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

• Published in: Ultrasonics sonochemistry 2018-11, Vol.48, p.110-117
• Main Authors: Meichtry, Jorge M., Slodowicz, Mariel, Cancelada, Lucía, Destaillats, Hugo, Litter, Marta I.
• Format: Article
• Language: English
• Subjects: Cr(VI); INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Organic additives; Sonochemical reduction
• ISSN: 1350-4177; 1873-2828
• DOI: 10.1016/j.ultsonch.2018.05.014

•Sonochemical Cr(VI) reduction was studied at pH 2 in air using different additives.•The mechanistic pathways depend on the phase where the additive reacts.•With carboxylic acids, phenol, and t-butanol, kinetics was zero-order.•With methanol, ethanol and 2-propanol, deviation from zero-order was observed.•EDTA and citric acid are the best additives. 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) reduction efficiency of added formic acid (FA, 10 mM), citric acid (Cit, 2 mM), ethylenediaminetetraacetic acid (EDTA, 1 mM), methanol (MeOH, 0.1 M), ethanol (EtOH, 0.1 M), 2-propanol (2-PrOH, 0.1 M), tert-butanol (t-BuOH, 0.1 M), phenol (PhOH, 2 mM) and sodium lauryl sulfate (SLS, 1 mM) have been evaluated in comparison with the system in the absence 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 their degradation products were detected as final products. For EDTA, Cit, t-BuOH, FA and SLS, 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)