Alkaline reactivity of arsenical natrojarosite

• Autor(a) principal: Reyes,Iván A.
• Data de Publicação: 2011
• Outros Autores: Patiño,Francisco, Rivera,Isauro, Flores,Mizraím U., Reyes,Martín, Hernández,Juan
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Journal of the Brazilian Chemical Society (Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S0103-50532011001200004
• topic: reactivity; arsenical natrojarosite; kinetics; arsenate; decomposition; amorphous

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 × 10(9) exp(-57.110/RT) [OH-]0.7 t. 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 × 10(11) exp(-48.610/RT) [OH-]1.51 t.