United States Patent [19]
Stephens, Jr. et at
[11]
[45]
4,396,423
Aug. 2, 1983
FOREIGN PATENT DOCUMENTS
20 Claims, 1 Drawing Figure
4,053,301 10/1977 Stephens, Jr 75/11
4,071,357 1/1978 Peters 75/103
4,256,496 3/1981 Brandstatter 106/43
2212351 3/1974 Fed. Rep. of Germany .
Primary Examiner-L. Dewayne Rutledge
Assistant Examiner-Christopher W. Brody
[57] ABSTRACT
The object of the invention is to provide a process for
the recovery of iron and zinc from steel making flue
dust.
The process comprises subjecting the flue dust to a
carbiding step in a fluid bed in the presence of a reducing
agent and a carbon supplying agent to break down
the zinc ferrite structure and convert the iron to iron
carbide, followed by heating the residue or product of
the carbiding step to recover zinc by evaporization.
, The iron carbide produced may be introduced into a
steel making furnace for the production of steel.
An alternative procedure is the recovery of iron carbide
and zinc by magnetic separation !from the gangue after
the carbiding step and before separation of zinc from
iron carbide.
[54] PROCESS FOR RECOVERING IRON AND
ZINC FROM STEEL MAKING DUSTS
[76] Inventors: Frank M. Stephens, Jr., 12225 W.
18th Dr., Lakewood, Colo. 80215;
James C. Blair, 3255 Moore Ct.,
Wheat Ridge, Colo. 80033
[21] AppI. No.: 275,799
[22] Filed: Jun. 22, 1981
[51] Int. CI.3 C22B 19/30; C21B 15/00
[52] U.S. CI. 75/25; 75/26;
75/88; 75/69; 75/71; 75/77; 75/85; 75/11;
423/148
[58] Field of Search 75/25, 26, 21, 88, 69,
75/71, 85, 11; 423/107, 148, 138
[56] References Cited
U.S. PATENT DOCUMENTS
1,780,323 11/1930 Waring 423/105
1,879,834 9/1932 Waring 75/109
2,774,662 12/1956 Graham et al. 75/26
3,262,771 7/1966 Ban 75/11
3,754,890 8/1973 Fitch 75/3
3,756,804 9/1973 Stevenson 75/25
3,770,416 11/1973 Goske1 75/25
3,785,802 1/1974 Roberti et al. 75/26
3,849,121 11/1974 Burrows 75/103
3,896,211 7/1975 Mayor el al. 423/138
3,999,981 12/1976 Brandstatter 75/84
STEELMAKING DUST ,__J _
I I
BINDER - - ---iO-J PELLETIZING I
I- JI
-,
-..I_-- l
AGNETIC I
PARATION I
-T---..J
I
I
...
GANGUE
EAT !
2
FLU I DIZED -BED
CARBON CARBURIZATION
CONTAINING
GAS -----------
r--
HEAT ZINC __ £'l:!C__J M
01 STI LLAT ION IRON I SE
CARBIDE L __
IAON LABIO'
~ ZINC PRODUCT
CONDENSATION
H
H
ZINC PRODUCT
u.s. Patent' Aug. 2, 1983 4,396,423
STEELMAKING DUST
r---J---_ I I
BINDER - - --+oj PELLETIZING I
. I
'- J
HEAT------,
CARBON
CONTAINING
GAS
FLU IDIZED -BED
CARBURIZATION
HEAT--1001
f-------- ----..,
r---:t--- l
ZINC r-- ZINC I MAGNETIC I
DISTILLATION TRON- -1 SEPARATION I
CARBIDE L - __ T ...J
I
,I
IRON CARBIDE GANGUE
ZINC PRODUCT
CONDENSATION
ZINC PRODUCT
1.
