Rare Earth Elements (REEs) are crucial components driving technological advancements due to their unique properties, and are currently confronted with a growing demand crisis and supply constraints. This study investigates the recovery of REEs using modified diglycolamide and carbamide resin TK221 through extraction chromatography. The extraction behaviour of Nd(III) and Fe(III) from hydrochloric acid, nitric acid, and sulfuric acid was studied as a function of various parameters such as acid concentration, extraction kinetics, concentration of metal in the aqueous phase, amount of resin, resin acid stability after prolonged acid exposure, and influence of interfering ions. The results revealed that resin TK221 showed extremely fast kinetics that fit a pseudo-second order model, along with a high Langmuir adsorption capacity (40 mg.g−1). The high selectivity and enrichment of REE over other metal ions, together with the efficient recovery from real permanent magnet leachate and simulated coal fly ash leachate solution, indicate that TK221 is a promising candidate for the recovery of REE from leachate solutions.

The depletion of easily milled (free-milling) gold deposits has driven the mining industry to increasingly rely on refractory ores, particularly those containing arsenic (As)- and antimony (Sb)-bearing sulfides, for future gold (Au) production. Today, Au derived from refractory ores accounts for roughly one-third of global output, and this share is expected to increase further. Conventional extraction methods are often ineffective for these ores because of their complex mineralogy, where Au is encapsulated within sulfide matrices such as pyrite, arsenopyrite, and stibnite, while coexisting metal elements consume leaching reagents and hinder Au dissolution. In this review, strategies to enhance Au extraction from As/Sb-bearing refractory ores are discussed, including Ultrafine Grinding, Bio-oxidation, Pressure Oxidation, Alkaline Pretreatment, and cyanide-free leaching systems, together with the mechanistic relationships between pretreatment, sulfide decomposition, lixiviant stability, and downstream Au recovery. Among these, Ultrafine Grinding, Bio-oxidation, and Alkaline Pretreatment exhibit strong potential for liberating encapsulated Au prior to leaching. Of the alternative leaching reagents, thiosulfate systems have emerged as promising replacements for cyanide; however, significant challenges remain, including sulfide-induced reagent decomposition, passivation phenomena, high reagent consumption, and inefficient downstream Au recovery. Emerging techniques such as Au cementation using activated carbon and zero-valent aluminum from thiosulfate pregnant solutions have shown encouraging results. In addition, recent advances in selective pretreatment and improved recovery technologies indicate that integrated hydrometallurgical systems may provide more sustainable approaches for processing refractory Au ores. Future industrial implementation will depend on the development of integrated hydrometallurgical flowsheets capable of simultaneously optimizing sulfide decomposition, reagent stability, environmentally responsible management of As/Sb-bearing residues, and efficient Au recovery from cyanide-free systems.

The global commitment to achieving a carbon-neutral society has accelerated the transition toward renewable energy, electric mobility, and advanced electronic systems [...]

Coal fly ash (CFA), a by-product of coal combustion, represents a potential secondary source of rare earth elements (REEs) that can support resource diversification in coal-based economies. This study investigated the effect of hydrogen peroxide (H2O2) on REE recovery from desilicated CFA via sulfuric acid (H2SO4) leaching. An initial alkaline desilication stage increases the total REE (TREE) content from 245 to 476 ppm by decomposing the amorphous aluminosilicate matrix and improving REE accessibility. Subsequent acid leaching with varying H2O2 ratios relative to H2SO4 (0 vol%, 5 vol%, 10 vol%), together with a comparative H2O2-only system (100%), demonstrates that efficient REE dissolution requires both acidic conditions and controlled oxidant addition. The highest recovery (88.5%) is achieved in the H2SO4–H2O2 system at 10 vol%. This performance is attributed to a coupled mechanism involving proton-driven dissolution and redox-assisted mobilization, particularly through the reduction of Ce4+ to soluble Ce3+. In contrast, H2O2 alone results in limited recovery (33.2%), indicating that oxidant activity without sufficient proton availability is ineffective for comprehensive REE extraction. In addition to REE recovery, the process enables by-product valorization within a mine waste utilization framework. This integrated approach supports circular coal utilization and highlights CFA as a potential secondary REE resource for sustainable mining and energy systems.

