Phosphogypsum (PG), a by-product of phosphate fertilizer production, poses several environmental risks including heavy metal contamination, geotechnical stability of tailing ponds, and radioactivity levels. Only 15% of PG is being utilized for cement and agricultural applications. Current developments have been exploring PG for mineral carbonation (MC). In this study, the calcium extraction process from Philippine PG was established and optimized via salt and acid leaching. Optimal Ca extraction efficiencies of 18.3% (2.5 M NaCl, 38 degrees C, 60 min, and 26 mL/g L/S ratio) and 93.0% (2.3 M HCl, 62 degrees C, 60 min, and 26 mL/g L/S ratio) were obtained for salt and acid leaching, respectively. Life cycle impact assessment of a theoretical MC plant utilizing acid leaching for Ca extraction showed that while constructing an MC plant offsets benefits brought by carbon capture, mineral and resources use, reduced landfill, and process water recirculation can still be achieved. This study proves that local PG can be a potential feedstock for indirect MC with manageable environmental impacts that can be further worked on with green extraction methods and possible resource recovery.

Coal fly ash (CFA) is a promising secondary resource for rare earth element (REE) recovery. This study characterized CFA using XRF, SEM-EDS, ICP-MS, and XRD, revealing critical REE concentrations of 26.3 ppm (Nd), 4.84 ppm (Dy), 2.89 ppm (Er), 1.69 ppm (Eu), and 0.85 ppm (Tb). REEs are distributed in Al-Si-Mg-Ca-rich aluminosilicates, except Dy, which is associated with Fe-rich phases. Leaching optimization using response surface methodology (RSM) with a central composite design (CCD) identified optimal conditions at 59.5% HCl:40.5% citric acid, 85 °C, and 720 min, achieving recoveries of 94.8% (Dy), 85.2% (Er), 73.1% (Eu), 79.1% (Nd), and 85.7% (Tb). These conditions provided the best balance between recovery, acid use, and selectivity, demonstrating potential scalability for industrial applications. The quadratic model accurately predicted REE recoveries, with accuracies of 95.61% (Dy), 97.76% (Er), 97.30% (Eu), 99.07% (Nd), and 99.17% (Tb). Thermodynamic analysis showed that mineral dissolution influenced REE selectivity, with anorthite (ΔG358K = −348.1 kJ·mol−1) dissolving readily, while ankerite (ΔG358K = 5.49 × 106 kJ·mol−1) contributed to high selectivity, particularly for Mg. Element selectivity followed Mg > Al > Si > Fe ≥ Ca, indicating Mg- and Al-bearing phases were more susceptible, while Fe- and Ca-bearing minerals remained more resistant under mixed-acid conditions.

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.

Acid mine drainage (AMD) is an environmental concern that needs to be addressed by some mining industries because of its high concentrations of metals and acidity that destroy affected ecosystems. Its formation typically persists beyond the operating life of a mine site. Its management is even more challenging for sites that are abandoned without rehabilitation. In this study, a legacy copper–gold mine located in Sto. Niño, Tublay, Benguet, Philippines, generating a copper- and manganese-rich AMD (Cu, maximum 17.2 mg/L; Mn, maximum 2.90 mg/L) at pH 4.59 (minimum) was investigated. With its remote location inhabited by the indigenous people local community (IPLC), a novel limestone-based hybrid passive treatment system that combines a limestone leach bed (LLB) and a controlled modular packed bed reactor (CMPB) has been developed from the laboratory and successfully deployed in the field while investigating the effective hydraulic retention time (HRT), particle size, and redox conditions (oxic and anoxic) in removing Cu and Mn and increasing pH. Laboratory-scale and pilot-scale systems using simulated and actual AMD, respectively, revealed that a 15 h HRT and both oxic and anoxic conditions were effective in treating the AMD. Considering these results and unsteady conditions of the stream in the legacy mine, a hybrid multi-stage limestone leach bed and packed bed were deployed having variable particle size (5 mm to 100 mm) and HRT. Regular monitoring of the system showed the effective removal of Cu (88.5%) and Mn (66.83%) as well as the increase of pH (6.26), addressing the threat of AMD in the area. Improvement of the lifespan of the system needs to be addressed, as issues of Cu-armoring were observed, resulting in reduced performance over time. Nonetheless, the study presents a novel technique in implementing passive treatment systems beyond the typical treatment trains reported in the literature.

