Alkaline decomposition of synthetic jarosite with arsenic

F. Patiño, M. U. Flores, Iván A. Reyes, M. Reyes, I. Rivera, J. Hernández and J. C Juarez
Geochem. T., 14:2,1-8 doi: 10.1186/1467-4866-14-2, 2013.


The widespread use of jarosite-type compounds to eliminate impurities in the hydrometallurgical industry is due to their capability to incorporate several elements into their structures. Some of these elements are of environmental importance (Pb2+, Cr6+, As5+, Cd2+, Hg2+). For the present paper, AsO4 3− was incorporated into the lattice of synthetic jarosite in order to carry out a reactivity study. Alkaline decomposition is characterized by removal of sulfate and potassium ions from the lattice and formation of a gel consisting of iron hydroxides with absorbed arsenate. Decomposition curves show an induction period followed by a conversion period. The induction period is independent of particle size and exponentially decreases with temperature. The conversion period is characterized by formation of a hydroxide halo that surrounds an unreacted jarosite core. During the conversion period in NaOH media for [OH−] > 8 × 10−3 mol L−1, the process showed a reaction order of 1.86, and an apparent activation energy of 60.3 kJ mol−1 was obtained. On the other hand, during the conversion period in Ca(OH)2 media for [OH−] > 1.90 × 10−2 mol L−1, the reaction order was 1.15, and an apparent activation energy of 74.4 kJ mol−1 was obtained. The results are consistent with the spherical particle model with decreasing core and chemical control.