GB2050430A

GB2050430A - Desulphurisation of iron

Info

Publication number: GB2050430A
Application number: GB8008110A
Authority: GB
Original assignee: Aikoh Co Ltd
Current assignee: Aikoh Co Ltd
Priority date: 1979-03-30
Filing date: 1980-03-11
Publication date: 1981-01-07
Also published as: IT1153795B; IT8009395A1; FR2452521A1; IT8009395A0; NL8001834A; AU524961B2; CA1139568A; AU5680280A; DE3009477A1; JPS55131112A; BE881916A; LU82305A1

Abstract

Molten pig iron is desulphurized by treatment with metallic aluminium (a) and an alkali metal oxide desulphurizing agent (b), for example soda ash, the amount of (a) representing 1-30% by weight of (a) + (b). Sodium hydroxide may also be present.

Description

SPECIFICATION A method for desulphurizing pig iron The present invention relates to an improved method of desulphurizing pig iron by treating molten pig iron with substances capable of removing sulphur from the pig iron.

The adoption of an easy and convenient method for using a desulphurizing agent to treat molten metals is regarded as important. As the most suitable desulphurizing agents used in a presetting method there may be mentioned alkali metal oxide desulphurizing agents, which react rapidly and result in the production of a low melting slag, i.e. agents such as sodium carbonate, caustic soda, potassium carbonate and caustic potash or mixtures thereof with small amounts of calcium fluoride, sodium fluoride, iron oxide, aluminium fluoride, sodium aluminium fluoride, potassium aluminium fluoride and magnesium fluoride.

Known desulphurizing agents such as lime, calcium carbonate, "lime nitrogen" and metallic magnesium are not suitable for the desulphurizing operation by a presetting method because they act either too slowly or too quickly, and they must be introduced into the melt by using a large sized apparatus so that they are not economical desulphurizing agents. A desulphurizing reaction with molten metal when using an alkali metal oxide desulphurizing agent is carried out theoretically in the presence of a reducing element.That is, it can be presumed from the relevant reaction equation that free alkali metal is formed from alkali metal oxide by means of a reducing agent such as carbon, silicon, aluminium, magnesium, titanium and zirconium, it is bonded with sulphur and thereby converted into alkali metal sulphide and then the alkali metal sulphide is dissolved in the slag and remains dissolved therein when the slag is separated from the molten metal being treated. It is evident from the phase diagram of Fe-AI that aluminium is the very element which is meltable in molten iron and has the maximum chance of exhibiting a desulphurizing action until it is all used up. Magnesium which is a highly reactive metal on the other hand melts to a lesser degree in molten iron than does aluminium so that its reactivity is substantially inferior to that of aluminium.There is the further advantage of aluminium when used for the desulphurization of molten pig iron, that it does not lower the basicity of slag whereby the desulphurizing reaction is carried out continuously under the same conditions.

The object of the present invention is to provide a method of desulphurizing pig iron which is easy and convenient and which can employ a presetting method.

According to the present invention the method comprises treating molten pig iron with metallic aluminium (a) and an alkali metal oxide desulphurizing agent (b), the amount of (a) representing 1-30%, preferably 1-20%, by weight (a) + (b). For instance, the desulphurizing agent (b) may comprise soda ash or soda ash and caustic soda. The metallic aluminium (a) may be accompanied by alumina.

With the method of this invention the aluminium (a) may be introduced previously into molten pig iron so that the aluminium is itself in the molten state and then the pig iron may be reacted with the alkali metal oxide desulphurizing agent (b), or alternatively it is possible to add simultaneously or consecutively the desulphurizing agent (b) and the aluminium (a) to the molten pig iron. Preferably the aluminium (a) is added to the molten pig iron before the desulphurizing agent (b) is added to the molten pig iron.

In one method embodying the invention the metallic aluminium (a) and the desulphurizing agent (b) may be previously disposed within a pig irontreating vessel before molten pig iron is poured into the vessel. In an alternative embodiment the metallic aluminium (a) may previously be disposed within a pig iron-treating vessel before molten pig iron is poured into the vessel, and the desulphurizing agent (b), introduced into a flow of the molten pig iron while it is being poured into the vessel.

With regard to the alkali metal oxide desulphurizing agent (b), which may be applied using a presetting method, this agent (b) may be in massive form or in the form of powder, grain or flake. It may be anhydrous or a salt hydrate. It may be a hydrogen carbonate of bicarbonate of one or more potassium carbonate, sodium carbonate, caustic soda, caustic potash and potassium sodium carbonate. Furthermore, when the desulphurizing agent (b) is used in massive or granular form it may incorporate a small amount of an organic binder, e.g. starch, dextrin, glue, natural resin or synthetic resin, or a small amount of an inorganic binder, e.g. cement, water glass, clay, colloidal silica or aluminium phosphate.

