Alkaline reactivity of arsenical natrojarosite

Journal of the Brazilian Chemical Society

Iván A. Reyes¹  Francisco Patiño¹  Isauro Rivera¹  Mizraím U. Flores¹  Martín Reyes¹  Juan Hernández¹ 

[1] ,Universidad Autónoma del Estado de Hidalgo Centro de investigaciones en Materiales y Metalurgia Pachuca Hidalgo ,México

关键词: reactivity;    arsenical natrojarosite;    kinetics;    arsenate;    decomposition;    amorphous;   

DOI  :  10.1590/S0103-50532011001200004

来源: SciELO

【 摘 要 】

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.

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