AU2021107693A4 - Processing of mineral sand particulates - Google Patents

Abstract

This invention relates to processes for removing contaminants from a mineral sand particulate. Also described are apparatus for carrying out the processes, and the purified products of the reaction. 2/5 FIGURE 3 Variant A S3 Zircon - SULFATION S New Opacifer Sodium Sulfate 700°CMLeachCI 70-75% Yield tou SZirconia or Chemical SodiumSulfate Recovery Scandium Waste Variant B SO 3 Zircon - . SULFATION LS New Opacifer Sodium Sulfate 700°C L >95% Yield Sodium Sulfate Recovery Scandium - Waste FIGURE 7 SILI[DN [ARBIDE CASTABLE REFRACTDRY - CEMENT ,IF STAINLESS TEEL 160 FRAME (3SIDES A[D REAR C\LY' 5ES T ;] ['N A- A

Description

2/5

FIGURE 3

Variant A S3

Zircon - SULFATION S New Opacifer 700°CMLeachCI 70-75% Yield Sodium Sulfate

tou SZirconia SodiumSulfate Recovery Scandium or Chemical

Waste

Variant B SO 3

Zircon - . SULFATION LS New Opacifer Sodium Sulfate 700°C L >95% Yield

Sodium Sulfate Recovery Scandium

- Waste

FIGURE 7

SILI[DN [ARBIDE CASTABLE REFRACTDRY - CEMENT ,IF

STAINLESS TEEL 160 FRAME (3SIDES A[D REAR C\LY' 5ES T ;] ['N A- A

Processing of mineral sand particulates

This application is a divisional of Australian patent application no. 2021221764, the entire disclosure of which is incorporated herein by reference.

Field of the invention

The invention relates to a process for removing contaminants from a mineral sand particulate.

Background of the invention

Mineral sand particulates are a source of a range of discrete minerals of economic interest, including zirconium (as zircon), titanium bearing minerals (such as ilmenite, leucoxene and rutile) and rare earths hosted in matrix consisting predominantly of silicon (as silica and quartz). However, depending on source, the individual minerals derived from mineral sands ores typically can also contain a mixture of undesirable elements, such as iron, titanium, uranium and thorium, which are unsuitable for the various end-uses of the minerals of economic interest. Of these, the radioactive elements - uranium and thorium - are particularly undesirable.

Due to the chemical properties of the various minerals present in some mineral sands, it is an ongoing challenge to develop robust and economic processes for separating one or more of the undesirable elements on the larger scales typically required.

Zircon (mainly zirconium silicate - ZrSiO4 ) is a mineral contained in many mineral sands. Zircon is used in tiles and ceramics as an opacifier and to add whiteness, brightness, chemical resistance and scratch resistance to glazes and tiles. The presence of impurities such as iron, .0 titanium, lanthanides and actinides can reduce the brightness imparted by zircon and introduce colour to glazes and tiles. The presence of radioactive elements above certain prescribed limits, such as >500 ppm uranium and thorium, makes the zircon unsuitable for use in the ceramics industry.

The presence of iron in glazes can impart many different colours depending on its form and ?5 other species present in the glaze. Iron has been reported to generally darken and contribute red or yellow tinges.

Titanium dioxide can be used in glazes as an opacifier but is found to introduce coloured hues to glazes. The use of anatase has been found to introduce a blue hue, whilst rutile has been found to introduce a slight yellow tint to glazes. Trivalent titanium (Ti+ or Ti 2O 3 ) is black and consequently, when present, will increase the light absorption of a glaze, reducing its brightness.

Lanthanide (rare earth) elements are known glass colourants. Praseodymium in particular is known to produce yellow to green colours in glazes and a powerful yellow colour when combined with zircon (commercial name praseodymium zircon yellow). Similarly neodymium is known to produce blue to violet colours in glazes, erbium may produce pink hues and cerium can add red tints. Uranium is also known to produce strong orange to red colours in glazes in a +4 oxidation state and yellow to green colours in glasses and glazes when in a +6 oxidation state. To visibly achieve these effects a substantial amount of element is required (i.e. >1%), however even at trace levels these are still likely to effect the overall whiteness of a glaze.

Currently, mined zircon is sold as either premium grade (or ceramic grade), or chemical grade. o Premium grade zircon is suitable for the dominant market use as an opacifier for ceramics. Chemical grade zircon typically has higher concentrations of contaminant elements that disqualify it from use as an opacifier. Chemical grade zircon is more suitable for processing to zirconium oxychloride, the precursor of most zirconium chemicals.

There are known processes for improving the optical quality of premium grade zircon. One such process is the Hot Acid Leach (HAL) process. This process is described in EP0670376. The HAL process involves mixing zircon with minimal concentrated sulfuric acid. The acid wets the zircon particle surfaces and when a small amount of water is added it rapidly generates a large amount of heat on the surface of the particles due to the hydration of the sulfuric acid. The combination of sulfuric acid and heat causes iron and other impurities on the surface of the zircon to react with the acid. The reacted zircon is then washed to remove any residual acid and sulfated species such as iron and titanium.

The HAL process relies on heat generated from the reaction between water and sulfuric acid and is only effective at removing surface coatings from zircon. The HAL process also has a relatively short reaction time (approximately 1 hour). The HAL process is not effective for ?5 removing impurities present in forms other than coatings. Such other forms may include discrete particles and impurities present in the zircon grain or structure.

Variations of this process are commonly practised by different commercial suppliers of zircon.

International patent publication WO 2005/116277 discloses a process for "upgrading an inferior grade of zircon to a superior grade... suitable for use as a glaze opacifier". The process involves calcining a mixture of ground zircon and a mineraliser (e.g. an alkaline metal halide or ammonium sulfate) at 600 to 900°C, and thereafter washing and further comminuting the calcined product. The achievement of the higher grade suitable for use as a glass opacifier was viewed as necessarily involving removal of a proportion of the ferric and titanium oxide impurities.

More generally, a known means of cracking or decomposing refractory minerals is via reaction with concentrated sulfuric acid at elevated temperatures. Two examples of this include the Sulfate Process for producing TiO 2 pigment from ilmenite or titanium slags, and sulfuric acid cracking of rare earth phosphates, such as monazite. In each case the process involves decomposing the ore using concentrated sulfuric acid at temperatures in the vicinity of 150 250°C. The resulting mixtures are then dissolved in water or dilute acid to extract valuable species. This approach is not suitable for zircon because zircon is highly refractory, and it will not adequately react under the above conditions.

International patent publication W02016/127209 discloses a process for improving the grade and optical quality of zircon. The process includes baking zircon with sulfuric acid. However, while this acid bake process is able to remove some of the impurities present in the zircon containing mineral sand, it does not always remove sufficient uranium and thorium impurities.

There would be considerable value in a cost-effective process for mineral sand processing capable of reducing the concentration of radioactive elements to below that present in the ore. This process may advantageously enable utility of ores previously considered unsuitable to mine due to the presence of undesirable radioactive elements.

Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art.

Summary of the invention

In one aspect, there is provided a process for removing a contaminant from a mineral sand particulate, comprising:

• heating a reaction mixture comprising the mineral sand particulate and a salt comprising one or more of sodium sulfate, sodium bisulfate, sodium hydroxide, sodium chloride, sodium carbonate, potassium sulfate, potassium bisulfate, potassium hydroxide, potassium chloride, potassium carbonate, lithium sulfate,lithium bisulfate, lithium hydroxide, lithium chloride and lithium carbonate, to a temperature of at least about 400 °C under an atmosphere of sulfur trioxide to provide a reaction product; and

• after cooling the reaction product, extracting contaminant from the reaction product with an aqueous extractant.

In some embodiments of any aspect described herein, the contaminant comprises at least uranium, thorium or a combination thereof.

In some embodiments, the processes described herein comprise heating the reaction mixture to a temperature of at least about 900°C.

As claimed, another aspect is provided in a composition produced by a process for removing a contaminant from a mineral sand particulate, the process comprising:

heating a reaction mixture comprising the mineral sand particulate and a salt, wherein the salt is selected from sodium sulfate, sodium bisulfate, and a combination thereof, under an atmosphere of sulfur trioxide at a temperature of at least about 400°C to provide a reaction product; and

after cooling the reaction product, extracting contaminant from the reaction product with an aqueous extractant.

The processes described herein may provide a product composition comprising 60-100wt% zircon, 0-15wt% zirconia and 0-25wt% silicon dioxide, and not more than 500 ppm uranium and thorium.

In another aspect, there is provided a composition comprising, or consisting of, zircon, zirconia (ZrO2 ), and silicon dioxide (SiO2 ),wherein the composition comprises not more than 500 ppm uranium and thorium.

Further aspects relating to apparatus for refining a mineral sand particulate are set out further below.

Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

Brief description of the drawings

?5 In order that the invention may be more fully understood, some embodiments will now be described, by way of example, with reference to the figures in which:

Figure 1 shows a muffle furnace closed reactor for carrying out the processes described herein.

Figure 2 shows a rotating kiln reactor for carrying out the processes described herein.

Figure 3 shows a schematic of 2 variants of the processes described herein.

