US3318685A - Calcium chloride treatment of oxygen-process steel fume - Google Patents

Description

United States Patent C 3,318,685 CALCIUM CHLORIDE TREATMENT OF OXYGEN-PROCESS STEEL FUME Erwin C. Handwerk, Grosse Ile, Mich., assignor to Wyandotte Chemicals Corporation, Wyandotte, Mich., a corporation of Michigan No Drawing. Filed Mar. 2, 1964, Ser. No. 348,794

9 Claims. (Cl. 75-3) This invention relates to the production of hard agglomerates suitable for a furnace charge from particulate oxidized iron material. More specifically, this invention relates to the production of such hard agglomerates from particulate oxidized iron material wherein said agglomerates are substantially free from zinc and lead impurities.

In the production of steel, recently developed processes involve the use of pure oxygen or relatively pure oxygen which is blown into the molten metal or onto the surface thereof. Such processes generally involve blowing oxygen onto or beneath the surface of molten metal in a container similar to that of a vertical type Bessemer converter through a Water-cooled pipe or lance, or blowing the oxygen onto or beneath the surface of the molten metal in an open hearth furnace. The fume from such processes incorporates a considerable amount of finely divided or particulate oxidized iron material, which may be collected by the use of suitable precipitators such as electrostatic precipitators. It is, of course, desirable to recover the iron values from such finely divided oxidized iron material. However, these materials, because of their fineness, tend to fuse and bridge over or to be flushed out with the early slag before accomplishing their metallurgical function if added in an open hearth steel-making furnace and tend to be carried out through the top if used in a blast furnace and thus are not suitable in their naturally occurring condition for use in open hearth steelmaking furnaces or in blast furnaces.

In order to be able to recover the iron from finely divided oxidized iron materials, it has been a practice in the prior art to take such finely divided materials and agglomerate them by sintering at high temperatures or by bonding together with hydraulic cement. The preparation of such agglomerates or pellets, sometimes referred to as pelletizing or pelleting, involves subjecting a tacky or moderately cohesive material to a rolling motion as in a rotating open end drum or cylinder or a rotating disc, whereby the material rolls upon itself and thereby gradually agglomerates into small, generally spheroidal bodies or agglomerates. These agglomerates may subsequently be indurated by heat.

The formation of agglomerates which satisfactorily withstand shipping and handling, the impact of being dropped into a blast furnace and the crushing due to the weight of additional agglomerates superimposed on them, has been very difiicult.

Further, the finely divided particulate oxidized iron material, obtained from the fume of an oxygen steel process, generally contains lead and zinc impurities. This is particularly true of the material from an open hearth furnace where galvanized iron and tin-plated steel scrap may be employed. When both the metal and the slag are blown with oxygen to burn out the carbon and silicon from the metal and oxidize the slag, most of these metals volatilize and are collected with the iron oxide fumes. By recycling such fumes to the blast furnace after an agglomerating operation, they will collect in the pores of the brickwork near the top of the furnace and gradually destroy the refractory lining.

Accordingly, it is a purpose of this invention to produce hard agglomerates suitable as a charge for a furnace, such as a blast furnace or an open hearth furnace, from particulate oxidized iron material and particularly the type obtained from oxygen steel processes, which agglomerates are substantially free from zinc and lead impurities.