Conservation of architectural heritage structures (AHS) requires compatible built her-itage materials with aesthetic, physical, chemical, and mechanical properties similar to those of the original materials. In recent years, however, urbanization, land reclamation, depletion of stone quarries, anti-mining and anti-quarrying legislation have limited access to original heritage materials. In the absence of the original heritage materials, ce-ment-based alternatives have been developed and widely applied for conservation. Major drawbacks of concrete- and cement-based materials include their large carbon footprint and long-term damage to the original rock or substrate, due to inadvertent promotion of salt efflorescence. This study systematically reviewed geopolymer-based materials as a sustainable, greener alternative to concrete- and cement-based materials for tuff- and coral rock-built heritage structures. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were implemented for the literature review, using Scopus, Web of Science (WoS), and Google Scholar (supplementary) as databases, between 2013 and 2024. Inaccessible items, non-English, reviews, conference proceedings, book chapters, errata, and papers unrelated to geopolymers, tuff, and coral rock were excluded, resulting in a total of 103 articles. These works were classified into geopolymers (34 arti-cles), tuff-built heritage structures (60 articles), and coral rock-built heritage structures (9 articles). This review included 103 items in the qualitative analysis; however, only 34 arti-cles contained meaningful data for content analysis. These 34 articles were categorized in terms of the (i) main precursors; that is, metakaolin, fly ash, slag, and pyroclastic materi-als (i.e., pumice, volcanic ash, and volcanic soil), ceramic, others (i.e., tuff waste, silica fume, and mine wastes), (ii) formulations (i.e., precursors, activators, admixtures, and ag-gregates), and (iii) compressive strength. Furthermore, critical factors for compatibility were reviewed and classified into aesthetics (e.g., color, presence of efflorescence, and tex-ture) and physical, chemical, and mechanical properties. This review also explored recent applications of geopolymers in heritage structures, indicating that geopolymers are typi-cally used as repair mortar and consolidants. Finally, a bibliometric analysis was con-ducted to evaluate research trends on geopolymers, including a critical assessment of their aesthetic compatibility with heritage structures in the Philippines built with volcanic tuff and coral rock.

Acid mine drainage (AMD) is generally managed via active or passive treatment strategies. Between the two, passive treatment is explored as a more sustainable alternative, especially for abandoned and legacy mines due to their low energy, manpower and material requirements. Recent studies of the authors have explored the use of limestone and waste materials like low-grade ores (LGO), fly ash (FA), and concrete wastes (CW) for AMD treatment and found that although these materials generated alkalinity individually, they could only partially remove sulfate (SO4 2-) and some heavy metals. To address this limitation, a mixed media approach using these four materials is proposed to neutralize the pH of AMD and maximize metal and SO4 2- removal. A total of twenty (20) mixtures of the four materials were identified based on the response surface methodology (RSM) experimental design. Laboratory-scale experiments using simulated AMD were performed to assess the performance of each mixture by monitoring the pH, oxidation-reduction potential (Eh), electrical conductivity (EC), and concentrations of metals and SO4 2-. Based on the results, three optimized mixed media compositions were identified. Overall, simulated AMD passively treated by the optimized mixed media compositions met the Philippine effluent standards except for SO4 2-.

This study investigates the removal of microplastics (MPs) from simulated freshwater, brackish water, and seawater using a novel agglomeration–micro-flotation technique. This method combines particle size enlargement, facilitated by kerosene as a bridging agent, with bubble size reduction through column flotation to enhance the removal rate. Six common MP types—polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC)—were evaluated under varying salinity levels and kerosene dosages. Results showed that increasing kerosene dosage significantly improved removal rates, achieving up to ~99% recovery at 10 µL for low- and medium-density MPs (PP, PE, ABS, and PS), while a higher dosage of 30 µL was required for high-density MPs (PET and PVC). Elevated salinity levels (50–100%) promoted bubble stabilization and reduced coalescence, enhancing particle–bubble collisions and the overall flotation performance. This work addresses a key research gap in flotation-based MP removal under saline conditions and highlights the dual benefits of using kerosene—not only to enhance the removal rate but also to enable energy recovery, as both kerosene and plastics are combustible. The proposed technique presents a promising approach for microplastic remediation in aquatic environments, supporting sustainable water treatment and circular resource utilization.

