Deflocculant effects on the surface properties of kaolinite investigated through malachite green adsorption

The adsorption of malachite green (MG) on sodium-exchanged kaolinite and on the same clay treated with two widely used deflocculants, sodium hexametaphosphate (NaHMP) and sodium disilicate (NaDIS), was investigated. The results indicate that the deflocculants affect the adsorption process. In particular, DIS treatment increases physisorption, whereas HMP treatment almost completely prevents it. The Frumkin isotherm accurately describes MG adsorption for all of the adsorbents investigated and the Frumkin interaction parameter is found to be repulsive, in keeping with the cationic nature of the adsorbed species. The temperature dependences of the adsorption constant and the related thermodynamic parameters Delta H degrees(ads) and Delta S degrees(ads) were also determined and discussed. (C) 2008 Elsevier B.V. All rights reserved.