SE519776C2 - Method of producing steel, whereby a metal and fluoride-containing hydroxide slurry is returned to a steel melt - Google Patents

Abstract

Method in the manufacture of steel, especially stainless steel, one or more metal-containing residues from the steel manufacturing process being mixed with an admixture which has a content of a substance in group 14 of the periodic system, following which the mixture is allowed to solidify and the mixture thus solidified is returned to a steel melt in connection with the manufacture of steel. The said residues preferably comprise a metal-containing hydroxide sludge from a steel pickling stage and/or metal-containing, finely dispersed or powdery residues from the steel manufacturing process.

Description

l5 ~. V - H 519 776 the metal hydroxide sludge, after which the mixture is allowed to solidify for 2-30 days by exotic reaction between the lime, the water and the oil. The solidified product is preferably crushed and granulated, after which it can be returned to the steel production, e.g. in converter. Utilization of lime, however, entails some disadvantages, e.g. corrosive alkaline effect on linings.

DE 34 14 400 relates to a method in which hydroxide sludge is mixed with a hydraulic binder (according to the examples cement), after which it is deposited.

JP 6184798 (abstract) refers to sedimentation and centrifugation of sludge of iron hydroxide in order to be able to reuse the electrolyte, WO 97/16573 describes agglomeration of fine iron oxide waste from e.g. pickling liquid used in steel galvanizing. The iron oxide waste, which also contains iron hydroxides, is mixed with a source of calcium ions, eg, lime, a binder, water and possibly carbon in some form. The agglomerates formed can be used in metal fabrication.

DE 41 Ol 584 describes the manufacture of briquettes from roll sinter. The roll sinter is mixed with a binder in the form of molasses and a catalyst in the form of calcium hydroxide.

The briquettes can be used instead of scrap or ore in steel production in converters or directly in blast furnaces.

BRIEF DESCRIPTION OF THE INVENTION The present invention aims to present a method for disposing of metal-containing residual products from steel fraying, such as e.g. acidic, metal-contaminated pickling liquid obtained as a residual product in connection with the manufacture of steel, * whereby the metals in the residual products are recycled in steel production. The invention further aims to present a method for similarly disposing of already deposited hydroxide sludge originating in acidic, metal-contaminated pickling liquids, and also to recover its metal content. Another object of the invention is the disposal also of other metal and / or metal oxide and / or metal hydroxide-containing residual products from steel production, mainly atomized or solid ones, and to recycle their metal content in steel production. The invention is primarily developed for use in connection with the production of stainless steels, but can also be used in connection with other steel production, e.g. production of carbon steel. 519 776 l. = »R. | These and other objects are achieved by the method according to the invention, such as that defined in claim 1.

The invention is based on the idea that metal-containing residues, comprising a metal-containing hydroxide sludge from a pickling step for the steel, which hydroxide sludge comprises at least one fluoride-containing compound, can be recycled in steel production, to a steel melt, when mixed with an additive containing group 14 the periodic table, especially coal and / or silicon. Suitably the additive has a content of said substance in group 14 in the periodic table of at least 30% by weight, preferably at least 35% by weight, even more preferably at least 40% by weight and up to 100% (optionally water not including). The additive is preferably made in the form of a viscous, viscous liquid. However, solids can also be used, preferably in powder form, e.g. pure coal in the form of charcoal or other form.

Liquids that have been tested with good results consist of water glass (NagO * x SiO 2, x = 3-5) and / or molasses. It is assumed that a reaction takes place with the water glass, in which reaction water in the residual product mixture is bound by the water glass, whereby the residual products are bound together and solidify / harden. The additive according to the invention thus constitutes a hardening additive in this case. The same thing happens with silica (SiO 2) in solid form, e.g. powder form, is added, which constitutes an alternative embodiment of the invention. When mixing with molasses, which has a rich carbon content, it is assumed that a polymerization takes place in connection with water loss, which causes the mixture to solidify. It may be assumed that the additive acts as a reducing agent.