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 global accumulation of phosphogypsum (PG), with annual generation exceeding 175 Mt/year, presents significant environmental challenges. While studies have demonstrated PG's potential as a filler material in geopolymer composite, comprehensive environmental impact assessments of such valorization approaches remain limited. This study presents the first comparative life cycle assessment (LCA) of acid-and alkali-activated PG-CFA geopolymers in the context of sustainable industrial waste management. Geopolymer technology can eliminate the need for traditional landfilling of PG in coastal areas and, therefore, reduce their negative environmental impacts. LCA was conducted to assess the impacts of repurposing 1kg functional unit of PG as geopolymer precursors coupled with acid-and alkali-based activators compared to the current disposal practices of these solid wastes. The inventory was modeled after a phosphoric acid plant using the wet dihydrate process, a coal-fired power plant, and a laboratory-scale coal fly ash-phosphogypsum geopolymer (FAPG) synthesis upscaled for industrial application. The most number of environmental benefits was observed for acid FAPG particularly via reductions in CO2-eq emissions by 40%, 90% in energy consumption, and 36% in mineral resource extraction. Alkali FAPG excelled in water acidification and scarcity by 60% and it could outperform acid FAPG environmentally via sensitivity analysis under a similar formulation blend. Further research can focus on optimizing FAPG formulation, finding alternatives for the acid and alkali activators, and reviewing industrial standards for widespread FAPG applications. These results imply the potential of integrating FAPG manufacturing in PG-and CFA-generating industries to emulate a circular economy.

The success of rehabilitating legacy or abandoned mines is highly dependent on engaging the community in the program. Although there is consensus among stakeholders that this line of enquiry and process is critically important, there is no coherent understanding of this concept. We reviewed the literature on engaging the community in the rehabilitation of legacy mines using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). We accessed peer-reviewed publications from Scopus, Web of Science, and ProQuest databases. Upon application of a set of exclusion criteria, 53 articles were further considered for full analysis. Based on our results, we have established the continuum of involving the host community in the rehabilitation process, from information dissemination, consultation, engagement, partnership, and empowerment to leadership. Also, we have identified factors that influence rehabilitation programs, including policy, people, process, context, and mining processes. We discuss the implications of these findings, emphasizing the gaps that warrant further investigations.

