Effect and Behavior of Liquid Additive Molecules in Dry Ultrafine Grinding of Limestone

Effect and Behavior of Liquid Additive Molecules in
Dry Ultrafine Grinding of Limestone†
M. Hasegawa1, M. Kimata and M. Yaguchi
Department of Chemistry and Chemical Engineering
Yamagata University*
Abstract
?The effect of liquid additives such as alcohol and glycol on the ultrafine grinding of limestone was
investigated by using a vibration rod mill. Liquid additives used in the present work were three alco-
hols and two glycols with different alkyl groups. The experiments were carried out by a batch opera-
tion, and the change in specific surface area of limestone with grinding time was measured by BET
adsorption method. The behavior of methanol molecules added as an additive was traced by monitor-
ing the temperature and pressure in the grinding pot during grinding. The results showed that alco-
hols and glycols promote the ultrafine grinding of limestone, and that the maximum specific surface
area of limestone obtained with additives is proportional to the amount of the additive. The stepwise
addition of a small amount of additive was more effective rather than adding the whole amount at
once in increasing the grinding rate of limestone. It was also found that the degradation of crystal
structure of limestone was controlled by the addition of alcohol. The grinding status of limestone
could be traced by monitoring the temperature in the grinding pot, and the measurement of pressure
change in grinding pot revealed that the additive molecules are chemisorbed on fresh surface of lime-
stone created by the grinding.
Keywords: Grinding Aid, Limestone, Ultrafine Grinding, Alcohol, Pressure Change, Temperature Change
vation. Although the greatest problem in the use of
1. Intoroduction
grinding aids is contamination of product ground
?It is known that grinding is one of unit operations
by additives, it can be solved through selecting or
with the lowest energy efficiency. Grinding aids
designing an appropriate additive that has no detri-
which can improve the efficiency of the grinding re-
mental effect on downstream processing or the final
markably with a small amount addition should more
product.
positively be applied to the grinding operations, es-
?In the cement industry, grinding aids have been
pecially to dry ultrafine grinding with higher energy
studied and used practically for a long time. However,
consumption, from the viewpoint of energy conser-
grinding aids have scarcely been utilized in fields
other than the cement industry, because of the unde-
sirable contamination of the product and the lack of
instruction in application of grinding aids. In most of
† This report was originally printed in J. Soc Powder Tech-
the studies on grinding aids, the effects of grinding
nology, Japan, 42, 178-184 (2005) in Japanese, before
being translated into English by KONA Editorial Com-
aids have been discussed to get the fine powders of
mittee with the permission of the editorial committee of
micron sizes, but there are only a few reports1, 2) as to
the Soc. Powder Technology, Japan
ultrafine powders with submicron size.
* 4-3-16, Jonan, Yonezawa 992-8510, Japan
1
?In our laboratory, the effects of various liquid ad-
Corresponding author
ditives on dry ultrafine grinding of some minerals,
TEL&FAX: +81-238-26-3162
E-mail: mhase@yz.yamagata-u.ac.jp
such as feldspar3), quartz4) and alumina5), have been
KONA No.24 (2006)
213

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investigated to apply grinding aids to dry ultrafine
of grinding and stepwise addition of a small amount
grinding process. In this paper, the same experi-
(1ml) every one hour. All the experiments were con-
ments on limestone were successively carried out to
ducted in a batchwise closed system for a required
accumulate the data of additive effects and to investi-
time considering the volatilization of additives and
gate the addition methods of additives. Furthermore,
moisture in atmosphere.
the measurements of the temperature and pressure
?A solid sample used in this work was limestone
in grinding pot were also attempted to elucidate the
from Okayama and its density was 2.70×103 kg/
behavior of limestone powder and additive molecules
m3. The sample was crushed previously with a jaw
in grinding pot during grinding.
