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The world's seas and oceans contain vast amounts of lithium, but the low concentration hereof renders solvent extraction impractical for its recovery. By contrast, seawater desalination brine, after treatment by nanofiltration, contains a roughly tenfold greater concentration of lithium than raw seawater. Hence, lithium can be effectively recovered from such streams using solvent extaction. Compared with other techniques to sequester lithium from dilute solutions, solvent extraction offers the advantages of simple operations, robust and well-established technology and high recovery yields. Thus, we propose a solvent-extraction based process to recover lithium from seawater desalination brine, treated by nanofiltration. The first step comprises the removal of magnesium and calcium using methyltrioctylammonium neodecanoate in p-cymene. This is followed by a lithium extraction step using the extractants Mextral 54–100 and Cyanex 923 in Shellsol D70 diluent. The lithium extract is then scrubbed with water and stripped with hydrochloric acid. Subsequently, residual alkaline earth metals are removed with sodium hydroxide in ethanol and finally lithium is precipitated using sodium carbonate. The solvent extraction, scrubbing and stripping steps were demonstrated on mini-pilot scale in continuous countercurrent mode (in mixer-settlers), while the precipitation steps were demonstrated in batch. The process was found to have an overall yield of 74%, affording a lithium carbonate product with a purity of 97 wt%.

This paper reviews the properties of methanesulfonic acid (MSA) and its potential for use in hydrometallurgy. Although MSA is much less known than sulfuric, hydrochloric or nitric acid, it has several appealing properties that makes it very attractive for the development of new circular flowsheets in hydrometallurgy. Unlike other organic acids such as acetic acid, MSA is a very strong acid (pKa = − 1.9). In addition, it is very stable against chemical oxidation and reduction, and has no tendency to hydrolyze in water. In terms of its environmental impact, MSA has low toxicity and is biodegradable. In nature, it is part of the geochemical sulfur cycle. A useful property is the high solubility of its salts in water: methanesulfonate salts have a much higher solubility in water than sulfate salts. Additionally, MSA and its salts are compatible with the electrowinning of metals because the anode reaction involves the formation of oxygen gas (unlike chlorine gas formation in chloride electrolytes) and no cathodic reduction of the anion occurs (unlike nitrate reduction in nitrate electrolytes). MSA is particularly interesting for lead hydrometallurgy, where it offers more environment-friendly alternatives to HBF4 and H2SiF6. However, MSA can also be adopted in all hydrometallurgical processes that require strong Brønsted acids. It can be used in the metallurgy of copper, zinc, cobalt, nickel, and rare earths, as well as in the recycling of metals from end-of-life products. Although MSA itself is a non-oxidizing acid, in combination with hydrogen peroxide it yields strongly oxidizing lixiviants that can leach copper from chalcopyrite or dissolve metallic silver. The global production of MSA is expected to increase rapidly in the near future thanks to both the industrialization of a new sustainable synthesis process and its many applications (cleaning fluids, electrolytes for electroplating, redox-flow batteries, catalysts in organic synthesis, and as a solvent for high-molecular-weight polymers). As a result, MSA will become more widely available and a lower price will make it an increasingly attractive option. Graphical Abstract

In this academic position paper, we propose the 12 Principles of a novel and more sustainable approach to hydrometallurgy that we call “circular hydrometallurgy.” The paper intends to set a basis for identifying future areas of research in the field of hydrometallurgy, while providing a “sustainability” benchmark for assessing existing processes and technological developments. Circular hydrometallurgy refers to the designing of energy-efficient and resource-efficient flowsheets or unit processes that consume the minimum quantities of reagents and result in minimum waste. The application of a circular approach involves new ways of thinking about how hydrometallurgy is applied for both primary and secondary resources. In either case, the emphasis must be on the regeneration and reuse of every reagent in the process. This refers not only to the acids and bases employed for leaching or pH control, but also any reducing agents, oxidizing agents, and other auxiliary reagents. Likewise, the consumption of water and energy must be reduced to an absolute minimum. To consolidate the concept of circular hydrometallurgical flowsheets, we present the 12 Principles that will boost sustainability: (1) regenerate reagents, (2) close water loops, (3) prevent waste, (4) maximize mass, energy, space, and time efficiency, (5) integrate materials and energy flows, (6) safely dispose of potentially harmful elements, (7) decrease activation energy, (8) electrify processes wherever possible, (9) use benign chemicals, (10) reduce chemical diversity, (11) implement real-time analysis and digital process control, and (12) combine circular hydrometallurgy with zero-waste mining. Although we realize that the choice of these principles is somewhat arbitrary and that other principles could be imagined or some principles could be merged, we are nevertheless convinced that the present framework of these 12 Principles, as put forward in this position paper, provides a powerful tool to show the direction of future research and innovation in hydrometallurgy, both in industry and in academia. Graphical Abstract

UNLABELLED: A hydrometallurgical process is described for conversion of an aqueous solution of lithium chloride into an aqueous solution of lithium hydroxide via a chloride/hydroxide anion exchange reaction by solvent extraction. The organic phase comprises a quaternary ammonium chloride and a hydrophobic phenol in a diluent. The best results were observed for a mixture of the quaternary ammonium chloride Aliquat 336 and 2,6-di-tert-butylphenol (1:1 molar ratio) in the aliphatic diluent Shellsol D70. The solvent extraction process involves two steps. In the first step, the organic phase is contacted with an aqueous sodium hydroxide solution. The phenol is deprotonated, and a chloride ion is simultaneously transferred to the aqueous phase, leading to in situ formation of a quaternary ammonium phenolate in the organic phase. The organic phase, comprising the quaternary ammonium phenolate, is contacted in the second step with an aqueous lithium chloride solution. This contact converts the phenolate into the corresponding phenol by protonation with water extracted to the organic phase, followed by a transfer of hydroxide ions to the aqueous phase and chloride ions to the organic phase. As a result, the aqueous lithium chloride solution is transformed into a lithium hydroxide solution. The process has been demonstrated in continuous counter-current mode in mixer-settlers. Solid battery-grade lithium hydroxide monohydrate was obtained from the aqueous solution by crystallization or by antisolvent precipitation with isopropanol. The process consumes no chemicals other than sodium hydroxide. No waste is generated, with the exception of an aqueous sodium chloride solution. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s40831-022-00629-2. ispartof: JOURNAL OF SUSTAINABLE METALLURGY vol:9 issue:1 pages:107-122 ispartof: location:Netherlands status: published

