The Bureau of Mines conducted laboratory batch and small-scale continuous tests to remove traces of dissolved molybdenum from water simulating waste discharged from a molybdenum concentrator. Molybdenum concentrations, initially ranging from 2 to 10 ppm, were decreased to 0.5 Ppm or less by coprecipitation of the molybdenum with freshly precipitated ferric hydroxide. The precipitate was separated as a froth by dissolved-air flotation for subsequent disposal. Although the treated water met current environmental standards for contained molybdenum, contained particulate iron might have to be removed by filtration for the water to be acceptable. Estimated costs of treating concentrator effluent water were 55 cents, 57 cents, and 64 cents per 1,000 gal at initial molybdenum concentrations of 2, 4, and 10 ppm, respectively.