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.

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 repurposing of gold (Au) mine tailings from artisanal and small-scale mining (ASGM) operations via alkali activation technology is a promising strategy for waste reduction in developing countries. Direct activation of mine tailings, however, is challenging because these materials contain relatively low aluminum (Al)-bearing minerals. In this study, palm oil fuel ash (POFA) was elucidated as a high Al-bearing waste derived-admixture for the synthesis of an ASGM tailings-based geopolymer composite. Semi-quantitative XRD analysis showed that the tailings contained quartz (SiO2) (~58%), pyrite (FeS2) (~20%) and calcite (CaCO3) (~15%) with minor to trace amounts of aluminosilicates (~7%). Substantial amounts of environmentally regulated pollutants such as mercury (Hg) (40 mg/kg), lead (Pb) (8430 mg/kg) and arsenic (As) (300 mg/kg) were also found in the tailings. SEM-EDS, XRD and ATR-FTIR results showed the successful formation of a hybrid geopolymer-CASH matrix, which improved the unconfined compressive strength (UCS) of geopolymer composites from ~5 MPa to ~7 MPa. Furthermore, POFA did not significantly affect the thermal resistivity of geopolymer composites based on thermal analysis. Finally, the TCLP results showed that the Pb leaching concentrations from ASGM tailings exceeded environmental standards (~15,000 µg/L), which was suppressed after alkali activation to 300–500 µg/L. This means that POFA addition to ASGM tailings-based geopolymer composite improved not only its applicability as backfill, pavements and bricks but also its ability to immobilize toxic elements.

Nickel (Ni)-laterite mining is a major industry in the Philippines but is generating large amounts of Ni-laterite mining waste (NMW) that threatens surrounding water bodies due to siltation. To repurpose this waste as magnetic iron (Fe)-based adsorbent, a three-step extraction-reduction-coprecipitation approach was developed, and the adsorption properties of synthesized product for arsenate (As(V)) and arsenite (As(III)) were investigated. The three-step approach extracted > 90% Fe from NMW and produced fine (<4 mu m), high-purity magnetite based on XPS, XRD, FTIR and SEM-EDS. NMW-derived magnetite also exhibited a positively charged surface between pH 5 and 8 (i.e., IEP of 8.5), which could be attributed to the incorporation of impurities like Mg, Al and Cr. The kinetic and isotherm adsorption results at pH 5 showed that NMW-derived magnetite had high maximum adsorption capacities (q(max)) for As(V) and As(III) estimated at 714 mg/g and 435 mg/g, respectively. The good fit of pseudo-second-order rate law to the kinetic results implied that chemisorption was a dominant removal mechanism for both As(V) and As(III), which likely occurred via inner sphere complexation based on the XPS results. NMW-derived magnetite could also act as an oxidant or reductant depending on the dominant As species in solution. When As(V) species dominated, they were reduced to As(III) via Fe(II)-surface species. Meanwhile, Fe(III)-surface species on the adsorbent oxidized As(III) to As(V) that improved As(III) removal from solutions. These results demonstrate the potential of NMW as raw material for magnetic adsorbent synthesis for environmental applications.

Abiotic component, biotic component, land cover/land use, riparian, rivers

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

The continuous accumulation of artisanal and small-scale gold mining (ASGM) tailings in the Philippines without adequate storage and disposal facility could lead to human health and environmental disasters in the long run. In this study, ASGM tailings was simultaneously stabilized and repurposed as construction material via geopolymerization using coal fly ash, palm oil fuel ash and a powder-based alkali activator. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) identified iron sulfides in the tailings containing arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn), which could be released via weathering. The average unconfined compressive strengths (UCS) of tailings-based geopolymers at 14 days curing were 7.58 MPa and 7.7 MPa with fly ash and palm oil fuel ash, respectively. The tailings-based geopolymers with palm oil fuel ash had higher UCS most likely due to CASH reaction product formation that improved strength formation. The toxicity characteristic leaching procedure (TCLP) results showed very low leachabilities of As, Pb and Fe in the geopolymer materials suggesting ASGM tailings was effectively encapsulated within the geopolymer matrix. Overall, the geopolymerization of ASGM tailings is a viable and promising solution to simultaneously stabilize mining and industrial wastes and repurpose them into construction materials.

