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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

Electric waste from numerous devices that are put out of use every day has some form of printed circuit board that contains precious and valuable metals in their components. In order to extract these metals, the printed circuit boards were crushed and pyrolyzed into powder. The fine pyrolyzed printed circuit board (PPCB) powder was separated into fractions, and the fine metallic fraction was used as a raw material for metal leaching extraction. In order to better understand how various metal species react in leaching media, several leaching agents were used (sulfuric acid, nitric acid, glycine, and acid mine drainage-AMD) alone, and with the addition of hydrogen peroxide. Additionally, the influence of the S/L ratio and leaching temperature were investigated in sulfuric acid leaching solutions, as this is the one most widely used. In one case, the reactor was heated in a thermal bath, while in the other, it was heated in an ultrasonic bath. Lastly, several experiments were conducted with a (consecutive) two-pronged leaching approach, with and without applied pretreatment. The aim of this paper is to give a multifocal and detailed approach to how metals such as Al, Cu, Co, Zn, Sn, and Ca behave when extracted from fine PPCB powder. However, some attention is given to Nd, Pd, Pb, and Ba as well. One of the main findings is that regardless of the pretreatment or the sequence of leaching media applied, consecutive two-pronged leaching cannot be used for selective metal extraction. However, AMD was found to be suitable for selective leaching with very limited applications.

The need to recover critical elements from lithium-ion batteries is undisputed. The further development of cathode materials and the move towards cheaper alternatives make it necessary to adapt the corresponding hydrometallurgical recycling processes. In the best case, however, a process is so flexibly structured and designed that it can be used for a variety of cathode materials with different compositions. The leaching of nickel manganese cobalt oxide with sulfuric acid and a reducing agent has already been demonstrated and optimized in previous research work. Based on these data, an evaluation of the process as well as a parameter study for lithium iron phosphate cathode material, which has recently been used with increasing frequency but has a significantly lower valuable metal content, was carried out within the scope of this publication. By using the synergy effects that occur, an optimized parameter combination for the leaching of the critical element lithium could be found and further critical factors identified.

Lithium-ion battery (LIB) recycling has received continued interest in recent years due to its benefits, which include reducing the environmental impact of spent LIBs and providing a secondary source of valuable metals, such as Li, Co, and Ni. This paper characterized the Li separation with D2EHPA from citrate media as a function of pH and identified the optimal overall Li separation at a pH of 5.5. The Li separation was optimized at a pH of 5.5, with which it was concluded that 23 vol.% D2EHPA and an O/A ratio of 4 provided the best Li separation, for which 66.1% Li was extracted with 26.9% residual Mn, 6.8% Co, and 7.7% Ni in a single stage. The formation of a reversible hydrophobic third phase was identified during Li extraction at a pH of 5.5 or greater. Investigation of the third phase revealed that more than 99% of the Li, Co, and Ni were extracted to the third phase, while more than 69% of the Mn was extracted to the organic phase. STEM images of the third phase revealed a honeycomb-like structure, which was hypothesized to be a 2D mesoporous film caused by the insolubility of the organometallic complexes in the aqueous and organic phase.

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 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.

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.

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%

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.

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.

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.

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.

The stability constants of Sb5+ with Cl− as well as thermodynamics of the Sb–S–Cl–H2O system were calculated. The stability constants of Sb5+ with Cl− were obtained by theoretical calculations of the absorbance of a Sb5+-containing solution at different Cl− concentrations, which was detected by spectrophotometric analysis at certain wavelengths of light (380 nm). The logarithmic values versus 10 of stability constants of Sb5+ with Cl− were 1.795, 3.150, 4.191, 4.955, 5.427 and 5.511, respectively, and partly filled the data gaps in the hydrometallurgy of antimony. The presence and distribution of pentavalent antimony compounds under different conditions were analyzed based on equilibrium calculations. Thermodynamic equilibrium calculations were performed for Sb–S–Cl–H2O system, which included the complex behavior of Sb with Cl, and the equilibrium equations of related reactions in this system were integrated into the potential–pH diagram.

