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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%.

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.

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.

This article introduces an efficient decomposition process that uses sodium carbonate (Na2CO3) and activated carbon (C) as additives to decompose Bayan Obo mixed rare earth concentrate (hereinafter to be referred to as RE concentrate) by nonoxidative microwave radiation roasting. The roasting temperature, holding time, and contents of Na2CO3 and activated carbon are investigated. The optimum process parameters for decomposition are 800 °C and 30 min. The ratio of m(Na2CO3)/m(RE concentrate) is 0.5, and the ratio of m(C)/m (ER concentrate and Na2CO3) is 0.2 based on experimental data. Under the above conditions, the decomposition rate (shortened to DR) of RE concentrate is 98.58%, and the removal rates (shortened to CRs) of fluorine (F) and phosphorus (P) reached 80.35 and 46.75%, respectively. These rates are higher than traditional oxidation roasting under the same conditions. The three reasons for the result are the unique microwave heating characteristics, the overall efficient reaction of the mixture (RE concentrate, Na2CO3, and activated carbon), and the high nonoxidation rate of cerium. For these reasons and large experimental data, the reaction rate of the mixture is improved, and the efficiency of dilute hydrochloric acid for leaching rare earth elements is enhanced. In this article, the valence of rare earth elements in the roasted ore is all in the form of trivalence. Importantly, this nonoxidative roasted product can avoid the generation of chlorine in hydrochloric acid leaching. Moreover, such a short holding time is scarce in traditional roasting. When the mixture was roasted by utilizing microwave heating, the sinter phenomenon of the roasted product was avoided at high-temperature roasting. Finally, the surface morphology of RE concentrate at different conditions was observed by scanning electron microscopy (SEM) analysis, which can be used to compare the specific differences of roasting methods. According to these results, this process is beneficial for the decomposition of RE concentrate in terms of Na2CO3 roasting and is helpful for improving the clean and green technology method of hydrometallurgy.

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.

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.

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.

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

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%

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.

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.

Interfacial separation of components of extractants based on di-(2-ethylhexyl)phosphoric acid (di-2EHPA) in toluene and a mixture of di-2EHPA with trioctylamine in toluene has been studied in the course of treatment with aqueous sodium hydroxide solutions yielding an organic phase and an aqueous colloidal solution of di-2EHPA sodium salt. Conditions have been found for the isolation of almost pure di-2EHPA and toluene, as well as di-2EHPA and a trioctylamine solution in toluene. The aqueous colloidal solutions have been studied by conductometry, dynamic light scattering, and 1H-NMR spectroscopy. The considered systems are promising to be used in hydrometallurgy for improving parameters of extraction of metals and their concentrating in re-extracts.

In the process of mineralization and the extraction, the solubilities of metal minerals are affected by chlorides of alkali and alkaline earth metals, such as NaCl, KCl, MgCl2 and CaCl2, the studies on solubilities of chloride minerals in solutions are of significance for the separation and enrichment of elements in hydrometallurgy. To study the solubility relationships of minerals (such as KCl, MgCl2 and ZnCl2) in aqueous solutions, the phase equilibria of the quaternary system KCl−MgCl2−ZnCl2−H2O at 323 K were investigated by means of the isothermal dissolution equilibrium method. These investigations were carried out and the mineral solubilities were measured. The dry salt phase diagram and water content diagram were plotted and there are three double salts formations of MgZnCl4·6H2O, KMgCl3·6H2O (Car) and 2KCl·ZnCl2. The dry salt phase diagram contains four invariant points and nine isothermal solubility curves, which divide the phase diagram into six crystallization regions, and the crystallization regions correspond to the existence of six equilibrium solid phases, namely ZnCl2, 2KCl·ZnCl2, MgZnCl4·6H2O, MgCl2·6H2O (Bis), Car and KCl. The crystallization zone of KCl is the largest, and those of ZnCl2 and MgCl2·6H2O are the smallest. In addition, the equilibrium solid phases at the invariant points of ternary subsystems at 323 K and 373 K were compared and discussed.