the change of carbonate sum may take place only due to CO
2
exchange with
environment (atmosphere), i.e.
0
X
X
3
1
+
,
)
X
(X
a
X
X
2e
_
2
2
dg
2
2
−
=
=
, consequently X
8
≈ Const, (18)
This pH range is interesting from the viewpoint of investigation of solid
carbonates dissolution peculiarities if they are available in water systems.
Ca
2+
dynamics within the range of 6.5 < pH < 8.5. Within the range of 6.5 < pH
< 8.5 we can consider that X
3
<< X
1
+ X
2
, therefore, the change of Ca
2+
ions
concentration takes place due to the change of HCO
3
-
, CO
2
concentration and gas
exchange of carbon dioxide with atmosphere
)
X
(X
a
X
X
X
2e
_
2
2
2
1
8
+
+
=
,
(5a)
For pH close to neutral Ca
2+
concentration change and, consequently, CaCO
3
crystallization takes place due to Ca
2+
ions interaction with HCO
3
-
ions with the
simultaneous CO
2
emission. Such process may be described by the scheme [1,5],
.
CO
HOH
H
HCO
,
H
CaCO
HCO
Ca
2
3
3
3
2
+
+
+
+
+
−
+
−
+
(19)
Since solid CaCO
3
formation within this range is controlled by the interaction of
calcium and bicarbonates ions and CO
2
degassing we can call the process that
corresponds to the equations (19) as bicarbonate crystallization regime.
If CO
2
removal is difficult (closed system, a
2
= 0) the situation may be realized
when
0
X
X
X
2
1
8
+
=
,
(20)
in this case the rate of Ca
2+
concentration change is determined by intrasystem
transformations in CHCS.
Ca
2+
dynamics for pH > 10. For pH > 10 in the right hand side of (5) only item
remains essential that is referred to the carbonate ion concentration change and the
expression (5) is reduced to
X
)
X
(X
a
X
X
3
2e
_
2
2
3
8
+
=
,
(21)
In this case the reaction of CaCO
3
formation runs by the standard scheme
+
−
+
3
2
3
2
CaCO
CO
Ca
,
(22)
Integrating (21) within t
0
to t
1
for the case a
2
= 0, we obtain
)
t
(
X
)
t
(
X
)
t
(
X
)
t
(
X
3
o
3
o
8
8
+
−
=
,
(23)
It follows from (23) that depending on the initial values of X
3
(t
0
) and X
8
(t
0
) the
expense of X
8
runs to the end when X
3
(t
0
) > X
8
(t
0
) or stops at the level
)
(t
X
)
(t
X
X
o
3
o
8
8
−
=
, when
)
t
(
X
o
8
>
)
t
(
X
o
3
,
(24)
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