METHOD FOR TREATING SLAG

Abstract

A method for treating converter slag for the purpose of recirculating iron, wherein a converter slag is brought into contact with oxygen in such a way that by means of turbulence, the slag is mixed, the iron and iron oxide components that are present are oxidized, and the slag is then allowed to stand in the vessel or a vessel until a segregation into a solidifying, silicate and phosphorus-rich first fraction and an underlying liquid iron oxide-rich second fraction has taken place, with the converter slag that is used being mixed with a partial flow from the iron oxide-rich second fraction in such a way that the total FeO content of the slag that is to be treated with oxygen is over 35% by weight, thus enabling the segregation into two fractions.

Claims

1. A method for treating converter slag for the purpose of recirculating iron, the method comprising the steps of: contacting a converter slag with oxygen in such a way that by means of turbulence, the slag is mixed, and iron and iron oxide components that are present are oxidized; and resting the slag such that is allowed to stand until a segregation into a solidifying, silicate and phosphorus-rich first fraction and an underlying liquid iron oxide-rich second fraction has taken place.

2. The method according to claim 1, wherein after the contacting step the slag rests for 24 hours.

3. The method according to claim 1, wherein during the contacting step oxygen, air, or mixtures of oxygen and air or oxygen and gas are blown onto or into the slag in order to bring it into contact with oxygen.

4. The method according to claim 1, further comprising measuring the FeO and iron content of a first liquid melt of a pre-contacting step portion of converter slag and measuring the iron content of the second fraction as a second liquid melt generated after the contacting and resting steps; and, then, calculating and mixing a ratio of the two liquid melts so that after the mixing, a FeO content of over 35% by weight of the mixed liquid melts is achieved.

5. The method according to claim 4, further comprising, prior to the contacting step, feeding the converter slag into a receptacle and supplying iron-rich second fraction residual melt to the receptacle, in accordance with the calculating, and then the contacting with oxygen in the vessel and the resting take place until the solidification of the first fraction has taken place and the second liquid fraction is present underneath it.

6. The method according to claim 1, characterized in that a vessel with two chambers is used; first and second chambers of the vessel are separated from each other by a partition having at least one opening above a bottom of the wall; the first chamber is filled with liquid converter slag and after each filling of the first chamber with a slag charge, oxygen is introduced above the slag charge in the first chamber in that oxygen or an oxygen-containing gas is blown onto or through it; through an opening near the bottom of the partition wall, slag flows into the second chamber, which is embodied as a quieting and sedimentation tank; the second chamber comprising a scouring apparatus; solidified slags composed predominately of silicates are removed; the supply with fresh slag takes place in such a way that a relatively constant bath level is present in the chambers; and liquid FeO-rich residual melt that collects at a bottom of the second chamber is removed and is supplied to the first chamber in order to adjust the FeO content.

7. The method according to claim 6, characterized in that the iron content of the freshly supplied slag is continuously measured and the FeO content of the residual melt is measured in order to adjust to a FeO content that is always above 35% in the continuous process.

Description

[0027] The invention will be explained by way of example based on the drawings. In the drawings:

[0028] FIG. 1: shows a schematic flowchart showing the method according to the invention;

[0029] FIG. 2: shows the schematic diagram and a mass flow graph for a second exemplary embodiment;

[0030] FIG. 3: is a table showing a mass flow balance and FeO balance for a continuous process according to example 2;

[0031] FIG. 4: shows sample analysis values for the charges that accumulate in the process.

[0032] According to the invention, it has been discovered that anot yet performedrecovery of iron oxide from LD slags succeeds because the accumulating LD slag is treated in such a way that a segregation into a FeO-rich fraction and a FeO-poor fraction takes place.

[0033] Here, this segregation succeeds solely because after the treatment, an iron-rich slag partial flow is recycled and before the treatment, the FeO content of the slag used is adjusted to the required value of >35%.

[0034] Only with iron oxide contents above 35% does the segregation effect occur, which then results in a relatively large FeO-poor partial flow and a relatively small FeO-rich partial flow. According to the invention, this FeO-rich partial flow is partly used for increasing the FeO content of freshly introduced slag so that it contains above 35% FeO.

[0035] This melt with the adjusted FeO content is treated with an oxygen lance, which causes heavy turbulence that results in a thorough mixing and the oxidation of the metallic and bivalent iron generates a significant temperature increase.

[0036] For example (FIG. 1), an iron-poor converter slag has a FeO content of 25%, a metallic iron content of 0.7%, a calcium oxide content of 43%, a magnesium oxide content of 6%, a silicon oxide content of 15%, and a phosphorus oxide content of 1.2%. This slag is dispensed into a receptacle and is supplied with an iron-rich residual melt from a preceding treatment. For example, this iron-rich residual melt has an iron oxide content of 55%, a metallic iron content of 1.8%, a calcium oxide content of 21%, a magnesium oxide content of 7%, a silicon dioxide content of 6%, and a phosphorus oxide content of 0.5%.