In this study, we assessed soil pollutants and surveyed the bacterial communities using 16S rRNA sequencing to better understand how to improve rehabilitation strategies for nickel-laterite mines in the Philippines. Representative soil samples and rhizospheres from Saccharum spontaneum L. in three post-mining sites rehabilitated in 2015, 2017, and 2019 were collected and analyzed. X-ray diffraction (XRD) identified iron oxyhydroxides, silicates, and clays as major soil components. Based on the pollution load index and contamination degree, the 2015A and 2015B sites were classified as “pristine” and had a “low degree of pollution”, while the remaining sites (2017A, 2017B, 2019A, and 2019B) were considered “moderately contaminated” with nickel, chromium, cobalt, lead, zinc, and copper. An analysis of the bacterial community composition revealed that the phyla Proteobacteria and Actinobacteria, along with the genus Ralstonia, were the most abundant groups across both control and rehabilitated sites. Our results showed that the soil pH and organic matter contents were strongly linked to specific bacterial community composition. These taxa have potential for inoculation in nickel-laterite soils to promote the growth of hyperaccumulator plants. Our results also showed a significant correlation between the structure of the bacterial communities and nickel, chromium, and manganese soil contents, but not with rehabilitation time. Furthermore, we identified the genera Diaphorobacter as potential bioindicators because they are sensitive to nickel and chromium. This study provides valuable baseline data on heavy metal pollution and microbial diversity in a rehabilitated Ni-laterite mine site.

Bimetals—materials composed of two metal components with dissimilar standard reduction–oxidation (redox) potentials—offer unique electronic, optical, and catalytic properties, surpassing monometallic systems. These materials exhibit not only the combined attributes of their constituent metals but also new and novel properties arising from their synergy. Although many reviews have explored the synthesis, properties, and applications of bimetallic systems, none have focused exclusively on iron (Fe)- and aluminum (Al)-based bimetals. This systematic review addresses this gap by providing a comprehensive overview of conventional and emerging techniques for Fe-based and Al-based bimetal synthesis. Specifically, this work systematically reviewed recent studies from 2014 to 2023 using the Scopus, Web of Science (WoS), and Google Scholar databases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and was registered under INPLASY with the registration number INPLASY202540026. Articles were excluded if they were inaccessible, non-English, review articles, conference papers, book chapters, or not directly related to the synthesis of Fe- or Al-based bimetals. Additionally, a bibliometric analysis was performed to evaluate the research trends on the synthesis of Fe-based and Al-based bimetals. Based on the 122 articles analyzed, Fe-based and Al-based bimetal synthesis methods were classified into three types: (i) physical, (ii) chemical, and (iii) biological techniques. Physical methods include mechanical alloying, radiolysis, sonochemical methods, the electrical explosion of metal wires, and magnetic field-assisted laser ablation in liquid (MF-LAL). In comparison, chemical protocols covered reduction, dealloying, supported particle methods, thermogravimetric methods, seed-mediated growth, galvanic replacement, and electrochemical synthesis. Meanwhile, biological techniques utilized plant extracts, chitosan, alginate, and cellulose-based materials as reducing agents and stabilizers during bimetal synthesis. Research works on the synthesis of Fe-based and Al-based bimetals initially declined but increased in 2018, followed by a stable trend, with 50% of the total studies conducted in the last five years. China led in the number of publications (62.3%), followed by Russia, Australia, and India, while Saudi Arabia had the highest number of citations per document (95). RSC Advances was the most active journal, publishing eight papers from 2014 to 2023, while Applied Catalysis B: Environmental had the highest number of citations per document at 203. Among the three synthesis methods, chemical techniques dominated, particularly supported particles, galvanic replacement, and chemical reduction, while biological and physical methods have started gaining interest. Iron–copper (Fe/Cu), iron–aluminum (Fe/Al), and iron–nickel (Fe/Ni) were the most commonly synthesized bimetals in the last 10 years. Finally, this work was funded by DOST-PCIEERD and DOST-ERDT.

