AU2018247275A1 - Processing of impure titanium dioxide ore - Google Patents

Abstract

Abstract A process is disclosed for extracting crystalline TiO 2 from impurity-containing ilmenite, leucoxene, and/or rutile. The process includes the steps of creating a feed mixture of the mineral plus iron ore if required, and a reducing agent, and fluxing agents arranged to bring SiO2, CaO and A1203in the feed mixture into the molar ratio of 1:1:2; smelting the feed mixture; oxidising the resulting slag to convert lower oxide states to higher oxide states; cooling the molten slag at a slow rate between the liquidus and the solidus of the molten slag to promote crystallisation of TiO2; and separating the crystalline TiO 2 formed from the solidified slag. The method also proposes the use of additional fluxing agents to capture residual oxides of magnesium, manganese, chromium and/or vanadium in auxiliary silicate crystalline phases.

Description

“PROCESSING OF IMPURE TITANIUM DIOXIDE ORE”

Applicant:

TIMAG TECHNOLOGIES PTY LTD

Associated provisional applications: Number 2017904144 filed 13 October 2017

The following statement is a full description of the invention, including the best method of performing it known to me:

2018247275 11 Oct 2018 “PROCESSING OF IMPURE TITANIUM DIOXIDE ORE”

Field of the Invention [0001] The present invention relates to a process for extracting crystalline titanium oxides, in particular to extracting crystalline titanium oxides from the titanium oxides-bearing ores ilmenite, leucoxene and rutile.

Background to the Invention [0002] It is known to require the extraction of various titanium oxide species (ΤϊχΟυ) in crystalline form from ores and other materials bearing these titanium oxides. Known processes for extraction of titanium oxides from ilmenite include the Becher process, in which ilmenite is subjected to a reductive process to reduce the iron oxide content to metallic iron, and then the metallic iron is reoxidised in an aqueous solution to separate the metallic iron from the ilmenite, producing a synthetic rutile product and separate iron oxide waste product; and the conventional titanium slag process in which ilmenite is reductively smelted to produce an enriched titanium oxide slag and a pig iron by-product.

[0003] The Becher and conventional titanium slag processes both require feedstock that is low in CaO, MgO, AI2O3 and S1O2 in order to produce synthetic rutile and titanium slag that have a sufficiently low content of CaO, MgO, AI2O3 and S1O2 to be acceptable as feedstock in the chloride process for producing titanium dioxide pigment. Both processes enrich the titanium oxide content, and consequently the CaO, MgO, AI2O3 and S1O2 contents, only by depletion of the iron oxide content.

[0004] The chloride process generally requires a feedstock having a T1O2 content above 75%, an FexOy content below 25%, and impurity oxides content substantially no more than as follows (by weight): CaO 0.13%, MgO 1.2%, AI2O3 1.5%, SiO₂2.0%, MnO 2.0%, Cr₂O₃ 0.25%, V2O5 0.6%.

[0005] The low feedstock impurity content requirement means that a substantial portion of the available resources of ilmenite and other titanium

2018247275 11 Oct 2018 oxides-bearing materials are unable to be exploited using the chloride process. A wider range of ilmenite can be processed to obtain T1O2 using the sulphate process, but this process produces large quantities of metal sulphate waste and is considered environmentally unsound.

[0006] The same impurity oxide content restrictions also apply to leucoxene and natural rutile feedstock, which can only be utilised in the chloride process and not the sulphate process.

[0007] The present invention attempts to provide an alternative method for extracting T1O2 in a crystalline form from titanium oxides-bearing materials that have levels of oxides of calcium, magnesium, aluminium, and/or silicon, that make them generally unacceptable as feedstock for the Becher process, the conventional titanium slag process, or directly to the chloride process. The invention also proposes a method to manage levels of manganese, chrome, and/or vanadium impurities which are above previously acceptable limits.

