Process for recovering metal materials from steel slag

Abstract

A process for recovering (1) metal materials from slag of steel industry and wherein the slag comprises EAF slag. The EAF slag is heated (2) in a furnace to enhance the extraction of the metal materials from the EAF slag being in molten state. The process further comprises lowering viscosity (3) of the molten EAF slag by adding at least one alkaline material. The EAF slag is also arranged to foam (4) and thereby provide stirring for the molten EAF slag. Further, the metal oxides of the molten EAF slag are reduced (5) by means of at least one reducing agent.

Description

[0001] Process for recovering metal materials from steel slag

[0002] Background of the invention

[0003] The invention relates to a new solution for processing steel slag and recovering metals from the steel slag .

[0004] The obj ect of the invention is described in more detail in the preamble of independent claim of this document .

[0005] In steel industry huge amounts of metal containing slags are produced . Metals included in the slags hamper utili zation of the formed slags . Especially heavy metal components , such as Cr and V, included in the s lags . Nowadays the slags are treated as waste materials and they cause significant waste costs . Some attempts have been disclosed for recovering the metals from the slags . However, the known solutions have shown to include some drawbacks , such as high content of unrecovered metals remaining in the slag . That usually prevents producti zation of the slags into market as safe materials . Additional difficulties are faced when utili zing remaining slag as a binder material .

[0006] It has been noted that especially EAF slag is a difficult slag to be treated . EAF slag is a steel-making slag generated from electric arc furnace treatment wherein high-power electric arcs are implemented . The maj or component of EAF slag is calcium oxide (CaO) and this is considered to be problematic for the further treatments unless chemical composition and process conditions are optimi zed .

[0007] Brief description of the invention

[0008] The idea of the invention is to provide a new and improved process for recovering metals from steel industry slag containing EAF slag . The characteristic features of the process according to the invention are set forth in the characteri zing part of the independent claim .

[0009] An idea of the disclosed solution is to provide a process for recovering metal materials from slag comprising EAF slag with metal oxides . The process comprises heating the EAF slag in a furnace to enhance the extraction of the metal materials from the EAF slag . The process further comprises lowering viscosity of the molten EAF slag by adding at least one alkaline material and thereby improving fluidity of the molten EAF slag . With some slags , or slag-side stream combinations , optimi zing may need, in addition, either silicon, aluminum, or magnesium containing materials to optimize viscosity of the slag . The process further comprises providing slag foaming for stirring the molten EAF slag and extracting the metal materials included in the molten EAF slag . The metal oxides of the molten EAF slag are reduced by means of at least one reducing agent .

[0010] In other words , recovery of metal materials included in the molten EAF slag is facilitated by the mentioned three measures in the furnace , namely lowering the viscosity, providing the foaming and executing the reduction .

[0011] An advantage of the disclosed solution is that recovery of metal materials can be enhanced by implementation of the disclosed process . This way EAF slags can be utilized effectively, and environmental ris ks of metal containing EAF slags are decreased .

[0012] According to an embodiment , wherein the process comprises heating the EAF slag in a furnace and extracting metals from the molten EAF slag . Share of the liquid state and viscosity can be optimi zed with additive chemicals , elements or side streams in manner that reduced molten metals can be separated . Thus , at least the metal materials are melted down and are in liquid state and increase the size of metal droplets to improve separation based on gravity . In addition, there may be sol id slag particles in the furnace which produce refined slag from which binder material can be produced .

[0013] According to an embodiment , additive materials may cons ist of commercial chemicals or mineral s , or industrial side stream materials , or their combinations .

[0014] According to an embodiment , the process comprises heating the EAF slag in an induction furnace .

[0015] In other words , the process may implement induction furnace heating which is an energy efficient method for heating and melting metal containing EAF slags . A further advantage of the induction heating is that the heating process can be controlled accurately and loss of valuable metals during the heating process can be decreased .