According to this invention a method is provided for producing hard agglomerates suitable for a furnace charge from particulate oxidized iron material, wherein said agglomerates, are substantially free from zinc and lead impurities by agglomerating a mixture comprising the particulate oxidized iron, finely divided carbon and calcium chloride in the presence of water and heating the resulting agglomerates at 'a temperature from about 1100 1500 C. The amount of calcium chloride and carbon required would depend on the amount of zinc and lead present in the oxidized iron material. With the particulate oxidized iron from oxygen steel processes, particularly open hearth processes, generally at least about 2 percent by weight calcium chloride and at least about 1 percent by weight carbon is required in the mixture. There is no upper limit to the amounts of calcium chloride and carbon which may be employed, however, for practical purposes not more than 25 percent by weight calcium chloride and 10 percent by weight carbon are employed. In carrying out this process the particulate oxidized iron material is mixed with the calcium chloride, finely divided carbon preferably of a particle size at least capable of passing through a screen of about 20 mesh and an amount of water sufiicient to impart proper consistency for agglomeration. This generally amounts to from about 7 to 25 percent by weight of water, depending on the method of agglomeration. The moist mix is then agglomerated by one of the conventional techniques such as described above, i.e., by subjecting the mix to a rolling motion as in a rotating open end drum or cylinder or on a rotating disc. For small batches the agglomerates may also be prepared by hand rolling or by spreading out a thin layer and scoring the layer of material with a sharp instrument such as a knife or plurality of knives. For a furnace charge material it is preferred to prepare pellets having a thickness in their maximum dimension of from about A to 1 inch.

The agglomerates formed as described above, hereinafter termed pellets, are then fed into a suitable heating device or furnace, wherein the pellets are dried, then heated or sintered at a temperature of from about 1100 to 1500 C. A sintering apparatus such as, for example, a machine of the type shown and described on pages 225 and 226, volume 8 of the Kirk-Othmer Encyclopedia of Chemical Technology, Interscience Encyclopedia, Inc., New York, or a countercurrent oil-, coalor gas-fired rotary kiln may be employed for the sintering step. By heating or sintering at such temperature, it is believed that the calcium chloride and carbon react with the oxides of any zinc and lead, which may be present in the finely divided oxidized iron produced by the oxidizing in the steel process, to produce volatile chlorides of any zinc and lead present, plus carbon monoxide and carbon dioxide. Hard, dense pellets of agglomerated particulate oxidized iron material, suitable for a furnace charge are produced, which are believed to be at least partially due to the combination of calcium with the oxygen and iron oxide to form a calcium ferrite. These pellets generally contain from about 78 to 93 percent by weight of oxidized iron, calculated as Fe O and are substantially free from Zinc and lead impurities.

The following examples illustrate the practice of this invention.

chloride and carbon in producing hard pellets suitable for a furnace charge from particulate oxidized iron material, which pellets are substantially free from impurities such as zinc and lead, and also illustrates the superiority of such pellets to pellets made under the same conditions, with the exception that sodium chloride is substituted for calcium chloride. One portion of fume ride, i.e., those after sintering, were not quite as strong as those made with calcium chloride but appeared sufficiently strong to be suitable for charging into a blast furnace. However, it can be seen that the impurity removal from an open hearth furnace employing oxygen in the 5 was very poor for the sodium chloride containing pellets processing, containing 0.96% lead, 3.28% zinc and apsince only 50% of the lead and 29.5% of the zinc values proximately 8.0% other impurities, balance oxidized iron have been removed at 1200 C. and even at 1450 C. was mixed with finely divided carbon, capable of passing less than half, i.e., only 44.2% of the zinc had been rethrough a 20-mesh screen, and calcium chloride flakes. moved. With calcium chloride more than 80% of both Another sample of the same fume was mixed with finely the lead and zinc had been removed at 1200 C. with even divided carbon of the same size as the first sample and better removal at higher temperatures. Thus, this exsodium chloride. In each case the amounts of carbon ample demonstrates the great superiority of calcium chloand chloride were sufficient to make up a composition ride over sodium chloride for producing pellets free from containing 2.0% carbon and 9.2% of the chloride. An zinc and lead impurities. amount of water suflicient to impart proper consistency Example H for making a thick paste was then added to each mixture which amount of water amounted to about 25% of the Fume from an P hearth furnace, p y g yg l i h f h mixture" in the processing, containing 0.96% lead, 3.28% zinc The paste was formed int approximately M -inch and approximately 8.0% other impurities, balance OXicubes by spreading onto a sheet of metal, such as alumidized iron was mixed with finely divided carbon, capable num or stainless steel, to a thickness of about 4 inch. of passing through a 20 mesh screen, and calcium chloride Using an ordinary table knife, the material was then flakes. The amounts of carbon and chloride were sufliscored into approximately At-inch cubes. On drying in cient to make up a composition containing 2.0% carbon an oven maintained at approximately 110 C. for about 3 by weight of the mixture and 9.2% calcium chloride by hours, the material was readily removed from the metal Weight of the miXtllfe- An m unt Of Wat r sufilcient t sheet in the form of cubes. Pellets of each composition impart proper consistency for agglomeration was then were treated in a muffie-type furnace heated by electrical added to each mixture, which amount of water was about resistance heating elements. Four batches of each of the 25% of the total weight of the mixture. Pellets were compositions were treated at four different temperatures, formed from this mixture by hand rolling into approxii.e. 1200 C., 1350 C., 1450 C. and 1500 C., respecmately /-inch to /s-inch diameter spheres. The pellets tively. All batches weighed 25 grams each, except for or spheres were dried overnight in an oven maintained that treated with calcium chloride at 1200" C. which at 110 C. An approximately l-pound batch of these weighed 125 grams. Tabulated in Tables I and II are pellets was treated in a rnuflle-type furnace heated by the results of analyses of each of the treated calcium electrical resistance heating elements for two hours at chloride containing pellets and each of the treated sodium 1350 C. The treated pellets were analyzed and found chloride containing pellets, respectively. to contain 0.02% lead and 0.30% zinc and thus the re- TABLE I HIGI I TEEIPERATURE TREATBIENT OF InOVa]. Of impurities Was of thfi lead and XY E -PR C P H TH FUME P L E of the zinc. The pellets were sufliciently strong to be IZED WITH CACL suitable for charging into a blast furnace.

