This Special Issue of Minerals presents recent, select studies that highlight advances in the fields of hydro- and biohydrometallurgy. It aims to attract the interest of readers and especially of ...young scientists and students in this fascinating scientific discipline. The topics addressed include the following:• Stirred reactor and heap leaching of laterites (limonitic and saprolitic), as well as iron control during atmospheric acid leaching;• Leaching of a typical porphyry copper sulfide deposit from Antofagasta, Chile, using chloride-ferrous solutions;• Leaching of chalcopyrite ores with various leaching media;• Leaching of white metal from a Teniente converter in NaCl-H2SO4 media; • Study of the galvanic effect of pyrite and arsenopyrite during the leaching of gold ores;• Leaching of marine nodules in the presence of reducing agents to extract Mn;• Bioleaching of gold ores in the presence of iodide-oxidizing bacteria;• A two-step sequential leaching process, involving bioleaching and chemical leaching, to treat apatite ores containing P and U impurities;• Bioreductive dissolution of iron minerals present in monazite in stirred reactors using Acidithiobacillus (A.) species;• Heap leaching of municipal solid waste incineration bottom ash (MSWI BA) for the recovery of Zn and Cu.
Rare earth (RE) with specific application value has become the relatively important strategic resource for all countries. Weathered crust elution-deposited rare earth ore (WCED-REO) are rich in ...middle-heavy RE, and its exploitation restrict the global supply of the middle-heavy RE. The leaching technology directly determines the leaching efficiency of RE in WCED-REO. The selection and use of the leaching agents are the most important parts of the leaching technology. The leaching mechanism is at the core of the leaching technology and also affects the effective utilization of the leaching agents. The research and development of leaching technologies, leaching agents, and leaching mechanisms of WCED-REO are discussed in this article. The development processes of exiting leaching technologies are introduced. The advantages and disadvantages of barrel leaching, pool leaching, heap leaching, in-situ leaching, and other leaching technologies are compared. And the new and practical leaching technologies are put forward. The research progresses of ammonium salt leaching agents, composite ammonium salt leaching agents, and novel non-ammonium leaching agents in recent years are reviewed. The leaching effects of different leaching agents are compared comprehensively to provide guidance for industrial application and research direction of the best leaching agent in the later period. The leaching basic theory, as well as the mass transfer process and leaching kinetics of rare earth are introduced. The mass transfer processes in leaching mechanism are explained from the macroscopic and microscopic perspectives. The further research directions of the leaching technologies, leaching agents, and leaching mechanism of WCED-REO are put forward, which provide the theoretical guidance and technical supports for the green and efficient exploitation of WCED-REO.
•Discussion of the development of the leaching technologies.•Description of the current new and practical leaching technologies.•Compilation of leaching agents in literature.•Overview of advantages and disadvantages of various leaching agents.•Explanation of the leaching mechanism in terms of leaching basic theory of rare earth, mass transfer process, and leaching kinetics.
This is a Special Issue of Metals devoted to aspects of Advances in Mineral Processing and Hydrometallurgy. This includes a global call for article submissions that also included Characterization ...along with Recycling and Waste Minimization. As such, both primary and recycled aspects will be considered. Possible specific topics included Mineralogy, Geometallurgy, Thermodynamics, Kinetics, Comminution, Classification, Physical Separations, Liquid–Solid Separations, Leaching, Solvent Extraction, Ion Exchange, Activated Carbon, Precipitation, Reduction, Process Economics and Process Control. Suggested application areas were in Gold, Silver, PGM’s, Aluminum, Copper, Zinc, Lead, Nickel, and Titanium. Critical Metals articles on topics such as Lithium, Antimony Tellurium, Gallium, Germanium, Cobalt, Graphite, Indium, and Rare Earth were also welcome. As such, this Special Issue of Metals was well supported by diverse submissions and the final publication of high-quality peer-reviewed articles.
Abstract
The antileaching efficacy of sol-gel-derived TiO
2
- and SiO
2
-based precursors has been evaluated through laboratory leaching trials with pine sapwood in two different ways. In a one-step ...process, wood was vacuum impregnated by the precursor solutions containing CuCl
2
. The copper (Cu) emission rates of the sol-gel-based impregnated woods were up to 70% lower than that of wood treated with pure CuCl
2
solution at the same level of concentration. More improvement (80%) could be achieved in a two-step process, in which sol-gel precursors were introduced into an already CuCl
2
-treated wood. The refinement was attributed to several effects. In the one-step approach, Cu was embedded in the TiO
2
/SiO
2
gels formed in the wood texture. During a two-step impregnation, gel layers that were formed in the wooden interior acted as an effective diffusion barrier. The sol-gel impregnations made wood more hydrophobic; therefore, the low amount of water that penetrated the cell wall was less efficient to leach out Cu.