[0016] According to an embodiment , magnetic flux generated in the induction furnace induces eddy currents by means of electromagnetic induction inside the metal contained in the molten EAF slag and produce heat and mixing of the molten EAF slag .

[0017] According to an embodiment , the process implements vortex stirring or induction stirrer for mixing the molten EAF slag inside the crucible . In the vortex stirring the stirring effect is enhanced by pulsating the magnetic fields to alternate forces subj ected to the molten EAF slag . The magnetic fields can also be traveling which also produces vortex stirring .

[0018] According to an embodiment , the process implements pulsating magnetic fields for heating the EAF slag . Then the pulsating magnetic fields cause pulsating heating effect in the treated molten EAF slag . It has been noted in the experiments that higher efficiency during a heating cycle can be reached when the magnetic field and the produced heat fluctuated . The improved energy efficiency is reached because mass in separated edge surfaces of the treated EAF slag is higher than in the whole mass . Greater magnetic fields are induced at the edge areas of the molten EAF slag, and the entire EAF slag material needs not to be heated to as high temperatures as the edge areas . This of course improves energy efficiency .

[0019] According to an alternative embodiment , the process implements an electric arc furnace (EAF) for heating the slag .

[0020] According to an embodiment , the process comprises reducing the metal oxides of the molten EAF slag by means of hydrogen gas . In other words , hydrogen gas is used as the reducing agent and is arranged to flow inside the furnace during the heating process . The gas can be directed from a top part of the furnace towards the EAF slag inside the crucible . An advantage of the embodiment is that the hydrogen gas is an effective reducer . When using the hydrogen gas C02 emissions can be significantly lower compared to conventional reducing agents .

[0021] According to an embodiment , the reducing agent may be a gas mixture comprising the hydrogen gas and one addition gas , such as argon or nitrogen gas .

[0022] According to an embodiment , the process utili zes black liquor as the reducing agent . The black liquor is fluid containing lignin removed from wood material in a pulping process of paper industry .

[0023] According to an embodiment , the process utili zes nanocarbon material or carbon from biomass as the reducing agent .

[0024] According to an embodiment , the process utili zes municipal sewage sludge as the reducing agent . The municipal sewage sludge is produced as a by-product during sewage treatment of municipal wastewater .

[0025] The sewage sludge can comprise iron compounds and precious metal compounds whereby it can serve as an additional iron and metal source for the recovery process .

[0026] Further , other organic reducing agents may al so be utili zed in the disclosed process . According to an embodiment , the process can implement green liqueur dreg as the source of calcium and other alkaline materials . In addition to, the green liqueur can serve as a reducing agent .

[0027] According to an embodiment , the process utili zes two different slags at a time and wherein at least one of the slags is the EAF slag .

[0028] According to an embodiment , the process utili zes two different slags at a time and wherein the slags are the EAF slag and Argon Oxygen Decarburi zation (AOD) slag . The AOD may be implemented as Ca and Al containing material .

[0029] According to an embodiment , the process utili zes two different slags at a time and wherein the slags are the EAF slag and slag from oxygen converter processes . Those slags may also be implemented as Ca and Al containing material .

[0030] According to an embodiment , the process utili zes two different slags at a time and wherein the slags are the EAF slag and slag from directly reduced iron ( DRI ) smelting furnace processes . Those slags may also be implemented as Al containing material .

[0031] According to an embodiment , the process utili zes at least one of the two types of steel s lags generated in the EAF process : an EAF-C slag from carbon steel production, and an EAF-S slag from stainless steel production .

[0032] According to an alternative embodiment , the process utili zes only one slag at a time whereby the slag being treated is the EAF slag .

[0033] According to an embodiment , the process comprises lowering viscosity of the molten EAF slag by adding at least one first alkaline slag material . In other words , the alkaline slag material provides the desired effect of lowering the viscosity .

[0034] The alkaline slag material may as such provide the desires viscosity lowering without a need to use any other alkaline material in addition to the alkaline slag, or alternatively, the alkaline slag and one or more other alkaline materials may be implemented together to provide the desired viscosity lowering for the EAF slag .