In this work, previously produced black mass was treated in sequence by milling, water leaching, and sulfuric acid leaching. Two goals were set: first, whether milling, with reductive additives, could impart reductive phase changes which would allow Li extraction to water in the water leaching; second, co-leaching of the black mass with the additive, CoS, was explored as to ascertain whether synergistic effects could be detected in a leaching system composed of reductive (CoS) and oxidative (NMC oxides) materials in the presence of redox mediator (Fe2+/Fe3+ redox pair). It was found out that in all experiments, similar Li concentration was obtained despite milling. Fluoride analysis indicated high F concentrations in the water solution and implicated formation of insoluble products such as LiF(s). Water-soluble fluoride ended up in all fractions: water leaching filtrates (ca. 500 mg/L), acid leaching filtrates (ca. 800–1700 mg/L), and leach residues (ca. 68–382 mg/kg). In acidic leaching, CoS appeared to enhance extraction of elements from cathode-active materials, improving extraction from 78 to 92% for Ni under relatively mild leaching conditions (T = 30 °C, solid conc. = 100 g/L, [H2SO4] = 1.4 M). Graphical Abstract

The past 10–20 years have seen numerous academic papers describing the benefits of ionic liquids (ILs) and deep-eutectic solvents (DESs) for leaching, solvent extraction and electrowinning. The scientific community—including the authors of this opinion article—have frequently proclaimed these neoteric solvents as game-changers in extractive metallurgy. Despite this, there have been no commercial breakthroughs. In this paper we reflect on the reasons why ILs and DESs seem to have failed to impact on the metallurgical industry. These include: (1) issues with high viscosity; (2) limited chemical stability under the conditions of metallurgical processes; (3) difficulties with recycling and reuse; (4) a lack of demonstrated unit processes and flowsheets on the pilot scale; (5) insufficient material-property data available for engineering purposes; (6) the administrative burden of obtaining licenses and safety permits; (7) very high costs for large-scale operations; and (8) minimal added value compared to state-of-the-art hydrometallurgical processes. Our belief is that innovations in hydrometallurgy based on ILs or DESs are unlikely. Instead, we should be aiming for a deeper understanding of hydrometallurgical processes at the molecular level. This is because advances are more likely to derive from the refocused efforts of experienced IL/DES researchers investigating the speciation and chemical thermodynamics of hydrometallurgical solutions, which will then hasten the transition from linear to low-energy-input, circular hydrometallurgy. Graphical Abstract

The recovery of rare earths elements (REEs) from NdFeB slurry by traditional hydrometallurgy has been limited becuase a large number of REEs are lost during separation together with iron. In this paper, a simple and sustainable method is proposed to efficiently separate and recover REEs and iron from NdFeB slurry. REEs were recovered by one-step selective precipitation in phosphoric acid, and the dissolved iron was recovered by oxalic acid. Phosphoric acid leaching results show that under the conditions of 4 mol/L phosphoric acid, 80 °C, L/S of 30:1 and 90 min, the leaching efficiencies of Fe and REEs reach 98.76% and 1.09%, respectively. While the rest of REEs remained in the leaching residue in the form of REEPO4·nH2O precipitation. Subsequently, the mixed rare earth oxide (rare earth oxalate roasted at 800 °C) and FeC2O4·2H2O are obtained by oxalic acid precipitation with purities of 99.49% and 97.17% from the REEPO4·nH2O dissolving solution and the phosphoric acid leaching solution. Moreover, the phosphoric acid is regenerated while recovering iron, and it can be reused in the phosphoric acid leaching step after removing the impurity C2O42−. In summary, this work provides an efficient and environmentally friendly method for recovering REEs and iron from NdFeB slurry waste.

The aim of this study was to investigate the synthesis of iron oxide pigments from IOT. The sample of IOT was obtained through mining activity of the Quadrilátero Ferrífero in the state of Minas Gerais, Brazil. The procedure was carried out by hot acid leaching with hydrochloric acid (HCl) which allowed the recovery of about 95% of the iron in a liquor. The iron-based pigments— red (IBP_R), black (IBP_B), and yellow (IBP_Y)—were synthetised from the liquor by selective precipitation, crystallisation, and thermal procedures. The pigments were characterised by particle size distribution, mineral and chemical compositions, as well as colourimetric properties. The process of synthesis was successful and the procedure was shown to maximise the utilisation of mineral resources and minimise the environmental, social, and economic impacts associated with IOT disposal.

The article discusses the types of various dusty iron‑containing waste generated in metallurgical and foundry production. Rational waste processing technologies are considered. The analysis of the chemical composition of iron‑containing waste, morphology and particle size is presented. Variants of processing and use technology that are acceptable for the conditions of the Republic of Belarus are proposed.

