The interaction between a basic dye, rhodamine B, and a separated fine fraction from natural clay was studied. Chemical analysis, X-ray diffraction and Fourier-transform infrared spectroscopy confirmed the predominance of beidellite in the fine clay fraction. The interaction of rhodamine B with the fine clay fraction showed that sorption was fast and followed a pseudo-second-order kinetic model. The comparison between sorbed rhodamine B amounts as a function of the various experimental parameters such as pH, sorbent mass, dye concentration and the presence of competing ions suggests that: (1) the sorption process is largely pH-dependent; (2) significant competition is observed between the dye and the Ca2+ and Mg2+ ions; (3) the sorption proceeds, principally, by a cation-exchange mechanism; and (4) the sorption capacity of the fine fraction in the presence of competing cations such as Ca2+ is ~0.28 mmol g–1.

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