Figure 4 shows a schematic of the furnace setup for the rotating kiln reactor shown in Figure 2 and described in Example 2.

Figure 5 shows a powder X-ray diffraction pattern for a composition prepared by the processes of the invention.

Figure 6 shows a schematic of a vessel for a reactor apparatus in accordance with another embodiment of the present invention.

Figure 7 is a cross-sectional view through A-A of Figure 6.

Definitions

As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

Likewise, the term "contain" and variations of the term such as "containing", are not intended to be construed exclusively as excluding further additives, components or integers.

It must be noted that as used herein and in the appended claims, the singular forms "a", "an" and "the" include plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to "a salt" may include a plurality of salts and a reference to "at least one heteroatom" may include one or more heteroatoms, and so forth.

The term "and/or" can mean "and" or "or".

The term "(s)" following a noun contemplates the singular or plural form, or both.

?0 Various features of the invention are described with reference to a certain value, or range of values. These values are intended to relate to the results of the various appropriate measurement techniques, and therefore should be interpreted as including a margin of error inherent in any particular measurement technique. Some of the values referred to herein are denoted by the term "about" to at least in part account for this variability. The term "about", when ?5 used to describe a value, may mean an amount within ±10%, ±5%, ±1% or±0.1% of that value.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Detailed description of the embodiments

The invention relates to a process for removing a contaminant from a mineral sand particulate. The process comprises reacting the mineral sand particulate with a specified salt under an atmosphere of sulfur trioxide (S03) at a temperature of at least about 400 °C to provide a reaction product. After cooling the reaction product, the process also comprises aqueous extraction of contaminant from the reaction product.

The inventors surprisingly found that reaction of the mineral sand particulate with the salt resulted in the extraction of undesirable contaminants into a water soluble phase. This enabled separation of contaminant from the mineral of interest of the mineral sand particulate through aqueous extraction . Surprisingly, this process was able to more effectively extract uranium and thorium contaminants than other conventional methods. Uranium and thorium, in particular, are widely regarded as difficult to extract from some minerals, eg zircon, using conventional techniques.

Mineral sand particulate

The mineral sand particulate used as feedstock for this process may be derived from any mined mineral sand deposit. Typically, the mineral sand ore derived directly from the deposit undergoes one or more conventional refining steps to provide the mineral sand particulate. Conventional refining processes for mineral sands are described in Kelly, E. G. and Spottiswood, D. J. "Introduction to Mineral Processing", Wiley (1982), the contents of which are hereby entirely incorporated by reference. A typical refining process starts with the mineral sand ore, which typically mineral sand ore may comprise 0.5wt% to 40wt% of minerals of interest. The mineral sand ore is refined to provide a heavy mineral concentrate, which comprises a mixture of all the minerals of interest present in the ore. The heavy mineral concentrate is then refined further into separate minerals. The processes described herein typically utilise a mineral ?5 refined by these conventional techniques. Thus, the mineral sand particulate is a composition comprising a mineral of interest refined from a mineral sand ore. The mineral sand particulate is enriched in a mineral of interest compared to the mineral sand ore.

The mineral sand particulate comprises at least one contaminant that is removed by the process. The contaminant may be one or more of iron, titanium, lanthanides, actinides and radioactive elements (such as uranium and thorium). In some embodiments, the process removes uranium and/or thorium from the mineral sand particulate.

In some embodiments, the mineral sand particulate comprises zircon. The zircon may be present in the mineral sand particulate in a major amount, for example at least about 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%,

85wt%,90wt%, 95wt%, 99wt%, or greater. The mineral sand particulate may comprise zircon in an amount from any of these values to any other of these values, for example, from about 20wt% to about 99wt% or about 50wt% to about 80wt%. The remainder of the zircon-containing mineral sand particulate (which may be referred to herein as a zircon particulate) may comprise any mineral or contaminant of mineral sand ore described herein. In some embodiments, the contaminants comprise uranium, thorium or a combination thereof. In some embodiments, the remainder of the zircon-containing mineral sand may comprise one or more further minerals comprising quartz, staurolite, kyanite, sillimanite, garnet, leucoxene, kaolinite and combinations thereof. Each of these additional components may be present in a ratio substantially proportional to their natural abundance, or they may be independently enriched in the zircon particulate, eg enriched by any of the prior refining steps. For example, in some embodiments, the mineral sand particulate comprises from about 50-99wt% zircon comprising about 800 1500ppm uranium and thorium combined contaminant, and about 1-50wt% further minerals (typically about 90-99wt% zircon and about 1-1Owt% further minerals or about 95-99wt% zircon and about 1-5wt% further minerals, wherein the zircon comprises the contaminants).

There are a large number of resources of zircon characterised by the presence of high levels of uranium and thorium radioactive elements, which precludes their use as ceramic opacifiers - a major commercial use of zircon. Zircon comprising radioactive impurities may be characterised by the presence of a degraded zircon structure in intimate association with undamaged zircon. o Insome embodiments, in addition to reducing the uranium and thorium concentration in the ore, the processes may also increase the degree of crystallinity of the ore (eg zircon contained in the reaction product).

The mineral sand particulate may comprise at least about 500ppm, 600ppm, 700ppm, 800ppm, 1000ppm, 1100ppm, or 1200ppm of radioactive elements or greater. The mineral sand ?5 particulate may comprise the radioactive elements between any of these amounts. The processes described herein may reduce the uranium and thorium content of the mineral to not more than about 500ppm, 490ppm, 480ppm, 460ppm, 450ppm, 440ppm, 430ppm, 400ppm, 300ppm, 200ppm or lower. The uranium and thorium content may be determined by any suitable technique, including X-ray fluorescence (XRF) and inductively coupled plasma (ICP) optically emission spectroscopy (OSE)/mass spectrometry (MS) (ICP-OES/MS). The ppm values described herein are intended to be determined primarily by XRF using standard operating protocols.

For example, a zircon particulate may additionally comprise traces (eg not more than about 2wt%) of calcium and rare earth phosphates, scandium, iron, titanium as impurities. In some embodiments, the concentration of one or more of these impurities is reduced by the processes described herein.

The particle size of the mineral sand particulate typically depends on the source of the mineral sand ore from which the mineral sand particulate is derived. Typically, the particle size of the mineral sand particulate is described in terms of d50. The d50 is the size in microns of the diameter of particles within a sample that splits the distribution with half of the particles above and half of the particles below this diameter. Therefore, typically d50 represents the median particle size of a sample and defines the pore size of a mesh through which 50% by weight of a particulate sample passes through. The mineral sand particulate may a minimum particle size (d50) of at least about 20pm, 25pm, 30pm, 40pm, 50pm, 60pm, 70pm, 80pm, 90pm,1OOpm, 110pm or 120pm, The mineral sand particulate may have a maximum d50 of not more than about 50pm, 60pm, 70pm, 80pm, 90pm,100pm, 110pm, 120pm, 130pm, 140pm, 150pm, 160pm, 170pm, 180pm, 190pm, 200pm, 210pm, 220pm, 230pm, 240pm, 250pm, 260pm, 270pm, 280pm, 290pm or 3000pm. The mineral sand particulate may have a d50 from any of these minimum values to any of these maximum values provided the minimum value is lower than the maximum value. For example, the d50 of the mineral sand particulate may be from about 20-300pm, about 30-60pm or 100-150pm.

Reaction step

The process comprises heating a reaction mixture comprising the mineral sand particulate and the salt under an atmosphere of sulfur trioxide(SO3) at a temperature of at least about 400 0C to provide a reaction product.

Salts

The inventors surprisingly found that heating the mineral sand particulate in the presence of a salt under theSO 3 atmosphere was able to selectively extract contaminants, including uranium and thorium, from the mineral sand particulate into a water-soluble phase, which could be separated by aqueous extraction.

Any salt capable of selectively solubilising a contaminant present in the mineral sand particulate relative to the mineral of interest may be used in the methods. Suitable salts include sodium, potassium and lithium salts of sulfate, bisulfate, hydroxide, chloride, and carbonate and combinations thereor.

In some embodiments, the salt comprises one or more of sodium sulfate, sodium bisulfate, sodium hydroxide, sodium chloride, sodium carbonate, potassium sulfate, potassium bisulfate, potassium hydroxide, potassium chloride, potassium carbonate, lithium sulfate, lithium bisulfate, lithium hydroxide, lithium chloride, lithium carbonate.

In some embodiments, the salt may be selected from any of these suitable salts, preferably sodium sulfate and/or sodium bisulfate.

The salt is typically provided in an excess by weight compared with the mineral sand particulate. The salt may be present in a minimum amount of at least about 20wt%, 25wt%, 30wt%, 40wt%, 50wt%, 60wt%, 70wt%, 80wt%, 90wt%, 100wt%, 125wt%, 150wt%, 175wt%, 200wt%, 350wt%, 300wt%, 350wt% or 400wt% relative to the total weight of the mineral sand particulate. The salt may be present in a maximum amount of not more than about 5000wt%, 4500wt%, 4000wt%, 3500wt%, 3000wt%, 2500wt%, 2000wt%, 1500wt%, 1000wt%, 500wt%, 450wt% or 400wt% relative to the total weight of the mineral sand particulate. The salt may be present from any of these minimum amounts to any of these maximum amounts provided the minimum is less than the maximum. For example, the salt may be present in an amount of from about 300wt% to about 500wt% relative to the total weight of the mineral sand particulate.

