NZ271025A

NZ271025A - Process for making steel and hydraulically active binders using slags rich in iron oxide

Info

Publication number: NZ271025A
Application number: NZ271025A
Authority: NZ
Inventors: Alfred Edlinger
Original assignee: Holderbank Financ Glarus
Priority date: 1993-09-07
Filing date: 1994-08-24
Publication date: 1997-01-29
Also published as: HU219946B; ES2102869T3; AU7452794A; AU678516B2; ATE151118T1; CN1115580A; SK281859B6; CZ291176B6; CA2148226A1; GR3023849T3; HU9501320D0; BR9405583A; RU2127765C1; DE59402298D1; EP0666930A1; HUT75853A; CZ107495A3; EP0666930B1; SK58495A3; KR950704516A

Abstract

The process for making steel and hydraulically active binders uses slags rich in iron oxide, such as steel slag, as oxidizing agent for carbon in pig iron. The slag is reduced, yielding a type of blast furnace slag with improved hydraulic properties.

Description

<div class="application article clearfix" id="description"> New Zealand Paient Spedficaiion for Paient Number £71 0£5 New Zealand No. International No. 271025 PCT/AT94/00122 Priority Date(s): Complete Specification Filed: Claw: (6) G.aACSi3k>:,.CX?XS3.|.Otp:/. Pub llctftion Date: 2„9.. .v! A N.. .{§97 P.O. JoufnatNb: Title of Invention: Process for making steel and hydraulically active binders Name, address and nationality of applicant(s) as in international application form: HOLDERBANK FINANCIERE GLARUS AG, a Swedish company of Haupstrabe 44, Ch-8750 Glarus, Switzerland NEW ZEALAND PATENTS ACT 1953 COMPLETE SPECIFICATION / L U L» - 1 - Process for producing steel and hvdraulicallv active binders The invention relates to a process for producing steel and hydraulically active binders, such as, e.g., blast furnace slag, clinker and the like. When producing steel, steel slag is formed, which has a relatively high iron oxide content due to the refining process involved. Conventional steel slag contains MnO and FeO in amounts up to 33 % by weight. While blase furnace slag is remarkable by its favorable hydraulic properties and by a substantially lower iron oxide content, thus being more readily apt for utilization as a basic construction material, the disposal of slags from steelworks has become increasingly difficult, since steelworks slag in the incurring composition, i.e., without any metallurgical aftertreatment, cannot be readily used for construction purposes or the like. It has already been proposed to granulate steelworks slags along with blast furnace slags and use them as bottoming material in road construction. However, the relatively high CaO content of steelworks slag allows for the use of only limited amounts of steelworks slag also in that case. In order to obtain a product of higher quality, the metallurgical processing of steelworks slag, as a rule, involves high energy consumption and, therefore, is not really economical. Yet, slags-having relatively high contents of iron oxide also incur in other metallurgical processes or combustion processes. In particular, it is known that Cu converter slags frequently have iron oxide contents of above 50 % by weight, and slags from waste and garbage combustion plants that are characterized by relatively high iron oxide contents are also known. - 2 - The invention aims at further processing steelworks slags and slags having relatively high iron oxide contents of the initially defined kind directly in a steelworks and to convert the same into more readily usable end products, namely hydraulically active binders. In order to solve this problem, the process according to the invention consists in that pig iron is refined by adding slags containing iron oxides in amounts exceeding 5 % by weight, such as, e.g., steel slags, Cu converter slags after reaction with a lead bath or oxidized slags from waste combustion plants. In this process, the high iron oxide content of the liquid slags, such as, e.g.,of the steel slag, thus is utilized to refine molten pig iron having relatively high carbon and silicon contents. In doing so, iron oxide basically reacts with carbon or iron carbide to form iron and carbon monoxide, whereas the iron oxide of the slag reacts with the silicon of the pig iron bath to form iron and Si02 • These reactions partially are exothermic so as to provide for a high degree of economy. Due to the iron oxide content in the steel slag being reduced, an analysis deviating from the original slag analysis is obtained, resulting in substantially more favorable hydraulic properties. The iron oxide content is utilized to oxidize the pig iron bath, and, for instance, in the case of steel slags reduction of the iron oxide content to below one third of the original value may be achieved, the volume portions of the other components of the original steel slag thus increasing in respect of their portions in the overall slag. Hence results a new slag analysis no longer corresponding to the original steel slag analysis. The new slag analysis is characterized by a substantially more favorable hydraulic module and a relatively high content of alite. Even though the thus obtained slag end product, which may be denoted as cement clinker, does not conform to standardized Portland cement clinker, a highest-quality alite cement clinker is obtained which is suitable as an extremely favorable base for mixing with other hydraulic or latent hydraulic substances. The cement clinker to be obtained in this manner is