Summary of the Invention [0008] In accordance with a first aspect of the invention there is provided a process for extracting crystalline T1O2 from titanium oxides-bearing material comprising the steps of:

a) providing a feed mixture to a reductive smelting process comprising (i) ilmenite, (ii) leucoxene, and/or (iii) rutile plus iron ore, a reducing agent, and fluxing agents comprising S1O2, CaO and AI2O3;

b) reductive smelting the feed mixture, reducing agent, and fluxing agents to produce a molten slag of a mixture of titanium oxides, gangue oxides, and fluxing agents, wherein the molar ratio of CaO, AI2O3 and S1O2 in the molten slag substantially favours the formation of a base mineral species including CaO, AI2O3 and S1O2 in the molar ratio of 1:1:2 together with the formation of comparable mineral species containing any oxides present of magnesium, manganese, chrome, or vanadium, the ΤϊχΟυ concentration in the molten slag being at least 25% by weight;

2018247275 11 Oct 2018

c) oxidising the molten slag to convert lower oxide states to higher oxide states;

d) cooling the molten slag at a slow rate between the liquidus and the solidus of the molten slag to promote crystallisation of T1O2; and

e) separating the crystalline T1O2 formed in step (d) from the solidified slag.

[0009] It is preferred that the slag produced in step (b) contains a ΤϊχΟυ concentration of 40-50% by weight.

[0010] It will be appreciated that the addition of fluxes to form the base mineral species will dilute the T1O2 concentration to that preferred.

[0011] It will be appreciated that step (e) produces a spent base mineral from which the crystalline T1O2 has been separated. Where ΤϊχΟυ concentration in the slag of step (b) is greater than preferred, it is envisaged that previously obtained spent base mineral may be added to the slag in order to reduce the ΤϊχΟυ concentration.

[0012] It is envisaged that during slow cooling and formation of the T1O2 crystals the impurity oxides will remain in the residual molten slag until formation of T1O2 crystals is complete and the base mineral species begin to solidify.

[0013] It is anticipated that the reductive smelting process of step (b) will reduce a proportion of the impurity oxides (such as manganese, chrome, or vanadium oxides, resulting in the production of metals which are expected to report to pig iron produced in the smelting process.

[0014] The fluxing agent additions may be varied from that required to form the base mineral species as in step (b) to promote the sequestering of certain impurity oxides to auxiliary mineral species.

2018247275 11 Oct 2018 [0015] Where magnesium oxides are present in the feed mixture the amounts of CaO and S1O2 flux can be increased in order to allow for the formation of CaO.MgO.2SiO2 in addition to the base mineral species.

[0016] Where manganese oxides are present in the feed mixture the amounts of AI2O3 and S1O2 flux can be increased in order to allow for the formation of mineral species incorporating manganese oxides in addition to the base mineral species. It will be appreciated that the smelting process will reduce much of the manganese oxides present to manganese, which will report to the pig iron. Where excess S1O2 is present it is anticipated that the remaining MnO will solidify by forming the auxiliary mineral species MnO.SiO2 or 2MnO.SiC>2. This can be encouraged by the addition of S1O2 flux, or by a reduction in the added quantities of CaO and/or AI2O3. Alternatively, it is possible that remaining MnO will report to the silicate phase to form species such as 2MnO.2Al2O3.5SiO2. or 3MnO.Al2O3.3SiO2. Where there is insufficient silica then the species MnO.AbOs may form. Where manganese also oxides to Μη2θ3 it is anticipated that the addition of fluxes may result in species such as MnO.3Mn2O3.2SiO2, Mn2O3.Al2O3.2SiO2, CaO.3Mn2O3.SiO2, CaO.MnO.SiO2, or CaO.MnO.2SiO2 reporting to the silicate phase.

[0017] Where both chromium oxides and magnesium oxides are present in the feed mixture a slightly different process is expected. It will be appreciated that the smelting process will reduce much of the chromium oxides present to chromium, which will report to the pig iron. The remaining Cr2O3 is anticipated to solidify by forming one of the auxiliary mineral species MgO.Cr2O3, Cr2O3.Al2O3 or MgO.(Cr, ΑΙ)2θ3. In the event that the molar ratio MgO:Cr2O3 is less than 1:1, additional MgO can be added as a fluxing agent. Where the molar ratio is greater than 1:1, excess MgO can be managed as described above. It is also possible that silicates such as 3CaO.Cr2O3.3SiO2, or 3MgO.Cr2O3.3SiO2 may form given the right conditions, thus exhibiting as a Cr impurity within the primary CaO.Al2O32SiO2 phase.

2018247275 11 Oct 2018 [0018] Where vanadium oxides such as VO2, V2O3 or V2O5 are present in the feed mixture the relative amounts of CaO and S1O2 flux can be increased in order to allow for the formation of species such as CaO.VO2.SiO2 or 3CaO.V2O3.3SiO2 in addition to the base mineral species. It will be appreciated that the smelting process will reduce much of the vanadium oxides present to vanadium, which will report to the pig iron. Where excess CaO is present it is anticipated that the remaining V2O5 will solidify by forming an auxiliary mineral species such as CaO.V2Os, 2CaO.V2Os, 3CaO.V2O5 or 4CaO.V2Os. This can be encouraged by the addition of CaO flux, or by a reduction in the added quantities of S1O2 and/or AI2O3.

[0019] Where Fe2O3 is present in the slag after oxidation the relative amounts of CaO, AI2O3 and S1O2 flux may be increased in order to allow for the formation of species such as 2CaO.Fe2O3.Al2O3.3SiO2 in addition to the base mineral species. Depending on the available fluxes, other species such as 2CaO.(Fe,AI)2O3, CaO.3(Fe,AI)2O3, 2CaO.Fe2O3, CaO.Fe2O3, CaO.2Fe2O3 or CaO.3Fe2O3 may form. Alternatively, it may be acceptable to simply allow Fe2O3 to associate with T1O2 crystals which can then be used as feed for the chloride process.

[0020] Fluxing agents are preferably added to the feed mixture prior to smelting. In an alternative some fluxing agents may be added during smelting. In another alternative, some fluxing agents may be added to the slag following smelting. The addition of fluxing agents after smelting may be beneficial for making minor correction to the slag composition before cooling.

[0021] It is preferred that the slag is oxidised while still fully molten. Preferably this is achieved with the use of 02(g).

[0022] Where the titanium oxides bearing material is rutile, it may be mixed with ilmenite and/or leucoxene to provide the feed mixture of step (a). Alternatively, rutile may be mixed with iron ore.

2018247275 11 Oct 2018 [0023] Step (e) is preferably achieved by the crushing and grinding of the solidified slag, and the separation of T1O2 crystals using electrostatic separation, gravity separation, and/or flotation separation.

[0024] The separated T1O2 crystals may be subsequently treated with HCI(aq) to remove adhering slag phases.

Detailed Description of Preferred Embodiments [0025] The present invention is based on an initial discovery that a molten slag comprising a mixture of T1O2 and CaO, AI2O3 and S1O2, wherein CaO, AI2O3 and S1O2 are in particular molar ratios, will differentially solidify to afford a plurality of crystalline phases, where a primary crystalline phase comprises crystalline T1O2 in the form of rutile and a secondary silicate phase substantially comprises silicate mineral species CaO.Al2O3.2SiC>2 when the molten slag is cooled at a slow rate between the liquidus and the solidus of the molten slag, provided that the T1O2 content of the molten slag composition is sufficiently high for crystalline T1O2 to form.

[0026] The present invention is also based on a further discovery that other oxide impurities in the slag, including those of iron, magnesium, manganese, chrome, and vanadium, may also be captured within the secondary silicate phase or in another separate mineral phase with accurate ‘dosing’ of fluxing agents.

[0027] Therefore, high purity crystalline T1O2 can be produced from a titanium oxides-bearing material having excess impurities of oxides of calcium, aluminium or silicon by reductive smelting a mixture of titanium oxides-bearing material, and fluxing agents comprising S1O2 and metal oxides from a group including CaO, and AI2O3 at a high temperature to afford a molten slag, and then slowly cooling the slag. The fluxing agents are present in the molten slag in an amount to adjust the molar ratio of CaO, AI2O3 and S1O2 in the molten slag to substantially favour formation of silicate mineral species CaO.Al2O3.2SiO2, together with any auxiliary silicate mineral specie which may include some or all of the oxide impurities subsequent to

2018247275 11 Oct 2018 formation of crystalline T1O2 when the molten slag is cooled. However, the

T1O2 concentration in the molten slag must also be sufficient to afford crystalline T1O2 when the molten slag is cooled.

