Surface-Catalyzed Chromium(VI) Reduction:  Reactivity Comparisons of Different Organic Reductants and Different Oxide Surfaces

Cr VI reduction by low molecular weight organic compounds with various functional groups was examined in the presence and absence of oxide surfaces. Surface-catalyzed Cr VI reduction has been demonstrated with α-hydroxyl carboxylic acids (glycolic acid, lactic acid, mandelic acid, and tartaric acid) and their esters (methyl glycolate, methyl lactate, and methyl mandelate), with α-carbonyl carboxylic acids (glyoxylic acid and pyruvic acid), with oxalic acid, and with substituted phenols (salicylic acid, 4-methoxyphenol, and resorcinol). Both goethite (α-FeOOH) and aluminum oxide (γ-Al 2 O 3 ) exert an appreciable catalytic effect, although somewhat less than that observed with titanium dioxide. This study indicates that surface-catalyzed Cr VI reduction may occur in soils, sediments, aquifers, and other aquatic environments rich in mineral surfaces.