According to an embodiment of the invention, the same is intended to provide, by means of the additive ;; .. ^. R ;; _ ,. 1 .. ,,. | _. ^ _.:,. 1, _1 _, ___- Hzn.-. 1 .. | __9n: ._ __: _ 1 .____...__ |: ___ ..: __., ___. . -%, preferably not more than 10% by weight, before returning to steel production.

According to a preferred embodiment of the invention, the additive is mixed both with hydroxide sludge and with metal and / or metal oxide and / or metal hydroxide-containing residual products, which are tin-distributed or present in dust form, after which the mixture is allowed to solidify to a water content of not more than 15% by weight. %, preferably at most Vu, and then transferred to steel productivity.

The initial mixture of hydroxide sludge and possibly metal substances and the additive have a consistency similar to clay embankment, which solidifies to solid form within 24 hours. 1 1 »« m 519 776 When using molasses, solidification normally takes place within 15 hours and when using water glass even faster. The solidifying product can then be mixed into the steel, preferably in connection with the steel melting in an arc furnace in the steelworks, whereby the metals in the product go down into the steel melting, carbon is emitted as carbon dioxide, water as water vapor (in small quantities) and silicon, oxides, fluorides etc. in the product goes up the slag. The amount of slag-forming substance added during the steel smelting can thereby be advantageously reduced, which also means that the amount of slag formed does not increase overall.

DETAILED DESCRIPTION OF THE INVENTION Acidic metal contaminated and spent pickling liquids, which can be disposed of according to the invention, consist of both chemical pickling liquids and pickling liquids for electrolytic pickling. These spent beet fluids include residual acids, e.g. Hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, salts of these acids, as well as dissolved metals and metal oxides. In connection with the method, a neutralization to a pH of about 9-10, known per se, of the consumed beet liquid is carried out by adding alkali, usually lime milk, but other alkaline additives can also be used. The neutralized beet liquid is then dewatered. läinpli gen mechanically in e.g. filter press, to a dry matter content of at least 30% by weight, preferably at least 40% by weight and up to 80% by weight, normally not more than 70% by weight. The dewatered product is called hydroxide sludge.

The hydroxide sludge comprises e.g. CaFz saint Fe, Cr, Ni and Mo hydroxides, at least when hydrochloric acid is used in the pickling liquid and when it comes to stainless steel production.

Slung oxide and grinding chips are typical examples of metal and / or metal oxide and / or metal hydroxide-containing residues from steel production, which can be used for mixing in the hydroxide sludge. Slung oxide and abrasive chips include metals, metal hydroxides and the like. metal oxides, o fi a spinel type, for example Fc (FcCrx0y), where x = 1-2 and 'y = 2-4. Also e.g. used slung sand, which is a form of blasting sand consisting of iron balls, can be mixed in. Cutting slag from string castings or blank treatment can also be used.

Other examples of substances that can be used are certain fuel substances, flue gas substances and extraction from cooling stages, as long as these do not contain excessive levels of undesirable substances, such as As, Zn or Pb. It is an advantage if the metal and / or metal oxide and / or metal hydroxide-containing additives are finely divided, preferably in mare form or in the form of, for example, chips.

The additive according to the invention which causes hydroxide sludge and any metal substances to harden, solidify or polymerize into a substantially solid product, consists according to - win 519 776 above of an additive containing a substance in group 14 in the periodic table, in particular carbon and / or silicon.

The mixture of hydroxide sludge, residual products in distributed form or mare form and the inventive additive may comprise from 1% by weight and up to 50% by weight, preferably up to 40% by weight and even more preferably up to 30% by weight hydroxide sludge and optionally also from 1% by weight and up to 90% by weight, preferably up to 80% by weight and even more preferably up to 70% by weight of residues in a distributed form or mare form, and up to 55% by weight, preferably at least 10% by weight. % and even more preferably at least 15% by weight of a suitable additive. Optionally, aluminum can also be mixed into contents of from 0.1 to 5% by weight. Taken together, said ingredients preferably form 100% by weight of the mixture, it being understood, of course, that neither the stated maximum contents nor the stated minimum contents can be present at the same time. It should also not be ruled out that other ingredients may be used, however, the ingredients mentioned here constitute at least 80% by weight and more preferably at least 90% by weight of the mixture.

