PURPOSE: To convert a polyvalent metal chelate of a low valence state to a polyvalent metal chelate of a high valence state by introducing an aq. alkaline soln. of the polyvalent metal chelate of the low valence state into the anode chamber of an electrochemical cell, then maintaining the anode potential at specific oxidation potential.

CONSTITUTION: The aq. alkaline soln. of the polyvalent metal chelate of the low valence state is introduced into the anode chamber of the electrochemical cell having the porous anode of a wide surface area and an ion exchange membrane for separating the anode chamber from a cathode chamber. The anode potential of the electrochemical cell is the maintained at the oxidation potential of the polyvalent metal chelate or above and below the oxidation potential of the chelate part of the polyvalent metal chelate. As a result, the polyvalent metal chelate of the low valence state is electrochemically oxidized to the polyvalent metal chelate of the high valence state. The regeneration of the polyvalent metal chelate-contg. spent scrubbing soln. after removal of hydrogen sulfide from a sour gaseous stream is facilitated.