Process for recovering metal materials from slag

Abstract

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

Description

[0001] Process for recovering metal materials from slag

[0002] Background of the invention

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

[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 Ni , included in the slags . 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 .

[0006] Brief description of the invention

[0007] The idea of the invention is to provide a new and improved process for recovering metals from steel industry slags .

[0008] 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 comprises ferrochrome slag ( FCS ) with metal oxides . The process comprises heating the slag in a furnace to enhance the extraction of the metal materials from the slag being in molten state . Also , molten or hot slag already solidified directly from the preceding process may be used, then reducing the need of heating of the slag . In one embodiment , the preceding process is a smelting process . In another embodiment , the preceding process is a melting process . In still another embodiment , there i s no preceding melting or smelting process but the claimed process for recovering metal materials from slag of steel industry is a part of or included in a steel production process , i . e . , in a process for producing ferrochrome .

[0010] The process further comprises lowering viscosity of the molten slag by adding at least one alkaline material and thereby improving fluidity of the molten slag . The process further comprises providing stirring molten slag and extracting the metal materials included in the molten slag . Another alternative is to apply stirring by gas inj ection into the slag .

[0011] The metal oxides of the molten slag are reduced by means of at least one reducing agent .

[0012] In other words , recovery of metal materials included in the molten slag is facilitated by the mentioned three measures in the furnace , namely lowering the viscosity, providing the stirring and executing the reduction . According to an embodiment , the stirring comprises slag foaming .

[0013] An advantage of the disclosed solution is that recovery of metal materials can be enhanced by implementation of the disclosed process . This way slags can be utilized effectively, and environmental ris ks of metal containing slags are decreased .

[0014] In addition to the metal oxides , the slag may also comprise one or more metals in metallic form, e . g . as metallic droplets . These one or more metals may have been reduced in one or more preceding phases of metal process ing . Lowering the viscosity can improve the separation of the one or more metals in metallic form from the metallic oxides .

[0015] According to an embodiment , the process comprises heating the slag in an induction furnace or by other heating means . I f molten feed is used the need for heating is smaller .

[0016] In other words , the process may implement various means for heating, such as heating in an induction furnace , a plasma furnace or converter furnace , or use of a ladle , a Top-Blown-Rotary ( TBR) converter, a Top-Submerged-Lance ( TSL) furnace , or an electric furnaces (EF) , such as an electric arc furnace (EAF) , which are all energy eff icient methods for heating and melting metal containing 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 . A further advantage of the plasma furnace is that very high temperatures and quick processing time can be reached . A further advantage of the converter furnace heating is that its external energy input can be low . A further advantage of the use of a ladle is that a high utili zation rate can be reached, as well as the possibility to move the material to another point of the plant . A further advantage of the TBR converter is that easy loading operations both for batch or continuous use as well as high heat and mass transfer rates for rapid processing may be achieved . A further advantage of the TSL furnace is that it may provide feed flexibility and high conversion rates . A further advantage of the EF, such as the EAF, is that it is very energy efficient , especially if there is a need for melting materials in the process .

[0017] 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 slag and produce heat and mixing of the molten slag .

[0018] According to an embodiment , the process implements vortex stirring or induction stirrer for mixing the molten slag inside a vessel , such as a crucible . In the vortex stirring the stirring effect is enhanced by pulsating the magnetic fields to alternate forces subj ected to the molten slag . The magnetic fields can also be traveling which also produces vortex stirring .

[0019] According to an embodiment , the process implements pulsating magnetic fields for heating the slag . Then the pulsating magnetic fields cause pulsating heating effect in the treated molten 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 slag is higher than in the whole mass . Greater magnetic f ields are induced at the edge areas of the molten slag and the entire slag material needs not to be heated to as high temperatures as the edge areas . This of course improves energy efficiency .

[0020] According to an alternative embodiment , the process implements an electric arc furnace (EAF) for heating and processing the slag .

