Elimination of carcinogenic chromium(VI) by reduction at two-phase system

The novel complexing agent (N,N-dihexyl-N'-hydroxypyridine-2-carboximidamide) and commercial ionic liquid (Aliquat (R) 336) were used as Cr(VI) reducers, in order to eliminate carcinogenic chromium from aqueous solutions. To set an optimum condition allowing to the efficient Cr(VI) reduction, various factors, like effect of pH, contact time, Cr(VI) concentration, were examined. It was shown, that regardless on the used compounds, the conducting of the experiments at pH of 0 results in 100% Cr(VI) reduction, and the reactions follow a first-order kinetic. Moreover, the using of N,N-dihexyl-N'-hydroxypyridine-2-carboximidamide, the reduction was very fast, and required just 1 min shaking. The studies of changes in the Aliquat 336 structure indicated that the ionic liquid compounds degraded to tertiary amine (mechanism according to the rearrangement generates the protonated dialkylhydroxyamine), while DH2PIA proceeded through the iminoxy specie, which undergone either hydrogen atom abstraction allowing for regeneration of DH2PIA.