METHOD FOR REDUCING IRON SILICATE MELT IN ORDER TO PRODUCE FIRE-RESISTANT AND CHEMICALLY RESISTANT FIBER AS WELL AS BOTTOM METAL

Abstract: The present invention relates to a method for utilizing iron silicate slag in order to produce fibers resistant to high temperatures and severe chemical conditions, as well as bottom metal containing precious metals. The properties of the fiber produced of the molten slag are good when the molar alkalinity (FeO+CaO+MgO)/(SiO2+Al2O3) of the slag to be defibrated is 0.5-8.

Description: METHOD FOR REDUCING IRON SILICATE MELT IN ORDER TO PRODUCE FIRE-RESISTANT AND CHEMICALLY RESISTANT FIBER AS WELL AS BOTTOM METAL The present invention relates to a method for ulitilizing iron silicate slag in order to produce fibers resistant to high temperatures and severe chemical conditions, as well as bottom metal . Metallurgical slags as such are not suitable for fibration. The previously known methods for utilizing these slags in fiber production are based on the mixing of the slags with additives. These mixing agents are used to change the physical properties of the slag melt so as to be suitable for the fibration. Industrial production uses almost exclusively blast furnace slags which are smelted in a cupola furnace and defibrated with a four-wheel centrifugal machine. The most generally produced end products are building insulation materials. The use of other than blast furnace slags has been extremely rare. For instance the iron silicate slags created as by¬ products in copper and nickel processes have not been used in fiber production, irrespective of the many advantadges offered by these slags. The unique chemical composition of iron silicate slags enables for example the production of fibers with a resistance to exceptionally high temperatures and severe chemical conditions. That these possibilities have been left unused has been mainly due to the restrictions of the smelting unit, i.e. the cupola furnace, of the fiber production. The fact is that coke used in cupola furnace smelting tends to reduce the iron contained in the raw materials into metal, which again disturbs the defibration process. There are restrictions for the grain size of the raw material as well. The materials fed into a cupola furnace must be in bulk size, so that the gases created in the smelting can be discharged from the furnace through the mater ial bed . Electric furnace smelting, which during the past years also has been assumed to fiber production, is now changing the situation and has enabled the utilization of new raw materials. The use of an electric furnace is known for instance from the FI patent 72502. The use of iron silicate slags in fiber production is known from the FI patent application 845114, which introduces two methods for mixing the slag in order to obtain a defibratable slag melt. Generally speaking the purpose of the mixing is to change the slag properties by adding acidic slag components, so that the slag melt becomes well defibrating and that the final product achieves the desired properties . The present invention is based on a different outlook. The idea of this invention is to change the chemical composition of the iron silicate slag so as to be suitable for fibration by removing iron oxide from the slag. Iron is present in the slag mainly as bivalent and bound in oxygen, in the form of FeO. In the slag, iron oxide - FeO - is an alkaline component which prevents the acidic slag components from forming continuous net structures, the existence of which is necessary for the defibration of the slag melt. By removing iron oxide from the slag, the slag composition is changed towards a more acidic direction, so that the SiO and l-O- j contents in the slag are increased and the physical properties of the slag are changed to be favourable for defibration. The essential novel features of the invention are apparent from the appended patent claims. The removal of iron oxide is carried out by making use of the tendency to reduction of the iron oxide, which tendency is already known from cupola furnace smelting. The iron oxide content of the slag is reduced by oxidizing iron from the slag for example by means of fine grounded coke or coal dust. The metal obtained as the reduction product is separated from the slag and settles onto the bottom of the smelting furnace to form bottom metal. The precious metals contained in the slag, such as copper, nickel and cobalt, are also concentrated in the bottom metal. The Fe content of the slag, as well as the amount of created metal, is controlled by means of the amount of the reductive agent fed into the furnace. As a result from the reduction reactions, there is also created exhaust gas containing CO and CO . The reduction of iron silicate slag according to the present invention is carried out in a suitable furnace unit, for instance in an electric furnace. The iron silicate slag can be fed into the furnace either in solid or in molten state. The reductive agent, for instance fine grounded coke, can be fed into the molten slag for instance by injecting through a lance or through electrodes. This also brings about a mixing in the molten slag, which is necessary for the reduction reactions. The mixing is also needed for enhancing the separation of the created metal drops from the slag. As a result of the reduction reactions, the melting point of the slag is raised and the slag is discharged from the furnace at an increased temperature. The tapping of slag for defibration is arranged to be continuous. As for the metal, it is removed from the furnace discontinuously through a particularly arranged tapping hole. In the method of the present invention, iron oxide is reduced from iron silicate slag to such extent that the obtained alkalinity for the slag is suitable for defibration, and the molar percentage of (FeO+CaO+MgO)/(SiO^+Al-,0 ) = 0.5-0.8. Thereafter the slag melt can be processed into fibers resistant to high temperatures and severe chemical conditions according to generally known defibration methods. While reducing iron silicate slag according to the present invention, the composition of the created metal is essentially dependent on the amount of reductible metal oxides contained in the slag. The Fe content of the bottom metal is generally over 90%, while the rest metals are among others precious metals such as copper, nickel and cobalt. If it is for some reason desired, at the reduction stage of iron silicate slag according to the invention it is also possible to add such mixing agents which have a positive effect for instance to the properties of the final product. Among the advantages of the method of the present invention for utilizing iron silicate slag let us mention the following: 1) iron silicate slag renders two valuable end products: fiber and metal; 2) apart from the reductive agent, the slag itself suffices by 100% as the required raw material; 3) iron silicate slag can be fed into the reduction furnace in molten state, so that the thermal energy contained by the slag is also made use of. The method of the present invention for utilizing iron silicate slag is further illustrated by means of the following example. Example As a by-product from the nickel process we obtain iron silicate slag, its typical chemical composition being: Fe 41.5%, SiO^ 29.5%, CaO 1.5%, MgO 6.5% and A1 2 _0 3 4.1%. When 75% of the iron contained in the slag is reduced according to the invention, we obtain defibratable slag with the following composition: Fe 17.6%, Sio^ 51.0%, CaO 2.6%, MgO 11.1% and Al^O j 7.5%. All percentages are percentages by weight. The molar alkalinity of the slag is 0.69. Per each consumed ton of iron silicate, the yield of defibratable slag mixture is roughly 590 kg and that of metal roughly 325 kg.

