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Dissolution rates of talc as a function of solution composition, pH and temperature
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 °C. All rates were measured in mixed flow reactors and exhibited stoichiometric or close to stoichiometric...
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| Published in: | Geochimica et cosmochimica acta 2007-07, Vol.71 (14), p.3446-3457 |
|---|---|
| Main Authors: | , , , |
| Format: | Article |
| Language: | English |
| Citations: | Items that this one cites Items that cite this one |
| Online Access: | Get full text |
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| Summary: | 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
°C. All rates were measured in mixed flow reactors and exhibited stoichiometric or close to stoichiometric dissolution. All measured rates at pH
>
2 obtained at a fixed ionic strength of 0.02
M can be described to within experimental uncertainty using
r
+
=
s
BET
A
A
a
H
+
2
a
Mg
2
+
1
/
4
+
A
B
exp
(
-
E
A
/
RT
)
where
r
+ signifies the BET surface area normalized forward talc steady-state dissolution rate,
s
BET denotes the BET surface area of talc present in the reactor,
A
A and
A
B refer to pre-exponential factors equal to 5.0
×
10
−9 and 0.8
×
10
−9
mol/cm
2/s, respectively,
E
A designates an activation energy equal to 45
kJ
mol
−1,
R represents the gas constant,
T denotes absolute temperature, and
a
i
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 Mg
2+ 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 Mg
2+ 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 pH
⩾
7. |
|---|---|
| ISSN: | 0016-7037 1872-9533 0016-7037 |
| DOI: | 10.1016/j.gca.2007.04.015 |