Thiocyanate (SCN-) Reactivity with Iron Oxides.

Determining the fate of SCN^- within the soil ecosystem is relevant to gaseous S fluxes, rhizosphere reactions, organic agriculture, microbial ecology, bioproducts/biofuels, natural pesticides, and anthropogenic contaminants.  Little is known concerning the reactivity of SCN^- with solid phase soil constituents.  Our objective was to determine the bonding mechanisms responsible for SCN^- interaction with oxides, likely sorbents within soil. We used FTIR to probe surface interactions of SCN^- with iron oxides. The determined C-N stretching band of free SCN^- (2066 cm^-1) is in good agreement with previously reported infrared spectra.  The shift of the main peak position to 2058 cm^-1 upon complexation with ferric iron indicates that the metal is bonding to the nitrogen lone pair of electrons. In contrast to aqueous complexation, sorption of thiocyanate to ferric hydroxide shifts the peak to a greater frequency (2069 cm^-1). This suggests that thiocyanate is bonding to the surface via the S moiety rather than through N group of the SCN^-. Our work has relevance to abiotic reactions that influence SCN^- cycling within soil environments. The experiments will provide fundamental information on the importance of Fe oxides on SCN^- retention.  Such reactions are significant in soil systems subjected to varying redox potentials.