Sonochemical reduction of Cr(VI) in air in the presence of organic additives: what are the involved mechanistic pathways?

JORGE M. MEICHTRY; SLODOWICZ, MARIEL; LUCIA CANCELADA; MARTA I. LITTER

ULTRASONICS SONOCHEMISTRY.

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2018 vol. 48 p. 110 - 117

1350-4177

The sonochemical (850 kHz) reduction of Cr(VI) (0.3 mM, pH 2, reactor open to air)was analyzed in the presence of different additives. The effects on Cr(VI) reductionefficiency of added formic acid (FA, 10 mM), citric acid (Cit, 2 mM),ethylenediaminetetraacetic acid (EDTA, 1 mM), methanol (MeOH, 0.1 M), 2-propanol(2-PrOH, 0.1 M), tert-butanol (t-BuOH, 0.1 M), phenol (PhOH, 2 mM) and sodiumlauryl sulfate (SLS, 1 mM) have been evaluated in comparison with the system in theabsence of additives. Complete Cr(VI) reduction was obtained only when using EDTA(at 120 min) and Cit (at 180 min). Cr(III) complexes with these compounds or with theirdegradation products were detected as final products. For EDTA, Cit, t-BuOH, FA andSLS, the Cr(VI) decay could be adjusted to a zero-order kinetics; in the cases of MeOH,EtOH and 2-PrOH, there was a deviation from the zero-order kinetics. The Cr(VI)conversion increased in the order SLS (very low) < no additive  MeOH  EtOH  2-PrOH < FA < t-BuOH < PhOH < Cit < EDTA. The role of EDTA and Cit in stabilizingintermediate Cr(V) peroxo compounds and enhancing their direct transformation intodifferent Cr(III) species is considered a major factor in the acceleration of Cr(VI)reduction processes. Mechanistic pathways are proposed.