[0021] According to an embodiment , the process comprises reducing the metal oxides of the molten slag by means of hydrogen gas , carbon monoxide , hydrocarbon gas , such as methane or propane , ferrosilicon, aluminum or carbon . These reducing agents can be added to the process , e . g . , by pouring, by using suitable lance , from bottom of the furnace , etc . In other words , hydrogen gas may be 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 slag inside the vessel , such as a 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 .

[0022] According to an embodiment , the reducing agent may be a gas mixture comprising the hydrogen gas and at least one addition gas , such as argon or nitrogen gas . According to an embodiment, the process utilizes 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 utilizes carbon material, such as synthetical carbon formed from methane or other hydrocarbons, as the reducing agent. The carbon material may be at least partly in the form of nano or micro sized particles, for instance.

[0024] According to an embodiment, the process may utilize carbon dioxide, hydrocarbons or solid carbon.

[0025] According to an embodiment, the process utilizes municipal sewage sludge as the reducing agent. The municipal sewage sludge is produced as a by-product during sewage treatment of municipal wastewater.

[0026] 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.

[0027] Further, other organic reducing agents may also be utilized in the disclosed process.

[0028] According to an embodiment, the process may utilize at least two different slags at a time and wherein at least one of the slags is the ferrochrome slag (FCS) .

[0029] According to an embodiment, the process utilizes two different slags at a time and wherein the slags are the ferrochrome slag (FCS) and Argon Oxygen Decarburization (AOD) slag.

[0030] According to an embodiment, the process utilizes two or more different slags at a time wherein said slags comprise or consist of the FCS slag and a slag from a directly reduced iron (DRI) process, such as a DRI smelting furnace process. In the DRI process, the DRI may be used as a feed to produce the slag to be used together with the FCS. The DRI may be fed to a furnace for heating to produce molten crude iron, which can in turn be processed to produce the slag to be used together with the FCS. According to an alternative embodiment, the process utilizes only one slag at a time whereby the slag being treated is the ferrochrome slag (FCS) .

[0031] According to an embodiment, the process comprises lowering viscosity of the molten 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.

[0032] 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 slag.

[0033] According to an embodiment, the process comprises lowering viscosity of the molten 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 slag.

[0034] According to an embodiment, the at least one first additive alkaline material for lowering the viscosity of the molten slag is at least one of the following natural minerals or side stream materials rich in either i) Mica- group minerals, for example flogopite, muscovite, biotite, chlorite or clay minerals, or ii) f eldspars-group minerals like albite, anorthite or K-feldspar, or iii) amphiboles, like hornblendes or iv) Pyroxenes, like aegirine, spodumene and wollastonite or v) other alkaline waste materials, like analcime, lime, calcite, dolomite, lime-rich ash, lime dust, lime mud, calcium carbonate sludge or sodiumaluminate.

[0035] According to an embodiment, the first additive alkaline material may alternatively be magnesium, calcium or other alkaline materials.

[0036] According to an embodiment, the alkaline materials may be side stream materials such as slag, or oil shale ash, mine tailings, mine side streams such as waste rock. According to an embodiment, the alkaline material for lowering the viscosity of the molten slag may be green liquor which is a dissolved smelt produced in a recovery boiler in a pulping process.

[0037] According to an embodiment, the alkaline material for lowering the viscosity of the molten slag may be natural alkaline containing material.

[0038] According to an embodiment, it is possible to add to the slag one or more natural acidic containing material (s) for enhancing at least one property of the slag or the method.

[0039] According to an embodiment, the slag stirring is provided by means of the first alkaline additive material vaporizing and forming gas bubbles in the molten slag. In other words, the added alkaline material smelts, vaporizes and forms gas bubbles which rise towards an upper surface of the molten slag in the vessel.

[0040] According to an alternative embodiment, any other alkaline material included in the molten 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 slag.

