Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
2000-02-17
2002-04-30
King, Roy (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C075S659000, C075S669000, C075S694000, C075S695000, C075S769000, C588S253000, C266S156000, C266S157000, C266S172000, C266S195000, C266S197000, C266S249000
Reexamination Certificate
active
06379421
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and systems for removing undesirable metals from iron-containing waste materials produced in the steelmaking industries, such as Electric Arc Furnace (EAF) dusts or mill scale. In particular, this invention describes methods and systems for removing one or more toxic metals as for example: zinc, cadmium, lead, and others from such iron-containing wastes and recycling the iron contained for its utilization in steelmaking.
BACKGROUND OF THE INVENTION
The steel industry produces each year large quantities of wastes which desirably could be recycled and utilized after proper treatment for economic value and for compliance with environmental regulations, for example: Electric Arc Furnace (EAF) dusts, mill scale, iron ore fines, etc., with the EAF dusts and mill scale being typically the principal sources. Particularly the EAF dusts pose a difficult problem to steel producers regarding their handling and disposal due to the leachable toxic elements they contain (resulting in being classified by the U.S. Environmental Protection Agency as a hazardous waste). Each year the EAF steelmaking plants produce about 650,000 metric tons of EAF dusts, as reported in 1996.
Because of environmental concerns and costs, there is a continuing interest in developing commercially-viable treatments that have the ability to recover metal values, render the dusts less hazardous and/or gain beneficial use by re-utilizing the metals. Zinc is the contained metal value usually considered for recovery, followed by iron. The amount of zinc available for recovery is expected to increase in the future as galvanizing becomes ever more common for rust-proofing automotive steels.
There are numerous proposals in the literature for removing the toxic metals: zinc, cadmium, and lead from iron wastes, especially with increased regulation in the last decade, having the aim of recycling and/or safely disposing of the wastes. Few of these appear to have been used even as marginally acceptable commercially (primarily because of cost), and none have proven to be universally practical, even when limited to only EAF dust. See the article entitled “Treatment Option for Carbon Steel Electric Arc Furnace Dust”, by Arthur E. Morris et al, (University of Missouri-Rolla & Rolla Research Center, U.S. Bureau of Mines). See also U.S. Pat. No. 5,667,553 for a representative collection of background literature and patents (beginning with an Arthur D. Little, Inc. report “Electric Arc Furnace Dust-1993 Overview, A Summary of Dust Generation, Status of Regulations, Current and Emerging Treatment Processes, and Processing Costs”). These prior processes can be generally classified as pertaining to three categories:
(a) Removal of the toxic metals by hydrometallurgical processes. These methods require carrying out the chemical reactions in aqueous environments and have the objection of being costly, adding to landfill bulk and/of producing large volumes of polluting effluents.
(b) Agglomerating the dusts in combination with coal, coke or other hydrocarbon and heating and thereby reducing the metallic oxides at a highly elevated temperatures. Here the undesirable metals are evaporated and separated from the reduced metallic iron and condensed for their utilization or disposal;
(c) Agglomerating the EAF dusts and reducing them with a gaseous reductant, such as hydrogen, carbon monoxide or mixtures thereof, at high temperature in fixed or fluidized bed reactors and separating the undesired metals by condensation thereof outside the reduction reactor. These latter methods are preferred for in site treatment of the wastes.
The most used methods for the processing of electric-arc-furnace fines and the recovery of undesirable metals like zinc, lead and cadmium, involve the operation of horizontal rotary kilns, flat rotary hearth furnaces and grate furnaces, but up to date there have been few, if any, proposals for utilizing efficient moving bed reduction reactors for this purpose.
The following patents were found by applicants relative to the present invention: U.S. Pat. No. 4,673,431 to Bricmont; U.S. Pat. No. 5,013,532 to Sresty; and U.S. Pat. No. 5,470,375 to Greenwalt. These and the other patents and articles cited herein are incorporated by reference.
Bricmont (U.S. Pat. No. 4,673,431) relates to an electric arc furnace dust recovery process wherein pellets are formed from a waste dust and are charged to an oxidizing chamber
14
in an oxidizing atmosphere. The chamber is heated to quite high temperatures (e.g. 2700° F., i.e., 1482° C.), sufficiently to vaporize lead oxide and oxides of cadmium, potassium and sodium, if present, but not to vaporize zinc oxide or iron oxide. The vapors are drawn from the chamber with flue gases and delivered cooled to a bag house where flue gases are separated from solidified particles of the vapors. The residual oxidized mass is cooled after removal from the chamber and fed to a reduction chamber for further processing. Bricmont thus first separates the solidified particles of most of the undesirable metals from a residual oxidized mass of iron and then the iron and zinc oxides are reduced to metallic iron and zinc for further separation by volatilization of the zinc. The high temperature separation of zinc in its oxide form would appear to be unnecessarily expensive in view of the present invention as discussed below.
Sresty (U.S. Pat. No. 5,013,532) describes a process for recovery of metals from EAF dust wherein the raw material is charged to a furnace in the form of pellets, briquettes, granules or lumps and is heated sufficiently to permit vaporization and removal of the undesired metals by a flowing gas stream. To this end an excess of hydrogen gas is introduced into the furnace to reduce the metal oxides and sweep the vapors out of the furnace. The hydrogen gas containing the metallic vapors is cooled down with water and the condensed metals are separated in a bag filter. The main characteristics of Sresty is that hydrogen is the sole reducing agent and that hydrogen is regenerated by reaction of the zinc metal swept from the flue dust with the water during a reoxidation step.
Greenwalt (U.S. Pat. No. 5,470,375) describes a process for treating EAF dusts and petroleum refinery residues (with toxic metals) in a reduction reactor/melter gasifier combination where the refinery residues are fed to the melter/gasifier and the dust is agglomerated into ½ inch particles with lime or Portland Cement, “allowed to age”, and then fed to a reductive reactor. Reducing gas is generated in the melter gasifier, sweeps through the reduction reactor, and carries off vapors or aerosols of zinc, cadmium and lead for subsequent separation and recovery.
One of the objectives of the present invention is to recover safely yet economically undesirable metals like zinc, chromium, cadmium, and mixtures thereof contained in EAF dusts, mill scale, iron ore fines, metallic powder, or other particulate iron-containing materials, particularly waste and other by-products of the steel-making industry. Another object of the invention is to recover the iron content of such materials, producing a pre-reduced product or direct reduced iron. Another object of the invention is to reduce the impact of the steel-making industry and to reduce the EAF dust deposits accumulating in the world in an environmentally acceptable manner.
Other objects and advantages of the invention will be evident to those skilled in the art or will be described in this specification of the invention and appended drawings.
SUMMARY OF THE INVENTION
The objects of the present invention are generally achieved by providing processes and apparatus for recovering undesirable metals from iron-containing materials and for recycling the iron content of said materials, including as one preferred embodiment a method comprising: sintering said iron-containing material producing sinter masses; breaking as may be needed such oxidized mass(es) into manageable sinter lumps; separating sinter lumps of a size above
Aparicio-Arranz Jose María Eloy
Guerra-Reyes Maria Teresa
Pedroza-Contreras Miguel Angel
Salinas-Fernández Mario Alberto
Villarreal-Treviño Juan Antonio
Hylsa S.A. de C.V.
King Roy
McGuthry-Banks Tima
S. Safford A. Thomas
LandOfFree
Method and apparatus removing undesirable metals from... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus removing undesirable metals from..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus removing undesirable metals from... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2919940