Process For Recovery Of Metals Research Articles

Towards circular economy of wasted printed circuit boards of mobile phones fuelled by machine learning and robust mathematical optimization framework

Estimating the operating conditions using conventional process analysis techniques for the maximum metal extraction from the wasted printed circuit boards (WPCB) can provide sub-optimal solutions leading to the low yield of the process. In this paper, we present a closed-loop methodological framework built on machine learning and robust mathematical optimization technique, that offers the mathematical rigour, to determine the optimum operating conditions for the maximum Cu and Ni recovery from the WPCB. Alkali leaching based novel metals recovery process from the WPCB is designed, and the experiments are conducted to collect the data on the percentage recovery of Cu and Ni against the operating levels of the process input variables (ammonia concentration (NH3 conc. (g/L)), ammonium sulfate concentration ((NH4)2SO4 conc. (g/L)), H2O2 concentration (H2O2 conc. (M)), time (h), liquid to solid ratio (L/S ratio, (mL/g)), temperature (Temp. (°C)), and stirring speed (rpm)). The experimental data is deployed to construct the functional mapping between the nonlinear output variables of metals recovery process with the hyperdimensional input space through artificial neural network (ANN) based modelling algorithm – a powerful universal function approximator. Well-predictive ANN models for Cu and Ni recovery are developed having co-efficient of determination (R2) value more than 0.90. Partial derivative-based sensitivity analysis is then carried out to establish the order of the significance of the input variables that is backed by the domain knowledge, thus promotes the interpretability of the trained ANN models. The hybridization of ANN with NLP (nonlinear programming) framework is implemented for the determination of optimized operating conditions to extract maximum Cu and Ni under separate and combined model of metal extraction. The robustness of the determined solutions is verified, the determined optimized solutions for the metal recovery are validated in the lab, and the maximum metal recovery, i.e., 100 % Cu and 90 % Ni is extracted from the WPCB. This research demonstrates the effective utilization of ANN model-based robust optimization approach for the metal recovery from the WPCB that supports the circular economy for the metal extraction industry.

OREATE as a High Yield and Purity Electrochemical Process for Transition and Rare Earth Metal Recovery

Developing a process that can consistently convert transition and rare earth metal oxides to chemically pure metals in near quantitative yield will have significant impact in many levels, from fundamental science to national security-related applications. Traditional separation methods of lanthanides and actinides from aqueous media have been based on liquid-liquid extractions that have proven to be quite efficient, though they are expensive and require complex engineering. Likewise, separation by pyro-chemistry provides a good recovery performance but requires the use of high temperatures that adds technological difficulties to the process. An alternative method that has grown interest in the last few years is the utilization of the difference in the metals’ reduction potentials from ionic state to metallic state. However, this electrochemical approach requires more negative reduction potentials than hydrogen evolution, which requires a very challenging control of their electrolytic deposition onto solid cathodes.In recent years, our team at LANL has been working on the development of OREATE (Oxide Reduction by Electrochemical Amalgamation and Thermal Extraction). OREATE is a holistic electrochemical approach that involves an initial step wherein the metal oxide is dissolved and chlorinated into an acidic medium. The dissolved metal cation is then electrochemically amalgamated via reduction using a mercury pool cathode. Finally, mercury's high vapor pressure allows an easy thermal extraction process to obtain the metal. From the conceptual perspective and preliminary results, the OREATE process appears easier and simpler than traditional separation methods and is suitable for small- and large-scale preparation of high purity metals.The results obtained using Cerium (Ce) as a surrogate metal demonstrated near quantitative yield of the electrochemical amalgamation (yield > 99%), almost complete mercury recovery during the thermal extraction (Hg recovery > 99.5%), and high purity of the Ce metal product (purity > 99%). Moreover, a variety of system parameters such as the pH of the buffered solution, concentration of cerium, reduction potential, and temperature were explored to evaluate the effect that the scaling up of the OREATE process may have on reaction rate, current efficiency, process yield, and temperature management.

