NL8001834A - METHOD FOR DESULFULIFYING MOLED METAL. - Google Patents

Description

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Method for desulfurizing molten metal.

The invention relates to a method for desulphurizing molten metal, in particular molten pig iron.

A desulfurization agent is preferably used for desulfurizing molten metals. Suitable desulfurizing agents which are added beforehand are, for example, alkali metal oxides. which react rapidly and provide a low melting temperature slag such as, for example, sodium carbonate, sodium hydroxide, potassium carbonate and potassium hydroxide, or mixtures thereof with small amounts of calcium fluoride, sodium fluoride, iron oxide, aluminum fluoride, sodium aluminum fluoride, potassium aluminum fluoride or magnesium fluoride.

Known desulfurization agents such as calcium oxide, calcium carbonate, calcium nitride and magnesium metal are unsuitable for desulfurization by pre-addition, since these agents are either too slow or too fast, while they must be hot melted using bulky devices which is not economical. The desulfurization of molten metal using a desulfurizing agent of the alkali metal oxide type is theoretically done in the presence of a reducing element.

It can be deduced from the reaction equation that free alkali metal from the alkali oxide is formed by a reducing agent such as carbon, silicon, aluminum, magnesium, titanium or zircon, after which this metal forms with the sulfur from the metal sulfide an alkali metal sulfide, which is then dissolved in the slag and thus separated from the metal. The Fe-Al phase diagram shows that aluminum is best melted in molten iron, and therefore has the greatest chance of fully contributing to desulfurization. Although magnesium is a much more active metal, it melts considerably less in the molten iron, so that the final effect is worse. An advantage of aluminum for the desulfurization of molten pig iron is further that it does not reduce the basicity of the slag, so that the desulfurization reaction can continue under the same conditions.

The invention provides a desulfurizing agent, which is very suitable for these purposes, and which can furthermore be used in a simple and convenient manner for desulfurizing molten metals, and in 800 1 8 34 - 2 - in particular molten pig iron. as well as a method of adding this desulfurization agent. Either aluminum is pre-melted in the molten pig iron, which can then react with a desulfurizing agent, or the aluminum is added to the molten metal together with the desulfurizing agent. Preferably, the aluminum is added before the desulfurization agent is added.

The desulfurizing agent of the alkali metal oxide type suitable for this mode of operation can be used in the form of powder, granules, cohesive mass or flakes of the anhydrous substance, the salt hydrate or the acid carbonate, namely of potassium or sodium carbonate , sodium or potassium hydroxide, or potassium sodium carbonate. When the desulfurizing agent is used in the form of granules or of a solid mass, it can be added together with an organic binder, such as a small amount of starch, dextrin, glue, rosin or synthetic resin, or of an inorganic binder, such as cement , water glass, clay, colloidal silica or aluminum phosphate.

Aluminum metal in the form of a mass, granules or powder is fed into the hot melt, whereby to delay the reaction on the outside of the mass, the granules or the powder particles can be coated, coated or supported which consists of a material which has no harmful effect on the hot melt or on the refractory inner wall of the melting vessel.

In the process of the invention, a desulfurizing agent of the alkali metal oxide type and aluminum metal are either mixed together just before use, or added to the melt simultaneously as separate batches. It is also possible to cast the hot melt after the aluminum metal has already been placed in a treatment vessel, while the desulfurizing agent is added to the casting stream mid-casting. The ratio between the aluminum mass and the total mass of the desulfurizing agent is about 1..30% · When less than 1% aluminum is used, its reducing effect does not affect the desulfurizing agent, while at more than 30% the desulfurizing agent decreases in amount so that a larger amount thereof must be added. So much aluminum oxide is then formed that the fluidity of the slag is reduced, so that an excess is not desired.

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The method according to the invention will now be further elucidated on the basis of comparative examples.

In each of these examples, the desulfurization activity upon addition of aluminum was compared to that of non-addition thereof when using pig iron of the same composition, while using a metal vessel of the same content, the addition being done beforehand. The containment capacity of the vessel was 250 Mg, with 2.0 Mg of pig iron being poured into the vessel using a mixer wagon to carry out a desulfurization treatment therein.

These comparative experiments show that when the desulfurizing agent is used together with aluminum, a 5 ·· 12 better desulfurization can be obtained than without the use of aluminum. These experiments are summarized in the following table.

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Claims (3)

Process for desulfurizing molten metal, in particular molten pig iron, characterized in that aluminum metal is used together with a desulfurizing agent of the alkali metal oxide type, in an amount of 1..30 #, 3 based on the total mass of the desulfurization agent. A method according to claim 1, characterized in that the desulfurizing agent and the aluminum are pre-placed in a treatment vessel before the hot metal is poured. 3. A method according to claim 1, characterized in that the aluminum is pre-introduced in the treatment vessel before the hot metal is poured, while the desulfurization agent is added to the casting stream. 800 1 8 34