A large amount of acid-leaching residue is produced during the conventional Zn hydrometallurgy process, and this residue has a large concentration of a variety of valuable metals. The purpose of this study was to evaluate the ability of a procedure that entails the use of sulfation roasting, water leaching, and chlorination leaching (blowing oxygen technique) to recover Pb and Ag, followed by cooling crystallization and the replacement of Ag with lead sheet, to realize the full recovery of all valuable metals from zinc acid-leaching residue; consequently, good results were achieved. The best results were obtained under the following conditions: a sulfuric acid at 70% of the raw material quality, roasting temperature of 300 °C and roasting time of 2 h, followed by the process of leaching the roasted residue for 1 h by applying a water-to-solid ratio of 5:1 at room temperature. The recovery rates of Zn and Fe were 98.69% and 92.36%, respectively. The main parameters of the chlorine salt leaching system were as follows: Cl− concentration of 300 g/L, Fe3+ concentration of 25 g/L, acid concentration of 2 mol/L, liquid-to-solid ratio of 9 mL:1 g, temperature of 90 °C, and leaching time of 0.5 h; this leaching process was followed by filtration separation. These conditions resulted in high extents of leaching for Pb and Ag (i.e., 98.87% and 96.74%, respectively). Finally, the kinetics of the process of Ag leaching using Cl− ions in an oxygen-rich medium was investigated. It was found that the leaching process was controlled by the diffusion of the product layers, and the activation energy was 19.82 kJ/mol.

Abstract The state of the art for the recovery of metals from steel industry by-products using hydrometallurgical processes is reviewed. The steel by-products are different slags, dusts, and sludges from a blast furnace (BF), basic oxygen furnace (BOF), electric arc furnace (EAF), and sinter plant, as well as oily mill scale and pickling sludge. The review highlights that dusts and sludges are harder to valorize than slags, while the internal recycling of dusts and sludges in steelmaking is inhibited by their high zinc content. Although the objectives of treating BF sludges, BOF sludges, and EAF dust are similar, i.e., the removal of zinc and the generation of an Fe-rich residue to be returned to the steel plant, these three classes of by-products have specific mineralogical compositions and zinc contents. Because wide variations in the mineralogical composition and zinc content occur, it is impossible to develop a one-size-fits-all flow sheet with a fixed set of process conditions. The reason for the interest in EAF dust is its high zinc content, by far the highest of all steel by-products. However, EAF dust is usually studied from the perspective of the zinc industry. There are not only different concentrations of zinc, but also variations in the all-important ZnO/ZnFe2O4 (zincite-to-franklinite) ratio. In many chemical processes, only the ZnO dissolves, while the ZnFe2O4 is too refractory and reports to the residue. It only dissolves in concentrated acids, or if the dust is pre-treated, e.g., with a reductive roasting step. The dissolution of ZnFe2O4 in acidic solutions also brings significant amounts of iron in solution. Finally, due to its high potassium chloride content, sinter-plant dust could be a source of potassium for the fertilizer industry. Graphical Abstract

In this study, the mechanism of enhancing Fe removal from metallurgical grade silicon (MG–Si) by the novel metal-assisted chemical leaching (MACL) purification methods have been investigated. The typical impurity phase Si2Fe was selected to study interface reactions between the impurity phase and lixiviant. Based on density functional theory (DFT), the interactions of HF leaching, CuACL and AgACL on Si2Fe were revealed through studying the evolution behaviors of atom geometric structure, density of states and bond population, which showed that the stability of Si2Fe structure weakened with the orders of AgACL > CuACL > HF leaching. It was found that the lengths of Si–Fe bonds and metallicity of Si2Fe were successively increased when Si2Fe interacted with HF leaching, CuACL and AgACL, respectively. Compared with HF leaching, MACL weakened Si–Fe bond populations and increased H Fe bond populations, further destroyed the stability of Si2Fe structure. The experimental results showed that the impurity Fe removal rates were 94.30% for HF leaching, 95.75% for CuACL, and 97.27% for AgACL, respectively, which was highly consistent with the theoretical simulation results. The study provides a theoretical basis for enhancing Fe removal from silicon through MACL produces, indicating that MACL methods have a potential application in deep removal of impurity Fe from silicon in the future.

Modern hydrometallurgy has been developing for more than 100 years and the related articles keep piling up. Based on a bibliometric analysis of the articles in Hydrometallurgy, the most authoritative journal in the field of hydrometallurgy, we try to catch the research and development trends from a global perspective. Firstly, keywords burstness shows that rare earth, recycling, lithium, ionic liquid, and thorium are the hotspots in recent years, and the economic and technological reasons behind them were discussed in depth. Secondly, the proportion of biohydrometallurgy grows fast from 5% to 13% and the related articles are almost all about bioleaching. There are some new directions such as direct preparation of materials in hydrometallurgical processes and ion-imprinted techniques. Thirdly, the advanced instrument analysis methods such as XAFS (X-ray absorption fine structure), gene sequencing, and micro-CT promote the deep understanding of hydrometallurgy mechanism. Finally, the cooperation network and contribution of the main institutes were mapped.

