainable development (i.e., survivability and purposive needs) for all stakeholders (i.e., industrial enterprise, individual stakeholders, and social/ecological systems). Such a path should deal with issues beyond pollution prevention, product stewardship and clean technologies. [Copyright &y& Elsevier]

Bimetallic (Ag–Pd/ α -Al 2 O 3) catalysts are essentially applied to naptha-cracking process with a controlled CO 2 emission. After losing the catalytic properties in long run, the landfilling disposal of spent catalysts poses severe stress to the environment and deprivation of precious metals. Therefore, an innovative solvo-chemical recycling approach that involving the solid-liquid and liquid-liquid mass transfer phenomena was studied. The parametric variations for dissolving precious metals yielded >98% efficiency at a lixiviant concentration, 2.0 mol L−1 HCl; pulp density, 20% (wt./vol.); agitation speed, 300 rpm, temperature, 90 °C, and duration, 60 min. The activation energy of silver (6.9 kJ mol−1) and palladium (11.9 kJ mol−1) leaching indicated that the process was governed by a diffusion-controlled mechanism. Subsequently, silver and palladium were separated using 0.15 mol L−1 LIX 84-I at different acid concentration that yielding the maximum separation factor (β (Ag/Pd) = 12,501) at 2.0 mol L−1 HCl. Stripping of separately (Ag/Pd)-loaded organic solutions with different solutions of HNO 3 , (NH 4) 2 SO 4 , and CH 4 N 2 S showed higher affinity for thiourea, yielding 56%, 38%, and 87% efficiency, respectively. Thus the counter-current extraction at an organic-to-aqueous (O:A) ratio of 1:2.5 and stripping with 0.5 mol L−1 CH 4 N 2 S at an O:A ratio of 2:1 yielded a five-fold enrich solutions of precious metals (75.2 mg L−1 Ag and 188.5 mg L−1 Pd) with a purity of >99.9%. The process essentially aims to Goal 12 under the United Nations' Sustainable Development Goals for sustainable recycling of industrial wastes consequently conserving the natural mineral reserves. [Display omitted] • Hydrometallurgical recycling for treating Ag–Pd/ α -Al 2 O 3 spent catalysts was studied. • Ag and Pd were efficiently leached in HCl using solution chemistry of precious metals. • E a values of leaching (<12 kJ mol−1) indicated for the diffusion-controlled mechanism. • Higher β (Ag/Pd) of 12,501 was achieved using LIX 84-I at different HCl concentrations. [ABSTRACT FROM AUTHOR]

For the first time, the basics of waste-free technology for capturing heavy metal ions from urban surface runoff from residential areas of the city with the final utilization of the regenerate were developed. The technology eliminates the subsequent contamination of the lithosphere and atmosphere by regeneration products. The expediency of using fibrous chemosorbents (cationic and polyampholyte) for capturing heavy metal ions from urban surface runoff of residential areas of megalopolises has been justified because of possibility of recycling heavy metal ions and regenerating the sorbent. Model solutions of Fe, Cu, Zn, Pb salts, as well as samples of solutions of real surface effluents were studied. Small experimental samples of filters of various designs were designed and manufactured. The filters were tested at a functioning treatment facility. It was demonstrated that the content of Fe3+, Cu2+, Zn2+, and Pb2+ ions in real surface effluents decreased by 1.4–7 times after passing the effluents even through these small experimental filters. The expediency and possibility of recycling the regenerate as inorganic pigments for the paint industry is shown. [Display omitted] • Fibrous chemosorbents has an advantage of their regeneratability and allows heavy metal recycling. • The bases of full cycle technology for surface runoff purification has been laid. • Heavy metal recycling regenerate may be used as inorganic pigments for the paint industry. [ABSTRACT FROM AUTHOR]

Recycling precious elements from the electronic waste could be an environmental friendly way to avoid likely ecological damages caused by leaching of heavy metals and toxic elements as well as an economically attractive option to recover valuable materials that would otherwise be wasted. This research assessed the environmental and economic performance of recovering nine metal elements (aluminum (Al), copper (Cu), gold (Au), lead (Pb), nickel (Ni), silver (Ag), tin (Sn), zinc (Zn), and iron (Fe)) and two non-metal materials (resin and glass-fiber) from the waste printed circuit boards (PCBs), one of the vital components of electronic-waste (e-waste). SimaPro software was used to assess the environmental performance of recycling waste PCBs. Data were collected from recycling plants in Taichung City, Taiwan, and Eco-invent database was also used in the study. The impacts of metal recycling from PCBs were compared with the impacts caused by the mining of respective metals from their natural ores. Among the analyzed elements, only the recovery of Au from waste PCBs proved to have less environmental impacts than the mining from the natural ore. Among 16 environmental impact categories (ILCD midpoint 2011+ method of impact analysis) considered in the present study, cancer and non-cancer human toxicity were the most affected categories followed by minerals, fossils, and resource extraction. However, the economic analysis showed that the recycling of all elements from waste PCBs had a net positive benefit. When considering both the environment and economic performance, the recycling of Au proved to be a beneficial option. • Recycling metals except gold had more negative environmental impacts than mining. • Copper recycling had the highest negative environmental impacts. • Gold recycling had the lower environmental impact than gold mining. • There was a net positive economic benefit for recycling of all metals. [ABSTRACT FROM AUTHOR]

Strict environmental regulations as well as requirement of conservation of natural resources compelled the researchers to recycle the metal values from secondary resources. The scrap magnets found to be a potential alternative resource to extract rare earth metal, Nd. Present paper reports a novel process flow-sheet for the recycling of scrap Nd-Fe-B magnets to recover Nd as marketable salt and other valuable by-products. The Nd-Fe-B magnets were demagnetized, crushed and charged to atmospheric leaching resulting in ~99.99% recovery of REMs (Nd, Pr, Dy) and Fe using 1 M H 2 SO 4 solution at room temperature for 90 min and pulp density 50 g/L. The obtained leach liquor was subjected to acid extraction procedure by mixing the liquor with 70% TEHA diluted in kerosene for 10 min, which requires five stages for complete extraction of acid from the liquor having O/A ratio 2:1. Ammonia solution was used to increase the pH of acid free leach liquor to 1.65 for the precipitation of Nd (with minor amount of Pr and Dy) and above that to precipitate Fe. Further, processing of these valuables make them industrially applicable. The leached residue was checked using Toxicity Characteristics Leachability Procedure (TCLP) test and found the remained metals within the permissible limit. This process offers a simple and efficient means to reduce the toxicological effect by recovering Nd from magnets of computer hard disks. • A novel process flow-sheet for the recycling of Nd-Fe-B magnets was proposed. • Reports atmospheric leaching followed by selective precipitation of Nd salt. • Marketable salt of Nd of purity ~98% was produced. • Red oxide was produced as marketable by-product. • Conservation of natural resources as well as mitigation of pollution. [ABSTRACT FROM AUTHOR]