Spectroscopic study of soil particle surface redox reactions.

Abstract

influence its solubility, mobility and toxicity. Quantitative examination of redox reactions are challenging in soils for a number of reasons ,including: a lack of reliable analytical methods to study reactions; the heterogeneity of the mineral components and redox systems occurring in nature; the irreversibility or slow approach to equilibrium of many redox reactions; and the probability that many redox reactions are biologically and/or surface-mediated. Traditionally the redox potential of a soil or sediment sample has been determined and quantified electrochemically. Such a measurement reflects a quasi-steady state electronic snapshot of a weighted sum of those redox pairs present in the system and capable of reversibly interacting with a redox electrode at that point in time. Although we know pure mineral surfaces may contribute to redox activity and assume soil surfaces to be active as well, greater understanding is needed. A review of some important factors operating in the soil redox system has recently been prepared Bartlett (1986). Recent advances in spectroscopic techniques suggest the possibility of evaluating in situ redox reactions involving a redox center in a mineral and a redox pair member the solid-liquid interface. by now at Spectral information in the uv-visible region provides structural and atomic level information that is difficult to obtain from other methods. Karickhoff and Bailey (1973) were able to assign specific electronic transitions (primarily associated with Fe, but also for other constituents of clay minerals) to bands observed in the uv–visible regions of the spectra. Johnston et al. (1990) used uv-visible spectroscopy to follow reversible single electron transfer reactions on the surface of transition-metal-containing clay minerals, and Anderson and Stucki (1979) observed changes in