[0035] According to an embodiment , the process comprises lowering viscosity of the molten EAF slag by adding at least one first additive alkaline material . In other words , one or more alkaline additive materials can be added to the furnace when treating the EAF slag .

[0036] According to an embodiment , the at least one first additive alkaline material for lowering the viscosity of the molten EAF slag is at least one of the following side stream materials : Analcime , Phlogopite , Spodumene , or Biotite .

[0037] According to an embodiment , the first additive alkaline material may alternatively be magnesium, calcium or other alkaline materials . The material can consist of industrial side-stream materials , or other suitable materials , such as wollastonite or pyroxenes , and calcium or magnesium containing feldspars instead of carbonate bearing minerals .

[0038] According to an embodiment , the alkal ine materials may be side stream materials such as slag, or oil shale ash, mine tailings , mine side streams such as waste rock . Said materials may also contain various contents of aluminum and silicon for optimi zing Ca-Si and aluminum ratios of slag . High alkaline or calcium containing slags may be adj usted with silicon containing waste streams or minerals like silicates and quartz .

[0039] According to an embodiment , the alkaline material for lowering the viscosity of the molten EAF slag may be green liquor which is a dissolved smelt produced in a recovery boiler in a pulping process .

[0040] According to an embodiment , the alkaline material for lowering the viscosity of the molten EAF slag may be natural alkaline containing material . According to an embodiment, lowering viscosity and to increase share of liquid phases of the slag can be increased by adding silicon-rich industrial side streams from constructing-, energy-, mining and metal industries and are used as silicon-rich sources: mineral wastes which contains quartz, phlogopite, analcime, waste glass and rock- and glass wool.

[0041] According to an embodiment, lowering viscosity and to increase share of liquid phases of the EAF slag can be influenced by adding industrial side streams from constructing-, energy-, mining and metal industries and are used as aluminum-rich sources: phlogopite, red mud, bauxites, sodium aluminate, demolished aluminate-cement , wastes from water purification.

[0042] According to an embodiment, the slag foaming is provided by means of the first alkaline additive material vaporizing and forming gas bubbles in the molten EAF slag. In other words, the added alkaline material smelts, vaporizes and forms gas bubbles which rise towards an upper surface of the molten EAF slag in the furnace.

[0043] According to an alternative embodiment, any other alkaline material included in the molten EAF slag, such as alkaline slag or alkaline side stream material, can also vaporize in the furnace and generate gas bubbles which cause foaming of the molten EAF slag.

[0044] According to an embodiment, the process provides the slag foaming by injecting at least gas to the EAF slag.

[0045] According to an embodiment, the injected gas is one of the following: argon or nitrogen gas which are inert gases .

[0046] Alternatively, the injected gas may be another inert gas or a reducing gas, or a combination of the inert gas and the reducing gas . The reducing gas can be carbon monoxide or hydrogen gas, for example. According to an embodiment , one or more of the above mentioned gases can be fed inside the furnace to cause the desired slag foaming without the mentioned inj ection .

[0047] According to an embodiment , the process comprises adding at least one second additive material for lowering melting temperature of the EAF slag . An advantage of thi s embodiment is that the process temperature for the metal recovery can be lowered whereby energy can be saved . Thus , the use of the second additive material may provide significant improvement to the energy efficiency of the metal recovery .

[0048] According to an embodiment , the second additive material for lowering the melting temperature of the EAF slag may be silicon ( Si ) .

[0049] According to an embodiment , alternative materials for lowering the melting temperature may be one of the following : boron, boric acid, borax, colemanite , ulexite , fluorine compounds .

[0050] According to an embodiment , the process comprises removing crystalline water from one or more of the implemented materials prior to being charged into the furnace .

[0051] In other words , the used materials are pre-treated to remove the crystalline water from their composition so that steam explosion in the furnace can be prevented .

