October – December 2009
347
P
e e r
R
e v i e w e d
or in partnership with CPAM was not able
to produce a limiting effect even after 40
recycle operations.
Interaction mechanism of nano-
sized TiO
2
with DCS
The nanosized TiO
2
colloidal particles,
which possess positive surface charges
and plenty of surface hydroxyl groups,
can interact with electronegative DCS.
When the nanosized particles are added
into pulp suspension, they absorbed
strongly on DCS to form complexes,
which gradually grow to generate floccu-
lation. This process was confirmed by the
autotitration of nanosized TiO
2
colloidal
solution to DCS solution. As shown in
Figure 3 (inset to upper left), at the initial
stage of titration, as the dosage of nano-
sized TiO
2
was increased to 26 % (W/W,
TiO
2
/DCS), the particle size in the system
showed a slight increase from 208 nm to
321 nm. With the dosage further increas-
ing from 26 % to 36 % (see the right hand
Fig. 3
Changes of mean size and zeta potential of parti-
cles in the titration system.
0
10
20
30
40
50
0
5
10 15 20 25 30
-10
-15
-20
-25
-30
-35
-40
-45
300
250
200
3500
3000
2500
2000
1500
1000
500
0
Dosage, %
Zeta P
, mV
D size, d.nm
Dosage, %
D size, d.nm
Fig. 1
COD of whitewater with increasing recycle count with various retention aids.
0
10
20
30
40
80
60
40
20
Blank
APAM
CPAM/Nano-Sio
AmS
1a
1b
2a
2b
Number of times recycled
COD
cr
, mg/L
0
10
20
30
40
80
60
40
20
Nano-Tio
2
Nano-Tio
2
/CPAM
Nano-Tio
2
/AmS
Nano-Tio
2
/APAM
Number of times recycled
COD
cr
, mg/L
Fig. 2
Changes of turbidity values of whitewater with increasing recycle count.
0
10
20
30
40
250
200
150
100
50
0
Blank
CPAM/Nano-Sio
2
APAM
AmS
Number of times recycled
T
urbidity
, NTU
0
10
20
30
40
250
200
150
100
50
0
Number of times recycled
T
urbidity
, NTU
Nano-Tio
2
Nano-Tio
2
/CPAM
Nano-Tio
2
/APAM
Nano-Tio
2
/AmS
Nano-Tio
2
/APAM
APAM
AmS
Nano-Tio
2
/AmS
Blank
Nano-Tio
2
Fig. 4
Influence of nanosized TiO
2
on dewatering time in
handsheet- making operation.
0
10
20
30
40
25
20
15
10
5
0
Number of times recycled
Dewatering Time, s