Percent Analysis Percent Removal Examp HI Furnace Time at of Product of Impurities Temp, C. Tempera- Three portions of fume from a top-blown oxygen steel ture Pb Zn Pb Zn process converter and containing the amounts of impurities shown in Table III below and the balance oxidized 2 016 Q33 833 m 9 iron are mixed with finely divided carbon particles having 2 0. 08 0.12 91.0 90.3 the sizes indicated in Table III below and with calcium 8:8; 33:3 33:2 chloride flakes. In each case the amounts of carbon and calcium chloride are sufficient to make up a pelleting mixture containing the amounts of carbon and the TABLE I[ H1GH TEMPERATURE TREATMENT OF amounts Of calcium chloride in weight percent Of the mix- OXYGEN-PROCESS OPEN HEART}! FUME PELLET- ture indicated in Table III below. An amount of water IZED WITH NACl suflicient to impart proper conslstency for agglomeratlon Percent Analysis Percent Removal is added to each mixture and in each case the amount is Furnace Time at Product ()flmpuritigs the percentage by welght of the mixture indicated in Temp, C. 'Iempgg- Table III below.

Pb Zn Pb Zn The pellets are formed into spheres of /2 inch to inch in diameter by rolling on a 3-foot diameter disc 2 0. 4s 2. 24 50.0 29.5 pelletizer being rotated at approximately 15 rpm. The 2 g-gg 3% 3-2 22-; pellets are dried in an oven maintained at about 110 C. 2 0110 0101 3910 8114 for about 3 hours. One batch of pellets of each composition, weighing about pounds, is treated for the amount The green pellets, prepared by employing sodi hl of time indicated in Table III below in a conventional ride, tended to crumble easily and did not have the dey kiln feet long, 15 inches inside diameter, sirable physical strength of those made with calciu ing a refractory lining, rotating at 1.5 rpm. and heated chloride. The treated pellets, containing sodium chloby hot furnace gases at approximately 1205 C.

TABLE III Percent by Weight of Impurities in Original Oxidized Percent of Added Ingredients in Iron Material Pelleting Mixture Carbon Time at Portion Particle Size, Rotary Kiln Number Mesh Passing Temp, min. Zn Pb sn Other CaCh 0 H20 Through Impurities 1.78 0. 52 1. 2s 4. 9s 5 1 11 20 a0 3. 2s 0. 96 2. 30 s. 00 9. 2 3 s 20 30 3. 28 0. 2. 30 8.00 9. 2 2 10 20 30 All pellets are sufiiciently strong and hard to be suitable for charging into a blast furnace, and the percentage removal of zinc and lead impurities is very good.