BACKGROUND:The Sto. Niño site in Benguet province, Philippines was once a mining area that has now been transformed into an agricultural land. In this area, there has been significant integration of the three indigenous people (IPs) Ibaloi, Kankanaeys and Kalanguyas with the Ilocano community. These IPs safeguard biodiversity and traditional knowledge, including medicinal plant use. However, the documentation of these plant species and their medicinal applications has not been systematic, with the resultant loss of knowledge across generations. This study aims to document the medicinal and ritual plants used by the indigenous communities at the site, in order to preserve and disseminate traditional medicinal knowledge that would otherwise be lost. METHODS:Ethnobotanical data were collected in Sto. Niño, Brgy. Ambassador, Municipality of Tublay, Benguet, Philippines, and collected through semi-structured interviews, together with focus group discussions (FGD). A total of 100 residents (39 male and 61 female) were interviewed. Among them, 12 were key interviewees, including community elders and farmers, while the rest were selected through the convenience and snowball technique. Demographic information collected from the interviewees included age, gender, and occupation. Ethnobotanical information collected focused on medicinal plants, including the specific parts of plants used, methods of preparation, modes of treatment, and the types of ailments treated. Ethnobotanical quantitative indices of the relative frequency of citations (RFC) and informant consensus factor (ICF) were calculated to evaluate the plant species that were utilized by the community. RESULTS:A total of 28 medicinal plants from 20 different families and 6 ritual plants from 5 different families were documented. Asteraceae, Poaceae, and Lamiaceae (10.71%) family are the most mentioned medicinal plant species, followed by Myrtaceae and Euphorbiaceae (7.14%). The most widely used growth form were herbs (46.4%), while leaves (61.5%) were the most utilized plant part, and the preparation of a decoction (62.2%) was the most preferred method of processing and application. The medicinal plants were most commonly utilized for wound-healing, cough and colds, stomachache and kidney trouble, whereas ritual plants were largely used for healing, protection, and funeral ceremonies. CONCLUSION:This study marks the first report on the medicinal and ritual plants used by a group of indigenous communities in Sto. Niño, Brgy. Ambassador, Tublay, Benguet Province. The data collected show that plant species belonging to the Asteraceae, Poaceae, and Lamiaceae family were the most mentioned and should be further evaluated by pharmacological analysis to assess their wider use for medicinal treatment.

Design optimization of high-rise buildings plays a crucial role in mitigating the significant impact of seismic events on structures and human lives. This study focuses on optimizing frameless high-rise buildings to enhance their resilience against earthquakes. Specifically, a comprehensive investigation is conducted on a 30-story frameless high-rise building, employing a single-objective Genetic Algorithm within the ANSYS application. The optimization process aims to minimize von Mises Stress by targeting key design parameters such as slab thickness, shear wall thicknesses, and vertical loads per floor. ANSYS Transient Structural Analysis simulates the structural behavior, subjecting the building to the September 2007 Magnitude 8.4 Sumatra earthquake and validation using six additional earthquake datasets. The optimized design is characterized by a slab thickness of 260 mm, shear wall thicknesses of 780 mm (excluding $t_{4}$ and $t_{5}$ , which are equal to 540 mm), and specific vertical loads ranging from 7.65 kPa to 11.05 kPa for different floors. This study evaluates the maximum von Mises stresses for earthquakes of various magnitudes to assess the structural performance. The resulting maximum von Mises stresses are as follows: 66 MPa for magnitude 6, 158 MPa for magnitude 6.69, 50 MPa for magnitude 6.93,97 MPa for magnitude 7.01, 72 MPa for magnitude 7.6, 19.16 MPa for magnitude 8.1, and 19.19 MPa for magnitude 8.4. Future research directions involve physical testing to validate simulation outcomes and refine the optimization process. The findings can contribute to developing more efficient and sustainable designs for high-rise buildings, thereby ensuring the safety of occupants and enhancing their resilience against seismic events.

The Philippines is endowed with large deposits of mineral resources, but mining operations have the potential to negatively impact the environment. For example, acid mine drainage (AMD) is a problem that occurs when sulfide minerals are exposed to air, water, and microbial activity, releasing hazardous elements. Many treatment options have been proposed to date to address these negative impacts of AMD. However, little effort has been made over the years to develop a generalized framework for the selection of the optimum technology for AMD treatment. This study thus proposes the spherical fuzzy analytic hierarchy process (SFAHP) as a multi-criteria decision analysis tool to select the best treatment technology for the treatment of AMD. The use of SFAHP is novel in this context as it addresses uncertainty due to indeterminacy by incorporating a "hesitancy parameter" in the decision-making process. Three treatment options were evaluated using a set of criteria such as technical, economical, and environmental aspects. The results showed that the combination of the two-step neutralization ferrite formation and sulfidogenic bioreactor (TSNFF + SB) was considered the most sustainable, with the environmental aspect being the most important factor. The second most preferred option is the high-density sludge (HDS) process while the least preferred is the combination of the conventional lime neutralization and sulfidogenic bioreactor (CLN + SB). A sensitivity analysis was also done, and a comparison with traditional AHP was conducted, which also found TSNFF + SB to be the best option. This illustrative case study demonstrates the robust framework built from SFAHP for selecting the best technology to manage AMD and addresses uncertainty in the decision-making process.

