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The possibility of heterocoagulation between montmorillonite and humic substances
Applied Clay Science, 5 (1990) 265-270
265
Elsevier Science Publishers B.V., Amsterdam
The possibility of heterocoagulation between montmorillonite and humic substances Etelka Tomb~icz, Imre Abraham and Ferenc Sz~tnt6 Department of ColloidChemistry,AttilaJ6zsef University, 1-1-6720Szeged (Hungary) (Received March 9, 1989; accepted after revision November 7, 1989 )
ABSTRACT Tomb~icz, E., Abraham, I. and Sz~lnt6,F., 1990. The possibility of heterocoagulation between montmorillonite and humic substances. Appl. Clay Sci., 5: 265-270. Calculationswere performed on the basis of the theory of coUoid stability to reveal a new possibility of interaction between montmorillonite and humie substances. The calculations indicated that heterocoagulation of these species can take place in the presence of salts and is also dependent upon pH. In a slightly alkaline medium, heteroeoagulation of humate or fulvate and montmorillonite particles is more pronounced than coagulation of identical particles. At low pH, coagulation of humic or fulvic acid has virtually the same probability as heterocoagulation with montmoriUonite.
INTRODUCTION
In our previous papers (Tomb~tcz et al., 1988, 1990), results were published on the interactions between montmoriUonite and humic substances. We established that, besides the adsorption of humic substances, coaggregation of the components also takes place to some degree, depending on the pH and electrolyte concentration. The usual method of measuring adsorption does not make it possible to reveal the nature of the interaction. An experimental separation of adsorption and coagulation is not possible in such systems. Besides coagulation of identical particles, i.e. the homocoagulation of humic and fulvic species, and also of montmorillonite particles, heterocoagulation of components may also take place. Heterocoagulation, i.e. the coagulation of dissimilar particles, is well described in colloid science (Hogg et al., 1966; Usui, 1972; Void and Void, 1983). The purpose of this article is to direct attention to heterocoagulation as a new possibility of interaction between montmorillonite and humic substances. For this purpose, theoretical analyses as a function of pH and 1:1 electrolyte concentration were made on two samples of humic substances which had extremely different molecular weights and total acidity. 0169-1317/90/$03.50
© 1990 - - Elsevier Science Publishers B.V.
266
E. -FOMBACZETAL.
METHODS
The effects of pH and sodium chloride on the interaction of humic and fulvic acid and their sodium salts with montmorillonite have been examined previously (Tomb~icz et al., 1988, 1990). In this paper we present calculations. Experimental data and parameters for the calculations found in the above references. RESULTS
The interaction energy between particles can be given as a sum of the attractive (VA) and repulsive (VR) energies. The attractive energy (VA) between two dissimilar plates of thickness 81 and 82 at a distance of 2d from each other (Hamaker, 1937 ) is: VA =
l -~4 (d+81/2+82/2)2
,
(d+8,/2)
2
1
1
(d+~2/2) 2
(1)
where d is the Hamaker constant, and a~ and 82 are the thicknesses of particle 1 and particle 2. We used the previously published data (Tomb~cz et al., 1988, 1990 ), namely:A = 5- 10-2°J; 81 = 6.6- 10-10 m, thickness of montmorillonite plate; 82 = 4.65- 10-1o m, thickness of humic and fulvic acid layers. The repulsive energy (VR) can be calculated from the equation suggested by Hogg et al. ( 1966)" VR=2[
(~b¢021"~-~//022) ( 1 --coth 2xd)"+" 2/ff01~ffO2 cosech 2xd]
(2)
where ~ is the permittivity of the medium, x = ( 2 c e 2 v 2 / & T ) 1 / 2 , c is the electrolyte concentration in number of i o n s / m 3, v is the valence of the ions, e is the electronic charge, k is the Boltzmann constant, T is the temperature, and ~Uo~and ~Uo2are the surface potentials of particle 1 and particle 2. Eq. 2 can give the exact values of VR at low surface potentials (~Um,~Uo2< 25 m V ) but it is considered to be a good approximation at higher (50-60 m V ) potentials, too. The calculations were carried out with the following data: e= 80- 8.85- 10- t2 As V - ~mk T = 4.04- 10-21J e = 1.6- 10-19C c = 1- 1000 mmol d m - 3 ( 1- 1000- 6.1023 number of i o n s / m 3 ) 1:1 electrolyte ~Uo,= S t e m potentials of montmorillonite at different concentrations of 1:1 electrolyte (Table II, in Tomb~icz et al. 1988 ) ~Uo2= surface potentials of humic substances at given pH and electrolyte con-
HETEROCOAGULATIONBETWEENMONTMOR1LLONITEAND HUMICSUBSTANCES
267
centrations, calculated on the basis of the ionization model (Tables III-V in Tomb~icz et al., 1988, and Tables I-II in Tomb~tcz et al., 1990) We calculated the total energy of interaction of dissimilar particles as a function of distance, and determined the maximum value of this function (Vx,max). VT,max,which is characteristic of the stability of the colloidal system, is plotted as a function of salt concentration for humic acid and montmorillonite, humate and montmorillonite (Fig. 1 ), fulvic acid and montmorillonite, and fulvate and montmorillonite (Fig. 2). For comparison, previously published data related to the homocoagulation in the same systems are inserted (e.g. Tomb~lcz et al., 1988 ). The curves describing the interactions between dissimilar particles lie between the curves of identical particles, when the electrolyte concentration is more than 50 mmol dm -3, for all the systems examined, i.e. montmorillonite-humic acid, montmorillonite-Na-humate,
f-..,, \ 2
A - 5"10 -z° J
\
\
\
\
\
\
\
\
\
\ \
~-~
\
\
\
\
\
\
\ \
.