crusher and a stamp mill, and then was prepared to
particle size below 200mesh (74?m). The specific
2. EXPERIMENTAL
surface area of the limestone sample before grinding
was 9.89×102 m2/kg. Three kinds of alcohols and
?A grinding apparatus and grinding conditions were
two kinds of glycols were used as liquid additives,
the same as used in the previous paper5). The appa-
as shown in Table 1. These additives were special
ratus was a vibration rod mill with two grinding pots
grade reagents (Kanto Chem. Co., Inc.) and used
with an internal volume of about 1.0 liter. Grinding
without further purification.
media loaded in the pot were rods with dimensions
?After grinding for a required time, the specific
of 11×11 mm in diameter and length. Both the pots
surface area of the ground products sampled by cone
and the rods were made of silicon nitride for the
and quartering was measured by the BET adsorption
importance of wear-resistance. A desired amount
method (Micromeritics Co., Flowsorb II). The tem-
of solid sample (weight 89.4g, fractional sample fill-
perature degassing before the measurement was 200
ing 0.11) were charged to the pot filled with rods
?.
(weight 1371g, fractional rod filling 0.8). The addition
?The temperature in grinding pot, as shown in
methods of additives were carried out by two ways,
Fig. 1, was measured by setting a thermocouple,
a collective addition of the whole amount at the start
which did not touch the grinding pot wall and rods,
Table 1?Liquid additives used
additives
Molecular
Molecular Boiling
formula
weight
point[K]
Methanol
CH3OH
32.0
337.8
Ethnol
C2H3OH
46.1
351.5
1-Propanol
(CH3)2CHOH
60.1
370.2
Ethylene glycol HOCH2CH2OH
62.1
470.4
Propylene glycol CH3CH(OH)CH2OH
76.1
460.5
Thermocouple
Cold junction
Grinding pot
Membrane ?lter & Silicone rubber
O-Ring
Recorder
Pressure
sensor
6mm
15mm13mm
Receiver
Pot cover
(stainless steel)
O-Ring
Fig. 1? Measurement method of the pressure and temperature in grinding pot.
214
KONA No.24 (2006)

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through a silicone ling packed the grinding pot. To
time. However, at all addition amounts of additives
measure the gage pressure in grinding pot a small
the increasing rate of specific surface area gradu-
pressure sensor (Yokogawa M&C Co., FP-201) was
ally slowed down at long grinding time, and then the
also attached to center in the pot cover made of stain-
specific surface area maintained a constant value or
less steel. Data of temperature and pressure obtained
decreased. Although the maximum value of specific
were recorded to a industrial chart multi-recorder
surface area and the grinding time at the maximum
(Yokogawa Electric Co., ?R1000) and a pen recorder
value differed with the amount of additives, the both
(Yokogawa Electric Co., Type3066), respectively.
showed a tendency to increase with the amount of
additive. These agreed roughly with the results on
three organic oxides in previous papers3-5).
3. RESULTS AND DISCUSSION
?Fig. 4 shows the variations of the specific surface
3. 1 Effect of liquid additives as grinding aid
area of limestone as a function of grinding time at
?Figs. 2 and 3 show the variations of the specific
the different addition amounts of ethylene glycol.