The mixture should be stirred well before it is allowed to solidify. In connection with the mixing, or before the mixing, any larger lumps or “cakes” of the hydroxide sludge should be crushed and it should also be ensured that other utilized residual products are in a distributed form.

According to an embodiment of the invention, the mixture, which directly after the mixing has a loose consistency similar to clay gruel, is poured into vessels to solidify, which vessels can preferably be introduced into the steel melt together with the mixture, which has solidified after normally no more than about 24 hours after mixing. Such vessels can consist of residual products per se, suitably wooden, berry, cellulose, berry or metal-based vessels, e.g. leftover cardboard tubes or other cardboard products such as waste paper barrels, or metal containers. Examples of metal vessels that can be used consist of scrap to be melted down for steel production, leftover pipes of steel or aluminum, etc. A variant of filling the mixture into vessels is, of course, to granulate it. Another variant is to simply pour the mixture into a mold or directly on a substrate of e.g. concrete.

When the mixture solidifies, it comes loose, which can, however, be facilitated by e.g. a coating or a powder layer in the tyrrons or on the substrate.

The mixing of the solidified product in the steel is preferably done in connection with the melting of scrap in an arc furnace, but it is also conceivable that the solidified product (519 776) can be mixed into a converter. Additives of from 1% by weight and up to 50% by weight of the solidifying mixture in the scrap are conceivable, even if smaller amounts are normally used, e.g. up to 40% by weight * l / o or preferably up to 30% by weight, based on scrap or other steel raw material plus the solidified product according to the present invention.

As an alternative to using the addition of aluminum in the mixture, as a "igniter" to start the steel melting in the arc furnace, aluminum can be charged together with the solidified mixture during the sintering. If the mixture is filled in aluminum tubes to solidify, however, no extra aluminum additive is usually needed. Extra carbon can also be mixed in (eg in the form of wood, coke, charcoal, paper, iron with a high carbon content, etc.), for to function as a reducing agent, especially in the case where the additive according to the invention consists of other than pure or substantially pure carbon, e.g. as the thawing-like additive consists of water glass. carbon from graphite electrode can be mixed in. However, it is not always certain that the addition of extra carbon is needed, especially when molasses is used in the mixture. The water content of the solidified product should be as low as possible. It is possible to mix the solidified product into the steel tube at water contents of up to 15% by weight, preferably 10 to 15% by weight or even more preferably below 10% by weight. EXAMPLE In a series of experiments, samples of hydroxide sludge and metal / metal oxide / metal hydroxide-containing dust-containing or finely divided residues, with molasses and carbon (Experimental series 1), water glass and carbon (Experimental series 2) and molasses and water-glass (Experimental series 3). The mixtures were allowed to solidify and then melted down together with aluminum and iron, in order to mimic large-scale immersion in an arc furnace. Table 1-3 shows the composition of the various mixtures and the melting response in the form of the proportion of Cr, Fe and Ni and the exchange of Cr and Ni in the product obtained.

