to the period of sensors verification, sharp drop of pH – CHCS saturation with carbon
dioxide, pH growth – CO
2
degassing, section after pH maximum presents total CaCO
3
crystallization, monotonous pH growth – final crystallization phase. The range of pH
change is 5.3 ÷ 8.4.
The reproduction of the experiments within the series is demonstrated in Fig. 3
where pCa data for the series of five experiments are shown. We can see the
satisfactory data agreement dispersion of which within (5–10 %) may be noticed only
at the final phase of crystallization. A thick curve in Fig. 3 is the averaging by the series
of five runs. CaCl
2
solution was injected into the measuring cell starting from 50
th
run
as we can see in Fig. 3. During 55 - 70 runs there is a specific area (of 7 min duration)
on the kinetic calcium curve where Ca
2+
ions active concentration grows. This growth
is associated with CaHCO
3
+
complexes dissociation caused by CO
2
degassing. The
sum of calcium ions and calcium ion complexes concentrations remains stable since
for this time period solid CaCO
3
formation is still not available.
The comparison of experimental data and
Ca
2+
active concentration calculations within
quasiequilibrium approximation by the formula
(10) without crystallization is shown in Fig. 4
and 5. We can see that the calculated
concentration
differs
essentially
from
measurements data.
In particular, in Fig.4 experimental Ca
2+
concentration demonstrates the growth till
measurement i = 70 and quasiequilibrium
calculation gives gradual fall without initial
growth. It indicates that the process of calcium
ions concentration change caused by carbon
dioxide removal from CHCS is essentially non
equilibrium and the use of equilibrium relations
(10) for concentration calculations results in the difference between the calculated and
experimental Ca
2+
concentration being larger than 25%. Relative difference between
measured and calculated by (12) data is shown in fig 6.
From Fig. 5, curve 2 and Fig. 6 we can see that calculations by the formula (12)
for the period of 22÷54 min. (50÷120 measurements) differ from measured values and,
moreover, Ca
2+
has not got physical meanings (current calculated concentration is
larger than initial calcium concentration of 5 mol/dm
3
). Only starting from i = 120 (time
moment 54 min) the calculated values approach to the measured ones and actually
agree at the final stage of crystallization for i > 220 (99 min. from the measurements
start).
Figure 4. Comparison of calcium
concentrations mol/dm
3
experimental,
curve 1 and calculated by (10) data,
curve 2 with no CaCO
3
crystallization.
There is the number of measurement on
the horizontal axle. Interval between
measurements – 27s.
1
2
і
[Ca
2+
]
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