surface area of limestone as a function of grinding
From Fig. 4, ethylene glycol was found to be one of
time at the various addition amounts (1?8ml) of
effective grinding aids as well as alcohols. We also
methanol and ethanol, respectively. Each plot in the
confirmed the effectiveness of grinding aid for pro-
figures is an independent experiment. The result
pylene glycol. At the addition amount of 8 ml the spe-
without an additive (0ml) is also shown in these
cific surface area after grinding for 72 h, which was
figures. The specific surface area without an addi-
not shown in Fig. 4, was almost equal to that at the
tive was at most about 8.5 times as large as the area
grinding time of 48 h. Consequently, the maximum
before grinding over the grinding time from 4-8 h,
value of specific surface area with ethylene glycol
and hardly increased with subsequent grinding and
was estimated to reach at the grinding time between
inversely decreased. On the other hand, the results
48 h and 72 h, which was the same as that with alco-
with alcohol additives indicated that both two al-
hol additives. The horizontal solid lines at the specific
cohols were effective as grinding aids and that the
surface area of 11000 m2/kg in Figs. 2, 3 and 4 were
specific surface areas increased with an increase in
equivalent to the specific surface area diameter of
the addition amount of alcohol at the same grinding
around 0.2 ?m assuming ground limestone particles
5 ×104
4 ×104
Methanol
4
3
8 ml
8 ml
/kg]2
/kg]2
3
2
5 ml
5 ml
2
3 ml
Speci?c surface area [m
Speci?c surface area [m
1
1
1 ml
1 ml
0 ml
0 ml
Ethanol
0
0
0
20
40
60
80
100
0
20
40
60
80
100
Grinding time [h]
Grinding time [h]
Fig. 2? Variations of specific surface area of limestone as a function of
Fig. 3? Variations of specific surface area of limestone as a function of
grinding time with the addition amount of methanol.
grinding time with the addition amount of ethanol.
KONA No.24 (2006)
215

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5 ×104
5 ×104
Ethylene glycol
4
4
8 ml
/kg]2
/kg]2
3
3
5 ml
2
2
3 ml
Speci?c surface area [m
1 ml
Methanol
1
Maximum speci?c surface area [m 1
Ethanol
1-Propanol
Ethylene glycol
0 ml
Propylene glycol
0
0
0
10
20
30
40
50
0
2
4
6
8
10
Grinding time [h]
Amount of additives [wt%]
Fig. 4? Variations of specific surface area of limestone as a function of
Fig. 5? Relationships between maximum specific surface area and the
grinding time with the addition amount of ethylene glycol.
amount of additives.
to be spheres. Thus, the ultrafine grinding of lime-
stepwise added a small amount of additives, 1ml, was
stone implied to be achieved sufficiently in this work.
attempted to investigate the effect of the addition
?Fig. 5 shows the relationships between the maxi-
methods of additives.
mum specific surface area and the weight percent-
?The results with methanol additive are shown in
age of amount of additives for limestone sample.
Fig. 6. The Data with stepwise and collective addi-
The results with propylene glycol are not contained
tion of methanol are represented by broken lines
in the figure because the specific surface area does
and solid lines, respectively. When the total amount
not reach clearly a maximum value. As can be seen
of additives was the same, the specific surface areas
from the figure, the maximum specific surface area
with stepwise addition were larger than that with col-
obtained with any additive was found to be linearly
lective addition at the grinding time longer than 4 h.
proportional to the amount of additives within the ex-
The results with ethanol additive showed also a simi-
perimental range in this work. The slope of lines dif-
lar tendency. It was found that the stepwise addition
fered with the kinds of additives and the slopes with
method could reach a certain value of the specific
alcohol additives were larger than that with glycol.
surface area with the shorter grinding time. The ef-
These tendencies were also in accord with results in
fect of stepwise addition is considered to be due to
the previous papers3-5).
the favorite dispersion state of additives in the initial
grinding stage. Therefore, it is suggested that the
3. 2 Effect of addition method of liquid addi-
addition method, which increases the amount of ad-
tives
ditives with the increasing the specific surface area,
?The effect of grinding aids is not only to increase
may be more advantageous.
the maximum specific surface area, but also to in-
?Fig. 7 shows the scanning electron micrographs
crease a grinding rate at the initial stage of grinding.
of limestone before and after grinding for 24h? (a)
From Figs. 2, 3 and 4, the initial grinding rate was
original before grinding; (b) after grinding without
found hardly to change with the different amount of
an additive; (c) after grinding with collective addition
additives. In general, a whole amount of grinding aids
of 3ml methanol; and (d) after grinding with stepwise
have been collectively added at the start of grind-
addition of 3ml methanol. For the product without an
ing, but in this work a novel addition method which
additive (b), a large amount of the agglomerates of
216
KONA No.24 (2006)

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×104
the fine powder ground were observed. On the other
4
hand, there were hardly agglomerates in the prod-
8 ml
ucts with methanol additive (c) and (d), and those
micrographs revealed the presence of limestone pow-
der with submicron size. Compared with the collec-
3
tive addition method, the stepwise addition method
was found to give the fineness and good dispersion of
/kg]2
5 ml
product ground.
