US3770213A

US3770213A - Process for separating carbon from iron-bearing fines in blast furnace flue dusts

Info

Publication number: US3770213A
Authority: US
Inventors: J Lynn; J Sloughfy
Original assignee: Bethlehem Steel Corp
Current assignee: Bethlehem Steel Corp
Priority date: 1972-01-18
Filing date: 1972-01-18
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

Carbon particles can be separated from iron oxide particles and other gangue particles contained in blast furnace flue dust. The blast furnace flue dust is mixed with water to form a slurry containing 50 percent to 70 percent solids. A flotation agent and a forthing agent are added to the slurry. The slurry is vigorously agitated to thoroughly coat the carbon particles with the flotation agent. The slurry is diluted and passed to flotation cells. The carbon particles float on the surface of the slurry and the iron oxide particles and other gangue particles do not float atop the slurry. The carbon particles are collected as a float product while the iron oxide particles and other gangue particles are collected as a sink product.

Description

United States Patent Lynn et a1.

[5 PROCESS FOR SEPARATING CARBON FROM IRON-BEARING FINES 1N BLAST FURNACE FLUE DUSTS [75] Inventors: John D. Lynn, Center Valley; James L. Sloughfy, Bethlehem, both of Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

221 Filed: Jan. 18, 1912 211 App]. No.: 218,828

[52] US. Cl. 241/24, 209/166 [51] B03d 1/02 [58] Field of Search 209/166, 167, 3,

[56] References Cited UNITED STATES PATENTS 1,329,493 2/1920 Bacon 209/166 1,552,197 9/1925 Bates 209/166 1,787,938 1/1931 Eisele 209/166 1,840,267 1/1932 Tschudy 209/166 1,984,386 12/1934 Tschudy 209/166 UX Nov. 6, 1973 Primary ExaminerR0bert Halper Attorney.loseph J. OKeefe [57] ABSTRACT Carbon particles can be separated from iron oxide particles and other gangue particles contained in blast furnace flue dust. The blast furnace flue dust is mixed with water to form a slurry containing 50 percent to 70 percent solids. A flotation agent and a forthing agent are added to the slurry. The slurry is vigorously agitated to thoroughly coat the carbon particles with the flotation agent. The slurry is diluted and passed to flotation cells. The carbon particles float on the surface of the slurry and the iron oxide particles and other gangue particles do not float atop the slurry. The carbon particles are collected as a float product while the iron oxide particles and other gangue particles are collected as a sink product.

14 Claims, No Drawings 1 PROCESS FOR SEPARATING CARBON FROM IRON-BEARINGFINES IN BLAST FURNACE FLUE DUSTS Y BACKGROUND OF THE INVENTION This invention in general is directed to a method for separating carbon particles from iron oxide particles and gangue particles. More specifically, the invention is directed to a method for separating carbon particles from iron oxide particles and gangue particles contained in blast furnace flue dusts and to recover the carbon particles as a float product and to recover the iron oxide particles and gangue particles as a sink product which can be pelletized and charged into a metallurgical furnace. The carbon content of the sink product is reduced to a minimum.

Prior art practices to treat blast furnace flue dusts which contain carbon particles, iron oxide particles and gangue particles include passing a slurry of flue dusts to froth-flotation cells wherein the carbon particles are floated and recovered as a float product and the iron oxide particles and gangue particles are recovered as a sink productpThe priorart practices are exemplifiedin u.s. Pat. No. 1,984,386 issued Dec. 18, 1934 to Frederich Tschudy and entitled, Process of Separating Composite Materials. Such processes are partially successful. However, the amount of carbonremaining in the sink product with the iron oxide particles and gangue particles is more than about percent. This amount of carbon negates the recovery of the iron oxide particles as a balled and pelletized product. The amount of carbon in the sink product and consequently in the balled product is sufficient to cause overheating and fusion of the balls during heating for pelletization. The result is a clinker-type product rather than discrete pellets as desired. I

It is an object of this invention to provide a method for separating carbon particles from iron oxide particles and gangue particles in a material containing said particles.

It is an object of this invention to provide a method for separating the carbon particles in wet blast furnace flue dusts from iron oxide particles and gangue particles contained therein.

It is an object of this invention to provide a method for separating the carbon particles in dry blast furnace flue dusts from iron oxide particles and gangue particles contained therein.

It is an object of this invention to provide a method for separating the carbon particles in mixtures of wet and dry blast furnace flue dusts from iron oxide particles and gangue particles contained therein.

