MXPA99003719A - METHOD OF DE-CHROMING AND/OR DEPLETING THE MgO CONTENT OF STEEL SLAG - Google Patents

Abstract

The invention concerns a method of de-chroming steel slag, oxygen being introduced into the liquid steel slag in an amount sufficient to convert iron quantitatively into iron oxide and at least 5 wt%of the iron oxide present in the slag into iron-III oxide. The resultant oxidized slag is hardened and comminuted, the paramagnetic portions formed then being separated magnetically and dissociated from the de-chromed slag.

Description

Process for removing the chromium and / or depleting the MgO content in the steel slag The invention relates to a process for removing the chromium and / or depleting the MgO content of the steel slag. The use of slags as starting products or fluxes in the production of cement has been proposed on several occasions. For example, it is known from United States Patent No. 4,174,974 to react coal slag in the solid state with mineral substances and, in particular, calcium oxide, calcium hydroxide or calcium carbonate, with the aim of produce clinker or cement in this way. In the same U.S. Patent No. 4,174,974, the use of blast furnace slag for comparable purposes is described. Also, the slag mixture has been suggested in a rotary tubular furnace loaded with kaolin, bauxite and lime. The extensive use of steel slags as fluxes in the production of clinker or cement, as a rule, generates a conflict with the high content of different iron metals that contain these slags. With the increase in the use of fragments as a precursor for the production of steel, the portion of alloy metals in the steel slag rises. In particular, the high chromium content largely excludes the use of these slag as raw material or flux. Due to the high toxicity of CrVI salts, only slight amounts of CrVI can be tolerated in the building materials. Another disadvantage of the use of steel slag as a flux in the production of clinker and cement consists in the high content of MgO usually present, which can vary between 10 to 15% by weight of the slag. In the hydration of cement, the MgO is converted into Mg (OH) 2 (brucite), so that the compression force is seriously reduced in relation to the volume of expansion. For this reason, it is usually anticipated that the MgO content in the clinker should not exceed 6% by weight. Therefore, the invention seeks to remove the chromium from the steel slags and / or reduce the MgO content in a simple form, which makes them suitable for use in the production of cement clinker in a simple manner. To achieve this objective, the process of the invention essentially consists in that oxygen is introduced into the liquid steel slag in an amount sufficient to "quantitatively convert the iron to iron oxide and at least 5% by weight of the oxide of the iron. iron contained in the slag iron oxide III is converted, this obtained oxidized slag solidifies and disintegrates, whereby the paramagnetic portions formed ("magnetite, Fe304) are magnetically isolated and separated from the slag without chromium.

By immediately refining the liquid steel slag, by the introduction of oxygen, the residual iron contained in the steel slag is oxidized quantitatively, so that disintegration can be carried out without risk, for example, by granulation in water or using steam Due to the fact that not only the remaining iron is oxidized and forms iron oxide, but iron oxide present in the steel slag as iron oxide III is additionally converted to iron oxide III at least partially, it forms a spinel phase, in which chromium is incorporated almost quantitatively during crystallization. Thus, during the solidification of this derived, partially oxidized steel slag in iron III, a minimum defined portion of magnetite is formed, in whose spinel structure chrome is incorporated quantitatively. On the basis of its paramagnetic properties, the iron oxide III can be separated magnetically, after disintegration, so that a slag of chromium-free steel and free-form iron is obtained after the magnetic separation. Surprisingly, it was found that if in addition to Cr 03 MgO is also incorporated in magnetite to a high degree, so that the MgO content can be substantially reduced at the same time by the magnetic separation of magnetite. In the case of the slags containing vanadium oxide, it was found that vanadium is incorporated in the spinel structure in a sufficiently quantitative quantity so that it affects the enrichment, thus allowing an economic recovery. This chromium-free, purified, derivatized slag is suitable as a filler for the production of clinker without fearing a very high chromium content in the clinker or in the cement produced from it. Advantageously, the process according to the invention is carried out in such a way that the oxygen is blown in the liquid slag in the form of air and / or pure oxygen. After this liquid slag is charged, the purification step can be carried out directly in steel work, followed by the production of steel, while obtaining, simultaneously, a phase of spinel suitable as an initial product for the production of ferrocro or. According to a further preferred development of the process according to the invention, the procedure is carried out in such a way that the oxidation is carried out until the formation of a Fe304 content of the slag with a variation that is between 5 and 20% by weight. Therefore, it is ensured that the chromium can be separated magnetically, since it is incorporated quantitatively into the spinel structure of the magnetite. Without forgetting the fact that the iron-free product is obtained by refining the steel slag with oxygen or air, the slag can be granulated with water and / or steam after oxidation, without any risk, as corresponds with the preferred embodiment of the process according to the invention. In this case, metallic iron can include the risk of oxyhydrogen gas formation and run the risk of explosions. - In order to ensure that the chromium is dissolved quantitatively in the spinel phase, the process according to the invention is advantageously carried out so that the basicity of the steel slag is maintained at higher CaO / SiO values to 2.5, As a rule, the steel slags have a basicity that varies from 2.5 to 4.8, the CrVI almost does not dissolve in the calcium-silicate phase with a basicity greater than 2.5 and preferably is recovered in the spinel crystals. Due to the strong enrichment of the chromium in the spinel phase of paramagnetic magnetite, this phase is preferably used as raw material for the reduction of chromium after the magnetic separation. The removal of chromium from steel slag is suitable, in particular, for use in rotating tubular kilns for the production of cement clinker. The usual steel slag compositions can be taken from the table below, where the numerical data are "indicated in% by weight and the balance up to 100% by weight is constituted by undetermined impurities.

