Abstract
Zinc in electric arc furnace (eaf) dusts is reduced, volatilized, and recovered as liquid zn in a splash condenser or as zno in bag filters. Chlorine and fluorine in the dusts enter the gas phase and appear as dross in the splash condenser or as salts that contaminate the zno product. This research examined the use of pyrohydrolysis as a pretreatment of the eaf dust to remove halogens. Representative eaf dusts were secured and characterized by x-ray diffraction, scanning electron microscopy, and Mossbauer analysis. The effects of temperature, retention time, water partial pressure, and various additives on halogen extraction were tested. Experiments proved that 97 to 99 pct chlorine extraction and 80 to 85 pct fluorine extraction were consistently achieved when eaf dusts are blended with silica and roasted at temperatures of 850 deg c or higher in a furnace atmosphere of 75 pct steam-25 pct air. Statistical analysis established the fact that more than a single optimal point exists, thus affording flexibility in parameter selection (e.g., by increasing temperature, retention time and additive concentration may be decreased). The end product of the pyrohydrolysis procedure is a dehalogenated, self-fluxing calcine that can be directly charged to a plasma or flame reactor. The report includes design parameters and flow diagrams showing the pyrohydrolysis process integrated with plasma and flame reactor technologies.