2
3. 3 Ef fect of liquid additive on cr ystalline
3 ml
structure of product
?The crystalline structure of limestone ground
with collective addition of ethanol was examined by
Speci?c surface area [m
1 ml
means of a powder X-ray diffraction apparatus. Fig.
1
8 shows the variations of peak intensity ratio in (104)
lattice plane, which had the greatest diffraction in-
0 ml
tensity, with grinding time. The intensity ratio was
Methanol
taken as the value divided by the intensity before
0
grinding. The parameter in figure was the amount of
0
10
20
30
40
50
ethanol. In ordinary grinding operation, the crystal-
Grinding time [h]
linity of solid sample lowered and the peak intensity
Fig. 6? Effect of the addition method of methanol on specific surface
decreased as the grinding proceeded. From the Fig.
area of limestone.
8, the intensity ratios in all cases decreased with
grinding time, especially the intensity ratio without
an additive remarkably decreased at the grinding
time of 8h. After grinding for 8h, the specific surface
area without an additive must reach a maximum,
when the grinding in pot will be in equiliburium. On
(a) Limestone powder before grinding
(b) Product without additives
(c) Product with collectively addition of menthanol (3ml)
(d) Product with stepwise addition of menthanol (3ml)
Fig. 7? Electron scanning micrographs of limestone before and after grinding for 24 hours, (a) before grinding (b) after grinding without additives (c) with
collective addition of methanl (d) with stepwise addition of methanol.
KONA No.24 (2006)
217

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1.2
in the intensity ratio was inversely controlled. With
Ethanol
ethanol additive, the crystallinity of limestone de-
0 ml
graded to some extent when the specific surface area
]
1
1 ml
reached a maximum at the grinding time longer than
?
3 ml
5 ml
about 48h. This suggested that the grinding energy
8 ml
is dissipated to degrade the crystalline structure of
0.8
limestone when the grinding is in equiliburium or
negative grinding occurs.
0.6
3. 4 Variations of temperature and pressure in
grinding pot
?In vibrating ball mill, most of the mechanical ener-
0.4
gy given to grind a solid sample converts into a ther-
mal energy due to the collision and rubbing between
solid sample and grinding media, grinding media
Peak intensity ratio in (104) lattice planes [ 0.2
themselves, and pot wall and media6). Fig. 9 shows
the results of the temperature measurement in the
grinding pot when the different amount of ethanol
0 0
10
20
30
40
50
was collectively added. The variations of temperature
Grinding time [h]
were shown as the temperature difference with a
room temperature. Four photographs of (a) - (d) in
Fig. 8? Plots of peak intensity ratio in (104) lattice plane vs. grinding
time.
Fig. 9 were the inside state of the pot immediately
after grinding at each grinding condition. Without
ethanol additive, the temperature in the pot increased
the other hand, the decrease in intensity ratios with
rapidly with the grinding time from the start of grind-
ethanol additive was found to be smaller than that
ing and rose to about 39? at the grinding time of 5h,
without an additive at the grinding time longer than
which was about 18? in terms of the temperature
8h. Although the specific surface area with ethanol
difference with room temperature. The high temper-
additive was about twice that without an additive at
ature difference was kept on until grinding finished.
the grinding time of 24h because the addition of etha-
The specific surface area without ethanol reached a
nol promoted the grinding of limestone, the decrease
maximum at grinding time of 4h and then grinding
30
Ethanol
25
]
(a)
(b)
(c)
(d)
20
15
0 ml
8 ml
3 ml
10
Temperature di?erence [?
