wAbstract
@Steady-state talc dissolution rates, at far-from-equilibrium
conditions, were measured as a function of aqueous silica and
magnesium activity, pH from 1 to 10.6, and temperature from 25
to 150. All rates were measured in mixed flow reactors and exhibited
stoichiometric or close to stoichiometric dissolution. All measured
rates at pH2 obtained at a fixed ionic strength of 0.02 M can
be described to within experimental uncertainty using
@r+ = SBET (AA
(aH+2/aMg2+)1/4
+ AB) exp (-EA/RT)
where r+ signifies the BET surface area normalized
forward talc steady-state dissolution rate, SBET
denotes the BET surface area of talc present in the reactor, AA and AB refer to pre-exponential
factors equal to 5.0~10-9 and 0.8~10-9 mol/cm2/s,
respectively, EA designates an activation
energy equal to 45 kJ mol-1, R represents the gas constant,
T denotes absolute temperature, and ai refers
to the activity of the subscripted aqueous species. The first
term of this rate expression is consistent with talc dissolution
rates at acidic pH being controlled by the detachment of partially
liberated silica tetrahedral formed at talc edge surfaces from
the exchange of Mg2+ for two protons. Corresponding
atomic force microscopic observations confirms that dissolution
proceeds by the removal of T-O-T sheets from talc edges. At pH
2,
the Mg2+ for proton exchange is so extensive that talc
T-O-T sheets break apart leading to increased surface area and
accelerated rates, whereas rates appear to be pH independent at
pH7.x
1. Introduction
2. Theoretical background
3. Materials and methods
4. Results and discussion
5. Conclusions
Acknowledgments
References