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Physical and chemical changes of sulphides during intensive grinding in organic liquids
POWDER 11ECHNOLO ELSEVIER
Powder Technology 98 ( 1998 ) 74-78
Physical and chemical changes of sulphides during intensive grinding in organic liquids P. Bai~,~ *, A. Mockov~iakovfi, E. Boldi~.firov~, J. Ficeriov~ Institute qf Geotechnics qf SAS. Watstmm'a 45. 043 53 Ko,~ice, Sha'ak Republic Received 6 June 1997: received in revised form 14 October 1997; accepted 2 December 1997
Abstract The properties of different sulphides (chalcopyrite--CuFeS,, pyrite--FeS,, galena--PbS, tetrahedrite--Cu~.,Sb4S~.~, stibnite--Sb.,S~) which were ground in a planetary mill in polar alcohols containing I-5 carbon atoms ( methanol, ethanol, n-butanol,/-butanol, n-propanol, ipropanol and i-amyl alcohol) were studied, it was found that the maximal increase of specific surface area can be achieved by milling in organic liquids with high/,t/V values (p,, dipole moment; 1/, molecular volume). A high degree of sulphide structure disordering can be achieved if organic liquids with a higher molecular density are employed. The results of the increase in specilic surface and structured disordering were related to the Vicker's hardness of the investigated sulphides. © 1998 Elsevier Science S.A. All rights reserved. Kev=~onls: Grinding: Sulphide: Alcohol: Surface area; Amorphization
I. Introduction The process of grinding is an area of constant interest in mineral processing research. One o1" the processes investigated here is the grinding environment and it was found that grinding in a liquid was more effective for new surl'ace formation than dry grinding [ I i . In the case of grinding i~a water, chemical reactions between broken surface bonds and water molecules occur [21. A reduction in hardness was discovered in the case of such minerals as oxides, silicates and carbonates. A more detailed study of the effect of the quality of wet grinding environment on the properties of minerals has been given by Rehbinder 131. He used such liquids as inorganic salt solutions ( NaCI, NaOH, NaaCO~and AICL ) and organic l~flar compounds. In the latter case, it was found that the hardness ot'the ground substancesdecreased with an increase in the number of carbon atoms in the molecules of organic compounds. Grinding in organic liquids is often more effective than in water [ 1,4,5 I. It is assumed that during grinding in this environment a slowing down o1" the formation of agglomerates and enhanced material flow occurs and as a result, improved grinding is achieved, lkazaki et al. [6,'7] studied the interaction between the ground material and organic liquids and * Corresponding author.
0032-5910/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. Pli S 0 0 3 2 - 5 9 1 0 ( 98 ) 0 0 0 3 8 - 2
introduced the term "chemically-assisted comminution', meaning that particles which are to be ground are made fragile or more easily broken by chemical interaction of the particles ill the grinding environment. For mills that transfer a lot of energy to the ground material (such as vibratory and planetary mills, attrition mills, etc.), the grinding liquid plays an important role. In these cases the material is not only comminuted and its specific surface increased, but its structure is also disordered [ 8 ]. Tanaka [ 9 ] and later Chodakov [ 10] described the process of ~cw surfiice formation by the following equation:
S=S,,,.,,(I-e t.,)
(I)
where S is specific surface area in time t. S,,,,,, the maximum surface area and k, a rate of new surface formation. The aim of this paper is to study the formation of new surfaces and the structure disordering in a series of sulphides (chalkopyrite. pyrite, galena, tetrahedrite and stibnite) that were subjected to intensive milling in different organic liquids (alcohols with one to five carbon atoms in their molecules) in a planetary mill.
2. Experimental The investigations were carded out with minerals of SIovak provenance (chaicopyrite--CuFeS2, pyritemFeS2,
P. Bah't3et al. /Powder Technology 98 (1998) 74-78
75
Table I Mineral deposits and chemicalcomposition Mineral
Deposit
chalcopyriteCuFeS, pyrite FeS_, galena PbS tetrahedrite CuI_,Sb4S.~ stibnite Sb_,S,
Slovinky Smoln& BanskfiStiavnica Rudfiany Rud~any
Chemicalcomposition ( '/~ ) Cu
Fe
S
As
31.55 0.02
31.44 42.81
32.54 49.6
0.20 33.40
0.7 ! 4.42
13.74 30.74
0.01
0.04
26.60
Hg
Zn
Sh
Ph
0.03
2. I0
5.02
2.3 ! 0.80
78.41 20.24 62.35
0.33
Sit'),
Insoluble remains
4. I I 6.52
0.24 0.3 I
2.73 2.83
1.56 0.43
I0.12
0.50
2.3. X-ray diffraction
g a l e n a ~ P b S , tetrahedrite~Cu~_,Sb4Sj~, stibnite~SbeS~). The chemical cornposition as well as the deposit is given in Table I.