Sample 1 2 3 4 5- 6 Average Si02 14.92 13.80 13.26 13.26 14.44 13.91 13.93 A1203 7.37 7.01 6.51 6.21 7.70 6.51 6.89 FeO 25.31 25.31 27.02 26.94 25.95 26.09 26.10 CaO 34.10 37.07 37.07 32.18 3Í.28 34.77 34.91 MgO 6.54 7.54 7.33 6.75 7.38 6.41 6.99 S03 0.23 0.26"- 0.11 0.06 0.19 0.08" 0.17 Cr203 1.27 1.19 1.22 1.2TJ 1.07 1.01 1.16 Mn203 7.00 6.63 6.17 6.54 6_62_ 6 ^ 54 -6.58 Na20 0.13 0.12 0.10 0.17 0.14 0.07 J3.12 K20 0.02 0.02 0.02 0.03 0.02 0.01 13.02 ZnO 0.07 0.13 0.02 0.02 0.02 0.01 005 SrO 0.04 0.04 0.02 0.04 0.04 0.04 004 From the usual compositions of the steel slag, it can easily be seen that the average Cr203 content of 1.16% by weight only allows the use of slight amounts of steel slag in conventional clinker production. By carrying out the process according to the invention, the content of Cr203 can be reduced to values well below the CrVI content tolerated for the clinker that is produced from this prior matter. In the process according to the invention, the oxidized chromium is incorporated quantitatively into the magnetite and is not soluble in the mineral phase of the slag.

In order to carry out the magnetic separation, it is advantageous to properly disintegrate the slag, in principle the mechanical disintegration is sufficient until obtaining particles with a size smaller than 5 cm. Thus, the sifted product of this disintegrated oxidized slag is immediately separated into a chromium-rich phase and a chromium-free phase by magnetic separation. Thus, the slag produced has good hydraulic properties and can replace the clinker portion in the mixed cement up to 35% without losing quality. Example 1: The aggregate process served as a typical secondary metallurgical pouring ladle in which oxygen is injected by means of the lower porous bricks of deslagging. The combustion of the total heat of iron or iron oxide II that occurs is sufficient to compensate the thermal loss of the "fusion with the spoon for refining" (radiation, convection). If refining is not carried out exclusively by means of air, energy can be added in the form of fuel. It is also possible to use mixtures of air and 02. In this case, the refining is carried out with the help of pure oxygen technically.

