The Bureau of Mines tested chromium-bearing waste slags from industrial stainless steel and other chrome alloy operations to determine their chromium leachability characteristics under acid precipitation conditions and to devise measures to prevent any pollution originating from this source. Two critical slag composition factors were found to control the chromium leachability: (1) cao:sio2 ratio and (2) magnesium content. Above a 2.0 Cao:sio2 ratio, chromium exists in slag as cao.Cr2o3, which can be vulnerable to leaching by acid precipitation especially if oxidized to cacro4 when exposed to the environment over an extended period. Maximum chromium leachability from industrial slags occurred when the composition of the slag had about a 2.0 Cao:sio2 ratio. Between a 1.0 and 2.0 Cao:sio2 ratio, in the presence of sufficient magnesium, mgo.Cr2o3 was formed, which is very resistant to oxidation and to dissolution by simulated acid precipitation. Addition of magnesium silicates to molten slag to fix the chromium in the mgo.Cr2o3 form was successful in preventing chromium leaching in simulated acid rain solutions. Experiments showed olivine and waste taconite tailings were suitable for this purpose. Olivine addition to a waste slag having a composition vulnerable to leaching (cao:sio2 > 2) reduced the chromium leachability more than 80 pct.