4,396;423
2
73
0.13
3.0
Percent
Percent
Material
Material
Material Percent
Fe 56.7
Zn 4.78
Si02 2.47
AI203 0.8
C 0.14
Fe
Zn
C
The product or residue from the carbide conversion
step was placed on a" tube furnace using a nitrogen
sweep gas to provide an inert atmosphere. The furnace
temperature was raised to 1800° F. and held for 120
minutes during which time, the zinc was vaporized as
metallic zinc which condenses at the cold end of the
furnace combustion tube.
After cooling, the residue was removed from the
furnace and analyzed. This material had the following
composition:
A magnetic separation test was run on a portion of
the fluidized-bed carbide product or residue to determine
the feasibility of this method of separation of zinc
and iron carbide from the gangue. The following results
were obtained:
EXAMPLE 1
The feed material of typical BOF dust had the following
chemical analysis:
The oven-dried pellets were transferred to a 4-inch
diameter fluidized-bed reactor where the iron-beafing
materials were converted toironcarbide using a temperature
of 1120° F. and a balanced mixture of carbon
monoxide, carbon dioxides, water vapor and methaneas
.a fluidizing gas. After eight hours of treatment, the
reactor was cooled off and the treated product dis~
charged.
Although there was some degradation of the pellets,
in general the product remained as pelletized material.
This product had the following analysis:
and steel making steps of the patent. This includes the
carbiding temperatures, reducing and carbiding materials,
ratios of additives, as well as the conditions and
features associated with the steel making step.
5 In the examples which follow the flue dust feed material
was first pelletized for the carbiding step into oneeighth
inch diameter miniballs on a 24-inch laboratory
balling disc using conventional binders, such as benton-
IO ite and one percent dextrose, followed by oven dryil'lg
at 230° F. The invention is not restricted to the pelletizing
step.
20
PROCESS FOR RECOVERiNG IRON AND ZINC
FROM STEEL MAKING DUSTS
DESCRIPTION
DISCLOSURE OF INVENTION
In accordance with the present invention the' flue 35
dust containing iron and zinc, including zinc ferrite, is
subjected to a carbiding step in a fluid bed in the presence
of a reducing agent and a carbon supplying agent
to disrupt the zinc ferrite structure, and convert the iron
to iron carbide in accordance with the teaching of U.S. 40
Pat. No. 4,053,301, followed by recovering the zinc by -----------'-----------'----
distillation after the carbiding step. The remaining iron Fe 64
carbide is in a condition without further refining for ~n ~:~~
introduction into a steel making furnace to produce
steel in accordance with the process of U.S. Pat. No. 45
4,053,301.
The process has the advantage that large recoveries
of relatively pure zinc are made and the ironcarbide
produced is suitable for use in steel making furnaces.
Further, it eliminates the problem of disposing of zinc 50
ferrite in a manner to comply with environmental regulations.
BRIEF DESCRIPTION OF THE DRAWING
The single drawing is a flowsheet of the process of
the invention. . 55
BEST MODE OF CARRYING OUTTHE
INVENTION
The term "flue dust" as used herein includes materials
containing iron and other metals which are readilly 60
separated from iron carbide, such as, zinc, lead, cadmium
and others normally associated with flue dust
from steel making.
Because of the fine particle size of the steel making
flue dust, it is preferable to pelletize the starting material 65
before the carbiding step, although this is not required.
The disclosure of U.S. Pat. No. 4,053,301 is incorporated
herein by reference, including both the carbiding
1. Technical Field
The invention relates to the metallurgy of iron and
zjnc and particularly to the recovery of these metals
from flue dust from furnaces used in the steel making
industry.
The problem of economically recovering valuable
metals, such as, iron and zinc from steel making flue
dusts has received attention for some time in the industry.
Part of the problem stems from the difficulty df
separating these metals from each other because much 15
of the zinc is combined with the iron as zinc ferrite. It is
desirable to recover the iron in a condition, which permits
its use in steel making furnaces without further
refining.
