This project investigates the recovery of residual platinum-group metals (PGMs) from mine tailings by diagnosing froth-flotation constraints and defining a rigorous optimization pathway. Tailings from the PGM mining operation were sampled across the dam; the material was air-dried, crushed to ≤2 mm, riffle-split, and characterized for particle-size distribution. Mineralogical studies were conducted by XRD, and chemical composition was assayed by ICP-OES to inform the reagent strategy. The feed is ultra-fine, with a particle size of 78.6 % passing 75 µm. Baseline rougher flotation employed a 42 % w/w pulp with isobutyl xanthate as collector, X3-DEP as depressant, sodium silicate as dispersant, copper sulphate as activator, and X2-froth as frother under controlled aeration. Product streams were filtered, weighed, and assayed for PGMs and Cr₂O₃ to compute mass pull, grade, and recovery. Results show pronounced sensitivity to feed characteristics and operating variability. Across tests, increasing mass pull increased recovery but diluted concentrate grade, evidencing gangue entrainment; conversely, higher grades were obtained at lower mass pull with associated recovery penalties. Monitoring of Cr₂O₃ in the concentrate constrained mass pull to meet smelter compliance. These inverse grade–recovery responses are consistent with ultra-fine feeds, surface oxidation of PGM minerals, and froth drainage constraints. Performance differences were attributed to reagent dosage and pH control, conditioning and residence time, and hydrodynamics. The recommended pathway is a constrained operating window centered on ~42 % solids, with reagent set points and control loops for pH and dosing, explored via designed experiments spanning collector/frother dosages, air rate, and conditioning time. Feed-grade variability should be dampened by blending to stabilize head grade and mineralogy. Where mineralogical analysis confirms locked PGMs or oxide coatings, targeted ultrafine grinding in inert media and/or tertiary scavenging circuits may be justified on a cost-normalized metal basis. Consequently, the study confirms technical feasibility but emphasizes process-control rigor to achieve predictable recovery from tailings and to manage the grade–recovery–mass-pull variables.

Efficient copper concentration via froth flotation hinges on balancing collector selectivity, frother strength, and slurry density to maximize concentrate grade at acceptable recovery and cost. This study systematically evaluates two collectors, namely K1 and K2 with a common frother across pulp densities of 34, 42, and 48% solids by mass. Batch laboratory froth flotation tests were executed under controlled hydrodynamics with rigorous, reproducible sample preparation, calibrated chemical dosing, and time-resolved concentrate pulls. Kinetics, cumulative recovery, froth stability, and grade-recovery curves were computed to quantify performance. Raising solids from 34 to 48% increased concentrate grade but depressed overall recovery, consistent with higher pulp viscosity, reduced bubble mobility, and shorter froth residence favouring selective attachment. An operational optimum emerged at 42% solids: grade improved relative to 34% with only moderate recovery loss, yielding the most cost-effective outcome when reagent consumption is included. At 34% solids, recovery was highest but concentrate grade was diluted; this regime suits scenarios prioritizing metal units. At 48% solids, selectivity improved further but recovery penalties became prohibitive. Across densities, Test 2 employing a higher-activity selective collector (K1-based) with tuned dosage outperformed alternatives, delivering superior grades at equal or better recoveries. Relative to K2, the selective regime reduced gangue entrainment and stabilized froth morphology in conjunction with the frother, enabling cleaner, faster flotation without excessive reagent addition. In conclusion, results show that (i) density is a first-order lever governing the grade recovery of copper through concentration by froth flotation; (ii) selective collector chemistry, properly dosed, shifts the frontier upward; and (iii) an operating window near 42% solids with a K1-dominant collector suite and moderated frother addition provides robust performance and lower unit reagent cost. These insights further support reagent and density set-point optimization in industrial circuits targeting higher-value concentrates with controlled chemical spend.