[0041] In one enbodiment, viscosity and melting point is lowered via adjusting the silicon and aluminium content with non-alkaline mineral wastes, mineral side products or natural minerals; like quartz, silica or siliceous fly or bottom ashes (comprising CaO 37 % and Si02 32 %, for instance) or slags with high silicon content as an example.

[0042] According to an embodiment, the process provides the slag stirring by injecting at least one gas to the slag.

[0043] According to an embodiment, the injected gas may comprise an inert gas, such as argon or nitrogen gas.

[0044] Alternatively, the injected gas may be another inert gas or a reducing gas, or a combination of the inert gas and the reducing gas, or combination of the inert gas with particles of a reducing agent. The reducing gas can be carbon monoxide or hydrogen gas, hydrocarbon, such as methane or propane, for example.

[0045] According to an embodiment, one or more of the above-mentioned gases can be fed inside the furnace to cause the desired slag stirring without the mentioned injection.

[0046] According to an embodiment, the stirring is caused by a mechanical means, such as an agitator or rod(s) arranged to move or stir in the slag.

[0047] According to an embodiment, the stirring is caused by dropping or forcing material in the furnace or ladle such that suitable movements, flows and / or wavefronts are caused in the slag already in said furnace or ladle. Said material may comprise the slag or any material needed in the process, and it may be in molten and / or solid state when being dropped. According to an embodiment, the material is dropped freely due to gravity force. According to another embodiment, the dropping is accelerated or forced act, i.e., the material is thrown or pushed by force in the furnace or ladle .

[0048] According to an embodiment, the process comprises adding at least one second additive material for lowering liquidus temperature of the slag. An advantage of this 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 .

[0049] According to an embodiment, the second additive material for lowering the liquidus temperature of the slag may be silicon (Si) .

[0050] According to an embodiment, alternative materials for lowering the liquidus temperature may be one of the following: boron, boric acid, borax, colemanite, ulexite, fluorine compounds.

[0051] According to an embodiment, the process comprises removing crystalline water, when applicable, from one or more of the implemented materials prior to being charged into the furnace . In other words , the used materials may be pre-treated to remove the crystal line water, if present in substantial amounts , from their composition so that steam explosion in the furnace can be prevented .

[0052] According to an embodiment, a small amount of crystalline water within one or more of the implemented materials is allowed to be charged in the furnace , preferably gradually charged, for serving as a foaming agent and enhancing stirring in the process .

[0053] According to an embodiment , the material is preheated prior to being charged into a vessel , such as a crucible , of 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 . Alternatively, if molten material directly from the preceding process is used, it may be charged directly to the furnace with less preheating or optionally without any pre-heating .

[0054] According to an embodiment , the process is conf igured to recover at least one of the following metal materials from the molten slag : iron ( Fe ) , chromium (Cr) .

[0055] According to an embodiment , the following metal material can also be recovered from the molten slag : nickel (Ni ) , vanadium (V) , titanium ( Ti ) , molybdenum (Mo ) , manganese (Mn) , bismuth (Bi ) , phosporus ( P) , cobalt (Co ) , heavy metals .

[0056] According to an embodiment , the processed slag is conveyed directly from the steel production plant in molten state to the extraction process . An advantage of this embodiment is that the recovery process utili zes high temperature of the slag whereby energy efficiency of the recovery process is good . This has a positive impact on aims lowering CO2 emissions .

[0057] According to an embodiment , the processed 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 slag material that has been previously stored on a storage area. Then old slag piles and storages can be utilized, 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 utilized for other purposes.

[0058] According to an embodiment, the processing unit for the recovery process may be located at distance from the steel refining plant and the storage area of the slag since the slag being in solid state can be transported by means of conveyors and vehicles to desired location.

[0059] According to an embodiment, the processing unit for the recovery process is the very same process unit where the steel refining is taking place.

[0060] According to an embodiment, the slag is processed in batches in the processing unit.

[0061] According to an embodiment, the slag is processed continuously in the procession unit.

