Adsorption behavior of Cr(VI) on organic-modified rectorite

The natural rectorite (REC) was modified with the surfactant of dodecyl benzyl dimethyl ammonium chloride, hexadecyl trimethyl ammonium bromide and octadecyl trimethyl ammonium bromide, respectively. Three kinds of organic-modified rectorite (OREC), termed OREC1, OREC2 and OREC3, respectively, were prepared. Three kinds of OREC were used as adsorbents for Cr(VI) removal in aqueous solution. Through FrIR and X-ray diffraction (XRD) analyses, it was confirmed that they indeed carried out cation exchange reaction between REC and surfactant. Through the research of Cr(VI) adsorption, the removal percentage (%) of Cr(VI) increased with increasing adsorbents dose. The adsorption efficiency of OREC adsorbent was greatly affected by the initial solution pH value. According to thermodynamics study, it can be concluded that the adsorption of Cr(VI) with three adsorbents was carried out spontaneously. The research of adsorption isotherm demonstrated that, adsorption reactions of three prepared OREC adsorbents belonged to Langmuir model. The kinetic data of Cr(VI) with OREC adsorbents were well fitted to the Lagergren rate equation, which indicated that the three adsorption processes belonged to first-order adsorption reaction. Values of coefficients of intra-particle diffusion and mass transfer have been determined for three different OREC adsorbents. Intra-particle diffusion analysis demonstrated that Cr(VI) ions diffused quickly at the beginning of the adsorption process, and then intra-particle diffusion slowed down and stabilized. Mass transfer analysis showed the process of transfer of Cr(VI) removal onto the adsorbents surface was rapid enough. (C) 2007 Elsevier B.V. All rights reserved.