\
~\ \ ~'\
,, "",.,,
~,,.~. \. \'.. ...\ .....2"--. "-'~..
Fig. 1. Maximum total interaction energy (VT,max) for parallel flat plates of humic acid, Nahumate and montmorillonite as a function of 1 : 1 electrolyte concentration ( g : ~): interaction between identical particles (curves of fig. 9, Tomb~icz et al., 1988): montmorillonite-montmorillonite (dotted line), humic acid-humic acid (shorter broken line), Na-humate (longer broken line); interaction between dissimilar particles: montmorillonite-humic acid (dots and shorter dashes), montmorillonite-Na-humate (dots and longer dashes).
268
E. TOMBACZETAL.
~E
A - 5"10 J
\
\
l
F\ L.\
..
\
\
\
\
\\ \\
\ \',, \,, \
\
.~
\ ~ \ ,, -
.~
\
\
\
\\ ',,,
200
\
z.oo
...... 600 .-~00 CI 4 , rnrf~l om
Fig. 2. Maximum total interaction energy ( VT.... ) for parallel fiat plates of fulvic acid, Nafulvate and montmorillonite as a function of the 1:1 electrolyte concentration (q: l): interaction between identical particles (curves of fig. 7 in Tomb~icz et al. 1990): montmorillonitemontmorillonite (dotted line), fulvic acid-fulvic acid (shorter broken line), Na-fulvate-Nafulvate (longer broken line); interaction between dissimilar particles: montmorillonite-fulvic acid (dots and shorter dashes), montmorillonite-Na-fulvate (dots and longer dashes).
montmorillonite-fulvic acid and montmorillonite-Na-fulvate. Heterocoagulation significantly decreases the interaction energy in a slightly alkaline medium. In an acidic medium the probabilities of homo- and heterocoagulation are roughly the same, while the heterocoagulation of montmorillonite and humate or fulvate plates is much more probable in slightly alkaline systems. The maximum values of the total interaction energy (VT,max) for some characteristic systems (Tomb~lcz et al., 1988, 1990) are listed in the last column of Table I. This table also contains the experimental conditions of the adsorption measurements and the adsorption capacities, as well as the results of our former calculations on the interaction between identical plates. Again it can be seen that VT,m~xof interactions between identical and dissimilar plates differ only slightly from each other in acidic systems, whereas the Va-.ma,for
HETEROCOAGULAT1ON BETWEEN MONTMORILLONITE AND HUM1CSUBSTANCES
269
TABLE I
Interaction between identical or dissimilar flat plates at different l-1 electrolyte concentrations in an acidic and slightly alkaline medium Range ofpH
CNaO "Adsorption" (mmoldm -3) capacity (#eq g - t )
2.4...2.6
l0
100...230
20
550
2.3...3.0
l0 20
120 150
6.5...7.0
50 200
7.0...7.7
50 200
VT. . . . 103, J m -2 (A~- 5" 10 -20 J )
Homocoagulation
Heterocoagulation
humic acid-humic acid
montmorillonite-humic acid
0.278 0.831 0.014
0.345 0.978 0.052
fulvic acid-fulvic acid montmorillonite-fulvic acid
15 80... 100 45 140
2.227 2.504
2.816 2.679
humate-humate
montmorillonite-humate
3.571 2.222
2.687 0.856
fulvate-fulvate
montmorillonite-fulvate
3.854 2.787
2.813 0.983
heterocoagulation is much smaller than for homocoagulation when Na-humate or Na-fulvate are present. SUMMARY
In composite systems of montmorillonite, humic substances and electrolytes, adsorption, homocoagulation and heterocoagulation of the components can take place. Experimentally, these processes cannot be separated. The relative probabilities of these processes depend mainly on the properties of the humic substances, pH and the concentration of salts. The main tendencies are: the adsorption of fulvic acid (low molar mass and high acidity) is significant at low pH and low salt concentration; homo- or heterocoagulation can take place to a high degree mainly in the case of humic acid (higher molar mass) at low pH and very low electrolyte concentration; in slightly alkaline systems and at high salt concentration, the heterocoagulation of the components is most likely.