5
1 ml
5 ml
0 0
10
20
30
40
50
60
70
80
Grinding time [h]
Fig. 9?Variations of the temperature and status in grinding pot as a function of grinding time with different amount of ethanol.
218
KONA No.24 (2006)

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scarcely proceeded. Consequently, it is considered
the pot added methanol, which was set in a constant
that a rise of temperature in pot is attributed to the
temperature tank, and confirmed the validity of a
grinding equilibrium at the initial grinding stage. In
trial pot cover prior to grinding experiments. As the
the photograph (a) without ethanol after 16h, in fact,
temperature in pot increased after the start of grind-
the thick coating layer of limestone powder was ob-
ing, as can be seen in the figure, the pressure with
served on the pot inside wall and grinding media.
each amount of methanol also increased rapidly be-
?On the other hand, it was found that the tempera-
cause the vapor pressure of methanol increased. At
ture difference at the various amount of ethanol was
the addition amount of 1ml the specific surface area
remarkably lower than that without an additive. The
reached a maximum at the grinding time of about 8h.
specific surface area at the addition amount of 1ml
The temperature increased also up to the grinding
and 3ml reached a maximum at the grinding time of
time of 8h, but the pressure rapidly decreased after
16h and 48h, respectively, and the temperature differ-
grinding for about 2h. Although the pressure in pot
ences gradually increased with grinding time since
without grinding increases in proportional to the tem-
then. Although at the addition amount of 8ml the
perature rise, the reduction of pressure with grind-
specific surface area hardly increased at the grinding
ing can be explained by the adsorption of methanol
time longer than 48h, a negative grinding phenom-
molecules on the fresh surface of limestone created
enon did not appear clearly and the coating layer
by the grinding. In the case of 1ml addition, the pres-
of limestone powder on the pot wall and grinding
sure in pot became lower than atmospheric pressure
media could not confirm also, as can be seen from
at the grinding time longer than 8h and then showed
Fig. 9 (d). It is obvious that the ethanol addition
a constant pressure regardless of some variations
contributed to keeping the dispersibility of limestone
of the temperature. This indicates that methanol
powder and controlled the agglomerate of powder
molecules adsorbed on limestone powder surface do
themselves and the adhesion of powder to pot wall.
not desorb, that is, methanol molecules chemisorb
Thus, the variation of temperature in pot was found
evidently. In the experiment at the addition amount of
to reflect adequately the grinding state in pot during
1ml, in fact, the pot cover could not be opened easily
grinding.
due to the lower of pressure in pot after grinding.
?Fig. 10 shows measurement results on the tem-
?The maximum specific surface area at the addition
perature (broken line) and pressure (solid line) in
amount of 3ml reached at the grinding time of 24h.
the grinding pot with the collective addition of etha-
Then, the temperature in pot was relatively stable
nol 1ml and 3ml. The abscissa of the figure is the
around 15? , but the pressure in pot was gradually
grinding time, and left and right ordinates show the
decreased and kept at a constant pressure at the
gage pressure and temperature in pot, respectively.
grinding time longer than 40h. In the case at the ad-
We traced the temperature and pressure change in
dition amount of 5ml and 8ml, whose data were not
20
30
25
15
Methanol
]
1 ml
20
10
15
5
3 ml
Pressure in pot [kPa]
10
Temperature in pot [?
1 ml
0
5
?5
0
0
10
20
30
40
50
60
Grinding time [h]
Fig. 10?Variations of the temperature and pressure in grinding pot as a function of grinding time with the addition of methanol.