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.

freshwater fish, introduced, native, turbidity, water quality

In this study, chemical and mineralogical characterizations of gold-mine tailings in key mining areas in Mindanao, Philippines were investigated for possible utilization as geopolymeric source material. Results of X-ray fluorescence (XRF) and energy dispersive X-ray spectroscopy (EDS) showed that the mine tailings samples have significant amounts of silicon, aluminum and calcium, which are crucial elements needed for geopolymerization. This was confirmed by the IR spectroscopic and mineralogical characteristics of the tailings where vibration bonds and minerals associated with Al and Si such as kaolinite and zeolite are detected. These minerals are already established as indicators for a material to be a good feedstock for geopolymerization. Furthermore, one of the tailings samples had an Si/Al ratio of 4.81, which was close to the recommended value of 3.0 for geopolymerization. The compressive strength of the synthesized geopolymer bricks gained an average of 5.48 MPa. The results suggested that gold mine tailings from key mining areas in Mindanao, Philippines could be used as geopolymer source material.

Pervious Concrete (PC) has long been used in surface runoff management. But one of its major drawbacks is its low strength. Several industrial wastes apparently contain properties that could aid the increase in strength of PC such as coal fly ash and fine sawdust. Thus, their utilization is a possible solution that could address the low-strength issues of PC along with industrial waste disposal management. This study was conducted to investigate the laboratory and field performance of PC while incorporating coal fly ash (CFA) as partial cement replacement and fine sawdust (FSD) as internal curing agent and filler admixture. Tests were performed in accordance with American Society for Testing and Materials (ASTM) standards. In general, the test results showed that PC with CFA and FSD as additives in PC gained enough strength to be considered for field application. In-situ infiltration and strength results showed that the pavement conformed to the typical values for a functional PC pavement.

Flooding in the Philippines is becoming more hazardous over the years intensified by climate change, poor drainage and expanding agricultural industries. In managing this natural disaster, flood hazard maps serve as a significant tool to local government in enabling them for adequate disaster response and planning. Through flood simulation and mapping using numerical models and GIS techniques, this study aimed to determine the amount of flood exposed building features and agricultural resources to different flood scenarios in the floodplain of Sawaga watershed. The Hydrologic Engineering Center’s, hydrologic modeling system and river analysis system of the US Army Corps were the models used for the flood simulation. Feature datasets utilized for flood exposure analysis were derived from Light Detection and Ranging data and satellite images. Results revealed that of the 12 flood-prone barangays in Sawaga floodplain, four (Managok, Santo Niño, Simaya, and Violeta) are most exposed to flood hazards when it comes to the count of affected building features and area of flood-exposed agricultural cultivations. Residential buildings associated as the local community are the most exposed to flood hazard accounting 94% of the total affected building features for all flood scenarios. Moreover, rice plantation is the most exposed agricultural land use to the flood hazard constituting 66%, 74% and 77% of the total flooded agricultural cultivation in the floodplain by the 5-year, 25-year, and 100-year return period scenarios, respectively. The generated maps and extracted information will serve as viable tools to guide disaster managers in the city in executing informed decisions in facing the onslaught of flood disasters.

Massive and ambitious underground space development projects are being undertaken by many countries around the world to decongest megacities, improve the urban landscapes, upgrade outdated transportation networks, and expand modern railway and road systems. A number of these projects, however, reported that substantial portions of the excavated debris are oftentimes naturally contaminated with hazardous elements, which are readily released in substantial amounts once exposed to the environment. These contaminated excavation debris/spoils/mucks, loosely referred to as "naturally contaminated rocks", contain various hazardous and toxic inorganic elements like arsenic (As), selenium (Se), boron (B), and heavy metals like lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn). If left untreated, these naturally contaminated rocks could pose very serious problems not only to the surrounding ecosystem but also to people living around the construction and disposal sites. Several incidents of soil and ground/surface water contamination, for example, have been documented due to the false assumption that excavated materials are non-hazardous because they only contain background levels of environmentally regulated elements. Naturally contaminated rocks are hazardous wastes, but they still remain largely unregulated. In fact, standard leaching tests for their evaluation and classification are not yet established. In this review, we summarized all available studies in the literature about the factors and processes crucial in the enrichment, release, and migration of the most commonly encountered hazardous and toxic elements in naturally contaminated geological materials. Although our focus is on naturally contaminated rocks, analogue systems like contaminated soils, sediments, and other hazardous wastes that have been more widely studied will also be discussed. Classification schemes and leaching tests to properly identify and regulate excavated rocks that may potentially pose environmental problems will be examined. Finally, management and mitigation strategies to limit the negative effects of these hazardous wastes are introduced.