The rehabilitation of legacy mines continues to be a big challenge because of the difficulties in returning them to safe and stable conditions and ensuring that the mined-out areas become productive to support the economic activity of the host community. Previous efforts are often focused on purely technical and environmental aspects, leading to resistance from the local community due to their exclusion from the rehabilitation process. To address the issues associated with legacy mines and lack of participation of the community, we have developed a project, Biodiversity Positive Mining For The Net Zero Challenge (Bio + Mine), focusing on the abandoned Sto. Niño copper mine (Benguet, Philippines). The mine was closed in 1982 without a plan involving local stakeholders and leaving a significant ongoing negative legacy. Using the social-ecological-technological system framework, we will explore the intersections of the structure and functions of socio-economicdemographic, ecological, and technological data useful in devising a more inclusive mitigation strategy for the reconstruction of the supporting ecosystem. We aim to develop a site-specific system, underpinned by the local community's knowledge and practices, that can be a model for wider implementation in other legacy and active mines worldwide.

Rare earth elements (REEs) are crucial for green energy applications due to their unique properties, but their extraction poses sustainability challenges because the global supply of REEs is concentrated in a few countries, particularly China, which produces 70% of the world’s REEs. To address this, the study investigated TK221, a modified extraction chromatographic resin featuring diglycolamide (DGA) and carbamoyl methyl phosphine oxide (CMPO), as a promising adsorbent for REE recovery. The elemental composition and functional groups of DGA and CMPO on the polystyrene-divinylbenzene (PS-DVB) support of TK221 were confirmed using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption kinetics of neodymium (Nd), yttrium (Y), cerium (Ce), and erbium (Er) followed the pseudo-second-order kinetic model and Langmuir isotherm, indicating monolayer chemisorption. Furthermore, iron (Fe) adsorption reached apparent equilibrium after 360 min, with consistent Fe adsorption observed at both 360 min and 1440 min. The inclusion of Fe in the study is due to its common presence as an impurity in most REE leachate solutions. The Fe adsorption isotherm results are better fitted with the Langmuir isotherm, implying chemisorption. Maximum adsorption capacities (qmax) of the resin were determined as follows: Nd (45.3 mg/g), Ce (43.1 mg/g), Er (35.1 mg/g), Y (15.6 mg/g), and Fe (12.3 mg/g). ATR-FTIR analysis after adsorption suggested that both C=O and P=O bands shifted from 1679 cm−1 to 1618 cm−1 and 1107 cm−1 to 1142 cm−1 for Y, and from 1679 cm−1 to 1607 cm−1 and 1107 cm−1 to 1135 cm−1 for Ce, implying possible coordination with REEs. These results suggest that TK221 has a huge potential as an alternative adsorbent for REE recovery, thus contributing to sustainable REE supply diversification.

Coal Fly Ash (CFA) is a hazardous waste from coal-fired power plants, but has increasingly become a popular supplementary cementitious material for cement in the construction industry. As a secondary resource of REE, its main advantage lies in its fine particle size that eliminates the need for costly and energy-intensive comminution. In this study, the potential of CFA from the Philippines as a secondary REE resource was investigated by direct leaching of REEs with hydrochloric acid (HCl). The CFA sample came from a coal-fired power plant with a circulating fluidized bed combustion (CFBC) technology. For the leaching tests, the effects of HCl concentration, leaching time and leaching temperature on REE extractions were elucidate optimized via Response Surface Methodology (RSM). The RSM results showed that the optimum leaching occurred at 3M HCl, 65 °C and 270 min with extractions of Nd, Er, Eu, Tb and Dy at 70.8%, 76.34%, 88.02%, 90.01% and 73.38%, respectively. According to these results, the CFA from the Philippines is a promising secondary resource of REE and the extraction method employed was effective in achieving a relatively high REE dissolution. Moreover, the empirical model that was established accurately predicted the dissolution of REE with an accuracy of 98.20%, 96.66%, 97.09%, 98.17% and 97.78% for Nd, Er, Eu, Tb and Dy, respectively.