The quantitative investigation of disordering of the sampies by intensive 3rinding was performed on a DRON 2.0 diffractorneter with GUR-5 goniometer (Techsnabexport, Russia) under the following conditions: Fe K a radiation. 24 kV. 10 mA and ! ° r a i n ~ goniometer rate. The extent of disordering of mineral structure was characterized by the content of the X-ray amorphous phase (amoq~hization) A which was calculated by means of the formula I I I I:
2. !. hm,nsive grinding Intensive grinding was carried out in a phmetary mill ( Pulverisette 4, Fritsch, Germany) under the following conditions: the mill was loaded with 25 balls of 10 mm diameter and five balls of 25 mm diameter; relative acceleration of the mill = 10.3: material of milling chamber and balls, tungsten carbide: size of the feed. 200 i.tm: mill charge weight, 20 g: grinding time. 10 min: grinding media: methanol, ethanol, npropanol, i-propanol, butanol./-butanol and i-amyl alcohol. The properties of the liquids used as grinding media are given in Table 2.
A =( I -U,,i,/I,,U, )X 100.
(2)
where U,,, U,. !,, and !, are the background of the reference sample, background of the ground sample, integral intensity of the reference sample and integral intensity of the ground sample, respectively.
3. R e s u l t s a n d d i s c u s s i o n
2.2. Sud'ace area
3. I. Changes of the surface during intensive grimling o.I stdphi&'.~ in ol:t,,anic liquids
The specilic surl~ce area S was determined by the low temperature nitrogen adsorption method in a Gemini 2360 sorption apparatus (Micromeritics. USA). The following temperatures were used for sample pretreatnlent before specific surface area measurements: methanol, 70°C: ethanol. 80°C: propanol, 105°C: i-propanol. 105°C: butanol, 105°C: /-butanol. 150°C; i-amyl alcohol, 150°C. The heating time was 60 rain for all samples.
3. !. !. The fimnathm ol'm,w smfaces and dependence on the magnitu&: q/'the law valm' fi,r the d~l/ferent ah'ohoi 137u,.~ (C~ to C s) A series of sulphides (Table I) were ground in organic liquid media trader the conditions given in Section 2. After filtration and drying, the specitic surface S was measured on
Table 2 Pmperliesof liquids used as grindingmedium Liquid
Molecular I'ormul:l
Molecular weight M
Molecular density p (kgm ~1
Molecular volume
l'=M/p ( Ill' kg
Methanol Ethanol Propanol i-Propanol Butanol /-Butanol i-Amylalcohol
CH ~OH CzHsOI-! C ~HTOH C ~HTOH C4H.,OH C.IH,,OH C~HIIOH
32.04 46.07
60. I0 60. i ,~ 74.12 74.12 88.15
792 789.2 804.4 785.5 810 81)5 881)
'
)
Dipole moment At x I11 "'
#/Vx Itl '" ((" kg m ')
( (" m I
0.04045 0.05838 0.07471
5.64 5.67 5.47
13.04 97 I 7.32
0.07651 0.09151 0.092{18 0.1(102
5.27 5.54 5.44 5.54
6.80 h.I)5 5.ql 5.53
P. Bahi~et al. /PowderTe¢'hnoiogy98 (1998) 74-78
76
¢,q I
I
I
I
I
'~ 1.2
S
FeSz
0.8 x .O
i
I
%
I
I
t
0.t,-
I
2
0
Sb2S3 2
3
t,
5
IogVHN
(MPa)
Fig. 2. Variation of the parameter Ii ( Eq. ( 3 }} with the value of Vicker's microhardness VHN ( after Ref. 1141 }. 3
4
'
' 8
'
"
12
'
-
16
I Ckg,m"~) Fig. I. Variationof .~pecilicsurl'ac¢area .5'with #/V values. Grinding time: I0 min. +u. V ' I x 10"z9
the selected samples. The resulting values were plotted against/z/V (Fig. I ), where p, is the dipole moment and V is the molecular volume. This ratio has been calculated for the individual organic liquids and the results are given in Table 2. From these data it follows that they can be described by an empirical linear function:
S=a+h(mlV),
(3)