suitable, in particular, for mixing with puzzolanes, wherein a particularly high 28-day strength could be attained. Analogous considerations as have been made in respect of steel slag also apply to Cu converter slag and other slags, wherein, in case of Cu converter slags, care has, of course, to be taken that copper will not get into the steel bath, being detrimental to steel. Consequently, copper must at first be separated above? a lead bath, the copper being eliminated from the slag prior to the iron bath. The lead itself subsequently is reduced in an iron bath reaction, wherein iron and lead can be drawn off separately in a simple manner, beause iron and lead together do not enter into solution. Below the iron or steel bath a sea of lead is formed, steel and lead being capable of being drawn off separately in such cases. Due to the possibility, beside the simultaneous recovery or recuperation of metal fractions, of converting the remaining slag into a superior product to be reused, a substantial economic advantage is achieved, slags being disposable for which no suitable application has existed so far. In order to enable the desired oxidation of the carbon content within the pig iron bath and hence the refining to steel, it is advantageously proceeded in a manner that the iron oxide content of the slag is chosen to exceed 8 % by weight, preferably 10 % by weight. For the initially mentioned basic reactions as they occur in the pig iron bath, the observance of relatively high temperatures is essential. Despite the at least partially exothermic reactions, the temperature required may drop on account of thermal losses, the lost heat being reintroducible via bath electrodes in a particularly simple manner. Due to its chemical composition, the molten bath may be used as an electric resistance in a particularly simple manner, the pig iron bath being usable as the counter electrode. In order to 2/ '025 - 4 - be able to carry out the process according to the invention in a particularly economic manner and, above all, to terminate the desired reactions within acceptable periods of time, it is required in any case to use the liquid steel slag at 5 temperatures of above 1550°C, in particular 1600°C, and molten pig iron at temperatures ranging from 1450 to 1550°C, wherein it is advantageously proceeded in a manner that the liquid phases together are maintained at temperatures of above 1550°C, in particular 1660°C to 1800°C, for 3 to 8 hours, in 10 particular about 6 hours. The upper limit of 1800°C is chosen in consideration of the upper limit of the stability of alite. The pig iron used as a reducing agent must be overheated to at least 13 50°C in order to render the formation of alite feasible at all. According to a preferred process control it 15 is provided to use the liquid steel slag at temperatures exceeding 1550°C in order to ensure the optimum phase formation for any further use of the slag. Due to the reduction of the iron bath, the iron oxide content 20 of the slag, for instance, is lowered to about 5 % by weight, the process advantageously being conducted in a manner that the slag is converted into a sinter phase consisting of 15 to 25 % by weight of molten phase (aluminates, ferrites) and clinker phase (minerals, alite, belite). 25 The required overheating, which partially results from the exothermic reactions of the slag with the pig iron bath, may be effected by external heating, advantageously by proceeding in a manner that an electrically heatable tilting converter is 30 employed as the mixing vessel. Another way of ensuring the appropriate temperature in addition to a relatively high iron oxide content in the slag consists in maintaining the slag at overheating temperature by blowing in or up oxygen. In particular, if the slag is to be maintained at overheating 35 temperature by blowing .up oxygen, it is advantageously proceeded in a manner that the slag bath height for the reaction with pig iron is chosen to be between 2 and 8 cm, 271025 * K> i preferably 2 to 6 cm, whereby it is ensured that merely the slag, but not the iron bath located therebelow is refined by means of oxygen. The sinter phase floats on the iron bath, reduced iron droplets sedimenting into the iron bath from the slag or sinter phase. Since there is a high resistance to sedimentation in the sinter phase, it is again advantageous, as already pointed out above, to limit the thickness of the slag or sinter phase to 2 to 6 cm, metallic iron being removable from the slag almost completely at residence times ranging between 3 and 8 hours. Another way of adjusting the desired slag parameters consists in that basic poor ores are added to the slags in order to increase their iron oxide contents to above 8% by weight. Preferably, also CaC03, A1203 and/or Si02 are used as additives. In particular, when using such further additives, the waste heat from the process, ie, both the sensible and the chemical heat, may be applied for preheating these substances. The term "basic poor ores" refers to sideritic ores rich in calcium. These ores are characterised in that they are almost free of sulfur and phosphorus, they contain MnC03 (1.5 or 3% Mn) and frequently form isomorphous mixtures with carbonates of Ca and Mg. As a result of the basicity of such ores, a favourable melting behaviour of the slag is promoted. S?0\LZ 27 10 ^ 5' -Sain addition to recovering