[0052] According to an embodiment , the material is preheated prior being charged into the furnace . The pre-heated material can be charged directly from the pre-heating treatment to the furnace , or alternatively, the material can be stored for later use .

[0053] According to an embodiment , the process is conf igured to recover at least one of the following metal materials from the molten EAF slag : iron ( Fe ) , chromium (Cr) .

[0054] According to an embodiment , the following metal material can also be recovered from the molten EAF slag : nickel (Ni ) , vanadium (V) , titanium ( Ti ) , manganese (Mn) . According to an embodiment , the processed EAF slag is conveyed directly from the steel production plant in molten state to the extraction process . An advantage of thi s embodiment i s that the recovery process utili zes high temperature of the EAF slag whereby energy efficiency of the recovery process is good . This has a positive impact on aims lowering C02 emissions .

[0055] According to an embodiment , the processed EAF slag is in solid state and is melted back into molten state prior executing the extraction process . An advantage of this embodiment is that it is possible to implement EAF slag material that has been previously stored on a storage area . Then old EAF slag piles and storages can be utili zed, and valuable metal material recovered from them . A further advantage is that environment of a steel refining plant can be improved when slag storages can be removed and land area at the plant can be utili zed for other purposes .

[0056] According to an embodiment , the proces sing unit for the recovery process may be located at distance from the steel refining plant and the storage area of the EAF slag since the EAF slag being in solid state can be transported by means of conveyors and vehicles to desired location .

[0057] According to an embodiment , the process implements combination of solid state EAF slag and molten state EAF slag . Then the molten state EAF slag can be used to heat the solid state EAF slag at least partly and energy bound in the molten state EAF slag can be utili zed in an energy effective way since less additional heating energy is needed .

[0058] According to an embodiment , the EAF slag is processed in batches in the induction furnace .

[0059] According to an embodiment , the EAF slag is processed continuously in the induction furnace .

[0060] According to an embodiment , the process implements target temperature which is 1500 to 1550 ° C . According to an embodiment , the process implements target temperature which is 1500 to 1650 ° C .

[0061] According to an embodiment , the process implements target temperature being below 1600 ° C .

[0062] According to an embodiment , it is possible to increasing relative amount of the additive materials so that the target temperature may be even lower, such as 1400 ° C .

[0063] According to an embodiment , properties of the produced refined slag and binder material produced of the refined slag can be influenced by means of additives . The additives can be added before grinding rapid cooled refined slag . Alternatively, or in addition to , the additives can be added to the molten slag, but the additives need to be selected so that they do not have negative influence on the metal extraction . A further possibility to adj ust properties of the binder material is to select suitable additive material being loaded into the furnace together with the EAF slag when initiating the extraction process . Thus , there are several possibilities to adj ust properties of the refined slag so that desired material for the binder material production is produced simultaneously with the metal extraction .

[0064] The above-described embodiments and their features may be combined to provide desired configurations .

[0065] Viscosity

[0066] The EAF slag has higher viscosity before adding the additives . When alkaline additives are added, pH-value of the EAF slag is increased . The resulted higher pH-value means lower viscosity for the EAF slag .

[0067] The addition of the alkaline material to the EAF slag may also lower melting temperature of the EAF slag .

[0068] The addition of the alkaline material to the EAF slag may also facilitate breaking up magnesium aluminum spinels . Further, the alkaline material may improve liberation of chromium and iron from mineral form into the EAF slag .

[0069] Slag foaming

[0070] The foamy EAF slag is porous and has greater surface area which enhances effect of the hydrogen or other gases during reduction .

[0071] The foaming improves movement of the molten EAF slag in the induction furnace .

[0072] Formed smaller metal droplets wil l be combined with each other and form heavier metal droplets which can pas s through the foamed molten slag easier and enter under gravity to a bottom part of the induction furnace .

