The invention relates to a process for synthesizing a high-purity AFX zeolite, comprising at least the following steps:
i) mixing, in an aqueous medium, of at least one source of silicon (Si) in SiO2 oxide form, at least one source of aluminum (Al) in Al2O3 oxide form, a nitrogenous organic compound of 1,6-bis(methylpiperidinium)hexane dihydroxide type, and at least one source of at least one alkali metal chosen from lithium, potassium or sodium, and the mixture of at least two of these metals, until a homogeneous precursor gel is obtained; ii) hydrothermal treatment of said precursor gel obtained at the end of step i) at a temperature of between 75° C. and 95° C., limits included, for a period of between 40 and 100 hours, limits included, to obtain a solid AFX-structure crystalline phase, termed “AFX zeolite”. The invention also relates to the high-purity AFX zeolite obtained.