where S is the specific surfitce ol" the ground specimens, # / V is a value describing the individual organic liquids and a, b are parameters, The linear character of this empirical t'unclion shows that the increase of surface is directly proportional to #IV, ikazaki et al. 1121 tbund a similar relationship between the median diameter of silicon nitride powder, alumina and soda glass ground in vibration mill and between/,t/ V values, It fi~llows then, that the increase of surface area is dependent also on the number of carbon atoms: the higher the number of atoms, the more space lilling adsorption is evident and the greater the surface area. For the propagation of cracks formed during intensive grinding, the value o f / z / V can be used as a means of assessing the grinding ability of the liquid and to characterize the milling environment 1131. We assume that the use of organic liquids--apart from sapporting the formation and propagation of cracks--aids also the disaggregation of freshly produced lines, The slopes in Fig, I depend on the properties of the minerals, Fig, 2 shows the relationship between parameter b and the values of Vicker" s microhardness (VHN). The parameter b was calculated by linear regression for all the minerals selected and shows that the rate of surface area production changes with respect to iz/V and is greater for harder minerals. Also the organic liquid chosen as the grinding medium
has a greater influence on surface growth in the case of the harder materials.
3. !.2. Application of Eq. (i)fiJr the desc'riptio,~ of the growth of new surfa('es of sulphMes in metham# (Ct) The relationships shown in Fig. I clearly indicate that organic liquids with a h i g h / z / V value are those best suited for the facilitation of new surface growth. From among the tested liquids, methanol had the most pronounced effect. This was therelbre chosen for the study ol'the relationship between new surfilce growth and milling time. Figs. 3 and 4 show the plot of Eq. ( I ) that tits the experimental data for galena ( Fig. 3 ) and chalcopyrite ( Fig. 4), ground in air (curve I ) and in methanol (curve 2). From the relationship presented it fol",~
2,4
--
I
-~
%,_ 1.6 / m
w 2 0 / 0 ' ' ~
~ ~ ± _ _...~....0---0"--0"--
'u
J.4 ~ /
"
|
oIo_.OlO._o_o__o__o___. °
0.8
0
I
I
I
l
I
I
5
10
15
20
25
30
t (rnin) Fig. 3. Variation of.specilic .surface area Swith grinding time t, for PhS: ( I ) dry grinding, ( 2 ) grinding in methanol. ~
4
% a2 ~'0
0
w
1
-'I - - - - - T .
0 ~ 0 ~ 0 ~ 0 ~ 0 ~ 0 " - ~ ' 0 "
2.~
0o8~~o'-o-olo--o'-o 0
I
I
I
5
10
15
-° I
o I__
20 25 t (min)
|
30
Fig. 4. Variation of specitic surface area S with the grinding time t. for CuFeS2: I I ) dry grinding, (2) grinding in methanol.
77
P. BaldY,el al. /Powder Technology 98 (1998j 74-78
lows that the increase in specific surface is dependent on the grinding environment. The grinding rate factor is the ra,tio of the surface produced by the use of chemical additives, namely methanol, to the surface produced during dry grinding I il. It equals !.65 for PbS and 3.5 ! for CuFeS:, showing that the grinding environment makes a significant difference.
=6° I ,,¢
80
0
I
I
I
.,.
I
I
<
60
1
F 40-
3.2. Bulk changes during intensivegrinding of suiphides in organic liquids Disordering of the structure of the sulphides ground in C t C5 organic liquids was evaluated on the basis of the amorphization of their structure using Eq. (2). The relationship between amorphization and # / V value for the two selected suiphides, chalcopyrite and pyrite, is shown in Figs. 5 and 6. The degree of amorphization of all the investigated sulphides (Table i) decreases as tz/V increases. The lowest values (i.e., the highest proportion of the crystalline phase in the material) were observed in case of using methanol (/z/ V= 13.94x 10-"J). The increase in the rate of tbrmation of new sulphide surfaces is facilitated by organic liquids of lower molecular density (high #/V values) which allow a free flow of pulp in the planetary mill. The disordering of their structure is facilitated if organic liquids with greater molecular density
I 0
0
0
2O
0
I
I
3
4
5 log VHN ( M Po) Fig. 7. Variation of AA values with the value of Vicker's microhardne.~,~ VHN for different minerals. Grinding time: 10 rain.