Multiple purification of zinc sulfate solution is an important process for zinc hydrometallurgy, and large quantities of copper-cadmium residues are generated as byproducts in this process. Copper-cadmium residues contain a large number of valuable metals that must be recovered. A comprehensive extraction process has been proposed using sulfuric acid as the leaching reagent and hydrogen peroxide as the oxidizing reagent. The effects of acid concentration, leaching temperature, leaching time, liquid-to-solid ratio, hydrogen peroxide dosage and stirring speed on the leaching efficiency were investigated. The optimum conditions were determined as an acid concentration of 150 g/L, liquid-to-solid ratio of 4:1, hydrogen peroxide amount of 20 mL, time of 60 min, temperature of 30 °C, particle size of −d75 μm, and agitation rate of 300 r/min. It was concluded that the leaching efficiency of copper and cadmium reached 97%, but because of the existence of zinc sulfide in the residues, a lower leaching efficiency of zinc was obtained. Furthermore, the leaching kinetics of copper was also studied based on the shrinking core model. The activation energy for copper leaching was 5.06 kJ/mol, and the leaching process was controlled by the diffusion through the product layer.

Purified liquid is obtained in the last stage of the zinc-smelting purification process, and real-time detection of its trace metal ion concentration is beneficial in providing effective information for the purification of zinc hydrometallurgy. We added Cu(Ⅱ), Co(Ⅱ) and Fe(Ⅲ) standard solutions to the purified liquid obtained from zinc smelting based on the analysis system of Nitroso R salt to simulate the fluctuation of the actual ion concentration, and adopted UV-vis spectrometry to determine the concentration of metal ions. Then, we adopted the strategy of "separation-extraction-calibration" strategy to quantitatively analyze the concentration of trace metal ions, namely, Cu, Co, and Fe, simultaneously. Elite Variable Cluster and Improved Local Weighted Partial Least Squares (EVC-ILWPLS) algorithm are proposed for feature extraction and multivariate calibration model. In the approach, the most effective information variable clustering is filtered using forward elimination and backward clustering, and then ILWPLS based on variable weighted and sample weighted is used to determine trace metal ions concentration. Experimental results indicate that EVC-ILWPLS can not only select effective variables quickly and accurately, but also establish a reliable regression model for spectral data with complex multivariate relationships and strong collinearity. A comparison between the proposed and other conventional methods shows that this proposed strategy can determine the concentration of Cu, Co, and Fe with the lowest RMSE and MRE. Therefore, the developed method can be implemented as a promising method for quantitatively analyzing trace metal ions concentration, and it provides a guiding significance in the analysis and processing of multivariate collinearity spectrum data.

Pressure hydrogen reduction (Pre-H2) is an important technology in hydrometallurgy, which is widely applied in the production of metal powders, coated composite powders, and metal oxides. In the 5G era, Pre-H2 is concerned in the electronic material manufacturing because of its clean, efficient, stable, and other characteristics. In this paper, the thermodynamic and kinetic principles of Pre-H2 in a liquid-phase environment are described, and the process methods, powder conditions, process parameters, and related applications of various products are summarized. In addition, this paper investigates the effect of liquid additives on powder morphology, reaction rate, quality of the process, and provides feasibility guidance for improving the process technology.

The recovery of metals from spent LiFePO4 batteries is arousing increasing concern due to its great market consumption, environmental impact, and wastage of valuable metallic resources. This work proposed an effective recycling approach for metals and promoted a simplified regenerative process. The innovative use of H4P2O7 as a leaching agent achieves the leaching of metals and their separation in one step. Under a modified leaching condition, the leaching efficiency of Li is close to 100%, and the precipitation amount of Fe is more than 97%. Then, the separated Fe in the form of Fe4(P2O7)3 and recovered Li2CO3 were used to regenerate LiFePO4 cathode material. It delivers an initial capacity of 167.8 mAh g−1 at 0.1 C and remains 91.31% after 100 cycles; the dynamic property and cycling stability are comparable to the unused commercial material. The application of H4P2O7 achieves separation of Li and Fe metals in parallel with leaching process with higher leaching efficiency and selectivity for the metals than the conventional leaching acids in hydrometallurgy technology.

Neodymium (Nd) is one of the most essential rare-earth metals due to its outstanding properties and crucial role in green energy technologies such as wind turbines and electric vehicles. Some of the key uses includes permanent magnets present in technological applications such as mobile phones and hard disk drives, and in nickel metal hydride batteries. Nd demand is continually growing, but reserves are severely limited, which has put its continued availability at risk. Nd recovery from end-of-life products is one of the most interesting ways to tackle the availability challenge. This perspective concentrates on the different methods to recover Nd from permanent magnets and rechargeable batteries, covering the most developed processes, hydrometallurgy and pyrometallurgy, and with a special focus on electrodeposition using highly electrochemical stable media (e.g., ionic liquids). Among all the ionic liquid chemistries, only phosphonium ionic liquids have been studied in-depth, exploring the impact of temperature, electrodeposition potential, salt concentration, additives (e.g., water) and solvation on the electrodeposition quality and quantity. Finally, the importance of investigating new ionic liquid chemistries, as well as the effect of other metal impurities in the ionic liquid on the deposit composition or the stability of the ionic liquids are discussed. This points to important directions for future work in the field to achieve the important goal of efficient and selective Nd recovery to overcome the increasingly critical supply problems.

Although the US has minimal reserves of the raw materials needed to make EV batteries, EOL material can contribute to domestic supply. However, this valuable resource will be exported if it is not economical to recycle it here. Hydrometallurgical recycling plants are being built now, with the expectation that they will be profitable, but profits will decline with cobalt content. By the time that happens, direct recycling will be sufficiently developed to take up the slack. Both processes will then be available to upgrade recovered materials to more up-to-date chemistries, securing a domestic supply of these materials.