The possibilities of extracting valuable components and producing selective good-quality concentrates from hard-to-beneficiate crude ores are considered for the disseminated copper–nickel ores from the Norilsk district. The stated aim is achieved by a combined technology including beneficiation and hydrometallurgical processes. Beneficiation is aimed at producing a rich copper concentrate and a nickel–pyrrhotite product. The aim of the hydrometallurgical process is the leaching of a nickel–pyrrhotite product followed by the flotation production of a nickel concentrate. The flotation hydrometallurgical processing of a nickel–pyrrhotite product makes it possible to produce nickel concentrates of a higher quality than those synthesized using a traditional technology.

Metallurgical & materials engineering 26(2), 199-208 (2020). doi:10.30544/513 special issue: "Hydrometallurgical operations and processes", Published by [Verlag nicht ermittelbar], Belgrade

Applications of solvent extraction operations and processes play one of the most important roles in Hydrometallurgy. Therefore, in this brief review, some general concepts for selected representative applications are discussed. Also, one particular entrainment problem solution is discussed in some more details. At first, the selected general concepts for metal production of copper and uranium from their ores are presented. Then after, the leaching-solvent extraction-electro winning process for copper is shown. Finally, the extraction of uranium from wet phosphoric acid is discussed.

Mixed hydroxide precipitate (MHP) is a nickel intermediate product that has economical benefits to downstream leaching of lateritic marginal ores. Usually, this product is subsequently processed and refined to produce nickel by hydrometallurgy, but an alternative route can be made integrating hydrometallurgy and pyrometallurgy. Assessing the overall consumption of ferroalloys to obtain stainless steel, as an increasing practice performed in China, the synergy of nickel extraction from laterites by leaching and precipitation as MHP with the production of MHP agglomerates applied as raw material to furnaces of ferronickel production is a very attractive practice. This work aims to further the technological development of an agglomerated product feasible to hydro-pyro integration. The agglomeration experiments were performed by traditional pelletizing (firing the pellets) and cold bonded pelletizing (aging the pellets by appropriate stocking). Appropriate compositions were prepared with MHP, additives and binders for each of these routes. A specific study of binder composition was made to find an adequate melting point. The produced pellets were tested to prove their properties by crushing strength tests. The standardization applied to iron ore was followed. The best result of crushing strength was 98.52 daN/pellet. The agglomerates with approved crushing strength for use in electric furnaces were smelted to produce alloys containing nickel; the agglomerates were characterized by scanning electron microscopy. The alloy obtained was metallic ferronickel with sulphide precipitates. Therefore, MHP pellets can be precursors of nickel alloys, which have to be refined to obtain the desirable composition.

Ionic liquids have emerged in hydrometallurgy as potential extractants for metals. In this work, the interactions of ALiCY (R4N+A-) synthesized by Aliquat336 and Cyanex272, and a mixture of ALiCY and TBP, were analyzed using extraction data and FT-IR spectroscopy. Co(II) and Ni(II) were extracted from two HCl concentrations (1.0×10-4 and 6.8 mol·L-1) using ALiCY and its mixture with TBP. The extraction results indicated that ALiCY has a dual function, as a cationic extractant at low HCl concentration and an anionic extractant at high HCl concentration depending on the types of metal complexes. The addition of TBP to ALiCY had a negative effect on the extraction of Co(II) from the 6.8 mol·L-1 HCl, while the effect was negligible from the 1.010-4 mol·L-1 HCl. The solvation of R4N+ by TBP significantly affected the extraction behavior of ALiCY for metal ions. The formation of hydrogen bonding between TBP and Cyanex272 was verified. These findings shed light on the behavior and interaction occurring between bif-ILs and solvating extractants for the extraction of metals in acidic media.

The Zijinshan gold-copper mine, in spite of the low-grade nature of the ore, has become one of the largest production-scale and most profitable non-ferrous metal mines in China. The successful application of hydrometallurgy as well as proper engineering design are the key factors for large-scale development of the Zijinshan gold-copper mine. In this contribution, the practical experience acquired in the development of the Zijinshan gold and copper mines is summarized. This covers most aspects of the production process including mining, beneficiation, ore stacking, heap (bio)leaching, carbon-in-leach, solvent extraction, electrowinning, wastewater and tailing treatments. The authors believe that this practical experience will not only help to promote the development of hydrometallurgy, but can also serve as a model for other gold and/or copper plants around the world.