Silica nanoparticles (nano-SiO₂) are essential in applications such as environmental
remediation, agriculture, and catalysis. They are synthesised from high-grade quartz, tetraethyl
orthosilicate (TEOS), and other costly and non-renewable precursors. The high cost of these
conventional silica precursors limits the sustainability of their large-scale production. Therefore,
identifying alternative, low-cost, and abundant silica sources is crucial to improving the economic
feasibility of nano-SiO₂ synthesis. This study explored the utilisation of plagioclase minerals
contained in abundance in a South African Bushveld Igneous Complex (BIC) mine residue as an
alternative, low-cost silica source for the synthesis of high-purity nano-SiO₂. The sample
contained 65.4 wt.% plagioclase, 15.5 wt.% clinopyroxene, 10.4 wt.% orthopyroxene, 5.1 wt.%
clinochlore, and trace amounts of other minerals. Its major chemical components were SiO₂
(47.6 wt.%), Al₂O₃ (18.4 wt.%), Fe₂O₃ (12.3 wt.%), CaO (9.2 wt.%), MgO (3.9 wt.%), and Na₂O (3.3
wt.%).
A multi-stage synthesis route was developed. It consisted of a calcination pretreatment step
which was designed to convert soluble iron-bearing minerals into insoluble iron oxides, followed
by direct acid leaching, precipitation, and surfactant-assisted refinement. The resulting silica
nanoparticles were characterised using X-ray diffraction (XRD), scanning electron microscopy
(SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission
spectroscopy (ICP-OES), and Brunauer–Emmett–Teller (BET) surface area analysis. The
integrated calcination–leaching–precipitation process enabled the successful formation of high-purity
(99%), predominantly amorphous nano-SiO₂ with controlled spherical morphology, a
primary particle size below 50 nm, and a high specific surface area of 576 m²/g.
These results highlight the untapped potential of plagioclase in mine tailings and other mineral-related
solid waste as a strategic feedstock for high-purity silica nanoparticles. This offers a
sustainable alternative to conventional silica precursors used today.

Rare earth elements (REEs), which are found and produced in only a limited number of countries worldwide, are projected to be insufficient to meet the growing global demand in the near future. This situation has prompted increasing interest in alternative production routes from secondary geological sources with low uranium (U) and thorium (Th) contents. Among these, ionic clays, red mud, fly ash, bauxite, and related ores have emerged as promising potential sources. In particular, bauxite and its associated ores are considered significant secondary geological resources due to their relatively high REE concentrations.

In this study, the recoverability of REEs and aluminum (Al) from high-silica bauxite ore that cannot be processed by the Bayer method was investigated. The Kemiklitepe bauxite ore (Karaman, Türkiye), characterized by its high silica content and appreciable REE concentrations, was evaluated as a potential alternative source of these critical materials. A novel and sustainable process was developed for the simultaneous recovery of Al and REEs through an alkali roasting–acid leaching route. The finely ground ore was alkali-roasted with Na₂CO₃ at 800–1000 °C, followed by a two-step leaching procedure involving water and sulfuric acid (H₂SO₄). Acid leaching achieved a total REE recovery of approximately 87%. Subsequently, the selective extraction of REEs and Al from the pregnant acidic leach solution was investigated using the solvent extraction (SX) method. Key operational parameters including extractant (D2EHPA) concentration, reaction time, pH, and organic-to-aqueous phase ratio were optimized using the Taguchi design method. The results demonstrate that the proposed process enables efficient and environmentally sustainable recovery of both Al and REEs from high-silica bauxite, highlighting its potential for resource diversification and zero-waste processing.

Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data were used to investigate structural features and hydrothermal alteration zones for mineral exploration in the Precambrian basement of the Bou Azzer–El Graara inlier, located in the Moroccan Central Anti-Atlas. This domain, recognized as a Pan-African suture zone, contains a complex accretionary mélange of arc-related terranes and dismembered supracrustal ophiolites hosting economically significant mineralizations such as Co, Au, and Cu. Its arid setting offers favorable conditions for satellite remote sensing to detect lineaments and alteration patterns indicative of potential metal resources.

To refine structural mapping of the study area, key lineaments were extracted from ASTER data and compared with existing geological interpretations. The identified NE–SW and E–W fault families are consistent with previous tectonic studies, confirming their strong control on the spatial distribution of mineralization. In addition, previously unmapped faults were revealed, requiring further field verification but providing valuable insights into the region’s complex geodynamic evolution. Many of these structures correspond to faults reactivated during the Pan-African, Variscan, and Alpine–Atlas tectonic events.