Experimental series 1 Table la kg% Cr (kg) Ni (kg) Slungsto fi 1.00 16.00 0.20 0.08 Fabric-Cooling distance 1.00 16.00 0.20 0.08 Sanding shavings (hot sanding) 1.00 16.00 0.20 0.08 Hydroxide sludge 0.50 8.00 0.01 0.00 Slung sand (consumed) 1.00 16.00 0.02 0.01 Coal coke 0.50 8.00 519 776 Molasses 1, 20.00 Total weight (sample) = 6.25 100.00 0.630 0.250 16.8 g of solidified sample were weighed in together with 40.5 g of Fe and 0.6 g of Al, which was then melted down for a melting time of 4 minutes. to a melt weight of 46.7 g. The melting was good. Result results and yields are shown in Table lb. In Table 1b, the yield of Cr and Ni refers to the proportion of Cr and Ni that ended up in the molten steel. Table 1b Weight Yield Cr 0.66% 20.67% Fe 97.98% Ni 0.66% 52.10% Residual = 0.70% Total = l00.00% Experimental series 2 Table 2a kg% Cr (kg) Ni (kg) Slung dust 1.00 16.67 0.20 0.08 Fabric cooling distance 1.00 16.67 0.20 0.08 Abrasive shavings (hot dip) 1.00 16.67 0.20 0.08 Hydroxide sludge 0.50 8.33 0.01 0.00 Slung sand (consumed) 1.00 16.67 0.02 0.01 Coal coke 0 .50 8.33 Water glass 1 .00 16.67 Total weight (sample) = 6.00 100.00 0.630 0.250 Weighed in 13.3 g of solidified sample together with 40.8 g Fe and 0.7 g Al, which then melted over a sintering time of 4 minutes to a melt weight of 44.1 g. The melt was good. Result response and yield are shown in Table 2b. In Table 2b, the exchange of Cr and Ni refers to the proportion of Cr and Ni that ended up in the molten steel.

Table 2b Weight Yield cr 1.80% 5s, 44% Fe 97, 10% Ni 0.80% 65.45% Residual = 0.30% Total = l00.00% <v -,. , 519 776 8 Trial Series 3 Table 3a (kg) “V0 Cr (kg) Ni (kg) Slungstoft 1.00 18.18 0.20 0.08 Fabric-Cooling distance 1.00 18.18 0.20 0.08 Sanding shavings (hot sanding) 1.00 18.18 0.20 0.08 Hydroxide sludge 0.50 9.09 0.01 0.00 Slung sand (consumed) 1.00 18.18 0.02 0.01 Water glass 0.50 9 .09 Molasses 0.50 9.09 Total weight (sample) = 5.50 100.00 0.630 0.250 16.4 g of solidified sample were weighed in together with 28.3 g of Fe and 0.8 g of Al, which was then melted down under a melting time of 4 minutes to a melt weight of 31.1 g. The melt was good. Result response and yield are shown in Table 3b. In Table 3b, the exchange of Cr and Ni refers to the proportion of Cr and Ni that has ended up in the liopsin-inlaid steel.

Table 3b Weight Yield Cr 1.69% 30.94% Fe 96.68% Ni 1.25% 57.66% Residual = 0.38% Total = l00.00% Experimental series 4 Experimental series 4 aimed to analyze where the or uorides in the hydroxide sludge takes the path in connection with the implementation of the invention, Table 4a (kg) ° / ° Cf (kg) Ni (kg) F (kg) Slungsto fi 0.50 5.56 0.10 0.04 0.00 fabric-Cooling rack 0, 50 5, 50 0, 10 0.04 0,00 Sanding chips (hot sanding) 3,00 33,33 0,60 0,24 0,00 Hydroxide sludge 2,00 22,22 0,04 0,01 5,56 Slung sand ( consumed) 0.50 5.56 0.01 0.00 0.00 Water glass 2.00 22.22 Molasses 0.50 5.56 Total weight (sample) = 9.00 100.00 0.850 0.332 5.556 519 776 It was weighed in 14.8 g of solidified sample together with 43.4 g of Fe and 0.9 g of Al, which was then melted down for a melting time of 4 minutes to a melting weight of 48.2 g. The melting was good. Result response and yield are shown in Table 4b. In Table 4b, the exchange of Cr and Ni refers to the proportion of Cr and Ni that ended up in the assembled steel. The yield of F, on the other hand, refers to the proportion of F that ended up in the slag, advantageously and desirably meaning that virtually all fl uoride present in the hydroxide linxnet ended up in the slag and not in the steel itself, Table 4b Weight Yield Cr 0.30% 10, 96% Ni 0.90% 84, in 5% F 9.00% 99.5 l ° / o The greatest benefit of the method according to the invention is the possibility of handling hydroxide sludge derived from spent beet liquid, especially spent beet liquid containing fl uorides and derived from the stainless steel manufacturing process. According to the invention, it is also impossible to take care of such hydroxide sludge which is already in a landfill, whereby such existing landfills can be worked off in the long term. Another important advantage of the method according to the invention is, of course, that dust-compatible or non-distributed residual products containing metals and / or metal oxides and / or metal hydroxides can be recycled in a simple manner in steelmaking.