Siltation is the biggest environmental challenge associated with nickel laterite mining in the Philippines. The amount of silt generated is huge and one mitigation strategy currently employed by the mining companies is the construction of siltation ponds where the bulk of the clayey- and silt-sized surface runoffs is collected. However, this poses several serious environmental hazards such as landslides due to heavy rainfall and the potential release of hazardous heavy metals. A promising approach to reduce the risks associated with long-term storage of nickel mine waste (NMW) is to employ circular economy by repurposing it for ceramic applications. While generating useful materials with economic value out of a mine waste, it will result in a reduction in volume of waste for disposal. In this study, the method employed to produce NMW-based ceramic wall and floor tiles is slip casting as it is the most appropriate method in forming tiles with complex surface features. Five formulations of NMW-based slips were made for the casting of ceramic tiles and each slip was characterized for its suitability as raw material. The results of NMW characterization show that NMW could be utilized as raw materials for both ceramic wall and floor tiles and the addition of feldspar can enhance casting and physical properties.

As the world transition towards a low-carbon future through renewable energy, mining of minerals and metals to attain this goal is substantial. The Philippines will play an important role in such global economy as it is the world’s fifth most mineral-rich country. However, their exploitation has not been maximized to benefit society. Benefits from the mineral resources sector remain less than 2 % of the country’s GDP since 2006, and the mining and mineral processing, including abandoned or legacy mines, are perceived negatively by the public. In low- and middle-income countries with weak implementation of mining and environmental legislation, the mining industry still operates in a linear system which is considered unsustainable. The mining, mineral extraction and processing, and metal extraction are designed to maximize profits with little plan on how to effectively manage mine wastes, protect the environment, transform post-mining land for beneficial use and empower impacted communities. This paper, thus, proposes a systems approach toward greener eco-efficient mineral extraction and sustainable land use management (SAGES). This approach will facilitate a paradigm shift, which is necessary to manage the country’s mineral endowments sustainably without compromising future land use of mining areas while at the same time supporting the needs and aspirations of the impacted host communities. It envisions extending the usability of mining areas beyond the life of the mine and integrating circular economy principles in addressing holistically mine waste management problems. The multi-R framework, originally developed in waste management (Reduce, Reuse, Recycle) and extended to circular economy strategies, has potential applications in mine waste management in the Philippines. An illustrative case study is then presented that employs a multi-R framework to address the mine waste in an operating Ni-laterite mining site.

Paper Received: 11 June 2021; Revised: 22 July 2021; Accepted: 23 August 2021 Please cite this article as: Promentilla M.A.B., Beltran A.B., Orbecido A.H., Bernardo-Arugay I., Resabal V.J., Villacorte-Tabelin M., Dalona I.M., Opiso E., Alloro R., Alonzo D., Tabelin C., Brito-Parada P., 2021, Systems Approach toward a Greener Eco-efficient Mineral Extraction and Sustainable Land Use Management in the Philippines, Chemical Engineering Transactions, 88, 1171-1176 DOI:10.3303/CET2188195 CHEMICAL ENGINEERING TRANSACTIONS

