Formation of Amorphous Silica Surface Layers by Dissolution-Reprecipitaton During Chemical Weathering: Implications for CO2 Uptake

Chemical weathering reactions at the Earthʹs surface and upper crust influence the chemical cycle of elements, chemical erosion rates, the quality of potable water resources, soil formation and nutrient availability, and ore genesis. Chemical weathering is also a major process controlling the regulation of the carbon cycle by CO2 consumption and sequestration by carbonation reactions. Based on nanometer-resolution TEM measurements, chemical weathering of silicates in both the laboratory and the field was found to result in the development of a distinct interfacial phase that is amorphous, hydrated, and silica-rich. An abrupt, step function-like change in chemistry and structure delimits the interface with the unaltered parent mineral, suggesting a dissolution-reprecipitation mechanism. The existence of these precipitated silica layers has important and so far unrecognized implications with respect to natural and industrial carbon sequestration processes, as surface silica layers may decrease the amount of atmospheric CO2 consumed during coupled silicate chemical weathering-carbonation reactions.