Calcium silicate minerals, including wollastonite, are considered promising feedstocks for mineral carbonation, particularly for applications in low-carbon building and construction materials; however, the mechanisms governing their behavior under mild wet carbonation conditions are not yet fully understood. While previous studies have primarily focused on enhancing carbonation through elevated temperatures, pressures, or chemical additives, the direct influence of operational conditions on reaction pathways and product evolution under additive-free mild conditions remains insufficiently explored. Here, two representative carbonated samples, exhibiting low (approximately 6%) and high (approximately 50%) carbonation efficiencies, were selected from a systematic screening for detailed analysis. These samples exemplify contrasting regimes of gas-liquid and solid-liquid mass transfer, primarily influenced by CO₂ flow rate and agitation speed. An integrated characterization strategy, incorporating XRF, TGA, XRD, BET, Pycnometry, and SEM-EDX, along with time-resolved kinetic model fitting, was employed. Phase and microstructural analyses reveal limited carbonate formation and sparse, discontinuous precipitates under mass-transfer-limited conditions, whereas extensive calcite precipitation and coalescing intergranular carbonate domains develop when mass transfer is enhanced. Variations in specific surface area, skeletal density, and thermal decomposition behavior correspond to progressive carbonate maturation during the reaction. Kinetic analysis of independent batch experiments at varying carbonation times indicates that both the Avrami model and the surface-reaction-controlled shrinking-core model provide the most suitable descriptions of the conversion data, suggesting that carbonation is mainly associated with surface-related dissolution, precipitation, and carbonate nucleation/growth. The diffusion-controlled shrinking-core model shows weaker agreement across the full reaction range, although transport limitations may become more relevant at later stages as carbonate-silica products develop. These findings provide a coherent mechanistic framework that links operational conditions to the evolution of reaction pathways during wet wollastonite carbonation under mild conditions.

Due to their complex structure and high metal content, printed circuit boards (PCBs) represent both a major challenge and opportunity for recycling. By weight, copper represents the main metallic fraction of PCBs. Thus, the selective removal and recovery of high-purity copper is crucial for efficient recycling, in addition to the extraction of minor, precious metal components, such as gold, silver, and palladium. This paper presents an integrated study of detailed characterization, process development, and the environmental impact of copper recycling from virgin PCBs using hydrometallurgical approaches - rather than the well-established pyrometallurgical route. Thorough mineral liberation analysis helped us understand specific processing and metallurgical approaches based on the accessibility of the target metal phases. Near quantitative copper leaching was achieved with H2SO4/H2O2 and HNO3, whereas heterotrophic bioleaching with citric acid and polyglutamic acid resulted in <13% of copper leaching. In a two-stage process, >98% of the leached copper was selectively transferred to the organic phase by solvent extraction with a LIX 84-I-kerosene/CuSO4-H2SO4 system. With the exception of Ni2+, co-extraction of further metal ions was not detected. Subsequently, up to 98% of the copper was recovered from the organic phase via stripping with a model electrolyte containing copper(ii) sulfate in H2SO4. From the enriched electrolyte solutions, metallic copper with a purity of 99.64-99.84% was electrodeposited on a stainless steel cathode, with a current efficiency of 98.66-99.85%. Residual copper obtained by washing the leaching residue was recovered by cementation with an iron powder according to a stoichiometric ratio of Fe/Cu2+ of 1.5 : 1. According to life cycle assessment, based on the energy and chemical consumption of the copper recycling process, the global warming potential of the tested approaches lies in the range 13.0 kg CO2 eq. per (kg Cu) - 40.3 kg CO2 eq. per (kg Cu). The greatest contributors to environmental impact are leaching and solvent extraction processes, which can be substantially improved by operating on a larger scale and recycling process ingredients. The proposed approach demonstrates end-to-end high-purity metal recovery with direct application to various circuit boards and copper-rich electronic components.