[0028] Thus, it is an important consideration in formation of the molten slag composition that adjustment of the molar ratios of CaO, AI2O3 and S1O2 in the molten slag to substantially favour formation of silicate mineral CaO.Al2O3.2SiC>2 and auxiliary species by addition of the fluxing agents does not, in fact, dilute the T1O2 concentration in the molten slag to a level where little or no crystalline T1O2 is formed when the molten slag is subject to slow cooling solidification.

[0029] The minimum T1O2 content of the molten slag sufficient for crystalline T1O2 to form with a crystal size of greater than 90pm varies depending on the relative proportions of CaO, AI2O3 and S1O2 in the molten slag, from about 25% to about 35%.

[0030] The preferred maximum smelting temperature is about 1600°C. The preferred T1O2 content in the molten slag varies depending on the relative proportions of CaO, AI2O3 and S1O2 in the molten slag, from about 40% to about 50%. Higher T1O2 content may be acceptable subject to slag liquidus and smelting conditions.

[0031] It is unlikely that a molten slag formed merely from the titanium oxides-bearing material (TOBM), regardless of whether it is a by-product of the reductive smelting process, would have appropriate inherent molar proportions of CaO, AI2O3 and S1O2 to coincide with the preferred molten slag composition. Accordingly, it is thus necessary to adjust the concentrations of some of the oxides, particularly those that are deficient in the slag, to the preferred molar ratios of CaO, AI2O3 and S1O2 with fluxing agents comprising CaO, AI2O3 and S1O2. Addition of CaO fluxes can be made as oxide, silicates, or carbonates, the latter subsequently needing to be burnt to the oxide form during either or both the iron oxide reduction and smelting steps of the reductive smelting process. Addition of AI2O3 fluxes

2018247275 11 Oct 2018 can be made as oxides of silicates. Flux additions in the form of sulphates, chlorides, phosphates or fluorides will be deleterious to the process of the present invention. One or more or all of the fluxes may be subject to preparation by conventional treatments. These may include but are not limited to drying, grinding, burning of carbonate forms to oxide forms, and agglomeration.

[0032] Flux additions can be made at three successive stages in the process of the present invention, including but not limited to during blending of the TOBM feedstock (and optionally the reductant) for the process, during smelting and/or during oxidation prior to slow cooling solidification of the molten slag. Staggering the addition of the fluxes may be beneficial.

[0033] However, if as a result of making the requisite flux additions to achieve the requisite proportions the T1O2 content of the molten slag is diluted by too much then crystalline rutile will not form when the molten slag is slow cooled.

[0034] In another embodiment of the invention, the molten slag may contain residual metal oxide impurities that may have originated as accessory oxides or/and accessory minerals in the titanium oxides-bearing material or/and fluxing agents or/and ash from the carbonaceous reductant(s). Typical oxides encountered include oxides of magnesium, vanadium, chromium, and manganese. In the first instance reductive smelting will substantially convert most or all of these to their metallic form, which will report to the pig iron. The present invention proposes, where practicable, binding any remaining residual oxide impurities as impurities within the silicate mineral phases. This is achieved by appropriate variation in the amounts of CaO, AI2O3 and S1O2 present in the slag.

[0035] For example, if magnesium is present and oxidised to magnesium oxide (MgO), it may be bound with CaO and S1O2 to form the substitution silicate mineral species CaO.MgO.2SiO2. This will manifest itself as an elemental impurity within the base CaO.MgO.2SiO2 phase. Accordingly, the

2018247275 11 Oct 2018 number of moles of AI2O3 flux required in the slag may be reduced by the number of moles of MgO present. Alternatively, if no AI2O3 flux is required to be added then additional CaO and S1O2 flux will instead be required.

[0036] It may be further required to create other auxiliary silicate mineral species to bind with particular metal oxides present, in order to preferentially retain these oxides within the base silicate mineral phase, and thus substantially prevent them becoming impurities within the

T1O2 crystals. Manganese oxides, for instance may be bound into the silicate phase as MnO.SiCte or 2MnO.SiO2, or possibly a species such as 2MnO.2Al2O3.5SiC>2. Similar species may be formed to account for oxides of vanadium or excess iron.

[0037] Chromium oxides may be incorporated along with magnesium oxide to form species such as MgO.Cr2C>3, Cr2O3.Al2O3, MgO.(Cr, ΑΙ)2θ3. 3CaO.Cr2O3.3SiC>2, or 3MgO.Cr2O3.3SiC>2. The particular species created will depend on matters such as the molar ratio of fluxes present and the cooling rate.

[0038] The titanium oxides-bearing materials that may be used as feed material or as fluxes in the process of the present invention include, but are not limited to, non-ferrous ores of titanium such as rutile (naturally occurring or synthetic), anatase, brookite, perovskite, and titanate (also known as sphene). Rutile, anatase and brookite are polymorphs of T1O2. The process of the present invention can also be used in relation to titanium ores containing iron oxides including, but not limited to, leucoxene, ilmenite (conventional or altered), ulvospinel, titanomaghemite, titanomagnetite, and vanadiferous titanomagnetite provided that the titanium ores containing iron oxides undergo standard reduction and melting or smelting processes, and which may include subjecting the titanium ores containing iron oxides to an oxidising roast. At the conclusion of this process pig iron is tapped from a smelting furnace and processed according to known techniques. Molten slag is also tapped from the smelting furnace, and it is this tapped molten slag which is subject to treatment according to the present invention.

2018247275 11 Oct 2018 [0039] The suitability of any titanium oxides-bearing material must be assessed on general criteria as described in more detail as follows. The titanium oxides-bearing material is typically comprised of T1O2, iron oxides (but not always), and other oxides. The other oxides are typically but not exclusively CaO, AI2O3 and S1O2. Examples of T1O2 source materials that do not specifically contain iron are the minerals perovskite [CaTiC>3], and titanate (also known as sphene) [CaTiSiOs].

[0040] Perovskite and titanate (sphene) cannot be used solely as the addition of requisite fluxes would dilute their T1O2 content to less than that required to adequately form crystalline T1O2 on slow cooling solidification. However, they may be used as combined sources of T1O2 and flux with other materials.

[0041] Thus, in all titanium oxides-bearing material it is necessary that following any beneficiation the ratio of T1O2 content be sufficiently high relative to the combined CaO, AI2O3 and S1O2 contents present naturally or as gangue in the source material and present as ash in the carbonaceous reductant so that the molten slag subsequently created together with any requisite fluxing additions of CaO, AI2O3 and S1O2 has sufficiently high T1O2 content. If a T1O2 source material contains various other metal oxides then these may also have to be allowed for. For example, if the molten slag is predominantly comprised of T1O2, CaO, AI2O3 and SiO2then any MgO content may be treated as broadly equivalent to AI2O3.

[0042] For example, a titanium oxides-bearing material that is by itself unsuitable for the chloride process but which may be suitable for the present process is an ilmenite by-product from garnet production having composition as shown in the following table:

Grain size (pm)	TiO2 (%)	Fe2O3 (%)	CaO (%)	MgO (%)	AI2O3 (%)	SiO2 (%)	MnO (%)	Cr2O3 (%)	V2O5 (%)
+180	48.1	43.9	1.80	0.58	1.55	3.03	0.75	0.06	0.20
-180	52.8	46.8	0.17	0.45	0.36	0.73	0.67	0.05	0.25

2018247275 11 Oct 2018 [0043] Accordingly, two or more TOBMs may be blended and used in the process of the present invention. Blending of the CaO, AI2O3 and S1O2 contained in the TOBMs can advantageously minimise the addition of the fluxing agents. Where natural rutile is the main source of T1O2 the addition of a FexOy source, which may be ilmenite or a suitable iron ore, will be required.

[0044] After removal of the molten slag from the furnace it is subject to an oxidising treatment with 02(g) to ensure that all ΤϊχΟυ oxide species are oxidised to T1O2.

[0045] At this time minor amounts of fluxes can be added to optimise the slag composition. In addition, rutile seed crystals may be added.

[0046] To promote crystallisation of TiO2the molten slag is cooled at a slow rate between the liquidus and the solidus of the molten slag. When the molten slag has solidified, the crystalline T1O2 can then be extracted from the solidified slag by various separation techniques.

[0047] Typically, the T1O2 rutile crystals will first be liberated from the solidified slag by breaking up, crushing and grinding the solidified slag to a particle size suitable to commence separation techniques. Typically the largest particle size at which separation of the rutile crystals from the silicate mineral phases of the solidified slag can commence is approximately 1mm, because usually the bulk of rutile crystals formed are less than 1mm in size. Breaking, crushing and grinding are performed by conventional means.

[0048] By way of example, breaking up of the solidified body of slag can be performed with a pneumatic or hydraulic powered breaking tool to produce lumps of slag less than 1000mm in size. These lumps are then crashed in a jaw crasher to less than 150mm in size. These subsequent lumps are then crashed in a cone crusher to less than 32mm in size, then ground using high-pressure grinding rolls (HPGR) to less than 1mm in size.

2018247275 11 Oct 2018 [0049] Grinding by HPGR has the beneficial characteristic of breaking materials along grain boundaries between phases. If the phases are similar in hardness then similar size particles of the different phases will be produced. If the phases have different hardness then the harder the phase the larger the relative particle size will be. Additional grinding, for instance by ball or rod mill, may be required.

[0050] Separation of the rutile crystals from the silicate phase minerals in the ground slag will be performed by conventional mineral particle separation methods, and may be augmented with finer grinding at intermediate stages to further liberate the rutile crystals.

[0051] Given the expected similar particle sizes and significantly higher density of rutile then gravity separation methods can be used to separate the denser rutile particles from the less dense silicate mineral phase particles. Gravity separation methods that could be employed include wet separation methods such as cones, spirals and shaking tables and dry separation methods such as air tables.

[0052] Because the electrical conductivity of rutile is high and that of all the silicate mineral phases formed in the slag is low then high tension (electrostatic) separation methods can also be employed.

[0053] In the case where one or more of the silicate mineral phases in the solidified slag is acid soluble then acid can be used to remove these phases, usually in a final liberation step. By way of example the silicate mineral phase CaO.Al2O3.2SiO2 is known to be soluble in hydrochloric acid. Thus, where minor quantities of CaO.Al2O3.2SiO2 remain attached to the rutile crystals, either on the surface or within exposed cavities in the bodies of the rutile crystals, then hydrochloric acid can be used to dissolve the residual CaO.Al2O3.2SiO2.

[0054] Thus a suitable combination of breaking, crushing and grinding liberation methods, and gravity and electrostatic separation methods, and in

2018247275 11 Oct 2018 some cases acid treatment for a final clean-up, will be effective in accomplishing liberation and separation of the rutile crystals.

[0055] The liberation and separation processes as described above will produce a proportion of particles that will be part rutile and part silicate mineral phase. While successively finer grinding will eventually liberate the rutile from the silicate mineral phases it will usually be more effective to recycle some or all of this proportion back into the smelting step. Without recycling, this proportion will become tailings and the rutile content will be lost when the tailings portion is disposed of.

[0056] In the case where substantial portions of all three of CaO, AI2O3 and S1O2 must be added to produce a molten slag with adequately low proportion of T1O2 so that its liquidus temperature is preferably less than 1600°C, so as to safely operate the melting furnace, it may be economically beneficial to recycle some of the rutile-free silicate slag phase instead of adding fresh CaO, AI2O3 and S1O2. The proportion of rutile-free silicate phase that can be recycled will be limited by its impurity oxide content and the need to create a proportion of fresh slag sufficient to take up the impurity oxides in the fresh feed mixture.

[0057] It will be understood that there is a natural limitation to the portion that can be recycled in that the total mass of materials leaving the process (rutile, tailings, process gases, yield losses, etc.) must balance with the total mass of materials entering the process (TOBM, carbonaceous reductant, the fluxing agents, etc.).

[0058] Where there is an excess of the rutile-free silicate phase slag it is known that it can be used in the production of anorthite based Type I Portland cement or anorthite based glass-ceramic glaze.