Design and Production of Functionalized Electrospun Fibers for Palladium Recovery.

Adsorption stands out as a leading wastewater treatment method for ion removal or recovery. Polymeric fibers, notably electrospun ones, are gaining prominence due to their high capacity and easy recovery. Electrospinning offers a cost-effective means to produce fibers with a large surface area and high adsorption capacity. These fibers can be further functionalized with chemical substances acting as specific ligands for metal ions, bolstering their adsorption capabilities. In this study, dithioester-functionalized electrospun fibers were synthesized as an alternative to conventional sorbents for palladium recovery from acidic chloride solutions, similar to those used in hydrometallurgical processes for platinum group metal recovery (Pd, Pt, Rh···) from spent catalysts. Fibers with identical chemical composition but varying morphology were examined to assess their impact on palladium adsorption efficiency (i.e., beads-free and beads-on-string morphologies). Experimental investigations involved model solutions with varying palladium concentration, temperature, acidity (adjusted with HCl content), and salinity (adjusted with NaCl), utilizing both pure and dithioester-functionalized fibers. Experimental results demonstrate enhanced adsorption efficiency at lower temperatures and in 0.1 M HCl, with a negligible influence from solution salinity. Moreover, both pure polymeric and dithioester-functionalized electrospun fibers exhibit highly efficient palladium recovery. Furthermore, under optimal conditions, starting from an 80 mg/L palladium solution, a 95% recovery of palladium can be achieved with a sorbent dosage below 4 g/L of functionalized electrospun fibers. The adsorption data are well described by the Langmuir isotherm model for the pure polymeric fibers. At the same time, the contribution of dithioesters has been separately accounted for to describe the behavior of functionalized electrospun fibers. Thermal recovery of palladium from the spent sorbents has also been investigated.

Recent and Novel Leaching Processes for Recovery of Metals from Spent Lithium-ion Batteries: A Review

Recent and Novel Leaching Processes for Recovery of Metals from Spent Lithium-ion Batteries: A Review

Tailoring the Use of 8-Hydroxyquinolines for the Facile Separation of Iron, Dysprosium and Neodymium.

Permanent magnets (PMs) containing rare earth elements (REEs) can generate energy in a sustainable manner. With an anticipated tenfold increase in REEs demand by 2050, one of the crucial strategies to meet the demand is developing of efficient recycling methods. NdFeB PMs are the most widely employed, however, the similar chemical properties of Nd (20-30 % wt.) and Dy (0-10 % wt.) make their recycling challenging, but possible using appropriate ligands. In this work, we investigated commercially available 8-hydroxyquinolines (HQs) as potential Fe/Nd/Dy complexing agents enabling metal separation by selective precipitation playing on specific structure/property (solubility) relationship. Specifically, test ethanolic solutions of nitrate salts, prepared to mimic the main components of a PM leachate, were treated with functionalized HQs. We demonstrated that Fe3+ can be separated as insoluble [Fe(QCl,I)3] from soluble [REE(QCl,I)4]- complexes (QCl,I -: 5-Cl-7-I-8-hydoxyquinolinate). Following that, QCl - (5-Cl-8-hydroxyquinolinate) formed insoluble [Nd3(QCl)9] and soluble (Bu4N)[Dy(QCl)4]. The process ultimately gave a solution phase containing Dy with only traces of Nd. In a preliminary attempt to assess the potentiality of a low environmental impact process, REEs were recovered as oxalates, while the ligands as well as Bu4N+ ions, were regenerated and internally reused, thus contributing to the sustainability of a possible metal recovery process.

