Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group iib metal
Reexamination Certificate
2001-04-30
2003-02-11
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group iib metal
C423S109000, C423S622000, C075S725000, C075S726000
Reexamination Certificate
active
06517789
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to a process for the reclamation of constituents contained in common industrial waste streams including essentially pure metal oxides and metals. This invention more specifically relates to a method for the recovery of essentially pure zinc oxide and other compounds such as lead compounds, copper compounds, silver compounds, and cadmium compounds from electric arc furnace (EAF) dust emanating from the steel industries processes.
2. Description of Related Art
Metallurgical processes, such as steel processes, result in waste by-products of iron and steel dust. There have been many attempts to recover valuable metal and chemical values such as zinc, lead, cadmium, silver, and copper in this dust and to obtain a by-product or final waste material that can be recycled or disposed of with minimal metal leaching problems.
Zinc oxide typically is a fine white or grayish powder that has a variety of uses including as a rubber accelerator, as a pigment, as a dietary supplement and in the semiconductor field. Zinc oxide is found in commercial by-products including waste material streams such as fly ash and flue dust. Methods for recovering zinc oxides are known in the art, including recovering zinc oxide from industrial waste materials. Such previous methods have included leaching with mineral acid, caustic soda, ammonium hydroxide, and ammonium carbonate solutions. However, these methods have low yields of zinc oxide and typically do not recover pure zinc oxide, the recovered zinc oxide being contaminated with other metal salts. Therefore, in order to obtain pure zinc oxide, subsequent reduction and washing processes were necessary.
One such method for recovering zinc and lead is the Waelz kiln. The Waelz kiln uses a directly heated counterflow rotary kiln to roast the materials under reducing conditions. The reducing roasting process comprises directly heating and roasting the iron and steel dust in the Waelz kiln in a reducing atmosphere under suitably selected conditions of temperature and retention time, thereby separating zinc and lead through volatilization from the dust and enabling iron to be discharged in the form of solid direct reduced iron. U.S. Pat. No. 4,525,208 to Yasukawa attempts to avoid perceived problems with the Waelz kiln caused by the depositing of material on the walls of the rotary kiln by running the volatilization in two stages. In the first stage the material is heated and zinc and lead are partially evaporated at a lower temperature in a rotary kiln. In the second stage, the solid material from the rotary kiln is continuously fed into the rotary smelting furnace where fluxes are added to the material to lower the melting point facilitating the evaporation of the metals from the molten stage.
U.S. Pat. No. 3,850,613 to Allen discloses a method for the treatment of steel mill waste dusts containing zinc. The Allen '613 method includes briquetting the dust with carbon to reduce the zinc and lead oxides to the zinc and lead metals and then volatizing the zinc and lead at high temperatures by heating the briquettes to 1800° F. to 2500° F., and then oxidized to ZnO and PbO in the gaseous phase. The ZnO and PbO then are recovered, with the remainder of the material used as the charge to a steel-making furnace.
U.S. Pat. No. 5,013,532 to Sresty discloses a method for recycling electric arc furnace dust. The Sresty '532 method for reducing the zinc contained in an EAF dust, volatilizing the metallic zinc so produced from the mass of the dust, and reoxidizing the metallic zinc to zinc oxide along with the simultaneous regeneration of hydrogen that can be recycled to treat additional EAF dust. The Sresty '532 process involves heating a raw material containing a mixture of metals and metal oxides in briquette, pellet, granular or lump form in a furnace to about 900° C. to about 1200° C., contracting the heated raw materials with a stream of hydrogen gas to reduce and vaporize the desired metal oxide or oxides, humidifying the stream of hydrogen gas and metallic vapors recovered from the furnace with water in the form of water vapor or steam to lower the temperature of the gas stream to about 700° C. to about 900° C. so that the metallic vapors react with the water to produce a solid metallic oxide or mixture of metallic oxides, humidifying again to a temperature in the range of about 150° C. to about 250° C., separating the solidified metal oxide from the hydrogen gas stream, condensing excess water from the hydrogen gas stream, and recycling the hydrogen gas stream.
U.S. Pat. No. 3,262,771 to Ban discloses a system for the recovery of steel and zinc from waste materials using a molten stage, including an electric arc furnace, an electrothermic smelting furnace and a slag fuming method. In the Ban '771 process, the recovery of zinc and lead is carried out in a molten stage by using an electric arc furnace. Zinc oxide is recovered as an overhead vapor, and iron is recovered as a liquid.
U.S. Pat. No. 5,188,658 Aune also discloses a method for the recovery of zinc from zinc-containing waste materials using a molten stage, including an electric arc furnace, an electrothermic smelting furnace and a slag fuming method. In the Aune '658 process, zinc and lead are recovered from the molten stage in an electrothermic smelting furnace. The electrothermic smelting furnace described in the Aune '658 patent requires that the furnace be kept at high temperatures in order to maintain a volume ratio between CO
2
and CO in the gas atmosphere in the smelting furnaces below 0.3.
U.S. Pat. No. 3,017,261 to Lumsden also discloses a method for the recovery of zinc from zinc-containing waste materials using a molten stage, including an electric arc furnace, an electrothermic smelting furnace and a slag fuming method. In the Lumsden '261 patent, zinc and lead are recovered from the molten stage with a slag fuming method using a stationary furnace where metals are volatilized by melting the iron and steel dust completely and blowing air and reducing agent such as coal or coke into the molten iron.
U.S. Pat. No. 4,840,671 to Lynn discloses a process to render such industrial waste non-hazardous without recovering zinc or lead. In the Lynn '671 process, electric arc furnace dust, steel dust from the production of certain specialty grades of steel, is rendered less hazardous by complexing the dust in a lime kiln dust, fly ash and hydrated lime mixture and then adding an aqueous solution containing ferrous hydroxide and calcium sulfate. The Lynn '671 process is based on the pozzolanic reaction of materials containing anhydrous alumino-silicates that, in the presence of lime, water and chemicals, adsorb and/or physically entrap the heavy metals present in EAF dust into a calcium-alumino-silicate matrix.
U.S. Pat. No. 3,849,121 to Burrows discloses a method for the selective recovery of zinc oxide from industrial waste. The Burrows '121 method comprises leaching a waste material with an ammonium chloride solution at elevated temperatures, separating iron from solution, treating the solution with zinc metal and cooling the solution to precipitate zinc oxide. The Burrows '121 patent discloses a method to take EAF dust that is mainly a mixture of iron and zinc oxides and, in a series of steps, to separate out the iron oxides and waste metals. However, the material obtained in the last step is a mixture of a small amount of zinc oxide, hydrated zinc phases that can include hydrates of zinc oxide and zinc hydroxide, as well as other phases and a large amount of diamino zinc dichloride Zn(NH
3
)
2
Cl
2
or other similar compounds containing zinc and chlorine ions. Currently, the Burrows '121 method is not economically viable because of Environmental Protection Agency guidelines established subsequent to the issuance of the Burrows patent. Additionally, the Burrows '121 method is not a continuous method and, therefore, is not economical as a continuous pr
Myerson Allan S.
Robinson Peter
Bos Steven
Technoprop Colton LLC
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