To ensure the controlled crystallization the reaction environment (NaHCO
3
solution, prepared on the distillate of 2÷3 mkSm/Cm conductivity) in the measuring
cell 14 was previously saturated with carbon dioxide from the vessel 17 to stable sensor
CO
2
values, thus creating CHCS. Crystallization was initiated by CO
2
removal from
CHCS with the help of air blowing using compressor 16 that was attached to the cell
through gas rotameter 18, air dispersion was ensured by checker 13. The crystallization
process was controlled by ion selective electrodes 1…8. Temperature in the cell was
maintained within (25±0.1)°C by thermostat 20 due to heat-transfer agent in water
jacket 15 of the cell 14. Homogenization of mother solution was ensured by propeller
mixer 12 with electric engine 10. After temperature stabilization and sensor verification
according to procedure [11] the parameters of the initial state (temperature pCa, pCO
2
,
pH, electric conductivity and light permeability) were written down. The initial section
of the curve corresponds to this in Fig. 2.
Then CO
2
degassing was carried out in automatic regime with the sensors data
fixed period of ∆t = 27s ( i = 51 – 300).
Every experiment did not run more that 180 min. For each CHCS composition
five series of experiments were carried out, the results were averaged. CO
2
degassing
from the saturated system "CaCl
2
+ NaHCO
3
+ CO
2
+ HOH" lead to pH growth and
respectively HCO
3
-
and CO
3
2-
ions concentration and total CaCO
3
crystallization
having been fixed by sensors in the real time regime. The results of investigations of
solutions with NaHCO
3
≈ 10 mol/dm
3
, CaCl
2
≈ 5 mol/dm
3
concentrations averaged for
the series of five experiments are shown in Fig. 2 – 7.
Results discussion. All stages of the dynamic process realized according to the
given procedure are shown in Fig. 2 on the example of pH changes plotting. One cycle
of measurements lasts for 135 min. The initial horizontal section in Fig. 2 corresponds
рН
9
8
7
6
5
25
50
75
100
125
0
time, min
.
Figure 2. Recording of pH data changes at
CaCO
3
crystallization from simulated
solution at AQWA complex. Horizontal
section in the left hand side of the curve –
initial state of the solution.
Figure 3. Kinetic curves of Ca
2+
ion
concentration activity mol/dm
3
. Degas-sing
was made from the measurement i = 50.
Specific feature of Ca
2+
ion activity behavior
is the growth for i = 55 ÷ 70.
CaCO
3
total
formation starts for i >70.
(Ca
2+
)
measurement number i
- 1375 -