2. Background Art
U.S. Pat. Nos. 1,780,323, 1,879,834; 3,849,121; and
4,071,357 as well as German Pat. No. 2,212,351 (ClC22b)
3/21/74 all relate to the recovery of zinc from
flue dust and similar materials. All of the disclosed processes
arehydrometallurgical processes typically in- 25
cluding a leaching, step with ammonium carbonate.
Most ofthese patents are directed towards the recovery
of zinc and other nonferrous metals and do not recover
the iron in a form suitable for reuse in steel making.
Complete recovery of zinc is not obtained. N0l'le of the 30
patents disclose a process for disrupting a zinc ferrite
structure and recovering zinc and iron therefrom.
3
4,396,423
4
-continued
15
The material was carbided and dezinced as· in Example
1, the results being summarized in the following
table.
After removal of the gangue constituents, the final
dezinced product was suitable as a steel making feed for
the process of U.S. Pat. No. 4,053,301.
EXAMPLE 4
Material
0.8
1.9
0.8
%C
5.5
4.5
0.D7
% Pb
0.16
Percent
5.2
6.22
12.2
% Si02
26.4 23.3
32.9 25.3
54.7 0.34
% Fe % Zn
S
Head Sample
Carbide Product
Dezinced Product
Distribution
Wt% Fe% Zn % Fe% Zn %
Magnetic Fraction 80.2 72.2 4.5 89.5 73 5
Nonmagnetic Fraction 19.8 34.2 6.8 10.5 27
Calculated Head 64.7 5.0
A second feed material of BOF dust had the following
chemical analysis:
Processing of the magnetic concentrate from this test
through the zinc distillation step produces a final iron 10
product assaying over 80 percent iron and less than 0.1
percent zinc. Such material is suitable for use as feed to
a steel making furnace in accordance with the procedure
of U.S. Pat. No. 4,053,301.
EXAMPLE 2
___________________ 20
Material Percent
Fe 54.4
Zn 6.5
Si02 1.2
C 0.3 25
Material Percent
Fe 66.8
Zn 8.06
Si02 1.58 35
Ca 4.86
Mg 1.30
C 5.8
The. material was pelletized and carbided following
the procedures of Example 1, the carbided product
having the following chemical analysis:
Comparative tests were made for zinc extraction on
the same feed material using the present process and a
conventional ammonium carbonate leach zinc recovery
process.
For one test, the carbiding and dezincing steps of
Example 1 were used for applying the present process
to the feed material.
The conditions for the ammonium carbonate leach
30 comparative test were as follows:
Feed: 50 grams
Leach Solution: 192 ml. (90 2/3NH3i 803/2 C02)
% Solids: 20%
Time: 3 hours
Temperature: Ambient
The comparative results obtained are summarized in
the following table.
% Zn
Feed Residue Ex-
G % Zn g % Zn Filtrate tracted
50.0 55.5 30.2 35.2 Yellow & 61.7
Opaque
50.0 42.2 48.5 40.8 Clear & 6.2
Colorless
2. Head
1. Present
Material Percent Process
Fe 82.5
Zn 0.07
Si02 2.20
Ca 5.45
Mg 1.55
C 2.1
Material Percent
Fe 26.4
Zn 23.2
Si02 5.2 65
C 0.8
Mg 1.8
Ca 2.2
Al 0.3
Recovery of zinc using the procedure of Example 1 40
resulted in a product or residue having the following
composition:
The product was suitable feed material for making
steel as disclosed in U.S. Pat. No. 4,053,301.
EXAMPLE 3
The feed material produced by roasting a high ironzinc
ore had the following composition. The high temperature
roasting step had converted part of the zinc
and iron to zinc ferrite.
50 From the results of Example 4 it is obvious that the
--------------------- carbiding step had altered the zinc ferrite to make the
zinc available to other recovery processes, such as ammonia
leaching.
The process is not limited to the recovery of zinc
55 from zinc ferrite, but includes the recovery of zinc and
other metals melting above 750· C. which accompany
iron in ores and other materials. Other metals than zinc
occurring with iron which are recoverable by the process
are antimony, cadmium, lead and tin. These metals
60 are all recoverable from the iron carbide residue by
distillation.
