Abstract: A method is disclosed for removal of free and complex cyanides from water-containing industrial effluents and wastes by treatment with insoluble solid iron sulfides at a pH in the range of about 7.0 to 8.5. The insoluble solid iron sulfides can be chemically prepared prior to treatment or prepared in situ, usually of a particle size smaller than about 5.mu., or supplied in the form of naturally occurring iron sulfides such as pyrrhotite or pyrite having a particle size smaller than about 300.mu., preferably smaller than about 150.mu.. The weight ratio of iron sulfide to total cyanide in the effluent is greater than 2:1, preferably greater than about 5:1 for prepared iron sulfides and greater than about 100:1 for mineral sulfides. The presence of a reducing agent such as ferrous ions or sodium sulfite to maintain a non-oxidizing environment during treatment enhances removal of cyanide.