Tandem catalysts can divide the reaction into distinct steps by local multiple sites and thus are attractive to trigger CO2RR to C2+ products. However, the evolution of catalysts generally exists ...during CO2RR, thus a closer investigation of the reconstitution, interplay, and active origin of dual components in tandem catalysts is warranted. Here, taking AgI−CuO as a conceptual tandem catalyst, we uncovered the interaction of two phases during the electrochemical reconstruction. Multiple operando techniques unraveled that in situ iodine ions leaching from AgI restrained the entire reduction of CuO to acquire stable active Cu0/Cu+ species during the CO2RR. This way, the residual iodine species of the Ag matrix accelerated CO generation and iodine‐induced Cu0/Cu+ promotes C−C coupling. This self‐adaptive dual‐optimization endowed our catalysts with an excellent C2+ Faradaic efficiency of 68.9 %. Material operando changes in this work offer a new approach for manipulating active species towards enhancing C2+ products.
The interplay of dual components in tandem catalysts is uncovered and utilized during the electrochemical reconstruction for promoting CO2 electroreduction to C2+ products. Taking AgI−CuO as a conceptual tandem catalyst, in situ iodine ions leaching from AgI restrain the entire reduction of CuO to acquire stable active Cu0/Cu+ species, thus achieving a high C2+ Faradaic efficiency of 68.9 %.
Rapidly rising temperatures in the Arctic might cause a greater release of greenhouse gases (GHGs) to the atmosphere. To study the effect of warming on GHG dynamics, we deployed open‐top chambers in ...a subarctic tundra site in Northeast European Russia. We determined carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes as well as the concentration of those gases, inorganic nitrogen (N) and dissolved organic carbon (DOC) along the soil profile. Studied tundra surfaces ranged from mineral to organic soils and from vegetated to unvegetated areas. As a result of air warming, the seasonal GHG budget of the vegetated tundra surfaces shifted from a GHG sink of −300 to −198 g CO2–eq m−2 to a source of 105 to 144 g CO2–eq m−2. At bare peat surfaces, we observed increased release of all three GHGs. While the positive warming response was dominated by CO2, we provide here the first in situ evidence of increasing N2O emissions from tundra soils with warming. Warming promoted N2O release not only from bare peat, previously identified as a strong N2O source, but also from the abundant, vegetated peat surfaces that do not emit N2O under present climate. At these surfaces, elevated temperatures had an adverse effect on plant growth, resulting in lower plant N uptake and, consequently, better N availability for soil microbes. Although the warming was limited to the soil surface and did not alter thaw depth, it increased concentrations of DOC, CO2, and CH4 in the soil down to the permafrost table. This can be attributed to downward DOC leaching, fueling microbial activity at depth. Taken together, our results emphasize the tight linkages between plant and soil processes, and different soil layers, which need to be taken into account when predicting the climate change feedback of the Arctic.
Experimental air warming increased emissions of all three greenhouse gases (GHGs), including the highly understudied N2O, clearly demonstrating the need to include N2O in future Arctic GHG budgets. Increased GHG fluxes were regulated by changes in plant functioning and biogeochemical processes, leading to an enhanced soil input of labile carbon compounds via leaching. Plants were also identified as the main regulator of arctic N2O emissions. Importantly, we highlight the tight linkages between plant and soil processes, and the interactions between the top‐soil and deeper soil layers, in regulating arctic GHG exchange.
The waste LiCl-Li.sub.2O oxide reduction salt was solidified and transformed into sodalite by the spark plasma sintering method. Compared with traditional solidification method, SPS operates at a ...lower pressure, lower temperature, shorter processing time, and without sintering additive. The SPS-solidified sodalite presents a low porosity of 0.37% and low leaching rates of 2.21 g m.sup.-2 d.sup.-1 for Cs, 3.05 x 10.sup.-1 g m.sup.-2 d.sup.-1 for Ba, and 3.12 x 10.sup.-1 g m.sup.-2 d.sup.-1 for Sr. Overall, the SPS is a promising method to solidify various waste OR salts.