It is an object of this invention to'provide a method for separating the carbon particles of wet, dry, and mixtures of blast furnace flue dusts containing iron oxide particles and gangue particles, wherein said blast furnace flue dusts are subjected to froth-flotation and the carbon particles collected as a float product can be used as a fuel and the iron oxide particles and gangue particles collected as a sink product have a carbon content of not more than about 5 percent can be balled, pelletized, and/or metallized and used as charge materials in furnaces, for example, a blast furnace, electric furnace, open hearth furnace, basic oxygen furnace.

PREFERRED EMBODIMENT OF THE INVENTION It has been found that wet or dry blast furnace flue dusts and mixtures thereof, which contain carbon particles, iron oxide particles and gangue particles can be treated to separate the carbon particles from the iron oxide particles and gangue particles. The carbon content of the iron oxide and gangue particles can be reduced to below about 5 percent.

The method of the invention has been found to be applicable to all mixtures of blast furnace flue dusts from 100 percent wet blast furnace flue dusts to 100 percent dry blast furnace flue dusts but it is preferred to use mixtures of about 25 percent wet blast furnace flue dusts and 75 percent dry blast furnace flue' dusts to 75 percent wet blast furnace flue dusts and 25 percent dry blast furnace flue dusts.

Blast furnace flue dusts can contain, for example, about to about 50 percent carbon, about to about 55 percent total iron of which'as much as 60 percent is in the form of Fe o about 5 percent to about 8.5 percent silica, about 1.0 to about 2.0 percent alumina, about 4.0'to about 6.0 percent calcium oxide and about 1.0 to about 2.5 percent magnesia. The blast furnace flue dusts are mixed with water to form a slurry having I a pulp density of about 50 to about 70 percent solids.

Hereinafter whenever sieve sizes are mentioned the sieves are of the Tyler series. The particles of the blast furnace flue dusts should be 28 mesh when added to water to form such a slurry. Particles of wet blast furnace flue dusts generally are 28 mesh size, therefore, they can be used as received. Dry blast furnace flue dusts on the other hand can contain particles which are +28 mesh size, therefore, a size separation-is made at 28 mesh. The +28 mesh size particles are ground to a 28 mesh size. The separation at 28 mesh is made to prevent overgrindingthe 28 mesh size particles which are in the dry blast furnace flue dusts. Of course, it is possible to add the dry blast furnace flue dusts to the wet blast furnace flue dusts prior to grinding but .to prevent overgrinding of the 28 mesh size particles con-' ferred to as MIBC) or a pine oil and the like. It is preferred to use No. 2 fuel oil as the flotation agent and MIBC as the frothing agent. It has been found that from about 0.5 of a pound to about 35 pounds of No. 2 fuel oil per dry ton of flue dusts in the slurry and about 0.06 of a pound to about 0.30 of a pound of MIBC per dry ton of flue dusts in the slurry are added to the slurry to obtain the results of the invention. The amount of flotation agent and frothingiagent added to the slurry is always on a dried flue dust basis although the slurry can contain wet and dry flue dusts.

The slurry is violently agitated in an appropriate apparatus. The violent agitation is necessary so that the immiscible flotation agent and water are mixed and discrete droplets of the flotation agent formed during agitation will come into contact with the particles in the about 4 minutes to achieve good results but for better results about 5 minutes of agitation is necessary. Of course, agitation times less than 4 minutes will result in the separation of some carbon particles during subsequent flotation. However, carbon contents greater than 5 percent will remain in the sink product. However, lengthy agitation times do not improve the results of the invention, therefore such lengthy times would not be economical. It is preferred to agitate the slurry between about 4 minutes to about'6 minutes. Any appropriate apparatus can be used to agitate the slurry but it is preferred to use a mixer having a stirrer rotating at relatively high speeds. While the speed and time of agitation are essential, they are merely indicative of the agitation desired in the method of the invention. The most important factor is the amount of heat energy formed in the slurry during agitation. The heat energy formed in a volume of slurry is greater than the heat energy formed in an equal volume of water substantially free of solids which is agitated under the same conditions as the slurry. The slurry can contain 50 to 70 percent solids which contain carbon, iron and other particles. Obviously, the amount and type of particles in the slurry will have an affect on the ease of agitation. To provide a basis for the amount of heat energy required to obtain the desired agitation an equal volume of water substantially free of solids was used. The water was agitated under the same conditions as the slurry. The heat energy so formed in the water is between about 0.25 calories per gram of water per minute to about 0.40 calories per gram of water per minute. It will be understood that hereinafter wherever heat energy is referred to such heat energy is predicated on the agitation of an equal volume of water substantially free of solids. The use of agitators which create heat energy lower than 0.25 calories per gram of water per minute do not achieve the degree of carbon separation which is desired. Agitators which create heat energy greater than 0.40 calories per gram of water per minute do result in obtaining the desired carbon separation. However, the degree of carbon separation is not any better than achieved with agitators which create heat energy of 0.40 calories per gram of water per minute. Therefore, the use of the more rigorous agitators is wasteful of electrical power which is used to operate the agitators.

