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Solvent extraction scheme to isolate Zn, Cu, and Ni from glutamate media as hypothetical product of electric arc furnace dust alkaline leaching was developed, with concentrations being 17.6, 0.35, and 0.14 g/L, respectively. Three extractants were investigated: Cyanex 272, DEHPA, and Acorga M5640 selectively separated Zn, Ni, and Cu from each other. Aside from pH, parameters investigated included O/A ratio, extractant concentration in kerosene as diluent, and sulfuric acid concentration as stripping agent. pH was the most critical factor in determining the separation factor among three metals since pH controlled metal speciation in pregnant leach solution and regulated the interaction between metal ions and extractant. Based on previous studies, a flowsheet for Zn, Cu, and Ni isolation is proposed, which obeys the following sequence: Zn separated from Cu and Ni by Cyanex 272 (in pregnant leach solution at pH 8, log separation factor Zn–Cu 4.78, Zn–Ni 2.51), followed by Ni separation from Cu by DEHPA (in raffinate at pH 7, log separation factor Ni–Cu 3.92), and finally Cu extraction (in raffinate at pH 4, log distribution coefficient 3.19). Sulfuric acid was proved to be a suitable stripping agent with optimum concentrations of Zn, Ni, and Cu being 0.5, 0.25, and 2 M, respectively.

Hoidas Lake lies in the Northern Rae Geological Province, in the general vicinity of many of Saskatchewan's large uranium mines. The mineralogy of the Hoidas Lake rare-earth deposit differs from most other such deposits in that it is hosted in equal abundance in veins containing apatite and allanite mineral groups. Hoidas Lake also differs from other deposits in that it contains a significant amount of heavy rare-earth elements, such as dysprosium. This abundance of heavy Rare Earth Elements (REE’s) is significant, as there is a growing demand for the heavier rare earths in high-tech manufacturing (such as the use of dysprosium in the manufacturing of hybrid car components). Recently, metallurgical testing was performed on a Hoidas Lake REE deposit composite. These investigations included characterization, flotation testing, heavy media separation, magnetic separation testing, whole ore leaching studies, bond work index grindability testing, and relative abrasion index testing. This paper summarizes this research effort.

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

Historically, the ability to effectively separate carbonate gangue from bastnaesite via flotation has frequently proven to be challenging without sacrificing significant rare earth oxide (REO) grade or recovery. However, in light of the fact that the rare earth bearing minerals often exhibit higher specific gravities than the carbonate gangue, the possibility exists that the use of gravity separation could be used to achieve such a selective separation. This however is complicated by the fact that, in cases such as this study when the liberation size is finer than 50 microns, most traditional gravity separation methods become increasingly challenging. The aim of this study is to determine the applicability of centrifugal concentrators to beneficiate ultra-fine (UF) bastnaesite and calcite bearing flotation concentrates. By using a UF Falcon, it was possible to achieve initial gravity REO recoveries exceeding 90% while rejecting on the order of 25% to 35% of the total calcium from an assortment of rougher and cleaner flotation concentrates. Additionally, when additional stages of cleaner UF Falcon gravity separation were operated in an open circuit configuration, it was possible, from an original fine feed of 35 microns containing 50.5% REO and 5.5% Ca, to upgrade up to approximately 59% REO and 2.0% calcium. While not the goal of this study, these results also support previous limited data to suggest that UF Falcons are potentially capable of treating a wider range of materials than they were originally designed for, including feeds rich in heavy mineral content.

