Abstract: The toxicity of industrial process waters due to the presence of hexavalent chromium compounds is efficiently eliminated through reduction of the hexavalent chromium to 1 ppm. or less by adjusting the pH of the waters to 1.0-2.6, and passing the acidified waters through a bed of non-powdery elemental iron particles, while maintaining in the reaction mixture stoichiometric amounts of sulfuric acid relative to the hexavalent chromium. The hexavalent chromium is thereby reduced to the relatively non-toxic trivalent state. The process is conducted either by multiple passes through one reactor or by passing the acidified waters through two reactors connected in series, containing beds of elemental iron particles.