The increasing demand for lithium-ion batteries (LIBs) and the critical need for lithium make the efficient recycling of secondary resources essential. Synthetic Li-bearing phases, some with lithium contents greater than natural sources (e.g., spodumene), can occur in slags produced by the pyrometallurgical recycling of end-of-life LIBs. This study investigates both the composition of synthetic model slags reproducing LIB recycling and the recovery potential of Li-bearing phases using SEM-based automated mineralogy and batch flotation tests, respectively. In particular, the efficacy of a novel zwitterionic collector, punicine, in contrast to the conventional collector, oleic acid, was evaluated with a focus on recovering Li-aluminate as a key engineered artificial mineral (EnAM). The flotation tests demonstrated that punicine provided a higher degree of selectivity for Li-aluminate over gehlenite, along with improved recovery of fine and well-liberated particles. The enhanced performance is attributed to punicine’s unique frothing properties and phase-specific interactions. Our findings highlight punicine’s significant potential as a collector for lithium-bearing EnAMs to advance lithium recovery from complex slag materials. The applied unique methodology supports the study of reagent regimes in relation to the flotation behavior of EnAM phases and the sustainable recycling of LIBs.

Advancements in modern technology are causing a rapid increase in the consumption of critical elements. Many of these elements are obtained as by-products from the extraction and processing of other raw materials. Yet, limited information is available on their concentrations in primary ores, behaviour during ore processing, and availability to the global economy. This study analysed ores and mineral processing samples from the Ruwai Zn-Pb-Ag skarn deposit to constrain the process behaviours of the critical elements As, Bi, In, Sb, and Te, alongside Ag and Cd, through mass-balancing. Bismuth and Te primarily report to the Pb concentrates at rates of 79-91 %, and 59-77 %, respectively, with losses to tailings below similar to 20 % for Bi, and similar to 30 % for Te. Antimony recovery to the Pb concentrate is lower (34-52 %), with notable losses to tailings (45-62 %). Indium preferentially reports to the Zn concentrates at rates of 61-84 %, with 14-33 % lost to tailings. By contrast, As is mostly lost to the tailings (77-86 %), with low recoveries in both the Pb and Zn concentrates (5-15 %). Silver and Cd show high recoveries (>76 %) to either the Pb or Zn concentrates. The similar behaviours of Ag, Bi, Sb, and Te to Pb, and Cd and In to Zn, suggest that these elements are either hosted by galena or sphalerite, or by minerals that behave like galena and sphalerite during the flotation process. The results of this study have major implications for the estimation of critical-element mass flows worldwide, providing the first detailed mass-balance data for As, Bi, In, Sb, and Te from a Zn-Pb-Ag skarn deposit.

Recycling is crucial for sustainable resource management including heterogeneous and contaminated waste fractions such as those derived from composite materials. This study examines the potential application of pyrolysis of a plastic-rich heterogeneous fraction from an advanced mechanical recycling cascade of refrigerators as a representative example of challenging waste streams from Waste Electrical and Electronic Equipment (WEEE). Advanced spectroscopic and chromatographic techniques are used for feedstock and pyrolysis product characterization. A screw reactor on pilot-scale is used to derive pyrolysis mass balances and to evaluate product yields. The organic condensate with a yield of 64 wt% is rich in styrene and lower aromatics. After further upgrading and separation, aromatic base chemicals and other fractions derived from the organic condensate could substitute fossil feedstocks in the chemical industry. The gas fraction yielding 13 wt% could also be suitable for producing basic chemicals after post-processing. Solid residues enriched with fillers and metals which account for 19 wt% of the pyrolysis products offer recycling opportunities although detailed concepts for pollutant removal and filler reuse remain to be validated. This study highlights the potential of pyrolysis for chemically recycling heterogeneous plastic-rich waste by presenting insights into feedstock and pyrolysis product characterization and by indicating sustainable recycling pathways.

The high-grade stratabound copper ores of the Central European Kupferschiefer are one of the world's most important sources of silver. Despite its economic significance, the mineralogical partitioning of silver within the Kupferschiefer ores is generally not well understood, other than the fact that silver minerals are not sufficiently abundant to account for the bulk of the silver content. This study provides the first fully quantitative silver deportment for Kupferschiefer-type ores, using the Spremberg-Graustein-Schleife project in Germany as a case study. Our comprehensive analytical approach integrates scanning electron microscope (SEM)-based automated mineralogy and electron probe micro-analysis (EPMA) on exploration drill-core samples collected from different host rocks and different metal tenor. The results were validated using bulk geochemical data, and uncertainties were assessed with Monte Carlo simulations. The results demonstrate that the majority of the silver within high-grade Cu-rich ores occurs as a trace constituent in the ore-forming Cu(-Fe) sulfides (chalcocite group minerals, covellite, bornite, and chalcopyrite). In samples containing little copper, however, Fe sulfides host the majority of the silver in the form of micro-inclusions within copper-enriched crystal growth zones and substitution within the crystal lattice. The close association of copper and silver has important implications for ore genesis and mineral processing. These implications may well transfer to other by-products and other examples of polymetallic sediment-hosted copper mineral systems.