Bimetallic materials-well-known for their strong reducing properties-are promising tools to recover battery/critical elements from waste streams for resources conservation and decontamination. To date, however, their synthesis has been limited to the use of pure monometallic elements. In this study, we synthesized magnetic bimetallic materials from aluminum wastes (Al-scrap) using a two-stage mechanical-chemical method composed of (1) polishing to remove protective coatings, and (2) etching-cementation for zero-valent iron (ZVI) deposition. Argon-etching using X-ray photoelectron spectroscopy (XPS) showed the effective removal of anodized/polymeric coatings on Al-scrap but the exposed Al-0 was rapidly passivated by an Al-oxyhydroxide/oxide film composed of corundum, bayerite, and boehmite. In the etching-cementation stage, the Al-oxyhydroxide/oxide film was removed using NaCl-HCl and Fe3+ was deposited in corrosion pits on Al-scrap. Strong "magnetic susceptibility" was observed in 1.0 M Fe3+/3.5 M Cl- synthesized products but not in 0.5 M Fe3+/2 M Cl-. This difference could be attributed to the prevalence of ZVI formation in the former but akaganeite precipitation in the latter. The results also showed "targeted" recovery of copper dissolved from Al-scrap on ZVI regions of synthesized product. Finally, two pathways are proposed for Fe3+ reduction: (i) direct cementation (Fe3+-> ZVI), and (ii) sequential reduction (Fe3+-> Fe2+-> ZVI).

This study describes the effects of ceria (CeO2) and dolomite [CaMg(CO3)(2)] additives on the pyrolysis behavior and fire resistive property of conventional intumescent flame retardant (IFR) coating system for I-beam steel substrate called ammonium polyphosphate-melamine-expandable graphite (APP-MEL-EG) system. The fire resistance of various formulations was evaluated using the standard vertical Bunsen burner fire test. Thermogravimetric analysis (TGA) was used to understand the degradation of coating formulations. Observations by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) demonstrated that significant amounts of additives favored the formation of homogeneous compacted char structures, which were predominantly composed of carbon (C), phosphorus (P) and oxygen (O). These three main components of the char were also found to be in various binding combinations with other lighter elements like nitrogen (N) and hydrogen (H) as illustrated by the attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy results. X-ray photoelectron spectroscopy (XPS) further suggest that polyethylene([(CH2-C2H2-CH2)(n-)]) free radicals were abundant on the char surface for the two best formulations and the binding energy of this radical promoted the formation of aromatic carbon chains that enhanced the char's thermal stability. This means that the selection of appropriate additives and combinations of flame-retardant ingredients could significantly change the morphology of the char layer and improve its thermal stability during fire exposure.

Artisanal and small-scale gold mining (ASGM) operations are major contributors to the Philippines' annual gold (Au) output (at least 60%). Unfortunately, these ASGM activities lacked adequate tailings management strategies, so contamination of the environment is prevalent. In this study, soil contamination with copper (Cu), lead (Pb), zinc (Zn) and arsenic (As) due to ASGM activities in Nabunturan, Davao de Oro, Philippines was investigated. The results showed that ASGM-impacted soils had Cu, Pb, Zn and As up to 3.6, 83, 73 and 68 times higher than background levels, respectively and were classified as 'extremely' polluted (CD = 30-228; PLI = 5.5-34.8). Minerals typically found in porphyry copper-gold ores like pyrite, chalcopyrite, malachite, galena, sphalerite and goethite were identified by XRD and SEM-EDS analyses. Furthermore, sequential extraction results indicate substantial Cu (up to 90%), Pb (up to 50%), Zn (up to 65%) and As (up to 48%) partitioned with strongly adsorbed, weak acid soluble, reducible and oxidisable fractions, which are considered as 'geochemically mobile' phases in the environment. Although very high Pb and Zn were found in ASGM-impacted soils, they were relatively immobile under oxidising conditions around pH 8.5 because of their retention via adsorption to hydrous ferric oxides (HFOs), montmorillonite and kaolinite. In contrast, Cu and As release from the historic ASGM site samples exceeded the environmental limits for Class A and Class C effluents, which could be attributed to the removal of calcite and dolomite by weathering. The enhanced desorption of As at around pH 8.5 also likely contributed to its release from these soils.