Ferric chloride is prepd. in the form of an aqs. soln. by intimately mixing an aqs. soln. of ferrous chloride with free oxygen, either (a) at 80 degrees C and a superatmospheric pressure, or (b) at an elevated temp. in the presence of a promoter contg. ammonium, Cr, Co, Cu, Mn, Ni and/or Zn ions. The process is used to convert FeCl2 in the residual liquor from steel pickling with HCl soln. into FeCl3. The FeCl3 soln. can be thermally decomposed to give gaseous HCl which is recovered in the form of hydrochloric acid.