Chemistry Reference
In-Depth Information
Table 11.5
Kinetic data for A and B in Equation 11.7 of the reduction of Ni(II) by
rongalite for different concentration ratios of rongalite/Ni(II)
c
ratio
A 10
2
B 10
2
K
mol l
-
1
298 K
313 K
333 K
353 K
298 K
313 K
333 K
353 K
298 K
313 K
333 K
353 K
1.5/0.1
-
0.41
-
6.65
-
9.34
-
10.4
8.79
2.85
2.17
2.25
0.999
0.997
0.998
0.998
1.5/0.3
-
3.34
-
6.61
-
8.91
-
13.1
3.19
5.80
3.66
3.00
0.996
0.999
0.999
0.998
1.5/0.5
-
5.42
-
9.00
-
11.7
-
13.6
5.95
3.14
3.51
3.76
0.998
0.999
0.999
0.999
1.5/0.7
-
3.24
-
5.13
-
11.0
-
13.5
4.69
4.20
3.62
2.27
0.995
0.999
0.999
0.999
0.5/0.5
-
0.87
-
1.01
-
2.45
-
4.03
3.85
3.22
6.35
5.86
0.994
0.999
0.999
0.999
0.7/0.5
-
1.40
-
1.81
-
4.22
-
8.06
8.50
5.12
2.82
6.80
0.999
0.999
0.999
0.999
1.0/0.5
-
4.36
-
4.83
-
5.98
-
8.45
2.45
2.98
4.08
8.52
0.995
0.999
0.999
0.999
much formaldehyde. The reaction rate for the reduction of Ni(II) by ron-
galite can be correlated with the following equation:
B
t
c
=+
A
[11.7]
0
1
+
B
t
where
c
and
c
0
are the actual and initial Ni(II) concentrations in solution,
respectively, t is the time (s), and A and B are constants. From the data
obtained in this set of experiments, A and B can be calculated with good
correlation coefficients for the first 20 min of the reaction. At longer reac-
tion times, the equation no longer expresses the kinetics owing to inhibit-
ing influences of formaldehyde. Table 11.5 shows the results of A and B for
different rongalite/Ni(II) concentration ratios. Differentiation of Equation
11.7 allows information about the reaction rate itself to be obtained:
d
d
c
t
AB
B
-=
-
[11.8]
2
(
)
1
t
This equation was used to calculate the reaction rates as a function of tem-
perature and rongalite/Ni(II) concentration ratio, and Table 11.6 shows the
results for a ratio of 1.5/0.5. The data in this table confirm the previous con-
clusion that a temperature of about 333 K should be used in order to have
an economical and technologically acceptable reaction rate for the reduc-
tion of Ni(II) by rongalite and to avoid the large influence of auto-
inhibition by formaldehyde, an unfavourable effect that increases with
temperature.
11.3.4 Ni(II) reduction by rongalite in presence of PAN fibre
During the production of cation-containing PAN fibres, it was found that
absorption of Ni(II) in the fibre structure and adsorption at the surface of
the fibre through formation of complexes with cyanide and carboxylic acid