Chalcopyrite is one of the most important copper minerals; however, the extracted efficiency of chalcopyrite is still not satisfactory in hydrometallurgy owing to its high lattice energy which leads to its low dissolution kinetics. To overcome the difficulties, many advanced technologies have been developed, including the selection of high effectively bacteria, the inhibition of the passivation film adhered onto the minerals surface, and the maintenance of solution redox potential under an optimum range. Up to date, considerable researches on the first two terms have been summarized, while the overview of the last term has been rarely reported. Based on corresponding works in recent years, key trends and roles of solution redox potential in copper hydrometallurgy, including its definition, effect and maintenance, have been introduced in this review.

Bioleaching is regarded as an essential technology to treat low grade minerals, with the distinctive superiorities of lower-cost and environment-friendly compared with traditional pyrometallurgy method. However, the bioleaching efficiency is unsatisfactory owing to the passivation film formed on the minerals surface. It is of particular interest to know the dissolution and passivation mechanism of sulfide minerals in the presence of microorganism. Although bioleaching can be useful in extracting metals, it is a double-edged sword. Metallurgical activities have caused serious environmental problems such as acid mine drainage (AMD). The understanding of some common sulfide minerals bioleaching processes and protection of Amd environment is reviewed in this article.

In order to recover pure alumina and synthesize magnesium spinel from black dross, a hydrometallurgical process was developed. This process consisted of 1) NaOH leaching of the mechanically activated black dross, 2) removal of silicate(IV) from the leaching solution by adsorption followed by coagulation, 3) precipitation of aluminum hydroxide from the purified leaching solution, 4) synthesis of magnesium spinel. Continuous experiments on the above-mentioned steps at optimum conditions were performed. Magnesium spinel was synthesized at 1000 °C for 5 hs by the co-precipitation method. The purity of spinel was 99.99 % and its characteristics were analyzed by XRD and SEM. Mass balance of the whole process indicated that the recovery percentage of alumina from the black dross was only 34 % owing to low leaching percentage. Further work on the pretreatments of black dross to improve its dissolution behavior is needed. Keywords: Aluminum hydroxide, Black dross, Spinel, Silicate, Hydrometallurgy

Manufacturing of nickel by hydrometallurgical technology at Harjavalta plant (Finland) had been caring out since 1960 by Outokumpu. Later on, the technology was modernized and currently Harjavalta plant belongs to PJSC “MMC Nornickel”. The plant is specializing on processing of copper-nickel mattes, converter mattes and by-products, originated from “Kola MMC” and third-party enterprises. Currently, the technology for the materials processing includes oxidative autoclave leaching (POX), solvent extraction, nickel electrowinning as well as solutions purification and metal salts obtaining stages. Selective POX produces nickel solution and copper cake (Cu-cake), which is a valuable by-product of the plant. The article presents the results on investigating the possibility of Cu-cake processing using POX in sulfate media at different temperature regimes. Low-temperature POX (105 oC) allowed to extract more than 95% Cu into solution within 30-60 min, while the dominating compound of solid residue was elemental sulfur; mass output of the solid residue was 20-25%. High-temperature POX (190 oC) allowed to extract more than 98% Cu in 60-80 min; mass output of the solid residue was 2.5-5%, which significantly increased a concentration of precious metals. Mid-temperature POX (150 oC) is characterized by increased duration. Copper extraction level of 95-98% is achieved at least after 120-180 minutes of leaching. Mass output of the solid residue was 6-10%. A detailed analysis of Cu-cake and the resulting products is provided. The behavior of precious metals was considered.