[0062] According to an embodiment, the process implements target temperature which is 1500 to 1550°C.

[0063] According to an embodiment, the process implements target temperature which is 1500 to 1750°C.

[0064] According to an embodiment, the process implements target temperature being below 1600°C.

[0065] According to an embodiment, the process implements target temperature is 1000 to 2500°C. In other words, the target temperature of the molten slag is 1000 to 2500°C.

[0066] According to an embodiment, it is possible to increase relative amount of the additive materials so that the target temperature may be even lower, such as 1400 °C.

[0067] The above-described embodiments and their features may be combined to provide desired configurations.

[0068] According to an embodiment, the remainder material from which the metal oxides have been reduced as disclosed in this description is handled in a post-treatment process . The post-treatment process may comprise , e . g . , cooling and granulating or milling / grinding of the reminder material . According to an embodiment , the reminder material is mixed with dry silicate , sodium silicate or sodium aluminate in the post-treatment process .

[0069] Viscosity

[0070] The slag is acidic and has higher viscosity before adding the additives . When alkaline additives are added, pH-value of the slag is increased . The resulted higher pH- value means lower viscosity for the slag .

[0071] The addition of the alkaline material to the slag may also lower liquidus temperature of the slag .

[0072] The addition of the alkaline material to the slag may also lower liquidus temperature of the slag .

[0073] The addition of the alkaline material to the slag may also facilitate breaking up magnesium aluminum spinels . Further, the alkaline material may improve liberation of chromium and iron from mineral form into slag .

[0074] Slag foaming

[0075] The foamy slag is porous and has greater surface area which enhances effect of the hydrogen or other gases during reduction .

[0076] The foaming improves movement of the molten slag in the induction furnace .

[0077] 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 .

[0078] Example

[0079] Waste materials , ferrochrome slag, AOD-slag and analcime sand, were tested in a batch reactor . Analcime sand was powdered in advance down to <200 microns particle si ze before use and slags were in 2 mm particle size. Firstly, analcime sand (0-10% proportion in dry weight (DW) basis) was used as an additive material with ferrochrome slag (Table 1 below, rows 1 - 6) .

[0080] In another set ferrochrome slag (FCS) and AOD slag (AOD) were mixed in relation of FCS / AOD = 1.9 and analcime sand was used as an additive material (0-8% proportion, Table 1 rows 7 - 9) .

[0081] The samples were loaded into graphite crucibles and set in a sealed reactor. Temperature was measured by thermocouples from an inner space just under a lid and under a bottom of the crucible. Before heating, air in the gas sealed 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 1500°C or 1550°C and were kept at the target temperatures from 10 to 30 minutes.

[0082] The samples were let to cool down about 3 hours (down to 400°C) before lifting them to room temperature. The samples with the crucibles were halved. The molten slag / metal samples were halved with an angle grinder. Metal droplets which were located at the bottom and side edges of the samples, were collected and 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) .

[0083] One side of the metal (10-20mm) droplets surface was cleaned by grinding with sandpaper and measured by the XRF. Metal fractions contained in all cases metals recovered from the slags in reduced metallic form. Some of the metals were at small metal droplets close to the edges. Metal contents varied from droplets to another, but all consisted mainly of iron and chromium (Fe concentration 17-70 wt-% and Or concentration 4-20 wt-%) .

[0084] Table

[0085] Table shows concentrations of the treated ferrochrome slags (samples 1 to 6) and the FCS and AOD slag mixtures (samples 7 to 9) , treatment parameters (target temperature, holding time and share of additive-%) and decrease of contents in the samples during the treatment.

[0086] As can be noted, especially chromium (Cr) and vanadium (V) recovery increased when the treatment times, the additive doses and the temperatures increased. The best recovering result of the metals was achieved, when Ca- and Si-contents were higher with the AOD slag as admixture together with the sodium-rich analcime sand. The temperatures used in the experiments were remarkable lower compared to temperatures in submerged arc furnaces in a FeCr-steel production (>1700°C) . The samples 1 to 3 are evidently at the limits where reactions begins and thus the metal recovery values in relation to additive dosage are conflicting (results with 5% and 10% additive amounts) .

