Abstract: The instant invention relates to a process for changing the oxidation state of a compound or ionic species preferably a dissolved ionic species, and the novel electrochemical cell utilized therein. In the instant process, the compound or ionic species is passed through a porous electrode, which is maintained at a voltage sufficient to change the oxidation state of said compound or ionic species. This process is especially useful for oxidation-reduction processes, wherein said species is an ion having the same charge as the porous electrode. The porous electrode is isolated from the oppositely charged electrode by a semipermeable membrane, said membrane being impermeable to said dissolved species. In a much preferred embodiment, the dissolved species is chromium in the +3 oxidation state, e.g., the chromium available in chromic acid solutions which have been "used" in plastic etching processes or in processes for the oxidation of organic compounds; and the membrane is fluoro sulfonic acid membrane.