Chalcopyrite is the most abundant copper ore and, consequently, the most utilised to pro-duce metallic copper. The main route of treatment is through pyrometallurgical processes,but these emit significant quantities of SO2into the atmosphere (e.g. 182,000 t/year among allChilean smelters), producing mighty concern in the community. In this context, hydromet-allurgy is presented as an alternative that may be more environmentally friendly; however,the difficulties of processing sulphide minerals prevent achieving sustainable efficienciesfor the industry. In this research, a pure chalcopyrite mineral is leached at 25◦C with theaddition of manganese nodules as an oxidizing agent, and wastewater with a high con-centration of chloride that both enhances the dissolution and avoid the passivation of thechalcopyrite. The high concentrations of MnO2(4/1 and 5/1) allows that the potential valuescan be between 580 and 650 mV, which favors the dissolution of CuFeS2. The XRD showedthe formation of non-polluting species and, besides, they do not cause obstacles to the cop-per dissolution. High concentrations of chloride enable increasing copper solutions fromCuFeS2, attaining favorable outcomes when working with wastewater instead of seawater. The authors are grateful for the contribution of the Scien-tific Equipment Unit- MAINI of the Universidad Católica delNorte for aiding in generating data by automated electronicmicroscopy QEMSCAN®and for facilitating the chemical anal-ysis of the solutions. We are also grateful to Marina VargasAleuy, María Barraza Bustos and Carolina Ossandón Cortésof the Universidad Católica del Norte for supporting theexperimental tests. R.I.J thanks Centro CRHIAM Project Coni-cyt/Fondap/15130015.

A novel hydrometallurgical process involving leaching, precipitation, solvent extraction (SX) using phosphonium-based ionic liquids (ILs), and crystallization stripping was developed in this study. First, the spent catalyst was completely leached in distilled water at 343 K for 24 h. The leaching percentage of W(VI) was >99.9% according to ICP/SEM/EDX analysis. After leaching, the phosphate ions were separated by precipitation using Fe(NO3)3･9H2O as the precipitating agent. The separation percentage of phosphate was 90.8% at pH 8.11 according to ion-chromatography (IC) analysis. After the removal of phosphate, Alamine 336 and triethyl-n-pentyl phosphonium bis(trifluoromethylaulfonyl)amide ([P2225][NTf2]) were used as the extractant and diluent, respectively, for SX. The extraction percentage (E) of W(VI) reached 94.6% at pH 1.03, and the separation factor, W/P, was 101. The extraction mechanism of W(VI) was based on the ion association reaction related to the extracted complex, [(R3NH)nHxWyOz]IL, where x, y, z, and n are pH-dependent stoichiometric coefficients. After SX, the stripping percentage of W(VI) reached 100% at pH 8. Finally, crystallization proceeded at pH ≈ 4.5, and the obtained precipitate was identified to be ammonium paratungstate (NH4)10(H2W12O42)･4H2O by XRD analysis. A series of novel hydrometallurgical processes using ILs led us to conclude that W(VI) was efficiently recovered from the spent tungstophosphate catalyst.

With this article, first time in the open literature, the synthesis, and the characterization of an anode material from a domestic, intermediate product (i.e. ferrochromium alloy) have been carried out. The presented approach sets an example for many researchers in the future, as it allows the fabrication of low carbon footprint electrodes cost-effectively without using materials that can cause serious harm to the environment during their production processes. The research consists of two steps. First, a dihydrate iron-rich oxalate in the columnar structure is attained by selectively precipitating manganese, nickel, and cobalt together with iron, from the leachate of the domestic ferrochromium alloy with sulphuric acid. Then, once the powder is calcinated in a vacuum at 180˚C for 3 h, the anhydrous iron-rich oxalate (S1) powder is obtained and tested as an anode material. Moreover, the dihydrate iron-rich oxalate powder is calcinated in an argon atmosphere at 550˚C for 2 h to successfully fabricate porous, columnar-shaped iron-rich oxide (S2) powder. Galvanostatic tests demonstrate that the calcination affects both the structure and the morphology, hence the electrochemical performance: After 250 cycles, S2 delivers 1034.75 mAh g-1, whilst S1 performs 725.39 mAh g-1. The characterizations reveal that the presence of Mn, Ni, Co, along with Fe, increases the cycleability by creating additional electron conductive pathways in the powder. Moreover, owing to the porosity formed as a result of the calcination in the argon atmosphere, both the mechanical tolerance of the anode against the volumetric expansion that occurs during the reaction with lithium and the electrolyte/electrode contact are improved which lead to a better cycle performance even at higher current loads. Berk Demirel ; Istanbul Teknik Üniversitesi