2
and lower/.t/V values (as well as higher number of C atoms) are applied. In this case, the interaction between the sulphide particles and grinding environment is facilitated, so that the crack propagation reaches subsurface zones and the bulk structure of the material. The change in crystal disordering relative to/.t/V of the grinding medium can be characterized by AA: AA =Am.,, - A rain,
(4)
where Am..,, is the amorphization for i.t/V= 5.53 x 10- 2,, ( iamyi alcohol) and Am,, is the amorphization for p./V= 13.94 x ! 0- 2,, ( methanol ). The relationship between AA and VHN is shown in Fig. 7. It can be seen that the organic liquids considered here the greatest structure disordering occurs with the softest sulphides ( i.e., those having the lowest VHN hardness values).
4, Conclusions
40 I
1
I
8
4
I
I
12 16 p. V "1 x 10"29 (C.kg.m "2)
Fig. 5. Variation of amorphization A with the value of #/V for CuFeS,. Grinding time: 10 rain.
i
i
i
i
<
The specific surface area of the ground sulphides increases with the increasing in #/V. The organic liquids with lower p./V values are more favourable for achieving structural disordering. Thus. by taking into consideration the results presented here, it is possible to create conditions more favorable to the production of either increased surface area or increase structural disordering, depending upon which end product is required.
30 5. Nomenclature S /.t V
20 O4
I
I
8
I
I
I
12 16 )J. V-1x 10"29 ( C.kg.m"2)
Fig. 6. Variation of amorphization A with the value of/z/Vfor FeS2. Grinding time: 10 min.
specific surface area (m= kg - ' ) dipole moment (C m) molecular volume ( m ~ kg- ~) #/V value describing the organic liquid (C kg m . , ) t time (min) VHN Vicker's microhardness (MPa)
78
P. Bald~ et al. / Powder Technology 98 (1998) 74-78
Acknowledgements The authors wish to express their thanks to Mrs. S. Rep~ o v ~ t for the measurement of specific surface area. This work was supported by the Slovak Grant Agency for Science VEGA (grant No. 95/5305/561 ).
References [ I l H. El-Shall, P. Somasundaran, Physicochemical aspects of grinding: a review of u~ of additives, Powder Technol. 38 (1984) 275. 121 IJ. Lin, A. Metzmager, Trans. AIME 241 (1968) 412. 131 P,A. Rehbinder, Physik 72 ( 1931 ) 191. 14l H, Schneider, Zement, Kalk, Gips 22 (1969) 193. 151 K.J. Savage, L.G. Austing, S.C. Sun, Trans. AIME 225 (1974) 89.
[6] F. ikazaki, K. Kamiya, K. Uchida, A. Gotoh, M. Kawamura, Chemically assisted comminution, Sibirskij Chim. Z. 5 ( 1991 ) I l. [7] F. lkazaki, K. Uchida, K. Kamiya, A. Kawai, A. Gotoh, E. Akiba, Chemically assisted comminution method accompanied by ion exchange, Int. J. Miner. Process. 44 (45) (1996) 93. 181 K. Tkaeova, Mechanical Activation of Minerals, Elsevier, Amsterdam, 1989. [91 T. Tanaka, Kagaku Kogaku 18 (1954) 160. I !01 G,S. Chodakov, Physics of Comminution, Nauka, Moscow, 1972. | I 1 ] S.M. Ohlberg, D.W. Strickler, J. Am. Ceram. Soc. 45 (1962) 170. i 12] F. lkazaki, K. Kamiya, K. Uchida, A, Kawai, A, Gotoh, E. Akiba, Chemically assisted dry comminution of inorganic powder, Proc. of First Int. Conf. on Mechanochem. InCoMe '93, vol. 2, Cambridge lnterscience Publishing, Cambridge, 1994, p. 140. ll31 K. Kubo, T. Miyazaki, Kogyo Kagaku Zasshi 71 (1968) 1301. 1141 J.W. Anthony, R.A. Bideaux, K.W. Bladth, M.C. Nichols, Handbook of Mineralogy, Vol. 1, Minerals Data Publishing, Tucson, AZ, 1990.
