With the aim of producing arsenic compounds suitable for inertization and disposal, the optimal conditions for the synthetis of Beudantite type phases, with high AsO4/SO4 and different Na/Pb molar ratios, are described. Two samples of the desired structural type were obtained. Their AsO4/SO4 molar ratios are higher than in any other previously reported sample. A study of structural characterization of these two samples was carried out. The Rietveld method was applied using as initial structural models a natural Beudantite and a potassium-Jarosite. The results of the refinements confirm that the analyzed compounds present the Beudantite-Jarosite structure and are consistent with the proposed formulas. The obtained cells of the two samples are clearly different as a consequence of their composition difference. The cell volume of the sample with Na in the alkali site is halfway between the Beudantite and the Natrojarosite ones whereas the cell volume of the Na free sample is very similar to the Beudantite one.