The recycling of interconnects from solid oxide electrolyzer (SOEL) stacks is essential for closing material loops in green hydrogen systems. Since it is mostly made of high-quality stainless steel, remelting is the most practical recovery route, but it inevitably generates slag, where strategic elements like chromium (Cr) are retained. This study investigates the mineralogical and grain characteristics of slag from SOEL interconnect remelting, with an emphasis on Cr distribution and its recovery potential. A correlative approach was applied using X-ray diffraction (XRD), scanning electron microscopy-based mineral liberation Analysis (MLA), and X-ray computed tomography (XCT). Cr was primarily found in magnesiochromite Mg(Al,Cr)2O4 (~54 wt.% Cr), constituting only ~5 wt.% of the slag, while lower concentrations were also detected in monticellite and åkermanite. XCT revealed the macroscopic heterogeneity of the slag system, with metallic inclusions and pores concentrated near the metal–slag interface, indicating density-driven settling. Cr-rich spinels were fine-grained (x50,2 ≈ 55 µm), irregular in shape, and partially intergrown, presenting challenges for mechanical liberation and physical recovery. These features, combined with their compositional selectivity, suggest that Cr-rich spinels are promising candidates for future Engineered Artificial Mineral (EnAM) strategies aimed at enhancing selective recovery from slag.

Slags from the metallurgical recycling process are an important source of resources classified as critical elements by the EU. One example is lithium from Li-ion battery recycling. In this context, the thermodynamic properties of the recycled component system play a significant role in the formation of the Li-bearing phases in the slag, in this case, LiAlO2. LiAlO2 crystal formation could be engineered and result in varying sizes and occurrences by different metallurgical processing conditions. This study uses pure ingredients to provide a synthetic model material which can be used to generate the valuable phase in the slag, or so-called engineered artificial minerals (EnAMs). The aim is to investigate the crystallisation of LiAlO2 as an EnAM by controlling the cooling conditions of the model slag to optimise the EnAM formed during crystallisation. Characterisation of the EnAMs is an important step before further mechanically processing the material to recover the valuable element Li, the Li-bearing species, respectively. Investigations are conducted using powder X-ray diffraction (XRD), X-ray fluorescence (µXRF), and X-ray Computer Tomography (XCT) on two different artificial lithium slags from MnO-Al2O3-SiO2-CaO systems with different cooling temperature gradients. The result shows the different EnAM morphology along the height of the slag, which is formed under different slag production conditions in a semi-pilot scale experiment of 5 kg. Based on the different EnAM morphologies, three defined qualities of the EnAM are identified: granular, dendritic, and irregular-shape EnAM.

In this work, the extraction of vanadium (V) ions from an alkaline solution using a commercial quaternary ammonium salt and the production of metal vanadates through precipitation stripping were carried out. The crystallization of copper vanadates from the extracts was performed using a solution containing a copper(II) source in concentrated chloride media as a stripping agent. In an attempt to control growth, a stabilizing polymer (polyvinylpyrrolidone, PVP) was added to the stripping solution. The structural characteristics of the crystallized products, mainly copper pyrovanadate (volborthite, Cu3V2O7(OH)2·(H2O)2) nanoflakes and nanoflowers and the experimental parameter influencing the efficiency of the stripping process were studied. From the results, the synthesis of nanostructured vanadates is a simple and versatile method for the fabrication of valuable three-dimensional structures providing abundant active zones for energy and catalytic applications.