We claim:
1. A process for the recovery of zinc and iron carbide
from a material containing zinc and iron which comprises:
(a) first subjecting the material to a carbiding step to
convert a major portion of the iron to iron carbide,
and
4,396,423
5
(b) subsequently recovering zinc from the product of
step (a) leaving a residue containing substantially
all the iron carbide.
2. The process of claim 1 in which in step (a) the
carbiding step is performed in a fluid bed in the presence 5
of a reducing agent and a carbon supplying agc;:nt to
convert the iron to iron carbide.
3. The process of claim 1 in which steel is made from
the dezinced iron carbide produced in claim'1.
4. The process of claim 1 in which the mixture is flue 10
dust.
5. The process of claim 1 in which in step (a) iron
carbide and zinc are separated from the gangue of the
product by magnetic separation prior to recovery of
zinc in step (b). 15
6. The process of claim l in which in step (b) zinc is
recovered by distillation.
7. The process of claim 2 in which the iron is converted
to iron carbide in a fluidized bed with a mixture 20
of hydrogren and a carbon containing material which
provides carbon for the iron carbide.
8. The process of claim 7 in which the carbon containing
material is carbon monoxide and hydrogen is
present in an amount over 60% by volume of the carbon 25
monoxide present.
9. The process of claim 7 in which the ratio of hydrogen
to formed water in the reaction medium of the
fluidized bed ismaintained from about 2.5 to I to about
8 to 1 andthe ratio ofCO/C02 is maintained from about 30
1 to 1 to about 4 to 1, the prescribed CO/C02hydrogen/
H20 rations being essentially in equilibrium
with methane.
10. The process of claim 7 in which the carbon containing
material is solid carbon. 35
11. The process of claim 7 in which the carbon con,
taining material is a lower alkyl hydrocarbon gas.
12. The process of claim 11 in which the ga~.is propane.
13. The process of claim 7 in which the temperature 40
of the mixture is between about 1100· F. and about
1300· F.
14. A process for the recovery of iron and zinc from
flue dust which comprises:
6
(a) subjecting' the flue dust toa carbidizing step in a
fluidized bed in the presence of a reducing agent
and a carbon supplying agent to convert a major
portion of the iron to iron carbide;
(b) heating the carbidized mixture of step (a) to recover
the zinc by vaporization; and
(c) making steel from the product resulting from step
(b).
is. A process for the recovery of iron carbide and a
metal having a vaporization point above about 1300· F.
from a mixture of iron and the metal which comprises:
(a) subjecting the mixture to a carbidizing step to
convert a major portion of the iron in the mixture
to iron carbide; and
(b) recovering iron carbide aI1ld said metal from the
product of step (a).
16. The process of claim 15 in which said metal is a
member selected from the group consisting of antimony,
cadmium, lead, tin and zinc.
17. The process of claim 16 in which said metal is
zinc.
18. A process for the recovery of iron and zinc from
zinc ferrite, the recovered iron being suitable for making
stc;:el without further refining, the process comprising:
(a) breaking down the ferrite structure and converting
the iron to iron carbide by heating the ferrite in
a fluidized bed in the presence of a reducing agent
and a carbon supplying material to a temperature
not in excess of about 750· C., and
(b) separating zinc from the residue of step (a) by
distillation to leave an iron carbide product which
is suitable for making steel without refining.
19. The process of claim 18 in which the zinc ferrite
is contained in flue dust.
20. A process for the recovery of zinc and iron carbide
from a material containing zinc and iron which
comprises:
(a) subjecting the mixture to a carbiding step to convert
the iron to iron carbide;
(b) separating the iron carbide and zinc from the
gangue of the product by magnetic separation; and
(c) recovering zinc from the product of step (b).
* * * * *
45
50
55
60
65