After agitation the pulp density of the slurry is adjusted by adding water thereto to obtain a slurry containing about to about 35 percent solids. The slurry is passed to froth-flotation cells, for example, Denver Sub A flotation cells. Air is bubbled upwardly through the slurry in the froth-flotation cells. The carbon particles are floated to the top of the slurry by the air while the iron oxide particles and gangue particles remain suspended in the slurry in the cells. Of course, it is virtually impossible to prevent very small iron oxide particles and gangue particles from being floated into the froth. However, the amount of such particles in the froth is negligible. It is also true that some carbon particles will remain suspended in the slurry with the iron oxide particles and gangue particles but the percentage of such particles is relatively small. It must be recognized that water and MIBC are lost during froth removal. It is, therefore, necessary to add water to maintain the level of the slurry in the cells so that the froth can be removed therefrom while still maintaining the pulp density of the slurry at about 10 to about 35 percent solids. About 0.03 of a pound of MIBC per ton of dry feed solids is added from time to time to maintain, a sufficient amount thereof in the slurry whereby efficient removal of carbon particles is realized. Usually, the time interval between MIBC additions is, between about 2 minutes to about 4 minutes of operating time. In the method of the invention about to about percent of the carbon originally contained in the blast furnace flue dusts is recovered as a float product and an iron oxide concentrate containing from about 0.75 to not more than about 5 percent carbon is recovered as a sink product. The float product can contain as much as 15 percent impurities, such as silica, alumina, magnesia and the like.

Wherever percentages are recited in this specification and claims such percentages are on a weight basis unless otherwise noted.

In a specific example of the invention a sample of dry blast furnace flue dust was screened at 28 mesh to separate the +28 mesh particles from the 28 mesh particles. The +28 mesh particles were ground so that percent of the particles passed a 28 mesh sieve. The ground particles and the original 28 mesh particles were then mixed. The blast furnace flue dust so treated had the following analysis:

CHEMICAL ANALYSIS (9%) II F61 24.9 *Fe total iron SiO, 8.4

CaO 7. l

About 414 grams of the dry blast furnace flue dust was mixed with 400 ml. of water to obtain a slurry having a pulp density of 51 percent solids. The slurry was conditioned by adding 3.9 pounds of No. 2 fuel oil per ton of dry flue dust and 0.03 of a pound of MIBC per ton of dry flue dust. The conditioned slurry was violently agitated in a mixer having an impeller speed of 1,800 rpm for 5 minutes and passed to Denver Sub A flotation cells. The heat energy in the slurry was found to be equivalent to about 0.25 calories per gram of water per minute. The slurry was diluted by adding 1400 ml. of water, thereto to adjust the pulp density to 18.7 percent solids. Air was bubbled upwardly through the slurry in the flotation cells. After 2 minutes of operation, 0.03 of a pound of MIBC per ton of dry flue dust was added to the slurry. Thereafter, 0.03 of a pound of MIBC per ton of dry flue dust was added to the slurry at 4 minute intervals until the end of the run. Water was added from time to time to maintain the slurry level in the cell. The float product referred to as a carbon concentrate and the sink product referred to as the iron concentrate were collected and dried. The chemical analyses of the concentrates are shown below:

Total iron content. Free carbon content.

Note that the carbon concentrate, that is, the float product contains 98.6 percent of the carbon in the original flue dust and only 12.8 percent of the iron oxides.

in another specific example of the invention, wet

was mixed with water to form a slurry having a pump density of 5l percent as in the first specific example. The slurry was conditioned and subjected to the frothflotation process as described in the first specific example. The chemical analyses of the carbon concentrate and iron concentrate are shown below:

d. agitating the slurry for a time not less than 4 minutes wherein heat energy formed in the slurry is greaterthan the heat energy formed by agitating an equal volume of water under the same conditions as the slurry, g I

e. diluting the slurry to a pump density of about 10 to about 35 percent solids,

f.'passing the slurry to froth-flotation cells,

g. bubbling air upwardly through the slurry for a time to selectively float substantially all the carbon particles into a froth formed atop the slurry while substantially all the iron oxide particles and gangue particlesremain suspended in the slurry, and

h. removing the carbon particles as a float product and the iron oxide particles and gangue particles as a sink product from the froth-flotation cells.