[0059] The rate of cooling of the molten slag affects the rutile crystal nucleation rate and subsequent growth and final crystal size. Cooling at a rate of approximately 2°C per minute or less during solidification is

2018247275 11 Oct 2018 advantageous but not mandatory. Quench cooling where solidification takes place in a few seconds or less will prevent the formation of crystals of rutile. Cooling at a rate well in excess of 2°C per minute, for example 5°C per minute, does not necessarily prevent formation of crystals of rutile but the faster rate of cooling will typically result in rutile crystals that are substantially smaller in size than would otherwise be obtained by slower cooling. This is typical of diffusion rate control, where the rate of diffusion of TiO2 in the molten slag towards solidifying crystals in conjunction with the cooling rate influences the size and number of rutile crystals that are formed. Diffusion rate will vary also with the relative proportions of CaO, AI2O3 and SiO2 in the molten slag.

[0060] While the formation of fewer and larger rutile crystals is desired and thermodynamically preferred, fewer and larger rutile crystals can only form if the rate of diffusion of TiO2 in the liquid slag surrounding the rutile crystals initially formed during the slow cooling period exceeds the rate of rutile crystal nucleation dictated by the rate at which the solidifying slag is cooling. If the cooling rate of the solidifying slag is too high then the liquid slag surrounding existing rutile crystals will become supersaturated in respect of its T1O2 content and new rutile crystals will begin to form so as to restore the concentration of TiO2 in the surrounding liquid slag to its equilibrium concentration. Thus the slower the cooling rate the greater the potential for existing rutile crystals to grow bigger without new rutile crystals forming.

[0061] Slow cooling need only proceed during solidification. Slow cooling the molten slag at temperatures substantially above the liquidus and below the solidus temperature does not have any effect.

[0062] Slow cooling of the molten slag may be effected by natural means or by controlled means, provided that the cooling rate is slow enough so as to promote the formation of rutile crystals. Slow cooling practice may employ any technique that may be advantageous to improving rutile crystal morphology and/or size, including but not limited to direction solidification by means of directional cooling.

2018247275 11 Oct 2018 [0063] It will be appreciated that the optimum rate at which the solidifying slag is cooled will be sensitive to the temperature difference between the liquidus and the solidus. In relation to a slag composition where a large difference between the liquidus and solidus exists, a faster cooling rate may be acceptable and yield T1O2 crystals, whereas in cases where a small difference between the liquidus and solidus exists, a very slow cooling rate may be required to afford crystalline T1O2.

[0064] The formation of crystals of mineral rutile during slow cooling solidification is not substantially affected by the presence of other oxides so long as they are present at sufficiently low concentrations. By way of example, the presence of a minor amount of Fe2O3 is expected to have little or no effect on the formation of crystals of rutile because at low concentrations Fe2C>3 can be incorporated into the AbOs-bearing mineral species that form subsequent to the formation of rutile crystals. This substitutional behaviour is the preferred method by which some if not all of the residual impurity metal oxides in the slag might be accommodated.

[0065] The efficiency of recovery of the rutile crystals from the solidified slag is highly dependent on crystal size and conformation. One method of promoting fewer and larger crystals of rutile to form is to seed the liquid slag with rutile crystals and cool it at sufficiently slow rate so that only the seed crystals grow.

[0066] If the slag is at its liquidus temperature then the T1O2 is at its saturation level. Decreasing the slag temperature will cause the slag to become supersaturated in T1O2 and rutile crystals will begin to precipitate. Increasing the slag temperature will cause the slag to become undersaturated in T1O2. Any rutile seed crystals that are added to an undersaturated molten slag will be at least partially dissolved up to the point that the new T1O2 equilibrium saturation level is achieved. Only if the quantity of rutile crystals added to an under-saturated slag is in excess of that required to saturate it in T1O2 will seeding be achieved. Accordingly, multiple methods of achieving seeding can be chosen.

2018247275 11 Oct 2018 [0067] Firstly, the ΤϊχΟυ content of the molten slag in the furnace may be controlled such that at the operating temperature the slag is both saturated in T1O2 and crystals of rutile will pre-exist in the slag following oxidation, before commencement of cooling.

[0068] Secondly, a molten slag that is close to saturation can be produced and just prior to commencement of the slow cooling step it is possible to stir in some rutile crystals that were previously extracted, ensuring that sufficient seed crystals are added to the molten slag allow for any portion thereof that will be dissolved in saturating the molten slag with T1O2.