[0087] As already disclosed, side stream materials such as slag, or oil shale ash, mine tailings, beneficiation tailings, mine side streams such as waste rock may be added to the slag. According to an embodiment, the material from which metal materials are recovered consists of one or more of said side stream materials, but not ferrochrome slag (FCS) . In other words, the material from which metal materials are recovered may consist, e.g., of mine tailings, beneficiation tailings, and / or mine side streams, such as waste rock. According to an embodiment, the major component of the material from which metal materials are recovered comprises one or more of said side stream materials , whereas there is also a minor component of ferrochrome slag ( FCS ) .

[0088] Brief description of the figures

[0089] Some embodiments of the proposed solution are illustrated in more detail in the following figures , in which

[0090] Figure 1 i s a schematic diagram illustrating basic features of recovering metal from ferrochrome containing slag,

[0091] Figure 2 is a schematic diagram illustrating features relating to heating of the slag,

[0092] Figure 3 is a schematic diagram illustrating features relating to reducing metal oxides of the molten slag,

[0093] Figure 4 is a schematic diagram illustrating features relating to lowering viscosity of the molten slag by means of alkaline material ,

[0094] Figure 5 is a schematic diagram illustrating features relating to slag stirring,

[0095] Figure 6 is a schematic diagram illustrating features relating to possibility to lower liquidus temperature of the slag,

[0096] Figure 7 is a schematic diagram illustrating purposes of the metal recovery from the slag containing ferro chrome ,

[0097] Figure 8 is a schematic side view of an induction furnace usable for the metal recovery process ,

[0098] Figure 9 is a picture of a laboratory test sample for examining properties of a recovered metal droplet ,

[0099] Figure 10 is a picture of a slag piece wherein al most all metal materials are removed,

[0100] Figure 11 is a field emission scanning electron microscope image of an inner surface of a crucible with a separated metal and slag layer,

[0101] Figure 12 is a picture of a halved a crucible and s amp 1 e ,

[0102] Figures 13 and 14 are additional pictures of halved crucibles and samples , Figure 15 is a schematic representation of a FeCr slag behaviour when being heated,

[0103] Figure 16 shows the effect of analcime (AnAlSi ) addition to the liquidus and solidus temperatures of the FeCr slag shown in Figure 15 ,

[0104] Figure 17 is a schematic representation of the FeCr slag with 15 wt-% AnAlSi behaviour when being heated, and

[0105] Figure 18 is a schematic representation of reduction of metal phase from the FeCr-AOD-AnAlSi slag .

[0106] 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 .

[0107] Detailed description of some embodiments

[0108] Figure 1 discloses basic features for a process for recovering metal materials 1 from slag of steel industry . The slag comprises ferrochrome slag ( FCS ) with metal oxides . It is to be noted herein that in some embodiments metal materials are recovered from side stream materials . Therefore , in some embodiments the terms "slag" or "FCS" may be replaced by the term "side stream materials .

[0109] In one embodiment , the slag is coming from a preceding process . In one embodiment , the preceding process is a smelting process . In another embodiment , the preceding process is a melting proces s . In still another embodiment , there is no preceding melting or smelting process but the claimed process for recovering metal materials from slag of steel industry is a part of or included in a steel production process .

[0110] The process compri ses heating 2 the slag in a furnace or a ladle to enhance the extraction of the metal materials from the slag being in molten state . The process further comprises lowering vi scosity of the molten slag by adding at least one alkaline material 3 and thereby improving fluidity of the molten slag . The process is also provided with slag stirring 4 for stirring the molten slag and extracting the metal materials included in the molten slag . The metal oxides of the molten slag are reduced 5 by means of at least one reducing agent .