Grinding and flotation processes are often studied independently, despite the well-established grinding influence on flotation performance, which affects not only particle size and thus liberation but also shape and leads to complex changes in pulp chemistry affecting the particle surface properties relevant for selective bubble attachment. Yet, no study jointly investigated these possible causes and many are limited to single mineral flotation. We relate grinding conditions to changes in pulp chemistry and particle surface properties and assess their impact on upgrading. We studied three non-sulfide ores with different feed grades and valuables: scheelite, apatite, and fluorite. These were dry-, wet-, and wet conditioned-ground before flotation in a laboratory mechanical cell. Results were evaluated with bulk- and particle-specific methodologies. The selectivity of the process is higher after dry grinding for the fluorite and apatite ores and irrelevant for the scheelite ore. Variations in flotation kinetics of individual particles associated to their size and shape are not sufficient to explain these results. The higher concentration of Ca2+ and Mg2+ observed in the pulp after wet grinding, altering particle surface properties, better explains the phenomenon. Additionally, we demonstrate how particle shape impacts are system specific and related to both entrainment and true flotation.

In this study, synthetic pure cassiterite and cassiterite doped with two different Fe contents were successfully recrystallized by means of sintering. Their crystal structure and chemical compositions were characterized by X-ray powder diffraction (XRD) as well as scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) analysis. Their floatability was studied by microflotation with a diphosphonic acid surfactant named Lauraphos301 as a collector. Unlike the addition of ferric ions in solution, which strongly depressed the floatability of all of the cassiterite samples, a much higher flotation efficiency of the Fe-doped cassiterite samples was found especially at lower collector concentrations. The cassiterite floatability is proportional to the Fe content in cassiterite at a broad range of pH, and the recovery has the following order: cassiterite with 1417 ppm Fe > cassiterite with 1165 ppm Fe > pure cassiterite. The electrokinetic behavior of the cassiterite samples with and without the collector was studied by electrophoretic measurements and revealed that the chemical interaction dominated the adsorption. With the help of the particle shape analysis, a more angular shape was found for the Fe-doped cassiterite samples. Moreover, without the influence of particle shape, much abundant adsorption of Lauraphos301 was found on the Fe-doped cassiterite samples by AFM topography imaging. The minor amount of Fe in the cassiterite lattice and a more angular shape of the Fe-doped cassiterite samples were believed to enhance floatability collectively. The study reveals that the influence of the chemical composition of the minerals on flotation was almost inextricably bound up with particle morphology and emphasizes the importance of considering both factors and investigating them individually for the flotation study.

The main techniques used to characterize raw materials are currently bulk or 2D. This is a consequence of the current lack of standardized and automated methods to characterize particulate materials in 3D. Here, we apply a workflow to characterize a crushed chromite ore with nine particle size classes below 1 mm using X-ray computed tomography. All data processing of all samples follows the same sequence of steps, which means that the analysis can be automated with limited user input as opposed to traditional 3D image processing methods that require user input specific to each particle size fraction. Results of chromite composition, particle size distribution and chromite liberation are obtained for individual particles and compared with the results from xray diffraction and 2D-based automated mineralogy. The results shows a consistent accuracy across all size classes down to 75 mu m. For the larger particle sizes (>600 mu m) the chromite liberation curves are more consistent than those obtained from 2D-based automated mineralogy, possibly due to the stereological bias of 2D sections. The particle size distributions is the property for which the 2D bias causes a larger divergence from 3D results across all particle sizes. In conclusion, the workflow is more automatable (thus, faster and cheaper) and less bias (thus, more accurate and standardisable) than other 3D image analysis methods. Additionally, it stands as complementary to established techniques for particle-based characterization, especially to measure particle properties that 2D-based methods may not measure representatively for larger particle sizes and when sampling is limited. Further testing of the workflow in progressively more complex materials is necessary, but its potential to transform the way mineral particulate materials are characterized is demonstrated.

Cobalt, nickel, manganese and zinc vanadates were synthesized by a hydrometallurgical two-phase method. The extraction of vanadium (V) ions from alkaline solution using Aliquat® 336 was followed by the production of metal vanadates through precipitation stripping. Precipitation stripping was carried out using solutions of the corresponding metal ions (Ni (II), Co (II), Mn (II) and Zn (II), 0.05 mol/L in 4 mol/L NaCl), and the addition time of the strip solution was varied (0, 1 and 2 h). The time-dependent experiments showed a notable influence on the composition, structure, morphology and crystallinity of the two-dimensional vanadate products. Inspired by these findings, we selected two metallic vanadate products and studied their properties as alternative cathode materials for nonaqueous sodium and lithium metal batteries.

