Geoscience Reference
In-Depth Information
(a)
(b)
10
0.5
0.4
0.3
5
: 15 MPa
: 30 MPa
: 45 MPa
: 60 MPa
0.2
0.1
0
100
150
200
100
150 200 250
Temperature (
°
C)
Temperature (
°
C)
(c)
0.05
0.04
0.03
0.02
0.01
0
100
150 200 250
Temperature (
°
C)
Figure 5.47 Solubility curves for calcite in different solvents: (a) in 1 M NH
4
NO
3
solution as a funciton of temperture under varying pressures; (b) in 1 M NH
4
NO
3
and
(c) in 3 M NH
4
NO
3
[183]
.
decreased with the increase in temperature, and it reached 6.0 at 200
C. This result
suggested that H
2
CO
3
was the main dissolved species in the solution at 250
C. When
calcite dissolves in water, the carbonate ion must change its ionic form to HCO
3
;
which is very essential for the crystal growth of calcite, whereas H
2
CO
3
does not con-
tribute to the growth of calcite crystals. The formation of the ionic species HCO
3
has
been noticed by several workers like Kikuta and Hirano
[186]
in the NH
4
NO
3
solu-
tions from FT-IR studies. This suggests that calcite dissolves in the solvent below
200
C as follows:
Ca
2
1
1
HCO
3
2
1
NO
3
2
1
NH
4
1
1
NH
4
NO
3
1
CaCO
3
1
H
2
O
!
OH
HCO
3
2
1
2NH
4
1
1
OH
2
2NH
4
F
CaCO
3
1
H
2
O
!
CaF
2
1
1
HCO
3
2
1
2NH
4
1
1
OH
2
ð
NH
4
Þ
2
SO
4
1
CaCO
3
1
H
2
O
!
CaSO
4
1