The demand for rare earth elements (REEs) is continuously increasing due to the important roles they play in low-carbon and green energy technologies. Unfortunately, the global REE reserves are limited and concentrated in only a few countries, so the reprocessing of alternative resources like tailings is of critical importance. This study investigated carrier magnetic separation using coarse magnetite particles as a carrier to recover finely ground monazite from tailings. The monazite and carrier surfaces were modified by sodium oleate (NaOL) to improve the hydrophobic interactions between them. The results of zeta potential and contact angle measurements implied the selective adsorption of NaOL onto the surfaces of the monazite and magnetite particles. Although their hydrophobicity increased, heterogenous agglomeration between them was not substantial. To improve heterogenous agglomeration, emulsified kerosene was utilized as a bridging liquid, resulting in more extensive attachment of fine monazite particles onto the surfaces of carrier particles and a dramatic improvement in monazite recovery by magnetic separation—from 0% (without carrier) to 70% (with carrier). A rougher–scavenger–cleaner carrier magnetic separation can produce REE concentrates with a total rare earth oxide (TREO) recovery of 80% and a grade of 9%, increased from 3.4%, which can be further increased to 23.2% after separating REEs and the carrier.

Abstract Acid mine drainage (AMD)—the strongly acidic and highly polluted effluents from mine sites—are generally managed via active or passive treatment. Active treatment strategies are effective but requires continuous input of energy, chemicals and manpower making them unsustainable in the long term. Because of this, passive treatment is explored as a more sustainable alternative especially for abandoned and legacy mines. Recent studies of the authors have explored the use limestone and waste materials like low-grade ores (LGO), fly ash (FA), and concrete wastes for AMD treatment and found that although these materials generated alkalinity individually, they could only partially remove sulfate (SO42−) and some heavy metals. To address this limitation, a mixed media approach using these four materials is proposed to neutralize the pH of AMD and maximize heavy metals (Cu, Fe, Mn, Ni, and Al) and SO42− removal. A total of twenty (20) mixtures of the four materials were identified based on the response surface methodology (RSM) experimental design. Laboratory-scale experiments using simulated AMD were performed to assess the performance of each mixture by monitoring the pH, oxidation-reduction potential (Eh), electrical conductivity (EC), metal concentrations, and SO42− concentration. Based on the results, three optimized mixed media compositions were identified in wt%: (i) 43% LGO, 40% limestone, 17% CW; (ii) 44% LGO, 51% limestone, 6% CW; and (iii) 89% limestone, 11% LGO. Overall, simulated AMD passively treated by the optimized mixed media compositions met the Philippine effluent standards except for SO42−. Simulated AMD treated by the optimized mixed media achieved pH values of < 9 and removal efficiencies for Cu, Fe, Mn, Ni, and Al of about 99%, 99%, 98%, 70%, and 96%, respectively.

This study investigates the modification and application of natural, micro-scale magnetite (Fe3O4)—an iron oxide mineral and one of the most abundant iron ores in the world—as a magnetic carrier for removing six common types of microplastics (MPs) from water: polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). Hexadecyltrimethoxysilane (HDTMS) was employed as a surfactant to modify the naturally hydrophilic magnetite, transforming it into a hydrophobic material. The characterization of magnetite treated with HDTMS for 0, 6, 12, 24, and 48 h was performed using a scanning electron microscope with energy-dispersive X-ray spectroscopy (SEM-EDS) and Fourier transform infrared spectroscopy (FT-IR). The results showed HDTMS sorption on the surface of natural magnetite, confirming successful surface modification. Carrier magnetic separation was then performed to remove PP, PE, ABS, PS, PET, and PVC using surface-modified, natural magnetite in two size fractions: +38–75 µm (fine-sized) and +75–150 µm (coarse-sized). Improved performance was observed with longer HDTMS treatment of magnetite, while greater than 90% MP removal was achieved using fine-sized, surface-modified, natural magnetite. These results suggest that surface modification enhanced the heterogenous interactions between magnetite and MPs via hydrophobic-hydrophobic interactions, leading to efficient MP removal via carrier magnetic separation.

