Title of Invention

METHOD FOR RECOVERING METALLIC CHROMIUM FROM SLAGS WHICH CONTAIN CHROMIUM OXIDE

Abstract The invention relates to a method for recovering metallic chromium from slag containing chromium oxide, from converter processes such as AOD, MRP, AOD-L, MRP-L, CLU, ASM, Conarc stainless steel or vacuum processes such as VOD, SS-VOD, RH and RH with lance. The slag produced at the end of a blasting or treatment process in a converter or a vacuum installation is tapped or drawn off unreduced. This slag is then charged into an electric furnace, which is also charged with a usual charge consisting of scrap and optionally, residual dust. Carbon and optionally, silicon are added. During the melting process, the chromium oxide contained in the slag is directly reduced to metallic chromium by the carbon and the silicon.
Full Text Method for recovering metallic chromium from slags which contain chromium oxide
The invention relates to a method for recovering metallic chromium from slags which contain chromium oxide.
In the conventional converter processes, such as the AOD, MRP, AOD-L, MRP-L, CLU, ASM, Conarc stainless steel or vacuum processes, such as VOD, SS-VOD, RH, RH with lanze, the basic decarburization reaction is carried out in a multiple substance system, the reduction of the chromium oxide using the carbon representing the basic mechanism.
After the primary oxidation of the chromium, which occurs in a high concentration in stainless steels, the carbon which is dissolved in the melt causes the chromium to be reduced at the bubbling surface and in what is known as the impingement area. The product of the reduction, namely the metallic chromium, is returned to the melt, and the carbon monoxide, after diffusion into the bubbles, is discharged into the gas atmosphere above the melt.
The chemical sequence of reactions is as follows:
{O2} = 2 [0] Dissociation (1)
[C] + [0] = {CO} Direct decarburization (2)
2[Cr] + 3[0] = (Cr203) Chromium oxidation (3)

The reactions proceed under the following thermodynamic equilibrium

where p = a parameter.
On account of the incomplete reduction of chromium during the decarburization, a partial quantity of the chromium oxide passes into the slag in the form of various i spinels. The reduction effect becomes increasingly weak as the decarburization progresses, since the amount of the reducing element carbon decreases over the course of time. The economic viability of the process is based on recovering a chromium which is bonded in this way. For this purpose, the reduction of the slag using high-affinity silicon in the form of FeSi is normally carried out at the end of the decarburization and of the oxygen blowing operation.
The invention is based on the object of providing a more simple and therefore more economical method for this purpose.
This object is achieved by the fact that the slag which is produced at the end of a blowing or treatment operation in a converter or a vacuum installation is tapped or drawn off in unreduced form,

that this slag is charged into an electric furnace, which is also charged with a standard charge of scrap and, if appropriate, dust residues,
that carbon and, if appropriate, silicon are additionally added, and
that during the melting process, the chromium oxide contained in the added slag is directly reduced to metallic chromium by the carbon and the silicon.
The conventional slag reduction step is omitted. The slag, which is highly saturated with chromium oxide and manganese iron oxide and is present, for example, after an oxygen blowing operation, is removed from the metal, i.e. is tapped or drawn off from the ladle, in unreduced form and is charged into the upstream electric furnace. The slag is directly reduced by an addition of carbon and silicon from the scrap which is usually present in the electric furnace, if appropriate together with dust residues. In this way, the chromium oxide is reduced in the electric furnace instead of in one of the downstream installations, and the metallic chromium is thereby recovered.
The reduction reaction proceeds in accordance with the following equation:
2 (Cr203)+3[Si]=4 [Cr]+3(Si02) (6)
In the electric furnace, direct reduction of the chromium oxide by means of the carbon and defined quantities

