In this work, PEO coatings were produced on AZ91 magnesium alloy, and a sealing treatment was successively performed with solutions containing Nd sulfate salt, recovered by magnets scraps, to produce a Nd-based conversion coating on the surface.For PEO process was employed a basic solution containing both silicates and phosphates as electrolyte, and high current densities (0.5 A/cm2) and short treatment times (2 min) were used. Different parameters were tested for sealing treatment. In detail, the concentration of the salt (6 or 12 g/l of NaNd(SO4)2) and the effect of H2O2 as accelerant were investigated. The conversion coating was produced by simple immersion in the Nd sulfate salt solution, maintained at 50 °C for 30 min. The thickness, composition and morphology of the obtained coatings were analyzed with SEM-EDS, XRD and XPS, whereas the corrosion performances were evaluated with potentiodynamic polarization, EIS and OCV decay tests. An oxide ceramic coating of about 20 μm thick resulted and all the samples treated with sealing process showed an increase in the corrosion resistance depending on the salt concentration. Moreover, the addition of hydrogen peroxide, which acts as accelerant in the formation of the protective layer, allowed to obtain the best results, decreasing the corrosion current density of the sealed samples of two orders of magnitude, in comparison with the untreated ones and producing a sealing layer on the surface more uniform and adherent to the substrate. The increased corrosion performances of the sealed samples can be due to the sealing of the pores that characterized PEO coatings and to the presence in the external layer of protective compounds such as Nd2O3, as evidenced by XRD and XPS.