Non-availability of rich primary resources of rare earth metals (REMs) and the generation of huge amounts of discarded magnets containing REMs, compelled the researchers to explore the possibilities for the recovery of REMs from discarded magnets. Therefore, the present paper reports the recovery of REMs (Nd, Pr, and Dy) from discarded Nd-Fe-B magnets. The process consists of demagnetization, pre-treatment, and hydrometallurgical processing to recover REMs as salt. Leaching studies indicate that 95.5% Nd, 99.9% Pr, and 99.9% Dy were found to be dissolved at the optimized experimental condition i.e., acid concentration 2 M H2SO4, temperature 75 °C, pulp density 100 g/L, and mixing time 60 min. Solvent extraction technique was tried for the selective extraction/separation of REMs and Fe. The result indicates that 99.1% (24.42 g/L) of Nd along with 90% (1.08 g/L) of Pr and total Fe were co-extracted using 35% Cyanex 272 at organic to aqueous (O/A) ratio 1/1, eq. pH 3.5 in 10 min of mixing time. It requires multistage separation and therefore, not feasible in view of economics. Thus, direct precipitation of REMs salt and iron oxide as pigment was studied using two stages of precipitation at different pH. The obtained precipitate of REMs and Fe hydroxides were dried separately to remove the moisture and further treated at elevated temperature to get pure REMs oxide and red oxide.

This article presents the results of studies of a low-waste technology for processing enrichment tailings using a combined enrichment–hydrometallurgical method. After washing the enrichment tailings from harmful products and reducing their size, multi-stage flotation of the crushed material of the enrichment tailings was carried out. The use of a new reagent in the flotation process was studied in order to ensure the maximum recovery of the main valuable components from the enrichment tailings. A new collector of Aero 7249 (Shenyang Florrea Chemicals Co., Ltd., Shenyang, China) type was used for the flotation. The recovery of valuable components was as follows: Cu, 6.78%, Zn, 91.69%, Pb, 80.81%, Au, 95.90%, Ag, 82.50%, Fe, 78.78%. Tailings of the flotation were re-enriched using a fatty acid collector (sodium oleate). Additional (reverse) flotation resulted in obtaining a product corresponding to the composition of building sand in terms of the content of valuable components of the waste rock. The studies of the conditions for processing the enrichment tailings of lead–zinc ore indicate the possibility of its optimization in order to maximize the involvement of waste in the production.

openaire: EC/H2020/721385/EU//SOCRATES The accomplishment of the goals set in the EU Green Deal and the Agenda 2030 for Sustainable Development requires a metallurgical industry that is even more resource-efficient, environmentally friendly and socially responsible than it is today. The European Training Network SOCRATES has taken this up by developing ground-breaking metallurgical processes for the valorisation of industrial intermediate products. This short article summarises the results obtained in the 4-year project and discusses the outcomes in light of the recently adopted EU Green Deal.

Steel is one of the most widely used materials in the past and today. Various techniques are used to recycle this material, including the electric arc furnace. This process has several advantages, but it also has a major disadvantage, namely, the generation of waste such as electric arc furnace dusts. Electric arc furnace dusts are classified as hazardous waste due to their high percentage of heavy metals, including zinc. Consequently, in the present research, the leaching of zinc for recovery with sulfuric acid solutions at ambient temperature and atmospheric pressure is evaluated, as well as the reuse of the leaching process residue as a raw material for ceramic materials. The sulfuric acid solutions were 0.125, 0.25, 0.5, and 1 molar, using clay for ceramic conforming and percentages of the leaching residue from 0–50%. The results showed that the optimum solution was 1 molar sulfuric acid, recovering all the zinc in the sample in 36 h. Furthermore, it was found that the clay-conformed ceramics with less than 40% leaching residue showed acceptable physical and mechanical properties according to standards. Therefore, this research develops a new environmental hydrometallurgy in which metallic elements of interest are valorized and the production of waste is avoided, reducing the deposition of hazardous waste in landfills and the extraction of raw materials for the manufacture of construction materials.

A Special Issue of Metals was commissioned that was devoted to aspects of Mineral Processing and Hydrometallurgy [...]

Heap leaching is a firm extractive metallurgical technology facilitating the economical processing of different kinds of low-grade ores that are otherwise not exploited. Nevertheless, regardless of much development since it was first used, the process advantages are restricted by low recoveries and long extraction times. It is becoming progressively clear that the selection of heap leaching as an appropriate technology to process a specific mineral resource that is both environmentally sound and economically feasible very much relies on having an ample understanding of the essential underlying mechanisms of the processes and how they interrelate with the specific mineralogy of the ore body under concern. This paper provides a critical overview of the role of gangues and clays minerals as rate-limiting factors in copper heap leaching operations. We aim to assess and deliver detailed descriptions and discussions on the relations between different gangues and clays minerals and their impacts on the operational parameters and chemical dynamics in the copper heap leaching processes. Validerad;2021;Nivå 2;2021-10-04 (alebob)