The possibility of sorption extraction of nickel from leaching solutions of oxidized nickel ores of the Buruktal deposit is considered. Ionite Lewatit TP220 with bis-picolylamine functional groups is effective for nickel recovery against the background of high iron contents. Lewatit TP220 is mechanically strong enough for use in the resin-in-pulp process. Nickel sorption with satisfactory performance occurs both in the variant of sorption leaching and extraction from clarified solutions. At sorption from the pulp, the capacity for nickel was 5.44 mg/g, for iron, 25.17 mg/g. The use of 20% sulfuric acid provides quantitative nickel desorption. To obtain a higher quality nickel-containing product, it is recommended to additionally purify the resulting eluates from iron.

Biochemical leaching of sea nodules using Bacillus circulans was carried in an external circulation-loop airlift bioreactor. In contrast to the slightly high recovery (92% Cu, 73% Ni, 72% Co, 38% Mn, and 17% Fe) with fine particles (

Industrial copper slag is among the most important wastes to be evaluated in terms of containing valuable metals and the amount of waste approaching 30 million tons per year. Therefore, in this study, it was aimed to propose a feasible route for copper and zinc recovery from copper converter slag (CCS) by using choline chloride (ChCl) based deep eutectic solvent which is applied on this type of slag for the first time. During the leaching experiments with the pure ChCl-2urea mixture, temperature (25–95 °C), leaching duration (2–72 h), and pulp density (1/10–1/40 g/mL) were selected as the parameters to be investigated for Cu and Zn extraction. After the experimental results, the optimized conditions for the ChCl-2urea leaching process, which gave 89.9% Cu and 65.3% Zn extraction was found at 48 h, 95 °C, 1/20 g/mL pulp density with 600 rpm stirring speed. It is noted that the iron dissolution ratio is very low (max. 4.7%) under the selected conditions. At the end of the iron cementation stage, the total recovery efficiency as a pure metallic copper was 63%. The calculated activation energy for the dissolution of the copper and zinc from CCS is 8.86 kJ mol−1 and 14.48 kJ mol−1, respectively.

This paper presents Cr(III) removal from nickel sulfate waste solutions as a pretreatment step for the modification of hydrogen storage alloys. Adsorption with two cation exchange resins, Dowex G26 (strongly acidic) and MAC-3 (weakly acidic), and precipitation with various solutions were chosen as simple operations for Cr(III) removal from waste solutions. The adsorption of Cr(III) was investigated for both model and real waste nickel solutions. Dowex G26 appeared to be more efficient in Cr(III) removal (RCr(III) from 43 to 80%) than MAC-3 (RCr(III) from 40 to 53%). However, the adsorption from multi-component solutions (presence of Co(II), Ni(II) and Cr(III)) showed no selectivity in Cr(III) adsorption in comparison to those of Co(II) and Ni(II). Cr(III), Ni(II) and Co(II) were removed at a comparable level (30–36%) from a three-component solution of 10 g/dm3 of each metal ion, and a 56–72% removal of these ions was achieved from the real solution. Therefore, the precipitation of Cr(III) was carried out from a real waste nickel solution to compare its performance with adsorption. The best precipitation solution appeared to be 3 and 30% NaOH due to the quantitative precipitation of Cr(OH)3 at pH 5 and relatively small co-precipitation of Ni(II) and Co(II) hydroxides (PCo(II) = 20–52%, PNi(II) = 0–54%). Based on the results of the research, it can be concluded that precipitation with a NaOH solution is an efficient pretreatment operation of an electrolyte for further steps of the hydrometallurgical process of nickel electrodeposition and appears to be more selective in the elimination of Cr(III) than adsorption with Dowex G26 resin.

The separation of Rare Earth Elements (REEs) is an important step in the valorization of REE ore and aims at producing individual rare earth compounds for the market. The separation is carried out industrially by solvent extraction (SX) using interconnected circuits consisting of cascades of mixer-settlers. The design of a REE separation circuit implies the selection of the operating conditions and of the number of mixer-settlers required to achieve a target degree of purity for the separated elements. This design work is either carried out by piloting a circuit or using a mathematical simulation. Independent of the method, the world expertise in this area is limited. This paper describes a simulation method requiring a minimum of calibration effort, which can be used to design a complete REE separation plant. The simulation enables assessment of the effect of the number of mixer-settlers per extraction, the scrubbing and stripping stage, as well as the pH of the aqueous solution and organic-phase contents of free and loaded extractant on the purity of the separated REEs. The simulation tool presented here has been developed from a fundamental analysis of the chemical reactions involved in the solvent extraction process. Unlike most of the simulation methods documented in the literature, the method requires no empirical calibration. The proposed method is validated using data from laboratory batch tests and with published data from continuous pilot and industrial REE separation circuits. The application of the simulation tool is illustrated with the planning of the test conditions for a forthcoming pilot test work and with the simulation of a 9-REE product SX separation plant.

Metals : open access journal 13(5), 969 (2023). doi:10.3390/met13050969 special issue: "Special Issue "Sustainable Gold Production and Recycling" / Special Issue Editors: Prof. Dr. Bernd Friedrich, Guest Editor; Dr. Alexander Birich, Guest Editor", Published by MDPI, Basel

Waste silicon powder produced during the production process of organosilicon materials is a major environmental concern that can lead to pollution and resource wastage. As a result, it is crucial to find efficient ways of recovering and utilizing this waste material. In this study, the morphology of waste silicon powder was systematically studied, and an optimized purification method was proposed based on a hydrometallurgical process and phase analysis. The complex composition of waste silicon powder presents a significant challenge during its recycling. However, the results of this study showed that metal-assisted chemical etching (MACE), followed by mixed acid system leaching, is the most effective method for removing impurities from the material. The superior order of different acid systems for removing metallic impurities was HCl < HF < HF + HCl < HF + H2O2 < CuACE. It is worth noting that CuACE treatment has a remarkable ability to remove more than 95% of Fe through hydrometallurgy.