Claims: PATENT CLAIMS 1. A method for utilizing iron silicate slag with a high iron content in the production of fire-resistant and chemically resistant fiber material, c h a r a c t e r i z e in that the iron oxide content of the iron silicate slag is decreased by reducing the slag so that the molar alkalinity (FeO+CaO+MgO/CSiO^+Al^O. ) of the slag melt is adjusted to fall within the range 0.5-8, in which case the obtained products are defibratable slag melt and molten metal containing precious metals, at least copper, nickel and cobalt in addition to iron. 2. The method of claim 1, c h a r a c t e r i z e d in that the FeO content of the slag melt as well as the amount of the created metal is regulated by means of the amount of the reductive agent fed into the furnace. 3. The method of claims 1 and 2, c h a r a c t e r i z e d in that the employed reductive agent is fine grounded coke. 4. The method of claims 1 and 2, c h a r a c t e r i z e d in that the employed reductive agent is coke dust. 5. The method of claim 1, c h a r a c t e r i z e d in that the reduction is carried out in an electric furnace.

Inventors: SALERVO AARNO TANELI, TUOVINEN FRANS HEIKKI, SALERVO, AARNO, TANELI, TUOVINEN, FRANS, HEIKKI
Applicants: OUTOKUMPU OY
Application year: 1988
Main classification: C03C13
IPC codes: C03C1, C03C13