Powder Technology 98 ( 1998 ) 74-78
Physical and chemical changes of sulphides during intensive grinding in organic liquids P. Bai~,~ *, A. Mockov~iakovfi, E. Boldi~.firov~, J. Ficeriov~ Institute qf Geotechnics qf SAS. Watstmm'a 45. 043 53 Ko,~ice, Sha'ak Republic Received 6 June 1997: received in revised form 14 October 1997; accepted 2 December 1997
Abstract The properties of different sulphides (chalcopyrite--CuFeS,, pyrite--FeS,, galena--PbS, tetrahedrite--Cu~.,Sb4S~.~, stibnite--Sb.,S~) which were ground in a planetary mill in polar alcohols containing I-5 carbon atoms ( methanol, ethanol, n-butanol,/-butanol, n-propanol, ipropanol and i-amyl alcohol) were studied, it was found that the maximal increase of specific surface area can be achieved by milling in organic liquids with high/,t/V values (p,, dipole moment; 1/, molecular volume). A high degree of sulphide structure disordering can be achieved if organic liquids with a higher molecular density are employed. The results of the increase in specilic surface and structured disordering were related to the Vicker's hardness of the investigated sulphides. © 1998 Elsevier Science S.A. All rights reserved. Kev=~onls: Grinding: Sulphide: Alcohol: Surface area; Amorphization
I. Introduction The process of grinding is an area of constant interest in mineral processing research. One o1" the processes investigated here is the grinding environment and it was found that grinding in a liquid was more effective for new surl'ace formation than dry grinding [ I i . In the case of grinding i~a water, chemical reactions between broken surface bonds and water molecules occur [21. A reduction in hardness was discovered in the case of such minerals as oxides, silicates and carbonates. A more detailed study of the effect of the quality of wet grinding environment on the properties of minerals has been given by Rehbinder 131. He used such liquids as inorganic salt solutions ( NaCI, NaOH, NaaCO~and AICL ) and organic l~flar compounds. In the latter case, it was found that the hardness ot'the ground substancesdecreased with an increase in the number of carbon atoms in the molecules of organic compounds. Grinding in organic liquids is often more effective than in water [ 1,4,5 I. It is assumed that during grinding in this environment a slowing down o1" the formation of agglomerates and enhanced material flow occurs and as a result, improved grinding is achieved, lkazaki et al. [6,'7] studied the interaction between the ground material and organic liquids and * Corresponding author.
0032-5910/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. Pli S 0 0 3 2 - 5 9 1 0 ( 98 ) 0 0 0 3 8 - 2
introduced the term "chemically-assisted comminution', meaning that particles which are to be ground are made fragile or more easily broken by chemical interaction of the particles ill the grinding environment. For mills that transfer a lot of energy to the ground material (such as vibratory and planetary mills, attrition mills, etc.), the grinding liquid plays an important role. In these cases the material is not only comminuted and its specific surface increased, but its structure is also disordered [ 8 ]. Tanaka [ 9 ] and later Chodakov [ 10] described the process of ~cw surfiice formation by the following equation:
S=S,,,.,,(I-e t.,)
(I)
where S is specific surface area in time t. S,,,,,, the maximum surface area and k, a rate of new surface formation. The aim of this paper is to study the formation of new surfaces and the structure disordering in a series of sulphides (chalkopyrite. pyrite, galena, tetrahedrite and stibnite) that were subjected to intensive milling in different organic liquids (alcohols with one to five carbon atoms in their molecules) in a planetary mill.
2. Experimental The investigations were carded out with minerals of SIovak provenance (chaicopyrite--CuFeS2, pyritemFeS2,
P. Bah't3et al. /Powder Technology 98 (1998) 74-78
75
Table I Mineral deposits and chemicalcomposition Mineral
Deposit
chalcopyriteCuFeS, pyrite FeS_, galena PbS tetrahedrite CuI_,Sb4S.~ stibnite Sb_,S,
Slovinky Smoln& BanskfiStiavnica Rudfiany Rud~any
Chemicalcomposition ( '/~ ) Cu
Fe
S
As
31.55 0.02
31.44 42.81
32.54 49.6
0.20 33.40
0.7 ! 4.42
13.74 30.74
0.01
0.04
26.60
Hg
Zn
Sh
Ph
0.03
2. I0
5.02
2.3 ! 0.80
78.41 20.24 62.35
0.33
Sit'),
Insoluble remains
4. I I 6.52
0.24 0.3 I
2.73 2.83
1.56 0.43
I0.12
0.50
2.3. X-ray diffraction
g a l e n a ~ P b S , tetrahedrite~Cu~_,Sb4Sj~, stibnite~SbeS~). The chemical cornposition as well as the deposit is given in Table I.