Efficient recovery of all valuable metals from spent HDS catalysts: Based on roasting mechanisms for enhanced selective leaching and separation

Recovery of all valuable metals such as Ni, Mo, V and Al from spent hydrodesulfurization (HDS) catalysts is beneficial to environmental protection and resource recycling. The current recycling process mostly considers the recovery of Mo and V than recovery of Ni and Al, and generates a large amount of difficult-to-decompose Ni-Al residue and wastewater. Aiming at the insufficiency of the current recycling process, in this study, a novel pyro-hydrometallurgical process for efficient and complete recovery of metals from spent HDS catalysts was proposed. The mechanisms of phase transformation during roasting and leaching are investigated by XRD, XPS and SEM in depth. The modulation of the phase transformation of the spent HDS catalyst in the oxidative roasting process is the key to the influence on the leaching of Ni and Al. Inhibition of θ-Al2O3 phase and Ni-Al spinel generation by controlled roasting can achieve efficient leaching of Mo, V, Ni and Al. Subsequently, Mo and V were selectively leached with 2 mol/L Na2CO3, and the alkaline leach residue obtained was treated with 6 mol/L HCl. The results showed that alkaline leaching efficiencies of Mo and V reached 99.73 % and 91.86 % while acid leaching efficiencies of Ni and Al reached 99.71 % and 90.27 %, respectively. The metals of acid leach solution were recovered by using N235, HBL110 and NaAlO2 stepwise. This new process has the advantages of high efficiency and comprehensive metal recovery, high product purity, and low amount of slag and wastewater, and has good prospects for industrial application.

Radiation Techniques for Tracking the Progress of the Hydrometallurgical Leaching Process: A Case Study of Mn and Zn

With advancements in hardware and software, non-destructive radiometric analytical methods have become popular in a wide range of applications. A typical case is the study of the leaching process of metals from mineral ores and mine tailings. The objective of the current study was to develop a radiometric method based on neutron activation analysis (NAA), in particular, delayed gamma neutron activation analysis (DGNAA), to monitor the process of Mn and Zn leaching from Ti ore, Cu mine tailings, and Zn-Pb mine tailings. The DGNAA method was performed using a neutron source: a deuterium-tritium (D-T) neutron generator for Mn and a MARIA research nuclear reactor for Zn. Laboratory-scale Mn leaching from Ti ores, Cu tailings, and Zn-Pb tailings was investigated using delayed gamma-rays of 56Mn (half-life of 2.6 h). The dissolution efficiencies of Mn were found to increase with interaction time and HCl concentration (1 to 5 M) and to vary with the leaching temperature (22.5 to 110 °C). Such results were found to agree with those obtained by total reflection X-ray fluorescence (TXRF) spectrometry for the same samples. 65Zn (half-life of 244 days) was chosen to investigate real-time/online leaching of Zn in Ti ore, Cu tailings, and Zn-Pb tailings. During online monitoring, Zn recovery was also reported to increase with increased leaching time. After approximately 300 min of leaching, 80%, 79%, and 53% recovery of Zn in Zn-Pb tailings, Ti ore, and Cu tailings, respectively, were reported. Theoretically, developed mathematical prediction models for 65Zn radiotracer analysis showed that the spherical diffusion model requires much less time to attain saturation compared to the linear diffusion model. The results of NAA for Zn were compared with those obtained by handheld X-ray fluorescence (handheld-XRF) and TXRF analysis. The analyzed samples encompassed leached Ti ore, Cu tailings, and Zn-Pb tailings which were subjected to different conditions of leaching time, temperature, and HCl concentrations. The XRF analysis confirmed that the leaching efficiencies of Zn rise with the increase in leaching time and HCl concentration and fluctuate with leaching temperature. The developed approach is important and can be applied in laboratories and industrial setups for online monitoring of the recovery of any element whose isotopes can be activated using neutrons. The efficiency of the metal-recovery process has a direct impact on the normal operation and economic advantages of hydrometallurgy.

