Dissolution of Hydrous Chromium Oxide in Acid Solutions

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  • Seo Masahiro
    Laboratory of Electrochemistry, Faculty of Engineering, Hokkaido University
  • Furuichi Ryusaburo
    Laboratory of Applied Chemistry, Faculty of Engineering, Hokkaido University
  • Okamoto Go
    Laboratory of Applied Chemistry, Faculty of Science, Science University of Tokyo
  • Sato Norio
    Laboratory of Electrochemistry, Faculty of Engineering, Hokkaido University

Abstract

The dissolution behavior of precipitated hydrous chromium oxide in perchloric acid solutions containing SO42− or Cl− was studied and the dissolution mechanism was discussed from the point of view of electrochemistry.<BR>The dissolution rate in acid solutions obeyed a linear rate law and was expressed as d[Cr3+]⁄dt=kaH+0.46×aA−m, where aH+ is the proton activity, aA− the anion activity and m=0.29 for SO42− and m=0.27 Cl−.<BR>The dissolution rate is determined by superimposing the following two coupling and coupled reactions whose rates depend upon the potential difference at the hydrous oxide-solution interface:<BR>OH(H.O.)−+Haq+→H2Oaq<BR>[chromium complex](H.O.)n+→[chromium complex]aqn+<BR>where H.O. denotes hydrous chromium oxide. An electrochemical dissolution mechanism is proposed which involves as an intermediate complex CrSO4+ for perchloric acid solutions containing SO42−, CrCl2+ or Cr(OH)Cl+ for those containing Cl−, and Cr(OH)2+ for pure perchloric acid solutions.

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