REFERENCES
Hamaker, H.C., 1937. L o n d o n - V a n der Waals attraction between spherical particles. Physica, 4: 1058-1072. Hogg, R., Healy, T.W. and Fuersteneu, D.W., 1966. M u t u a l coagulation of colloidal dispersions. Trans. Faraday Soc., 6 2 : 1 6 3 8 - 1 6 5 1 .
270
E. TOMBACZ ET AL.
Tombacz, E., Gilde, M., Abrah~lm, I. and Sz~int6, F., 1988. Effect of electrolyte concentration on the interaction of humic acid and humate with montmorillonite. Appl. Clay Sci., 3 : 3 1 52. Tomb~icz, E., Abrah~im, 1., Gilde, M. and Sz~int6, F., 1990. Effect of sodium chloride on the interaction of fulvic acid and fulvate with montmorillonite. Appl. Clay Sci., 5: 101-112. Usui, S., 1972. Heterocoagulation. In: J.F. Danielli, M.D. Rosenberg and D.A. Cadenhead (Editors), Progress in Surface and Membrane Science, 5, Academic Press, New York, N.Y., pp. 223-266. Void, R.D. and Void. M.J., 1983. Colloid and Interface Chemistry. Addison-Wesley, London, 694 pp.
265
Elsevier Science Publishers B.V., Amsterdam
The possibility of heterocoagulation between montmorillonite and humic substances Etelka Tomb~icz, Imre Abraham and Ferenc Sz~tnt6 Department of ColloidChemistry,AttilaJ6zsef University, 1-1-6720Szeged (Hungary) (Received March 9, 1989; accepted after revision November 7, 1989 )
ABSTRACT Tomb~icz, E., Abraham, I. and Sz~lnt6,F., 1990. The possibility of heterocoagulation between montmorillonite and humic substances. Appl. Clay Sci., 5: 265-270. Calculationswere performed on the basis of the theory of coUoid stability to reveal a new possibility of interaction between montmorillonite and humie substances. The calculations indicated that heterocoagulation of these species can take place in the presence of salts and is also dependent upon pH. In a slightly alkaline medium, heteroeoagulation of humate or fulvate and montmorillonite particles is more pronounced than coagulation of identical particles. At low pH, coagulation of humic or fulvic acid has virtually the same probability as heterocoagulation with montmoriUonite.
INTRODUCTION
In our previous papers (Tomb~tcz et al., 1988, 1990), results were published on the interactions between montmoriUonite and humic substances. We established that, besides the adsorption of humic substances, coaggregation of the components also takes place to some degree, depending on the pH and electrolyte concentration. The usual method of measuring adsorption does not make it possible to reveal the nature of the interaction. An experimental separation of adsorption and coagulation is not possible in such systems. Besides coagulation of identical particles, i.e. the homocoagulation of humic and fulvic species, and also of montmorillonite particles, heterocoagulation of components may also take place. Heterocoagulation, i.e. the coagulation of dissimilar particles, is well described in colloid science (Hogg et al., 1966; Usui, 1972; Void and Void, 1983). The purpose of this article is to direct attention to heterocoagulation as a new possibility of interaction between montmorillonite and humic substances. For this purpose, theoretical analyses as a function of pH and 1:1 electrolyte concentration were made on two samples of humic substances which had extremely different molecular weights and total acidity. 0169-1317/90/$03.50
© 1990 - - Elsevier Science Publishers B.V.
