the dependence of which upon the measurement number is shown in Fig. 8.
It follows from Fig. 8 that equilibrium in [X
1
, X
2
, X
3
, X
4
] subsystem comes after
125 run or 11 minutes after total crystallization start
that is close to data of Fig. 5-7.
Within the time (i= 5 ÷ 100) where intensive
CO
2
degassing and reactions take place during less
than 11 min. quasiequilibrium approximation is
not valid.
This approximation in our experiments gives
satisfactory results starting from 125 run for
reactions (7) and for CaCO
3
crystallization it
becomes practically accurate for i > 200. Thus,
quasiequilibrium approximation (reactions 7 are
considered equilibrium) is true only for the
processes taking place during characteristic time t >
11 min. For such processes non equilibrium does not depend on the availability of
crystallization. As we can see from Fig. 5 – 8 the use of expression (10) for CHCS
parameters calculations in the equilibrium area may give unreal values of parameters
or more than 50 % deviations of calculated values from measured ones see Fig. 6.
Formulation of dynamic models of СаСО
3
formation. The process of solid
phase formation from oversaturated solutions may be presented in the following
simplified way:
-
crystal nuclei formation (CN);
-
substance transport to crystal nuclei surface;
-
material editing into the crystal
nuclei structure.
The solid phase formation is described by different model equations depending
on the limiting mechanism.
With no surface being the crystallization prime the crystal nuclei formation is
limited by oversaturation that is sufficient for their fluctuation formation; with large
oversaturation and ready surface the crystal nuclei growth is limited by the process of
material editing into the crystal structure (surface process). With mean or small
oversaturation and the existing crystal nuclei the process of diffusion transportation of
the substance to the crystal nuclei surface [2] is the limiting one.
Formally, the equation (5) based on the second equation (2) responds to the task
to formulate kinetic equation regarding CaCO
3
formation. It expresses the rate of
calcium ions concentration change through the CHCS parameters: HCO
3
-
, CO
3
2-
and
CO
2
.
Figure 8. Dependence of G
123
factor of
mutual equilibrium regarding the reac-
tions (7) upon the number of mea-
surement i.
G
123
i
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