Structures and properties of bioorgano-clays

Interactions between microbial matter and clays are a common interfacial phenomenon in soil and sediment environments. However, fundamental mechanisms governing the formation and interactions of clay minerals with microbial-derived organic substances are still poorly understood. Therefore, our central aim was to study the formation of bioorgano-clay composites and their specific material properties and compare these properties with those of well-studied organo-clays. Pure organic cations (e.g., alkylammonium homologues) and complex microbial biomass (e.g., fungal biomass from Aphanocladium sp.) were used to prepare organo- and bioorgano-clays by varying the amount of clay (montmorillonite) and organic materials used. Interaction mechanisms between organic materials and clay and the resulting structure and physicochemical properties were explored by multiple experimental methods (e.g. IR spectroscopy, contact angle, zeta potential, X-ray photoelectron spectroscopy, transmission electron microscopy) in a combination with molecular modelling to determine the structure, composition, and properties of the prepared bioorgano-clays. Depending on origin, type, and size of the organic material and the clay, two basic types of bioorgano-clays were found: (i) bioorgano-clays having their clay particles coated by bioorganic matter with only limited or no penetration into interlayer galleries and (ii) bioorgano-clays having bioorganic matter distributed in the interlayer galleries and/or on the external surfaces of clay particles. Both types show heterogeneous arrangements of the amended organic matter inducing differences in shape and size of organo-clay particles. Consequently, changes in pore volumes, stability, and elemental interface properties can be verified. Compared to organo-clays, bioorgano-clays provided e.g. a higher adsorption capacity for uranyl, suggesting that modification of clays by rather unspecific microbial compounds significantly enhanced the number of exchange sites. Bioorganic-clays, although being less specific in nature, might therefore be applied more broadly in situations where a high sorption capacity, e.g., for contaminants, is required

Clay alteration of volcaniclastic material in a submarine geothermal system, Bay of Plenty, New Zealand

The Calypso Hydrothermal Vent Field (CHVF) is located along an offshore extension of the Taupo Volcanic Zone (TVZ), an area of abundant volcanism and geothermal activity on the North Island of New Zealand. The field occurs within a northeast-trending submarine depression on the continental shelf approximately 10–15 km southwest of the White Island volcano in the Bay of Plenty. The graben has been partially filled by tephra from regional subaerial volcanic eruptions, and active hydrothermal venting occurs at several locations along its length. The vents occur at water depths of 160 to 190 m and have temperatures up to 201 °C. Recovered samples from the vent field include variably cemented and veined volcaniclastic sediments containing an assemblage of clay minerals, amorphous silica, barite, As–Sb–Hg sulfides, and abundant native sulfur. The volcanic glass has been altered primarily to montmorillonite and mixed-layer illite–montmorillonite; illite, and possibly minor talc and mixed-layer chlorite–smectite or chlorite–vermiculite are also present. A hydrothermal versus diagenetic origin for the smectite is indicated by the presence of both illite and mixed-layer clays and by the correlation between the abundance of clay minerals and the abundance of native sulfur in the samples. The mineralization and alteration of the volcanic host rocks are similar to that observed in near-neutral pH geothermal systems on land in the TVZ (e.g., Broadlands–Ohaaki). However, the clay minerals in the CHVF have a higher concentration of Mg in the dioctahedral layer and a higher interlayer Na content than clay minerals from Broadlands–Ohaaki, reflecting the higher concentrations of Mg and Na in seawater compared to meteoric water. Minerals formed at very low pH (e.g., kaolinite and alunite), typical of steam-heated acid-sulfate type alteration in the TVZ geothermal environment, were not found. Mixing with seawater likely prevented the formation of such low-pH mineral assemblages. The occurrence of illite and mixed-layer illite–smectite close to the seafloor in the CHVF, rather than at depth as in the Broadlands system, is interpreted to reflect the higher pressures associated with submarine venting. This allows hotter fluids to be discharged before they boil, and thus minerals that are encountered mainly at depth in subaerial geothermal systems can form close to the seafloor

New insights on crystal violet dye adsorption on montmorillonite: Kinetics and surface complexes studies

Adsorption of crystal violet (CV) on montmorillonite (MMT) was investigated through kinetic analysis, microstructural characterization, surface charge and contact angle determination. Adsorption kinetic was studied in situ by attenuated total reflectance Fourier-transform infrared analysis (ATR-FTIR); MMT microstructural changes were determined by small angle X-ray scattering (SAXS) and N2 adsorption/desorption analysis; wettability and surface charge were determined by contact angle and a particle charge detection technique, respectively. Kinetic studies indicated that the analyzed total adsorption rate was the result of the combination of intraparticle diffusion and/or surface adsorption processes, where the contribution of each phenomenon depended on the initial concentration of CV. Obtained findings of characterization studies allowed proposing different molecular arrangements according to the concentration of adsorbed dye in water. For low CV concentration, the dye molecules entered in the MMT interlaminar space as a monolayer, with the aromatic rings parallel to the interlayer space surface. At medium CV content, the dye molecules entered the MMT interlaminar space either in a paraffin-like monomolecular arrangement with a tilt angle or in a bilayer configuration. In both cases, increment of the basal spacing, reduction of wettability, diminution of negative surface charge and the interaction of CV molecule with surface through its quaternary amine group were determined. At higher CV content, the wettability increases and surface charge shifted to positive values, indicating the presence of CV bilayer arrangements, with the positively charged region of the dye molecules facing away from the surface. Results of this work will help to develop efficient adsorbents and to achieve a deeper understanding on the fate of CV (and similar compounds) in water and sediments.Fil: Marco Brown, José Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; ArgentinaFil: Guz, Lucas Martín. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Olivelli, Melisa Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; ArgentinaFil: Schampera, B.. Leibniz Universität Hannover; AlemaniaFil: Torres Sanchez, Rosa Maria. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Curutchet, Gustavo Andres. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Candal, Roberto Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de San Martín. Instituto de Investigación en Ingeniería Ambiental; Argentin