Transformation of Cs-IONSIV® into a ceramic wasteform by hot isostatic pressing

A simple method to directly convert Cs-exchanged IONSIV® IE-911 into a ceramic wasteform by hot isostatic pressing (1100 °C/190 MPa/2 hr) is presented. Two major Cs-containing phases, Cs2TiNb6O18 and Cs2ZrSi6O15, and a series of mixed oxides form. The microstructure and phase assemblage of the samples as a function of Cs content were examined using XRD, XRF, SEM and TEM/EDX. The chemical aqueous durability of the materials was investigated using the MCC-1 and PCT-B standard test methods. For HIPed Cs-IONSIV® samples, the MCC-1 normalised release rates of Cs were <1.57 × 10−1 g m−2 d−1 at 0–28 days, and <3.78 × 10−2 g m−2 d−1 for PCT-B at 7 days. The low rates are indicative of a safe long-term immobilisation matrix for Cs formed directly from spent IONSIV®. It was also demonstrated that the phase formation can be altered by adding Ti metal due to a controlled redox environment

Technical note: Rapid phase identification of apatite and zircon grains for geochronology using X-ray micro-computed tomography

Apatite and zircon are among the best-studied and most widely used accessory minerals for geochronology and thermochronology. Given that apatite and zircon are often present in the same lithologies, distinguishing the two phases in crushed mineral separates is a common task for geochronology, thermochronology, and petrochronology studies. Here we present a method for efficient and accurate apatite and zircon mineral phase identification and verification using X-ray micro-computed tomography (microCT) of grain mounts that provides additional three-dimensional grain size, shape, and inclusion suite information. In this study, we analyze apatite and zircon grains from Fish Canyon Tuff samples that went through methylene iodide (MEI) and lithium heteropolytungstate (LST) heavy liquid density separations. We validate the microCT results using known standards and phase identification with Raman spectroscopy, demonstrating that apatite and zircon are distinguishable from each other and other common phases, e.g., titanite, based on microCT X-ray density. We present recommended microCT scanning protocols after systematically testing the effects of different scanning parameters and sample positions. This methodology can help to reduce time spent performing density separations with highly toxic chemicals and visually inspecting grains under a light microscope, and the improved mineral identification and characterization can make geochronologic data more robust.</p

Measurements of light-absorbing particles on the glaciers in the Cordillera Blanca, Peru

Glaciers in the tropical Andes have been rapidly losing mass since the 1970s. In addition to the documented increase in temperature, increases in light-absorbing particles deposited on glaciers could be contributing to the observed glacier loss. Here we report on measurements of light-absorbing particles sampled from glaciers during three surveys in the Cordillera Blanca Mountains in Peru. During three research expeditions in the dry seasons (May–August) of 2011, 2012 and 2013, 240 snow samples were collected from 15 mountain peaks over altitudes ranging from 4800 to nearly 6800 m. Several mountains were sampled each of the 3 years and some mountains were sampled multiple times during the same year. Collected snow samples were melted and filtered in the field then later analyzed using the Light Absorption Heating Method (LAHM), a new technique that measures the ability of particles on filters to absorb visible light. LAHM results have been calibrated using filters with known amounts of fullerene soot, a common industrial surrogate for black carbon (BC). As sample filters often contain dust in addition to BC, results are presented in terms of effective black carbon (eBC). During the 2013 survey, snow samples were collected and kept frozen for analysis with a Single Particle Soot Photometer (SP2). Calculated eBC mass from the LAHM analysis and the SP2 refractory black carbon (rBC) results were well correlated (r2 = 0.92). These results indicate that a substantial portion of the light-absorbing particles in the more polluted regions were likely BC. The 3 years of data show that glaciers in the Cordillera Blanca Mountains close to human population centers have substantially higher levels of eBC (as high as 70 ng g−1) than remote glaciers (as low as 2.0 ng g−1 eBC), indicating that population centers can influence local glaciers by sourcing BC

(K4Li4)Al8Ge8O32 8H(2)O, an Li+-exchanged potassium alumino-germanate with the zeolite gismondine (GIS) topology

The title compound, lithium potassium dialuminium diger-manium octaoxide dihydrate, (K,Li)-(Al,Ge)-GIS (GIS is gismondine), is the result of a 50% Li+ exchange into the K-(Al,Ge)- GIS structure. The (K,Li)-(Al,Ge)-GIS structure was determined from a 4 x 4 x 2 m m octahedral single crystal at the ESRF synchrotron X-ray source. The ion exchange results in a symmetry transformation from I2/a for K-(Al,Ge)-GIS to C2/c for (K,Li)-(Al,Ge)-GIS. The structural change is due to disordering of K+ ions with Li+ ions along the [001] channel and ordering of water molecules in the [101] channels. The distance between sites partially occupied by K+ ions increases from 2.19 (3) Angstrom in K-(Al,Ge)-GIS to 2.94 (3) Angstrom in (K,Li)-(Al, Ge)-GIS. The Li+ ions occupy positions along the twofold axis at the intersection of the eight-membered-ring channels in a twofold coordination with water molecules. For the four closest framework O2- anions, the Li ... O distances are 3.87 (4) Angstrom

