Experimental reports have shown that the rate of mineral weathering observed in the field differs from that determined in chemical laboratories. One reason for such difference might be found in time‑dependent and scale‑dependent variables that are generally assumed to be constant. Time‑dependent effects might include a change in chemical mechanism over time, for example dissolution followed by re-precipitation of a new phase. Scale‑dependent effects might include a change of the hydrodynamic conditions in the micro geometries of the geological material. A classic example of conflicting data is given by alkali feldspars, that have been reported to dissolve at rates 3 orders of magnitude slower in natural settings than in laboratory tests at neutral pH. Clarifying such disparities is necessary to advance the understanding of the fate of chemical species in soils and in the Earth’s subsurface. Key processes that will benefit from such understanding are the capture and storage of CO2, the management of radioactive wastes as well as the emerging field of agrominerals as sustainable fertilizers. In this contribution, we present a novel microfluidic device that allows the determination of weathering rates at the microscale, in flow and geometrical conditions inaccessible with traditional bench‑top apparatuses. As a case study, we investigate the leaching kinetics of K+ in strongly acidic condition (pH=0) from a K‑bearing rock rich in feldspar, syenite. Quantitative interpretations of the kinetic data obtained from this device will contribute substantially to clarify the scale‑dependence behavior of weathering rates.

Microfluidic device to determine the rate of mineral weathering

249th National Meeting (2015)

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