Chemical and mineralogical characterization of Malaysian monazite, a phosphate mineral, bearing rare earth elements separated from the tin tailings originated from Ipoh, Perak, Malaysia, was performed in this paper. The study aims to collect detailed information on the chemical composition, crystal phases, and microstructure of the mineral monazite concentrate that would aid to optimize the subsequent hydrometallurgical processes for high-efficient separation of thorium and other associated rare earth elements. A systematic characterization study of the concentrate was conducted using techniques such as optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FTIR). These techniques analyzed the morphological details on the surface, elemental analysis, and mineral association assessment and identified the surface functionalization groups. The bulk composition and the mineral phases in which the elements are present were studied by wavelength-dispersive X-ray fluorescence (WD-XRF) and X-ray diffraction (XRD) studies respectively. The XRF analysis confirmed the presence of Ce, La, Nd, Pr, and Y (rare earth oxides: REO’s ~ 60 wt.%) while thorium dioxide (ThO2) accounted for 7 wt.% of the total composition. Traces of Ca, K, Al, Fe, Ti, and Mn were also confirmed by SEM elemental mapping. The XRD results confirmed that the concentrate was primarily composed of monazite (Ce, La, Nd, Th (PO4)) along with minor impurity phases of quartz. Automated mineralogical analysis was used as a confirmatory tool to corroborate the preliminary evidences. Based on the particle size distribution analysis supported by SEM, the majority of monazite grains were found to be present in the size range of 170–210 μm. Strong bands of PO4 and SiO4 were observed in the IR spectra corresponding to the phospho-silicate matrix of the REE mineral.

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.

The efficacy of monosodium glutamate (MSG) as a lixiviant for the selective and sustainable leaching of zinc and copper from electric arc furnace dust was tested. Batch leaching studies and XRD, XRF and SEM-EDS characterization confirmed the high leaching efficiency of zinc (reaching 99%) and copper (reaching 86%) leaving behind Fe, Al, Ca and Mg in the leaching residue. The separation factor (concentration ratio in pregnant leach solution) between zinc vs. other elements, and copper vs. other elements in the optimum condition could reach 11,700 and 250 times, respectively. The optimum conditions for the leaching scheme were pH 9, MSG concentration 1 M and pulp density 50 g/L. Kinetic studies (leaching time and temperature) revealed that the saturation value of leaching efficiency was attained within 2 h for zinc and 4 h for copper. Modeling of the kinetic experimental data indicated that the role of temperature on the leaching process was minor. The study also demonstrated the possibility of MSG recycling from pregnant leach solutions by precipitation as glutamic acid (&gt, 90% recovery).

The recovery of platinum group elements (PGE (platinum group element coating), Pd, Pt, and Rh) from used catalytic converters, using low energy and fewer chemicals, was developed using potassium bisulfate fusion pretreatment, and subsequently leached using hydrochloric acid. In the fusion pre-treatment, potassium bisulfate alone (without the addition of an oxidant) proved to be an effective and selective fusing agent. It altered PGE into a more soluble species and did not react with the cordierite support, based on X-Ray Diffraction (XRD) and metallographic characterization results. The fusion efficacy was due to the transformation of bisulfate into pyrosulfate, which is capable of oxidizing PGE. However, the introduction of potassium through the fusing agent proved to be detrimental, in general, since potassium formed insoluble potassium PGE chloro-complexes during leaching (decreasing the recovery) and required higher HCl concentration and a higher leaching temperature to restore the solubility. Optimization on the fusion and leaching parameter resulted in 106% &plusmn, 1.7%, 93.3% &plusmn, 0.6%, and 94.3% &plusmn, 3.9% recovery for Pd, Pt, and Rh, respectively. These results were achieved at fusion conditions: temperature 550 &deg, C, potassium bisulfate/raw material mass ratio 2.5, and fusion time within 30 min. The leaching conditions were: HCl concentration 5 M, temperature 80 &deg, C, and time within 20 min.

This paper demonstrates the recovery of valuable metals from shredded Waste Printed Circuit Boards (WPCBs) by bromine leaching. Effects of sodium bromide concentration, bromine concentration, leaching time and inorganic acids were investigated. The most critical factors are sodium concentration and bromine concentration. It was found that more than 95% of copper, silver, lead, gold and nickel could be dissolved simultaneously under the optimal conditions: 50 g/L solid/liquid ratio, 1.17 M NaBr, 0.77 M Br2, 2 M HCl, 400 RPM agitation speed and 23.5 &deg, C for 10 hours. The study shows that the dissolution of gold from waste printed circuit boards in a Br2-NaBr system is controlled by film diffusion and chemical reaction.