of the silicon takes place under the atmospheric conditions, this reaction proceeding as follows:
(Cr203)+ 3 [C]=2[Cr]+3{CO} (7)
or with silicon
2 (Cr203)+3[Si]=4[Cr]+3(Si02) (8)
The flow of the slag back into the electric furnace can take place immediately after each treatment or as a cumulative quantity from a number of different treatments.
Depending on the overall technology, this operation can be optimized in terms of cost and energy. It is of no importance for the method whether the slag is in a solid, liquid or intermediate state. This only affects the melting time required in the electric furnace.
Overall, this procedure results in the following economic and technological advantages:
shortening of the overall treatment time of the melt to 15-20 min, depending on the type of technology
reduction in the consumption of FeSi
reduction in the consumption of slag-forming agents
high yields of metal
increased service life of the refractory material
increased service life of the nozzles and plugs
improved energy balance of the converter or the vacuum installation
improved purity of the metal

elimination or considerable reduction of protective slag zones in converters and ladles
The sequence can be seen once again from the method diagram illustrated in the figures, in which figure 1 represents a three-stage method sequence while figures 2 and 3 show a two-stage solution.


WE CLAIM:
1. A method for recovering metallic chromium from a slag containing chromium oxide in a steelmaking system having an electric furnace and at least one of a converter and a vacuum device, the slag being produced by one of a blowing and treatment operation in the at least one of the converter and the vacuum device, said method comprising:
(a) performing a steelmaking process including forming molten steel in the electric arc furnace, transferring the molten steel to that at least one of a converter and a vacuum device, and performing at least one of a blowing and treatment operation in the at least one of a converter and a vacuum device which forms a slag containing chromium oxide;
(b) drawing off the slag from the at least one of the converter and the vacuum device of the steelmaking system after the one of a blowing and treatment operation;
(c) charging the drawn off slag into the electric furnace of the
steelmaking system, wherein the electric furnace further has a charge of scrap;
(d) adding carbon to the drawn off slag and the charge of scrap in the
electric furnace; and

(e) melting the drawn off slag and scrap in the electric furnace with the carbon so that the chromium oxide is reduced to metallic chromium by the carbon.
2. The method as claimed in claim 1, wherein the steelmaking system
comprises a converter and a vacuum device and said step (b) comprises drawing
off the slag from both the converter and the vacuum device.
3. The method as claimed in claim 1, wherein said electric furnace further
has dust residues in said step (c) so that the drawn off slag is added to the charge
of scrap and the dust residues.
4. The method as claimed in claim 1, wherein said step (d) further
comprises adding silicon to the drawn off slag and the charge of scrap and
wherein the chromium oxide is reduced to metallic chromium by the carbon and
silicon in said step (e).

Documents:

in-pct-2001-1798-che abstract.pdf

in-pct-2001-1798-che claims-duplicate.pdf

in-pct-2001-1798-che claims.pdf

in-pct-2001-1798-che correspondence-others.pdf

in-pct-2001-1798-che correspondence-po.pdf

in-pct-2001-1798-che description(complete)-duplicate.pdf

in-pct-2001-1798-che description(complete).pdf

in-pct-2001-1798-che drawings-duplicate.pdf

in-pct-2001-1798-che drawings.pdf

in-pct-2001-1798-che form-1.pdf

in-pct-2001-1798-che form-19.pdf

in-pct-2001-1798-che form-26.pdf

in-pct-2001-1798-che form-3.pdf

in-pct-2001-1798-che form-5.pdf

in-pct-2001-1798-che others.pdf

in-pct-2001-1798-che pct.pdf

in-pct-2001-1798-che petition.pdf


Patent Number 215975
Indian Patent Application Number IN/PCT/2001/1798/CHE
PG Journal Number 13/2008
Publication Date 31-Mar-2008
Grant Date 05-Mar-2008
Date of Filing 21-Dec-2001
Name of Patentee SMS DEMAG AG
Applicant Address Eduard-Schloemann-Strasse 4, D-40237 Dusseldorf,
Inventors:
# Inventor's Name Inventor's Address
1 GOTZINGER, Karl, Reiner Kurt-Schumacher-Allee 25, D-47445 Repelen,
2 REICHEL, Jan Bockumer Strasse 368, D-40489 Düsseldorf,
PCT International Classification Number C21C 7/068
PCT International Application Number PCT/DE00/02030
PCT International Filing date 2000-06-23
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 199 29 551.4 1999-06-23 Germany