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.
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−.
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:
OH(H.O.)−+Haq+→H2Oaq
[chromium complex](H.O.)n+→[chromium complex]aqn+
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.