In embodiments wherein the salt is provided in an excess amount, it may be preferable to recover the salt by separating it from the reaction product. The recovered salt may be reused in subsequent reacting steps. Accordingly, in some embodiments, the processes comprise recycling the salt. This recycling may comprise evaporation (eg to substantially remove any water), crystallisation or precipitation of the aqueous extractant following the extracting step. Precipitation may be achieved by cooling the solution, which may reduce the solubility limit of the salt causing it to precipitate out of solution. In some embodiments, the salt may be separated from the reaction product prior to cooling the reaction product. This separation may be aided as at the reaction temperatures the salt is typically in a liquid state. The liquid salt may therefore be removed from the reaction product by, for example, decantation.

In some embodiments, the process comprises a step of combining the mineral sand particulate and the salt. The mineral sand particulate and the salt may be combined by any suitable means, ?5 and include addition of the salt to the mineral sand particulate, addition of the mineral sand particulate to the salt or adding both substantially simultaneously to a container. Once combined the salt and the mineral sand particulate may optionally be mixed to form a substantially homogeneous composition. Typically the mineral sand particulate and the salt are combined prior to the heating step. In some embodiments, the mineral sand particulate is combined with the salt that has been recycled from the process.

Sulfur trioxide

The mineral sand particulate and the salt are reacted under an atmosphere of sulfur trioxide. The atmosphere may comprise any concentration of sulphur trioxide suitable for the processes described herein.

In some embodiments, the SO3 atmosphere is maintained at a pressure greater than 1 atm. For example, it has been found that an atmosphere comprising 37-90% SO3 with the balance being S02 and 02 is effective when operating at a system pressure of 0.5kPa above 1atm. Accordingly, the minimum pressure of the SO3 atmosphere may be at least about 0.1kPa above 1atm, 0.2kPa above 1atm, 0.3 kPa above 1atm, 0.4 kPa above 1atm or 0.5kPa above 1atm. The maximum pressure of the SO3 atmosphere is limited by the vessel containing the atmosphere and the rate of SO3 generation being provided to the vessel. In some embodiments, the maximum pressure of the SO3 atmosphere may be not more than 10 kPa above 1atm, 9 kPa above 1atm, 8 kPa above 1atm, 7 kPa above 1atm, 6 kPa above 1atm, 5 kPa above 1atm, 4 kPa above 1atm, 3 kPa above 1atm, 2 kPa above 1atm, 1 kPa above 1atm or 0.5 kPa above 1atm. The pressure of the SO3 atmosphere may be from any of these minimum pressures to any of these maximum pressures provided the minimum pressure is lower than the maximum pressure, for example the pressure of the SO3 atmosphere may be from about 0.1 kPa above 1atm to about 10 kPa above 1atm, or about 0.1 kPa above 1atm to about 1 kPa above 1atm.

In some embodiments, the SO3 atmosphere may have a pressure below 1atm. In these embodiments, the minimum pressure of the SO3 atmosphere may be at least about 0.5atm, 0.6katm, 0.7atm, 0.8atm, 0.9atm, 0.95atm. The SO3 atmosphere may be between any of these minimum pressures to about 1atm, for example from about 0.5atm to about 1atm.

The SO3 may be generated by any means known in the art. For example, the sulfur trioxide may be generated by thermal decomposition of a sulfur trioxide precursor. Sulfur trioxide precursors include oxysulfates (eg TiOS0 4 ), sulphuric acid, and sulfate salts. Accordingly, in some embodiments, the SO3 precursor comprises one or more of an oxysulfate (eg titanium oxysulfate), sulfuric acid or a sulfate salt of sodium, potassium, lithium, and/or ammonium. In some embodiments, the SO3 precursor is TiOSO4 . TiOS04 decomposes to titanium oxide (TiO 2 )

?5 and SO3 at temperatures from about 500°C. Alternatively or additionally, sulfur trioxide may be provided by reacting sulfur dioxide (S02) and oxygen (02) gasses in the presence of a suitable catalyst, typically at high temperatures (eg about 350°C to about 550°C, or about 400°C to about 500°C) to ensure rapid reaction. Suitable catalysts include vanadium pentoxide (V 2 05 )

and other oxidation catalysts. S02 may be provided by burning sulfur (S). In some embodiments, the temperature of the SO3 gas stream may be modified (ie heated or cooled) prior to forming the SO3 atmosphere.

Depending on how the SO3 is generated, the SO3 atmosphere may comprise other gases. In some embodiments, the SO3 atmosphere may comprise nitrogen (N 2) and/or sulfur dioxide gases or a combination thereof. Nitrogen can be separated from SO3 by cooling the gas stream to condense the SO3 (eg to below the boiling point of S03, which is about 45°C) and then re vaporising the liquid SO3 into a vessel free of N 2. Accordingly, in some embodiments, the S03 atmosphere is substantially free of N 2 . Such N 2-free atmospheres may be preferred for reactions proceeding at a temperature from about 650-800°C.

The SO3 atmosphere may contain any concentration of SO3 sufficient to selectively extract contaminant from the mineral sand particulate in the presence of the salt at the reaction temperature. In some embodiments, the minimum concentration of SO3 in the SO3 atmosphere may be at least about 5%, 7%, 10%, 12%, 15%, 20%, 23%, 25%, 30%, 35%, 37%, 40%, 44%, 45%, 50%, 55%, 58%, 60%, 65%, 70%, 75%, 76%, 80%, 85%, 88%, 90%, 95%, 98%, or 99%. In some embodiments, the maximum concentration of SO3 in the SO3 atmosphere is limited only by how it is generated. For example, the maximum concentration of SO3 in the SO3 atmosphere may be not more than about 100%, 99.9%, 99.5%, 99%, 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, 90%, 88%, 85%, 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45% or 40%. The S03 atmosphere may comprise SO3 in a concentration from any of these minimum concentrations to any of these maximum concentrations provided the minimum is less than the maximum. For example, the concentration of SO3 in the SO3 atmosphere may be from about 5% to about 100%, or about 37% to about 90%. In any of these embodiments, the remainder of the S03 atmosphere may compise N 2 , S02 and 02, preferably S02 and 02. The concentration of each of these gasses is not particularly limited and is typically dictated by the SO3 generation technique employed.

In some embodiments, SO3 is recovered following cooling of the reaction product, and recycled with optional addition of make-up SO3 to offset any losses. The S02 and 02 resulting from any decomposition of the SO3 during the reaction may additionally or alternatively be recycled through the catalyst for conversion to S03. Recovery and recycling of SO3 may be achieved by recirculating SO3 into a reaction chamber, or collection of SO3 following the reacting step (eg by condensing the SO3 in a condensing tower, which also preferably may allow separation of any ?5 other gases, such as nitrogen, present in the SO3 atmosphere) and gasification of the condensed liquid SO3 prior to recycling to the reactor.

Reaction temperature

The reaction mixture is heated to at an elevated temperature of at least about 400 °C.

In some embodiments, the minimum temperature of the reacting step may be at least about 4000C, 4500C, 5000C, 6000C, 6500C, 6750C, 7000C, 7500C, 8000C, 8500C, 9000C, 9250C or 9500C. The maximum temperature for the reacting step may be not more than about 12500C, 12000C, 1100C, 10500C, 1000°C, 9500C, 8500C, 8000C or 7500C. The temperature range of the reacting step in the processes described herein may be from any of these minimum temperatures to any of these maximum temperatures, with the proviso that the minimum temperature is below the maximum temperature selected. For example, the reacting step may be carried out at a temperature from about 650 °C to about 1250 °C, about 650 °C to about 1000 °C, about 650 °C to about 750 °C or about 850 °C to about 1000 °C.

In some embodiments, the process comprises heating the reaction mixture to a temperature from about 650 °C to about 750 °C, preferably about 700 °C. Processes according to these embodiments may be referred to herein as process Variant A (Figure 3).

In some embodiments, the process comprises heating the reaction mixture to a temperature of about 850 °C to about 1000 °C, preferably about 900 °C to about 950 °C. Processes according to these embodiments may be referred to herein as process Variant B (Figure 3). It has been found that for mineral sand particulates comprising zircon, heating the reaction mixture to these higher temperatures, the yield of zirconium species (eg zircon and zirconia) in the reaction product is improved.

In some embodiments, the process comprises heating the mineral sand particulate with the salt to a first temperature from about 400 °C to about 750 °C, preferably about 700 °C, followed by optional cooling, and then heating to a second temperature from about 850 °C to about 1000 °C, preferably about 900 °C to about 950 °C. Processes according to these embodiments are a variant of Variant B processes, where the process comprises first heating the reaction mixture to a lower temperature, such as a temperature associated with Variant A embodiments. In some embodiments, the first temperature is achieved by adopting a suitable heating rate that maintains the reaction mixture within the first temperature range for a sufficient time as the reaction mixture is heated to a temperature within the second temperature range.