The treatment and hydrometallurgical recovery of Pb from zinc leaching residue (ZLR), a waste stream generated by the zinc refining process, is proposed in this work. Leaching achieved complete extraction of Pb (140 mg/g) within 24 h contact time using a 0.8 M sodium citrate solution. The batch leaching process that operates at ambient temperature results in a pregnant leachate solution of dissolved lead citrate. Pb is recovered from the dissolved organometal complex as a precipitate of PbSO4 after chemical reaction in acidic conditions that are maintained through continuous membrane electrolysis. In addition, an alkaline buffer is generated at the cell cathode to regenerate the leachate, so that the recycled lixiviant can be used in consequent leaching steps. Characterization of the final product by XRD, ICP-AES, and Raman spectroscopy identified an amorphous PbSO4 phase with traces of lead citrate. The overall purity of Pb is 46 ± 4%, representing a 3.3 fold concentration of ZLR. The integrated process is capable to treat ZLR sustainably. It can resolve the need for landfilling the mineral tailing and treat historic dump sites, respecting the zero-waste rationale, while also recovering raw material from a secondary source.

Spent catalyst used for denitration by selective catalytic reduction (spent SCR denitration catalysts) is one of the important urban mines due to the high content of TiO2 (~85 wt%) and the massive accumulation amount (over 100, 000 tons), therefore, value-added reutilization of titanium in spent SCR catalysts is considerably meaningful. In this paper, a novel method is proposed for converting the titanium oxide in spent SCR denitration catalysts to metallic titanium. Specifically, titanium dioxide (TiO2) was firstly obtained from spent SCR denitration catalysts after removing the impurities by hydrometallurgy process. Then, TiO2 is converted to Ti2CO by carbothermic reduction method, and Ti2CO was further purified by oleic acid capture. Finally, by utilizing the as-prepared Ti2CO as the consumable anode in the NaCl-KCl molten salt, high-purity metallic titanium was deposited at cathode, all confirming the feasibility for the conversion of low–grade TiO2 in the spent catalysts, from 60 wt% to high–purity metallic Ti (99.5 wt%), furthermore, the energy consumption of this process is 3950 kWh tonne−1 Ti, which is lower than that of most traditional titanium metallurgy methods. The method herein can provide new insights for the value-added recycling of titanium resources in urban mines.

The cathodes of spent ternary lithium-ion batteries (LIBs) are rich in nonferrous metals, such as lithium, nickel, cobalt and manganese, which are important strategic raw materials and also potential sources of environmental pollution. Finding ways to extract these valuable metals cleanly and efficiently from spent cathodes is of great significance for sustainable development of the LIBs industry. In the light of low energy consumption, ‘green’ processing and high recovery efficiency, this paper provides an overview of different recovery technologies to recycle valuable metals from cathode materials of spent ternary LIBs. Development trends and application prospects for different recovery strategies for cathode materials from spent ternary LIBs are also predicted. We conclude that a highly economic recovery system: alkaline solution dissolution/calcination pretreatment → H2SO4leaching → H2O2reduction → coprecipitation regeneration of nickel cobalt manganese (NCM) will become the dominant stream for recycling retired NCM batteries. Furthermore, emerging advanced technologies, such as deep eutectic solvents (DESs) extraction and one‐step direct regeneration/recovery of NCM cathode materials are preferred methods to substitute conventional regeneration systems in the future.

The destabilization of disperse systems using flocculation is an approach in hydrometallurgy, purification of wastewater, agriculture, etc. The recent efforts here have been made in development of polyelectrolytes. In this work, the bentonite clay hydrodispersions stability under the influence of polyelectrolytes, differing in molar ratio, and types of functionality, was investigated. The dispersions obtained were characterized by spectrophotometry, conductivity measurements, viscometry. The stability of clay hydrodispersions was studied by the turbidimetric method. Under the influence of a polyelectrolyte containing non-ionizable acetate and amide groups, a slight increase in hydrodispersions’ destabilization with the number of very weakly positively charged amide groups was observed. In the presence of polyelectrolytes containing vinyl acetate and well-ionizable aliphatic amine groups, the hydrodispersions’ destabilization was clearly expressed. A pronounced decrease in the hydrodispersion stability was observed under the influence of polyelectrolytes obtained from the highly-ionized 2-vinylpyridine and diethylaminoethylmethacrylate. Polyelectrolytes obtained from vinyl acetate and highly-ionized aliphatic amino-groups had more pronounced effect on destabilization. Hence, features of polyelectrolyte nature, composition, charge density and molecular weight effect on the stability of bentonite clay were elucidated. The selection of the appropriate dose of coagulants and flocculants was demonstrated to be nonlinear function of turbidity.

The authors attempted to investigate the copper recovery possibilities from low-grade mixed sulfide-oxide ore in the present paper. The randomized leaching experimental results in sulfuric acid sol...

Waste segments generated by the abrasion of diamond-impregnated cutting segments used in natural stone cutting processes have a high content of base and precious/critical metals (20-92% Cu, 10-38% Co and 0.1-0.9% Ag, 0-75 Fe) as well as synthetic diamonds. In this study, recovery of critical and precious metals (Co, Cu, Ag) from waste segments (0,91% Ag, 15,8% Co, 51,9% Cu) used in marble production was investigated using sulfuric acid leaching (0.1-0.53 M H2SO4) in the presence of an oxidizing reagent (H2O2, O2, air). Increasing the concentration of H2SO4 and H2O2, a complete dissolution of cobalt, copper, and iron were achieved, while 90% of Ag was extracted in the leach solutions containing 1.25 M H2SO4 and 0.5 M H2O2. The addition of air as an oxidizing agent had a limited enhancing effect on metal extractions in comparison with those extractions occurred under the non-oxidizing conditions, while the addition of oxygen significantly improved the metal extractions. It was determined that the synthetic diamonds obtained from the leaching residues were 0.4-0.6 mm in diameter, intact and reusable. These findings have shown that critical and precious metals could be extracted from waste segments at high recoveries using sulfuric acid leaching in the presence of a suitable oxidizing agent

