Materials based on inorganic phosphates, in particular iron monophosphates, exhibited significant applications in multiple fields due to their structural chemistry. In the present work, the synthesis of a new compound expressed as RbMgFe(PO4)2 was described using flux and solid state methods. The resulting product was analyzed by X-ray diffraction (XRD), Mössbauer and FT-IR spectroscopy and DR UV–vis. It crystallized in the trigonal system (space group P-3m1) with the cell parameters: a = 5.473(2) Å, c = 8.116(3) and Z = 1. Its structure was formed by isolated (Fe, Mg)O4 and PO4 tetrahedra shares vertices to form layers parallel to the ab plane. The Rb+ cations were located in interlayer space. The IR spectrum confirmed the presence of only PO4 group. The distribution of iron and its oxidation state and local environments were confirmed by Mössbauer spectroscopy. The ability of RbMgFe(PO4)2 to adsorb a cationic dye (Methylene Blue) was carried out under the variation of some experimental conditions (pH, concentration, duration and temperature). The adsorption process was chemical and favorable as proved by the data modeling along pseudo second order and both Langmuir and Freundlich theoretical equations.< Leer menos