A tandem approach for precipitant-free highly selective recovery of valuable metals from end-of-life lithium-ion batteries using a green deep eutectic solvent

Recently, recycling lithium-ion batteries (LIBs) waste and the efficient recovery of valuable metals has become crucial for the circular economy. Deep eutectic solvents (DESs) have shown immense potential for metal extraction from end-of-life (EoL) LIBs. However, a complicated subsequent separation process is required due to the non-selectivity of the DES components for metal. Herein, we propose a tandem precipitant-free hydrometallurgical process for the selective recovery of Li and other valuable metals (Ni, Co, Mn) from EoL LIBs using a green DES. The process parameters, viz., reaction temperature (T), time (t), pulp density (S/L), and molar ratio (MR) of ethylene glycol to tartaric acid, were optimized via the statistical optimization technique of response surface methodology. The results revealed maximum extraction efficiencies of 99.2 ± 0.5%, 96.1 ± 1.4%, 95.2 ± 1.2%, and 97.8 ± 1.5% for Li, Ni, Co, and Mn, respectively, under the optimized process conditions of T = 118 °C, t = 17 min, S/L = 42 g/L, and MR = 3:1. The kinetic study showed that interfacial reaction governed the extraction process. A plausible mechanism depicting the role of DES constituents in synergistically facilitating the extraction reaction was elucidated. Moreover, Li and other metals (Ni, Co, and Mn) were selectively separated and recovered with an overall efficiency of ∼99%. The reusability of the recovered metal products and the DES were also assessed for a closed-loop recycling process. At the outset, the proposed process paves the way for a greener alternative for recycling valuable metals from EoL LIBs rather than conventional acid-based leaching processes.

Comparative life cycle assessment of copper and gold recovery from waste printed circuit boards: Pyrometallurgy, chemical leaching and bioleaching

Printed circuit boards (PCBs) make up a substantial amount of electronic waste (e-waste) generated annually. Waste PCBs contain high quantities of copper and gold in comparison to natural ores. As such, “urban mining” of waste PCBs to recover these metals is of commercial interest. In this work, we used life cycle assessment to compare the environmental impact of four copper and gold recovery processes. We evaluated pyrometallurgy, chemical leaching, and bioleaching, as well as a hybrid leaching process that uses bioleaching to recover copper and chemical leaching to recover gold. Furthermore, we considered differences in environmental impact based on differences in electricity sources. If electricity comes from fossil fuels, the pyrometallurgical process results in the lowest environmental impact in all impact categories studied. If electricity comes from carbon-free sources, the pyrometallurgical process results in the lowest environmental impact in all categories studied except global warming, where the hybrid leaching process results in the lowest impact. In all cases, metal recovery from waste PCBs leads to lower environmental impact than primary metal production. Our goal is to guide e-waste recyclers towards more environmentally sustainable metal recovery processes and to provide knowledge gaps in the field to guide future research.

Mechanism of highly efficient oil removal from spent hydrodesulfurization catalysts by ultrasound-assisted surfactant cleaning methods

The removal of crude oil from spent hydrodesulfurization catalysts constitutes the preliminary stage in the recovery process of valuable metals. However, the traditional roasting method for the removal exhibits massive limitations. In view of this, the present study used an ultrasound-assisted surfactant cleaning method to remove crude oil from spent hydrodesulfurization catalysts, which demonstrated effectiveness. Furthermore, the study investigated the mechanism governing the process with calculation and experiments, so as to provide a comprehensive understanding of the cleaning method’s efficacy. The surfactant selection was predicated on the performance in the IFT test, with SDBS and TX-100 finally being chosen. Subsequent calculations and analysis were then conducted to elucidate their frontier molecular orbitals, electrostatic potential, and polarity. It has been found that both SDBS and TX-100 possess the smallest LUMO-HOMO energy gap (ΔE), registering at 4.91 eV and 4.80 eV, respectively, and presenting the highest interfacial reactivity. The hydrophilic structure in the surfactant regulates the wettability of the oil-water interface, and the long-chain alkanes have excellent non-polar properties that promote the dissolution of crude oil. The ultrasonic-assisted process further improves the interface properties and enhances the oil removal effect. Surprisingly, the crude oil residue was reduced to 0.25% under optimal conditions. The final phase entailed the techno-economic evaluation of the entire process, revealing that, in comparison to the roasting method, this process saves $0.38 per kilogram of spent HDS catalyst, with the advantages of operational simplicity and emission-free. Generally, this study shed new light on the realization of efficient oil removal, with the salience of green, sustainable, and economical.

