Kinetics of sodium dodecyl benzene sulfonate adsorption on hematite and its interaction with polyacrylamide

This article describes the adsorption of sodium dodecyl benzene sulfonate, an anionic surfactant, on a hematite surface and that when the surface is p readsorbed with polyacrylamide. The adsorption of surfactant on a hematite surface has been studied through equilibration and during kinetics measurem ents at three pH levels, viz. 4.0, 7.0, 8.9. The surfactant adsorbs strongl y on the hematite surface. The adsorption density at equilibrium as well as the rate of adsorption are dependent on the suspension pH. The maximum ads orption density has been observed at pH 4, which reflects strong adsorption of negatively charged sulfonate ions on the oppositely charged Fe2O3 surfa ce (point of zero charge, 6.4). The adsorption density reaches its equilibr ium value sooner in the case of an alkaline suspension and later in the cas e 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 pread sorbed with the polymer draws fewer of the surfactant molecules at lower su rface coverage (during the initial period of the kinetics measurement) irre spective of the pH. When the adsorption of the surfactant reaches a value w hich 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 preadso rbed 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 t he flocculant compared to the bare surface. The particles also remain flocc ulated till the end of the experiment, whereas at pH 4 the particles are de flocculated. In addition to pH, the electrostatic nature of the adsorbent a nd the presence of anionic surfactant have an influence on the flocculation -deflocculation phenomena. The polymer-surfactant interaction has been sche matically represented. The surfactant is bound with polymeric chains as a c ombination of its monomeric form as well as in the form of association in t he case of acidic media and in competition with polymer in the case of alka line media.