The process comprises heating to a temperature of at least 400°C. The heating may be achieved at any suitable rate. In some embodiments, the heating rate is linear, for example the heating rate is maintained until the reaction reaches the desired temperature. The minimum ?5 heating rate may be at least about 0.5°C/min, 1°C/min, 1.5°C/min, 2°C/min, 2.5°C/min, or 3°C/min. The maximum heating rate may be not more than about 15°C/min, 10°C/min, 7.5°C/min, 5°C/min, 4°C/min, 3.5°C/min, or 3°C/min. The heating rate may be from any of these minimum rates to any of these maximum rates provided the minimum is less than the maximum. For example, the heating rate may be from about 0.5°C/min to about 15°C/min, or about 1°C/min to about 5°C/min. In some embodiments, the first temperature is achieved transiently as the vessel comprising the mineral sand particulate is heated to the second temperature. The time the first temperature is maintained may be proportional to the heating rate.

In addition to providing sufficient energy for the reaction to proceed in a suitable time, the elevated temperature of the reaction assists to control the physical state of the reaction products. For example, in embodiments of the process where the salt comprises sodium sulfate and the mineral sand particulate comprises zircon, heating sodium sulfate to temperatures of at least about 700 °C leaves sulfate phases other than the sodium sulfate in a liquid state with the unreacted zircon remaining as a solid within the melt.

In some embodiments of processes involving heating to a temperature of at least about 900°C, the processes may comprise replacing theS03atmosphere with an atmosphere comprising N 2

, for example air, or N 2 only, or a mixture of N 2 and02. Typically the atmosphere comprising N 2 is a dry atmosphere, ie a substantially anhydrous atmosphere. TheS03atmosphere may be replaced with an atmosphere comprising N 2 prior to the reaction reaching about 900°C, for example, once the temperature reaches about 750°C, 800°C, 850°C or 900°C theS03 atmosphere may be replaced with the atmosphere comprising N 2

. The reaction product therefore comprises a solid phase typically comprising the mineral of interest, and a liquid phase typically comprising contaminants and unreacted and/or reformed salt (if present). The physical differences between the solid and liquid phases of the reaction product assists in the separation of the contaminants from the mineral of interest at the conclusion of the reacting step. In addition, the elevated temperature of the reaction may assist in the thermal decomposition of any thermally unstableS03precursor selected to provide the desired reaction conditions and/or reactant species.

The time needed for the reaction depends on a number of factors, including temperature of the reacting step, scale of the reaction, salt selection, sourceof S03, the reactor set up, the amount of uranium and thorium in the parent mineral that needs to be extracted amongst others. Typically, the reacting step is allowed to progress for at least about 10 minutes (m), 15m, 20m, 25m, 30m, 35m, 45m, 55m, 1 hour (h), 1.5h, 2h, 2.5h, 3h, 3.5h or 4h.

In embodiments where the temperature of the reacting step is not more than about 800°C (such ?5 as about 650-750°C) the reaction times may be towards the longer times set out above, typically about 4h at the peak temperature.

In embodiments there the temperature of the reacting step is higher than about 800°C (such as about 850-1000C), the reaction times may be towards the lower end of those set out above, typically about 2h at the peak temperature.

In embodiments comprising heating to a first temperature from about 650 °C to about 7500C and heating to a second temperature from about 850 °C to about 1000 °C, the first temperature may be maintained for at least about 1Om, 15m, 20m, 25m, 30m, 35m, 45m, 60m or longer, and the second temperature may be maintained for any of the reaction times described above, preferably towards the lower end of those set out above, typically up to about 2h at the peak temperature.

Aqueous extraction

Following heating the reaction mixture, the process provides a reaction product.

At the completion of the reaction, the reaction product is cooled. In some embodiments, the reaction product is passively cooled, for example by removing a source of heat. In other embodiments, the reaction product is actively cooled. Typically, the reaction product is allowed to cool to ambient or to a temperature below the boiling point of the aqueous extractant, for example the reaction product may cool to a temperature of not more than about 70°C, 60°C, 500C, 400C, 300C, 250C or 200C.

After cooling the reaction product, the process comprises extracting contaminant (eg uranium and/or thorium) by contacting the reaction product with an aqueous extractant. The aqueous extractant may be contacted with the cooled reaction product by any suitable means. Any techniques known to carry out aqueous extraction or leaching of the reaction product may be employed.

The aqueous extractant may be water, or an aqueous acidic solution, typically aqueous sulfuric acid or hydrochloric acid. The concentration of acid is not particularly limited and can be varied depending on the make-up of the water-soluble phase requiring extraction from the reaction product. In some embodiments, the aqueous acidic solution may have a concentration of about 0.5M. In some embodiments, the extracting step is carried out with a volume of aqueous acidic solution to provide about 5% by weight solids in solution.

Post reaction processing

The extracting step removes contaminant (eg uranium and/or thorium) and other water soluble components (including, for example, residual salt if present) and typically provides a solid phase ?5 comprising the mineral of interest, for example zircon, zirconia and silicon dioxide. The solid phase may undergo one or more further treatment steps. These further treatment steps may include, for example, removal of residual salt through washing and/or calcining. The further treatment steps may additionally or alternatively also comprise removing residual radium by leaching with hydrochloric acid (Typically 0.5-1M HCI, 5%wt solids) and subsequent drying.

The aqueous extractant after extracting the reaction product provides a liquid phase, typically comprising uranium and/or thorium, soluble species present in the reaction product and it may further comprise residual salt. The liquid phase may therefore also benefit from one or more further treatment steps in order to, for example, create a stable waste product which would typically involve neutralisation with lime (or other alkali) to produce a stable gypsum product. However, it would also be considered appropriate to recover metal values from the solution such as Zr, Hf, Sc and rare earths (if present) as such species may also have been extracted from the mineral sand particulate in addition to uranium and thorium. Recovery of these elements may be achieved by any suitable separatory technique known in the art.

Further embodiments - zircon purification

In some embodiments, the processes are for removing uranium and/or thorium from a zircon containing mineral sand particulate. These processes comprise reacting the zircon-containing mineral sand particulate with a salt under an atmosphere of sulfur trioxide at a temperature of at least about 400°C to provide a reaction product; and, after cooling the reaction product, extracting uranium and/or thorium from the reaction product with an aqueous extractant. The salt may be any of the salts described herein.

The reaction mixture may be provided by forming an intimate mixture of the mineral sand particulate with a salt prior to the reacting step. In these embodiments, preferred salts include sodium sulfate and sodium bisulfate.

In other embodiments, the reaction mixture comprising zircon-containing mineral sand particulate and salt is heated at a temperature from about 650°C to about 750°C under theS03 atmosphere. In some embodiments, following optional cooling, the reaction product may further heated to a second temperature from about 850 °C to about 1000 °C. Heating to the second temperature may be carried out under an atmosphere comprising N 2 .

In some embodiments, the reaction mixture comprising zircon-containing mineral sand particulate and salt is heated to a temperature from about 850 °C to about 1000 °C. These temperatures are preferred as it has been shown that they result in an relatively increased yield ?5 of zirconium species in the reaction product. In these embodiments, theS03atmosphere may be maintained until the reaction mixture reaches a temperature of about 750°C, 800°C, 850°C, 875°C or 900°C, where the process may comprising replacing theS03atmosphere with an atmosphere comprising N2 .

Reaction product

The reaction product following the extraction step typically comprises less than 500 ppm uranium and thorium (ie less than 500 ppm of the combination of uranium and thorium). This product is solid. The reaction product comprises a combination of zircon (ZrSiO 4), zirconia (ZrO2 ) and silicon dioxide (Si02 ). The reaction product may comprise not more than about

500ppm uranium and thorium. The reaction product may be characterized by the XRD diffraction pattern shown in Figure 5. In some embodiments, the reaction product may be characterized by one or more characterizing peaks shown in the XRD diffraction pattern shown in Figure 5.

The reaction product comprising zircon following extraction may comprise a disproportionate ZrO2 :SiO2 ratio. Zircon obtained by existing processes typically contains a ZrO 2 :SiO 2 ratio of about 2:1 (this being the normal ratio of ZrO 2 :SiO 2 in the zircon mineral present in an ore). The reaction product comprising zircon obtained by the processes described herein typically comprise higherSiO 2 content. For example, the ZrO 2 :SiO 2 ratio for a zircon produced by the processes described herein may be from about 1.3-2.0:1. Zircon produced by processes of Variant A have been found to have a ZrO 2 :SiO 2 ratio of about 1.3-1.6:1 and Zircon produced by processes of Variant B have been found to have a ZrO 2 :SiO 2 ratio of about 1.8-2:1. The ZrO2 :SiO2 ratio may be determined by XRF. The relatively highSiO2 content may suggest that theSiO 2 from the dissolved zircon may be reciprocating as a distinctSiO 2 phase hosted within/on the original zircon grain.

The reaction product may provide a product composition comprising:

* 60-100wt% zircon,

* 0-15wt% zirconia

• 0-25wt% silicon dioxide, and

• and not more than 500 ppm uranium and thorium.

In some embodiments, the product composition may comprise 60-95wt% zircon, 0-15wt% zirconia, 5-25% silicon dioxide, and not more than 500 ppm uranium and thorium.

In some embodiments, the processes described herein provide a mineral composition comprising a mixture of zircon, zirconia and silicon dioxide. This combination is not typically ?5 obtained by conventional zircon refining techniques. Accordingly, also provided herein is a composition comprising, or consisting of, zircon, zirconia (ZrO 2), and silicon dioxide (SiO 2 ), wherein the composition comprises not more than 500 ppm uranium and thorium. This composition may comprise the zircon, zirconia andSiO 2 in any relative amount described herein for any product of the described processes.

The zircon reaction product may be used as an opacifier for ceramics or may be used as a frit, for example which may be used as a component of a glaze for ceramics.

Reactor(s) for the purification processes

The processes described herein are effective to reduce the concentration of uranium and thorium in a mineral sand particulate by reaction in the presence of a salt at the elevated reaction temperature and under a highly corrosiveS03atmosphere.

Another aspect provides an apparatus for refining a mineral sand particulate, the apparatus including:

* a vessel for containing the mineral sand particulate and a salt, the vessel being adapted to contain an atmosphere comprising sulphur trioxide (eg anyS03atmosphere described herein); and

• a heating device for heating the vessel and/or contents thereof to a temperature of at least about 400 °C.

The vessel may be a substantially closed vessel with one or more ports for the introduction and removal of sulphur trioxide gas. Preferably, the vessel is also provided with a port for introduction of the mineral sand particulate and other reactants such as the salt. Optionally a port is provided for the extraction of the products.

In an alternative form, there is provided an apparatus for refining a mineral sand particulate, the apparatus including:

• a substantially closed vessel of a ceramic material or lined with a ceramic material, the closed vessel for containing the mineral sand particulate, the vessel comprising one or ..O more ports for introduction and removal of reactant gas; and

* a heating device for heating the vessel and/or contents thereof to a temperature of at least about 400 °C.

The vessel is preferably housed within a chamber sized to accommodate the vessel. The chamber may be heatable to a temperature of at least about 400°C (preferably 1000°C), such ?5 as in the form of an oven or a furnace. Thus the heating chamber may constitute the heating device. The chamber may be adapted to accommodate a pressure of gas/sulphur trioxide of greater than 1 atm such that the vessel within is subject to the pressure of greater than 1 atm.

Alternatively, the vessel and the chamber (or furnace) may be fluidically separated such that the chamber (or furnace) is not exposed to the corrosive environment within the vessel.

The vessel may be rotatably mounted within the chamber, either about a substantially horizontal axis or a substantially vertical axis. The vessel may be in the form of a crucible or a pot within a rotating pot furnace (the furnace in this case comprising the heating chamber). In such a furnace, the pot may rotate about a substantially horizontal axis within the furnace. Alternatively, the pot may rotate about a vertical axis within a furnace.

Alternative forms of heating may be provided such as induction heating.

Preferably, the vessel is additionally provided with a port for the introduction of the mineral sand particulate and other reactants such as the salt. Additionally, the vessel may be provided with an output port for the reaction product.

o TheS03may be generated within the chamber or external to the chamber.

In addition to the vessel, the heating chamber may accommodate anS03precursor. The heating chamber may be shaped and/or sized to accommodate the vessel with theS03 precursor distributed around the vessel.

The apparatus may be fluidly connected with anS03generator. Or in other words the apparatus may be in gas phase connection with anS03generator. The vessel may be directly fluidly connected with the sulphur trioxide generator. The apparatus may also be in fluid/gas communication with anS03and/orSO2analyser. The vessel may be directly fluidly/gas phase connected with the analyser. Preferably, the reactant gas drawn to the analyser may be diluted prior to entry to the analyser. The analyser may be run intermittently or periodically or continuously to monitor theS03and/orSO2.

Alternatively, or optionally, the analyser may sample from the gas stream prior to entering the vessel.

A control system may be provided to receive signals corresponding toS03and/orSO2data from the analyser. The control system may control the fluid connection between theS03generator ?5 and the apparatus, depending upon theS03and/orSO2data. The control system may also ensure maintenance of the desired partial pressure range of sulfur trioxide and/or the desired gaseous composition rangeof S03and other gases such asS02and02. The control system may also control the operation of the analyser such as the frequency of sampling. The control system may also receive feedback of other parameters such as temperature and control the operation of the apparatus accordingly. For example, the control system may control the operation of the apparatus by coordinating the introduction and/or flow of reactant gas with the measured temperature of the vessel. The control system may also coordinate the exhaust of the reactant gas with the introduction of a less reactant gas or inert gas such as nitrogen. This feature is applicable with Variant B set out elsewhere. The control system may be programmed to operate the apparatus to carry out any features of the processes set out in the remainder of the specification.

The apparatus (or reactor) used for this process must be corrosion resistant. Suitable corrosion resistant materials may include ceramics, for example, silicon carbide and fused quartz. The reactor may be constructed from any suitable corrosion resistant material, or more typically, surfaces of the reactor that may contact the corrosive reagents/intermediates are coated with one or more of these suitable materials. In some embodiments, the reactor surfaces that may contact the corrosive reagents/intermediates comprise a coating of silicon carbide.

o The vessel or chamber may be sealed to maintain the desired partial pressure or desired gaseous composition within the vessel. Alternatively, the apparatus may allow for intermittent, periodic or constant introduction of reactant gas e.g. sulphur trioxide, into the vessel through the port(s), with the flow rate of introduction and removal of gas maintaining the desired partial pressure. In other words, the vessel is preferably physically closed apart from the one or more ports which allow for introduction and removal of gas (and optionally other port(s) for the introduction of mineral sand particulate, other reactants and removal of the product).

Furthermore, the apparatus may allow for intermittent, periodic or constant introduction of other gas, such as nitrogen, oxygen or air. The same port(s) used for the introduction and removal of reactant gas may be used for the introduction and removal of other gas.

o The heating, preferably electric, may be incorporated into the wall of the heating chamber. Alternatively, the heating, preferably electric, may be incorporated into the wall of the vessel.

Additionally, an air dryer may be provided to dry fresh air before injection into the apparatus, or more preferably, the vessel. AsSO3 rapidly forms sulfuric acid on contact with moisture, preferably the apparatus/vessel is retained in an anhydrous state.

?5 Additionally, a recycler may be provided for the sulfur trioxide to enable reuse in the apparatus.

In accordance with another aspect, there is provided the apparatus as set out above, when used to carry out the method according to any of the above aspects.

Given the corrosion potential of the reaction and the high temperatures involved, the inventors have developed 2 alternative batch reactors: a closed muffle furnace reactor (Figure 1) and a rotating pot reactor (Figure 2).

Figure 1 shows one embodiment of an apparatus for the processes described herein provided in the form of a closed muffle furnace reactor. The closed muffle furnace reactor is preferred for smaller scale runs of the process, for example gram scale processes. The closed muffle furnace comprises a reactor chamber 10 sealable to encase crucible 20. The seal of the reactor chamber is sufficient to prevent leakage of the reaction atmosphere. The reactor chamber is heatable to a temperature of at least about 650 °C as it is in thermal communication with a heater (not shown). In some embodiments, the reactor chamber includes an electric heating integrated into a wall of the reactor chamber.

In use, the fused quartz crucible 20 may be charged with an intimate mixture of mineral sand particulate and salt (such as sodium sulfate), and positioned within the reactor chamber 10. A S03precursor (eg TiOSO 4 ) is distributed within the reactor chamber around the crucible. The S03precursor undergoes thermal decomposition and provides theS03atmosphere within the internal space of the reactor chamber. The reactor chamber is heated to the desired reaction temperature (eg 700°C/950°C), maintained for the pre-determined reaction time (eg 2-4h) and then allowed to cool. Once cool, the reactor chamber may be vented. In some embodiments, theS03atmosphere may be vented and stored for later use, for example to provide theS03 atmosphere for further runs of the process, and/or to vent the internal atmosphere prior to carrying out the process again. The crucible is removed from the reactor chamber, and contents subjected to aqueous extraction which removes uranium and/or thorium impurities in the aqueous extractant to leave purified mineral sand particulate in a solid phase.

Figure 2 shows an embodiment of an apparatus for the processes described herein in the form of a rotating pot reactor. The rotating pot reactor of figure 2 allows active and controlled management of the gaseous environment (flow rate, gas composition and measurement). The rotating pot reactor comprises a reactor chamber in the form of furnace 100, and a vessel or crucible in the form of rotating pot 200. Furnace 100 is heatable to the desired reaction temperature. Rotating pot 200 is capable of containing the mineral sand particulate combined ?5 with a salt. Rotating pot 200 comprises silicon carbide coatings on all surfaces.

The furnace further comprises a gas inlet in communication with anS03generator 300. S03 generator system 300 comprises aS02source in the formof S02 tank 301, an02source in the form of 02 tank 302 and one or moreS03generators. TheS03generators 310 may be provided in any suitable form.

In Figure 2, theS03generators comprise a firstS03generator 310 comprising a tube furnace charged with a vanadium oxide catalyst and a secondS03generator 320 also comprising a tube furnace charged with a vanadium oxide catalyst, wherein the first and secondS03 generators are separated by an interstage cooler 330. The interstage cooler assists increase conversionof S02 to S03by preventing excessive heating by the exothermic reactionof S02 and02over catalyst, which may provide sufficient energy forSO3 toconvert back toS02and

02. TheS03generator system 300 is in gaseous communication with internal atmosphere of furnace 100. The rotating pot furnace also optionally comprises anS03/SO2analyser system 400 to analyse the gases entering the furnace100. S03/SO2analyser system 400 is adapted to receive a gas stream from theS03generator system before entering furnace 100. Furnace 100 andS03/SO2analyser system 400 are vented to an outlet connected to an exhaust or preferably a scrubber. In some embodiments, the outlet is connected to a condenser (eg a cooling tower) to retain and optionally store exhaustedS03,which may be recycled in future reaction runs.

In use, rotating pot 200 is charged with mineral sand particulate and the salt, and then sealed or closed. The sealed/closed rotating pot is inserted into the furnace 100. TheS02and02are discharged from tanks 301 and 302 and pass throughS03generator 310, intercooler 330 and S03generator 320 operating at elevated temperature sufficient for vanadium oxide catalyzed S03formation. The output from theS03generator system is analysed by theS03/SO2analyser and when theS03concentration is sufficiently high, the rotating pot 200 is charged withS03 produced in theS03generator system. The furnace 100 is then heated from ambient to about 700°C (Variant A) or about 950°C (Variant B) typically at 3-4°C per minute and rotating pot 200 is rotated to assist to evenly heat the contents. TheS03generator 320 remains in operation through the course of the reaction continuously supplyingSO3 to the rotating pot 200 and passing through the furnace to the exhaust or scrubber. At the conclusion of the reaction, the S03generator 320 is turned off and remainingS03atmosphere is vented to the exhaust or scrubber, and as described above, optionally retained for recycling. The rotating pot 200 is then removed from the furnace 100 and its contents leached with aqueous extractant as described herein.

Figure 4 illustrates the rotating pot furnace 100 in greater detail. The furnace 100 defines a ?5 chamber with internal walls of refractory material, with heating elements provided internally of the chamber, along the side walls (although shown here for the sake of clarity on the top and bottom walls).

The pot 200 includes an inner vessel 201 comprised of/lined with silicon carbide. The pot 200 has an outer housing 206 of metal such as stainless steel within which the inner vessel 201 is accommodated, with a gasket 207 disposed between the inner vessel 201 and the outer housing 206. The outer housing 206 affords the rotating connection described below such that the pot 200 can be sealed.

The outer housing 206 is contained substantially within the furnace. The inner vessel 201 is contained fully within the envelope of the furnace 100.

The metal outer housing 206 has a neck 208 extending outwardly from the furnace through an opening 210 in the furnace 100. The location of the opening 210 corresponds with the rotational axis of the pot 200. The central axis of the opening 210 may be coaxial with the rotational axis of the pot 200. The outer end of the neck 208 incorporates a swivel connection 202 which allows the pot 200 to rotate relative to a conduit assembly 204 which is inserted into the neck 208 of the outer housing 206. The swivel connection 202 provides a seal between the conduit assembly 204 and the neck 208.

The pot 200 is rotationally mounted on laterally spaced rollers 209, only one of which is shown in Figure 4. The rollers 209 are supported by bearings at opposite ends. One or both of the rollers 209 is driven to rotate about the substantially horizontal rotational axis by motor 211. The pot 200 may be driven to rotate: continuously in the same direction; intermittently in the same direction; alternating between rotational directions, either continuously or intermittently. The rotational speed may vary. The controller (not shown) may control the rotational speed and rotational direction. Conversely, the pot can be held static without any rotation.

The conduit assembly 204 may be provided for the gaseous portal of suitable gases such as sulphur trioxide, and optionally sulphur dioxide and02 tothe pot 200. The conduit assembly 204 may include a manifold 214 through which the gas introduction pipe 216 extends. The gas introduction pipe 216 extends through the manifold 214 and into the inner vessel 201. The gas introduction pipe 216 extends substantially inside the inner vessel 201. The gas introduction pipe 216 may extend to approximately the midway along its length, into the inner vessel 201. Additionally, the manifold 214 includes an exhaust conduit 218, which is also fluidly connected to the interior of the inner vessel 201. While the gas introduction pipe extends substantially coaxially with the rotational axis, the exhaust takeoff 218 is radial from the manifold 214.

During operation, according to the processes described above, sulphur trioxide, sulphur dioxide, ?5 oxygen, nitrogen and/or air enter through gas introduction pipe 216 and are exhausted through exhaust conduit 218. Typically, sulphur trioxide and/or sulphur dioxide will enter through the gas introduction pipe 216 at the commencement of the batch process. Later in the batch process, typically with Variant B, the atmosphere within the inner vessel 201 will be changed by the introduction of nitrogen or air through the gas introduction pipe 216. Accordingly, the newly introduced gas will displace the existing gaseous environment.

A heat trace is provided to regulate the temperature of the conduit assembly 204 to maintain a temperature above 45°C to avoid condensing of sulfur trioxide within the conduit assembly.

The upper end of the furnace 100 has a removable lid which enables removal of the pot 200. Although not shown, there would be a space to the right of the pot so that the pot could be moved rightward, facilitating withdrawal of the neck 208 from the opening 210 and facilitating removal of the whole pot 200 from the furnace 100. This enables charging and discharge of the pot 200.

Figure 6 illustrates another form of the vessel 300. The vessel 300 is in the form of a hollow cylindrical vessel constructed of a ceramic such as silicon carbide (eg SiSiC). The cylindrical vessel 300 has a base 302 and an annular wall 304. The base 302 and the annular wall 304 are integrally formed of the ceramic material. Additionally, the vessel 300 is provided with a ceramic lance 306 comprised of a ceramic such as silicon carbide, for the introduction of reactants. The lance 306 is in the form of an elongate cylindrical tube having a longitudinal axis which is o colinear with the longitudinal axis of the vessel 300. However, offset configurations are also possible. The lance 306 may be positioned within vessel 300 to input the reactant gas above or below the surface of any reactant mix contained within the vessel 300. Additionally, the vessel 300 has a lid (not shown) also comprised of a ceramic such as silicon carbide or metal with refractory coating. The lid may comprise one or more ports, for example, for the introduction of reactants and/or charging and discharging gas (eg through lance 306). The lid may also comprise an aperture for allowing the lance 306 to enter the vessel 300. The upper end of the vessel 300 is provided with an upper annular flange 308 for engagement with the lid.

In this embodiment, the longitudinal axis of the vessel 300 is upright. The vessel is non rotational in this embodiment.

o The vessel 300 sits within an electric furnace (not shown) for heating the contents of the vessel 300. The vessel has a 40L capacity and can produce up to 10 kg of upgraded zircon.

The vessel is provided with an outlet port 305. The outlet port 305 is comprised of an outlet portion 307 of the vessel 300. The outlet portion 307 is integrally formed with the ceramic vessel. The outlet portion 307 extends radially from the vessel 300 at the base 302 of the vessel ?5 300.

The outlet port 305 also includes a tubular extension 309 comprised of ceramic such as silicon carbide. The tubular extension 309 has an annular flange 311 provided at one end. The tubular extension 309 has a frusto-conical portion 313, extending away from the flange and defining an internal frusto-conical bore 315 with the conical sidewall diverging towards the other end. The annular flange 311 connects to a ceramic tubular extension fastener flange 312, preferably comprised of silicon carbide. As can be seen from figure 6, the outer end of the outlet portion 307 includes a peripheral flange 317. The tubular extension fastener flange 312 has an annular recess 319 such that the peripheral flange 317 is seated within the annular recess 319. When the tubular extension fastener flange 312 and the tubular extension 309 are fastened together, the peripheral flange 317 is clamped there between and the tubular extension 309 is thereby secured to the outlet port 305.

Once assembled, the outlet port 305 is embedded in castable refractory cement 321, preferably silicon carbide, as best shown in Figure 7. A stainless steel frame 322 is provided on three sides and the rear, in order to provide a mould for the castable refractory cement.

A removable plug 320, preferably of ceramic such as silicon carbide is received within the frusto-conical bore 315. The plug 320 may define a frusto-conical outer surface, commensurate with the frusto-conical bore 315 such that the plug 320 may sealingly engage with the frusto conical bore 315. The plug 320 may also have a handle 322 to facilitate removal.

o Examples

Example 1: Crucible Scale Roasting of Unmilled Zircon

Small scale crucible tests were initially undertaken to test viability of removing contaminants such as U and Th using a modified sulfation roast. Initially tests were done in single closed fused silica crucibles in a muffle furnace using sodium bisulfate as a means of generatingSO3 insitu within the closed crucible.

A variation of this technique used a double crucible arrangement which used the decomposition of titanyl sulfate (TiOSO 4) as a means of generatingS03externally to the zircon-sodium sulfate mix. Zircon and sodium sulfate were contained in a smaller inner fused silica crucible which was placed inside a larger closed fused silica crucible which contained the titanyl sulfate as shown in Figure 1.