266
E. -FOMBACZETAL.
METHODS
The effects of pH and sodium chloride on the interaction of humic and fulvic acid and their sodium salts with montmorillonite have been examined previously (Tomb~icz et al., 1988, 1990). In this paper we present calculations. Experimental data and parameters for the calculations found in the above references. RESULTS
The interaction energy between particles can be given as a sum of the attractive (VA) and repulsive (VR) energies. The attractive energy (VA) between two dissimilar plates of thickness 81 and 82 at a distance of 2d from each other (Hamaker, 1937 ) is: VA =
l -~4 (d+81/2+82/2)2
,
(d+8,/2)
2
1
1
(d+~2/2) 2
(1)
where d is the Hamaker constant, and a~ and 82 are the thicknesses of particle 1 and particle 2. We used the previously published data (Tomb~cz et al., 1988, 1990 ), namely:A = 5- 10-2°J; 81 = 6.6- 10-10 m, thickness of montmorillonite plate; 82 = 4.65- 10-1o m, thickness of humic and fulvic acid layers. The repulsive energy (VR) can be calculated from the equation suggested by Hogg et al. ( 1966)" VR=2[
(~b¢021"~-~//022) ( 1 --coth 2xd)"+" 2/ff01~ffO2 cosech 2xd]
(2)
where ~ is the permittivity of the medium, x = ( 2 c e 2 v 2 / & T ) 1 / 2 , c is the electrolyte concentration in number of i o n s / m 3, v is the valence of the ions, e is the electronic charge, k is the Boltzmann constant, T is the temperature, and ~Uo~and ~Uo2are the surface potentials of particle 1 and particle 2. Eq. 2 can give the exact values of VR at low surface potentials (~Um,~Uo2< 25 m V ) but it is considered to be a good approximation at higher (50-60 m V ) potentials, too. The calculations were carried out with the following data: e= 80- 8.85- 10- t2 As V - ~mk T = 4.04- 10-21J e = 1.6- 10-19C c = 1- 1000 mmol d m - 3 ( 1- 1000- 6.1023 number of i o n s / m 3 ) 1:1 electrolyte ~Uo,= S t e m potentials of montmorillonite at different concentrations of 1:1 electrolyte (Table II, in Tomb~icz et al. 1988 ) ~Uo2= surface potentials of humic substances at given pH and electrolyte con-
HETEROCOAGULATIONBETWEENMONTMOR1LLONITEAND HUMICSUBSTANCES
267
centrations, calculated on the basis of the ionization model (Tables III-V in Tomb~icz et al., 1988, and Tables I-II in Tomb~tcz et al., 1990) We calculated the total energy of interaction of dissimilar particles as a function of distance, and determined the maximum value of this function (Vx,max). VT,max,which is characteristic of the stability of the colloidal system, is plotted as a function of salt concentration for humic acid and montmorillonite, humate and montmorillonite (Fig. 1 ), fulvic acid and montmorillonite, and fulvate and montmorillonite (Fig. 2). For comparison, previously published data related to the homocoagulation in the same systems are inserted (e.g. Tomb~lcz et al., 1988 ). The curves describing the interactions between dissimilar particles lie between the curves of identical particles, when the electrolyte concentration is more than 50 mmol dm -3, for all the systems examined, i.e. montmorillonite-humic acid, montmorillonite-Na-humate,
f-..,, \ 2
A - 5"10 -z° J
\
\
\
\
\
\
\
\
\
\ \
~-~
\
\
\
\
\
\
\ \
.
\
~\ \ ~'\
,, "",.,,
~,,.~. \. \'.. ...\ .....2"--. "-'~..
Fig. 1. Maximum total interaction energy (VT,max) for parallel flat plates of humic acid, Nahumate and montmorillonite as a function of 1 : 1 electrolyte concentration ( g : ~): interaction between identical particles (curves of fig. 9, Tomb~icz et al., 1988): montmorillonite-montmorillonite (dotted line), humic acid-humic acid (shorter broken line), Na-humate (longer broken line); interaction between dissimilar particles: montmorillonite-humic acid (dots and shorter dashes), montmorillonite-Na-humate (dots and longer dashes).
268
E. TOMBACZETAL.
~E
A - 5"10 J
\
\
l
F\ L.\
..