Analysis of slag LD Component Portion (%) Si02 13 A1203 6 FeO 26 CaO 34 MgO 4 S03 0.2 Cr203 2 MnO 7 Na20 0.1 K20 0.5 (Fe) found 7 Usual balance of impurities Oxygen is blown into the liquid steel slag, very hot, 1580 ° C, through the inferior bricks of deslagging. Oxygen reacts rapidly and quantitatively with iron species. The oxygen balance for 1 ton of steel slag: In order to oxidize the 70 kg of (Fe) found in the LD slag, 90 kg is required. of FeO, 20 kg. of 02. Thus, the Feo content of the slag Ld reaches up to about 35%. In addition, 10% or 35 kg. of FeO is oxidized up to 33 kg. Fe203 for the help of 4 kg. of 02.

These 39 kg. of Fe203 reacts with 18 kg. of FeO to form 57 kg. of Fe304 (magnetite). Chromium is incorporated in that magnetite in the form of spinels practically quantitatively (mixed spinel, FeCr204 x Fe304). The spinel already separated from the molten slag and, in part, can be easily removed from the molten slag by sedimentation. The quantitative spinel composition is shown in the following table: Component Portion (%) Fe 53 Cr 17 O (oxygen) 30 After solidification and disintegration, the spinel fraction separates magnetically. The spinel constitutes a high amount of chromium and can be converted into high grade ferrochrome (carbide) by conventional reduction. After this, more advantageously, the remainder of the molten slag can be steam granulated, having an additional chromium content of about 500 ppm Cr (in the agnetira residue which has not been pelleted). This material already has good hydraulic properties. Example 2 In the analogous form, the slag has the following refined analysis: Analysis (%) Si02 9.5 CaO 44.6 MgO 7.4 A1203 0.6 MnO 6.7 Ti02 0.3 Cr203 1.4 S03 0.2 Na20 0.1 FeO 28.7 Total 99.5 Balance of usual impurities This slag was practically free from metallic and highly liquid iron at 1480 ° C. The oxygen is fed from the bottom of the slag bath causing an intense firmness of the slag due to the formation of magnetite (spinel). The magnetite (spinel) was magnetically removed from the cooled oxygen. The magnetite served to enrich the MnO, MgO, A1203, Cr203, FeO / Fe203.

The "mineral phase", which constitutes a materail load for the cement industry, which has the following composition: Mineral Phase (%) Si02 13 CaO 72 FeO 9 The balance consisted of MgO (<2%), MnO traces , Ti02, Cr203 (< 500 ppm), S02, Na20. The spinnel formed was composed as follows: Espinel Mg 12% by weight Al 1% by weight Mn 14% by weight Cr 3% by weight Fe 42% by weight O 28% by weight? N the case of vanadium is incorporated from the slag in the spinel, it can be recovered in the conventional manner by a carbon-free reduction, for example by reduction with aluminum, an enrichment of about 3% by weight in the spinel with the normal steel slags has been observed. In this case, the fusion with spoon must not be carried out by means of N2 with the objective of avoiding the formation of nitrites.

Claims (8)

Claims:

1. A process for removing the chromium and / or depleting the MgO content of the steel slags, which is characterized in that oxygen is introduced into the liquid steel slag, up to an amount sufficient to convert the iron quantitatively to iron oxide and, at least 5% by weight of the iron oxide contained in the slag is converted to iron oxide III, this obtained oxidized slag solidifies and disintegrates, whereby the paramagnetic portions formed are magnetically isolated and separated from the slag without chromium .

2. The process according to claim 1, characterized in that the oxygen is blown into the liquid slag in the form of air and / or pure oxygen.

3. The process according to claim 1 or the 2, which is characterized in that the oxidation is carried out until the formation of the Fe304 content of the slag varies between 5 and 20% by weight.

4. The process according to claim 1, 2 or 3, which is characterized in that the slag is granulated with water and / or with steam after oxidation.

5. The process of agreement "with any of the claims 1 to 4, which is characterized in that the The basicity of the steel slag is maintained at Ca0 / Si02 values that are greater than 2.5.

6. The process according to any of claims 1 to 5, characterized in that the spinel phase of paramagnetic magnetite is used as raw material for the production of chromium.

7. The process according to any of claims 1 to 6, characterized in that the chromium-free steel slag is loaded in a rotary tubular furnace for the production of cement clinker. The process according to any one of claims 1 to 7, characterized in that the vanadium oxide incorporated in the spinel phase is recovered by a carbon-free reduction, for example with aluminum.