『Abstract
The dissolution of most common multicomponent silicate minerals
and glasses is typically incongruent, as shown by the nonstoichiometric
release of the solid phase components. This results in the formation
of so-called surface leached layers. Due to the important effects
these leached layers may have on mineral dissolution rates and
secondary mineral formation, they have attracted a great deal
of research. However, the mechanism of leached layer formation
is a matter of vigorous debate. Here we report on an in situ atomic
force microscopy (AFM) study of the dissolution of wollastonite,
CaSiO3, as an example of leached layer formation
during dissolution. Our in situ AFM results provide, for the first
time, clear direct experimental evidence that leached layers are
formed in a tight interface-coupled two-step process: stoichiometric
dissolution of the pristine mineral surfaces and subsequent precipitation
of a secondary phase (most likely amorphous silica) from a supersaturated
boundary layer of fluid in contact with the mineral surface. This
occurs despite the fact that the bulk solution is undersaturated
with respect to the secondary phase. Our results differ significantly
from the concept of preferential leaching of cations, as postulated
by most currently accepted incongruent dissolution models. This
interface-coupled dissolution-precipitation model has important
implications in understanding and evaluating dissolution kinetics
of major rock-forming minerals.』
Introduction
Materials and methods
Experimental results and discussion
Implications
Acknowledgments
References cited