The solid-phase partitioning of mercury could provide necessary data in the identification of remediation techniques in contaminated artisanal gold mine tailings. This study was conducted to determine the total mercury content of mine wastes and identify its solid-phase partitioning through selective sequential extraction coupled with cold vapour atomic absorption spectroscopy. Samples from mine tailings and the carbon-in-pulp (CIP) process were obtained from selected key areas in Mindanao, Philippines. The results showed that mercury use is still prevalent among small-scale gold miners in the Philippines. Tailings after ball mill-gravity concentration (W-BM and Li-BM samples) from Mt Diwata and Libona contained high levels of mercury amounting to 25.024 and 6.5 mg kg-1, respectively. The most prevalent form of mercury in the mine tailings was elemental/amalgamated mercury, followed by water soluble, exchangeable, organic and strongly bound phases, respectively. In contrast, mercury content of carbon-in-pulp residues were significantly lower at only 0.3 and 0.06 mg kg-1 for P-CIP (Del Pilar) and W-CIP (Mt Diwata), respectively. The bulk of mercury in P-CIP samples was partitioned in residual fraction while in W-CIP samples, water soluble mercury predominated. Overall, this study has several important implications with regards to mercury detoxification of contaminated mine tailings from Mindanao, Philippines.

The synergistic interactions of supplementary cementitious materials (SCMs) with ordinary portland cement (OPC) in multi-blended systems could enhance the mechanical and durability properties of concrete and increase the amount of cement that can be replaced. In this study, the characteristics of the hydration products as well as paste microstructure of blended cement containing 20% coal fly ash, 10% rice hull ash and 10% sugar mill lime sludge in quaternary blended system was investigated. Portlandite content, hydration products, compressive strength, pore size distribution and microstructural architecture of hydrated blended cement pastes were examined. The quaternary blended cement paste showed lower compressive strength, reduced amount of Portlandite phases, and higher porosity compared to plain hardened cement paste. The interaction of SCMs with OPC influenced the hydration products, resulting to the formation of ettringite and monocarboaluminate phases. The blended cement paste also showed extensive calcium silicate hydrates and calcium aluminate silicate hydrates but unrefined compared to plain cement paste. In overall, the expected synergistic reaction was significantly hindered due to the low quality of supplementary cementitious materials used. Hence, pre-treatments of SCMs must be considered to enhance their reactivity as good quality SCMs can become limited in the future.

This study examines the possible immobilization of Se(VI) by Mg-bearing hydrotalcite and serpentine-like minerals. Selenate immobilization was carried out via adsorption and coprecipitation reactions under alkaline conditions. The effects of Mg/Al ratios, temperature and initial Se concentration on the adsorption and/or coprecipitation of Se6+ onto these Mg-bearing minerals were examined. The sorption mechanism of Se(VI) was examined by XAFS analysis to give account of its local coordination environment. The results showed that Se(VI) sorption behavior by hydrotalcite and serpentine-like minerals was mainly influenced by their Mg/Al ratio. Higher removal efficiency of Se(VI) (> 60 and 90% at 100 and 10ppm initial Se concentration) was observed during coprecipitation onto hydrotalcite and serpentine-like phases with Mg/Al ratios of 2 and 1.25, respectively. The formation of Mg-bearing minerals was enhanced at higher temperature (at 75°C) but the effect of temperature in Se(VI) immobilization was very minimal. Selenate was mainly retained via outer-sphere complexation but an irreversible fraction of sorbed selenate (about 20%) was observed in these mineral phases. In overall, this study has several important implications in the possible application of hydrotalcite and aluminian serpentine in Se(VI) immobilization.