a method for the pyrometallurgical treatment of environmentally hazardous steelmill flue dust and sludges to separate and recover the volatile heavy metals from the flue dust material and to convert the remaining iron into recyclable directly reduced iron pellets , or disposable non - hazardous reoxidized iron pellets , or pig iron or shot and slag . the dust is mixed with solid carbonaceous reductant and a binder , pelletized , optionally dried , and reduced in an inclined rotary reduction smelter vessel . the distilled heavy metals are reoxidized and may be selectively segregated to reduce the gangue and lead oxide contamination from the reconcentrated zind oxide dust . the reconcentrated heavy metal oxide dust is recycled by the zinc / lead industry .