The coordination compounds in the oxygen evolution reaction (OER) have been researched extensively. However, their poor durability (mostly < 100 h) and controversial reconstruction mechanism restrict ...their practical applications. Herein, a new‐type polyoxomolybdate‐organic complex (POMo) via wet‐chemistry synthesis with fixed coordination between metal centers (Ni2+ and Mo8O264−) and 2‐Methylimidazole ligand is introduced. After introducing iron, a series of Fe‐doped Ni‐POMo with porous and amorphous structures are fabricated. These features accelerate the diffusion‐leaching processes of ligands and anions, resulting in rapid and complete phase reconstruction during alkaline OER. As a result, nickel‐iron (oxy)hydroxides with rich vacancies and poly‐/low‐crystalline features are in situ generated through dissolution‐redeposition, and serve as the OER‐active species. The optimized Fe0.052Ni‐POMo array pre‐catalyst has excellent activity and sustains ultrastable catalysis for 545 h. The complete reconstruction of POMo enables high catalytic durability (230 h) and stable active phase under realistic conditions (30 wt% KOH, 60.9 °C). Accordingly, the completely reconstructed catalysts with unique structures and ultrastable catalysis have the potential to be applied in industry.
Novel polyoxomolybdate‐organic complex oxygen‐evolving pre‐catalysts are introduced via a wet‐chemistry synthesis with fixed coordination chemistry. Their porosity and low crystallization promote diffusion‐leaching processes of the ligand and anion during the alkaline oxygen evolution reaction, resulting in radical phase reconstruction and in situ generation of nickel‐iron (oxy)hydroxides with rich defects. High durability and a stable active phase of the completely reconstructed catalyst under realistic conditions are achieved.
Copper is one of the most important valuable elements in waste printed circuit boards (WPCBs), which can be finally recovered by hydrometallurgy. Environmentally-friendly copper leaching technology ...has become critical. In this study, two environmentally friendly leaching systems, namely ammonia-ammonium chloride leaching system and glycine-hydrogen peroxide leaching system, on copper leaching behavior was concerned, the influence of leaching time and leaching agent concentration on leaching rate of copper concentrate with different size was revealed. In addition, a simple but effective leaching kinetics model were proposed. The results show that with the extension of time, the leaching rate increases rapidly at first (0–10 min) and then slowly (10–25 min) until stable. The optimum leaching concentration of ammonia is 3 mol/L. For ammonia leaching system, the leaching rate increased from 76.92% to 90.05% with the decrease of particle size. Meanwhile, the leaching rate increased from 77.32% to 87.93% in the glycine leaching system. Finer particles have a larger contact area, resulting in higher leaching rates. The simple leaching kinetics model proposed in this study can accurately describe the leaching process of copper. These two environmentally friendly leaching systems can be used as substitutes for traditional inorganic acids.
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The increasing demand for some critical rare earth elements (REEs), which are crucial in the production of green and technologically advanced products, has sparked the development of novel processes ...to recover REEs from secondary resources, such as mine tailings, metallurgical slags, and phosphogypsum. These resources have low concentration of REEs, but are available in large volumes. Phosphogypsum (PG) is the main by-product of the production of phosphoric acid by sulphuric acid digestion of phosphate rock. The current study put the emphasis on the thorough characterization of phosphogypsum as well as investigation of the kinetics of the leaching process. The results show the leaching efficiency is controlled by the solubility limit of PG. Chemical modelling indicated that the systems are at the saturation level with respect to Ca. The instantaneous and saturation concentrations of Ca were used to model the dissolution kinetics. The apparent activation energy was determined to be 10.4kJ/mol. Furthermore; systematic leaching processes using three acids under various operating conditions were performed. The results indicate the optimal operation conditions are 1.5M, 80°C and solid-to-liquid ratio (S/L) of 1/8 and 20min residence time for all three acid, but the leaching efficiency using nitric and hydrochloric acids are higher than the sulfuric acid. This novel work investigates the feasibility of acid leaching of REEs from PG from both theoretical and practical standpoints.
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•Process and kinetics investigation of rare earth elements leaching from phosphogypsum was performed.•A thorough microscopy and spectroscopy characterization of the phosphogypsum (PG) sample was performed.•Systematic leaching experiments with three acids were conducted.•The leaching process/rate is controlled by the solubility limit of calcium sulfate (gypsum) and diffusion of lixiviant.
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