copper by means of the lead bath, it is, of course, also feasible to recover zinc advantageously by proceeding in a manner that, when using Cu converter slags, lead is drawn off below the steel bath and Zn is condensed from the gas phase. To supplement the lost heat, it is advantageously proceeded in a manner that an electrically heatable tilting converter is used as a mixing vessel. The iron oxide content of the slag is reduced as a function of the volume ratio of slag to pig iron, wherein, naturally, only balance reactions are brought about such that the complete reaction of the iron oxide content is not readily feasible. A particularly economic and efficient mode of operation results 271025 if molten pig iron is added to the liquid slag phase in amounts by weight ranging from 1 to 2 to 1 to 3. The sintered cement clinker can be processed further according to conventional technology. Advantageously, the reduced slag is supplied to a clinker cooling and granulating means, the clinker being cooled by air according to the direct method in a particularly simple manner. The direct method involves directing air onto the clinker in order to cool it down sufficiently fast so as to avoid crystallisation and to get a vitreous solidified product. Also the refined molten pig iron already largely conforming to a steel composition subsequently may be further processed according to known steel aftertreatment procedures. In the following, the invention will be explained in more detail by way of exemplary embodiments. 271025 Example 1 0.5 parts by weight of molten pig iron were added to a portion of steel slag, the two phases together having been maintained at 1660°C for 6 hours. During the reaction, 35g carbon monoxide, corresponding to 28 standard liters, formed per kg steel slag melt. The steel slag had the following analysis: SiOz 8 A1203 7 CaO 45 MgO 5 MnO + FeO 30.5 Ti02 1 The pig iron had the following analysis: Si 4 C 5 Fe 91 K; V..VM998 270?r, - 7 - After six hours of reaction, the slag analysis and the steel analysis had changed in the following manner: Slag analysis (%) Si02 13 AI2O3 8.9 CaO 60 MgO 6.4 MnO + FeO 10.5 Ti02 1•3 Steel analysis (%) Si 0 C 2 Fe 97 When assessing the slag, which was used as a cement clinker, a conventional cement-technological assessment was made, yielding the following values. For comparison, the Table below also indicates the typical ranges for Portland clinker. Criterion Value Typical Range (Portland clinker) Hydraulic module 1.85 1.7 - 2.3 Silicate module 0.67 1.8 - 3.2 Silicic acid module 1.46 2.5 - 3.5 Alumina module 0.85 1,5 - 2.5 Lime standard 1,12 0.8 - 0.95 Alite content (C3S) 70.7 In total, a highest-quality alite cement clinker was obtained. The 28-day strength according to DIN 1164 was 62 N/mm^, which may be classified as extremely high. However, this is no standard Portland cement clinker, yet continued reduction of the iron oxide and slight addition of additives, such as, for instance, clays, for increasing the SiC>2 and AI2O3 contents are 02" » feasible if Portland cement clinker according to standards is desired. Example 2: 5 To react the steel slag already indicated in Example 1 to a target slag which might be denoted as blast furnace slag having the following composition: 3 Target Slag 10 Si02 36.5 A1203 8.5 CaO 48 MgO 5.5 MnO + FeO 0 15 Ti02 1.5 the original steel slag is reduced to the target slag. 733 g pig iron are required per kg steel slag with 950 g steel being formed and 60 g CO, or 48 standard liter CO, being released. In addition, 225 g quartz sand were admixed to produce the 20 above-mentioned target slag. The pig iron and steel compositions are indicated in the Table below: % Pig Iron Steel Si 4 0 C 5 1.5 25 Fe 91 98 The melting temperature was approximately 1600°C, a redox time of approximately 4.5 hours having been observed. The blast furnace slag formed is excellently usable as a hydraulically 3 0 active binder. The relevant characteristic data have been determined to be as follows: Hydraulic index (wedge) = 92 % (very good) Puzzolanity (ASTM C 618) = 118 (excellent) 35 27'02? Exgunple 3; Using Cu slag from a converter, a starting slag having the following chemical analysis was used: 5 Main component Portion Secondary component Portion (%) Si02 28 SO3 0.5 AI2O3 6 K2O 0.13 10 Fe203 53 Na20 0.64 CaO 8 Ti02 0.36 MgO 2 Cr203 1.4 Mn203 0.35 P2O5 0.27 15 CI + F 1 Nonferrous Metal ppytion (ppm) Cu 11'000 Pb 6'800 20 Zn 3'760 Due to the high copper content of the slag, copper was removed from the slag prior to the iron bath by previously arranging a lead bath. As a result, lead was reduced, wherein iron and 25 lead together do not enter into solution such that a lead sea formed below the iron or steel bath. Steel and lead could be drawn off separately. The relatively high portion of zinc in the slag was reduced 30 above the iron bath and condensed in the vapor phase. The remaining heavy metal concentration was within the range of cement clinker raw material. After reduction of the slag by aid of the carbon dissolved in the iron bath, the following 3 5 slag analysis was obtained: - 10 - Component Portion (%) Si02 60 AI2O3 13 Fe203 0.5 CaO 17 MgO 4 / ft <- ! : y The slag was cooled in the water bath and exhibited excellent puzzolanic properties. Simultaneously with the recovery of the metal fraction zinc from the gas phase by condensation and with the recovery of copper