Synthesis and Characterization of Beudantite

摘要

This piece of work is part of a wider study on the alkaline reactivity of jarosite-type compounds which contain arsenic that focuses on determining the conditions for the inactivation of arsenic in this kind of compounds. This particular study consisted of 4 syntheses (S1, S2, S3, S4) that were carried out in a glass kettle coupled to a refrigerating system and a mechanical stirring device, using different reagent concentrations at 94°C and 600 rpm. A beudantite sample with the following formula was obtained: (PbFe_3(SO_4)(AsO_4)(OH)_6). The syntheses' precipitates were thoroughly washed with ammonium acetate and hot water in order to eliminate lead sulfate and ferric sulfate excess. The syntheses were characterized with gravimetric analysis, dichromatometry, Inductively Coupled Plasma, Atomic Absorption Spectroscopy, X-ray diffraction and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). Synthesis S4 presents the best experimental conditions to obtain beudantite: 0.25 M Fe_2(SO_4)_3, 0.02 M H_3AsO_4, 0.15 M Pb(NO_3)_2, 94°C and 600 rpm for 32 hours. The approximate formula of the synthesized sample is [Pb_(0.39)(H_3O)_(0.22)]Fe_(2.89)[(SO_4)_(1.84)(AsO_4)_(0.16)][(OH)_(5.51)(H_2O)_(0.49)]. The obtained beudantite sample is predominantly spherical and has an even particle size distribution (30 - 35 μm). It is made of rhom-bohedral microcrystals that are strongly bound in a compact structure. The density of the sample is 3.03 g/cm~3. Its morphology, particle size and compact texture are suitable for heterogeneous kinetic studies.