A NEW APPROACH TO EXPERIMENTAL DETERMINATION OF COUPLED SILICATE DISSOLUTION - PRECIPITATION REACTION RATES AT AMBIENT CONDITIONS WITH SI ISOTOPE SPIKES

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Many of society's urgent environmental concerns and problems, such as global warming and strategies that mitigate it, and the stresses on the Earth's Critical Zone - the thin veneer on the Earth's Crust from vegetation canopy to the soil and groundwater which sustains human life and is where most terrestrial life thrives on Earth - have something to do with the rates of feldspar dissolution. Feldspars are the most abundant minerals in the Earth's crust, comprising of more than 50% of the Crust volume. For the former, one global warming mitigation strategy is geological carbon sequestration, for which CO2 is stored in deep underground geological formations. However, the injected CO2 will acidify the native brine and dissolve feldspars in the reservoirs, which could affect the reservoir quality and the long-term safety of storage. For the latter, the weathering of feldspars as an abundant mineral in the Critical Zone is critical to rates of soil development and the buffer capacity of the Critical Zone to stresses. However, to assess how fast feldspar dissolution or weathering takes place (chemical kinetics), we need to wrestle with one of the fundamental challenges in geochemistry. It has been known for a long time that the laboratory measured dissolution rates of feldspars are two to five orders of magnitude faster than rates estimated from field studies. Without resolving this seemingly intractable obstacle, we cannot quantitatively evaluate a number of environmental and geological processes, such as those mentioned above. This study is designed to test the promising hypothesis that would partly resolve the apparent discrepancy: A large part of the discrepancy between in situ field and laboratory rates results from the coupling of the dissolution and precipitation reaction in the field systems which is absent in most laboratory experiments. Historically, the determination of very slow feldspar dissolution rates in laboratory at ambient temperatures has been problematic. Slow reaction rates mean that solutes may be below analytical detection limits, thus affecting the accuracy of the experiments. Here, the investigator proposes an innovative utilization of newly developed technology - High-Resolution Multi-Collector Inductively-Coupled Plasma Mass Spectrometry - and uses a novel design of stable silicon isotope 'spikes' to overcome these obstacles in order to determine feldspar reaction rates at ambient and near equilibrium conditions, not previously possible. The work will involve cooperation among the investigator at Indiana University and his colleagues at Ben-Gurion University of the Negev in Israel, and at Trent University in Canada. Funding is requested only for the US organization. This study will enhance international and multi-disciplinary collaboration and contribute to the training of a post-doctoral associate and an exchange student from Israel. Te investigator is currently conducting research on the industrial scale CO2 storage project in Norway (the Sleipner project) and will communicate the results from this study to the CO2 storage community and the Critical Zone research community.