Hyperspectral data, encompassing hundreds of spectral wavelengths, is a powerful tool for mineral processing, as minerals display unique reflection spectra. Machine learning can identify mineral species from hyperspectral data, but its high dimensionality poses challenges for ordinary users. To address this, we developed APiS (AI Powered intelligence Spectrum Analyser), an interactive hyperspectral analysis application requiring no coding. APiS offers a user-friendly interface for data visualisation, learning data generation, advanced machine learning analysis, and model evaluation. This App surpasses previous script-based methods, enabling diverse users in geometallurgy to conduct sophisticated hyperspectral data analysis and fostering creativity in their work. Our proposed APiS (AI Powered intelligence Spectrum analyser) allows for advanced analysis of hyperspectral data in an intuitive manner.APiS provides powerful support for hyperspectral data visualisation, learning data generation, machine learning, and evaluation of learning models.A user-friendly application has been developed with the objective of facilitating the development of hyperspectral sensor-based mineral processing technology.

Selective flotation of copper sulfides like chalcopyrite (CuFeS2) from Cu-Zn mixed sulfide ores with high Cu/Zn ratios has proven difficult due to undesired activation of sphalerite (ZnS). Although the addition of excess zinc sulfate (ZnSO4)-a sphalerite depressant-can achieve the selective flotation of chalcopyrite, the presence of pyrite (FeS2) promotes the activation of sphalerite due to enhanced dissolution of chalcopyrite by galvanic interaction between chalcopyrite and pyrite, making both Cu and Zn sulfides float. To address this problem, this study investigated the applicability of microencapsulation technique followed by selective flotation of sphalerite to improve the separation efficiency of Cu and Zn. Microencapsulation using ferrous and phosphate ions could yield hydrophilic ferric phosphate (FePO4) coating on the surface of chalcopyrite, effectively diminishing its floatability from similar to 60 % to below 20 %. In contrast, the surface of sphalerite was not affected by microencapsulation treatment, so it could float with the assistance of activator and collector. The results of mixed minerals flotation indicated that the application of microencapsulation as a pretreatment of Zn flotation improved the separation efficiency from 15 % to 62 %.

Ionic liquids (ILs) have recently been reported as promising collectors for rare earth minerals (REMs), but how they improve REM floatability is still not well understood. In this study, six types of acid-base ILs-tetraethyl-, tetrabutyl-, tetraoctyl-ammonium mono-(2-ethylhexyl) 2-ethylhexyl phosphonate and tetraethyl-, tetrabutyl-, tetraoctyl-ammonium di(2-ethylhexyl) phosphate-were investigated to understand how the cationic and anionic moieties of these compounds as well as the conditioning temperature influence REMs (i.e., monazite and xenotime) and zircon floatabilities. Flotation experiments were conducted at pH 5, 7, and 9 under both ambient conditions and 60 degrees C to assess the performance of the ILs. Zeta potential measurements coupled with Fourier transform infrared spectroscopy (FTIR) characterization of minerals were also done to identify the adsorption mechanism of ILs on mineral surfaces. The results showed that tetraoctyl-ammonium di(2-ethylhexyl) phosphate effectively separated monazite from xenotime and zircon via reverse flotation, particularly at pH 9, with conditioning at 60 degrees C. These findings suggest that the structural characteristics of ILs and their interactions with mineral surfaces, influenced by pH and temperature, play a significant role in enhancing the floatability of REMs. Furthermore, the study demonstrated that using ILs as collectors combined with elevated temperatures during the conditioning stage significantly enhances selectivity. This suggests the potential for effectively separating monazite from xenotime by froth flotation using ILs as collectors without the need for depressants. This innovative method could greatly benefit the REM processing field, particularly in flotation technology.

Iron oxides (hematite, Fe2O3, and magnetite, Fe3O4), previously used as electron mediators in the galvanic system with zero-valent aluminum (ZVAl), have been shown to recover Au upon cementation in Au–Cu ammoniacal thiosulfate media selectively, and this warrants further investigation. This research is focused on investigating the role of the semiconductive properties of metal oxides by performing a cementation experiment by mixing 0.15 g of electron mediators (Fe3O4, Fe2O3, TiO2 (anatase and rutile)) and 0.15 g of zero-valent aluminum powder as an electron donor in various electrochemical experiments. The results revealed that upon the cementation experiment, synthetic Fe2O3 and Fe3O4 were consistently able to selectively recover Au at around 90% and Cu at around 20%. Compared to activated carbon (AC), TiO2, in anatase and rutile forms, obtained selective recovery of gold, but the recovery was utterly insignificant compared to that of iron oxides, obtaining an average of 93% Au and 63% Cu recovery. The electrochemical and surface analysis supports the results obtained upon the cementation process, where TiO2, upon cyclic voltammetry (CV), obtained two reduction peaks centered at −1.0 V and −0.5 V assigned to reducing Au and Cu ions, respectively. Furthermore, various electrochemical impedance spectroscopic analyses revealed that the flat band potential obtained in the Mott–Schottky plot is around −1.0 V and −0.2 V for iron oxides and titanium oxides, respectively, suggesting that the electrons travel from semiconductor interface to electrolyte interface, and electrons are accessible only to Au ions in the electrolyte interface (reduction band edge around −1.0 V). The determination of this selective cementation mechanism is one of a kind. It has been proposed that the semiconductive properties of Fe2O3, Fe3O4, and, by configuring their relative energy band diagram, the travel of electrons from the iron oxide–electrolyte interface facilitate the selective cementation towards Au(S2O3)23+ ions in gold–copper ammoniacal thiosulfate solutions.

Microbially induced carbonate precipitation (MICP), a widespread phenomenon in nature, is gaining attention as a low-carbon alternative to ordinary Portland cement (OPC) in geotechnical engineering and the construction industry for sustainable development. In the Philippines, however, very few works have been conducted to isolate and identify indigenous, urease-producing (ureolytic) bacteria suitable for MICP. In this study, we isolated seven, ureolytic and potentially useful bacteria for MICP from marine sediments in Iligan City. DNA barcoding using 16s rDNA identified six of them as Pseudomonas stutzeri, Pseudomonas pseudoalcaligenes, Bacillus paralicheniformis, Bacillus altitudinis, Bacillus aryabhattai, and Stutzerimonas stutzeri but the seventh was not identified since it was a bacterial consortium. Bio-cementation assay experiments showed negligible precipitation in the control (without bacteria) at pH 7, 8, and 9. However, precipitates were formed in all seven bacterial isolates, especially between pH 7 and 8 (0.7–4 g). Among the six identified bacterial species, more extensive precipitation (2.3–4 g) and higher final pH were observed in S. stutzeri, and B. aryabhattai, which indicate better urease production and decomposition, higher CO2 generation, and more favorable CaCO3 formation. Characterization of the precipitates by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and attenuated total reflectance Fourier transform spectroscopy (ATR-FTIR) confirmed the formation of three carbonate minerals: calcite, aragonite, and vaterite. Based on these results, all six identified indigenous, ureolytic bacterial species from Iligan City are suitable for MICP provided that the pH is controlled between 7 and 8. To the best of our knowledge, this is the first report of the urease-producing ability and potential for MICP of P. stutzeri, P. pseudoalcaligenes, S. stutzeri, and B. aryabhattai.

Rare earth minerals (REMs) contain rare earth elements (REEs) that are important in modern technologies due to their unique magnetic, phosphorescent, and catalytic properties. However, REMs are not only non-renewable resources but also non-uniformly distributed on the Earth's crust, so the processing of REE-bearing secondary resources via recycling is one potential route to ensure the long-term sustainability of REE supply. Flotation-a method that separates materials based on differences in their surface wettability-is a process applied for both mineral processing and recycling of REEs, especially when the particles are fine and/or a high-purity product is required. In this review, studies about rare earth flotation from 2012 to 2021 were systematically reviewed using the PRISMA guideline. It was found that most REM flotation research works focused on finding better collectors and depressants while, for recycling, studies on advanced flotation techniques like froth flotation, ion flotation, solvent sublation, electroflotation, and adsorbing colloid flotation with an emphasis on the recovery of dissolved REEs from aqueous solutions dominated.