『Abstract
Weathering rates of silicate minerals observed in the laboratory
are in general up to five orders of magnitude higher than those
inferred from field studies. Simple calculations show that even
if the field conditions were fully simulated in standard laboratory
experiments, it would be impossible to measure the slow rates
of mineral dissolution that are observed in the field. as it is
not possible to measure the dissolution rates under typical field
conditions, one should extrapolate the available data to the field
conditions. To do this, a rate law for the dissolution of plagioclase
in the field was formulated by combining the far from equilibrium
dissolution rate of weathered natural oligoclase at 25℃ with the
effect of deviation from equilibrium on dissolution rate of fresh
albite at 80℃. In contrast to the common view that laboratory
experiments predict dissolution rates that are faster than those
in the field, the simulation based on this rate law indicates
that laboratory dissolution experiments actually predict slower
rates than those observed in the field. This discrepancy is explained
by the effect of precipitation of secondary minerals on the degree
of saturation of the primary minerals and therefore on their dissolution
rate. Indeed, adding kaolinite precipitation to the simulation
significantly enhances the dissolution rate of the plagioclase.
Moreover, a strong coupling between oligoclase dissolution and
kaolinite precipitation was observed in the simulation. We suggest
that such a coupling must exist in the field as well. Therefore,
any attempt to predict the dissolution rate in the field requires
knowledge of the rate of the secondary mineral precipitation.
Keywords: Aqueous geochemistry; Ground water; Waste water』
Introduction
Discussion
It is not possible to measure field dissolution rates of
silicates using standard laboratory experiments
The extrapolation of laboratory dissolution rates to field conditions
The effect of secondary mineral precipitation on the dissolution
of primary minerals
Summary and conclusions
Acknowledgments
References