[0111] Figure 2 discloses that the heating process 2 may include melting and heating 6 when the slag is in solid state when charged into the furnace or ladle . In an alternative solution the process is arranged to heat s lag 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 . In one embodiment , the heating can be executed in an induction furnace 10 wherein Eddy Currents cause magnetic stirring 11 for the molted 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 . In another embodiments , the heating can be executed in a plasma furnace , in a converter furnace , in a ladle , or in an electric arc furnace (EAF) .

[0112] Figure 3 discloses possible processes and reducing agents for reducing the metal oxides 5 of the molten slag . Hydrogen gas can be fed 13 inside the furnace or the ladle 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 . Also , ferrosilicon, aluminum, hydrocarbon or carbon may be used as reducing agents .

[0113] Figure 4 discloses possible alkaline materials that can be used for lowering viscosity of the molten slag 3 . The viscosity can be lowered by using alkaline slag material 18 together with the ferro chrome slag, whereby combination of two slags is implemented . An alternative is to add a first additive alkal ine mineral material 19 , such as Analcime , Phlogopite , or Spodumene , Spodumene tailings , Biotite , Plagioclase , sodium feldspar or potassium feldspar or some minerals from mica- , feldspar-containing materials which are rich in alkaline or earth alkaline metals . Use of two or all of them simultaneously may also be possible . However, it has also been 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 different alkaline materials can be implemented for lowering the viscosity of the molten slag .

[0114] Figure 5 discloses that foaming 4 of the molten slag can be executed in many 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 vapori zed in the furnace or the ladle and produces gas bubbles 23 . Also mechanical stirring or dropping method described in this description can be used in stirring .

[0115] Figure 6 discloses that liquidus temperature of the slag can be lowered 24 by adding a second additive material 25 . The second additive material may be silicon . Alternative liquidus 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 , or any types of reducing agents , for lowering the liquidus temperature .

[0116] Figure 7 discloses some purposes 26 for the metal recovery process for the ferro chrome containing slags . 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 material s are removed from the slag, the 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 . 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 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 . 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 generates a rapidly reversing magnetic field and generates 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 slag, heat the slag 36 . Once the 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 slag .

[0117] Figure 8 further illustrates that metal droplets 40 inside the molten 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 stirring measures and by the vi scosity lowering measures . In the foamed lower viscosity molten slag, the droplets move more easily to the sides inside the molten slag bath . The movement can be further improved by means of pulsating the magnetic fields and utili zing other vortex stirring possibilities . Figure 9 is a picture of a laboratory test sample piece 43 produced for examining properties of a recovered metal droplet 42 formed by means of the di sclosed process . The droplet 42 is cast into a res in material 44 . There is also a metallic part 45 which relates to the testing process and the test sample piece 43 .

[0118] Figure 10 is a picture of a residual slag piece 46 wherein almost all metal materials are removed by utili zing the process disclosed in this document . Material of the residual slag piece is safe to be utili zed in different purposes since the metal materials are removed .

[0119] Figure 11 is an electron microscope picture of a side surface of a crucible used in the induction heating of the disclosed process . Outl ines of different metal materi als are clear and well detectable . Figure 11 shows that the metal materials are collected to the sides inside the crucible . In Figure 11 the following metal materials can be seen aluminium 47 , silicon 48 and iron 49 . Areas of residual slag 50 are also clearly visible .

[0120] Figure 12 is a picture showing a halved crucible 32 and a sample 51 inside it . As can be seen, smaller metal droplets 42 are collected on lateral sides and bigger and heavier metal droplets 42a are collected to a bottom part of the crucible 32 . Figure 12 further shows that residual slag 50 comprises cavities 52 which indicates the use of the slag stirring measures during the process .