The quantitative investigation of disordering of the sampies by intensive 3rinding was performed on a DRON 2.0 diffractorneter with GUR-5 goniometer (Techsnabexport, Russia) under the following conditions: Fe K a radiation. 24 kV. 10 mA and ! ° r a i n ~ goniometer rate. The extent of disordering of mineral structure was characterized by the content of the X-ray amorphous phase (amoq~hization) A which was calculated by means of the formula I I I I:
2. !. hm,nsive grinding Intensive grinding was carried out in a phmetary mill ( Pulverisette 4, Fritsch, Germany) under the following conditions: the mill was loaded with 25 balls of 10 mm diameter and five balls of 25 mm diameter; relative acceleration of the mill = 10.3: material of milling chamber and balls, tungsten carbide: size of the feed. 200 i.tm: mill charge weight, 20 g: grinding time. 10 min: grinding media: methanol, ethanol, npropanol, i-propanol, butanol./-butanol and i-amyl alcohol. The properties of the liquids used as grinding media are given in Table 2.
A =( I -U,,i,/I,,U, )X 100.
(2)
where U,,, U,. !,, and !, are the background of the reference sample, background of the ground sample, integral intensity of the reference sample and integral intensity of the ground sample, respectively.
3. R e s u l t s a n d d i s c u s s i o n
2.2. Sud'ace area
3. I. Changes of the surface during intensive grimling o.I stdphi&'.~ in ol:t,,anic liquids
The specilic surl~ce area S was determined by the low temperature nitrogen adsorption method in a Gemini 2360 sorption apparatus (Micromeritics. USA). The following temperatures were used for sample pretreatnlent before specific surface area measurements: methanol, 70°C: ethanol. 80°C: propanol, 105°C: i-propanol. 105°C: butanol, 105°C: /-butanol. 150°C; i-amyl alcohol, 150°C. The heating time was 60 rain for all samples.
3. !. !. The fimnathm ol'm,w smfaces and dependence on the magnitu&: q/'the law valm' fi,r the d~l/ferent ah'ohoi 137u,.~ (C~ to C s) A series of sulphides (Table I) were ground in organic liquid media trader the conditions given in Section 2. After filtration and drying, the specitic surface S was measured on
Table 2 Pmperliesof liquids used as grindingmedium Liquid
Molecular I'ormul:l
Molecular weight M
Molecular density p (kgm ~1
Molecular volume
l'=M/p ( Ill' kg
Methanol Ethanol Propanol i-Propanol Butanol /-Butanol i-Amylalcohol
CH ~OH CzHsOI-! C ~HTOH C ~HTOH C4H.,OH C.IH,,OH C~HIIOH
32.04 46.07
60. I0 60. i ,~ 74.12 74.12 88.15
792 789.2 804.4 785.5 810 81)5 881)
'
)
Dipole moment At x I11 "'
#/Vx Itl '" ((" kg m ')
( (" m I
0.04045 0.05838 0.07471
5.64 5.67 5.47
13.04 97 I 7.32
0.07651 0.09151 0.092{18 0.1(102
5.27 5.54 5.44 5.54
6.80 h.I)5 5.ql 5.53
P. Bahi~et al. /PowderTe¢'hnoiogy98 (1998) 74-78
76
¢,q I
I
I
I
I
'~ 1.2
S
FeSz
0.8 x .O
i
I
%
I
I
t
0.t,-
I
2
0
Sb2S3 2
3
t,
5
IogVHN
(MPa)
Fig. 2. Variation of the parameter Ii ( Eq. ( 3 }} with the value of Vicker's microhardness VHN ( after Ref. 1141 }. 3
4
'
' 8
'
"
12
'
-
16
I Ckg,m"~) Fig. I. Variationof .~pecilicsurl'ac¢area .5'with #/V values. Grinding time: I0 min. +u. V ' I x 10"z9
the selected samples. The resulting values were plotted against/z/V (Fig. I ), where p, is the dipole moment and V is the molecular volume. This ratio has been calculated for the individual organic liquids and the results are given in Table 2. From these data it follows that they can be described by an empirical linear function:
S=a+h(mlV),
(3)
