Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-07-27
2001-08-07
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S569000, C075S662000, C075S669000, C075S695000
Reexamination Certificate
active
06270551
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for treating metal oxide fines. More particularly, this invention relates to a process for treating metal oxide fines to recover elemental iron from iron-bearing materials including iron-bearing ores, steel mill waste and other metallurgical process waste.
BACKGROUND OF THE INVENTION
Waste material is a natural byproduct of steel making and other metallurgical processes, such as the refining of iron-bearing ores. Steel making processes employing either a basic oxygen furnace or an electric arc furnace typically use large amounts of scrap, much of which is galvanized. Thus, the waste produced includes a dust containing oxides of iron as well as oxides of impurities such as zinc, lead and cadmium.
Electric arc furnace dust has been declared hazardous due to the high levels of lead and cadmium oxides and must therefore be collected and reprocessed in order to protect the atmosphere and groundwater. Basic oxygen furnace dust has been or is expected to be declared hazardous under future environmental regulations. Because of the presence of zinc and lead oxides, attempts to reclaim the iron oxides directly for reuse have not proved to be practical. Various alternatives to the direct recovery of the iron oxides have been proposed. One such proposal is to pelletize moist dust and then subject it to a very high temperature for a short period of time to sinter the pellets and to volatize the impurities. The very high temperature partially melts the iron oxide which rapidly forms a glass-like material which when it cools fuses the pellets together. The resultant iron-oxide mass is difficult to reduce and recovery of impurities is relatively ineffective.
Similarly, the recovery of elemental iron from iron-bearing materials such as iron-bearing ores have presented many difficulties. Generally, natural ore fines are too course for pelletization and too fine for iron making processes using conventional technology. Accordingly, it will be appreciated that there is still a significant need for an improved process for treating metal oxide fines to recover elemental iron from iron- bearing materials including iron-bearing ores, steel mill waste and other metallurgical process waste.
For a more detailed discussion of various known processes and apparatus for metal oxide recovery reference is made to U.S. Pat. Nos. 5,186,741; 4,701,2:4; 4,251,267; 3,452,972 and 2,793,109 all of which are hereby fully incorporated by reference.
An object of the present invention is to provide a process for agglomerating a dry mixture of mill waste having metal oxides including iron oxides therein, and a carbonaceous material containing less than about 20 wt % volatile matter under conditions to bond the dry mixture and form green compacts for recycling that is simple and economical. Yet another object of the present invention is to provide a process for treating metal oxide fines to recover iron from steel mill waste and other metallurgical process waste that is simple and economical.
SUMMARY OF THE INVENTION
Briefly, according to this invention there is provided a process for treating metal oxide fines. The process according to the invention involves the steps of providing a mixture of iron-bearing materials having iron oxides therein and a carbonaceous material containing less than about 20 wt % volatile matter. An organic binder is then blended with the mixture. The mixture is then agglomerated under conditions sufficient to form green compacts. The green compacts are then loaded into a preheated rotary hearth furnace void of compacts to form a layer of compacts no more than about two compacts high. The green compacts are heated for about 5-12 minutes at a temperature of between about 2200-2500° F. to reduce the compacts and evolve undesirable elements and oxides from the compacts. The reduced compacts are then discharged from the rotary hearth furnace.
The rotary hearth furnace is divided into four zones, a preheat zone, a loading zone, a reduction zone and a discharge zone. The preheat zone of the rotary hearth furnace is a zone of the furnace that precedes the charging zone and the introduction of the green compacts. The preheat zone, void of green compacts, is preheated to a temperature of about 2000° F. After preheating of the rotary hearth, green compacts are charged into the loading zone directly onto the heated hearth of the furnace. The compacts are then conveyed to the reduction zone of the furnace and reduced. The carbon contained in the carbonaceous material within the compacts reacts with iron, zinc, lead and cadmium oxides forming the respective elemental metals and carbon monoxide. Air is added to the reduction zone to combust the carbon monoxide and volatile matter from carbonaceous material and form carbon dioxide and water vapor to release required heat for the reduction process. The reduced compacts are then discharged from the rotary hearth furnace to a soaking pit wherein the reduction of the iron is completed and over 99% of the oxides of zinc, lead and cadmium are removed. The reduced iron remains in the compacts throughout the passage through the zones of the rotary hearth furnace along with normal non-reducing oxide materials and excess carbon in the mill waste. The reduced compacts contain substantially all of the elemental iron introduced with the mill waste and virtually all of the iron oxide is reduced to the elemental metal state.
REFERENCES:
patent: 5601631 (1997-02-01), Rinker et al.
patent: 5782957 (1998-07-01), Rinker et al.
patent: 5865875 (1999-02-01), Rinker et al.
patent: 5873925 (1999-02-01), Rinker et al.
Daiga Valdis R.
Horne Deane A.
Rinker Franklin G.
Thornton James A.
Andrews Melvyn
MacMillan Sobanski & Todd LLC
Maumee Research & Engineering Inc.
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