Complete recovery of valuable metals from chlorinated titanium-white waste acids: Focus on solvent extraction for recovery and preparation of battery-grade manganese sulfate (MnSO4·H2O) from lab to pilot scale

Chlorination titanium-white waste acid (CTWA) is known to contain a substantial number of valuable metals, including Mn, which can be utilized in the manufacturing of high-value battery cathode materials. Based on the concept of complete resource recovery and zero pollution, a novel process for metal recovery from CTWA has been developed. D2EHPA was used to extract Sc, V from CTWA. Al was completely removed by slowly adding 1.5 mol/L NaOH until the solution pH reached 4.20 and stabilized for 0.5 h. This process resulted in a limited loss of 11 % for Fe and 5 % for Mn. An oxidative precipitation method was proposed to process the Al-free solution to preparate a pure and easily filterable FePO4 product, which can be used in the production of battery materials. Additionally, the loss of Mn in this process was less than 0.5 %. After removing Fe and Al, the pre-extraction feed has an O/A ratio of 2.5:1, a temperature of 40 °C, and an equilibrium pH of 4.5 ∼ 5.0, it is possible to extract Mn at over 99.50 % using a 5-stage extraction. The loaded phase is scrubbed with 5 g/L H2SO4, O/A = 5:1. It is then cyclically stripped with 75 g/L H2SO4, O/A = 8:1, to obtain a battery-grade MnSO4 solution. The stripped solution can be 100 % crystallized to obtain battery-grade MnSO4·H2O products after removing heavy metals using BaS and removing oil with activated carbon. The recovery of Mn in the extraction process was 97.59 %. The pilot test was conducted to demonstrate that the extraction process can be efficiently and continuously produced. The process achieved the recovery of valuable metals from CTWA and the preparation of corresponding products. This process is comprehensive and environmentally friendly, which has an industrial foundation.

Implementing a sustainable process for the recovery of palladium from spent catalysts at industrial scale: A LCA approach

Due to its unique physicochemical properties, palladium is widely used in several industry applications (e.g., vehicle emission control). In view of the circular economy, it is essential to explore secondary sources of palladium, such as urban mines. Current technologies for effective palladium recovery involve high energy consumption and severe environmental impact. More recently, a novel green method for recovering palladium from spent catalysts through a combination of mild acidic leaching and photodeposition on ZnO nanoparticles was proposed on a laboratory scale. In the present study, the environmental impacts of this recovery method, properly upscaled and modelled, was assessed by employing the LCA approach. Specifically, a comparative LCA was carried out for the process with as well as without recycling key components, such as Cu (II) and NaCl for the leaching solution and ZnO. The outcomes identified critical areas and drove the investigation of alternative process configurations to reduce its environmental footprint, such as the use of carbon dioxide in the photodeposition process with the aim of decreasing the resulting terrestrial ecotoxicity. This study marks a significant step forward in advancing research toward industrial−scale implementation of palladium recovery. It provides valuable insights for researchers in the field of green physicochemical processes for metal recovery, thus offering guidance for future decision−making towards more sustainable practices.