In particular, it is an advantage that Ni, Cr and Mo can be recovered from the residual products. In addition, the amount of slag former added during the steel inhalation can be reduced, at the same time as no more slag is formed than normal due to the addition to the steel meal.

Claims (13)

1. 0 15 20 25 30 35 \ 2> 519 776 2. PATENT REQUIREMENTS A method in connection with the manufacture of steel, preferably stainless steel, wherein one or more of the metallic residues from the steel production are mixed with an additive containing a substance in group 14 in the periodic table, after which the mixture is allowed to solidify and the mixture thus solidified is returned to a steel smelter in connection with the steel production, characterized in that said one or more of its residual products comprises a metal-containing hydroxide sludge from a pickling step for the steel, which hydroxide sludge comprises at least one fluoride-containing compound. 4. A method according to claim 1, characterized in that said additive has a content of a substance in group I4 in the periodic table of at least 30% by weight, preferably at least 35% by weight, even more preferably at least 40% by weight. and up to 100%. Method according to claim 1 or 2, characterized in that said additive has a content of carbon and / or silicon, wherein said additive preferably consists of a liquid, most preferably a viscous liquid. or an additive in solid form, said additive preferably being selected from the group consisting of molasses, water glass, silica and carbon. A method according to any one of the preceding claims, characterized in that said hydroxide sludge is prepared by neutralizing spent pickling liquid, after which the neutralized pickling liquid is dewatered to a dry matter content of at least 30% by weight, preferably at least 40% by weight and up to 80% by weight, preferably up to 70% by weight of said hydroxide sludge. A method according to any one of claims 1-3, characterized in that said hydroxide sludge is retrieved from landfill. Method according to any one of the preceding claims, characterized in that said hydroxide sludge also comprises hydroxides of chromium and / or nickel and / or molybdenum. Method according to any one of the preceding claims, characterized in that said one or more residual products comprise metal and / or metal hydroxide- and / or metal oxide-containing residues from the steel production, which residues are preferably in distributed form or dust lining and which residual products are preferably selected from the group consisting of sling oxide, grinding chips, slung sand, cutting slag, olter residues, 10 20 25 30 10. 11. 12. 13. 519 776 flue gas stoves and extraction from cooling stages, Method according to one of the above requirements, characterized in that aluminum is also mixed into the mixture. Method according to one of the preceding claims, characterized in that the mixture is brought to comprise from 1% by weight and up to 50% by weight, preferably up to 40% by weight and even more preferably up to 30% by weight of hydroxide sludge and preferably also from 1% by weight and up to 90% by weight Wo, even more preferably up to 80% by weight and most preferably up to 70% by weight of metal-containing residual products in distributed form or dust form, and up to 55% by weight Wo, preferably at least 10% by weight. % and even more preferably at least 15% by weight of said additive. A method according to any one of the preceding claims, characterized in that the solidified mixture has a dry content of up to 15% by weight, preferably 10-15% by weight and more more preferably under 10 wt. Method according to one of the preceding claims, characterized in that the mixture is poured into a vessel for solidification, which vessel is preferably introduced into the molten steel together with the solidified mixture, and which vessel preferably consists of a residual product per se, preferably a tratibene, cellulose fiber or metal-based vessel, even more preferably a vessel selected from the group consisting of carton products and scrap metal. Method according to one of the preceding claims, characterized in that the mixture ß. T, _ a form or on a solid support 'Stein-ande CL. E! Lällnl x .. ._ L anal ", .._ ^ .... _ .. llallb l lUl dlL btCllld, VdlUllUl the mixture is detached from the mold or substrate. Method according to one of the above claims, characterized in that the mixture is returned to said steel melt in amounts of from 1% by weight and up to 50% by weight, preferably up to 40% by weight and even more preferably up to 30% by weight, based on scrap or other steel raw material plus the solidified mixture.