Chelo S. Pascua

Arsenic-bearing smectite from the geothermal environment

Abstract Arsenic-rich scales are widely associated with geothermal fields and constitute a potential hazard to human health. Such arsenic has hitherto been reported to be almost exclusively hosted by sulphide or oxide phases or occurring as surface species. We report here, however, the occurrence of an arsenic- rich (1500 to 4000 mg kg-1 As) smectite from geothermal precipitates from a geothermal field in northwestern Japan and present evidence that the arsenic is predominantly hosted within this silicate mineral. Consistently ~80% of the total arsenic determined in these geothermal precipitates was found by selective chemical extractions to be associated with an operationally defined clay mineral fraction, with lesser proportions being associated with operationally defined amorphous silica, Fe oxide and sulphide fractions. Analysis by XRD, ATR IR and XRF showed the clay fraction to be dominated by Mg-rich trioctahedral smectite. Arsenic K-edge XAS spectra of the smectite suggested the dominance of As(III)-O coordinated species with significant contributions from As(V)-O coordinated species. Both XPS and a magnesium chloride chemical extraction indicated minimal adsorption of arsenic on smectite surfaces suggesting that the arsenic was predominantly either dissolved within the smectite or occurred within mineral occlusions. No such occlusions greater than 1 μm in size were observed in the As-rich smectites. The potential occurrence of arsenic-bearing clays should be considered when determining remediation strategies for geothermal environments or evaluating risks associated with the industrial usage of geothermal precipitates.

A structural model guide for geothermal exploration in Ancestral Mount Bao, Leyte, Philippines

Abstract The Tongonan Geothermal Field is the largest producing geothermal field in the Philippines having an installed capacity of 700 MW. It hosts several major power plants that tap geothermal power from the northern flank of the eroded Ancestral Mount Bao (AMB) volcano in Leyte Island, Philippines. A structural model guide is presented to delineate exploration targets in other flanks of the 1200 km 2 area of the AMB volcano. If applied, the model constrains the coverage of geothermal exploration to areas where more detailed investigations involving geological, geophysical, and geochemical methods can be conducted. Analog sand cone experiments and their comparison with the deformation of the AMB volcano were used to interpret wells within the Tongonan Geothermal Field. The study shows that existing producing wells in Tongonan straddle the crypto-Philippine fault, a N34°W (azimuth=326°) trending master fault inferred to traverse the base of the AMB volcano. This master fault induced fracture-controlled permeability where fluids in the Tongonan Geothermal Field circulate. The structural model suggests that the south-southeastern flank of the AMB directly above the southern extension of the master Philippine fault is an ideal geothermal target amenable to detailed exploration.

Pleated Surface Morphology of C60 Fullerene Nanowhiskers Incorporated by Polyaniline in N-Methyl-2-Pyrrolidone

The addition of polyaniline emeraldine base dissolved in N-methyl-2-pyrrolidone (PAni/NMP) on fullerene C60 whiskers (FW) by direct-mixing technique resulted to the formation of a hybrid material herein called FW/PAni hybrid. The FW/PAni hybrid has a tubular structure with pleated surface texture. It is thinly coated with PAni and has a higher surface area relative to pristine FW and PAni. Beneath the amorphous outer covering, the hybrid shows a crystalline structure as shown by high resolution TEM and selected area electron diffraction. Charge transfer (CT) interaction from electron-rich PAni to electron deficient FW may have resulted to the physical chain entanglement of PAni to FW. The tubular structure of the hybrid is likely caused by the lone pair electrons present in both NMP and PAni causing dissolution inside the whisker. The FW/PAni hybrid having a large surface area and narrow pore size distribution has potential use as hydrogen adsorbent for fuel cell applications, catalysts, and templates for nanofabrication.