A novel bacterium, designated as strain M3T, was isolated from a hyperalkaline spring in the Philippines and identified as a new species within the genus Lysinibacillus through 16 S rRNA gene sequence and genomic analyses. Although strain M3T shared a high 16 S rRNA gene sequence similarity (> 98.7

Mine tailings generated from hydrometallurgical processing of nickel-cobalt laterite deposits contain high levels of chromium (Cr), with the hexavalent species being a toxic pollutant and carcinogen. However, the partitioning, speciation, and local bonding environment of Cr in the mine tailings remain largely unknown, hindering our ability to predict its toxicity and long-term behavior. Coupling detailed mineralogical, spectroscopic, and geochemical characterization with sequential extraction of tailings from active and rehabilitated dams, we show that Cr is present in its least toxic form, Cr(III), and largely immobilized by recalcitrant minerals. This immobilization also regulates dissolved Cr concentrations in the interacting waters to levels up to five times lower than the global regulatory limit (50 μg L-1). Solid-phase Cr concentrations were ≤1.5 wt % with 39-61% of Cr incorporated into hematite, and to a lesser extent, alunite, both of which formed early in the hydrometallurgical extraction process of mined laterite ores. The remaining Cr was present as recalcitrant chromite residues from the primary source laterites. We highlight that, although hydrometallurgical extractions liberate Cr from laterite ores during processing, they also provide ideal chemical pathways for the formation of highly stable, crystalline hematite that successfully sequesters Cr, while restricting its environmental mobility.

The global demand for rare earth elements (REEs) has been associated with the increased use of renewable energy technologies. However, due to the low occurrence of REEs in economic sources, such as geologic samples, it is essential to employ suitable sample preparation methods and measurement techniques that allow for reliable quantification. While acid digestion procedures have been conventionally used to free metals from silicate rocks, few studies have evaluated these methods for quantitative measurement of REEs, including Sc and Y in mafic-ultramafic rocks. This study involves validating a modified digestion procedure to facilitate the determination of Sc, Y, and REEs in mafic-ultramafic matrices. Three reference materials (RMs) (OKUM, BHVO-1, and JB-1a) were used to assess the performance of this modified method. The calculated percent error (< 10%) for most elements was in good agreement with the reference values, except La in OKUM, Er in BHVO-I, and Eu, Gd, Tb, Ho, and Er in JB-1a. The precision of the modified method was satisfactory, with values generally below 5%. The smooth chondrite normalized REE patterns indicate good quality data. The t-values of the studied elements were lower than the t-critical value (+/- 12.71), suggesting no significant differences between the analytical and Intertek values. Thus, the modified method could be used as a viable alternative in determining REEs in Ni laterite samples by ICP-MS.

Abstract Silicate glasses are durable materials in our daily life, but corrosion rate accelerates under alkaline aqueous environment. Such situation has raised concerns, for example, in nuclear waste disposal where vitrified wastes encounter to alkaline leachate from surrounding concrete materials. Here we report volcanic glass example surviving with a hyperalkaline groundwater (pH > 11) and high flow rate for about 4000 years. The tiny glass fragments were extracted from the volcanic ash layer sandwiched between ultramafic sediments using microanalytical techniques. Sharp elemental distributions at the glass surface, where amorphous-like smectite precursors and crystalline smectites coexist, suggest the corrosion by an interface-coupled dissolution-precipitation mechanism rather than inter-diffusion. The secondary minerals acted as a protective film for the glass by limiting water accessibility. The corrosion rate was maintained at, the minimum, 2.5 orders of magnitude less than the rate observed for fresh glass, even in the presence of Fe and Mg that might have consumed Si through the silicate precipitation.

In this study, we present mineralogical and geochemical characterization of samples systematically collected from a nickel laterite profile at the Sta. Cruz nickel laterite deposit, Zambales, Philippines. Wavelength-dispersive X-ray fluorescence spectroscopy (WDSXRF), mass-balance element mobility calculations, transmitted and reflected light microscopy, and previously reported results from coupled X-ray diffraction (XRD) and Rietveld refinement analyses reveal that the laterite profile investigated is composed of two main horizons—the limonite and saprolite zones—separated by a thin transitional zone. Based primarily on the mineral assemblage and major element chemistry, the main zones are further subdivided into subzones: upper limonite, lower limonite, transitional zone, upper saprolite, and lower saprolite. Garnierite veins were observed cutting the upper and lower saprolite subzones. Investigation of the structure of goethite within the limonite zone via Rietveld refinement shows that the crystallinity of goethite decreases with increasing Ni content and increasing crystallite size. This suggests that upwards through the limonite zone, as goethite ages, its crystallinity increases, which possibly results in the removal of Ni from its crystal structure and eventual remobilization to the lower laterite zones.