In recent years, critical and secondary raw materials (CRMs and SRMs, respectively) have received great interest within the circular economy model. In this work, the mycorrhizal-assisted phytomining (MAP) system, composed of Helianthus annuus–arbuscular mycorrhizal fungus Rhizophagus intraradices–Zn-volcanic ashes, was applied in bioreactors for the recovery of CRMs (Sr, P) and SRMs (Cr, Zn, Cu, Mn, Rb, Ni) from mining wastes of the Los Cóndores mine (Argentina). Our results showed high bioaccumulation of Sr, P, Mn, and Zn in the aerial tissues, and a high root-to-shoot translocation for Mn (4.02) > Sr > P > Rb > Zn (0.84). Mycorrhization treatment increased the root-to-leaf translocation for Cr and P and prevented translocation towards flower tissues in most elements. The estimated bioextracting potential of the MAP system (290 plants) in a vegetable depuration module (VDM) ranged from 158 mg/m3 P > Zn > Mn > 15.1 mg/m3 Sr. We demonstrated a promising and cost-effective biotechnology applicable in agronomical practices, given the exclusion of toxic elements in flower parts, as well as for the recovery of CRMs and SRMs by hydrometallurgy from plant biomass.

Chlorine is generated during iron ore sintering, mostly in the form of alkali chlorides and primarily accumulates in sintering dust, which must be removed before reusing. In this study, an in-situ monitor leaching system based was designed to detect chloride ion water leaching behaviors in real-time and improve the understanding of chlorine dissolution kinetic behaviors in water. Various parameters, including water leaching temperature, solid/liquid ratio, stirring speed, particle size and surfactant addition have been studied. Meanwhile their chlorine dissolution data exhibited a good fit to Stumm’s kinetic models. The results of kinetics analysis and transition state theory calculation on apparent activation energy demonstrated that the dissolution process was controlled by diffusion at low S/L ratio, while changed to be controlled by surface chemical reaction as the S/L ratio increased. Furthermore, increasing both temperature and stirring speed improved the chlorine removal speed. Moreover, reducing the particle size and adding 0.2% nonionic surfactant Triton X-100 reduced the surface energy and accelerated surface chemical reaction, which were also beneficial for removing chlorine from sintering dust. In addition, the SEM-EDS examination inferred that the existence of laurionite (PbOHCl) limited the chlorine dissolution rate to less than 97%, while beneficiation or hydrometallurgy treatment was needed to further remove chlorine.

In this work, mycorrhizal-assisted phytoextraction (MAP, Helianthus annuus–arbuscular mycorrhizal fungus Rhizophagus intraradices–Zn-volcanic ashes) was applied for the recovery of secondary and critical raw materials (SRMs and CRMs, respectively) from Joda West (Odisha, India) mine residues, within a novel multidisciplinary management strategy. Mine residues were preliminarily characterized by using advanced analytical techniques, and subsequently mapped, classified and selected using multispectral satellite Sentinel-2A images and cluster analysis. Selected mine residues were treated by MAP at laboratory scale, and the fate of several SRMs (e.g., Zn, Cr, As, Ni, Cu, Ca, Al, K, S, Rb, Fe, Mn) and CRMs (such as Ga, Ti, P, Ba and Sr) was investigated. Bioconcentration factors in shoots (BCS) and roots (BCR) and translocation factors (TF) were: 5.34(P) &gt, BCS &gt, 0.00(Al), 15.0(S) &gt, BCR &gt, 0.038(Ba), 9.28(Rb) &gt, TF &gt, 0.02(Ti). Results were used to predict MAP performance at larger scale, simulating a Vegetable Depuration Module (VDM) containing mine residues (1 m3). Estimated bio-extracting potential (BP) was in the range 2417 g/m3 (K) &gt, BP&gt, 0.14 g/m3 (As), suggesting the eventual subsequent recovery of SRMs and CRMs by hydrometallurgical techniques, with final purification by selective electrodeposition, as a viable and cost-effective option. The results are promising for MAP application at larger scale, within a circular economy-based approach.