Blast furnace slag (BFS) is a typical solid waste generated in the steel production. Most of previous investigations have reported that the BFS has been used as traditional construction materials (cement, roadbed filling, concrete). In this study, a novel use route for BFS was proposed to prepare high-temperature composite phase change materials (C-PCMs) for thermal energy storage. Three typical inorganic PCMs (NaNO3, Al and Na2SO4 with different operating temperature) were blended with the pre-ground BFS to fabricate BFS-based C-PCMs by means of a mixing and sintering process. The results showed that NaNO3 had excellent chemical compatibility with BFS and the prepared C-PCMs had perfect phase change performance. The enthalpies of NaNO3/BFS C-PCMs was 65.53 J/g with melting point 300.5 °C and the super-cooling was only 0.1 °C. Furthermore, the NaNO3/BFS C-PCMs could retain good thermal reliability after 100 thermal cycles, which presented a potential application in the thermal energy storage system. In addition, the morphological structure, thermal reliability and heat transfer property of the NaNO3/BFS C-PCMs were characterised by using SEM, TGA and TG-DSC.

Historically, the ability to effectively separate carbonate gangue from bastnaesite via flotation has frequently proven to be challenging without sacrificing significant rare earth oxide (REO) grade or recovery. However, in light of the fact that the rare earth bearing minerals often exhibit higher specific gravities than the carbonate gangue, the possibility exists that the use of gravity separation could be used to achieve such a selective separation. This however is complicated by the fact that, in cases such as this study when the liberation size is finer than 50 µm, most traditional gravity separation methods become increasingly challenging. The purposes of this study is to determine the applicability of gravity concentrators to beneficiate bastnaesite from deleterious calcite bearing flotation feed material. Via the use of a UF Falcon, it was possible to achieve rougher gravity REO recoveries approaching the upper 80% range while rejecting on the order of 30% of the total calcium. In terms of purely REO recovery, this represents a significant improvement over results obtained via a traditional Falcon in previously reported studies.

The Bear Lodge Project is an important rare earth deposit in the United States. While extensive previous studies have settled on a crushing, screening, gravity and magnetic separation process, this study sets out to investigate an alternative flowsheet based on flotation and wet high intensity magnetic separation (WHIMS) to effectively beneficiate the rare earth oxide (REO) content of the Bear Lodge ore. Mineral characterization found ancylite was the dominant rare earth mineral, associated mainly with calcite and strontianite. Electrokinetic studies on the effects of pH, concentrations of various ions (Sr2+, HCO3− and CO32−) and hydroxamate concentrations were performed to establish the electric nature of the Bear Lodge ore. The isoelectric points (I.E.P) of the material in distilled water was around 5.27. The Sr2+ and CO32− ions in solution significantly affected the surface charge of the material. Adsorption studies suggested that the mechanism of hydroxamate adsorption is chemisorption, as hydroxamate adsorption increased on the Bear Lodge ore with an increase in temperature. WHIMS was employed to remove the iron content to reduce the interference of iron in following flotation process and consumption of hydroxamic acid. After cleaner flotation a REO grade of 11.2% at 72.7% recovery from a feed material of 4.5% REO was obtained. In light of the loss of REO in WHIMS process, it is possible to produce a concentrate containing 11.2% REO grade at 61.2% recovery.

