Silica-coated magnetite (Mag-Sil) was prepared by the co-precipitation method using sodium metasilicate under an inert atmosphere and a fine pH control. Cetyltrimethylammonium bromide (CTAB) was adsorbed onto Mag-Sil aiming at decreasing the natural hydrophilicity of the silica surface, allowing the study of the hydrophobic interaction with sodium dodecylbenzenesulfonate (SDBS) to be carried out. Mag-Sil presented low surface Bronsted acidity once the pH at the point of zero charge was 7.5. The synthesized materials were characterized by X-ray diffraction (XRD), nitrogen physisorption analysis, thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) and transmission electron microscopy (TEM). Moreover, results were discussed in terms of CTAB concentration and arrangement onto the Mag-Sil surface based on two-step and four-region models for surfactant adsorption. (C) 2017 Elsevier B.V. All rights reserved.