2. The method of claim 1 in which the flotation agent Percent Analysis (Percent) distribution Fe C SiOz A1203 Ca0 MgO I F' C Carbon Concentrate 8.8 70.4 4.2 1.6 2.3 1.1 18.2 97.6 Iron Concentrate 46.0 2.0 12.8 1.3 8.9 2.7 81.8 2.4

In a third specific example, a mix consisting of percent of the screened ground and remixed dry blast furnace flue dust of the first specific example and 50 percent of the wet blast furnace flue dust of the second specific example was made. A chemical analysis of the mix follows:

CHEMICAL ANALYsIs CaO 6.1

MgO 2.2

SiO

A slurry of the mix was made and conditioned as in the first specific example. The conditioned slurry was sub- 1 jected to the froth-flotation process of the firstspecific 5 example. The chemical anslyse's of the carbon concentrate and iron concentrate recovered in the froth- 4O flotation process follows:

added to the slurry in step (c) is No. 2 fuel oil 3. The method of claim 1 in which the frothing agent added to the slurry in step (c) is methylisobutylcarbinol.

4. The method of claim 2 in which the frothing agent added to the slurry in step (c) is methylisobutylcarbinol.

(Percent) Analysis (percent) distribution Fe C S102 A1 0: 0210 MgO Fe C Carbon concentrate 8. 2 70 5 4. 5 1. 8 2. 5 1. 1 17. 2 98. 0 Iron concentrate 44. 6 1. 6 11. 6 1. 9 10.1 3. 4 82. 8 2. 0

i We claim:

gram of water per minute.

Improved method for treating blast furnace flue I 7. Improved method for treating dry blast furnace dusts by froth-flotation to separate substantially all the carbon particles from iron oxide particles and gangue particles contained therein, said carbon particles being recovered as a float product and said iron oxide particles and gangue particles being recovered as a sink product containing not more than 5 percent carbon, said method comprising:

a. reducing substantially all the particles in the blast furnace flue dusts to a 28. mesh size, b. adding the blast furnace flue dusts to water to for a slurry having a pump density of about 50 to about percent solids,

c. adding at least one flotation agent taken from the group consisting of No. 2 fuel oil and kerosene, and

at least one frothing agent taken from the group consisting of methylisobutylcarbinol and pine oil, to the slurry,

flue dusts by froth flotation to separate substantially all the carbon particles from iron oxide particles and gangue particles contained therein, said carbon particles being removed as a float product and said iron oxide particles and gangue particles being removed as a sink product containing not more than 5 percent carbon, said method comprising:

7 aTEFrEiIEgTHe'T'J blast furnace flue dust to obtain a particle size separation at 28 mesh, I

b. grinding the particles larger than 28 mesh toa size smaller than 28 mesh,

c. mixing the particles smaller than 28 mesh of step (a) and of step (b),

d. forming a slurry of the particles of step (c) and water, said slurry having a pump density of about 50 percent to about 70 percent solids,

"f. agitating the slurry for a time not less than 4 minutes wherein heat energy created in the slurry is equivalent to not less than about 0.25 calories per gram of water per minute,

g. diluting the slurry to a pump density of about to about 35 percent solids,

h. passing the slurry to froth-flotation cells,

i. bubbling air upwardly through the slurry for a time to selectively float substantially all. the carbon particles in a froth formed atop the slurry, while substantially all the iron oxide particles and gangue particles remain suspended in the slurry, and

j. removing the carbon particles as a float product and the iron oxide particles and gangue particles as a sink product from the froth-flotation cells.

8. The method of claim 7 in which the flotation agent added in step (e) is No. 2 fuel oil.

9. The method of claim 7 in which the frothing agent added in step (e) is methylisobutylcarbinol.

10. The method of claim 8 in which the frothing agent added in step (e) is methylisobutylcarbinol.

11. Improved method for treating wet blast furnace flue dusts by froth-flotation to separate substantially all the carbon particles from iron oxide particles and gangue particles contained therein, said carbon particles being removed in a froth as afloat product and said iron oxide particles and gangue particles being removed as a sink product containing about 0.75 to about 5 percent carbon, said method comprising:

a. forming a slurry of water and wet blast furnace flue dusts having a pump density of about 50 to about percent solids,

b. adding at least one flotation agent taken from the group consisting of No. 2 fuel oil and kerosene, and at least one frothing agent taken from the group consisting of methylisobutylcarbinol and pine oil, to the slurry,

c. agitatin the slurry for a time not less than 4 minutes wherein a heat energy created in the slurry is equivalent to not less than 0.25 calories per gram of water per minute,

(1. diluting theslurry to a pump density of about 10 to about 35 percent solids,

e. passing the slurry to froth-flotation cells,

f. bubbling air upwardly through the slurry for a time to selectively float substantially all the carbon particles in the slurry to the froth formed atop the slurry while substantially all the iron oxide particles and gangue particles remain suspended in the slurry, and

g. removing substantially all the carbon particles as a float product and substantially allthe iron oxide particles and gangue particles as a sink product.