Tin-, iron-bearing tailing is a typically hazardous solid waste in China, which contains plenty of valuable tin, iron elements and is not utilized effectively. In this study, a multistage utilization process was put forward to get the utmost out of the valuable elements (tin and iron) from the tailings, and a gradient-recovery method with three procedures was demonstrated: (1) An activated roasting followed by magnetic separation process was conducted under CO-CO2 atmosphere, tin and iron were efficiently separated during magnetic separation process, and 90.8 wt% iron was enriched in magnetic materials while tin entered into non-magnetic materials; (2) The tin-enriched non-magnetic materials were briquetted with CaCl2 and anthracite and roasted, then tin-rich dusts were collected during the chloridizing roasting process; (3) The roasted briquettes were infiltrated in melting NaNO3 to prepare NaNO3/C-PCMs by a infiltration method. Three kinds of products were obtained from the tailings by the novel process: magnetic concentrates containing 64.53 wt.% TFe, tin-rich dusts containg 52.4 wt.% TSn and NaNO3/C-PCMs for high temperature heat storage. Such a comprehensive and clean utilization method for tin-, iron-bearing tailings produced no secondary hazardous solid wastes, and had great potential for practical application.

Electric vehicles (EVs) will be an important part of a low-carbon economy. Future EV adoption depends on overcoming multiple barriers, including charging infrastructure, sufficient electricity generation, and the availability of battery raw materials at acceptable costs, including cobalt, copper and nickel – which typically are co-produced. Various EV projections have been made, along with associated requirements for battery raw materials (demand). There have been separate assessments of the availability of raw materials (supply). However, integrated assessments of supply and demand and their interaction over time are lacking to support decision-making. Using a dynamic market model that reflects the co-produced nature of cobalt, copper and nickel production as well as recycling, we estimate global output of these three metals under different EV growth scenarios from 2020 to 2040. Results suggest that starting in 2025, replacement demand for battery raw materials becomes important. Thus, estimates for future material demand that consider only demands from new EVs are incomplete and misleading. EV deployment and associated increased demand for raw materials will have a greater impact on prices for cobalt than nickel and, in turn, for nickel than copper. High EV deployment scenarios will be difficult to achieve without larger supplies of copper, nickel and cobalt than forthcoming under the conditions modeled here, which anticipates a six-year time lag between a demand increase and the expansion of metal-production capacity. Shortening battery lifetimes and improving collection and recycling rates increase secondary supply, but the extent to which these factors support additional EV deployment is mixed.

Flash furnace electrostatic precipitator dust (FF-ESP dust) is a recycle stream in some primary copper production facilities. This dust contains high amounts of copper. In some cases, the FF-ESP dust contains elevated levels of bismuth and arsenic, both of which cause problems during the electrorefining stages of copper production. Because of this, methods for separation of copper from bismuth and arsenic in FF-ESP dust are necessary. Hydrometallurgical leaching using a number of lixiviants, including sulfuric acid, sulfurous acid, sodium hydroxide, and water, were explored. Pourbaix diagrams of copper, bismuth, and arsenic were used to determine sets of conditions which would thermodynamically separate copper from bismuth and arsenic. The data indicate that water provides the best overall separation between copper and both bismuth and arsenic. Sodium hydroxide provided a separation between copper and arsenic. Sulfurous acid provided a separation between copper and bismuth. Sulfuric acid did not provide any separations between copper and bismuth or copper and arsenic.

Global demand and consumption of rare earth elements and compounds have led to increasing research to further our understanding of their beneficiation and recovery. Monazite is the second-most important rare earth-bearing mineral that can be exploited. In this study, the surface chemistry of monazite in terms of zeta potential, adsorption density, and flotation responses using octanohydroxamic acid is determined. Apatite, ilmenite, quartz, rutile, and zircon are the minerals that frequently occur with monazite, and hence they were chosen as gangue minerals in this study. The isoelectric points of monazite, apatite, ilmenite, quartz, rutile, and zircon are 5.3, 8.7, 3.8, 3.4, 6.3, and 5.1, respectively. Thermodynamic parameters of adsorption were evaluated. Ilmenite has the highest driving force for adsorption. Adsorption density value shows that octanohydroxamic acid adsorbs onto monazite and its gangue minerals. This observation was further confirmed by microflotation experiments. Increasing the temperature to 80 °C raises the adsorption and floatability of monazite and gangue minerals, which does not allow for separation. Monazite is best recovered at a pH range of 7.5–10. Appropriate use of depressant is recommended in order to enhance the separation of monazite from its gangue.

