Ion partitioning and element mobilization during mineral replacement reactions in natural and experimental systems
Christine V. Putnis, Lurdes Fernández Díaz, 2011. "Ion partitioning and element mobilization during mineral replacement reactions in natural and experimental systems", Ion Partitioning in Ambient-Temperature Aqueous Systems, M. Prieto, H. Stoll
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Mineral replacement is a common phenomenon in a wide range of geological environments. Metasomatism, metamorphism, weathering, diagenesis and fossilization are examples of processes that can involve the replacement of one or more minerals associated with extensive chemical change. Such replacements are very often pseudomorphic. At relatively low temperatures such as those at the surface or within the upper part of the Earth’s crust, where solid-state diffusion can be considered negligible, mineral replacement is the result of interface-coupled dissolution-precipitation reactions, driven by the interplay between the degrees of saturation of natural fluids with respect to different mineral phases. These reactions can play an important role in the mobilization and partitioning of elements. Mineral replacement is accompanied by the generation of porosity, which provides a pathway for the penetration of the fluid within the original parent mineral and facilitates mass transport. This chapter highlights the importance of dissolution-precipitation mineral replacements for element mobilization and ion partitioning in the Earth by presenting and discussing both experimental models and examples of natural processes, development of which can involve significant chemical change, such as during serpentinization and bone fossilization.
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Ion Partitioning in Ambient-Temperature Aqueous Systems
On the surface of the Earth, the intermingling of water and minerals gives rise to a diverse suite of reactions that determine the purity of water we drink, the fate of contaminants we emit, and the composition of minerals and biominerals that we use to interpret past environmental conditions from the sediment archive. Human societies have ubiquitous exposure to the outcome of these mineral—water reactions. Understanding in detail the ion partitioning in mineral—water interactions is of fundamental importance to geochemical studies and ultimately to society. The solid-solution properties of minerals are a significant part of the complexity, and also the importance, of these ion-partitioning reactions. Natural minerals always contain a certain proportion of trace elements in solid solution. These trace elements, precisely because of their rarity, often have a disproportionately large impact on living organisms as is the case for familiar toxic metals such as As and Cd. A clear understanding of ion partitioning behaviour is therefore essential for environmental objectives such as scavenging heavy metals from solution, remediating contamination in soils, or ensuring safe, long-term storage of anthropogenic CO2 or radionuclides in geological reservoirs. Materials science has also taken a new look at the role of trace-element and ion partitioning in regulating biomineralization. Finally, the last several decades have seen a surge in interest in reconstructing past climate and environmental conditions from the sediment archive. An accurate interpretation of ion partitioning is essential to the correct interpretation of records from diverse systems like stalagmites, corals, or shells of marine foraminifera. Given this wide range of applications for ion partitioning, it is fortunate that theoretical and thermodynamic frameworks for modelling ion partitioning have advanced significantly in the last decade. We believe that it is an opportune time to convene experts on ion partitioning from a range of perspectives, from theoretical to applied, to exchange knowledge across these topics and through this exchange, maximize the advances that have been made in the discipline. We are pleased to be able to convene these experts in person, at the European Mineralogical School in Oviedo in June 2010 to share these advances with each other and with the next generation of geochemists. It is our hope that this book will serve most crucially as a bridge through which researchers in one aspect of ion partitioning will be able to productively venture into complementary systems and models to better solve their research goals and perhaps be inspired with new research questions.