as well as recovery of the lead bath, a hydraulically active material was obtained, which exhibited a high final strength, a low hydration heat and a high chemical resistance on grounds of its favorable puzzolanic properties. Example 4: Copper was extracted from liquid oxidized waste slag by means of the redox reaction described in Example 3 at a period of reaction of 3.5 hours and a melting temperature of 1500°C. The starting slag had the following analysis: Component Portion (%) Nonferrous Metals Portion (%) Si02 42 Cu 1.2 AI2O3 8 Pb 0.25 Fe203 28 Zn 0.3 CaO 11 Sn 0.1 MgO 2 Ni 0.1 K2O 1 Na20 3 Ti02 1 P2O5 0.1 7ri ' ft 0 ^ i . U Lc 11 At a copper activity in the lead bath of 30 to 40 % and a slag layer height of 3.5 cm, the equilibrium concentration of copper in the slag amounted to 200 ppm. 5 From the decoppered liquid slag, the remaining heavy metals lead, zinc, tin, nickel and iron were subsequently reduced and separated. Separation of the two metal phases iron/lead assured the 10 recovery of hiqh-grade pig iron practically free of copper and having the following analytical data: Cooling, granulating and grinding of the liquid slag enriched with heavy metals yielded the slag product "puzzolane" having 20 the following analysis: Nonferrous Metal Portion (%) 15 Ni Sn 0.34 0.13 0.07 Cu 25 Component Si02 AI2O3 Fe203 CaO MgO K2O Na20 Ti02 P2O5 Portion (%) 59 12 0.5 16 2.5 1.5 4.5 30 1.5 0.2 35 On account of the relatively high AI2O3 content, the puzzolane cement has a high early strength. Its wedge index is about 95 %. 27 025 - 12 - On the whole, optimized blast furnace slags may be produced by the addition of Si02 and, if required, AI2O3 carriers, such as clays, quartz sand and bauxite, the melt viscosity being considerably lowered at the same time. When reducing such melts, steel droplets are more easily eliminated by sedimentation such that the free iron content in the hydraulic binder can be substantially lowered. The process according to the invention may be realized in a steelworks in a simple manner. On the assumption of about 15 t of slag incurring per hour, a converter having an active weight of about 125 t, or an active volume of 35 m^, would have to be employed in order to be able to mix 90 t, or about 3 0 m-3 , of steel slag each with approximately 34 t (approximately 5 m^) of pig iron. The clinker phase is drawn off separately from steel and is tapped into a mixing vessel to be completed there. In that mixing vessel, processing to Portland cement clinker may be effected, for instance, by the addition of additives, such as, for instance, clays, and further reduction. Yet, such a mixing vessel, in the first place, also may serve to balance out slag fluctuations. The clinker cooling and granulating means may be cooled by air in the direct method. In such cases, air at temperatures of 20°C is heated to about 1100°C, the clinker being cooled from approximately 1600°C to 250°C. The amount of CO formed constitutes a further source of energy. CO incurs at temperatures of about 1600°C, thus also containing sensible heat in addition to the latent chemical thermal energy. If a thermal loss of 30 % at the most is taken into account with a suitably well insulated metallurgical vessel, this means that the process according to the invention might be operated exothermally for the production of steel and clinker, provided the combustible gases formed could be utilized to the optimum degree. Z'; 025 - 13 - The process according to the invention renders feasible in a particularly simple manner the conversion of a hardly reusable steel slag to ore cement clinker under simultaneous refining. The process according to the invention, furthermore, enables the utilization of heat amounts not readily applicable in conventional processes and, in this way, also the decrease of emissions of gases, in particular, CO2. Within the scope of the process according to the invention, the decisive reactions each occur on the interfaces of the melts, the process being realizable in a sintering furnace. The carbon monoxide evoluting from the interface reduces dissolved iron oxide in the slag bath layer, the CO2 portion of the reducing gas in the slag layer naturally increasing.'-From a volume portion of about 15 % by vol. of CO2 # the gas looses its reducing effect, wherein, however, further energetic use remains possible at least partially, since such gases may be burnt by ventilation or oxygen or air-oxygen mixtures above the slag layei. Heat transfer to the slag and iron phases in that case occurs practically exclusively through radiation procedures. As already mentioned, the waste heat developing may be used for preheating additives, the sinter phase floating on the surface being withdrawable separately. The temperature control according to the invention is adjusted to the stability range of alite, from which the initially demanded overheating results. The alite sinter formed may be frozen to alite clinker by conventional clinker cooling technique, the main target in that context having to be the minimization of the content of free lime. Optionally desired introduction of carbon for controlling the melting temperature of pig iron and the reduction potential may be effected by saturation with carbon in the bath, for instance, by means of immersed lances or the like. Carbon introduction may be effected on several x^oints in counterflow </div>