ABSTRACTThe Storkwitz carbonatite breccia, located near Delitzsch, Germany, is one of the few European domestic rare earth elements (REE) deposits, but is relatively understudied owing to more than 100 m of Cenozoic sedimentary cover. We present the results of a petrological investigation of the recently acquired ∼700 m-deep SES 1/2012 borehole. The Storkwitz breccia is composed of clasts of country rock and carbonatite ranging from <1 mm to ∼30 cm in size, cemented by ankeritic carbonatite. Extensive fenitization and biotitization mainly affects clasts of coarse-grained granitoids and medium-grained dolomite-calcite-carbonatites. An intersection of Storkwitz breccia at 425 m to 542 m contains local REE enrichment up to ∼1.7 wt.%. total rare earth oxides, which is predominantly contained in a REE-fluorcarbonate bearing mineral assemblage. The assemblage locally forms irregularly shaped vug-like features and rare hexagonal pseudomorphs in clasts of fine-grained ankerite-carbonatite. The REE-fluorcarbonate mineral assemblage formed prior to brecciation in the ankerite-carbonatite, which paragenetically fits with recent experimental and fluid inclusion data demonstrating the importance of late magmatic processes in forming carbonatite-hosted REE mineralization, possibly from an evolved ‘brine-melt' phase. Our findings indicate that minor REE recrystallization and redistribution occurred during late-stage hydrothermal or supergene processes, without leading to significant REE enrichment in the upper part of the breccia compared to the lower part. Cross-cutting faults represent the last deformation event and post-date carbonatite intrusion and fenitization. They may represent important conduits for late-stage hydrothermal or supergene fluids responsible for recrystallization of the breccia matrix to a cryptocrystalline oxide mineral assemblage. Our findings highlight the importance of REE enrichment in late-stage ‘brine-melt' phases through magmatic fractionation and in situ hydrothermal replacement.

Sulfidic mine waste usually contains elevated amounts of valuable and hazardous metal(loid)s, which may pose environmental risks but can also provide opportunities for resource recovery. Reprocessing of mine waste can offer both economic and environmental benefits by supplying some of the ever-growing global demand for valuable metals, as well as reducing environmental risks. The present study aimed to simultaneously recover both valuable and hazardous metal(loid)s from two sulfidic mine waste samples (waste rock (NC_01) and tailings (NC_02)) from the Neves Corvo mine, Portugal, using a novel acidophilic consortium dominated by iron -oxidizing Leptospirillum genus and Acidiphilium sp. Bioleaching results showed that over 70% of the total Zn, Co, In, As, and Cd contents of NC_01 and NC_02 were leached within 21 days, while 55%-62% Mn was leached. Copper behaved in a refractory manner, as only 33% and 21% Cu were leached from NC_01 and NC_02, respectively. X-ray diffraction (XRD) and Scanning electron microscope-based automated image analyses (SEM/ MLA-GXMAP) of the bioleached residues revealed an almost complete absence of residual pyrite in NC_01 and a reduction of pyrite in NC-02, as well as the formation of secondary minerals, especially jarosite. In most cases, the biogenic jarosite co-precipitated some of the leached elements again, e.g., Cu and Pb. In conclusion, a synchronized method for bioleaching valuable and hazardous metal(loid)s was developed using a novel acido-philic consortium, thereby demonstrating the potential for the generation of economic value and environmental risk reduction for sulfidic mine waste samples.

Better quality control for alloy manufacturing and sorting of post-consumer scraps relies heavily on the accurate determination of their chemical composition. In recent decades, analytical techniques, such as X-ray fluorescence spectroscopy (XRF), laser-induced breakdown spectroscopy (LIBS), and spark optical emission spectroscopy (spark-OES), found widespread use in the metal industry, though only a few studies were published about the comparison of these techniques for commercially available alloys. Hence, we conducted a study on the evaluation of four analytical techniques (energy-dispersive XRF, wavelength-dispersive XRF, LIBS, and spark-OES) for the determination of metal sample composition. It focuses on the quantitative analysis of nine commercial alloys, representing the three most important alloy classes: copper, aluminum, and steel. First, spark-OES is proven to serve as a validation technique in the use of certified alloy reference samples. Following an examination of the lateral homogeneity by XRF, the results of the techniques are compared, and reasons for deviations are discussed. Finally, a more general evaluation of each technique with its capabilities and limitations is given, taking operation-relevant parameters, such as measurement speed and calibration effort, into account. This study shall serve as a guide for the routine use of these methods in metal producing and recycling industries.