DELTA-MIN · Mechanisms of Mineral Replacement Reactions

Mechanisms of Mineral Replacement Reactions

The report below is also attached as a pdf file. Mechanisms of Mineral Replacement Reactions Contact Details: Delta-Min Office, Prof. Andrew Putnis, Institut für Mineralogie, Corrensstrasse 24, 48149, Münster, Germany Project Website: www.delta-min.com The scientific objective of the DELTA-MIN project was to significantly advance the understanding of fluid-induced mineral transformation mechanisms by exploring a wide range of diverse phenomena from a unified point of view. The project combined observations of fluid-induced replacement in natural rocks, experimental studies of mineral-fluid interaction and fundamental theory to understand dissolution, precipitation and mass transport. Observations ranged from the mega- to the nano-scale: from estimating the extent of metasomatism in rocks, to high resolution transmission electron microscopy of reaction interfaces. The methods used to achieve these objectives included: • In situ Atomic Force Microscopy to study crystal growth and dissolution mechanisms • Hydrothermal experiments in various types of reactors to study mineral replacement mechanisms • Dissolution rate studies in both flow-through and batch reactors • Field work in areas where fluid-rock interaction can be studied on an outcrop scale • Scanning and transmission electron microscopy to study reaction microstructures in both experimental and natural samples Significant breakthroughs were made on a number of research problems: • Atomic Force Microscopy of in situ crystal growth and dissolution mechanisms has demonstrated that background electrolytes can have a significant effect on kinetics by modifying water dynamics. • Hydrothermal experimental studies coupled with observations from natural rocks have identified replacement mechanisms and mass transport pathways. • The mechanism of leaching was unambiguously identified as a sequential process of congruent dissolution coupled with reprecipitation, in contrast to the accepted view of solid state interdiffusion. • A unified concept of fluid-induced mechanisms of metasomatism and metamorphism in natural rocks has been published. • Carbonation mechanisms of silicate rocks have been described from both experiments and studies of natural carbonated rocks. • Dissolution rates of minerals have been related to surface crystallographic orientation, providing a a more mechanism-based interpreatation of rate data. • The crucial importance of an interfacial boundary layer at the mineralfluid interface has been demonstrated experimentally, showing that supersaturation in the bulk fluid is not a criterion for precipitation. The overall conclusions of these results are that in multicomponent minerals fluid-mineral interactions take place by (i) a dissolution step which usually results in a supersaturation in a boundary layer at the fluid-mineral interface (ii) precipitation of a product phase which may take place within this boundary layer, and (iii) establishment of a feedback between dissolution and precipitation. This coupled process, which may be manipulated by changing the fluid composition, is the primary mechanism of mineral reequilibration in the presence of a fluid phase. The applications of these results are a significant improvement in • understanding how one rock type can be transformed to another • using replacement mechanisms to produce more stable coatings on marble cultural heritage • understanding how the reactions between phosphate fertilizer and lime-rich soils can limit the bioavailability of phosphate • applying a better understanding of dissolution mechanisms to contribute to modelling long term stability in nuclear waste repositories • applying "geo-inspired" fabrication of new materials by pseudomorphic replication. The dissemination of the project was through peer-reviewed publications (40 publications in international ISI listed journals with more either already submitted or in preparation), through many international conference abstracts (~90) and presentations and convened special sessions in international conferences. A highlight of the project was the Final International Conference held at the University of Oviedo, Spain from 28 February - 2 March 2012. This was attended by over 100 participants. The Conference Agenda is attached to this report. A further highlight was the Arne Richter Award for Outstanding Young Scientists of the European Geoscience Union (2012) to Dr Encarnación Ruiz- Agudo, a Delta-Min Experienced Researcher Marie Curie Fellow.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз