AU2010290830A1

AU2010290830A1 - Processing of metallurgical slag

Info

Publication number: AU2010290830A1
Application number: AU2010290830A
Authority: AU
Inventors: Anton Mecchi
Original assignee: Waks Anthony Raymond
Current assignee: Waks Anthony Raymond
Priority date: 2009-09-07
Filing date: 2010-09-07
Publication date: 2012-05-03
Also published as: WO2011027334A1; ZA201008736B

Abstract

The invention relates to a method of processing metallurgical slag containing at least one desired metal slag compound. According to the method, the slag is admixed with a reductant and a preferred metal ore to obtain a reaction mixture. The reaction mixture is then heated to cause the reductant to reduce at least the desired metal slag compound, thereby to obtain a molten metal product. The molten metal product comprises at least the desired metal. The desired metal and the preferred metal may be the same, in particular manganese.

Description

WO 2011/027334 PCT/IB2010/054008 1 PROCESSING OF METALLURGICAL SLAG 5 THIS INVENTION relates to processing of metallurgical slag. More particularly, the invention relates to a method of processing metallurgical slag containing at least one 10 desired metal slag compound and further relates to a metallurgical feedstock for processing. The invention extends to a molten metal product and a valuable by-product produced in accordance with the method of the invention. In producing metal alloys by means of ore smelting, oxides of metal alloy 15 components, for example manganese (IV) dioxide (MnO 2 ) and iron (Ill) oxide (Fe 2

O

3 ), are reduced in the presence of a suitable reductant, such as carbon, to metals, thereby to produce a metal alloy product comprising the metals, such as ferromanganese (FeMn). Metallurgical slags containing non-reduced metal oxides and other impurities are produced in addition to the alloy product. In many cases, 20 such non-reduced metal oxides contained in the slags include desired metal oxides, useful for alloying. In the production of high carbon ferromanganese (HCFeMn), for example, a slag is produced which typically has a relatively high manganese (Mn) content, usually in the form of manganese (II) oxide (MnO). As MnO is a thermodynamically stable oxide and reduction of the manganese ion to Mn with a 25 carbon reductant usually occurs only at temperatures above 1420 0C, the further processing of such slags to reduce the desired metal compounds and obtain a metal alloy product is not generally considered to be economically viable. Producing a metal alloy product from such slags is further hampered by the presence of impurities, in particular large amounts of silica (SiO 2 ), contained in the slag. Silica 30 presents a problem as, during reduction of a desired metal oxide in the slag, large amounts of silicon (Si) are formed due to simultaneous reduction of the silicon ion in the silica. This leads to an alloy product produced from the slag containing unacceptably high levels of Si. The reduction of silica to silicon can be counteracted by the addition of a calcium-containing fluxing agent, but this solution is not WO 2011/027334 PCT/IB2010/054008 2 economically attractive, since large quantities of fluxing agent are required and addition of such large quantities of fluxing agent reduces the overall throughput of the system, thus also reducing metal alloy yield. 5 It is thus an object of the present invention to address the abovementioned difficulties in processing metallurgical slag by providing a means whereby metallurgical slags can be further processed to obtain a metal alloy product therefrom, which product conforms to desired specifications, inter alia of composition. 10 According to one aspect of the invention, there is provided a method of processing metallurgical slag containing at least one desired metal slag compound, the method including the steps of admixing the slag with a reductant and a preferred metal ore to obtain a reaction mixture; 15 heating the reaction mixture to cause the reductant to reduce at least the desired metal slag compound, thereby to obtain a molten metal product, comprising at least the desired metal, and molten processed slag; and separating the molten metal product from the processed slag. 20 In this specification, the phrase "desired metal slag compound" is to be understood to refer to a compound contained in the metallurgical slag which contains a metal which is desired to be included in the molten metal product. Further, "preferred metal ore" is to be understood to refer to an ore of a metal which metal is preferred also to be included in the molten metal product. It will therefore be appreciated that the 25 adjectives "desired" and "preferred" are employed in qualifying the respective metals and the desirability of including these metals in the molten metal product. The desired metal and the preferred metal may be the same metal. In a particular embodiment of the invention, the desired metal and the preferred metal may be 30 manganese. The desired metal slag compound may comprise a desired metal oxide. When the desired metal is manganese, the desired metal slag compound may be manganese (II) oxide (MnO).

WO 2011/027334 PCT/IB2010/054008 3 The preferred metal may be expressed in the preferred metal ore in the form of a preferred metal compound. Typically, the preferred metal compound may comprise a preferred metal oxide. When the preferred metal is manganese, the ore may be a 5 Mn-containing ore and the preferred metal oxide may be manganese (II) oxide. . It will be appreciated that, in the heating step, at least some of the preferred metal compound will also be reduced by the reductant, thereby contributing molten metal to the molten metal product. 10 The ore may comprise 10%-50%, by mass, of the reaction mixture. Typically, the ore comprises 15%-40%, by mass, of the reaction mixture. Some of at least one of the desired metal and the preferred metal may be present in the reaction mixture in a native metallic form, the metals simply being melted in the 15 heating step and being included in the molten metal product. The method may include admixing a metal alloying component comprising at least one additional metal, other than the desired metal and the preferred metal, with the reaction mixture. The additional metal may be at least partly contained in at least 20 one of the metallurgical slag and the preferred metal ore. The additional metal may be at least partly in native metallic form. Alternatively, or additionally, the additional metal may be at least partly expressed as an additional metal compound. Typically, the additional metal compound is in the form of an additional metal oxide. In a particular embodiment of the invention, the additional metal is iron and the additional 25 metal compound comprises iron (Ill) oxide (Fe 2

O

3 ). When the additional metal is at least partly in native metallic form, metal fines, such as Fe fines when the additional metal is iron and the alloy is a ferro-manganese alloy, may thus be employed in addition to or instead of additional metal-containing slags, e.g. iron-containing BOF slags. 30 It will be appreciated that the additional metal compound, when present, may also be reduced by the reductant in the heating step and may therefore contribute the additional metal to the molten metal product. In such a case, the molten metal product will thus be in the form of an alloy, comprising a molten mixture of at least the WO 2011/027334 PCT/IB2010/054008 4 desired metal and the additional metal. When the desired metal is Mn and the metal alloying component is Fe, the alloy will thus be a ferro-manganese (FeMn) alloy, such as high carbon ferro-manganese (HCFeMn), medium carbon ferro-manganese (MCFeMn) or low carbon ferro-manganese (LCFeMn). 5 Metals other than the desired metal and the additional metal may be present in at least one of the ore and the slag. At least some of the other metals may be expressed as metal compounds capable of being reduced by the reductant. Typically, such other metal compounds comprise metal oxides, metal silicates, and 10 mixtures thereof. Typically, such other compounds include silica (SiO 2 ), which may typically be present in the slag. At least some of the silica will therefore be reduced by the reductant in the heating step to form silicon (Si), which is incorporated in the molten metal product. 15 Naturally, other metals referred to above can also be present in the slag in a native, metallic form. Thus, these metals will also be melted in the heating step and be included in the molten metal product. The reductant, the metal ore, and at least a part of the slag may be in solid form 20 when being admixed to form the reaction mixture. Alternatively, at least a part of the slag may be in molten form when being admixed, typically being at a temperature of 1100 OC-1650 OC, e.g. 1200 OC-1550 OC. This may be the case when raw slag is available in solid form, such as from a tip or dump 25 located near a metallurgical furnace which produces raw slag in molten form with the slag thus readily being available in both solid and molten form. It will be appreciated that, through using molten slag, an energy reduction in the heating step may be achieved. It is expected that this reduction may be up to 35% or more of the heat energy which would be required in the absence of molten slag. 30 The method may include, prior to the admixing step, comminuting at least one of the slag, the reductant and the metal ore in solid form to obtain comminuted material. The comminuted material may be subjected, prior to the admixing step, to size classification to obtain a size fraction thereof having an average particle size of at WO 2011/027334 PCT/IB2010/054008 5 most about 50mm. It will be appreciated that the obtained size fraction will then be admixed with the reductant to obtain the reaction mixture. The comminution of the raw slag, prior to admixing thereof with the reductant may, for example, be by crushing, to cause the size reduction thereof. 5 The reaction mixture may be heated in the heating step to a temperature from about 13500C to about 16500C. Typically, heating the reaction mixture is selected from being conducted on a continuous basis by means of an induction furnace or on a batch wise basis by means of an arc furnace. The arc furnace may be a submerged 10 arc furnace or, more preferably, may be an open arc furnace. It is expected that an open arc furnace would be employed particularly when the reduction rate is to be retarded so as to ensure that the processed slag contains not more than 6% by mass MnO. 15 Notwithstanding the nature of the furnace used and the nature of the operation allowed by the furnace, i.e. continuous or batch wise, the other steps of the method may be conducted more-or-less continuous or batch wise, as desired. The slag may be selected from metallurgical furnace slags obtained from one or 20 more metallurgical furnaces used for metal, typically alloy production. The slag may typically be selected from manganese-containing slags, iron-containing slags, ferromanganese slags and mixtures thereof. Such slags may include not only basic oxygen furnace (BOF) slags or arc furnace (AF) slags obtained during steel production, but importantly also include slags obtained from furnaces used in the 25 production of other metals, which may comprise alloys such as ferro-manganese alloys. Such slags may typically be toxic. The slags may be obtained from metal producers located off-site, or, optionally, after production may be used immediately on-site in molten form or, after solidification by air cooling thereof by natural convection on-site, may be stockpiled. Thus, a stockpile of raw slag may be provided 30 from which raw slag to be processed in accordance with the method of the invention, may be withdrawn, continuously or batch wise, as desired, for further processing in accordance with the method of the invention.

WO 2011/027334 PCT/IB2010/054008 6 Preferably therefore, the raw slag may comprise a mixture of at least one manganese-containing slag and at least one iron-containing slag, such as a BOF slag, so that the metal product comprises a ferro-manganese alloy. Preferably, however, the slag is a ferro-manganese slag, containing manganese and iron, 5 typically in the forms of MnO and Fe 2

O

3 , originating from a ferro-manganese alloy production operation. The slag may, of course, also be a mixture of a ferro-manganese slag and one or more manganese-containing and/or iron-containing slag. 10 The manganese-containing slags may typically be obtained from ferro-manganese production, the manganese being in the form of MnO. Typically, the manganese-containing slag may comprise, by mass, 15%-30% manganese, expressed as MnO. 15 The iron-containing slag may be a slag obtained from a BOF steel production process. The iron-containing slag may typically comprise, by mass, 25%-50% iron, expressed as Fe 2

O

3 . The reductant may be solid and may be any or more of a silicon-containing 20 reductant, and an aluminium-containing reductant, a ferrosilicon-containing reductant, and a carbon-containing reductant. Preferably, the reductant is a carbon-containing reductant and is selected from coal and anthracite. Carbon-containing reductants, such as coal, are preferred by virtue of their ready availability at low cost and can be contrasted with aluminium-containing or 25 ferrosilicon-containing reductants which, in certain circumstances, can be regarded as contaminants. The quality of carbon reductant employed will, of course, depend on the quality of pure carbon present in the reductant. For example, a typical coal reductant with an average carbon content of 50% by mass for manufacturing HCFeMn alloy will typically comprise about 10% by mass of total reaction mixture 30 feed. It will, however, be appreciated that this quantity will vary from case to case. Various optional additives or reagents, in addition to the reductant, may be added to the reaction mixture. Typically, the method includes admixing a calcium-containing fluxing agent with the reaction mixture, such as lime (CaO), typically in the form of WO 2011/027334 PCT/IB2010/054008 7 limestone (CaC0 3 ). The addition of the calcium-containing fluxing agent may be used to optimize the basicity of the reaction mixture, expressed in a CaO:SiO 2 mass ratio, thereby to limit the formation of silicon and the inclusion thereof in the metal product. 5 The composition of the reaction mixture may be selected to produce a molten metal product, in the form of an alloy, having, by mass, a silicon content of between 0.4 % and 0.9%, typically 0.5 - 0.7 %. When the molten metal product is in the form of a ferromanganese alloy, the composition of the reaction mixture will typically be 10 selected is such that the alloy has a manganese content of 70% to 90%, by mass, preferably 76% to 80%, and an iron content of 5% to 20% by mass, preferably 6% to 15%. Typically, the composition of the reaction mixture may further be selected such that its basicity, expressed as CaO+MgO/SiO 2 by mass, is in the region of 1.3 to 1.5 with the final basicity of the slag after reduction, measured as CaO/SiO2 by mass, 15 being between 1 and 1.25. Separating the molten metal product, or alloy, from the molten processed slag may be by way of gravity separation. The molten metal product typically has a higher density than the molten processed slag, and therefore the molten processed slag will 20 typically float as a layer on the molten metal product. The separation may thus, for example, take place in the furnace itself, or in another vessel, such as a tilting crucible, which may have a tapping opening at a low level. The molten metal product can then be tapped from the vessel at the low level and the molten processed slag can be poured or decanted, e.g. as an overflow from the vessel at a high level, by 25 tilting the vessel. Instead, the slag can be decanted first, followed by decanting of the metal product. The separation of the processed slag and the metal product, both in molten form, from each other, has a major advantage in that the molten metal product can be 30 obtained in relatively slag-free form, uncontaminated by the processed slag. The gravity separation made possible by this feature of the method of the invention furthermore lends itself to a variety of different separation methods, such as tapping, decanting, pouring, etc, and thus adds versatility to the method of the invention. Furthermore, the use of electrically powered furnaces, such as induction or arc WO 2011/027334 PCT/IB2010/054008 8 furnaces, facilitates keeping the slag and the metal product at a temperature at which they are molten at all times, after the reduction has taken place and until they are separated. It is to be emphasised that, regardless of the reaction temperatures employed, the heating should act at all times to keep the metal product and the 5 processed slag molten, at least until they have been separated from each other. The method may further include subjecting the molten processed slag, when separated from the molten metal product, to downstream processing to obtain therefrom a valuable by-product. In one embodiment of the invention, the method 10 may include allowing the molten processed slag to solidify to air-cooling, subjecting the solidified processed slag to comminution to achieve size reduction thereof and rendering the slag in the form of an aggregate, with the aggregate being the valuable by-product. Alternatively, the method may include causing the molten processed slag to solidify by contacting it with liquid water to cause granulation of the processed 15 slag and obtain a granulated processed slag, with the granulated processed slag then being the valuable by-product. In such a case, the method may include dewatering the granulated processed slag. The granulated processed slag may further be comminuted, for example by crushing and/or milling, for example by milling during or after the dewatering thereof. The comminuted dewatered processed slag 20 may then be stockpiled before use or before onward sale to users, or may be immediately on site for the manufacture of end product. Typically, the granulated processed slag is useful as an extender. While the processed air-cooled slag product in aggregate form will usually be 25 regarded as a final product for sale on to users thereof in the construction or building industry, the granulated processed slag product can be regarded as an intermediate product which can be stockpiled for further processing later, or can be sold on, for use as an extender or filler, to manufacturers of, for example, bricks, ready-mix concretes, slag-extended blended cements, or the like, after grinding or milling, if 30 necessary, to a sufficiently small particle size. Instead, the granulated processed slag intermediate product may be processed further to produce a more or less final processed slag product.

WO 2011/027334 PCT/IB2010/054008 9 The invention also extends to a molten metal product and to a valuable processed slag product, when produced in accordance with the method of the invention as described and defined above. 5 In accordance with another aspect of the invention, there is provided a metallurgical feedstock for processing, the feedstock comprising a mixture of metallurgical slag containing a desired metal compound; a reductant; and a preferred metal ore. 10 The desired metal and the preferred metal may be as hereinbefore described. Thus, the desired metal and the preferred metal may be the same metal, typically manganese. 15 The desired metal slag compound may at least partly comprise a desired metal oxide. When the desired metal is manganese, the desired metal oxide may typically be manganese (II) oxide. The preferred metal may be expressed at least partly in the preferred metal ore in the 20 form of a preferred metal compound, typically a preferred metal oxide. Thus, when the desired metal is manganese, the desired metal oxide may typically be manganese (II) oxide. The metallurgical slag may be as hereinbefore described and may be selected from 25 manganese-containing slags, iron-containing slags, ferro-manganese containing slags and mixtures thereof. The reductant may also be as hereinbefore described and may comprise a reductant for reducing the desired metal compound, preferably a carbon-containing reductant. 30 The preferred metal ore may be as hereinbefore described and may comprise 10% to 50%, more particularly 15% to 40%, by mass, of the feedstock.

WO 2011/027334 PCT/IB2010/054008 10 The feedstock may include a metal alloying component containing an additional metal to the desired metal and the preferred metal. The metal alloying component and the additional metal may be as hereinbefore described. Preferably, the additional metal is iron. 5 Typically, the reductant, the ore and at least a part of the metallurgical slag may be in solid form. It is expected that the metallurgical slag may, however, be at least partly in molten form. 10 The invention will now be described, with reference to the following non-limiting illustrative examples. EXAMPLES In order to assess the viability of the method of the invention, a theoretical model of 15 the method of the invention was prepared and executed for various scenarios of slag and ore inputs. Approach The model involved preparing mass and energy balances for the heating step of the 20 invention, i.e. for the various reduction reactions taking place in the heating step, for various scenarios of input materials. This was done with a view to predict what the effect of the addition of different quantities of a manganese (Mn) ore, in the form of a ferromanganese (FeMn) ore, would be on the composition of the metal product produced in the reduction of to two different raw input slags. 25 The model was prepared for a ferro-manganese (FeMn) slag and a silicon manganese (SiMn) slag. As mentioned above, the aim of the model was to predict the effect which the 30 addition of the Mn ore, respectively to the FeMn slag and to the SiMn slag, in accordance with the method of the invention, can have on the composition of the metal product obtained by reduction of the slags by a suitable reductant, particularly as regards silicon content of the metal product. The model also aimed to determine WO 2011/027334 PCT/IB2010/054008 11 what effect such Mn ore addition would have on the amount of lime fluxing agent required to limit silicon content in the metal product. The Mn ore was taken to have an essential chemical analysis, on a mass basis, as 5 follows: Mn 37.9% Fe 5.4% MgO 2.0% A1 2 0 3 0.3% 10 SiO 2 6.3% CaO 13.8%

P

2 0 5 0.018% It was assumed that all the Mn was present in the ore as MnO and that all the Fe was 15 present in the ore as Fe 2

O

3 . It should be kept in mind, however, that this assumption could be improved by mineralogical analysis of the ore. However, it is expected that an error in this assumption would not have an affect on a mass balance in respect of manganese, but rather on the amount of reductant required. 20 Further input data and process parameters used in the model were as shown in Table 1 below: TABLE 1: Process parameters Batch mass The mass of a single batch that is processed in the furnace. 15,000 kg Reaction temperature The temperature at which carbo-thermic reactions occur in the slag bath 1,500 C and at which the chemical equilibrium is calculated. Carbon bypassed The mass fraction of carbon bypassing the process (after dust loss) and 30 % do not participate in reduction reactions. Offgas Temperature The temperature of the gas exiting the furnace. 1650 0 C Slag Temperature The temperature at which the slag is tapped from the furnace. 1650 C Alloy Temperature The temperature at which the alloy is tapped from the furnace. 1600 0 C Offgas Temperature (after The temperature of the offgas after the final point of heat loss. 160 C final heat loss) ________ Furnace rating The smelting furnace power rating. 20 MVA Power factor The smelting furnace power factor. 0.7085 Load factor The smelting furnace load factor. 90% Operating time The smelting furnace operating time. 95% Availability The smelting furnace availability. 90% Furnace Excess Power The extra power that has to be added to the furnace to smelt raw 3MW material. This includes the furnace heat losses.

WO 2011/027334 PCT/IB2010/054008 12 Alloy Recovery The percentage of the alloy produced in the furnace that is recovered. 98% Slag Recovery The percentage of the slag produced in the furnace that is recovered. 98% Alloy Carbon Content The mass fraction of Carbon in the alloy produced. 7.5% In Table 2 below, the composition and nature of each of the input streams, used in the mass and energy balance model, save for the composition of the Mn ore which is given above, are summarised. For each stream, the mass per batch, temperature, 5 and mass fraction bypassing the process to dust must be specified in order to execute the model. The chemical species for each stream are listed for which the mass percentages need to be provided, as well as the calculations that are made to transfer the chemical analyses before they are used in the mass and energy balance. The values of the chemical analysis used for scenarios that were executed with the 10 model are also provided. For Table 2 below, it should be noted that the all the streams are assumed to enter the process at ambient temperature (250C) while the molten slag streams enter at 12500C. This assumption is based thereon that the molten slag will be tapped from 15 the furnace at 14000C and is expected to loose heat at a rate of 500C/h, which implies 3h from being tapped until feed into the furnace. It should further be noted that, although three BOF slags, designated respectively as BOF(I), BOF(II) and BOF(Ill), are identified, only BOF(II) slag was used in executing 20 the model. TABLE 2: Input streams 26.33% MnO 31.4% CaO FeMn Molten Slag 5.52% MgO 1250c 0% Use percentages as is but for the 32.24% SiO 2 representative chemical species. 0.5% FeO 4.83% A1 2 0 3 FeMn Air Cooled Slag Same as above. 25 0 C 5% Use percentages as is but for the _____________________________ ________________representative chemical species. 17.36% MnO 26.34% CaO SiMn Molten Slag 4.86% MgO 12500 0% Use percentages as is but for the 48.47% SiO2 representative chemical species. 0.64% FeO 3.19% A1 2 0 3 WO 2011/027334 PCT/IB2010/054008 13 SiMn Air Cooled Slag Same as above. 25 c 5% Use peroentachemical s ecest for the 10.34% MgO 21.3% SiO2 1.86% A1203 BOF(I) Slag 0.63% P 25 c 5% Use percentages as is but for the 1.17% S representative chemical species. 38.28% CaO 4.78% MnO 23.06% FeO 4.48% MgO 16.96% SiO 2 BOF(II) Slag 0.248 25 Use percentages as is but for the 29.91% CaO representative chemical species. 1.06% MnO 40.01% Fe 2 0 3 7.4% MgO 9.57% SiO 2 BOF(Ill) Slag 5.7% A1 2 0 3 25c 5% Use percentages as is but for the 31.1% CaO representative chemical species. 3.24% MnO 38.7% FeO Proximate (Dry basis): 3.94% H 2 0 50.7% Fixed C Normalise proximate analysis to 100% 30.6% Volatiles minus % H 2 0, and then the ash analysis to 16.7% Ash add up to the ash percentage. Use the Coal 1% S 25cc 5% calculated specie percentages for the 0.6% P 2 0 5 representative chemical species. Use the Ash: ultimate analysis specie percentages for 24.2% CaO the representative species (except C). 0.3% MgO 30.7% A120 3 6.7% Fe20 3 Proximate (Dry basis): 2.83% H2O 78.13% Fixed C 4.7% Volatiles 14.34% Ash 1.5% S 0.048% P 2 0 5 Normalise proximate analysis to 100% Ash: minus % H2O, and then the ash analysis to 56.33% SiO2 add up to the ash percentage. Use the Anthracite 3.38% CaO 25cc 5% calculated specie percentages for the 1.02% MgO representative chemical species. Use the 25.66% A120 3 ultimate analysis specie percentages for 6.24% Fe20 3 the representative species (except C). Ultimate: 90.46% C 3.77% H 2.39% N 1.8% S 1.58% 0 FeSi 100% FeSi 25 0 C 5% Use percentages as is but for the representative chemical species. 4.53% C 88% SiC SiC 1.5% A120 3 250 5% Use percentages as is but for the 0.29% FeO representative chemical species. 0.22% CaO 0.11% MgO 1.3% Si02 0.2% Fe2O3 Burnt Lime 87% CaO 25c 5% Use percentages as is but for the 1.6% MgO representative chemical species. 0.2% A120 3 1% Mn20 3 WO 2011/027334 PCT/IB2010/054008 14 3.6% CaC03 Combustion/= 21 Vol% O2 25'cC - Use percentages as is but for the TDilution Air 79 vol% N2 -representative chemical species. In the case of carbonaceous materials, i.e. coal and anthracite, where an ultimate analysis was not available, assumptions had to be made regarding the volatile matter content of the materials. 5 The process model parameters calculated as desired outputs from the mass and energy balance are summarised in Table 3, where applicable target values are given for which the input parameter values must be adjusted. 10 TABLE 3: Desired outputs The mass fraction of slag solids predicted in the Slag Percentage Solids slag output stream. This parameter is important 5% - 9% AVE. 5% to monitor to ensure that the slag can be tapped from the furnace. The slag basicity calculated as the mass Basicity (CaO + MgO / SiO 2 ) fraction of CaO and MgO in the slag divided by 1.35- 1.4 the fraction of SiO 2 The slag basicity calculated as the mass Basicity (CaO / SiO 2 ) fraction of CaO in the slag divided by the 1.1 - 1.2 fraction of SiO 2 I I It is expected that the desired values for slag percentage solids will be determined more accurately by pilot scale testing of the method of the invention. 15 Scenarios The following scenarios, as set out below, were considered by the mass and energy balance model for the heating step of the method of the invention, respectively for the FeMn slag, in combination with BOF(II) slag, and for the SiMn slag: 20 1. FeMn slag Each scenario was executed with a reaction mixture comprising variable quantities of BOF slag and/or Fe fine, and variable amounts of Mn ore per 100kg of Mn ore plus FeMn slag air cooled slag as set out hereunder: a. Mn ore (kg/1 00 kg slag feed) = 0% + air cooled FeMn slag + BOF (II) 25 b. Mn ore (kg/100 kg slag feed) = 15% + air cooled FeMn slag + BOF (II) WO 2011/027334 PCT/IB2010/054008 15 c. Mn ore (kg/1 00 kg slag feed) = 0% + air cooled FeMn slag + Fe fines d. Mn ore (kg/1 00 kg slag feed) = 15% + air cooled FeMn slag + Fe fines e. Mn ore (kg/1 00 kg slag feed) = 20% + air cooled FeMn slag + Fe fines f. Mn ore (kg/1 00 kg slag feed) = 25% + air cooled FeMn slag + Fe fines 5 2. SiMn slag Each scenario was executed with a reaction mixture comprising 0% BOF slag/Fe fines, air cooled SiMn slag and variable amounts of Mn ore per 100kg of molten SiMn slag, as set out hereunder: 10 a. Mn ore (kg/1 00 kg slag feed) = 0% + air cooled SiMn slag b. Mn ore (kg/1 00 kg slag feed) = 37.5% + air cooled SiMn slag Mass and energy balances were prepared for the various chemical species taking part in reduction reactions which would, thermodynamically and theoretically, take 15 place in each of the abovementioned scenarios. The mass and energy balances were then solved for a reaction temperature of 15000C. In each case, the mass and energy balances were solved for amounts of reductant and lime required to meet a desired final slag basicity, expressed as a ratio of CaO concentration/SiO 2 by mass. In the case of the FeMn slag, the desired basicity was 1.2 and in the case of the 20 SiMn slag, the desired basicity was 1.1. The results of the mass and energy balances executed in respect of the FeMn slag and the SiMn slag are presented respectively in Table 4 below.

WO 2011/027334 PCT/IB2010/054008 16 6% dN-Q -N- m66 - om - o=m o Q Q - Q 9 -, RN'- " 2 2. Z N6.- -- g 8~ 06 8,8s8 No=.o RSO 9RRSM 436 NN66 qNNO S g*ON O. N 9 N6E,- -MR 9 .0 N 66 6q" -- ,o6 9 6 6966666M<K626 z 6 88 O 9 NNNf 9 OOO 0G NST T 9 + d- 80'-0 N 08s8 N0 S.0 8~~ S8 d ZZ o~~~~ 20 8.10.10E ee . ,. ZZ +ONNN9O ,-o8,NN9-N 9 O O9O9O9T =E E Ze E ooo N RO3O O ,-OO $oo0$o$o .6co N. NONNN $$ O$$$AN$ 2 d 6 990NN me - NNom*e-6o 6 M 066669 9 *6 6 - -O0 O-O- 6 - - -O O- N N - - O- -OO OON.NNNNNN0.g0 0 NNN';6 NNgo co r - g g f gg F < NNNQON 2 $0 9 $ G O-O9O00OOOO ON ,- ONOO 8% 88906 f 59 NOOO TNN 9'NT 9f 9f06 6ff 8 ff f f - - - Oo N-o o o - 96r6O No i8 NN - ~ - - - -~ r - N N0O -066-O O6 O O O6-6O O6 9 T - 9- NNN tR - O 99 NN9.O .00 ... - NNoO Neo oeo NN NNNN O oN.NN o o N N-0 N NO-- ~ - 0 9 NN - oo N o -- N- m oN -o- 66d6 =0 N0 -66- f -_,- N - _N 9psFe m 9 - 8o8 E < <<NU' N -e N .o D_ ,,22DNNBECo-omi ON' g 8 Z OO O c=O N''-NN66NN Iz Nu 1-.NNN9 - u ~ U 05 5 .E E 0 2 c U E 00 88 8 = 2 N8 N88 Ef0 N - E Z 0 K K E ~ I - a-a- U _ 66,.i ,ooo 0 g< - 0 -'-' l- DEE8 9- N O N o . 0 cc o 6ga 8 . b5 b 6N0 * 9900005 *690,* 9 UUa 66g 11 N~ t -i 1 _ __O_ _ _ _ _ _ ' WO 2011/027334 PCT/IB2010/054008 17 Discussion From the results set out in Table 4 above, the following observations were made: Reduced alloy silicon content: 5 The silicon content in the metal alloy product decreases when Mn ore is added to the feed slag. An alloy is predicted with a composition closer to the desired specification in the case of the SiMn slag, and within the desired specification in the case of the FeMn slag. 10 It is important to note that, in the model used, the reduction reactions are modelled by calculating thermodynamic equilibrium at each reduction step and therefore ideal conditions were assumed where mass transfer does not limit the reduction reactions. This then means that the predicted silicon content in the alloy is expected to be the maximum value possible. In practice, it is expected the silicon content will be lower 15 than predicted, due to mass transfer limitations reducing the reduction rate of the SiO 2 to Si. Alloy yield: The alloy yield (in kg per 100 kg slag and FeMn ore feed) increases with the addition 20 of Mn ore to the slag feed. In the case of the SiMn slag feed, this increase is significant. Lime requirement: The requirement for lime in the feed mixture is significantly reduced when Mn ore is 25 added to the feed mixture. Less CaO is therefore required to obtain the desired CaO/SiO2 ratio in the product slag, comprising the processed slag and the molten metal. Reductant requirement: 30 The manganese oxide and iron oxide content of the FeMn ore increases the total amount of oxides which may be reduced, thus requiring more reductant to reduce the oxides to alloy species when the ore is added to FeMn slag or SiMn slags. Liquidus temperature and slag solids for FeMn slag: WO 2011/027334 PCT/IB2010/054008 18 An increase in the final slag liquidus temperature is predicted when Mn ore is added to the FeMn slag, as well as more solids (5-7%) in the final slag. This is a result of the CaO/SiO 2 being set to 1.2 . To obtain the higher ratio, more lime had to be added which resulted in the solid solution phase Ca 2 SiO 4 becoming more stable around the 5 operating temperature. A higher liquidus temperature is therefore necessary to melt all the solids in the liquid slag. Metal product manganese content: In the case of the SiMn slag feed, an increase in manganese content of the metal 10 product is predicted when the Mn ore is added to the feed. Alloy silicon content for higher basicities: The FeMn slag scenarios were also solved for a final slag CaO/SiO 2 ratio of 1.1 rather than the 1.2 value on which the results are based. At the lower basicities, a 15 higher silicon content in the alloy is predicted, but still lower than that where no Mn ore was added. At the higher CaO/SiO 2 ratios the Ca 2 SiO 4 solid solution phase becomes more stable which appears to inhibit the reduction of SiO 2 from the slag and lowers the Silicon 20 content in the alloy predicted. It therefore appears to be more feasible to operate the process at the higher CaO/SiO 2 ratio. Use of Fe fines as alternative to BOF slags From the results presented in Table 4 the above conclusions can be drawn for the 25 effect of the addition of Mn ore to the FeMn and SiMn slags on alloy recovery. However, the results of the execution of the model for Fe fines used as alternative to BOF slags predict that Fe fines is a viable alternative to BOF slags. Conclusion 30 The Applicant has thus unexpectedly found that the reduction of a metallurgical slag, containing a desired metal compound, in the presence of a metal ore limits the reduction of silica contained in the slag and therefore limits the amount of silicon contained in a metal alloy product, which is produced in accordance with the method of the invention. It has thus unexpectedly been found that the method of the invention WO 2011/027334 PCT/IB2010/054008 19 enables the production of a commercially exploitable alloy from metallurgical slags which contain unreduced desired metal compounds. The Applicant has also found that the quantity of calcium-containing fluxing agent, 5 such as lime (CaO), typically in the form of limestone (CaC0 3 ), required to achieve or to maintain a desired basicity of the reaction mixture, expressed as CaO:SiO 2 decreases due to the presence of the ore in the reaction mixture, leading to higher throughput and higher metal product yield. 10 The Applicant has also found that an additional advantage of the invention is that the processed slag obtained in accordance with the method of the invention is amenable to downstream processing to produce cement extender products which comply with toxicological and technical specifications. 15 The Applicant has further found that, when Fe-containing slags are used or required, these Fe-containing slags may effectively be substituted with another source of Fe, particularly Fe-fines.

Claims

1. A method of processing metallurgical slag containing at least one desired metal slag compound, the method including the steps of 5 admixing the slag with a reductant and a preferred metal ore to obtain a reaction mixture; heating the reaction mixture to cause the reductant to reduce at least the desired metal slag compound, thereby to obtain a molten metal product, comprising at least the desired metal, and molten processed slag; and 10 separating the molten metal product from the processed slag.

2. The method according to Claim 1, wherein the desired metal and the preferred metal are the same metal. 15

3. The method according to Claim 2, wherein the desired metal and the preferred metal are manganese.

4. The method according to any of Claims 1 to 3, wherein the desired metal slag compound at least partly comprises a desired metal oxide. 20

5. The method according to Claim 4, wherein the desired metal oxide is manganese (II) oxide.

6. The method according to any of claims 1 to 5 inclusive, wherein the 25 preferred metal is expressed at least partly in the preferred metal ore in the form of a preferred metal compound.

7. The method according to Claim 6, wherein the preferred metal compound comprises a preferred metal oxide. 30

8. The method according to Claim 7, wherein the preferred metal oxide is manganese (II) oxide. WO 2011/027334 PCT/IB2010/054008 21

9. The method according to any of the preceding claims, wherein the ore comprises 10% to 50%, by mass, of the reaction mixture.

10. The method according to any of the preceding claims, wherein at least 5 some of at least one of the desired metal and the preferred metal is present in the reaction mixture in native metallic form.

11. The method according to any of the preceding claims, which includes admixing a metal alloying component comprising at least one additional metal other 10 than the desired metal and the preferred metal with the reaction mixture.

12. The method according to Claim 11, wherein the additional metal is at least partly contained in at least one of the metallurgical slag and the preferred metal ore. 15

13. The method according to Claim 11 or Claim 12, wherein the additional metal is present at least partly in native metallic form.

14. The method according to any of claims 11 to 13 inclusive, wherein the 20 additional metal is at least partly expressed as an additional metal compound.

15. The method according to Claim 14, wherein the additional metal compound comprises an additional metal oxide. 25

16. The method according to Claim 15, wherein the additional metal is iron and the additional metal oxide is iron (Ill) oxide.

17. The method according to any of claims 11 to 16 inclusive, wherein the molten metal product is in the form of a metal alloy comprising a molten mixture of at 30 least the desired metal and the additional metal.

18. The method according to Claim 17, wherein the desired metal is manganese, the additional metal is iron, and the metal alloy is ferro-manganese. WO 2011/027334 PCT/IB2010/054008 22

19. The method according to any of the preceding claims, wherein the reductant, the metal ore, and at least a part of the slag are in solid form when being admixed. 5

20. The method according to any of the preceding claims, wherein at least a part of the slag is in molten form, with the reductant and the metal ore being in solid form.

21. The method according to any of the preceding claims which includes, 10 prior to the admixing step, comminuting at least one of the slag, the reductant and the metal ore in solid form to obtain comminuted material.

22. The method according to Claim 21, which includes, prior to the admixing step, subjecting the comminuted material to size classification to obtain a 15 size fraction thereof having an average particle size of at most about 50mm.

23. The method according to any of the preceding claims, wherein the reaction mixture is heated to a temperature from about 13500C to about 16500C. 20

24. The method according to any of the preceding claims, wherein heating the reaction mixture is selected from being conducted on a continuous basis by means of an induction furnace or on a batch wise basis by means of an arc furnace.

25. The method according to any of the preceding claims, wherein the slag 25 is selected from metallurgical furnace slags obtained from one or more metallurgical furnaces used in metal production.

26. The method according to any of the preceding claims, wherein the slag is selected from manganese-containing slags, iron-containing slags, ferromanganese 30 slags, and mixtures thereof.

27. The method according to Claim 26, wherein the manganese-containing slags comprise 15% to 30%, by mass, manganese expressed as manganese (II) oxide. WO 2011/027334 PCT/IB2010/054008 23

28. The method according to Claim 26, wherein the iron-containing slags comprise 25% to 50%, by mass, iron expressed as iron (Ill) oxide. 5

29. The method according to any of the preceding claims, wherein the reductant is any one or more of a silicon-containing reductant, an aluminum containing reductant, a ferrosilicon-containing reductant and a carbon-containing reductant. 10

30. The method according to Claim 29, wherein the reductant is a carbon containing reductant and is selected from coal and anthracite.

31. The method according to any of the preceding claims, which includes admixing a calcium-containing fluxing agent with the reaction mixture. 15

32. The method according to any of the preceding claims, wherein the molten metal product is in the form of an alloy having a silicon content of between 0.4 % and 0.9% by mass. 20

33. The method according to any of the preceding claims, wherein the molten metal product comprises a ferromanganese alloy and has a manganese content of 70% to 90% by mass and an iron content of 5% to 20% by mass.

34. The method according to any of the preceding claims, wherein the 25 reaction mixture has a basicity, expressed as CaO+MgO/SiO 2 by mass, from 1.3 to 1.5 and the processed slag has a final basicity, expressed as CaO/SiO2 by mass, from 1 to 1.25.

35. The method according to any of the preceding claims, wherein 30 separating the molten metal product from the processed slag is by way of gravity separation. WO 2011/027334 PCT/IB2010/054008 24

36. The method according to any of the preceding claims, which includes subjecting the molten processed slag, when separated from the molten metal product, to downstream processing to obtain therefrom a valuable by-product. 5

37. The method according to Claim 36, which includes allowing the molten processed slag to solidify through air-cooling, subjecting the solidified processed slag to comminution to achieve size reduction thereof and rendering the slag into aggregate, with the aggregate being the valuable by-product. 10

38. The method according to Claim 36, which includes causing the molten processed slag to solidify by contacting it with liquid water to cause granulation of the processed slag and obtain a granulated processed slag, with the granulated processed slag being the valuable by-product. 15

39. A metallurgical feedstock for processing, the feedstock comprising a mixture of metallurgical slag containing a desired metal compound; a reductant; and a preferred metal ore. 20

40. The feedstock according to Claim 39, wherein the desired metal and the preferred metal are the same metal.

41. The feedstock according to Claim 40, wherein the desired metal and 25 the preferred metal are manganese.

42. The feedstock according to any of claims 39 to 41, wherein the desired metal slag compound at least partly comprises a desired metal oxide. 30

43. The method according to Claim 42, wherein the desired metal oxide is manganese (II) oxide. WO 2011/027334 PCT/IB2010/054008 25

44. The method according to any of claims 39 to 43 inclusive, wherein the preferred metal is expressed at least partly in the preferred metal ore in the form of a preferred metal compound. 5

45. The method according to Claim 44, wherein the preferred metal compound comprises a preferred metal oxide.

46. The method according to Claim 45, wherein the preferred metal oxide is manganese (II) oxide. 10

47. The feedstock according to Claim 39, wherein the metallurgical slag is selected from manganese-containing slags, iron-containing slags, ferro-manganese containing slags and mixtures thereof. 15

48. The feedstock according to any of claims 39 to Claim 47, wherein the reductant is a reductant for reducing the desired metal compound.

49. The feedstock according to any of claims 39 to 41 inclusive, wherein the preferred metal ore comprises 10% to 50% by mass of the feedstock. 20

50. The feedstock according to any of claims 39 to 49 inclusive, which includes a metal alloying component containing an additional metal to the desired metal and the preferred metal. 25

51. The feedstock according to Claim 50, wherein the additional metal is iron.

52. The feedstock according to any of claims 39 to 51, wherein the reductant, the ore and at least a part of the metallurgical slag is in solid form. 30

53. The feedstock according to any of claims 39 to 52 wherein the metallurgical slag is at least partly in molten form.

54. A molten metal produced in accordance with the method of Claim 1. WO 2011/027334 PCT/IB2010/054008 26

55. A valuable by-product produced in accordance with the method of any of claims 36 to 38.