Green and selective recovery process of Mo, V, and Ni from spent hydrodesulfurization catalysts via novel ionic liquids and deep eutectic solvents technology

Ionic liquids (ILs) and deep eutectic solvents (DESs) are promising candidates as viable alternatives in the metal recovery process. Conventional methods predominantly concentrated on the extraction of metals employing ionic liquids or deep eutectic solvents from either acidic or alkaline media subjected to leaching by acids or bases. Therefore, in this work, a novel approach integrating ILs and DES was investigated, wherein the entire sequence from the leaching process to the precipitation step exclusively involves the utilization of DES and ILs. Firstly, the spent hydrodesulfurization (HDS) catalyst underwent leaching with an ionic liquid (IL), which selectively leached molybdenum (Mo) and vanadium (V). Subsequently, the residual material remaining after IL leaching underwent a further leaching process utilizing a deep eutectic solvent (DES) to facilitate the recovery of nickel (Ni). The effect of different parameters on the leaching percentage was studied and optimized for both IL and DES. Vanadium was recovered as NH4VO3 from the loaded IL phase, which was selectively precipitated over molybdenum using NH4Cl solution and molybdenum was precipitated as BaMoO4 by introducing an excess of BaCl2 solution to the filtrate. For the nickel recovery, the residue obtained after leaching using ionic liquid was treated with DES-1 and finally nickel was recovered from the mixture through cementation with aluminum. This study establishes a novel green approach based on IL and DES to recover Mo, V, and Ni from the spent catalysts without roasting and harsh acidic or basic conditions.

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.

Research on the recycling of waste lithium battery electrode materials using ammonium sulfate roasting

Owing to resource limitations, environmental pollution concerns, and the increasing global demand for lithium-ion battery raw materials, the recycling of discarded electrode materials from lithium-ion batteries has emerged as a prominent research area. Nevertheless, among various types of discarded lithium battery electrode materials, limited research has been conducted on the recycling of ternary electrode materials (LiNixCoyMn1-x-yO2). This study proposes an eco-friendly process for the efficient recovery of valuable metals and carbon from mixed materials of discarded ternary lithium-ion battery electrodes. This study investigated the influence of various roasting using ammonium sulfate and leaching conditions on the conversion and extraction rates of valuable metals. Under the condition of a 3:1 mass ratio of ammonium sulfate to lithium battery electrode mixed material, roasting temperature of 450 °C, roasting time of 30 min, liquid-solid ratio of 20:1, leaching time of 20 min, and leaching temperature of 60 °C, the recovery rates of various valuable metals including Li, Ni, Co, and Mn reached 99.99%. For the above process, the chemical control reaction prevailed in the initial 10 min of the roasting reaction, succeeded by the dominance of diffusion control reaction in the subsequent 20 min. In the leaching process, the chemical control reaction governed the first 2 min, succeeded by diffusion control reaction for the next 18 min. Analysis of the reaction's macroscopic and microscopic mechanisms reveals that ammonium sulfate roasting of waste ternary lithium-ion batteries constitutes a typical liquid-solid reaction. In the molten state, NH4+ decomposition releases high-energy H+ ions that break the bonds between metals and oxygen. Consequently, metal atoms from the waste battery's crystal structure combine with ammonium sulfate's sulfate groups, forming various metal sulfates. This paper establishes an eco-friendly process for the efficient recovery of valuable metals by employing the ammonium sulfate roasting method to convert valuable metals in discarded electrode mixed materials into water-soluble sulfates.

Precious Metals Recovery Process from Electronic Boards: Case Study of a Non-Profit Organization (QC, Canada)

The growth in the consumption of electronic products in recent years has resulted in increasing electronic device waste. At the same time, there is a decrease in the availability of raw metals required to produce electronic boards. Recycling through the recovery of precious and critical metals contained in electronic board waste is a solution, but the processes need to be safer for the environment. This paper presents the steps that lead to investment in the development of an eco-friendly and cost-effective process for recovering precious metals from end-of-life electronic telecommunications cards. Social organizations can also become involved in the recycling of electronic cards, thus enabling the integration of marginalized people into society. We examine the case of a non-profit organization whose mission is to help people living with mental health problems through the recycling of end-of-life telecommunication devices. This recycling process must operate within constraints specific to this organization and to the employment of people with mental health issues. The literature review showed that considering ecological and economic factors, the hydrometallurgical process appeared to be a logical choice.