Because of their selective depressing power, sodium silicate and lignosulfonate have been widely used as depressants in rare-earth mineral flotation to separate minerals from specific types of gangue minerals. In this project, the microflotation of a xenotime pre-concentrate and pure samples of the selected gangue minerals ilmenite, zircon, schorl and staurolite was carried out. This utilized octano-hydroxamic acid and sodium oleate as the collectors and the research was conducted in a Partridge-Smith microflotation cell. The flotation of the mixed samples (weight ratio = 1:1) of xenotime and each one of its gangue minerals was also investigated at both room temperature and 80 °C, using sodium silicate or ammonium lignosulfonate in the presence of octano-hydroxamic acid and sodium oleate respectively. The flotation results are described and compared with those observed by previous researchers. The effects of sodium silicate and ammonium lignosulfonate on weight recoveries and grade of xenotime are also discussed and compared.

The fundamentals of the surface chemistry of ancylite, strontianite, and calcite in the presence of hydroxamic acid (HXY) were investigated based on their zeta potential, adsorption, infrared measurement, and microflotation. Zeta potential studies indicate that the isoelectric points of ancylite, strontianite, and calcite are around 5.46, 4.50, and 5.50, respectively. HXY is chemically adsorbed onto the surface of ancylite, which was confirmed by both zeta potential and infrared measurements. At room temperature, the monolayer coverage of HXY on ancylite is shown as 20 µmol/m2, which is much higher than the monolayer coverages for strontianite and calcite. In the comparison of adsorption densities of strontianite, calcite, and ancylite at both room temperature and 50 °C, the results show that strontianite and calcite appear more sensitive to temperature than ancylite. Microflotation studies of pure minerals show that theoretically, calcite could be separated from strontianite and ancylite at pH 7.5 in the presence of 5 × 10−4 M HXY, and ancylite can be separated from strontianite in the presence of 2 × 10−4 M HXY when pH is around 9. However, as indicated from the zeta potential results, the dissolved species from minerals significantly change the flotation behavior of minerals’ mixture. Thus, a successful flotation separation could not be achieved without any modifiers.

Rare earths, sometimes called the vitamins of modern materials, captured public attention when their prices increased more than tenfold in 2010 and 2011. As prices fell between 2011 and 2016, rare earths receded from public view, but less visibly, they became a major focus of innovative activity in companies, government laboratories, and universities. Geoscientists worked to better understand the resource base and improve our knowledge about mineral deposits that can be mines in the future. Process engineers carried out research that is making primary production and recycling more efficient. Materials scientists and engineers searched for substitutes that require fewer or no rare earths while providing properties comparable or superior to those of existing materials. As a result, even though global supply chains are not significantly different now than they were before the market disruption, the innovative activity motivated by the disruption will likely have far-reaching, if unpredictable, consequences for supply chains of rare earths in the future.

This research study was designed to investigate the principles of surface chemistry and microflotation of xenotime and selected gangue minerals, and to achieve a better understanding of the factors affecting flotation performance and separation of xenotime from associated gangue minerals in an efficient way. A preconcentrated xenotime sample and four selected gangue minerals such as ilmenite, zircon, schorl, and staurolite were used in this study. Using octanohydroxamic acid as a collector, surface chemistry was investigated through surface area measurements, zeta potential tests, and adsorption density determinations. The zeta potential of xenotime was measured as 3.90 in this study. The results of adsorption studies showed a mechanism of chemisorption and correlated well with the results of microflotation tests conducted at room temperature in a Partridge–Smith cell. In this paper, the surface chemistry and microflotation behaviors are discussed based on both the lab observations and literature review, in the hope to shed light on further research and industrial flotation operation.