On January 12, 2020, Taal volcano in Philippines erupted, 43 years after its previous eruption in 1977. This eruption was preceded by diffuse CO2 degassing precursory signals. Significant temporal variations in diffuse CO2 emission from Taal Main Crater Lake (TMLC) were observed across the ~ 12 years reaching high CO2 degassing rates in 2011 and 2017, with values typical of plume degassing volcanoes. In addition to these CO2 surveys at the TCML, soil CO2 efflux continuous monitoring was implemented at Taal volcano since 2016 and a clear increasing trend of the soil CO2 efflux in 2017 was observed. These geochemical observations are most simply explained by magma recharge to the system, and represent the earliest warning precursor signals to the January 2020 eruptive activity.

Silicate glasses are durable materials in our daily life, but corrosion rate accelerates under alkaline aqueous environment. Such situation has raised concerns, for example, in nuclear waste disposal where vitrified wastes encounter to alkaline leachate from surrounding concrete materials. Here we report volcanic glass example surviving with a hyperalkaline groundwater (pH > 11) and high flow rate for about 4000 years. The tiny glass fragments were extracted from the volcanic ash layer sandwiched between ultramafic sediments using microanalytical techniques. Sharp elemental distributions at the glass surface, where amorphous-like smectite precursors and crystalline smectites coexist, suggest the corrosion by an interface-coupled dissolution–precipitation mechanism rather than inter-diffusion. The corrosion rate was maintained at, the minimum, 2.5 orders of magnitude less than the rate observed for fresh glass, even in the presence of Fe and Mg that might have consumed Si through the silicate precipitation.

Significant temporal variations in the chemical and isotopic composition of Taal fumarolic gas as well as in diffuse CO2 emission from Taal Main Crater Lake (TMLC) have been observed across the ~12 years of geochemical monitoring (Arpa et al., 2013; Hernández et a., 2017), with significant high CO2 degassing rates, typical of plume degassing volcanoes, measured in 2011 and 2017. In addition to these CO2 surveys at the TCML, soil CO2 efflux continuous monitoring was implemented at Taal volcano since 2016 and a clear increasing trend of the soil CO2 efflux in 2017 was also observed. Increasing trends on the fumarolic CO2/St, He/CO2, CO/CO2 and CO2/CH4 ratios were recorded during the period 2010-2011 whereas increasing SO2/H2S, H2/CO2 ratios were recorded during the period 2017-2018. A decreasing on the CO2/CH4 and CO2/St ratios was observed for 2017-2018. These changes are attributed to an increased contribution of magmatic fluids to the hydrothermal system in both periods. Observed changes in H2 and CO contents suggest increases in temperature and pressure in the upper parts of the hydrothermal system of Taal volcano. The 3He/4He ratios corrected (Rc/Ra), and δ13C of fumarolic gases also increased during the periods 2010-2011 and 2017-2018 before the eruption onset. During this study, diffuse CO2 emission values measured at TMCL showed a wide range of values from >0.5 g m−2 d−1 up to 84,902 g m−2 d−1. The observed relatively high and anomalous diffuse CO2 emission rate across the ~12 years reached values of 4,670 ± 159 t d-1 on March 24, 2011, and 3,858 ± 584 t d-1 on November 11, 2017. The average value of the soil CO2 efflux data measured by the geochemical station showed oscillations around background values until 14 March, 2017. Since then at 22:00 hours, a sharp increase of soil CO2 efflux from ~0.1 up to 1.1 kg m-2 d-1 was measured in 9 hours and continued to show a sustained increase in time up to 2.9 kg m-2 d-1 in 2 November, that represents the main long-term variation of the soil CO2 emission time series. All the above variations might be produced by two episodes of magmatic intrusion which favored degassing of a gas-rich magma at depth. During the 2010-2011 the magmatic intrusion of volatile-rich magma might have occurred from the mid-crustal storage region at shallower depths producing important changes in pressure and temperature conditions, whereas a new injection of more degassed magma into the deepest zone of the hydrothermal system occurring in 2017-2018 might have favored the accumulation of gases in the subsurface, promoting conditions leading to a phreatic eruption. These geochemical observations are most simply explained by magma recharge to the system, and represent the earliest warning precursor signals to the January 2020 eruptive activity.Arpa, M.C., et al., 2013. Bull. Volcanol. 75, 747. https://doi.org/10.1007/s00445-013-0747-9.Hernández, P.A., et al., 2017. Geol. Soc. Lond. Spec. Publ. 437:131–152. https://doi.org/10.1144/SP437.17.