[0073] Example

[0074] Waste materials , EAF-slag, quartz , analcime sand and feldspar-mine tailing sand were tested in a batch reactor . Additional waste materials were crushed in advance down to <0 , 5 mm particle si ze before use and slags were in 4 mm particle si ze . Shares of side streams in blends were calculated to have dif ferent Ca / Si / Al-relations mitigating normal chemical variation of commercial cement qualities .

[0075] The samples were loaded into graphite crucibles and set in a sealed reactor . Temperature was measured by thermocouples under a bottom of the crucible and by optical thermometer through a lid . Before heating, air in the gas sealed gas container and in the crucible were removed by feeding formier-5 gas (nitrogen / H2 95 / 5% ) 2 1 / min for 15 minutes and thereafter samples were heated within 60 minutes to target temperatures 1600 ° C and were kept at the target temperatures for 40 minutes .

[0076] After treatment and cooling, the samples with the crucibles were halved . The molten slag / metal samples were halved with an angle grinder . Metal droplets which were located mostly at the bottom and side edges of the samples, were collected and remaining slag was analyzed by XRF device on a core part (20*20 mm area) on the halved surface of the slag samples (results are shown in the Table 1) . Blend S+F turned out to be fine dust after cooling (with maxim particle sizes < 75microns) and that was sampled by separating metals by magnet.

[0077] Table 1

[0078] Oxid-contents and metal concentrations of commercial cements, EAF-slag and treated slag + analcime (S-A) , slag + quartz (S-Q) , and slag + phlogopite (S + F) blends. Metal concentrations of cement are maximum concentration values observed in reference samples.

[0079] Cements EAF S-A S-Q S-F

[0080] When good recovery of metals in the mixtures were observed in the previous studies, S-F sample was decided to cool faster, and minerology of the sample was analyzed by X-ray diffraction. Sample was cooled down to 700°C in 5 minutes by lifting the sample into room temperature. Most of crystalline mineral-phases composed on Ca2SiO4, were synthetic calcio-olivines with some larnite (61.5 %) , while other Al-Si-Mg containing crystalline-phases content was 20% with some uncertainty in identification. Dolomite was also identified as minor fraction (1.28%) and other unknown- phases consisted mostly of amorphous-mineral phases. Cal- cio-olivines were synthesized, instead of alite and belite, due to non-optimized cooling rates, as well as other alu- minum-silicates . Low amount of free lime indicates, that with optimized heating-cooling, cement-clinker-kind of binders are possible to produce from this kind of materials. Those first-phase experiments done were focused on recovery of metals and heavy metals from slags, not optimizing of binder synthesizing.

[0081] Graph 1.

[0082] Particle size distribution of treated EAF slag phlogopite sample after treating sample at 1600°C and cooling at room temperature.

[0083] As can be noted, calcium, silicon, aluminum and magnesium contents enriched during treatments, since metals recovered from slag were up to 20% of initial weight of EAF- slag samples. Heavy metals with the highest concern in alkali-activated concretes and cements, chromium and vanadium, were close to, or under concentrations of commercial cements. The use of magnesium containing materials may be favorable when chromium may cause a problem for commercialization of slag. All mixes were close or within variation of analyzed commercial reference cement-samples and pointing the potential for upcycling processes of EAF slags to OPC-like binder materials .

[0084] Brief description of the figures

[0085] Some embodiments of the proposed solution are illustrated in more detail in the following figures , in which

[0086] Figure 1 i s a schematic diagram illustrating basic features of recovering metal from EAF slag,

[0087] Figure 2 is a schematic diagram illustrating features relating to heating of the EAF slag,

[0088] Figure 3 is a schematic diagram illustrating features relating to reducing metal oxides of the molten EAF slag,

[0089] Figure 4 is a schematic diagram illustrating features relating to lowering viscosity of the molten EAF slag by means of alkaline material ,

[0090] Figure 5 is a schematic diagram illustrating features relating to slag foaming,

[0091] Figure 6 is a schematic diagram illustrating features relating to possibility to lower melting temperature of the EAF slag,

[0092] Figure 7 is a schematic diagram illustrating purposes of the metal recovery from the EAF slag,

[0093] Figure 8 is a schematic side view of an induction furnace usable for the metal recovery process , and

[0094] Figure 9 is a schematic diagram showing a process of executing metal extraction and producing binding material .