Recently, leaching of gold with cyanide has come under scrutiny for its possible detrimental effects to the environment. Also, in some gold bearing ores and concentrates, conventional cyanide leaching is not the best method for gold extraction. This is due to gold particle encapsulation, cyanicides or pregrobbing carbon such as found in refractory ores and concentrates. Hence, there is much interest in developing an alternative way to extract gold from ore. Possible benefits of leaching gold with something other than cyanide include easier processing of refractory ore bodies including: carbonaceous, cyanicides, and sulfides, cheaper reagent and operating costs and opening of mine properties in places where cyanide use has been limited by the law. Hence, this paper details the fundamentals and development of the Alkaline Sulfide Gold Leaching system.

Summary Separating rare-earth-element-rich minerals from unwanted gangue in mined ores relies on selective binding of collector molecules at the interface to facilitate froth flotation. Salicylhydroxamic acid (SHA) exhibits enhanced selectivity for bastnäsite over calcite in microflotation experiments. Through a multifaceted approach, leveraging density functional theory calculations, and advanced spectroscopic methods, we provide molecular-level mechanistic insight to this selectivity. The hydroxamic acid moiety introduces strong interactions at metal-atom surface sites and hinders subsurface-cation stabilization at vacancy-defect sites, in calcite especially. Resulting from hydrogen-bond-induced interactions, SHA lies flat on the bastnäsite surface and shows a tendency for multilayer formation at high coverages. In this conformation, SHA complexation with bastnäsite metal ions is stabilized, leading to advanced flotation performance. In contrast, SHA lies perpendicular to the calcite surface due to a difference in cationic spacing. We anticipate that these insights will motivate rational design and selection of future collector molecules for enhanced ore beneficiation., Graphical Abstract, Highlights • Salicylhydroxamic acid (SHA) is an effective collector for flotation of bastnäsite • DFT calculations show that the phenol group anchors SHA flat to bastnäsite surface • Spectroscopic results suggest SHA multilayers on bastnäsite at high coverage • This peculiar adsorption explains efficacy of SHA in bastnäsite flotation from ores, Chemical Engineering; Spectroscopy; Physical Inorganic Chemistry; Surface Chemistry

Globally, copper, silver, and gold orebody grades have been dropping, and the mineralogy surrounding them has become more diversified and complex. The cyanidation process for gold production has remained dominant for over 130 years because of its selectivity and feasibility in the mining industry. For this reason, the industry has been adjusting its methods for the extraction of gold, by utilizing more efficient processes and technologies. Often, gold may be found in conjunction with copper and silver in ores and concentrates. Hence, the application of cyanide to these types of ores can present some difficulty, as the diversity of minerals found within these ores can cause the application of cyanidation to become more complicated. This paper outlines the practices, processes, and reagents proposed for the effective treatment of these ores. The primary purpose of this review paper is to present the hydrometallurgical processes that currently exist in the mining industry for the treatment of silver, copper, and gold ores, as well as concentrate treatments. In addition, this paper aims to present the most important challenges that the industry currently faces, so that future processes that are both more efficient and feasible may be established.

NdFeB permanent magnet scrap is regarded as an important secondary resource which contains rare earth elements (REEs) such as Nd, Pr and Dy. Recovering these valuable REEs from the NdFeB permanent magnet scrap not only increases economic potential, but it also helps to reduce problems relating to disposal and the environment. Hydrometallurgical routes are considered to be the primary choice for recovering the REEs because of higher REEs recovery and its application to all types of magnet compositions. In this paper, the authors firstly reviewed the chemical and physical properties of NdFeB permanent magnet scrap, and then carried out an in-depth discussion on a variety of hydrometallurgical processes for recovering REEs from the NdFeB permanent magnet scrap. The methods mainly included selective leaching or complete leaching processes followed by precipitation, solvent extraction or ionic liquids extraction processes. Particular attention is devoted to the specific technical challenge that emerges in the hydrometallurgical recovery of REEs from NdFeB permanent magnet scrap and to the corresponding potential measures for improving REEs recovery by promoting the processing efficiency. This summarized review will be useful for researchers who are developing processes for recovering REEs from NdFeB permanent magnet scrap.