In-situ adsorptive pyrolysis of e-waste using coal and rice husk fly ash as alternative adsorbents for energy and precious metal recovery by solvent extraction

This paper aims to use in-situ adsorptive pyrolysis combined with ultrasonication and solvent extraction for precious metal recovery from e-waste. The pyrolysis of discarded printed circuit board (PCB) and waste cable (WC) resulted in pyrolysis oil yields of 4.2–13.0 and 6.8–13.5%, respectively. Aliphatic and single-ring compounds were the major components of the pyrolysis oil. The pyrolysis char was ultrasonicated at 40 kHz for 20, 30, and 40 min at 35 °C to separate precious metals in pyrolysis char. The amounts of Au and Ag recovered by solvent extraction experiments with 2%vol HCl/2%vol HNO3, 2%vol HNO3 and 2%vol I2/2%vol H2O2 were 36.3–61.4 and 60.7–79.9%, respectively. The total energy recovery from the pyrolysis char, oil, and gas obtained from the pyrolysis of PCB was 9.0–9.2 MJ/kg. These results indicated that in-situ adsorptive pyrolysis with ultrasonication and solvent extraction could potentially facilitate e-waste conversion for energy and metal recovery processes at a lower cost.

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.

Characterization of the effects of acetic acid on the recovery of valuable contents from flotation tailings of non-sulfide metals

Non-sulfide lead flotation tailings draw attention in terms of their valuable contents. Dissolution studies have been carried out with strong inorganic acids, especially in ore form, but these acids have been unfavorable in removal in the context of metal recovery processes. Organic acids, on the other hand, are notable for their environmentally friendly properties and selective metal recovery opportunities. In this study, the effects of acetic acid on metal recovery from oxidized waste were investigated with different experimental parameters at a laboratory scale. Optimal conditions were determined depending on the increase in acetic acid concentration. At 0.75-1.0 M acid concentrations, 49-55% Pb and 49-54% Zn recovery efficiencies were obtained with grades of 7.0-7.2% and 19.5-19.7%, respectively. The recovery of Pb/Zn by the leaching process with acetic acid and the selective non-recovery of iron were also observed through characterization studies. With the Rietveld XRD method, an increase in iron minerals such as goethite and a decrease in smithsonite-hydrozincite minerals were determined. These changes were seen as a decrease in the contents of these minerals in SEM/EDX analysis and as a decrease in smithsonite mineral bond structures in the FT-IR analysis. This study showed that acetic acid has many advantages in the utilization of zinc-lead-containing oxide flotation tailings, which have high economic value, such as selective metal recovery, easy biodegradability, environmental friendliness, and non-corrosiveness.

Study on metal recovery process and kinetics of oxidative leaching from spent LiFePO4 Li-batteries

A green environmental protection and enhanced leaching process was proposed to recover all elements from spent lithium iron phosphate (LiFePO4) lithium batteries. In order to reduce the influence of Al impurity in the recovery process, NaOH was used to remove impurity. After impurity removal, the spent LiFePO4 cathode material was used as raw material under the H2SO4 system, and the pressure oxidation leaching process was adopted to achieve the preferential leaching of lithium. The E-pH diagram of the Fe-P-Al-H2O system can determine the stable region of each element in the recovery process of spent LiFePO4 Li-batteries. Under the optimal conditions (500 r·min–1, 15 h, 363.15 K, 0.4 MPa, the liquid-solid ratio was 4:1 ml·g–1 and the acid-material ratio was 0.29), the leaching rate of Li was 99.24%, Fe, Al and Ti were 0.10%, 2.07% and 0.03%, respectively. The Fe and P were precipitated and recovered as FePO4∙2H2O. The kinetic analysis shows that the process of high-pressure acid leaching of spent LiFePO4 materials depends on the surface chemical reaction. Through the life cycle assessment (LCA) of the spent LiFePO4 whole recovery process, eight midpoint impact categories were selected to assess the impact of recovery process. The results can provide basic environmental information on production process for recycling industry.