[0095] For the purpose of clarity, some embodiments of the proposed solutions are illustrated in the figures in a simplified form . The same reference numerals are used in the figures to refer to the same elements and features .

[0096] Detailed description of some embodiments

[0097] Figure 1 discloses basic features for a process for recovering metal materials 1 from slag of steel industry . The slag comprises EAF slag with metal oxides . The process comprises heating 2 the EAF slag in a furnace to enhance the extraction of the metal materials from the EAF slag being in molten state . The process further comprises lowering viscosity of the molten EAF slag by adding at least one alkaline material 3 and thereby improving fluidity of the molten EAF slag . The process is also provided with slag foaming 4 for stirring the molten EAF slag and extracting the metal materials included in the molten EAF slag . The metal oxides of the molten EAF slag are reduced 5 by means of at least one reducing agent .

[0098] Figure 2 discloses that the heating process 2 may include melting and heating 6 when the EAF slag is in solid state when charged into the furnace . In an alternative solution the process is arranged to heat EAF slag being already in molten state 7 . Figure 2 also discloses that the heating can be a batch process 8 or alternatively it can be a continuous process 9 . The heating can be executed in an induction furnace 10 wherein Eddy Currents cause magnetic stirring 11 for the molted EAF slag . The stirring can be enhanced by implementing in the heating vortex stirring 12 , wherein the magnetic field can be pulsated or moved, or can be both pulsated and moved during the heating .

[0099] Figure 2 further discloses that the EAF slag being in solid state can be pre-heated by using energy sources of different processes at a production plant . It is possible to use for example superheated steams for the pre-heating purposes . Further, energy captured from a process of rapid cooling of produced binder material can be used for preheating the EAF slag . This way, when available energy sources at the production plant are utili zed and energy capturing is implemented, energy efficiency of the metal extraction process can be improved .

[0100] It is also possible to combine EAF slag being in molten state with EAF slag in solid state and thereby utili ze the energy of the molten EAF slag to melt the sol id state EAF slag . This way energy required in the heat treatment inside the furnace can be lower .

[0101] Figure 3 discloses possible proces ses and reducing agents for reducing the metal oxides 5 of the molten EAF slag . Hydrogen gas can be fed 13 inside the furnace during the heating, or alternatively gas mixtures 14 comprising hydrogen and argon cases can be used as reducing agents . It is also possible to use black liquor 15 , nanocarbon materials 16 or municipal sewage sludges 17 as reducing agents .

[0102] Figure 4 discloses possible alkaline materials that can be used for lowering viscosity of the molten EAF slag 3 . The viscosity can be lowered by using alkaline slag material 18 together with the EAF slag, whereby combination of two slags is implemented . An alternative is to add a first additive alkaline mineral material 19 , such as Anal cime , Phlogopite or Spodumene . Use of two or all of them simultaneously may also be possible . However, it has also noted that alkaline side stream materials 20 , such as green liquor serve as viscosity lowering materials , as well as natural alkaline containing materials 21 . Thus , a relatively wide variety of dif ferent alkaline materials can be implemented for lowering the viscosity of the molten EAF slag .

[0103] Figure 5 discloses that foaming 4 of the molten EAF slag can be executed in many different ways . Gas can be inj ected 22 to the molten slag . The inj ected gas may be inert gas , reducing gas , or their combination . Alternatively, or in addition to , the foaming is produced by means of an alkaline material which is vapori zed in the furnace and produces thereby gas bubbles 23 .

[0104] Figure 6 discloses that melting temperature of the EAF slag can be lowered 24 by adding a second additive material 25 . The second additive material may be silicon rich material . Alternative melting temperature lowering materials are boron, boron acid, borax, colemanite , ulexite , and fluorine compounds , for example . It is also possible to use gaseous second additive material and to inj ect combination of inert gas and reducing gas for lowering the melting temperature .