Several recent studies have reported a strong association between Sc and goethite (α-FeOOH) in synthetic analogs and natural samples. However, the mechanism of Sc immobilization by goethite and controlling factors remain unclear. This study investigated the adsorption behavior and molecular-scale immobilization mechanisms of Sc at water/goethite interfaces through a combination of batch adsorption and desorption experiments, X-ray absorption fine structure (XAFS) analyses, and density functional theory (DFT) calculations. Results indicate that Sc is preferentially adsorbed on goethite with the formation of bidentate-binuclear inner-sphere complexes at the corner-sharing sites. Bulk Sc K-edge XAFS analyses suggest that Sc is incorporated into the goethite structure by substituting for Fe(III) within the crystal in synthetic Sc-substituted goethite, which is further confirmed in natural goethite particles in the laterite by using micro-focused XAFS (μ-XAFS). Furthermore, we demonstrate that the adsorbed Sc on the goethite surface can be structurally incorporated into the goethite lattice in the presence of aqueous Fe(II) possibly through goethite recrystallization induced by aqueous Fe(II). This process may affect the (re)partitioning of Sc between the goethite surface and the mineral bulk, which could be used to rationally explain disparate Sc speciation in laterites from different regions. Our study elucidates the molecular-scale mechanisms underlying Sc adsorption on and structural incorporation into goethite, providing critical insights into the understanding of geochemical behavior and environmental fates of Sc.

Significant changes in the chemical and isotopic composition of Taal fumarolic gas have been recorded observed before the January 2020 eruption, during the periods 2011 and 2016–2018. Increasing CO2/St, He/CO2, CO/CO2 and CO2/CH4 ratios were recorded during 2011 whereas increasing SO2/H2S, H2/CO2 ratios were recorded during the period 2017–2018. A decreasing on the CO2/CH4 and CO2/St ratios was observed for 2017–2018. These changes are attributed to an increased contribution of magmatic fluids to the hydrothermal system in both periods. Observed changes in H2 and CO contents suggest increases in temperature and pressure in the upper parts of the hydrothermal system of Taal volcano. The 3He/4He ratios corrected (Rc/Ra), and δ13C of fumarolic gases also increased during the periods 2010–2011 and 2017–2018 before the eruption onset. These variations were produced by two episodes of magmatic intrusion which favored degassing of a gas-rich magma at depth. During the 2010–2011 the magmatic intrusion of volatile-rich magma might have occurred from the mid-crustal storage region at shallower depths producing important he observed changes in pressure and temperature conditions, whereas a new injection of more degassed magma into the deepest zone of the hydrothermal system occurring in 2017–2018 might have favored the accumulation of gases in the subsurface, promoting conditions leading to a phreatic eruption.

While there are extensive studies on the mineralogy and geochemistry of laterites worldwide, the temporal and spatial mineralogical development of a typical nickel laterite profile is still poorly constrained. In this study, we present a detailed mineralogical and geochemical characterization of samples systematically collected from a nickel laterite profile at the Sta. Cruz nickel laterite deposit, Zambales, Philippines, to describe the temporal and spatial development of the laterite profile. Wavelength-dispersive X-ray fluorescence spectroscopy (WDSXRF), mass balance-element mobility calculations, transmitted and reflected light microscopy, and previously reported results from coupled X-ray diffraction (XRD) and Rietveld refinement analyses, reveal that the laterite profile investigated is composed of two main horizons: the limonite and saprolite zones, separated by a thin transitional zone. The main zones are further subdivided into subzones based primarily on the mineral assemblage and major element chemistry: upper limonite, lower limonite, transitional zone, upper saprolite, and lower saprolite. Late-stage garnierite veins were observed cutting the upper and lower saprolite subzones. Investigation of the structure of goethite within the limonite zone via Rietveld refinement show that the crystallinity of goethite decreases with increasing Ni content and increasing crystallite size. This suggests that upwards through the limonite zone, as goethite ages, its crystallinity increases which possibly results in the removal of Ni from its crystal structure and eventual remobilization to the lower laterite zones. We propose a spatio-temporal model of the formation of the Sta. Cruz laterite consisting of four stages: (1) early-stage alteration, (2) continued serpentinization and volume expansion, (3) late stage serpentinization and incipient oxide formation, and (4) goethite ageing and garnierite formation.