Assessing the origin of pisoids within a travertine system in the border of Puna Plateau, Argentina

The origin of pisoids in a diversity of environments has been recently discussed. While traditionally considered physico-chemical sedimentary products developed in turbulent environments, or even grown in situ, new results show that microbes may influence their development. In the Terma Los Hornos travertine system, two types of actively forming pisoids were recognized: (i) laminated pisoids with a concentrically laminated crust surrounding a nucleus; and (ii) dendriform radial pisoids with no distinct nucleus. Laminated pisoids form in turbulent pools at the base of waterfalls, while dendritic pisoids develop within small depressions between terracettes, and they can occur superposed as a result of episodic transport and recycling within the travertine system (for example, dendritic textures as nucleus of laminated pisoids). The laminated pisoids are characterized by laterally constant laminae thickness with high inheritance and low amounts of randomly distributed organic matter and microbial remains, suggesting a predominantly abiogenic origin. In contrast, the dendritic pisoids exhibit an intimate relationship with diatoms and filamentous bacteria suggesting a stronger biotic influence in their formation. Thus, both abiogenic and biogenic carbonate structures can coexist in the same hydrothermal system. Pisoids found in the stratigraphic record of Terma Los Hornos allowed to test the preservation potential of the primary signals and reconstructing early diagenetic overprints.Fil: Mors, Rodolfo Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Gomez, Fernando Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Astini, Ricardo Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Celestian, Aaron J.. Natural History Museum Of Los Angeles County; Estados UnidosFil: Corsetti, Frank A.. University of Southern California; Estados Unido

Measurements of light-absorbing particles on the glaciers in the Cordillera Blanca, Peru

Glaciers in the tropical Andes have been rapidly losing mass since the 1970s. In addition to the documented increase in temperature, increases in light-absorbing particles deposited on glaciers could be contributing to the observed glacier loss. Here we report on measurements of light-absorbing particles sampled from glaciers during three surveys in the Cordillera Blanca Mountains in Peru. During three research expeditions in the dry seasons (May–August) of 2011, 2012 and 2013, 240 snow samples were collected from 15 mountain peaks over altitudes ranging from 4800 to nearly 6800 m. Several mountains were sampled each of the 3 years and some mountains were sampled multiple times during the same year. Collected snow samples were melted and filtered in the field then later analyzed using the Light Absorption Heating Method (LAHM), a new technique that measures the ability of particles on filters to absorb visible light. LAHM results have been calibrated using filters with known amounts of fullerene soot, a common industrial surrogate for black carbon (BC). As sample filters often contain dust in addition to BC, results are presented in terms of effective black carbon (eBC). During the 2013 survey, snow samples were collected and kept frozen for analysis with a Single Particle Soot Photometer (SP2). Calculated eBC mass from the LAHM analysis and the SP2 refractory black carbon (rBC) results were well correlated (<i>r</i>² = 0.92). These results indicate that a substantial portion of the light-absorbing particles in the more polluted regions were likely BC. The 3 years of data show that glaciers in the Cordillera Blanca Mountains close to human population centers have substantially higher levels of eBC (as high as 70 ng g⁻¹) than remote glaciers (as low as 2.0 ng g⁻¹ eBC), indicating that population centers can influence local glaciers by sourcing BC

Evidence for benthic oxygen production in Neoarchean lacustrine stromatolites

The evolution of oxygenic photosynthesis fundamentally altered the global environment, but the history of this metabolism prior to the Great Oxidation Event (GOE) at ca. 2.4 Ga remains unclear. Increasing evidence suggests that non-marine microbial mats served as localized ¡°oxygen oases¡± for hundreds of millions of years before the GOE, though direct examination of redox proxies in Archean lacustrine microbial deposits remains relatively limited. We report spatially distinct patterns of positive and negative cerium (Ce) anomalies in lacustrine stromatolites from the 2.74 Ga Ventersdorp Supergroup (Hartbeesfontein Basin, South Africa), which indicate that dynamic redox conditions within ancient microbial communities were driven by oxygenic photosynthesis. Petrographic analyses and rare earth element signatures support a primary origin for Ce anomalies in stromatolite oxides. Oxides surrounding former bubbles entrained in mats (preserved as fenestrae) exhibit positive Ce anomalies, while oxides in stromatolite laminae typically contain strong negative Ce anomalies. The spatial patterns of Ce anomalies in Ventersdorp stromatolites are most parsimoniously explained by localized Ce oxidation and scavenging around oxygen bubbles produced by photosynthesis in microbial mats. Our new data from Ventersdorp stromatolites supports the presence of oxygenic photosynthesis ¡«300 m.y. before the GOE, and add to the growing evidence for early oxygen oases in Archean non-marine deposit