KONA No.24 (2006)
219

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shown here, the greater amount of methanol, the
4) The degradation of crystalline structure of lime-
higher initial pressure in pot. The change of pres-
stone can be controlled by the addition of liquid addi-
sure, however, was found to maintain a constant
tives.
if there was no change of temperature in pot. The
5) The grinding status can be estimated by moni-
methanol molecules, therefore, will evaporate by the
toring the changes of temperature and pressure in
corresponding amount to the quantity of molecules
grinding pot during grinding.
adsorbed on powder. The results with ethanol ad-
6) The additive molecules are chemisorbed on the
ditive showed also a similar tendency to those with
fresh surface of limestone created by the grinding.
methanol additive.
References
4. CONCLUSION
1) Pol manns, J., G.J.Pol mans, H.Hoberg and F.U.Schneider:
?The dry ultrafine grinding of limestone was carried
“Ultrafine Grinding with Solid Additives”, Proceeding
out with the liquid additives, three alcohols and two
of XVIII International Mineral Processing Congress,
glycols, and the influence of the amount and addition
pp. 219-226, Sydney (1993).
method of additives on the grinding effect was inves-
2) Ohsawa, T., S.Yasue, A.Suganuma and T.Hamada:
Preprint of 33rd Autumn meeting of the Soc. of Chem.
tigated by using a vibration rod mill. The temperature
Eng., Japan, pp. 205, Yonezawa (1998).
and pressure in grinding pot was also measured to
3) Hasegawa, M.and Y.Kanda?“The Effect of Alcohol
elucidate the behavior of solid sample and additive
Grinding Aids on Ultrafine Grinding of Feldspar”,
molecules. The results obtained are as follows:
J.Soc. Powder Technol., Japan, 30, 570-575 (1993).
1) All additives used are satisfactorily effective as
4) Hasegawa, M., M.Kimata, M.Shimane, T.Shoji and
grinding aids, and the ultrafine grinding of limestone
M.Tsuruta: “The Effect of Liquid Additives on Dry
is easily achieved by means of additives.
Ultrafine Grinding of Quartz”, Powder Technol., 114,
145-151 (2001).
2) The maximum specific surface area with additives
5) Hasegawa, M., M.Kimata and T.Shoji: “The Effect of
is proportional to the amount of the additive within
Liquid Additives and Behavior of Alumina Powder in
the experimental range in this work.
Ultrafine Grinding of Alumina”, J.Soc. Powder Technol.
3) To increase the initial grinding rate, the stepwise
Japan, 39, 736-742 (2002).
addition method of a small amount of additive is
6) Arai, Y.: “Huntai no Zairyo Kagaku”, p. 84, Baifukan
more effective rather than adding the whole amount
(1987).
at once at the start of grinding.
Author’s short biography
Masahiro Hasegawa
Dr. Masahiro Hasegawa is Professor of the Department of Chemistry and Chemi-
cal Engineering at Yamagata University. He received his PhD from Tohoku Uni-
versity in 1987. His research interests are in the field of fine particle productions
by breaking down and building up processes, and included the design of grinding
aids, mechanochemical reaction, functional composite particles, photocatalytic par-
ticles with magnetism.
220
KONA No.24 (2006)

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Author’s short biography
Mitsumasa Kimata
Dr. Mitsumasa Kimata is an Associate Professor in the Department of Chemistry
and Chemical Engineering at Yamagata University. He received his PhD in Ma-
terials Science and Energy Engineering and MS in Chemical Engineering from
Yamagata University in 1997 and 1991, respectively. He has served as a researcher
or a Research Associate at Ube-Nitto Kasei Co., Kanagawa Institute of Technology,
the University of Birmingham, and Yamagata University. In 2006 he became an As-
sociate Professor at Yamagata University. His research interests are monodisperse
nanoparticles, sol-gel method, photocatalyst, surface potential, powder property,
mechanochemical reaction, and ultrafine grinding.
Masakazu Yaguchi
Masakazu Yaguchi received his Batchelor degree on Chemistry and Chemical En-
gineering and Masters degree in Materials Science and Engineering from Yamaga-
ta University in 2000 and 2002, respectively. He currently works on Engineering
Department at Taiheiyo Cement Corporation.
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