Recent studies suggest the existence of two ophiolites in Palawan Island: the Central Palawan Ophiolite (CPO) and the Southern Palawan Ophiolite (SPO). New geochemical data in this study from the volcanic rocks of the Palawan ophiolites further support this interpretation. The CPO lavas have back-arc basin basalt (BABB) affin-ities with LILE enrichment and depleted LREE. In contrast, volcanic rocks of the SPO are geochemically diverse, including low-TiO2 boninitic andesites, MORB-like lavas, and high TiO2, high Nb lavas. Sr, Nd and Pb isotopic ratios of the CPO and SPO samples suggests that a mantle source was enriched due to the interaction of depleted MORB mantle with EMI component and ancient Mariana Trench-like sediment. Utilizing available paleomagnetic data and regional plate reconstruction models, we propose that the CPO represents the Late Eocene back-arc basin fragments formed within the proto-South China Sea. The SPO has a subduction initiation origin and formed in the Sundaland-Eurasian margin in Early Cretaceous. Both ophiolites were emplaced on the Palawan Continental Terrane (PCT) due to the collision of the PCT with Borneo and Cagayan Ridge.

A significant amount of scandium (Sc) has been found in the laterites developed over ultramafic and mafic rocks, but much less knowledge is available regarding Sc speciation in laterites. The geochemistry of Sc is unique compared with other rare earth elements (REE), however, the controls of their different partitioning behaviors are still poorly understood. In this study, the distribution and speciation of Sc and yttrium (Y) in the Philippine nickel (Ni) laterites were determined by a combination of sequential extraction, synchrotron-based micro-focused X-ray fluorescence (μ-XRF) and X-ray absorption fine structure (XAFS) techniques, to clarify different geochemical behaviors between Sc and other REE in Ni laterites. Here we demonstrate that Sc can be structurally incorporated into goethite in Ni laterites apart from the adsorption on the goethite surface, while Y is mainly adsorbed on goethite via the bidentate-binuclear inner-sphere complexation. The striking disparity regarding the speciation could result from ionic radius of Sc3+ and Y3+ (REE3+) with respect to Fe3+ in iron (oxyhydr)oxides, which is likely responsible for the relatively lower mobilization and (re)distribution of Sc than other REE in Ni laterites. Our study firstly reports disparate chemical speciation of Sc and Y in Ni laterites and provides molecular-scale insights into the control of different solubility and partitioning behaviors of Sc and other REE.

The Intex laterite deposit in Mindoro, Philippines is derived from the weathering of the ultramafic rocks under a tropical climate. This study investigates the several types of serpentines and the effect of the degree of chemical weathering of ultramafic rocks and laterites on the enrichment of Ni in the deposit. The five types of serpentines are differentiated based on their textural features and Raman spectral data. Type I, type II, type III, and type IV serpentines contain a low amount of NiO (average 0.15 wt%), and their formation is linked to the previous exhumation of the ultramafic body. Conversely, type V serpentines show the highest NiO contents (average 1.42 wt%) and have the composition of serpentine-like garnierites, indicating a supergene origin. In the limonite horizon, goethite is the main ore mineral and shows high NiO contents of up to 1.68 wt%, whereas the Mn-oxyhydroxides (i.e., asbolane and lithiophorite–asbolane intermediate) display substantial amounts of CoO (up to 11.3 wt%) and NiO (up to 15.6 wt%). The Ultramafic Index of Alteration (UMIA) and Index of Lateritization (IOL) are used to characterize the different stages of weathering of rocks and laterites. The calculated index values correspond to a less advanced stage of weathering of the Intex laterites compared with the Berong laterites. The Berong deposit is a Ni-Co laterite deposit in the Philippines, which is formed from the weathering of the serpentinized peridotite. The less extreme degree of weathering of the Intex laterites indicates less advanced leaching, and thereby the re-distribution of Ni, Si, and Mg from the limonite towards the saprolite horizon may have resulted in the poor precipitation of talc-like (kerolite-pimelite) and sepiolite-like (sepiolite-falcondoite) phases in the studied saprolite horizon. Nickel in the Intex deposit has undergone supergene enrichment similar to other humid tropical laterite deposits.