In the second part of this study, ASTER surface reflectance data were used to map hydrothermal alteration zones through targeted band ratios, enabling the identification of iron oxides, hydroxyl-bearing minerals, sulfates, and carbonates. When combined with available geochemical information, the results show that cobalt anomalies correlate with carbonate–chlorite–epidote alteration, gold anomalies with alunite–kaolinite–pyrophyllite and locally sericite–muscovite–illite–smectite assemblages, and chromium and nickel anomalies with both carbonate–chlorite–epidote and sericite–muscovite–illite–smectite alteration types.

Overall, this integrated approach improves structural and alteration mapping and provides valuable guidance for future mineral exploration in the Bou Azzer–El Graara inlier.

Grinding operations play a pivotal role in enabling the effective separation of minerals, as it directly dictates the degree of mineral liberation and a critical prerequisite for subsequent beneficiation processes. In this study, a combination of advanced analytical techniques, including X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), and the Advanced Mineral Identification and Characterization System (AMICS), was employed to systematically investigate four key aspects: (1) the mineral composition of the raw ore, (2) the grain size distribution of valuable minerals, (3) the degree of ionization, and (4) the intracrystalline relationships of titano-magnetite with other coexisting phases. The results indicated that titano-magnetite exhibits a strong associative relationship with gangue minerals (e.g., chlorite, pyroxene, and amphibole). This intimate association causes complete dissociation of titano-magnetite from gangue minerals to be challenging during grinding. Consequently, gangue minerals are prone to entrainment in the iron concentrate alongside titano-magnetite, which subsequently compromises the quality of the final iron concentrate. Based on the aforementioned mineralogical characteristics of titano-magnetite, the high-speed stirred mill was used to achieve the ultra-grinding of titano-magnetite and optimize operation parameters. The optimal grinding conditions were ultimately determined as follows: stirred speed of 2000 r/min, grinding concentration of 35%, feeding frequency of 5 Hz, and media filling ratio of 70%. Under these optimized conditions, an optimized magnetic separation process to improve the recovery of high-content iron concentrates from titano-magnetite was performed, eventually allowing the iron grade to reach 56.25%. This study provides crucial insights into addressing the issue of complex titano-magnetite, and the optimized grinding-magnetic separation process proposed herein offers theoretical and technical guidance for scaling up beneficiation operations in industrial settings, thereby facilitating the sustainable utilization of titano-magnetite resources.

Abstract

Determining the horizontal position of magnetic anomalies is essential for interpreting subsurface geological structures in geophysical exploration. Although numerous edge-detection techniques exist for outlining anomaly boundaries, many still struggle with issues such as false edge generation, poor resolution, and high noise sensitivity. This study introduces a new high-resolution approach that combines the Skewed-Sigmoid (Skewed-Sig) function with the Total Horizontal Gradient (THG) to overcome these limitations. The Skewed-Sig function resembles the commonly used arctangent operator found in many edge-detection filters, while the THG is a standard technique that often lacks sufficient edge-resolution when used alone. By integrating these two components, we develop a hybrid filter—referred to as SSF—that enhances the detection of mineralized targets. To evaluate the performance of the proposed SSF filter, we compare it with widely used methods, including the analytical signal (AS), THG, tilt angle (TA), theta map (TM), and total horizontal gradient of the tilt angle (TAHG), using a synthetic magnetic model with a complex subsurface structure. To create synthetic conditions that were close to the real world, noise was added to the model data, and the quality of the output maps was checked. The filter was then applied to magnetic data from the Shavaz iron deposit in Yazd Province, Iran. The study area lies within the Central Iran Block, a region that is known for its significant potential for iron mineralization, particularly hematite and magnetite. Our results demonstrate that SSF delineates the mine location with greater accuracy than traditional methods and shows strong agreement with existing geological information and previous investigations in the Shavaz region. Consequently, the SSF technique offers a reliable tool for detecting mineral deposits and other subsurface magnetic sources.