It is to be understood that various changes and modifications may be made in the foregoing apparatus and method of operation without departing from the spirit of the invention and scope of the appended claims.

I claim:

1. A method for producing hard agglomerates suitable for a furnace charge from particulate oxidized iron material, wherein said agglomerates are substantially free from zinc and lead impurities, comprising the steps of agglomerating a mixture comprising said particulate oxidized iron, carbon and calcium chloride and heating the resulting agglomerates at a temperature of from about l100 to 1500 C.

2. The method of claim 1 wherein said particulate oxidized iron is obtained from the fume produced by oxygen steel processes.

3. A method for producing hard agglomerates suitable for a furnace charge from particulate oxidized iron material, wherein said agglomerates are substantially free from zinc and lead impurities, comprising the steps of agglomerating a mixture comprising said particulate oxidized iron, carbon and calcium chloride in the presence of water and heating the resulting agglomerates at a tem perature of from about .1100 to 1500 C.

4. A method for producing hard agglomerates suitable for a furnace charge from particulate oxidized iron material produced by oxygen steel processes wherein said agglomerates are substantially free from zinc and lead impurities, comprising the steps of agglomerating a mix ture comprising said particulate oxidized iron, from about 1 to by weight of carbon and from about 2 to 25% by weight calcium chloride in the presence of water and heating the resulting agglomerates at a temperature of from about 1100 to 1500 C.

5. The method of claim 4 wherein said carbon is finely divided carbon capable of passing through a screen of about 20 mesh.

6. The method of claim 5 wherein the agglomerates before heating have a thickness in their maximum dimension of from about A to 1 inch.

7. An agglomerated particulate oxidized iron material product containing from about 2 to 25% calcium chloride, from about 1 to 10% carbon and sufficient water to impart an agglomerating consistency to the material wherein said particulate oxidized iron material contains zinc and lead impurities and is produced by oxygen steel processes.

8. The product of claim 7 wherein said carbon is finely divided carbon, capable of passing through a screen of about 20 mesh.

9. The product of claim 8 wherein the agglomerates of said product have a thickness in the maximum dimension of from about A; to 1 inch.

References Cited by the Examiner UNITED STATES PATENTS 1,858,274 5/1932 Kern et al. 3 2,844,457 7/1958 Amberg 75--3 2,888,341 5/1959 Lawless et al. 75-3 3,146,088 8/21964 Tsujihata et al. 755 3,149,958 9/1964 Ward 75--3 BENJAMIN HENKIN, Primary Examiner.

Claims (2)

1. A METHOD FOR PRODUCING HARD AGGLOMERATES SUITABLE FOR A FURNACE CHARGE FROM PARTICULATE OXIDIZED IRON MATERIAL, WHEREIN SAID AGGLOMERATES ARE SUBSTANTIALLY FREE FROM ZINC AND LEAD IMPURITIES, COMPRISING THE STEPS OF AGGLOMERATING A MIXTURE COMPRISING SAID PARTICULATE OXIDIZED IRON, CARBON AND CALCIUM CHLORIDE AND HEATING THE RESULTING AGGLOMERATES AT A TEMPERATURE OF FROM ABOUT 1100* TO 1500*C.

7. AN AGGLOMERATED PARTICULATE OXIDIZED IRON MATERIAL PRODUCT CONTAINING FROM ABOUT 2 TO 25% CALCIUM CHLORIDE, FROM ABOUT 1 TO 10% CARBON AND SUFFICIENT WATER TO IMPART AN AGGLOMERATING CONSISTENCY TO THE MATERIAL WHEREIN SAID PARTICULATE OXIDIZED IRON MATERIAL CONTAINS ZINC AND LEAD IMPURITIES AND IS PRODUCED BY OXYGEN STEEL PROCESSES.