Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Reexamination Certificate
2003-03-19
2004-02-03
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
C075S435000, C075S485000, C266S177000, C423S085000
Reexamination Certificate
active
06685761
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to an improved method for the beneficiation of titanium oxides. More particularly, the invention relates to a method of using a combination of furnaces operated under unique process conditions to effect the continuous beneficiation of titanium oxides from low-grade titanium materials and the production of iron.
BACKGROUND OF THE INVENTION
Mokleust, in U.S. Pat. No. 3,765,868, teaches a method for the selective recovery of metallic iron and titanium oxide values from ilmenites. The primary object of the invention is to provide an efficient and economical process for the selective recovery of metallic iron and titanium oxide values in high yields from lower grades of titanium ores, such as rock and beach sand ilmenites. The titanium oxides are recovered in the form of slag, containing 75 to 100% by weight of titanium oxide. The process of his invention involves electric arc smelting at high temperatures of substantially completely pre-reduced ilmenites.
In 1983, in U.S. Pat. No. 4,395,285, Merkert taught a low density, porous compact of prepared mix containing silica fume, finely divided carbonaceous reducing agents such as petroleum coke or coal, and optimally with iron and a binder.
In 1987, in U.S. Pat. No. 4,701,214, Kaneko et al. taught reduction by utilizing off gas generated by a smelting furnace in a moving hearth furnace. A method of operation was promoted which required less energy and a smaller smelting furnace by introducing gaseous reductants and fuel into the moving hearth furnace.
In 1987, in U.S. Pat. No. 4,731,112, Hoffman taught a method of making a molten ferroalloy product in a melting furnace from a feed briquette of metallized iron, granulated alloy metal oxide, and a carbonaceous material.
In 1998, in U.S. Pat. No. 5,730,775, Meissner et al. taught an improved method known by the trade name or trademark of FASTMET, which is an apparatus for producing direct reduced iron from iron oxide and iron bearing and carbon agglomerates that are layered no more than two layers deep onto a moving hearth, and are metallized by heating the agglomerates to temperatures of approximately 1316° C. to 1427° C. for a short time period. For a general understanding of the recent art, U.S. Pat. No. 5,730,775 is incorporated herein by reference.
All major iron making processes require the input of iron bearing materials as process feedstocks. A broadly used iron source is a product known as Direct Reduced Iron (“DRI”) which is produced by the solid state reduction of iron ore or iron oxide to metallized iron without the formation of liquid iron. Metallized in this sense, and throughout this specification, does not mean coated with metal, but means substantially reduced to the metallic state.
Improvements are sought within the industry for furnace modifications and improved methods of operation that provide for efficient, continuous production of titanium dioxide that is of sufficient purity that it can be processed as rutile, and simultaneously the production of high purity iron with a range of carbon content in which iron oxides are efficiently reduced to purified iron in the process, while slag components are separated from the purified iron as beneficiated titanium oxides.
The invention also in turn relates to charging hot, pre-reduced agglomerates containing highly metallized DRI and titanium oxide product to an ITmk3 “Finisher” furnace to effect melting of the DRI to produce melted agglomerates of nuggets of pure iron, which contain no gangue components, and fluid slag of titanium oxides that contain less than 10% gangue.
ITmk3 furnace technology was developed by Kobe Steel, LTD of Osaka, Japan, to separate metal from iron ore using coal. Briefly, ITmk3 technology employs a pellet of finely ground iron ore compounded with coal dust and a binder, to metallize the iron oxide into iron, melt and express slag, and then a means to separate a hot iron nugget from the slag.
Titanium is the world's ninth most abundant element, being about one fifth the abundance of iron. Titanium occurs in complex oxides, usually in combination with iron, and also with the alkaline earth elements. Titanium is commonly found as ilmenites, either as a sand or a hard rock deposit. Low-grade titanium ores, such as ilmenite sand are 45-65% TiO
2
, 55-35% iron, and 5-10% gangue. Rock deposits of ilmenites are reported to be 45-50% TiO
2
, 45-50% iron, and 5-10% gangue. The generalized formula for ilmenite is Fe
II
Ti
IV
O
3
, where from inspection it is apparent that iron is Iron II, and titanium is Titanium IV. Titanium also exists naturally at much higher grades. Rutile, which is relatively rare, is 92+% TiO
2
.
SUMMARY OF THE INVENTION
The present invention is a method and an apparatus for producing beneficiated titanium oxides from low-grade titanium materials containing iron, such as ilmenite. The invention minimizes the generation of gangue whose formation is commonly attendant to the process of reducing the iron oxide to iron. Gangue accrues in the fluid slag, and lowers the purity of the titanium. The source for the gangue is the reductant, which is commonly admixed with the titanium ore (ilmenites) to reduce iron oxide to iron. Coke and coke breeze are commonly employed as reductants, and the ash which is generated as a by-product, contributes to the gangue. Similar problems are also encountered with other reductants such as coal powder and coal fines. Reductants that are high in sulfur require that slag formers, such as limestone and lime, be added to remove the sulfur. Slag formers extract the sulfur and add to the slag layer, therein serving to lower the relative concentration of the titanium in the slag. The invention also reduces the total energy required for the beneficiation of the titanium oxides through the conservation of energy, the process by which the iron is reduced and through the conservation of materials.
The invented method continuously feeds titanaceous material containing iron oxide and carbon compounds into a sequence of hot process steps. The first hot process step employs a moving hearth, kiln or shaft furnace, operating below the melting point of the material, which effects pre-reduction of the material. The exit material from the moving hearth furnace is continuously and preferably hermetically introduced either directly into an electric melter or an intermediate hearth furnace operating at temperatures sufficient to melt the pre-reduced agglomerates therein forming melted agglomerate. The pre-reduced agglomerates exiting the pre-reduction furnace is preferably never exposed to air or cooled between the exit port of the pre-reduction furnace and entry into the electric melter. The invented method produces beneficiated titanium oxide and a high purity iron containing a specified percentage of carbon. Starting materials are introduced into the moving hearth pre-reduction process in layers in the form of agglomerates (e.g. pelletized or compressed material). Pre-reduced material from the moving hearth step is fed continuously and directly into the central interior area of the electric melter. The electric melter is maintained at a temperature exceeding the melting point of the material and the ingress of oxygen is minimized to guarantee efficient reduction. High purity iron product and beneficiated titanium oxide are periodically removed from the electric melter.
Utilizing a pre-reduction step of heating iron-bearing agglomerates in a moving hearth furnace, then directly and continuously feeding the carbon-containing metallized iron into an electric melter effectuates a very high iron content product having high percentages of carbon. Moreover, melting process conditions are such that the sulfur content is minimized and titanium oxides of titanium II, III and IV are produced.
The optional use of an intermediate hearth furnace, which employs ITmk3 furnace technology (such as a “finishing hearth melter” (FHM)), enables energy savings and increased production.
An extremely desirable high iron content product is provided fo
Gray Ronald D.
Hoffman Glenn E.
Andrews Melvyn
Dougherty Clements & Hofer
Midrex International B.V. Rotterdam Zurich Branch
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