Manguao Basalt is a Plio–Pleistocene basaltic lava flow located on the northeastern edge of Palawan Island, Philippines. The absence of active trenches surrounding the Palawan Continental Block (PCB) poses a challenge regarding the nature and origin of magmatism in the region. This study presents the petrographic and geochemical character of Manguao Basalt, as well as provides insights to the melt formation beneath the PCB. Manguao Basalt samples are olivine–phyric with minor pyroxenes, set in a plagioclase–dominated microcrystalline groundmass. Average bulk–rock major element composition of Manguao Basalt shows similarities to common olivine basalt tholeiite. Petrographic observations of the phenocrysts, however, show the unusual precedence of pyroxenes in the crystallization sequence. Calculated formation temperatures and pressures of the modal assemblage are consistent with this idea of early pyroxene formation. Simulations of mantle melting using the MELTS program show the formation of pyroxene–saturated primitive liquids. The evolution of these primitive liquids reaches similarities with Manguao Basalt composition at 1230–1260 °C. Simulations of equilibrium and fractional crystallization demonstrate the formation of olivine or orthopyroxene as the first crystals. However, the simulations done at equilibrium conditions are more consistent with the observed mineral chemistry of pyroxene phenocrysts in Manguao Basalt. Hence, maintaining the equilibrium between the source and melt is crucial for replicating the observed pyroxene chemistry. Magmatic underplating provides an excellent model for visualizing the melting and crystallization processes beneath the PCB. The model is also consistent with the narrative of other magmatic units in northern Palawan (e.g., Capoas Granite). The significant findings of this study contribute to the understanding of the tectonic evolution of the PCB.

Ultramafic rocks are considered as the most important geogenic sources of Cr whose hexavalent species is of environmental concern. In tropical to subtropical areas (e.g. New Caledonia, Brazil, Philippines), prolonged and pervasive weathering of ultramafic rocks produces Ni laterite ores which are further enriched in Cr. While elevated levels of Cr have been identified in Ni laterites, Cr availability and export from these deposits and its contribution to natural waters remain poorly understood. Therefore, this study examined the speciation and flux of Cr in a Ni laterite profile through sequential extraction and leaching experiments coupled with physical, mineralogical, and geochemical characterization. These were correlated to the behavior and export of Cr in surrounding surface waters studied through hydrochemical investigation. This work demonstrates, through the example of the Rio Tuba Ni laterite deposit, that pervasive weathering of ultramafic rocks in tropical areas generate very important reservoirs of Cr(VI). Although Cr is primarily fixed in insoluble fractions ( 89%) and least in bioavailable and easily mobilizable phases (< 1%), due to the inherent elevated Cr content (up to 2.9 wt %) of the Ni laterites, the latter still provided water-extractable Cr(VI) contents surpassing drinking water and freshwater standards. By comparison with the silicate-rich saprolite unit, the overlying Fe-(oxyhydr)oxide dominated laterite layer yielded lower Cr(VI) contents due to its acidic nature and higher amounts of organic matter and Fe-(oxyhydr)oxides which promote reduction and readsorption of Cr(VI). During water infiltration, Cr(VI) migrates downward along the profile at a rate of 62 to 3446 t/km(2)/yr. While the alkaline and oxidizing conditions of the surrounding surface waters favor Cr(VI) mobilization, only a fraction of Cr(VI) from the Ni laterites reaches these water bodies. Cr(VI) concentrations (<= 213 mu g/L) and fluxes (mostly <= 50 kg/km(2)/yr) in the surface waters being significantly lower than that of the Ni laterites reflect the action of processes (e.g. dilution, reduction, adsorption) that attenuate the release of this species along water flow paths.

Indium doping on superconducting bulk Bi2Sr2-xInxCaCu2O8+δ was found to be successful for low concentrations but can result to phase decomposition and suppressed superconductivity in high indium concentration. Impurities and secondary phases affect the superconductivity as it impede superconducting transitions and reduce activation energy. The effect on indium doping on the activation energy is correlated with phase purity, granularity and suppressed superconductivity. Reduced activation energy suggests that vortices can flow more easily in high indium doped samples through thermally activated flux flow.

The effect of In2O3 on grain connectivity and superconducting properties of Bi-2212 was investigated. Indium was intentionally doped on the Sr-site of BSCCO at doping levels from x = 0 to x = 0.8. Accessing the Sr lattice site in BSCCO provides useful control on the possible effect of indium on its superconducting behavior and microstructural properties. Results show that the superconductivity persists in BSCCO even at high indium concentration (x = 0.8). However, secondary phases form at x ≥ 0.4 indium concentration affecting normal resistivity, magnetic susceptibility response and superconducting transition temperature of BSCCO. Formation of secondary phases weakens the diamagnetic intergrain coupling. An apparent increase in the formation of micron-sized grains is related to the increased sinterability of BSCCO with indium doping. The enhanced sinterability of BSCCO with indium provides possibility of synthesizing thin films with reduced thermal heat treatment.