[0037] Based on the knowledge of the analysis values, it is thus possible to simply add enough iron-rich residual melt to the iron-poor converter slag that the total iron oxide content is adjusted to the required 35%.

[0038] This overall mix is then processed with an oxygen lance; in particular, oxygen is blown in, which, as already explained above, results in the heating and mixing effect. This slag mix is then allowed to cool for 24 hours, which then produces a segregation from an overlying, solidified iron-poor residual melt, which has an iron oxide content of 21%, a metallic iron content of 0.3%, a calcium oxide content of 47%, a magnesium oxide content of 5.5%, a silicon oxide content of 16%, and a phosphorus oxide content of 1.3%. Below this iron-poor residual melt, the above-described iron-rich residual melt has collected, which can then be supplied back to the iron-poor converter slag.

[0039] It is conceivable for there to be slightly different embodiments of the method here. In a first embodiment, an empty slag bucket is filled with an LD converter slag, which according to the analysis, is iron-rich (as happens from time to time). After 24 hours, the so-called cover composed of solidified slag is broken open and the remaining residual melt is dispensed into an empty slag bucket. During the dispensing, a sample is taken for the chemical analysis and the temperature is measured. The temperature is 1280 C., which is already close to the solidification temperature of calcium ferrites. An iron-poor converter slag is poured onto this residual melt. In terms of its contents, the slag bucket is approximately filled with the iron-rich residual melt. Then the mixture composed of more iron-rich melt and iron-poor converter slag is treated with an oxygen lance. The injection jet produces heavy turbulence, which results in a thorough mixing of the two slag types and the oxidation of the metallic and bivalent iron generates a significant temperature increase.

[0040] This heated and mixed slag is covered and allowed to stand for 24 hours and the cover is then once again broken open and samples are taken from the solidified crust and from the remaining residual melt.

[0041] The chemical analysis values are listed in FIG. 4. In this case, FeO should be understood as a collective analysis for the entirety of the oxidically bonded iron, calculated based on the entirety of the metallic iron. It is clear that the iron-rich first slag charge has a FeO content of 35.2%, which enables the segregation. The mineral cover that forms on it has an iron oxide content of 20.9% while the residual melt formed under the cover has a FeO content of 49.6%.

[0042] The subsequently added iron-poor converter slag has a FeO content of 25.5% and the cover has a FeO content of 21.5%.

[0043] After the oxygen treatment and the 24-hour rest phase, the resulting iron-rich residual melt has a FeO content of 53.1% so that this residual melt is once again favorably suitable for increasing the iron content of an iron-poor converter slag charge to above the required 35%.

[0044] For the start of the method, it is therefore advantageous to wait until a very iron-rich converter slag is present in order to provoke a segregation and thus to provide a base stock of a very iron-rich residual melt after the treatment.

[0045] Then according to the invention, through the addition of the very iron-rich residual melt from the segregation of the iron-rich converter slag, it is also possible to cause any subsequent iron-poor converter slag to undergo segregation.

[0046] In another advantageous embodiment, a corresponding treatment vessel is provided, the treatment vessel having two chambers, which are separated by a partition wall. Just above the bottom of the trough, the partition wall has window-like openings so that the two chambers can communicate with each other if so desired.

[0047] First, the liquid converter slag is dispensed directly into the first chamber. If it is a very iron oxide-rich converter slag, it can then be treated with oxygen.

[0048] The solidification of the slag begins by crystallization of the silicates, but the slag in the first chamber is always kept liquid by means of the oxidation of the metallic and bivalent iron with the introduced oxygen.

[0049] Through the opening near the bottom of the partition wall, slag flows continuously into the second chamber, which is embodied in the form of a quieting and sedimentation tank.

[0050] This second chamber is advantageously equipped with a scouring apparatus that is known from the desulfurization of liquid pig iron. It also includes a device for breaking open crusts made of solidified slags. With the scouring apparatus, the already solidified solid slag chunks, which are predominantly composed of silicates and float on the still-liquid slag that is continuously solidifying at the surface, are removed and broken loose if necessarily.

[0051] In intervals that are aimed at maintaining a bath level that is as constant as possible after the supplying of fresh slag, the liquid iron-rich residual melt that has collected at the bottom is also removed and part of it is conveyed back into chamber 1 in order to constantly enable a good segregation by means of a sufficiently high FeO content.

[0052] In this embodiment as well, it is possible to initially use a (randomly) occurring, very iron-rich converter slag with a FeO content of more than 35%. Alternatively to this, it is also possible to use an iron-poorer converter slag and correspondingly, as is also the case later in the continuous process, to then also use a previously collected liquid FeO-rich residual melt.

[0053] The invention has the advantage that without a high degree of complexity and especially without the addition of additives external to the process, it is possible to carry out the separation of converter slag into an iron oxide-rich fraction and a silicon and phosphorus-rich fraction so that the iron-rich residual melt is supplied back to the smelting furnace process, thus enabling the recovery of iron.