HR: 0830h
AN: V51H-0374    [PDF]
TI: Mineral Dissolution Rates as a Function of Distance From Equilibrium
AU: * Beig, M S
EM: mbeig@rice.edu
AF: Rice University, Dept. of Earth Science P.O. Box 1892, Houston, TX 77251-1892 United States
AU: Luttge, A
EM: aluttge@rice.edu
AF: Rice University, Dept. of Earth Science P.O. Box 1892, Houston, TX 77251-1892 United States
AB: The attempt to quantify silicate mineral dissolution kinetics close(r) to equilibrium faces a major problem: the rates are often very slow and hard, if not impossible, to measure. Therefore, only a handful of data sets are available. At the same time, our fundamental theoretical knowledge of the dependence of dissolution rate on the saturation state of the solution is limited. Some experimental studies with fine-grained mineral powders seem to indicate that the dissolution rate as a function of distance from equilibrium may be an s-shaped curve with a slow rate and almost linear dependence close to equilibrium. The results of the powder experiments seem to indicate that the rate will increase sharply when etch pits begin to open. Far away from equilibrium, the rate becomes independent of distance from equilibrium (dissolution plateau). Our experimental approach uses vertical scanning interferometry for direct observations of single-crystal albite cleavage surfaces and a hydrothermal reaction vessel with flow-through capabilities. Experiments were designed to confirm whether there is a continuous function of $\mathrm{\Delta G}$ that describes the dependence of the dissolution rate on equilibrium, or if the change in reaction mechanism when pits begin to open causes a bifurcation in the reaction pathway. The latter result would mean that the dissolution rate switches from slow (close to equilibrium without pits) to fast (further from equilibrium with pits). In this case, there would be a different function of $\mathrm{\Delta G}$ for each mechanism and no continuous one. Such a situation would have wide implications for modeling dissolution reaction kinetics. It would put in jeopardy any attempt to extrapolate experimental results obtained far from equilibrium to conditions close to equilibrium.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1030 Geochemical cycles (0330)
DE: 1099 General or miscellaneous
DE: 3947 Surfaces and interfaces
DE: 5112 Microstructure
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting