FIELD

[0001 ] The present application relates generally to upgrading slags and, more specifically, to practical application of dry slag atomization technology in upgrading titania-rich slags.

BACKGROUND

[0002] Metallic titanium is typically used as an alloying element for different metals that are used in space or biomedical applications. Titanium dioxide (Ti0 ₂ , known as titania), on the other hand, is extensively used as a white pigment.

Notably, however, the pigment industry prefers titania that is "highly pure," where "highly pure" may be defined as exceeding 99.9% Ti0 ₂ . The major minerals of titania are natural rutile Ti0 ₂ , which is around 95% Ti, and ilmenite FeTi0 ₃ , which has Ti in a range extending from 46% to 60%. Natural resources for rutile Ti0 ₂ is limited which has lead to extensive upgrading and use of ilmenite as a source of titania.

[0003] Two major methods have been used to upgrade ilmenite. In one major method, synthetic rutile (SR) is produced in a purity that can be used in a chloride pigment process. Another major method involves production of a slag that contains, and is rich in, Ti0 ₂ . It is known that a slag that is rich in Ti0 ₂ can be used in both a sulphate process (when Ti0 ₂ < 85%) and the chloride pigment process (when Ti0 ₂ > 90%).

[0004] With an aim to reduce the amount of waste and environmental concerns, the pigment industry is under an increasing pressure to use the chloride pigment process, with more than 90% Ti0 ₂ in the feed material, rather than the sulphate process. Correspondingly, there is an increasing demand for high-titania-containing synthetic rutile and upgraded Ti0 ₂ -rich slag.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Reference will now be made, by way of example, to the accompanying drawings which show example implementations; and in which: [0006] FIG. 1 illustrates a summary of two Synthetic Rutile production methods;

[0007] FIG. 2 illustrates, in a schematic representation, llmenite subjected to a smelting process;

[0008] FIG. 3 illustrates a Phase Diagram of a FeO-Ti0 ₂ System; and

[0009] FIG. 4 illustrates example steps in a method of upgrading slag in accordance with aspects of the present application.

DETAILED DESCRIPTION

[0010] According to an aspect of the present disclosure, there is provided a method including receiving molten slag, and atomizing the molten slag to atomized slag. The atomized slag includes: material in a glass phase and material in crystalline phases. The atomizing is carried out with varying gas composition to modify oxidation states and therefore chemical make-up of the glass phase and the crystalline phase, thereby permitting upgrading of the slag.

[0011 ] According to another aspect of the present disclosure, there is provided a method of upgrading slag, where it has been determined that when the slag has been atomized, the resultant atomized slag has a glass fraction that exceeds a threshold. The method includes receiving molten slag, atomizing the molten slag to atomized slag and cooling the atomized slag, thereby quenching the molten slag to form solidified atomized slag. The solidified atomized slag includes: material in an amorphous phase with concentrated gangue network formers and material in crystalline phases. The method further includes leaching gangue network formers from the atomized slag using a leaching process, thereby generating upgraded slag.

[0012] According to another aspect of the present disclosure, there is provided a method of upgrading slag, where it has been determined that when the slag has been atomized, the resultant atomized slag has a glass fraction that is less than the threshold. The method includes receiving molten slag, atomizing the molten slag to atomized slag, cooling the atomized slag, thereby quenching the molten slag to form solidified atomized slag that includes ferric iron, subjecting the solidified atomized slag to a reduction stage to produce a reduced slag wherein the ferric iron has been reduced to ferrous iron and subjecting the reduced slag to a high-pressure acid leaching process, thereby generating upgraded slag.

[0013] FIG. 1 illustrates a summary of the two Synthetic Rutile production methods.

[0014] In the reduction roasting process, represented in a left hand path in the illustration of FIG. 1 , ilmenite ore 102 may be subjected to reduction roasting (step 104) at ~950°C to convert all ferric oxides to ferrous oxides and facilitate their leaching. The process is followed by acid leaching (step 106) to remove iron- containing species 110 and leave a titania-rich (92-96% Ti0 ₂ ) synthetic rutile (SR) 108. The produced SR can subsequently be used (step 112) in the chloride process to produce pigments.

[0015] In a "Lurgi-Becher" process, represented in a right hand path in the illustration of FIG. 1 , the ilmenite ore 102 is subjected to thermal reduction (step 120) at high temperatures (~1200°C) to convert all iron oxides to particulate elemental metals. The material is then rusted (step 122) to hydrate iron oxide 124 and facilitate removal of the hydrated oxides by physical methods. By removing the hydrated oxides, a titania-rich SR 126 may be produced, which may subsequently be used in the chloride pigment process 128.

[0016] As represented schematically in FIG. 2, Ilmenite 202 can also be subjected to a smelting process (step 204), where metallic iron (hot metal) 206 can be separated from the material 202 producing a titania-rich slag (>80% Ti0 ₂ ) 208.

[0017] Slag 208 from the electric furnace is typically cooled, to solidified slag, in slag pots. It usually takes several days before the core of the material is solidified. Often, a water spray is used to accelerate the solidification process. The solidified slag is then reclaimed and crushed for further processing. The finer fraction of the slag (<106 μιη) has a relatively low value in the market and may be used in the sulphate pigment process (step 210). The coarser fraction (100-850 μιη) has a higher value in the market than the finer fraction of the slag and may be used in the chloride pigment process (step 212). [0018] The pigment industry is under a pressure to reduce the cost of production and reduce the amount of waste generated from an ilmenite smelting process.

Hence, chloride-grade titania slag is more favored by the pigment producers than sulphate-grade titania slag. However, although the market demands higher Ti0 ₂ concentrations in the feed material for the pigment process, e.g., slag, it is shown to be metallurgically challenging to obtain slags with >90% Ti0 ₂ directly from a smelting furnace. Because, by further decreasing the iron content of the titania slag, which is mostly in the form of FeO, slag liquidus temperature will increase sharply, see FIG. 3, which illustrates a Phase Diagram 300 of the FeO-Ti0 ₂ System (taken from FactSage™ thermodynamic package databases).

[0019] In addition, it has been shown that the reducing conditions that allow for metallization (removal) of iron will convert Ti0 ₂ to Ti ₂ 0 ₃ , which conversion is not desirable. This lack of desirability relates, to some extent, to the excessive exothermic oxidation of Ti ₂ 0 ₃ in the chlorination process, which oxidation may be shown to negatively influence the energy balance of the unit. Additionally, in the sulphate process, Ti ³⁺ is typically considered as the waste. Accordingly, it may be considered that excessive reduction in the smelting furnace will adversely affect the downstream processes.

[0020] Accordingly, slags with Ti0 ₂ contents less than 90% can be produced in the smelting furnace. Such slags may subsequently be upgraded to meet market demand.

[0021 ] In an example process described by Gueguin and Cardarelli (Mineral Processing & Extractive Metaii. Rev., 28: 1-58, 2007), solidified slag from the furnace is crushed, ground, sieved, sized and then sent to an oxidizer, where the slag is oxidized at ~1000°C to convert Ti ³⁺ to Ti ⁺ . Oxidizing titanium to its tetravalence form makes the titanium insoluble in a subsequent high-pressure acid leaching process. The high-pressure acid leaching process may be employed to leach iron so that the iron may be removed from the slag. However, in such an oxidizing atmosphere, ferrous iron (divalent Fe) will also be oxidized to ferric iron (trivalent Fe), which will reduce the kinetics of leaching significantly. Therefore, the ferric iron needs to be reduced back to its divalent form. To accomplish the reduction, the oxidized slag is forwarded to a reduction unit, where the material is subject to a reduction process wherein the material is treated at ~800°C. After the reduction process, high-pressure acid leaching is used to dissolve leachable cations (e.g., Fe, Mn, Mg, Al, Ca, V and Cr). The slag is then washed, dried and calcined, which results in a titania-rich slag (94.5% Ti0 ₂ ) suitable for the chloride pigment process.

[0022] The present application provides a method and an apparatus for upgrading slag. The method may render unnecessary several known intermediate process stages, e.g., crushing, grinding, sizing, oxidation in a separate unit, potentially the reduction process using a different leaching process.

[0023] Other aspects and features of the present disclosure will become apparent to those of ordinary skill in the art upon review of the following description of specific implementations of the disclosure in conjunction with the accompanying figures.

[0024] In the method of the present application, discharged molten slag from a smelting furnace is directly sent to a gas (e.g., air) atomization unit (via a launder or via slag pots) to be atomized. The gas atomization unit and process is described in International Application No. PCT/CA2015/050210. The gas atomization unit generates slag spheres, whose oxidation state can be controlled by the gas composition. Gases with low oxygen content may alter the composition of the slag slightly, whereas gases with high air content (e.g., air or air enriched with oxygen) will lead to highly oxidized slag spheres. With the use of oxidizing gases, the major part of the titanium is in the form of Ti0 ₂ and, as such, is unleachable.

[0025] Following the atomization process, depending on slag composition, two different routes can be taken.

[0026] In the first route, which may be taken responsive to determining that a concentration of network former cations (e.g., Si, Al, Fe ³⁺ ) are relatively high in the slag, rapid quenching of the material with gas will not allow full crystallization of the slag. It may be shown that, in this route, an amorphous (glassy) structure will be formed, which contains limited amount of the metal of interest (gangue network formers will be concentrated in the amorphous phase). It is known that glass thermodynamically has a higher internal energy and, hence, can dissolve in an aqueous solution more readily than a crystalline phase. Under this condition, the material can be directly leached using acidic/caustic solutions during which the leachable impurities may be removed from the material.

[0027] In the second route, which may be taken responsive to determining that the glass content of the atomized slag is low, the material follows a reduction and high-pressure acid leaching operation or a high-pressure acid leaching operation where the atomization gas composition has been set to achieve the desired degree of oxidation-reduction of the slag.

[0028] FIG. 4 illustrates example steps in a method of upgrading slag in accordance with aspects of the present application.

[0029] Two embodiments of the present application (which are examples for upgrading of titania-rich slags) share initial steps as follows.

[0030] Once molten slag 602 has been discharged from the furnace, the slag may be atomized (step 604) and then quenched such that the molten slag is cooled and solidified. Notably, during the slag atomization (step 604), Ti ³⁺ oxidizes to Ti ⁺ . Further notably, Ti ⁺ is known to be unleachable. Accordingly, an oxidation process, which is part of some known slag upgrading processes, can be skipped and the slag atomization (step 604) may be seen to obviate the known use of a separated unit to carry out an oxidation process on the slag. The atomized slag may then be comminuted and sized (step 606).

[0031 ] The next steps are dependent upon determining (step 608) whether a glass fraction in the atomized slag exceeds a threshold. That is, it may then be determined (step 608) whether there are a sufficient amount of network formers in the atomized slag. Where the term "sufficient" is defined by the threshold. Notably, the determining (step 608) whether a glass fraction in the atomized slag exceeds a threshold is not a step that occurs between the receipt of the molten slag and the subsequent steps. Instead, the determining (step 608) is carried out as part of an analysis used to assess a preferred manner of processing the atomized slag.

[0032] In the case wherein it has been determined (step 608) that a glass fraction in the atomized slag exceeds a threshold, the atomized slag may be subjected to direct leaching (step 61 1 ). The leaching process (step 611 ) may be, for only two examples, a caustic leaching medium leaching process or an acid leaching medium leaching process. Conveniently, the titanium in the form of Ti ⁺ does not dissolve in the leaching medium. After leaching, the slag may be subjected to washing (step 612), drying (step 614) and calcining (step 616), with the result being upgraded slag of a first type 618.

[0033] In the case wherein it has been determined (step 608) that a glass fraction in the atomized slag does not exceed the threshold, the atomized slag may be sent to a reduction stage (step 620) to reduce the ferric iron into ferrous iron, followed by a high-pressure acid leaching stage (step 621 ). After leaching, the slag may be subjected to washing (step 622), drying (step 624) and calcining (step 626), with the result being upgraded slag of a second type 628.

[0034] Notably, the path to the upgraded slag of the first type 618 uses the higher leach-ability of the glassy phases and involves leaching of amorphous gangue materials from the atomized slag using a leaching process (step 611 ) instead of the reduction (step 620) followed by the high-pressure acid leaching (step 621 ).

[0035] By adjusting the atomization parameters in step 604 to produce a finer particle size distribution for the atomized slag, the comminution and size-reduction step (step 606) may be eliminated. However, it should be noted that extremely fine particles improve the kinetics of the leaching processes (steps 611 , 621)

significantly. Accordingly, depending on slag composition and other requirements, the comminution and size-reduction step (step 606) may or may not be included in the process flow sheet.

[0036] Upgrading the slag from the smelting furnace by existing methods is typically associated with a number of difficulties and drawbacks: it can take up to two weeks for slag blocks (discharged from the furnace) to solidify and cool; there are often safety concerns regarding the breakage of a semi-solidified slag block with resultant ejection of liquid slag; there are perceived risks of steam explosion when slag is water sprayed to accelerate cooling and solidification of the slag; and typical processing of solidified slag blocks includes crushing, grinding and sizing of the solidified slag blocks, all of which are energy intensive dust-generating processes. [0037] In comparison to known processes, aspects of the present application have several advantages. Conveniently, aspects of the present application may only involve grinding of atomized spherical particles (~2 mm in diameter), which is less energy intensive and generates less amounts of dust than typical crushing, grinding and sizing of solidified slag blocks.

[0038] Furthermore, the slag atomization process (step 604) may be seen to eliminate solid slag handling operations. More importantly, the unit responsible for the slag atomization process (step 604) may be seen to replace some of the units in known upgrading processes (e.g., the oxidizer unit and the reducer unit of the process described by Gueguin and Cardarelli, referenced above).

[0039] The environmental footprint of aspects of the present application may not only be seen as significantly lower than other ilmenite smelting slag treatment methods, but also lower than those methods related to synthetic rutile production. For example, hydrated oxides generated in the Lurgi-Becher process represent a significant environmental concern. Whereas, aspects of the present application may be found to not produce any waste material.

[0040] Aspects of the present application do not employ an oxidizer, which is employed in known slag upgrading processes. Since the oxidizer operates at ~1000°C, the energy and oxygen consumption of a plant employing aspects of the present application, may be significantly reduced relative to the known slag upgrading processes.

[0041 ] As discussed hereinbefore, aspects of the present application take advantage of the higher leach-ability (high reactivity) of the amorphous structure of the atomized slag. Hence, the atomized (and in some cases oxidized) slag can be directly leached (step 611) and, thereby, upgraded. Using this method, the reduction unit (step 620) can also be removed, which further simplifies the flow sheet.

[0042] The above-described implementations of the present application are intended to be examples only. Alterations, modifications and variations may be effected to the particular implementations by those skilled in the art without departing from the scope of the application, which is defined by the claims appended hereto.