A large amount of dust is formed as one of the primary by-products during the blast furnace ironmaking process. Besides iron and carbon, it contains a variety of valuable metals such as zinc, lead, and indium widely applied in many industry fields. However, it is difficult to recycle and reutilize blast furnace dust (BFD) due to complex composition, fine particle size, and strong hydrophobic property. The extensive utilization of BFD wastes precious metal resources and decreases the additional value of recovery. Environment-oriented technologies have raised great attention in the recycling of precious metals. This article presents an overview of various technologies and the prospect of utilization on the recovery of BFD. The source, composition, and characteristics of BFD, as well as the recycling technologies within the blast furnace system are analyzed. Fundamental studies regarding pyrometallurgy and hydrometallurgy for recycling valuable metals from BFD such as direct reduction, leaching, and extraction, as well as its advantages and challenges, are also discussed. There is also great potential for BFD in other fields, including flocculants, cement raw materials, and adsorbents. The diverse chemical properties of BFD make it a contender for selective separation and adsorption in water pollution treatment. The development of pyrometallurgy technologies is mainly to realize its green and clean production. The innovative technologies in hydrometallurgy mainly aim to improve the leaching and extraction efficiency of high-valued metals. The combination of pyrometallurgy and hydrometallurgy technologies achieves the environment-friendly and sustainable recycling for precious metals with a higher recovery rate.

This study, which covered a set of leaching processes at a few stages, investigated the inclusion of iron found in mill scale, which is a waste of the iron-steel industry, in the solution as FeClx=2,3 in the presence of HCl and the conditions of using this solution with an oxidizing character in extraction of metals from chalcopyrite concentrate. Mill scale was treated with HCl, and an FeClx solution was obtained at a 100% Fe solubility and 83.43% Fe3+ conversion rate in the conditions of 60 min, 105 °C, 7 M HCl, and 1/10 solid-liquid ratio. This solution that was obtained was later used in copper extraction from a chalcopyrite concentrate. In the optimum conditions (120 min of leaching time, 105 °C of leaching temperature, 1/25 solid-liquid ratio, 400 rpm stirring speed), 95.04% of the copper was taken into the solution. In the leaching experiment in a medium containing mill scale + chalcopyrite and HCl at the same time, under the optimum conditions (120 min of leaching time, 105 °C of leaching temperature, 7 M HCl concentration, 1 g chalcopyrite concentrate, 1/25 solid-liquid ratio, 5 g mill scale, 400 rpm stirring speed), approximately 96% of copper was taken into the solution.

The recovery of Pd from spent catalysts has been gaining attention due to its high economic value and limited availability in nature. To recover and reuse Pd, leaching in HCl–H2O2 media and recovery of Pd from the Pd/SiO2 catalyst were investigated. The Pd/SiO2 catalyst was leached using 3 M HCl solution with different concentrations of H2O2; then 0.5 M NaOH was added to precipitate the Pd ions. The leaching parameters were as follows: temperature, time, H2O2 concentration, and pulp density. A 100% leaching efficiency of Pd was obtained through the addition of 5 vol% H2O2 in 3 M HCl at pulp density of 50 g/L at 80 °C for 120 min. Complete recovery of Pd was obtained at a pH = 9 due to the hydrolysis of Pd. These results indicate that the leaching time and presence of H2O2 played a key role in the stable formation of aqueous Pd–Cl complexes and in improving the mass transfer efficiency. The palladium powder obtained was palladium oxide, and the purity of palladium oxide was 86.6%. Consequently, it is expected that the obtained PdO powder can be utilized in glass, ceramic, and catalyst applications.

In this study, magnesia–nickel silicate ore was investigated, which contained 0.83% Ni and antigorite, chlorite, magnetite (Fe3O4), quartz, and mica as the main minerals. Chloride roasting and magnetic separation were used to treat the ore. The addition of red mud enhanced the transformation of nickel silicate to a strongly magnetic mineral mainly comprising metallic Ni and that of hematite to Fe3O4 and metallic Fe. Test results showed that a Ni concentrate with a Ni content of 11.41% and Ni recovery of 92.77% was achieved under the following optimal conditions: roasting temperature: 1373.15 K; roasting time: 120 min; CaCl2 dosage: 20%; coke dosage: 14%; red mud dosage: 30%; magnetic field intensity = 0.14 T; and grinding fineness: 90%

This paper characterized the microstructure and physical properties of the scale from a uranium mine in Xinjiang by SEM, XRD and FT-IR. Based on the orthogonal experiment design, the formula of HClO4: EDTA: (NaF + HNO3) = 4:1:5 is selected. The results show that the scale remover has the functions of dissolution, lattice damage and dispersion. The selected collaborative scale removal method can effectively remove the scale in the uranium mining process and has certain application value.

Poisoning of ion exchange resin often occurs in uranium hydrometallurgy processes, which reduces or even depletes the adsorption capacity of uranium adsorption. Many regeneration methods have been investigated but their static desorption efficiency is undesirable and only the recovery rate is considered in the selection of regenerant. In this paper, NaClO was selected as an antidote based on a series of investigation indexes. After detoxification by dynamic elution, all performance indexes of the regenerated resin are close to those of the new resin. Compared with static method, reagent consumption and detoxification time can be saved. At the same time of reducing the cost and waste liquid discharge, it also improves the work efficiency.