Metallic aluminium (a) in massive, granular or powdered form may be charged or inserted into a pig iron melt, but to delay the desulphurizing reaction it is possible to provide the metallic aluminium (a) within a receptacle, coating or carrier consisting of a material which will not adversely affect the melt or the inner refractory wall refractory of the vessel containing the melt.

As stated above the amount of (a) represents 1-30% by weight of (a) + (b). With less than 1% of metallic aluminium (a) the reducing action does not affect the desulphurizing agent (b), and with more than 30% by weight the relative amount of the desulphurizing agent (b) is substantially decreased, thereby requiring use of a correspondingly greater amount of the agent (b) to match the large amount of the aluminium (a) used. As a result, so much aluminium oxide is produced that the fluidity of the slag is significantly decreased, and therefore such an excess is not desirable.

The desulphurizing method ofthe invention will now be illustrated by the following examples with reference to comparative examples.

In each set of examples, desulphurizing effects of addition and non-addition of aluminium were compared by using the same pig iron and a hot-metal ladle of the same capacity and carrying out a presetting method. The capacity of the hot-metal ladle was 250 tons, and the appropriate molten pig iron (240 ton) was poured into the ladle by means of a pig iron mixing vessel thereby to carry out the required desulphurizing treatment.

Example 1 75 Kg ofaluminium shot (component (a)) and 720 Kg of dense soda ash (component (b)) were used to treat a molten pig iron having a sulphur content of 0.041% by weight by a presetting method to introduce components (a) and (b) into the melt. Afterthe desulphurization treatment was effected the sulphur content of the pig iron was reduced to 0.025% by weight Comparative Example I Example I above was repeated but omitting the use of the aluminium shot. Afterthe desulphurization treatment was effected the sulphur content of the pig iron was reduced to 0.027% by weight Thus the desulphurization was 11.4% better with the presence of aluminium than without.

Example lI 90 Kg of an aluminium ingot (component (a)) and 950 Kg of a component (b) consisting of 80% by weight of light soda ash and 20% by weight of caustic soda were used to treat a molten pig iron having a sulphur content of 0.035% by weight by a presetting method to introduce components (a) and (b) into the melt. After the desulphurization treatment was effected the sulphur content of the pig iron was reduced to 0.23% by weight.

Comparative Example II Example II above was repeated but omitting the use of the aluminium ingot After the desulphurization treatment was effected the sulphur content of the pig iron was reduced to 0.025% by weight. Thus the desulphurization was 12.0% better with the presence of aluminium than without.

Example 111 1200 Kg of aluminium dross containing metallic aluminium (component (a)) and 1200 Kg of a component (b) consisting of 90% by weight of dense soda ash, 5% by weight of caustic soda and 5% by weight of fluorite were used to treat a molten pig iron having a sulphur content of 0.031% by weight The aluminium dross had the composition by weight: 20% metallic aluminium + 60% alumina + 20% of chloride and fluoride. The aluminium dross was introduced into the melt by a presetting method and component (b) was introduced into a flow of the molten pig iron while it was being poured or cast.

After the desulphurization was effected the sulphur content of the pig iron was reduced to 0.018% by weight.

Comparative Example 111 Example Ill above was repeated but omitting the use of the aluminium dross. After the desulphurization treatment was effected the sulphur content of the pig iron was reduced to 0.022% by weight. Thus the desulphurization was 14.4% better with the presence of aluminium than without

Claims

1. A method of desulphurizing pig iron comprising treating molten pig iron with metallic aluminium (a) and an alkali metal oxide desulphurizing agent (b), the amount of (a) representing 1-30% by weight of (razz + (b).

2. A method according to Claim 1, wherein the desulphurizing agent (b) comprises soda ash.

3. A method according to Claim 1, wherein the desulphurizing agent (b) comprises soda ash and caustic soda.

4. A method according to any preceding claim, wherein the metallic aluminium (a) is accompanied by alumina.

5. A method according to any preceding claim, wherein the metallic aluminium (a) and the desulphurizing agent (b) are previously disposed within a pig iron-treating vessel before molten pig iron is poured into the vessel.

6. A method according to any one of Claims 1 to 4, wherein the metallic aluminium (a) is previously disposed within a pig iron-treating vessel before molten pig iron is poured into the vessel, and the desulphurizing agent (b) is introduced into a flow of the molten pig iron while it is being poured into the vessel.

7. A method according to any preceding claim, wherein the amount of (a) represents 1-20% by weight of (a) + (b).

8. A method according to Claim 1 substantially as herein described and exemplified.

9. Pig iron which has been desulphurized by the method claimed in any preceding claim.