[0105] Figure 7 discloses some purposes 26 for the metal recovery process for the EAF slag . Since metals are recovered in the process , valuable metal materials are provided 27 . These metals would be lost without utili zing the disclosed process . When the metal materials are removed from the EAF slag, the EAF slag contains no more harmful metals and substances and is therefore safe to store and use 28 . The process can also provide valuable binder material , filling material and other material components to be used in construction materials 29 .

[0106] The disclosed process provides refined slag which can serve as a basic material for producing binder materials properties of which corresponds to a standard Portland cement .

[0107] Figure 8 discloses an induction furnace 10 comprising a basic body or structure 30 provided with a space 31 inside which a nonconductive crucible 32 can be placed removably . This type of a furnace may also be called as an induction crucible furnace . The space 31 may be gas sealed by means of an openable lid 33 and desired gas or gas mixtures can be fed to the space 31 through one or more gas feed connections 34 . The basic structure 30 comprises coi ls 35 which are connected to an electric supply and control system . EAF slag 36 to be treated is charged inside the crucible 32 . When the induction furnace 10 is operating alternating electric current is arranged to flow through wires of the coils 35 . Then the electric current i . e . , coil current generate a rapidly reversing magnetic field and generate magnetic flux 37 . The magnetic field induces eddy currents 38 , which are circular electric currents 39 . The eddy currents 39 flowing through electrical resistance of the metal material in the EAF slag, heat the EAF slag 36 . Once the EAF slag is melted, the produced eddy currents cause vigorous stirring of the melt and provide good mixing . Characteristics for the induction heating is that the heat is generated within the metal material contained in the treated EAF slag .

[0108] Figure 8 further illustrates that metal droplets 40 inside the molten EAF slag 36 move towards lateral side and bottom areas inside the crucible 32 because of the circulating eddy currents 39 . Areas where metallic material is accumulated are shown in broken lines 41 . Smaller metal droplets 40 are combined and bigger combined droplets 42 are formed on the areas 41 . Movements of the droplets 40 are enhanced by the slag foaming measures and by the viscosity lowering measures . In the foamed lower viscosity molten EAF slag the droplets move more easily to the sides inside the molten EAF slag bath . The movement can be further improved by means of pulsating the magnetic fields and utili zing other vortex stirring possibilities .

[0109] Figure 9 discloses a process of executing metal extraction and producing binding material . Ingredients , or raw materials , comprising EAF slag and one or more additive materials are loaded in a furnace for providing heat treatment and metal extraction from the EAF slag . By means of the loaded additive material it is possible to influence to the extraction process and also to properties of refined slag . It i s also possible to add additives into the molten slag . The added additive can be selected so that it improves properties of the refined slag and thereby properties of the produced binder material . However, the additive needs to be selected so that it does not have negative influence on the extraction of metals . When the metals materials , including heavy metals are removed, the refined slag is produced . Additive materials can be added to the refined slag for further improving properties of the produced binding material . Thus , there are several possible phases wherein additive materials can be added and one, two , or all three are implemented for providing desired properties for the binding material corresponding standard Portland cement .

[0110] The hot refined slag leaving the furnace is rapid cooled and is there after subj ected to grinding and grading processes . The rapid cooling, grinding and grading can be executed in accordance with normal cement production principles and using similar process devices .

[0111] Thus , the refined slag serves as raw material for producing standard type of Portland cement . The figures and their description are intended only to illustrate the idea of the invention . However, the scope of protection of the invention is defined in the claims of the application .

