The invention relates to a method for increasing titanium oxide content in slag produced in connection of electric furnace smelting of titanomagnetite as defined in the preamble of independent claim 1.

In this document "titanium oxide" refers to all titanium oxide compounds, such as to TiO (non stochiometric), ro T1O2, and to Ti ₂ 0 ₃ .

There are many potential titanomagnetite deposits globally. A typical processing method for titanomagnetite is electric furnace smelting. In most cases the main products in titanomagnetite smelting are pig iron (rich in valuable metals, for example vanadium) and slag. Slag is not regarded as a commercial product and it is usually landfilled.

Depending on the titanomagnetite quality, slag may need fluxing in order to achieve good smelting properties. Traditionally slag fluxing is done with quartz or calcium oxide. Traditional fluxing leaves slag low in content of titanium oxide (Ti0 ₂ ) and the slag cannot be upgraded into a commercial product.

In the smelting process, raw materials are stored in their separate day bins. The raw materials are mixed together to a conveyor from the day bins, forming the furnace feed mix. The main feed material to the furnace is titanomagnetite concentrate, titanomagnetite prereduced concentrate, titanomangetite pellets or prereduced titanomagnetite pellets. The used reductant is usually carbon bearing material, such as coke or anthracite. In addition to concentrate and reductant, fluxing agents can be used to modify the slag composition so that the slag has desired liquidus (melting) temperature and low enough viscosity for smooth tappings. Traditionally slag fluxing is conducted by feeding calcium bearing material into the furnace, most commonly burnt lime (CaO). The slag, consisting mainly of Ti0 ₂ , Si0 ₂ , A1 ₂ 0 ₃ , MgO and CaO has been of no commercial value and is typically landfilled.

The furnace feed mix is normally directed into feed bins, located above the electric furnace The electric furnace can be of two types, AC or DC furnace. The feed mix is fed with vibrating feeders into feed tubes that lead the materials trough the furnace roof into the molten bath. The molten slag temperature is kept between 1500 and 1700 °C, depending on the slag liquidus temperature. The metal temperature is typically lower at 1450-1550 °C. The main process target in titanomagnetite smelting is to reduce the iron oxides present in the titanomagnetite concentrate into pig iron and the valuable metal oxides (such as vanadiumoxide) present in the concentrate into to the pig iron metal phase. The two basic reactions during the smelting process are the following: Reduction of FeO:

FeO + C→Fe + CO (1) Reduction of valuable metal oxides (example V2O5):

Small amount of other oxides such as S1O2 and MnO are also reduced to the metal phase. Other oxide components are left in the slag phase including most of the T1O2 present in the concentrate. Metal phase forms the bottom liquid layer and the slag with lower density remains on top of the metal phase. Metal and slag are tapped to product ladles alternately. The slag product may also be wet granulated to fine particle size directly from the furnace. Traditional fluxing leaves slag low in content of T1O2 and the slag cannot be upgraded into a commercial product.

In publication AU 656476 a process is provided for the production of a titanium rich slag and pig iron from titanomagnetite. The titanomagnetite is fed continuously, together with carbonaceous reductant, and in the absence of fluxes, to the molten bath of a circular d.c. arc furnace, preferably a plasma arc furnace, wherein the molten bath forms the anode and one or more electrodes in the furnace roof form the cathode. The feed materials are preferably preheated or prereduced. using heat contained in the off-gases from the process. Titanium rich slag which can be used as the feed to a sulphate based titanium dioxide production process is recovered continuously, or intermittently, and pig iron is lapped off as a by-product.

Publication WO 2011/143703 presents a direct smelting process that comprises supplying (a) a metalliferous feed material that contains iron oxides and at least 3 wt.% titanium oxides (b) a solid carbonaceous feed material, and (c) an oxygen-containing gas into a direct smelting vessel containing a molten bath of iron and slag and direct smelting the metalliferous feed material in the vessel and producing process outputs of molten iron, molten slag containing titanium oxides , and an off-gas. The process is characterised by controlling the process conditions, as described herein, so that the molten slag has a viscosity in a range of 0.5-5 poise when the slag temperature is in a range of 1400-1550 °C in the molten bath in the direct smelting vessel. Publication WO 2011/143703 presents also a direct smelting vessel when used to smelt a metalliferous feed material that contains iron oxides and at least 3 wt.% titanium oxides via a molten bath-based direct smelting process , with the vessel containing a molten bath of metal and slag, and with the molten slag having a temperature range of 1400-1550 °C and a viscosity in a range of 0.5-5 poise.

Objective of the invention

The object of the invention is to provide an effective method for the increasing of titanium oxide content in produced slag in connection with electric furnace smelting of titanomagnetite, making the slag a valuable by product. Short description of the invention

The method of the invention is characterized by the definitions of independent claim 1. Preferred embodiments of the method are defined in the dependent claims 2 to 9.

The invention relates also to the use of slag containing titanium oxide obtained from a method according to any of the claims 1 to 10 as a feedstock in the production of T1O2 pigment.

In the presented innovation traditional fluxing materials are replaced with titanium oxide bearing materials such as with ilmenite such as ilmenite concentrate in order to produce upgradeable Ti0 ₂ slag. Ilmenite concentrate is a commercial mineral product (rich in Ti0 ₂ ) which is widely available in the market. Also other titanium oxide bearing materials can be used. Ilmenite concentrate is incorporated into the furnace feed mix with titanomagnetite and reducing agent such as anthracite. The feed amount is calculated based on the target slag Ti0 ₂ content and the target slag liquidus temperature. Slag viscosity and the target slag liquidus temperature are factors that limit the maximum Ti0 ₂ content. In some embodiments of the method, the target slag Ti0 ₂ content in weight percentages is at least 55 , in other embodiments at least 70 % or at least 85 %.

In the electric furnace, if ilmenite is used as titanium oxide bearing material, the iron oxides in the ilmenite are reduced to metallic form therefore raising the furnace pig iron output. The Ti0 ₂ in the ilmenite is smelted and it dissolves into the slag originating from the titanomagnetite and anthracite ash components, therefore raising the slag Ti0 ₂ content.

The presented slag modification transforms the otherwise dischargeable slag into a commercial product. As a result the smelting operation becomes economically more viable and profitable. The presented innovation makes many potential titanomagnetite projects economically more viable. List of figures

In the following the invention will described in more detail by referring to the figures, of which

Figure 1 is a ternary phase diagram showing ilmenite fluxing and CaO fluxing of reference material 1,

Figure 2 is a ternary phase diagram showing ilmenite fluxing and CaO fluxing of reference material 2,

Figure 3 is a ternary phase diagram showing ilmenite fluxing and CaO fluxing of reference material 3, and

Figure 4 shows the relationship between slag capacity and slag vanadium oxide bearing capacity.

Detailed description of the invention

The invention relates to a method for increasing of titanium oxide content i.e. the relative weight percentage content of titanium oxide with respect to the other components of the slag, in slag produced in connection with electric furnace smelting of titanomagnetite.

The method comprises feeding titanomagnetite, reducing agent and fluxing agent into a smelting furnace such as into an electric funace.

The method comprises melting titanomagnetite, reducing agent and fluxing agent in the electric furnace to form a layer containing liquid metal and layer containing slag above the layer containing liquid metal.

The electric furnace is preferably, but not necessarily, an electric arc furnace, and consequently thermal energy for performing said melting is preferably, but not necessarily produced by electrical energy.

The method comprises withdrawing liquid metal and slag separately from the electric furnace.

In the method, the fluxing agent comprises in percentages of weight between 3 and 100 % titanium oxide bearing material such as ilmenite.

The method comprises preferably, but not necessarily, feeding an amount of titanium oxide bearing material such as ilmenite into the electric furnace from about 3 % to about 25 , preferably from about 10 to about 15 , more preferably about 15 % on titanomagnetite weight basis.

The method comprises preferably, but not necessarily, using carbonaceous material such as coke or anthracite as reducing agent.

The method comprises preferably, but not necessarily, feeding titanomagnetite containing in weight percentages between 75 and 95 , preferably between 80 and 90 % magnetite (Fe ₃ C"4), between 0.25 and 1.5, preferably between 0.45 and 1.5 % vanadium oxide (V2O5), and between 2.5 and 15 , preferably between 3 and 10 % titanium oxide including for example T1O2 and Ti ₂ 0 .

The method comprises preferably, but not necessarily, using titanium oxide bearing material such as ilmenite containing in weight percentages between about 40 and about 60 , preferably between about 50 and about 55 % titanium oxide including for example T1O2 and Ti ₂ 0 ₃ .

The method comprises preferably, but not necessarily, calculating the titanium oxide equivalent content in the titanomagnetite, calculating the titanium oxide equivalent content in the titanium oxide bearing material such as in the ilmenite, and adjusting the feed amount of titanomagnetite to the feed amount of titanium oxide bearing material such as of ilmenite.

The method comprises preferably, but not necessarily, feeding an amount of titanium oxide bearing material such as of ilmenite into the electric furnace so that from about 1 % to about 20 % titanium oxide, including for example T1O2 and Τΐ2θ ₃ , will be fed into the electric furnace with the titanium oxide bearing material such as with the ilmenite on titanomagnetite weight basis. Theoretical examples

In the following, three theoretical examples of ilmenite fluxing and the effect of the slag chemistry will be presented. In the theoretical calculations, the reference titanomagneties 1 to 3 (see table 1) was used as feed materials and reference ilmenite 2 (see table 2) was used fluxing agent. On the theoretical calculations, for comparison purposes, CaO was also used fluxing agent. Additionally, the theoretical result if no fluxing agent was used, was calculated in the theoretical calculations. The target slag T1O2 content in terms of percentages of weight in the calculations was 55 %. This can controlled directly by ilmenite feed amount in relation to the titanomagnetite feed amount.

Based on the theoretical approach in all of the three different titanomagnetite cases, ilmenite fluxing enables good slag liquidus temperature, and produces a slag that is a marketable product. Figures 1 to 3 also illustrate that with CaO fluxing the slag Ti0 ₂ content will become low, rendering the slag a disposable, non-commercial by product.