Neodymium (Nd) and dysprosium (Dy) based rare earth (RE) magnets are critical to green economy due to their vital role in permanent magnet applications such as electric motors and generators. The accumulating RE magnet waste in the form of end-of-life products (EoL), criticality of supply-demand, and the huge environmental costs associated with RE mining translated into an increased focus on RE recycling processes in the last decade. Environmentally friendly pyrometallurgical techniques were developed as an alternative to the traditional hydrometallurgical route due to the generation of large amounts of waste in hydrometallurgy. Liquid metal extraction (LME) is a promising pyrometallurgical technology as it has the ability to handle a wide variety of scrap feed materials, from swarf to ingots; to produce clean material with minimal impurities; and to allow the separation of metallic species without metallothermic reduction. So far, magnesium, silver, copper, and bismuth have been used as LME agents while exploration of other possibilities is ongoing. This article presents a systematic review of previous studies on the extraction agents in terms of the reaction mechanisms, behavior of the RE elements, extraction efficiencies, and the formation of intermetallic compounds during the process.

Lithium-ion batteries (LIBs) are employed in various electronic devices and industries. The recovery of valuable metals from spent LIBs has attracted much interest due to potential environmental is...

The growing demand for lithium-ion batteries will result in an increasing flow of spent batteries, which must be recycled to prevent environmental and health problems, while helping to mitigate the raw materials dependence and risks of shortage and promoting a circular economy. Combining pyrometallurgical and hydrometallurgical recycling approaches has been the focus of recent studies, since it can bring many advantages. In this work, the effects of incineration on the leaching efficiency of metals from EV LIBs were evaluated. The thermal process was applied as a pre-treatment for the electrode material, aiming for carbothermic reduction of the valuable metals by the graphite contained in the waste. Leaching efficiencies above 70% were obtained for Li, Mn, Ni and Co after 60 min of leaching even when using 0.5 M sulfuric acid, which can be linked to the formation of more easily leachable compounds during the incineration process. When the incineration temperature was increased (600–700 °C), the intensity of graphite signals decreased and other oxides were identified, possibly due to the increase in oxidative conditions. Higher leaching efficiencies of Mn, Ni, Co, and Li were reached at lower temperatures of incineration (400–500 °C) and at higher leaching times, which could be related to the partial carbothermic reduction of the metals.

Over the years, the generation of Waste Electric and Electronic Equipment has been significantly increased, which leads to environmental and economic concerns. Thus, it is fundamental to develop treatment methods for these residues. Printed Circuit Boards are essential components of electronic equipments. In this sense, printed circuit boards are composed of remarkable metals, in particular, copper and silver at high and low concentrations, respectively. These metals can be recovered by the hydrometallurgical process followed by a chemical purification step. Therefore, the aim of this study was to leach silver and copper from two different printed circuit boards (memory board and motherboard) from obsolete computers by hydrometallurgical route based on only one-stage leaching in oxidant media. When compared to the motherboard, a higher recovery rate of Ag was obtained from memory boards 83% and 33%, respectively. Whereas, similar recovery rates of copper were observed for memory board and motherboard, 48% and 46%, respectively.

Corresponding to the technological developments, production and consumption of nickel have increased greatly over time due to its unique mechanical and chemical properties. Therefore, the production of nickel will always keep its importance. The availability of laterite ores, which are oxide type ores, is 86% of the nickel reserves on the Earth, and the processes used in the production of nickel from sulfide type ores have negative environmental effects. Therefore, recovery of nickel from lateritic ores has become increasingly important in recent years. In this study, the aim was to determine the optimum parameters of nickel and cobalt production from limonite type lateritic nickel ores, which were taken from Manisa Caldag region of Turkey, using atmospheric pressure sulfuric acid leaching and pug-roast-leach process. When the results obtained in these processes were compared, it was found that the Ni leaching efficiency is nearly 8% higher and iron leaching efficiency (contamination) is nearly 4% lower in the pug-roast-leach process. Furthermore, the pug-roast-leach process was completed in 33% lower time compared to the atmospheric pressure sulfuric acid leaching process.

This study presents an up-to-date review on the methods and technologies applied for the recovery of Co from end-of-life Li-ion batteries. Considering the upcoming world demand for electric vehicle...

High consumption of acids and reductants is usually required when spent lithium-ion batteries are recycled using a hydrometallurgy route. The overstoichiometric chemicals end up as pollutants that have to be further treated. Low chemical and energy consumption have attracted considerable attention to achieve sustainability of a recycling process. In this research, LiFePO₄ was used as a reductant and induced crystallization was performed for the removal of Fe and P. More importantly, we demonstrate that it is possible to achieve additional reductant-free and near-to-stoichiometric acidic recovery of spent ternary lithium-ion batteries (NCMs) by introducing FePO₄·2H₂O seed crystals and using waste LiFePO₄. High efficiencies (>96%) of critical metals including Ni, Co, Mn, and Li are achieved, while iron phosphate remains as a solid product. Then, the leaching solution can be further used for the Ni–Co–Mn hydroxide precursor and lithium carbonate preparation. In addition, the mechanisms were subsequently investigated by combining thermodynamics analysis and systematic characterizations. This entire recycling process can be a highly economic, closed-loop alternative for recovering valuable metals from spent lithium-ion batteries.