Claims

Claims1. A process for recovering metal materials (1) from slag of steel industry, wherein the slag is EAF slag and comprises metal oxides ; and wherein the process comprises heating (2) the EAF slag in a furnace to enhance the extraction of the metal materials from the EAF slag; cha ra ct e r i z ed in that the process further comprises : lowering viscosity (3) of the molten EAF slag by adding at least one alkaline material and thereby improving fluidity of the molten EAF slag; providing slag foaming (4) for stirring the molten EAF slag and extracting the metal materials included in the molten EAF slag; and reducing (5) the metal oxides of the molten EAF slag by means of at least one reducing agent.

2. The process according to claim 1, c h a r a c t e r i z e d in that heating the EAF slag in an induction furnace (10) .

3. The process according to claim 1 or 2, c h a r a c t e r i z e d in that the process comprises reducing (5) the metal oxides of the molten EAF slag by means of hydrogen gas.

4. The process according to any of the preceding claims 1 - 3, c h a r a c t e r i z e d in that the process utilizes two different slags at a time and wherein at least one of the slags is the EAF slag.

5. The process according to claim 4, c h a r a c t e r i z e d in that the process comprises lowering viscosity (3) of the molten EAF slag by adding at least one first alkaline slag material (18) .

6. The process according to any of the preceding claims 1 - 5, c h a r a c t e r i z e d in that the process comprises lowering viscosity (3) of the molten EAF slag by adding at least one first additive alkaline material (19) .

7. The process according to claim 6, c h a r a c t e r i z e d in that the at least one first additive alkaline material (19) for lowering the viscosity of the molten EAF slag is at least one of the following side stream materials: Analcime, Phlogopite, Spodumene, or Biotite.

8. The process according to claim 7, c h a r a c t e r i z e d in that the slag foaming (4) is provided by means of the first alkaline additive material vaporizing and forming gas bubbles in the molten EAF slag.

9. The process according to any of the preceding claims 1 - 8, c h a r a c t e r i z e d in that the process comprises lowering viscosity and to increase share of liquid phases of the EAF slag by adding at least one silicon-rich industrial side stream material or waste material containing at least one of the following: quartz, phlogopite, analcime, waste glass, rock wool, glass wool .

10. The process according to any of the preceding claims 1 - 9, c h a r a c t e r i z e d in thatthe process comprises lowering viscosity and to increase the share of liquid phases of the EAF slag by adding at least one aluminum-rich industrial side stream material or waste material containing at least one of the following: phlogopite, red mud, bauxite, sodium aluminate, demolished aluminate-cement , wastes from water purification.

11. The process according to any of the preceding claims 1 - 10, c h a r a c t e r i z e d in that the process provides the slag foaming by injecting at least gas to the EAF slag.

12. The process according to any of the preceding claims 1 - 11, c h a r a c t e r i z e d in that the process comprises adding at least one second additive material (25) for lowering melting temperature (24) of the EAF slag.

13. The process according to any of the preceding claims 1 - 10, c h a r a c t e r i z e d in that the process comprises removing crystalline water from one or more of the implemented materials prior to be charged into the furnace.

14. The process according to any of the preceding claims 1 - 11, c h a r a c t e r i z e d in that the process is configured to recover at least one of the following metal materials from the molten EAF slag: iron (Fe) , chromium (Cr) , vanadium (V) , manganese (Mn) , nickel (Ni) .

15. The process according to any of the preceding claims 1 - 14, c h a r a c t e r i z e d in that the processed EAF slag is conveyed directly from the steel production plant in molten state (7) to the extraction process.

16. The process according to any of the preceding claims 1 - 14, c h a r a c t e r i z e d in that the processed EAF slag is in solid state and is melted back (6) into molten state prior executing the extraction process.

17. The process according to any of the preceding claims 1 - 16, c h a r a c t e r i z e d in that the EAF slag is processed in batches (8) in the furnace .

18. The process according to any of the preceding claims 1 - 16, c h a r a c t e r i z e d in that the EAF slag is processed continuously (9) in the furnace .

19. The process according to any of the preceding claims 1 - 18, c h a r a c t e r i z e d in that the process implements target temperature which is 1400 to 1650°C.

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