In the ternary phase diagrams in figures 1 to 3, the MgO component amount was added to CaO component in order to effectively illustrate the slag chemistry in the diagrams.

Table 1: composition of reference materials 1, 2 and 3 in percentages of weight

Table 2 composition of ilmenite material 3 in percentages of weight

The slag composition projections were conducted by normal mass balance calculations, where the titanomagnetite amount was fixed and ilmenite addition was calculated ( of titanomagnetite feed) based on the slag T1O2 content target (55 %). Recovery rates (distribution of elements into slag and metal) were estimated based on experimental tests. For the ternary phase diagrams in figures 1 to 3, the main slag component contents (S1O2, CaO, AI2O3 and T1O2) were projected to 100 , therefore excluding minor components from the ternary phase diagrams. Also due to the multiphase slag system, MgO was summed up with CaO in order to simplify the system and to enable phase diagram study.

The used recovery rates are illustrated in table 3. Table 3: Used recovery rates.

Reference Material 1

In the ternary phase diagram in figure 1, ilmenite and CaO fluxing of titanomagnetite reference 1 is represented. In the ternary phase diagram the slag compositions of the three cases (no flux, ilmenite flux and CaO flux) and the corresponding liquidus temperatures are shown.

From figure 1 it can be seen that in order to achieve slag T1O2 content of 55 %, the ilmenite flux feed amount should be 6.3 % of the titanomagnetite feed. At the same time a liquidus temperature of about 1550°C is achieved. This temperature enables good vanadium recoveries and a high Ti0 ₂ content of the slag which makes the slag a marketable product.

When CaO fluxng is used the CaO flux amount should be 3.3 % of titanomagnetite feed resulting in slag CaO content of 35 % and slag liquidus temperature of 1550 C. This fluxing leaves the slag Ti0 ₂ content at 27 %, rendering the slag a non-profitable side product.

Reference Material 2

In the ternary phase diagram in figure 2, ilmenite and CaO fluxing of titanomagnetite reference 2 is represented. In the ternary phase diagram the slag compositions of the three cases (no flux, ilmenite flux and CaO flux) and the corresponding liquidus temperatures are shown.

From figure 2 it can be seen that in order to achieve slag Ti0 ₂ content of 55 , the ilmenite flux feed amount should be 3.6 % of the titanomagnetite feed. At the same time a liquidus temperature of above 1600°C is achieved. This temperature enables good vanadium recoveries and a high Ti0 ₂ content of the slag which makes the slag a marketable product.

With CaO fluxing the fluxing amount should be 5.3 % of titanomagnetite feed resulting in slag CaO content of 35 % and liquidus temperature of 1550 °C. This fluxing leaves the slag Ti02 content at 35 , rendering the slag a non-profitable side product.

Reference Material 3

In the ternary phase diagram in figure 3, ilmenite and CaO fluxing of titanomagnetite reference 3 is represented. In the ternary phase diagram the slag compositions of the three cases (no flux, ilmenite flux and CaO flux) and the corresponding liquidus temperatures are shown.

From figure 3 it can be seen that in order to achieve slag T1O2 content of 55 , the ilmenite flux feed amount should be 15 % of the titanomagnetite feed. At the same time a liquidus temperature of above 1500°C is achieved.

With CaO fluxing the fluxing amount should be 3.8 % of titanomagnetite feed resulting in slag CaO content of 35 %. This fluxing leaves the slag T1O2 content at 35 , rendering the slag a non-profitable side product.

Higher recovery rates of valuable metals

High slag basicity lowers valuable metal recoveries, for example the recovery of vanadium into the pig iron. In figure 4, the relationship between slag optical basicity and slag vanadium oxide bearing capacity is seen.

CaO is a slag component which raises slag basicity. On the other hand T1O2 acts as an acid component, which lowers slag basicity. As CaO content increases in traditional fluxing, the vanadium capacity of the slag increases, therefore lowering the amount of vanadium that is reduced into metallic form. When ilmenite flux is used, slag CaO content is very low, and T1O2 content high. As a result slag vanadium oxide capacity remains low therefore raising the vanadium recovery to metal.

Ilmenite fluxing enables higher recovery of valuable metals making the process economically more viable, as less vanadium is lost into the slag.

Broader operating area with high T1O2 versus high CaO

As seen in figures 1 to 3, slag with high T1O2 resides in a temperature area where the liquidus temperature lines are further apart when compared to the area where CaO is used as flux. This means that deviations in normal smelter operation, such as raw material chemical composition changes, feed system inaccuracies, power and temperature changes, have less effect in slag characteristics (viscosity, liquidus temperature) compared to operation with CaO flux, making the smelter operation more smooth and predictable. Possibility for productification of the T1O2 rich slag

The slag T1O2 needs to be above 55 % for Ti02 pigment production. Therefore if ilmenite flux addition is adequate this limit can be reached.

It is apparent to a person skilled in the art that as technology advanced, the basic idea of the invention can be implemented in various ways. The invention and its embodiments are therefore not restricted to the above examples, but they may vary within the scope of the claims.