[0069] Thirdly, the slag can be allowed to cool, or be deliberately cooled, to just above its liquidus temperature and some rutile crystals could be stirred in.

[0070] There are advantages and disadvantages to all methods. The advantage of the first method is that it maximises the T1O2 productivity, but the disadvantage is that the denser rutile crystals may stratify in the slag. The disadvantage of the second method is that it is usually very difficult to control smelting processes to achieve a slag temperature in conjunction with a high T1O2 content. The disadvantage of the third method is that the T1O2 productivity of the furnace will be lower and slag temperature will have to be monitored. The advantages of the second and third methods will be that the rutile crystals that are added to the molten slag prior to the slow cooling step will be of a controllable size, number, quantity, etc.

[0071] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

2018247275 11 Oct 2018

Claims

Claims (14)

1. 2018247275 11 Oct 2018

   Claims

   1. A process for extracting crystalline T1O2 from titanium oxides-bearing material comprising the steps of:

   a) providing a feed mixture to a reductive smelting process comprising (i) ilmenite, (ii) leucoxene, and/or (ii) rutile plus iron ore, and a reducing agent, and fluxing agents comprising at least one of S1O2, CaO, MgO and AI2O3;

   b) reductive smelting the feed mixture, reducing agent, and fluxing agents to produce a molten slag of a mixture of titanium oxides, gangue oxides, and fluxing agents, wherein the molar ratio of CaO, AI2O3 and S1O2 in the molten slag substantially favours the formation of a base mineral species including CaO, AI2O3 and S1O2 in the molar ratio of 1:1:2 together with the formation of comparable mineral species containing any oxides present of magnesium, manganese, chrome, or vanadium, the ΤϊχΟυ concentration in the molten slag being at least 25% by weight;

   c) oxidising the molten slag to convert lower oxide states to higher oxide states;

   d) cooling the molten slag at a slow rate between the liquidus and the solidus of the molten slag to promote crystallisation of T1O2; and

   e) separating the crystalline T1O2 formed in step (d) from the solidified slag.
2. 2. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in claim 1, wherein the slag produced in step (b) contains a ΤϊχΟυ concentration of 40-50% by weight.
3. 3. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, whereby the feed mixture contains MgO, wherein the amounts of CaO and S1O2 flux are increased in order to allow for the formation of CaO.MgO.2SiO2 in addition to the base mineral species.

   2018247275 11 Oct 2018
4. 4. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, whereby the feed mixture contains manganese oxides, wherein the amounts of AI2O3 and/or S1O2 flux are increased in order to allow for the formation auxiliary mangnese oxide containing silicate species in addition to the base mineral species.
5. 5. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, whereby the feed mixture contains chromium oxides, wherein a quantity of MgO flux is added in order to allow for the formation of the auxiliary mineral species MgO.Cr2C>3.
6. 6. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, whereby the feed mixture contains vanadium oxides, wherein the amounts of CaO and/or S1O2 flux are increased in order to allow for the formation of auxiliary vanadium oxide containing species in addition to the base mineral species.
7. 7. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, whereby the molten slag contains Fe2O3 wherein the amounts of CaO, AI2O3 and/or S1O2 flux are increased in order to allow for the formation of auxiliary iron oxide containing silicate species in addition to the base mineral species.
8. 8. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, wherein fluxing agents are added to the feed mixture prior to reductive smelting.
9. 9. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, wherein some fluxing agents are added to the slag during reductive smelting.

   2018247275 11 Oct 2018
10. 10. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, wherein some fluxing agents may be added to the slag following reductive smelting.
11. 11. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim wherein step (c) occurs while the slag is still fully molten.
12. 12. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim wherein step (c) is achieved with the use of 02(g).
13. 13. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in any preceding claim, wherein step (e) is achieved by the crushing and grinding of the solidified slag, and the separation of T1O2 crystals using electrostatic separation, gravity separation, and/or flotation separation.
14. 14. A process for extracting crystalline T1O2 from titanium oxides-bearing material as claimed in claim 13, wherein the separated T1O2 crystals are subsequently treated with HCI(aq) to remove adhering slag phases.

    TIMAG TECHNOLOGIES PTY LTD