All crucible tests were subjected to the same standard leach conditions, namely; the crucible contents were leached in 0.5M H2 SO4at a solids density of 5 weight % for 3 hours at ambient temperature. The leach contents were filtered and the leach residue washed with water, dried and analysed.

?5 Selected examples of both techniques are briefly discussed below.

1.1. In situ S0aTests

1.1.1. Test 1

1Og of a high U+Th zircon was combined with 37 g of sodium bisulfate and placed in a fused silica crucible with a lid in a muffle furnace. The temperature was raised to 700°C and held for 4 hours and then allowed to cool. The crucible contents were leached using standard leach conditions. The results are shown in Table 1.

1.1.2. Test 2

40g of a high U+Th zircon was combined with 150 g of sodium bisulfate and placed in a crucible with a lid in a muffle furnace. The temperature was raised to 380°C, held at that temperature for 1 hour, then raised to 700°C and held for 4 hours and then allowed to cool. The crucible contents were leached using standard leach conditions. The results are shown in Table 1.

1.2. Ex-Situ SO 3Test (Ex-situ test 1)

5 g of a high U+Th zircon was combined with 11.8 g of sodium sulfate and placed in a fused silica crucible. This crucible was placed in a larger fused silica crucible with a lid which contained 74g of titanyl sulfate. The complete assembly was placed in a muffle furnace. The temperature was raised to 600°C, held at that temperature for 1 hour, then raised to 700°C, held for 4 hours and then allowed to cool. The crucible contents were leached using standard leach conditions. The results are shown in Table 1.

Table 1: Results of in situ test 1, in situ test 2 and ex-situ test 1

In situ Test 1 In situ Test 2 Ex-Situ Test 1 Analyte Feed Acid Extraction Feed Acid Extraction Feed Acid Extraction Zircon Leach from Feed ireed Leach from Feed ireed Leach from Feed Residue (%) Residue (%) Residue (%) ZrO2 61.4 60.4 17 62.9 57.7 26 32.3 60.2 18 SiO2 31.4 36.8 <0.2 32.3 39.8 <0.2 460 37.9 <0.2

(pm 450 140 74 460 150 77 543 110 80 U (ppm) 535 338 50 543 324 52 32.3 319 50

Example 2: Large Scale Laboratory Equipment Description

Sulfation tests were undertaken in a silicon carbide pot housed inside a larger stainless steel (253MA or 316) pot (Figure 2). The lid of the stainless steel pot has an opening where gases are injected and removed is sealed against the open end of the silicon carbide pot using high temperature gasket material. The pot assembly is supported on alumina rollers inside a ?0 temperature controlled box furnace which is operated in either a dynamic or static mode. A 50mm tube welded to the stainless steel lid protruded through the end wall of the furnace and was connected to a 38mm rotating swivel joint. A gas injection lance consisting of two concentric tubes and a thermocouple passed through the rotating swivel into the silicon carbide pot and the lance assembly fixed to the non-rotating side of the rotating swivel. This arrangement enabled a ?5 controlled sulfation gas composition to be maintained within the silicon carbide pot. A sulfur trioxide (S03) rich gas mixture together with sulfur dioxide (S02) and oxygen (02) entered the inner concentric tube and SO3 depleted gas flowed from the silicon carbide pot in the outer concentric tube and were exhausted into a hood that conveyed the gases to a caustic scrubber.

TheS03rich sulfation gas mixture was generated in two small tube furnaces (60mm and 80mm ID tubes) were operated in series supported vertically above the box furnace. A vanadium pentoxide catalyst was supported inside the alumina tubes inside the two tube furnaces which were connected by a water-cooled fitting clamped onto the alumina tubes with "O-rings". S02and 02 flowswere controlled through rotameters and passed down through both SO3 generators operating at 430°C furnace set-point. Thermocouples monitored both catalyst bed temperatures and exit gas temperatures of both furnaces. TheSO3 rich gas exited the bottom furnace through a water-cooled fitting connected to the gas injection lance which were all heat-traced to 60°C to ensureSO3 did not condense in the lines. The exhaust line from the furnace into the extraction hood was also heat-traced. A schematic of the furnace setup is shown in figure 4.

Process description

The process can be operated in several modes, namely:

1. Dynamic sulfation at 700°C;

2. Static sulfation at 700°C;

3. Dynamic sulfation at 700°C, followed by static decomposition at 950C on blended sulfated product;

4. Static sulfation at 700°C, followed immediately by decomposition at 950°C;

?0 5. Constant heating rate to 950°C under static conditions;

All sulfated products from either the sulfation or decomposition tests underwent standard ambient leach tests in stirred beakers for 1 hour using both 0.5M sulfuric acid and deionised water (DI). The leached solids were filtered and washed with deionised (DI) water and dried for analysis. The leach results were used to determine the success of the sulfation process based on Zr0 2 , U and ?5 Th recoveries into the leached resides.

2.1 Sulfation at 700°C

The only difference between dynamic and static sulfation tests at 700°C was whether the pot is rotated (dynamic) or not rotated (static) during sulfation, otherwise the test methods are the same.

Typically 90g of zircon (see anlysis in Table 2) is mixed with 360g of anhydrous sodium sulfate and place inside the silicon carbide pot. Other combinations or zircon and sodium sulfate were used with the total feed weight of 450g for each sulfation test. The pot is loaded into the stainless steel pot and furnace as described under the Equipment Description. The furnace is heated with a controlled heating program of 5°C/minute to 700°C. During heat-up the system is initially purged with 5L/minute nitrogen until theS03generators reach 430°C when nitrogen is replaced byS02 and02 flows based on the test conditions. When the temperature reaches 7000C the furnace controller automatically enters a "hold" period of 4 hours to complete the sulfation reactions before automatically shutting down. Initially the furnace cools to 4000C under the sameS02 and02 flowrates then the system is purge under nitrogen for 4h. The furnace cools to room temperature overnight. For a dynamic tests pot rotation is stopped during cooling to improve "pooling" of the sulfated material otherwise the sulfated material solidifies as coating on the inside of the pot.

Table 2: Assay of zircon particulate used in sulfation tests

Analyte Amount ZrO2 63.78 wt% SiO2 32.27 wt% A1203 0.62 wt% Fe2O3 0.12 wt% TiO2 0.513 wt% P205 0.352 wt% Y203 0.3297 wt% Sc203 0.06 wt% CaO 0.0538 wt% CeO2 0.017 wt% Hf02 1.4123 wt% Th 453ppm U 572ppm

Process variables studied during the dynamic tests included the impact of sulfation temperature, sulfation time, S03/SO2 ratios and sodium sulfate to zircon ratios on Zr0 2 , U and Th recoveries in the leached zircon residues.

Table 3 compares a number of dynamic sulfation tests with a static test under the same conditions.

Table 3: Comparison of dynamic and static sulfation tests under the same conditions

Calc. Acid Leached Sulfated Recovery SO 2 02Flow Sulfated Product Sulfated Dynamic Flow S03/ Product Rate Product (%) /Static Rate S02 (cc/min) ZrO2 Th U S03 ZrO2 Th U S03 (cc/min) Ratio ZrO2 Th U (%)(ppm) (ppm) (%) (%) (ppm) (ppm) (%) 864.0 380.5 3.83 7.1 68.0 58.0 56.6 60.8 162 339 55.5 15.4 37.7 864.0 380.5 3.83 11.0 75.0 80.0 49.7 55.3 119 270 64.1 20.3 43.2 864.0 380.5 3.83 6.6 76.0 63.0 57.0 55.5 154 297 82.8 20.0 46.6 864.0 380.5 3.83 10.1 68.0 77.0 52.2 56.4 130 293 72.2 24.6 49.0 Static 864.0 380.5 3.83 9.4 67.0 70.0 54.4 52.5 111 264 63.1 18.7 42.5

2.2 Sulfation at 700°C and Decomposition at 950°C

As indicated in the above table a significant amount of Zr02 is leached from the zircon. A number of crucible and leach tests were completed over a range of temperatures and times indicated that the yield of Zr is increased when the process is carried out at a temperature of 950°C for 2 hours.

All the 950°C decomposition tests were conducted under static conditions.

2.2.1 Decomposition of Dynamic Sulfated Zircon

700g of blended sulfated zircon from similar dynamic sulfation tests was placed in the silicon carbide pot. The test procedure followed the same "Sulfation at 700°C" procedure except that the furnace was programmed with a heating rate of 5°C/min to 950°C and then held for 2 hours. The heating and decomposition periods were done under a lowerS03/SO2gas composition that was used during sulfation. After the 2 hold period, the system was cooled under the sameS02 and02flowrates to 400°C then changed to nitrogen purge for 4 hours.

2.2.2 Static Sulfation and Decomposition

The sulfation stage followed the same procedure as "Sulfation at 700°C", with respect to feed preparation, heating and holding at 700°C for 4 hours. After 4 hour hold period the furnace program raised the temperature to 950°C at 5°C/min and was then held for 2 hours at a reduced S0 3 /SO2gas composition. Similarly the system was cooled under the sameSO 2 and02flowrates ?0 to 400°C then changed to nitrogen purge for 4 hours.