A new eco-friendly process to comprehensively utilize boron-concentrate is proposed in this paper. In this process, Iron-concentrate, silicon dioxide, magnesium oxide, and boric acid could be produced from boron-concentrate. The highlight of this process was minimal waste discharge during the whole process. Iron removal was a key step to ensure the quality of boric acid and magnesium oxide. The introduced goethite precipitation method could remove iron to a very low level. With the addition of 3 cm3 H2O2 (5 vol. %) as an oxidizing agent, more than 99% of iron was removed from the leaching liquor. After the removal of iron, the resulting liquor was used to prepare magnesium precipitate. And the optimal preparation conditions were: the temperature of 30 °C and precipitation time of 60 min, ammonium- magnesium ratio of 1.5, the magnesium ion concentration of 34.8 g·L−1. Under those conditions, the magnesium precipitation efficiency was up to 98.5%. Magnesium oxide was obtained by roasting magnesium precipitate at 550 °C for 2 h. Then the mixed crystals of ammonium sulfate and boric acid were obtained by evaporating the liquor after iron removing and magnesium precipitating. Boric acid was separated from ammonium sulfate by dissolving the mixed crystals in ethanol solution.

The bastnaesite used in hydrometallurgy usually contains 7%–11% fluorine, and the conversion of fluorine into high-value products is the key to achieving green production of rare earths and improving the comprehensive utilization of bastnaesite. In order to recover fluorine from bastnaesite in the form of KBF4, the mechanism of F− conversion to BF 4 − in sulphuric acid leaching solution of roasted bastnaesite was studied by using Eh–pH diagram and simulation experiment. It shows that the formation of BF 4 − is affected by pH in the absence of rare earths. BF 4 − is hydrolyzed to BF3OH− and F− when the pH is greater than 3.9, and part of F− exists as HF 2 − when pH is lower than 2. In the presence of La3+, the formation of BF 4 − is mainly affected by LaF3 when pH is greater than 0, and in the case that the pH is lower than 2, it is mainly affected by HF 2 − . When Ce4+ is present in solution, CeF 2 2 + can exist stably in sulphuric acid solution. Bringing down the pH can reduce the stability of CeF 2 2 + and increase the BF 4 − conversion rate. Based on these results, KBF4 was prepared in the alkaline solution of bastnaesite, and the conversion of BF 4 − is 84.31%. This provides a theoretical basis for the recovery of fluorine from bastnaesite in the form of KBF4.

Solid-state batteries (SSBs) are promising next-generation batteries due to their potential for achieving high energy densities and improved safety compared to conventional lithium-ion batteries (LIBs) with a flammable liquid electrolyte. Despite their huge market potential, very few studies have investigated SSB recycling processes to recover and reuse critical raw metals for a circular economy. For conventional LIBs, hydrometallurgical recycling has been proven to be able to produce high-quality products, with leaching being the first unit operation. Therefore, it is essential to establish a fundamental understanding of the leaching behavior of solid electrolytes as the key component of SSBs with different lixiviants. This work investigates the leaching of the most promising Al- and Ta-substituted Li7La3Zr2O12 (LLZO) solid electrolytes in mineral acids (H2SO4 and HCl), organic acids (formic, acetic, oxalic, and citric acid), and water. The leaching experiments were conducted using actual LLZO production waste in 1 M of acid at 1:20 S/L ratio at 25 °C for 24 h. The results showed that strong acids, such as H2SO4, almost completely dissolved LLZO. Encouraging selective leaching properties were observed with oxalic acid and water. This fundamental knowledge of LLZO leaching behavior will provide the basis for future optimization studies to develop innovative hydrometallurgical SSB recycling processes.

An innovative cryo-mechano-hydrometallurgical process (named LIBAT) was demonstrated at pilot scale for the treatment of EOL lithium primary batteries with chemistry Li(0)-MnO2. The process allowed the recycling of steel scraps from external cases after cryomechanical dismantling, and the recovery of Mn and Li products after hydrometallurgical processing. During demonstration activities, about nine tons of batteries were treated in the cryomechanical section, and one ton of black mass was treated in the hydrometallurgical section for the recovery of Mn hydroxides and Li2CO3. The environmental impacts of the process were evaluated in comparison with an innovative pyrometallurgical approach allowing Li recovery, confirming the benefits of the proposed process due to a reduction in energy consumption. Process simulations were performed considering different mixture feeds (only Li primary, or mixture with Li-ion batteries) and process options (only the cryomechanical section of the integral process) to assess the lower limits of potentiality that would ensure economic sustainability.

Arsenic–rhenium filter cake, one of the main wastes produced by copper smelting systems, is a vital source of rhenium (Re). Using traditional hydrometallurgy methods, rhenium can be leached by sulfuric acid solution with the help of oxidants. However, the residual oxidants can seriously affect the efficiency and lifetime of the extractants and ion-exchange resins. We herein propose a novel method to leach rhenium through a displacement reaction using copper sulfate solution, thereby avoiding the use of oxidants. The results show that Re element exists in the arsenic–rhenium filter cake in two forms: Re2S7 and (As,Re)S amorphous. The rhenium leaching efficiency can reach 93.18%, and the kinetic data fit the shrinking core model. The leaching rate is controlled first by chemical reaction, with an apparent activation energy of 78.46 kJ mol−1. Afterwards, the leaching kinetics of rhenium fits an internal diffusion model. The results provide theoretical guidance on how to make full use of waste residues from copper smelting systems.

Present research reports a novel and feasible process to recover Ag and generate concentrate of precious metals (Au, Pd and Pt) from waste ICs present in PCBs of computers. Initially, depopulated ICs were pulverized and beneficiated to obtain metallic concentrate, which contained (per ton) 7 Kg Ag, 5 Kg Au, 110 g Pd and 4 g Pt along with Cu, Pb, Fe and Ni. Leaching was carried out and found that at optimized condition i.e. 3 M HNO3, temperature 80 °C, pulp density 50 g/L and mixing time 1 h, >90% of Ag, Cu, Pb and Ni were leached leaving Au, Pt and Pd in the residue. From the leach liquor, Ag was precipitated using 1 M KCl in 30 min and other metals were recovered by precipitation, solvent extraction and cementation methods. All wastes (solid/ liquid) generated during process development could be treated using standard environmental procedure.