where S is the specific surfitce ol" the ground specimens, # / V is a value describing the individual organic liquids and a, b are parameters, The linear character of this empirical t'unclion shows that the increase of surface is directly proportional to #IV, ikazaki et al. 1121 tbund a similar relationship between the median diameter of silicon nitride powder, alumina and soda glass ground in vibration mill and between/,t/ V values, It fi~llows then, that the increase of surface area is dependent also on the number of carbon atoms: the higher the number of atoms, the more space lilling adsorption is evident and the greater the surface area. For the propagation of cracks formed during intensive grinding, the value o f / z / V can be used as a means of assessing the grinding ability of the liquid and to characterize the milling environment 1131. We assume that the use of organic liquids--apart from sapporting the formation and propagation of cracks--aids also the disaggregation of freshly produced lines, The slopes in Fig, I depend on the properties of the minerals, Fig, 2 shows the relationship between parameter b and the values of Vicker" s microhardness (VHN). The parameter b was calculated by linear regression for all the minerals selected and shows that the rate of surface area production changes with respect to iz/V and is greater for harder minerals. Also the organic liquid chosen as the grinding medium
has a greater influence on surface growth in the case of the harder materials.
3. !.2. Application of Eq. (i)fiJr the desc'riptio,~ of the growth of new surfa('es of sulphMes in metham# (Ct) The relationships shown in Fig. I clearly indicate that organic liquids with a h i g h / z / V value are those best suited for the facilitation of new surface growth. From among the tested liquids, methanol had the most pronounced effect. This was therelbre chosen for the study ol'the relationship between new surfilce growth and milling time. Figs. 3 and 4 show the plot of Eq. ( I ) that tits the experimental data for galena ( Fig. 3 ) and chalcopyrite ( Fig. 4), ground in air (curve I ) and in methanol (curve 2). From the relationship presented it fol",~
2,4
--
I
-~
%,_ 1.6 / m
w 2 0 / 0 ' ' ~
~ ~ ± _ _...~....0---0"--0"--
'u
J.4 ~ /
"
|
oIo_.OlO._o_o__o__o___. °
0.8
0
I
I
I
l
I
I
5
10
15
20
25
30
t (rnin) Fig. 3. Variation of.specilic .surface area Swith grinding time t, for PhS: ( I ) dry grinding, ( 2 ) grinding in methanol. ~
4
% a2 ~'0
0
w
1
-'I - - - - - T .
0 ~ 0 ~ 0 ~ 0 ~ 0 ~ 0 " - ~ ' 0 "
2.~
0o8~~o'-o-olo--o'-o 0
I
I
I
5
10
15
-° I
o I__
20 25 t (min)
|
30
Fig. 4. Variation of specitic surface area S with the grinding time t. for CuFeS2: I I ) dry grinding, (2) grinding in methanol.
77
P. BaldY,el al. /Powder Technology 98 (1998j 74-78
lows that the increase in specific surface is dependent on the grinding environment. The grinding rate factor is the ra,tio of the surface produced by the use of chemical additives, namely methanol, to the surface produced during dry grinding I il. It equals !.65 for PbS and 3.5 ! for CuFeS:, showing that the grinding environment makes a significant difference.
=6° I ,,¢
80
0
I
I
I
.,.
I
I
<
60
1
F 40-
3.2. Bulk changes during intensivegrinding of suiphides in organic liquids Disordering of the structure of the sulphides ground in C t C5 organic liquids was evaluated on the basis of the amorphization of their structure using Eq. (2). The relationship between amorphization and # / V value for the two selected suiphides, chalcopyrite and pyrite, is shown in Figs. 5 and 6. The degree of amorphization of all the investigated sulphides (Table i) decreases as tz/V increases. The lowest values (i.e., the highest proportion of the crystalline phase in the material) were observed in case of using methanol (/z/ V= 13.94x 10-"J). The increase in the rate of tbrmation of new sulphide surfaces is facilitated by organic liquids of lower molecular density (high #/V values) which allow a free flow of pulp in the planetary mill. The disordering of their structure is facilitated if organic liquids with greater molecular density
I 0
0
0
2O
0
I
I
3
4
5 log VHN ( M Po) Fig. 7. Variation of AA values with the value of Vicker's microhardne.~,~ VHN for different minerals. Grinding time: 10 rain.