This study aims to optimize the comminution process in light of the characteristics of fine embedded size and easy sliming of valuable minerals in complex rare-earth ores to achieve efficient grinding of the complex rare-earth ore. Firstly, taking a rare-earth ore from China as the research sample, the process mineralogy and crushing working index tests were conducted to explore the properties of the ore. Subsequently, crushing tests were conducted respectively using jaw crushers, double-roll crushers and high-pressure grinding rolls, and grinding tests were conducted using ball mills and rod mills. The particle size distribution, the liberation degree of gangue minerals and the microscopic morphology of different products were compared and analyzed. Finally, magnetic separation test was carried out, and the magnetic separation performance and energy consumption of different grinding products were compared and analyzed. The results show that HPGRs have higher crushing efficiency and produce more suitable particle size distribution of the product. Rod mills have the selective grinding effect on coarse-grained particles and the selective protection effect on fine-grained particles, which can effectively reduce mineral sliming formation and increase the recovery of the magnetic separation process under the similar concentrate grade. This research has certain guiding significance for solving the crushing and grinding problems of complex rare-earth ores, and can provide a reference for the efficient development and utilization of this ore type.

Phosphate mining activities generate enormous quantities of calcite-rich residues whose management poses both environmental and economic challenges, largely due to their low reactivity and limited industrial value. In this work, a sustainable valorization route is proposed to transform this carbonate waste into feed-grade calcium phosphates while simultaneously capturing carbon dioxide in a stable mineral form. The process is based on a two-step chemical pathway integrating alkaline conversion and phosphate synthesis.

In the first stage, the calcite-dominant residue was subjected to alkaline activation using sodium hydroxide (NaOH), leading to the in situ generation of calcium hydroxide [Ca(OH)₂] and sodium carbonate (Na₂CO₃). The reaction parameters were systematically optimized through a statistical design of experiments combining Plackett–Burman screening with a central composite design. Among the tested factors, NaOH concentration, solid-to-liquid ratio, and reaction time were identified as the most influential variables. The optimized conditions (7.95 mol L⁻¹ NaOH, 75 °C, S/L = 4.28 g per 50 mL, and 26 min) resulted in a conversion yield of 88%, confirming the spontaneous and exothermic character of the process (ΔG ≈ −58 kJ mol⁻¹; ΔH ≈ −59 kJ mol⁻¹). Sodium carbonate was recovered by crystallization from both the filtrate and washing effluents, achieving an average recovery of 86%, equivalent to the sequestration of approximately 0.33 t of CO₂ per ton of calcite treated.

The second step involved the neutralization of the Ca(OH)₂-rich product with phosphoric acid, enabling the controlled precipitation of monocalcium phosphate (MCP) or dicalcium phosphate (DCP) depending on the targeted Ca/P molar ratio. X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS) confirmed the formation of well-crystallized, pure calcium phosphates exhibiting high solubility in 2% citric acid (>90%), in accordance with international feed additive standards.

Brannberget is found close to the world-famous Løkken volcanogenic massive sulfide deposit (VMS), within the Løkken Ophiolites, Central Norwegian Caledonides (Grenne, 1989). Based on the Norwegian Geological Survey database, the study area represents a minor sulfide-quartz-bearing mineralization. Despite the historical mining activity at this location, no modern studies have been reported.

Field observations, petrographic investigations, mineral chemistry, and preliminary whole-rock geochemistry analyses were performed to characterize this mineralization. A network of ~3-5 cm thick quartz veins with Fe-oxyhydroxide and clay mineral-bearing alteration halo forms stockwork mineralization in the metabasaltic–doleritic greenstone. This rock is altered to albite, sericite, chlorite, and quartz. The quartz veins also contain iron-rich clay minerals, K-feldspar, disseminated pyrite, and chalcopyrite. The geochemical data revealed elevated concentrations of Cu (~ 7270 ppm), Zn (~236 ppm), and Bi (~ 74 ppm) in the quartz vein-bearing rock, compared to the host greenstone.

The observed mineral assemblage reveals high-temperature albitization, followed by intensive chloritization and lower-temperature silicification and sericitization as the fluid cooled owing to water–rock interaction. This multi-stage hydrothermal evolution, the appearing sulfides, and the observed geochemical data are typical of VMS stockwork feeder zones. Therefore, our study provides insights into the deep stockwork zones of this Ordovician VMS system. Further study is suggested to better understand the critical raw material potential of the locality, as our results prove that this stockwork zone might contain promising Cu amounts.

Acknowledgement

Sabina Strmić-Palinkaš, Máté Biró, and Tibor Németh are thanked for fruitful fieldwork conversations, SEM-EDS, and XRD analysis support, respectively. The ELTE Talent Fund supported the fieldwork.

Reference

Grenne, T. (1989): Econ Geol, 84/8: 2173-295