Determination of Site Specific Binding Environments of Surface Sorbed Cesium on Clay Minerals by Cs-EXAFS

Transport behavior of 137Cs in the environment is regulated by surface sorption reactions on clay mineral surfaces. To provide greater understanding of Cs transport processes, XAFS investigations of the local environments of 133Cs sorbed to clay minerals were conducted on Cs-Ca exchanged clay suspensions at the Cs LIII-edge. With decreased surface loadings of Cs, the Cs local environment exhibited increased long range order beyond 6 Å. Identification of Cs in expanded, semi-collapsed and collapsed interlayer environments was determined by correlating radial distances and Fourier transform peak amplitudes representing Cs-O and Cs-Al/Si in the octahedral and tetrahedral layers. Despite the difficulties of analyzing XAFS data of adsorbed atoms in multiple environments, isolation of Cs in more specific sites by selective exchange should allow detailed analysis and identification of predominant binding environments of cations to clay surfaces

Molecular Characterization of Cr Phases in Contaminated Soils by Cr and Fe EXAFS : A Tool for Evaluating Chemical Remediation Strategies

The successful remediation of Cr contaminated soils via chemical reduction and stabilization of soluble, toxic Cr(VI) species to insoluble Cr(III) species relies on the long term leachability and reoxidation of reduced Cr compounds. Information of Cr chemical environments is invaluable for evaluating the efficiency of proposed stabilization technologies. We describe a matrix of Fe and Cr K-edge EXAFS data on synthetic model compounds that have been used to identify different Fe and Cr local environments of two soil samples

The ChemCam Instrument Suite on the Mars Science Laboratory (MSL) Rover: Body Unit and Combined System Tests

The ChemCam instrument suite on the Mars Science Laboratory (MSL) rover Curiosity provides remote compositional information using the first laser-induced breakdown spectrometer (LIBS) on a planetary mission, and provides sample texture and morphology data using a remote micro-imager (RMI). Overall, ChemCam supports MSL with five capabilities: remote classification of rock and soil characteristics; quantitative elemental compositions including light elements like hydrogen and some elements to which LIBS is uniquely sensitive (e.g., Li, Be, Rb, Sr, Ba); remote removal of surface dust and depth profiling through surface coatings; context imaging; and passive spectroscopy over the 240-905 nm range. ChemCam is built in two sections: The mast unit, consisting of a laser, telescope, RMI, and associated electronics, resides on the rover's mast, and is described in a companion paper. ChemCam's body unit, which is mounted in the body of the rover, comprises an optical demultiplexer, three spectrometers, detectors, their coolers, and associated electronics and data handling logic. Additional instrument components include a 6 m optical fiber which transfers the LIBS light from the telescope to the body unit, and a set of onboard calibration targets. ChemCam was integrated and tested at Los Alamos National Laboratory where it also underwent LIBS calibration with 69 geological standards prior to integration with the rover. Post-integration testing used coordinated mast and instrument commands, including LIBS line scans on rock targets during system-level thermal-vacuum tests. In this paper we describe the body unit, optical fiber, and calibration targets, and the assembly, testing, and verification of the instrument prior to launch