12. The method of claim 11 in which the flotation agent added in step (b) is No. 2 fuel oil.

13. The method of claim 11 in which the frothing agent added in step (b) is methylisobutylcarbinol.

14. The method of claim 12 in which the frothing agent added in step (b) is methylisobutylcarbinol.

Claims

2. The method of claim 1 in which the flotation agent added to the slurry in step (c) is No. 2 fuel oil.
3. The method of claim 1 in which the frothing agent added to the slurry in step (c) is methylisobutylcarbinol.
4. The method of claim 2 in which the frothing agent added to the slurry in step (c) is methylisobutylcarbinol.
5. The method of claim 1 in which the heat energy formed when a volume of water equal to a volume of slurry is agitated in step (d) is not less than about 0.25 calories per gram of water per minute.
6. The method of claim 1 in which the flotation agent of setp (c) is No. 2 fuel oil, the frothing agent of step (c) is methylisobutylcarbinol, the time of agitation of step (d) is not less than 4 minutes and the heat energy formed in step (d) is not less than 0.25 calories per gram of water per minute.
7. Improved method for treating dry blast furnace flue dusts by froth-flotation to separate substantially all the carbon particles from iron oxide particles and gangue particles contained therein, said carbon particles being removed as a float product and said iron oxide particles and gangue particles being removed as a sink product containing not more than 5 percent carbon, said method comprising: a. screening the dry blast furnace flue dust to obtain a particle size separation at 28 mesh, b. grinding the particles larger than 28 mesh to a size smaller than 28 mesh, c. mixing the particles smaller than 28 mesh of step (a) and of step (b), d. forming a slurry of the particles of step (c) and water, said slurry having a pump density of about 50 percent to about 70 percent solids, e. adding at least one flotation agent taken from the group consisting of No. 2 fuel oil and kerosene, and at least one frothing agent taken from the group consisting of methylisobutylcarbinol and pine oil, to the slurry, f. agitating the slurry for a time not less than 4 minutes wherein heat energy created in the slurry is equivalent to not less than about 0.25 calories per gram of water per minute, g. diluting the slurry to a pump density of about 10 to about 35 percent solids, h. passing the slurry to froth-flotation cells, i. bubbling air upwardly through the slurry for a time to selectively float substantially all the carbon particles in a froth formed atop the slurry, while substantially all the iron oxide particles and gangue particles remain suspended in the slurry, and j. removing the carbon particles as a float product and the iron oxide particles and gangue particles as a sink product from the froth-flotation cells.
8. The method of claim 7 in which the flotation agent added in step (e) is No. 2 fuel oil.
9. The method of claim 7 in which the frothing agent added in step (e) is methylisobutylcarbinol.
10. The method of claim 8 in which the frothing agent added in step (e) is methylisobutylcarbinol.
11. Improved method for treating wet blast furnace flue dusts by froth-flotation to separate substantially all the carbon particles from iron oxide particles and gangue particles contained therein, said carbon particles being removed in a froth as a float product and said iron oxide particles and gangue particles being removed as a sink product containing about 0.75 to about 5 percent carbon, said method comprising: a. forming a slurry of water and wet blast furnace flue dusts having a pump density of about 50 to about 70 percent solids, b. adding at least one flotation agent taken from the group consisting of No. 2 fuel oil and kerosene, and at least one frothing agent taken from the group consisting of methylisobutylcarbinol and pine oil, to the slurry, c. agitatin the slurry for a time not less than 4 minutes wherein a heat energy created in the slurry is equivalent to not less than 0.25 calories per gram of water per minute, d. diluting the slurry to a pump density of about 10 to about 35 percent solids, e. passing the slurry to froth-flotation cells, f. bubbling air upwardly through the slurry for a time to selectively float substantially all the carbon particles in the slurry to the froth formed atop the slurry while substantially all the iron oxide particles and gangue particles remain suspended in the slurry, and g. removing substantially all the carbon particles as a float product and substantially all the iron oxide particles and gangue particles as a sink product.
12. The method of claim 11 in which the flotation agent added in step (b) is No. 2 fuel oil.
13. The method of claim 11 in which the frothing agent added in step (b) is methylisobutylcarbinol.
14. The method of claim 12 in which the frothing agent added in step (b) is methylisobutylcarbinol.