Kinetics of sodium dodecyl benzene sulfonate adsorption on hematite and its interaction with polyacrylamide |
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Authors: | R P Bhagat |
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Institution: | (1) Mineral Processing Division National Metallurgical Laboratory Council of Scientific and Industrial Research, Jamshedpur 831 007, India e-mail: rpb@csnml.ren.nic.in Tel.: +91-657-27170914 Fax: +91-657-270527, IN |
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Abstract: | This article describes the adsorption of sodium dodecyl benzene sulfonate, an anionic surfactant, on a hematite surface and
that when the surface is preadsorbed with polyacrylamide. The adsorption of surfactant on a hematite surface has been studied
through equilibration and during kinetics measurements at three pH levels, viz. 4.0, 7.0, 8.9. The surfactant adsorbs strongly
on the hematite surface. The adsorption density at equilibrium as well as the rate of adsorption are dependent on the suspension
pH. The maximum adsorption density has been observed at pH 4, which reflects strong adsorption of negatively charged sulfonate
ions on the oppositely charged Fe2O3 surface (point of zero charge, 6.4). The adsorption density reaches its equilibrium value sooner in the case of an alkaline
suspension and later in the case of acidic pH. The polymer surfactant interaction has been noticed in the present study and
is also a function of pH. The hematite mineral when preadsorbed with the polymer draws fewer of the surfactant molecules at
lower surface coverage (during the initial period of the kinetics measurement) irrespective of the pH. When the adsorption
of the surfactant reaches a value which is near the equilibrium one, the pH effect is evident. In the case of acidic pH, the
surfactant adsorbs more on the hematite surface when preadsorbed with the polymer compared to the bare surface. In the case
of neutral or alkaline pH, however, the density of surfactant adsorption remains lower throughout the kinetics measurement
when the surface is preadsorbed with the flocculant compared to the bare surface. The particles also remain flocculated till
the end of the experiment, whereas at pH 4 the particles are deflocculated. In addition to pH, the electrostatic nature of
the adsorbent and the presence of anionic surfactant have an influence on the flocculation–deflocculation phenomena. The polymer–surfactant
interaction has been schematically represented. The surfactant is bound with polymeric chains as a combination of its monomeric
form as well as in the form of association in the case of acidic media and in competition with polymer in the case of alkaline
media.
Received: 18 April 2000/Accepted: 2 August 2000 |
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Keywords: | Flotation Surfactant Hematite Adsorption Kinetics |
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