The Adsorption Of The Anionic Surfactants By Hydroxide Of Iron And Aluminium
THE ADSORPTION OF THE ANIONIC SURFACTANTS BY HYDROXIDE OF IRON AND ALUMINIUM
Е.А Streltsova, Е.А. Hromysheva, А.F. Тymchuk
Odessa I.I. Mechnicov National University,
Pastera st. 27, 65026 Odessa, Ukraine
The study of the adsorption of the surfactants on borders of a liquid – solid body and liquid – gas phases is urgent both for the further development of the theory of adsorption and for solving of a lot of practical tasks. Despite a large number of scientific works the quantitative information about adsorption surfactants by solid and gas adsorbents are inconsistent. The information about the thermodynamic characteristics of adsorption process is not numerous, also there is practically no information on free energy of Gibbs as criterion of adsorptional interaction.
This work is devoted to study of the adsorption of anionic surfactants on borders of a liquid - solid body and liquid – gas phases.
The objects of investigate were water solutions of the anionic surfactants: sodium dodecylsulfate (SDDS) and sulfanole NP-3 (sodium dodecylbensolsulfate) with the contents of the basic component 99,9 %. The hydroxides of iron (III) and aluminium were used as adsorbents.
The carried out investigations have shown, that isoterms of adsorption SDDS and sulfanole NP-3 by hydroxides of iron and aluminium have complicated S – like form caused by on the one hand, heterogeneity of adsorbate (the presence of colloid-dissolved form of anionic surfactants in it) and on the other hand – by polymolecular character of adsorption. For reception of the basic characteristics of adsorptional interaction SDDS and sulfanole NP-3 with the hydroxides of iron and aluminium the check of formal application of the theories of adsorption by Langmuir, Hill de Bure and also equation of Freundlich to experimentally received isoterms of adsorption was made. It was shown that the equations of Langmuir (, K) and Freundlich (k,n) describe the isoterms on initial stage corresponding to monomolecular adsorption (this area of concentration (0,2-1,4)×10-4 mol/l). The equation of Hill de Bure (K1 ,K2) describes the range of experimental isoterms appropriate to
small filling of the adsorbent surface by adsorbate (θ=0,4-0,6). The analysis of parameters describing the adsorption of investigated anionic surfactants by hydroxides of iron and aluminium (table), testifies that the adsorption SDDS and sulfanole NP-3 by hydroxides of iron and aluminium carries mainly chemical character (high, close to chemosorptions of value of ΔG°). The investigated systems concern the systems with the increased selectivity of the adsorption (value of K – (812-1665)×103 l/mol). The value n describing a degree of association of molecules surfactants in the adsorption layer is more than 1. It testifies that in process of adsorption of investigated surfactants by hydroxide of iron and aluminium alongside with ions and molecules the micelles of surfactants participate.
Table. Parameters describing the adsorption of surfactants on borders a liquid – solid body and a liquid – gas phases
Surfactants
Adsorbent
103 mol/g
k
N
-DG0 ads
кJ/mol
-DG0 ads кJ/mol
K 10-3,
l/mol
K1,
l/mol
K2,
l/mol
SDDS
Fe(OH)3
5,6
11,22
4,5
35,5
1665
99
2,0
Al(OH)3
4,5
10,03
5,3
35,0
1332
55
3,0
Air
27,6
Sulfanole NP-3
Fe(OH)3
3,7
7,94
2,9
33,8
827
55
5,0
Al(OH)3
3,7
7,59
2,8
33/7
812
54
4,7
Air
27,0
Thus the adsorption of investigated surfactants a surface of dispersed hydroxides of iron and aluminium may be considered as the process proceeding, a result of interaction of the ionic groups of the anionic surfactants with the positively charged surface of the sediments on the one hand, and on the other hand, like coagulational interaction.
The formation of the SDDS and sulfanole NP-3 adsorption layer on border of phases a solution – gas is accompanied by smaller change of free energy of Gibbs, than on border of phases liquid - solid body (in the first case -DG° =27,0-27,6 кJ/mol, in the second -DG° = 33,7- 35,5 кJ/mol). Hence, gas (air) is less effective adsorbent of the investigated anionic surfactants, than the hydroxides of iron and aluminium.
However, in spite of the fact that the adsorption of the anionic surfactants on border of phases liquid – air termodynamically is less profitable than on border of phases liquid – solid body. Availability of air and opportunity to carry out the adsorption processes in the simple flotational apparatus makes the usage of air as the adsorbent more perspective.
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