\
\
\
\
\\ \\
\ \',, \,, \
\
.~
\ ~ \ ,, -
.~
\
\
\
\\ ',,,
200
\
z.oo
...... 600 .-~00 CI 4 , rnrf~l om
Fig. 2. Maximum total interaction energy ( VT.... ) for parallel fiat plates of fulvic acid, Nafulvate and montmorillonite as a function of the 1:1 electrolyte concentration (q: l): interaction between identical particles (curves of fig. 7 in Tomb~icz et al. 1990): montmorillonitemontmorillonite (dotted line), fulvic acid-fulvic acid (shorter broken line), Na-fulvate-Nafulvate (longer broken line); interaction between dissimilar particles: montmorillonite-fulvic acid (dots and shorter dashes), montmorillonite-Na-fulvate (dots and longer dashes).
montmorillonite-fulvic acid and montmorillonite-Na-fulvate. Heterocoagulation significantly decreases the interaction energy in a slightly alkaline medium. In an acidic medium the probabilities of homo- and heterocoagulation are roughly the same, while the heterocoagulation of montmorillonite and humate or fulvate plates is much more probable in slightly alkaline systems. The maximum values of the total interaction energy (VT,max) for some characteristic systems (Tomb~lcz et al., 1988, 1990) are listed in the last column of Table I. This table also contains the experimental conditions of the adsorption measurements and the adsorption capacities, as well as the results of our former calculations on the interaction between identical plates. Again it can be seen that VT,m~xof interactions between identical and dissimilar plates differ only slightly from each other in acidic systems, whereas the Va-.ma,for
HETEROCOAGULAT1ON BETWEEN MONTMORILLONITE AND HUM1CSUBSTANCES
269
TABLE I
Interaction between identical or dissimilar flat plates at different l-1 electrolyte concentrations in an acidic and slightly alkaline medium Range ofpH
CNaO "Adsorption" (mmoldm -3) capacity (#eq g - t )
2.4...2.6
l0
100...230
20
550
2.3...3.0
l0 20
120 150
6.5...7.0
50 200
7.0...7.7
50 200
VT. . . . 103, J m -2 (A~- 5" 10 -20 J )
Homocoagulation
Heterocoagulation
humic acid-humic acid
montmorillonite-humic acid
0.278 0.831 0.014
0.345 0.978 0.052
fulvic acid-fulvic acid montmorillonite-fulvic acid
15 80... 100 45 140
2.227 2.504
2.816 2.679
humate-humate
montmorillonite-humate
3.571 2.222
2.687 0.856
fulvate-fulvate
montmorillonite-fulvate
3.854 2.787
2.813 0.983
heterocoagulation is much smaller than for homocoagulation when Na-humate or Na-fulvate are present. SUMMARY
In composite systems of montmorillonite, humic substances and electrolytes, adsorption, homocoagulation and heterocoagulation of the components can take place. Experimentally, these processes cannot be separated. The relative probabilities of these processes depend mainly on the properties of the humic substances, pH and the concentration of salts. The main tendencies are: the adsorption of fulvic acid (low molar mass and high acidity) is significant at low pH and low salt concentration; homo- or heterocoagulation can take place to a high degree mainly in the case of humic acid (higher molar mass) at low pH and very low electrolyte concentration; in slightly alkaline systems and at high salt concentration, the heterocoagulation of the components is most likely.
REFERENCES
Hamaker, H.C., 1937. L o n d o n - V a n der Waals attraction between spherical particles. Physica, 4: 1058-1072. Hogg, R., Healy, T.W. and Fuersteneu, D.W., 1966. M u t u a l coagulation of colloidal dispersions. Trans. Faraday Soc., 6 2 : 1 6 3 8 - 1 6 5 1 .
270
E. TOMBACZ ET AL.
Tombacz, E., Gilde, M., Abrah~lm, I. and Sz~int6, F., 1988. Effect of electrolyte concentration on the interaction of humic acid and humate with montmorillonite. Appl. Clay Sci., 3 : 3 1 52. Tomb~icz, E., Abrah~im, 1., Gilde, M. and Sz~int6, F., 1990. Effect of sodium chloride on the interaction of fulvic acid and fulvate with montmorillonite. Appl. Clay Sci., 5: 101-112. Usui, S., 1972. Heterocoagulation. In: J.F. Danielli, M.D. Rosenberg and D.A. Cadenhead (Editors), Progress in Surface and Membrane Science, 5, Academic Press, New York, N.Y., pp. 223-266. Void, R.D. and Void. M.J., 1983. Colloid and Interface Chemistry. Addison-Wesley, London, 694 pp.