Oxidation of Iron in Biotite by Different Oxidizing Solutions at Room Temperature

Abstract

AbstractBiotite samples (10–20 µm lepidomelane) were mixed with solutions that contained various oxidants (O2, NaOCl, H2O2, or Br2) and salts (NaCl, KCl, NaCl‐NaBPh4, or none) to compare the effectiveness with which these solutions oxidize structural Fe2+ at 25°C when customary procedures and mica samples at different stages of expansion are used. In general, the treatments that minimized interlayer K exchange did not oxidize detectable amounts of Fe2+, whereas those causing mica expansion oxidized equivalent fractions of the Fe2+ if they were given enough time. The rates of Fe2+ oxidation by the O2 and NaOCl‐O2 solutions were very slow in even the expanded mica and were similar enough to suggest the OCl‐ ions did not contribute to the process under these conditions. The Br2 and H2O2 treatments, on the other hand, oxidized 97 and 85% of the structural Fe2+ in a fully expanded mica, respectively, in a 24‐h period. The relative effects of Br2 and H2O2 solutions probably reflect differences in the oxidants themselves but are confounded by the low pH of the Br2 solution, NaBPh4 interactions and H2O2 decomposition. Indeed, all the results make it clear that more distinction needs to be made between the role of the oxidants and the side efects of the solutions and procedures that are used in oxidation experiments.