2
and lower/.t/V values (as well as higher number of C atoms) are applied. In this case, the interaction between the sulphide particles and grinding environment is facilitated, so that the crack propagation reaches subsurface zones and the bulk structure of the material. The change in crystal disordering relative to/.t/V of the grinding medium can be characterized by AA: AA =Am.,, - A rain,
(4)
where Am..,, is the amorphization for i.t/V= 5.53 x 10- 2,, ( iamyi alcohol) and Am,, is the amorphization for p./V= 13.94 x ! 0- 2,, ( methanol ). The relationship between AA and VHN is shown in Fig. 7. It can be seen that the organic liquids considered here the greatest structure disordering occurs with the softest sulphides ( i.e., those having the lowest VHN hardness values).
4, Conclusions
40 I
1
I
8
4
I
I
12 16 p. V "1 x 10"29 (C.kg.m "2)
Fig. 5. Variation of amorphization A with the value of #/V for CuFeS,. Grinding time: 10 rain.
i
i
i
i
<
The specific surface area of the ground sulphides increases with the increasing in #/V. The organic liquids with lower p./V values are more favourable for achieving structural disordering. Thus. by taking into consideration the results presented here, it is possible to create conditions more favorable to the production of either increased surface area or increase structural disordering, depending upon which end product is required.
30 5. Nomenclature S /.t V
20 O4
I
I
8
I
I
I
12 16 )J. V-1x 10"29 ( C.kg.m"2)
Fig. 6. Variation of amorphization A with the value of/z/Vfor FeS2. Grinding time: 10 min.
specific surface area (m= kg - ' ) dipole moment (C m) molecular volume ( m ~ kg- ~) #/V value describing the organic liquid (C kg m . , ) t time (min) VHN Vicker's microhardness (MPa)
78
P. Bald~ et al. / Powder Technology 98 (1998) 74-78
Acknowledgements The authors wish to express their thanks to Mrs. S. Rep~ o v ~ t for the measurement of specific surface area. This work was supported by the Slovak Grant Agency for Science VEGA (grant No. 95/5305/561 ).
References [ I l H. El-Shall, P. Somasundaran, Physicochemical aspects of grinding: a review of u~ of additives, Powder Technol. 38 (1984) 275. 121 IJ. Lin, A. Metzmager, Trans. AIME 241 (1968) 412. 131 P,A. Rehbinder, Physik 72 ( 1931 ) 191. 14l H, Schneider, Zement, Kalk, Gips 22 (1969) 193. 151 K.J. Savage, L.G. Austing, S.C. Sun, Trans. AIME 225 (1974) 89.
[6] F. ikazaki, K. Kamiya, K. Uchida, A. Gotoh, M. Kawamura, Chemically assisted comminution, Sibirskij Chim. Z. 5 ( 1991 ) I l. [7] F. lkazaki, K. Uchida, K. Kamiya, A. Kawai, A. Gotoh, E. Akiba, Chemically assisted comminution method accompanied by ion exchange, Int. J. Miner. Process. 44 (45) (1996) 93. 181 K. Tkaeova, Mechanical Activation of Minerals, Elsevier, Amsterdam, 1989. [91 T. Tanaka, Kagaku Kogaku 18 (1954) 160. I !01 G,S. Chodakov, Physics of Comminution, Nauka, Moscow, 1972. | I 1 ] S.M. Ohlberg, D.W. Strickler, J. Am. Ceram. Soc. 45 (1962) 170. i 12] F. lkazaki, K. Kamiya, K. Uchida, A, Kawai, A, Gotoh, E. Akiba, Chemically assisted dry comminution of inorganic powder, Proc. of First Int. Conf. on Mechanochem. InCoMe '93, vol. 2, Cambridge lnterscience Publishing, Cambridge, 1994, p. 140. ll31 K. Kubo, T. Miyazaki, Kogyo Kagaku Zasshi 71 (1968) 1301. 1141 J.W. Anthony, R.A. Bideaux, K.W. Bladth, M.C. Nichols, Handbook of Mineralogy, Vol. 1, Minerals Data Publishing, Tucson, AZ, 1990.