Alkaline Reactivite of Arsenical Natrojarosite

Reyes Iván A.,Patiño Fancisco, Rivera Isauro,Flores Mizraim U., Reyes Martín and Hernández Juan
J. Braz. Chem. Soc., 12 1-8. , 2011.


Jarosites are compounds that can undergo substitutions with several elements of environmental importance (such as As5+) during precipitation. Arsenic integrated in the structure could influence the solubility of the jarosite, potentially stabilizing the structure under a wide range of conditions that are tolerated by pure jarosite. Alkaline reactivity is characterized by the removal of sulfate and sodium ions from the lattice and by the formation of a gel consisting of iron hydroxides with adsorbed arsenate. The decomposition curves show an induction period, followed by a conversion period. The induction period is independent from the particle size and decreases exponentially as the temperature increases. The conversion period is characterized by the formation of a hydroxide halo around an unreacted arsenical natrojarosite core. The kinetic data are consistent with the chemical control of the process. The expression obtained in NaOH medium for [OH−] concentrations ranging from 3.84 × 10−3 to 1.08 × 10−1 mol L−1 is the following: r0/—v [1 − (1 − x)1/3] = 3.11 × 109 exp(−57.110/RT) [OH−]0.7t. The expression in Ca(OH)2 medium for [OH−] concentrations ranging from 2.21 × 10−2 to 6.98 × 10−2 mol L−1 is the following: r0/—v [1 − (1 − x)1/3] = 9.22 × 1011 exp(−48.610/RT) [OH−]1.51t.