[0121] Figure 13 is a picture of a halved crucible 32 and a sample 51 in an exploded view . Metal droplets 42 have been detached from their original positions 53 inside residual slag 50 . A porous slag piece 54 produced by gas bubbles during the implemented slag stirring is removed from a cavity 52 . The positions 53 again indicate that the metal lic droplets 42 are formed on s ide and bottom areas inside the crucible 32 .

[0122] Figure 14 is a picture of a halved crucible 32 and a sample 51 in an exploded view . The same observations as in connection with the Figure 13 can be done . Furthermore , shiny portions 55 on inner surfaces of the crucible 32 also indicate that the metal materials are collected to edge areas between the crucible 32 and the residual slag 50 .

[0123] Figure 15 is a schematic representation of a FeCr slag behaviour when being heated . The liquidus temperature of the FeCr slag is high, over 1800 ° C . The slag is saturated with spinel (MgA^Cg ) .

[0124] Figure 16 shows the effect of AnAlSi addition to the liquidus temperature of the FeCr slag shown in Figure 15 . As can be seen, liquidus temperatures are in range of 1620 - 1730 ° C . It can be seen that addition of 15 % AnAl Si causes the liquidus temperature to drop approximately 70 ° C . Furthermore , it can be estimated that liquidus temperature in practice is approximately 1650 ° C .

[0125] Also solidus temperatures - based on phase calculations - are shown in the Figure ( lower curve ) .

[0126] Figure 17 is a schematic representation of the FeCr slag with 15 wt-% AnAlSi behaviour when being heated . The effect of the added AnAlSi to liquidus temperature is significant .

[0127] Figure 18 is a schematic representation of reduction of a FeCr-AOD-AnAlSi slag as a function of carbon . At high chromium reduction levels , silicon begins to reduce from the s lag . This phenomenon is impeded by high alkalinity of the slag, i . e . , its CaO+MgO -percentage . Commodity grade FeCr can be appl ied directly from FeCr s lag reduction with AnAlSi addition . Only a small amount of reductant and additional energy is required .

[0128] 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 comprises ferrochrome slag (FCS) with metal oxides; and wherein the process comprises heating (2) the slag in a furnace or feeding slag in molten state to enhance the extraction of the metal materials from the slag being in molten state; characterized in that the process further comprises : lowering viscosity (3) of the molten slag by adding at least one alkaline material and thereby improving fluidity of the molten slag; providing stirring (4) the molten slag and extracting the metal materials included in the molten slag; and reducing (5) the metal oxides of the molten 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 slag in an induction furnace, a ladle, a plasma furnace, a converter furnace or an electric 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 slag by means of hydrogen gas, carbon monoxide, hydrocarbon gas, such as methane or propane, ferrosilicon, aluminum, coke and / or carbon.

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 thatthe process utilizes at least two different slags at a time and wherein at least one of the slags is the ferrochrome slag (FCS) .

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 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 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 slag is at least one of the following side stream materials: Analcime, Phlogopite, Spodumene, Biotite, lime, calcite, dolomite, lime-rich ash, lime dust, lime mud, calcium carbonate sludge .

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

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 that the process comprises adding at least one second additive material (25) for lowering liquidus temperature (24) of the slag.

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 comprises removing at least part of crystalline water from one or more of the implemented materials prior to be charged into the furnace.

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 is configured to recover at least one of the following metal materials from the molten slag: iron (Fe) , chromium (Cr) .

13. The process according to any of the preceding claims 1 - 12, c h a r a c t e r i z e d in that the processed slag is conveyed directly from the steel production plant in molten state (7) to the extraction process .

14. The process according to any of the preceding claims 1 - 12, c h a r a c t e r i z e d in that the processed slag is partly or entirely in solid state and is melted back (6) into molten state prior executing the extraction process.

15. The process according to any of the preceding claims 1 - 4, c h a r a c t e r i z e d in that the slag is processed in batches (8) in the furnace.

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 thatthe slag is processed continuously (9) in the furnace .

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 process implements target temperature which is 1000 °C to 2500 °C.

Images