The consumption of lithium has increased dramatically in recent years. This can be primarily attributed to its use in lithium-ion batteries for the operation of hybrid and electric vehicles. Due to its specific properties, lithium will also continue to be an indispensable key component for rechargeable batteries in the next decades. An average lithium-ion battery contains 5–7% of lithium. These values indicate that used rechargeable batteries are a high-quality raw material for lithium recovery. Currently, the feasibility and reasonability of the hydrometallurgical recycling of lithium from spent lithium-ion batteries is still a field of research. This work is intended to compare the classic method of the precipitation of lithium from synthetic and real pregnant leaching liquors gained from spent lithium-ion batteries with sodium carbonate (state of the art) with alternative precipitation agents such as sodium phosphate and potassium phosphate. Furthermore, the correlation of the obtained product to the used type of phosphate is comprised. In addition, the influence of the process temperature (room temperature to boiling point), as well as the stoichiometric factor of the precipitant, is investigated in order to finally enable a statement about an efficient process, its parameter and the main dependencies.

The demand for rare earth elements for everyday technology and applications has initiated much research into the extraction and recovery of these rare earth elements. An otherwise unknown group of minerals, eudialyte is a zircon silicate consisting of rare earth oxides (REO), contained in a unique mineral structure and represented by a complex chemical formula. Research into extraction and recovery of rare earth elements involves various beneficiation and hydrometallurgical techniques. The goal of beneficiation being to efficiently liberate and upgrade the REO content, followed by hydrometallurgy to extract the desired elements. This overview will discuss previous research on treating eudialyte group minerals via different mineral processing and extraction techniques.

CSIR-National Metallurgical Laboratory (CSIR-NML), India dealing with coal characterization, has recently made sincere efforts to develop a process to recover REMs from Indian coal bottom ash (CBA) using hydrometallurgical route. The developed process consists of REMs leaching from CBA followed by solvent extraction and selective precipitation. After the selection of suitable leachant, bench scale studies were performed to optimize various process parameters viz. concentration of leachant, mixing time, temperature and pulp density. Maximum dissolution of REMs were achieved using 4 mol/L HCl at 90 °C for 2 h and pulp density 50 g/L. Unused acid present in the leach liquor was further extracted and subsequently processed for selective precipitation of REMs at pH 1.67. A novel process flow-sheet is proposed for the effective recovery of highly pure REMs salt. Developed process at laboratory scale has potential to be commercialized after scale-up and feasibility studies.

With the rapid development of China's aluminum industry and the depletion of high-quality bauxite resources, technology for the clean and efficient utilization of non-traditional bauxite resources has become the focus in related fields. The alumina-to-silica mass ratio of low-grade high-iron sedimentary bauxite from Yunnan, China is 2.65; diaspore and goethite coexist in this bauxite. To enhance the utilization efficiency of bauxite, the hydrometallurgy process of the “calcification-carbonation method” (CCM) had been proposed, and the research results indicated that the addition of lime promoted the transformation of the goethite phase significantly, and the replacement ratio of Al in goethite decreased from 16.02% to 12.15% for a calcification temperature of 200 °C. The Gibbs free energy for the generation of Ca3(Fe0.87Al0.13)2(SiO4)1.65(OH)5.4 decreases gradually with an increase in the reaction temperature, and an excessive decomposition temperature in the carbonization process is not conducive to the decomposition of the garnet phase. The calcification reaction is controlled by diffusion and chemical reaction, and the activation energy in the temperature range from 220 to 260 °C (determined using a high-pressure DSC) is 38.4 kJ/mol; it is 19.6 kJ/mol in the temperature range from 260,276.8 °C. Fe completely dissociates from hydrogarnet upon carbonization, and the main silica-containing phases in the digested slag are unreacted hydrogrossular and calcium silicate. The CCM enhanced the recovery ratios of Al2O3 and Fe from high-iron diasporic bauxite by ~20% and 10%, respectively, compared with those in the Bayer process, and the Na content decreased to lower than 0.1% in the CCM slag; this can be used as cement raw material directly. Thus, the clean and efficient utilization of low-grade high-iron sedimentary bauxite was achieved using the CCM.

The present work addresses the recovery of rhenium from scrub liquor of molybdenite concentrate roasting fume and dust by solvent extraction method. According to the results, recovery of rhenium from the scrub liquor is not practical unless molybdenum is removed in advance. The extraction of molybdenum was carried out using a D2EHPA-TBP system which resulted in up to 99.8% Mo extraction in a two-stage solvent extraction at pH = 1 and O/A = 1. Up to 99.6% of Re was extracted subsequently using TOA in a single-stage extraction at pH = −0.3 and O/A = 1:20. The organic phase was stripped by ammonium hydroxide 32% and the resultant liquor was further subjected to evaporation as a result of which, an enriched purified solution was obtained. Ammonium perrhenate was precipitated from the enriched liquor by adjusting the pH to 6.5–7.