Claims

<div class="application article clearfix printTableText" id="claims"> > * . u. / i .) o ^ ' u C - 14 - or in co-current flow. In doing so, the iron bath not only functions as a reductant carrier, but also acts as a conveying medium for the slag and sinter phases, particularly simple furnace constructions being applicable. -15- •27 1 025' WHAT WE CLAIM IS:

1. A process for producing steel and hydraulically active binders from slag, characterised in that pig iron is refined by adding slags containing iron oxides in amounts exceeding 5% by weight.

2. A process according to claim 1 wherein the slags are selected from steel slags, Cu converter slags after reaction with a lead bath, or oxidised slags from waste combustion plants.

3. A process according to claim 1 or claim 2 characterised in that the iron oxide content of the slag is chosen to exceed 8% by weight.

4. A process according to claim 3 wherein the iron oxide content of the slag is chosen to exceed 10% by weight.

5. A process according to any one of the preceding claims characterised in that liquid steel slag at temperatures of above 1550°C and molten pig iron at temperatures ranging from 1450°C to 1550°C are used.

6. A process according to claim 5 wherein liquid steel slag at temperatures above 1600°C is used. N 5 MAY 1385 -16- 2? 1 0 z

7. A process according to claim 5 or claim 6 characterised in that molten pig iron is added to the liquid slag phase in amounts by weight ranging from 1:2 to 1:3.

8. A process according to any one claims 5 to 7 characterised in that the liquid phases together are maintained at temperatures of above 1500°C for 3-8 hours.

9. A process according to claim 8 wherein temperatures of between 1660°C to 1800°C are maintained for about 6 hours.

10. A process according to any one of the preceding claims characterised in that an electrically heatable tilting converter is employed as the mixing vessel.

11. A process according to any one of the preceding claims characterised in that the slags are maintained at overheating temperature by blowing in or up oxygen.

12. A process according to any one of the preceding claims characterised in that basic poor ores are added to the slags to increase their iron oxide content to above 8% by weight.

13. A process according to any one of claims 1 to 4 or claims 10 to 12 when dependent on claims 1-4, characterised in that, when using Cu converter slags, lead is drawn off below the steel bath and Zn is condensed from the gas phase. -17- 27 10

14. A process according to any one of the preceding claims characterised in that the slag bath height for the reaction with pig iron is chosen to be between 2 and 8 cm.

15. A process according to claim 14 wherein the slag bath height is chosen to be between 2 and 6 cm.

16. A process according to any one of the preceding claims characterised in that the slag is converted into a sinter phase consisting of 15-25% by weight of molten phase and clinker phase.

17. A process according to claim 16 wherein the molten phase includes aluminates and ferrites and the sinter phase includes minerals, alite and/or belite.

18. A process according to any one of the preceding claims characterised in that CaC03, A1203 and/or SiOz are used as additives.

19. A process according to any one of claims 1 to 15, or 18 when dependent on any one of claims 1 to 15, characterised in that the reduced slag is supplied to a clinker cooling and granulating means.

20. A process according to claim 16 or 17, or 18 when dependent on claim 16 or 17, characterised in that the sinter phase is supplied to a clinker cooling and granulating means. 271025 -18-

21. A process according to claims 19 or 20 characterised in that the clinker is cooled by air in the direct method.

22. A process according to claim 1 for producing steel and hydraulically active binders from slag substantially as herein described. RUSSELL McVEAGH WEST-WALKER by: ATTORNEYS FOR THE APPLICANT </div>