S91: Nano-scale investigations of mineral-water interface processes

Conveners:	Guntram Jordan	(guntram.jordan@lrz.uni-muenchen.de)
	Andrew Stack	(andrew.stack@eas.gatech.edu)
Keynote :	William H. Casey	(University of California, Davis)

Processes at mineral-water interfaces impact a huge range of length scales. To name just a few, global cycling of chemical elements is affected by mineral weathering or precipitation, local environmental conditions are influenced by the sorption onto mineral surfaces, and properties of composite materials are influenced by the growth morphology of crystals. However, despite this huge range of impact, all these processes take place at mineral-water interfaces at the molecular scale. Recent advances in experimental techniques allow direct access to these interfacial processes with a nano-scale resolution. First principles computational methods can now be used in direct comparison to these experimental observations. Therefore, this session aims at exploring new and exciting work done at, or relevant to, the mineral-water interface from both computational and experimental perspectives.

S92: Mechanisms of metasomatic reactions

Conveners:	Dan Harlov	(dharlov@gfz-potsdam.de)
	Timm John	(timm.john@fys.uio.no)
Keynote:	Håkon Austrheim	(Oslo)

Metasomatism is clearly recognised in many geological environments where evidence for the parent phases has been preserved. The mechanism by which a mineral assemblage is either partially or totally re-equilibrated in the presence of a fluid phase is a fundamental issue in geochemistry and petrology. This session will assess the extent to which geochemical, spectroscopic and microscopic methods have contributed to our understanding of such mechanisms.

S93: Microbially mediated processes governing the redox cycling of metals

Conveners:	Colleen Hansel	(hansel@deas.harvard.edu)
	Andreas Kappler	(andreas.kappler@uni@tuebingen.de)
Keynote:	Yuri Gorby	(San Diego, CA)

The redox cycling and mineralization of metals are dictated by the kinetics and thermodynamics of an intricate network of abiotic and biotic reactions. The overall operative pathway is a result of synergistic or competitive reactions, which may not be reflected in the broader redox signature and geochemical profile. In fact, the redox conversion and (bio)mineralization of metals is oftentimes a result of coupled biotic-abiotic pathways, including reactions induced by redox- and photo-active microbial metabolites. The ultimate pathway responsible for metal oxidation/reduction will dictate the speciation, structure, and subsequent reactivity of the resultant (bio)mineral. This session will explore and discuss the diverse range of microbial-induced (e.g. enzymatic, metabolite-driven) mechanisms responsible for the cycling and (bio)mineralization of metals within both terrestrial and aquatic environments. Topics include the biogeochemistry of microbial-induced metal cycling, the biochemistry of microbial metabolic pathways influencing metal cycles, phylogenetic influences on metal redox pathways, and the impact of contrasting (a)biotic redox pathways on the speciation, reactivity, and stability of metals (bio)minerals.

S94: Mechanisms of growth and dissolution of carbonates: Applications to the environment and industry

Conveners:	Susan Stipp	(stipp@geol.ku.dk)
	Eric Oelkers	(oelkers@lmtg.obs-mip.fr)

The aim of this session is to look at calcite from a variety of perspectives. These include the mechanisms important for growth and dissolution and their inhibition, for biomineralisation and the effects of organic and inorganic components, for the interaction of carbon dioxide and its sequestration, for the adsorption properties of methane and other hydrocarbons, for the uptake of trace components from drinking water or by industrially produced calcite, and for many others. We hope to assemble people from a variety of branches in the academic, industrial and consulting worlds, including those interested in oil, pharmaceuticals, building, paper, water treatment, CO₂ storage, etc. as well as those who study calcite from the fundamental level with traditional and high-tech experimental techniques and modelling. Our aim in this session is to pool our knowledge about calcite and other carbonate minerals and identify key questions for future research.

S95: Metal oxide surface reactivity from the nano to macro-scale

Conveners:	Moira K. Ridley	(Moira.Ridley@ttu.edu)
	Willem H. van Riemsdijk	(Willem.vanRiemsdijk@wur.nl)
	Michael L. Machesky	(machesky@sws.uiuc.edu)
Keynote:	Claudine Noguera	(Paris)

Chemical reactions at interfaces, particularly metal oxide-water boundaries, influence and control numerous geochemical processes. A better understanding of interface reactions and metal oxide surface reactivity has emerged by integrating experimental and modeling studies. This symposium aims to bring together scientists using a variety of experimental and modeling approaches concerned with quantifying the nano- and macro-scale reactivity of metal oxide surfaces. We encourage contributions focused toward elucidating the behavior of metal oxide phases as functions of particle size, and/or surface structure; and, studies that target both the macroscopic and microscopic manifestations of metal-oxide surface reactivity.

S96: Speciation and reactivity of trace elements in natural environments

Conveners:	Andreas Voegelin	(voegelin@env.ethz.ch)
	Farid Juillot	(Farid.Juillot@impmc.jussieu.fr)
	Ruben Kretzschmar	(kretzschmar@env.ethz.ch)
Keynote:	Daniel Strawn	(University of Idaho, USA)

The speciation of trace nutrients and contaminants strongly affects their reactivity in the environment. Therefore, detailed information on the speciation of trace elements in the solid and liquid phase is crucial in order to understand their bioavailability and mobility in terrestrial and aquatic systems. Characterization of natural samples with respect to the presence of different types of species provides detailed insight into relevant processes and mechanisms under field conditions. In addition, speciation studies in environmental systems also represent an important link to laboratory studies concerned with the reactivity of trace elements and allow mutual validation of model concepts. Because of the usually low concentrations of trace elements, their characterization in complex matrices requires the use of advanced analytical techniques. This session aims to provide a platform for researchers concerned with the speciation and reactivity of trace elements in the context of their biogeochemical cycling. Possible topics include the speciation of trace contaminants in soils and sediments using X-ray absorption spectroscopy and electron microscopy as well as the identification of dissolved trace species by hyphenated or voltammetric techniques.