Details

Autor(en) / Beteiligte

• Fendorf, S.E
• Zasoski, R.J
• Burau, R.G

Titel

Competing metal ion influences on Chromium (III) oxidation by birnessite

Ist Teil von

• Soil Science Society of America journal, 1993-11, Vol.57 (6), p.1508-1515

Ort / Verlag

Madison, WI: Soil Science Society of America

Erscheinungsjahr

1993

Beschreibungen/Notizen

• The oxidation of Cr(III) to Cr(VI) presents a significant environmental hazard due to the much greater mobility and toxicity of Cr(VI). Despite the importance of Cr(III) oxidation, many factors influencing this important chemical process in soils and waters remain unknown. In this study we investigated the effects of competing metal sorbates on Cr(III) oxidation by delta-MnO2. Aluminum, La, Co(II), Mn(II), and Cr(VI) were reacted with delta-MnO2 prior to the addition of Cr(III). Only Al affected the extent of Cr(III) oxidation at pH 4, and at pH 5 the presence of Al, with 2.84 micromoles Cr(III) initially present, decreased oxidation from 2.80 to 0.28 micromoles Cr(VI). None of the competing ions influenced the degree of oxidation at pH 3. Neither of the oxidation reaction products, Mn(II) or Cr(VI), affected the extent of oxidation. Electrokinetic investigations revealed that both Al and La induced a charge reversal on delta-MnO2. As pH increased from 3 to 5, the electrophoretic mobility (EM) of delta-MnO2 sharply increased at pH 4 in the presence of 2.90 x 10(-4) M Al. The sorption behavior and influences on EM of Al indicate that a surface alteration occurs whereby the oxidizing ability of delta-MnO2 (birnessite) is inhibited. High-resolution transmission electron microscopy revealed that an Al-hydroxide surface precipitate formed on delta-MnO2, thus accounting for the sorption, EM trends, and Cr(III) oxidation inhibition