Table 4 compares a number of dynamic decomposition tests done on blended sulfated zircon material with combined static sulfation and decomposition tests. The static tests indicate both the sulfation and decomposition conditions.

Table 4

S02 Calc. Sulfated Product Acid Leached Recovery Leached Dynamic Flow 02Flow SO3/ Temp. Sulfated Product Product(%) /Static Rate Rate S2(00) ZrO2 Th U S03 ZrO2 Th U SO3 (ccmin) (cc/min) So (ppm) (ppm) (ppm)(ppm) ZrO2 Th U Ratio

. 166.2 71.3 3.4 950 10.2 76 80 46.7 63.2 96 212 0.4 90.1 18.3 38.4 E

o 166.2 71.3 3.4 950 9.1 76 79 46.9 63.3 95 181 0.4 88.2 15.8 29.0

166.2 71.3 3.4 950 8.5 79 75 47.5 63.5 111 229 0.4 96.3 18.1 39.2

332.3 333.0 9.0 7001 10.1 79 84 46.0 64.2 113 245 0.3 88.6 20.0 40.8 166.2 71.3 3.4 9501

2 332.3 333.0 9.0 7001 9.8 83 84 47.6 63.9 123 255 0.3 98.0 22.4 45.8 166.2 71.3 3.4 9501

864.0 380.5 9.0 7001 7.9 83 78 49.7 63.2 119 263 0.3 84.3 15.1 35.6 166.2 71.3 3.4 9501

Notes: (1) These tests were carried out on the same feed zircon in two stages, the first stage was run to a maximum temperature of 700°C according to the conditions specified and on the next day run according to the conditions specified to maximum temperature of 950°C.

2.3 Constant Heating Rate to 950°C Under Static Conditions

Typically 90g of zircon is mixed with 360g of anhydrous sodium sulfate and place inside the silicon carbide pot. Other combinations or zircon and sodium sulfate were used with the total feed weight of 450g for each sulfation test. The pot is loaded into the stainless steel pot and furnace as described under the Equipment Description. The furnace is heated with a controlled heating program of 3°C/minute to 950°C. During heat-up the system is initially purged with 5L/minute nitrogen until theS03generators reach 430°C when nitrogen is replaced byS02and 02flows based on the test conditions. When the temperature reaches 950°C the furnace controller automatically enters a "hold" period of 2 hours to complete the decomposition reactions before automatically shutting down.

The procedure was modified compared to the sulfation at 700°C protocol, and theS02and02 flows were changed to 5L/min of nitrogen for the decomposition and subsequent cooling stages, which was found to increase product Zr yields.

Process variables studied during the constant heating rate work included impact of sodium sulfate to zircon ratio, decomposition temperature and time, heating rate and recycle on ZrO 2 , U and Th recoveries.

Table 5 compares the test conditions and results for a number of the process variables studied. Most of the tests were averages of two to three separate tests.

Table 5

S02 02 Calc Sulfated Product Acid Leached Sulfated Recovery Sulfated Test Na2SO4 Flow Flow Saic Product Product% No. Addition Rate Rate 02 ZrO2 Th U SO3 ZrO2 Th U SO 3 (CC (CC! Ratio (%) (ppm) (ppm) (%) (%) (ppm) (ppm) (%) ZrO2 Th U min) min) Avg 200 332.3 333.0 9.0 20.9 120 150 35.3 63.8 139 287 0.2 96.4 36.3 60.1 Avg 300 332.3 333.0 9.0 12.2 98 98 42.1 63.3 118 249 0.4 90.2 20.9 44.4 Avg 400 332.3 333.0 9.0 15.7 83 100 39.8 63.0 111 242 0.30 96.2 32.3157.3 SZ230(1 ) 400 332.3 333.0 9.0 9.8 77 75 45.8 64.9 108 230 0.22 91.0 19.2 41.9 SZ255(2) 400 332.3 333.0 9.0 6.9 81 63 47.0 62.9 107 243 0.38 73.1 10.6 30.9 Avg(3 ) 400 332.3 333.0 9.0 10.9 83 87 45.4 63.2 113 241 0.24 93.7 21.9 44.6 Avg(4 ) 200 864.0 475.7 9.0 13.0 106 113 39.6 63.3 132 243 0.32 92.8 21.7 37.4 Notes: (1) Test decomposition underS03,SO2and02, all other tests decomposition under nitrogen (2) Test at 900°C - all other tests at 9500C (3) Test at4 C/min heating rate all other tests at 3°C/minute heating rate (4) Test had half feed contents recycled from previous decomposition test, all other tests zircon plus sodium sulfate

Example 3 - General Procedures

X-Ray Fluorescence (XRF). XRF analysis was carried out by first forming a glass bead containing the sample (0.9 g; milled to 95% passing 75pm) with 9.9 g of flux (consisting of ?0 61.5% lithium metaborate, 33.5% lithium tetraborate and 5% sodium nitrate) fused at 1100°C for 30 minutes and analysed on a Malvern Panalytical Zetium Wave Dispersive X-ray fluorescence spectrometer.

X-Ray Powder Diffraction (XRD). XRD analysis was carried out by first forming a pressed powder sample (milled to 95% passing 75pm) analysed on a Malvern Panalytical CubiX X-Ray ?5 Diffractometer with a post-diffraction monochromators and a cobalt X-ray tube.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general spirit and scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

DISCLOSED HEREIN:

1. A composition produced by a process for removing a contaminant from a mineral sand particulate, the process comprising:

• heating a reaction mixture comprising the mineral sand particulate and a salt comprising one or more of sodium sulfate, sodium bisulfate, sodium hydroxide, sodium chloride, sodium carbonate, potassium sulfate, potassium bisulfate, potassium hydroxide, potassium chloride, potassium carbonate, lithium sulfate, lithium bisulfate, lithium hydroxide, lithium chloride, and lithium carbonate under an atmosphere of sulfur trioxide at a temperature of at least about 400°C to provide a reaction product; and

* after cooling the reaction product, extracting contaminant from the reaction product with an aqueous extractant.

2. The process of claim 1, wherein the salt is selected from sodium sulfate, sodium bisulfate, and a combination thereof.

3. The process of claim 2, wherein the mineral ore and the salt are provided in an intimate mixture and heated to the temperature.

4. The process of claim 2 or 3, wherein the salt is present in an amount of at least about 300wt% relative to the total weight of the mineral ore.

5. The process of any one of claims 1-4, wherein the temperature is from about 650°C to about 1000°C.

6. The process of any one of claims 1-5, wherein the temperature is from about 650°C to about 800°C.

7. The process of any one of claims 1-5, wherein the temperature is from about 800°C to about 1000°C.

8. The process of any one of claims 1-7, wherein prior to the heating step, the process comprises combining the mineral sand particulate with the salt to provide the reaction mixture.

9. The process of any one of claims 1-8, wherein the sulfur trioxide is generated by thermal decomposition of a sulfur trioxide precursor.

10. The process of claim 9, wherein the sulfur trioxide precursor comprises one or more of titanium oxysulfate, sulphuric acid or a sulfate salt of sodium, potassium, lithium, ammonium.

11. The process of any one of claims 1-10, wherein the atmosphereof SO3 has a partial pressure of greater than 1 atm.

12. The process of any one of claims 1-11, further comprising a step of recyclingS03within a reaction chamber.

13. The process of any one of claims 1-12, wherein the aqueous extractant is selected from water and aqueous sulfuric acid.

14. The process of any one of claims 1-13, wherein the mineral sand particulate comprises at least about 1000 ppm uranium and thorium.

15. The process of any one of claims 1-14, wherein the reaction product following the extracting step comprises less than about 500 ppm uranium and thorium.

16. A composition produced by the process of any one of claims 1-15.

17. A composition comprising zircon, zirconia and silicon dioxide, and not more than 500 ppm uranium and thorium.

18. An apparatus for refining a mineral sand particulate, the apparatus including:

a vessel for containing the mineral sand particulate and a salt, the vessel being adapted to contain an atmosphere comprising sulfur trioxide; and

a heating device for heating the vessel and/or contents thereof to a temperature of at least about 400°C.

19. An apparatus for refining a mineral sand particulate, the apparatus including:

a substantially closed vessel of a ceramic material or lined with a ceramic material, the closed vessel for containing the mineral sand particulate, the vessel comprising one or more ports for introduction and removal of reactant gas; and

a heating device for heating the vessel and/or contents thereof to a temperature of at least about 400°C.

Claims (5)

1. A composition produced by a process for removing a contaminant from a mineral sand particulate, the process comprising:

heating a reaction mixture comprising the mineral sand particulate and a salt, wherein the salt is selected from sodium sulfate, sodium bisulfate, and a combination thereof, under an atmosphere of sulfur trioxide at a temperature of at least about 400°C to provide a reaction product; and

after cooling the reaction product, extracting contaminant from the reaction product with an aqueous extractant.

2. The composition of claim 1, wherein the temperature is from about 650°C to about 1000°C, or from about 650°C to about 800°C or from about 800°C to about 1000°C.

3. The composition of claim 1 or 2, wherein the sulfur trioxide is generated by thermal decomposition of a sulfur trioxide precursor which comprises one or more of titanium oxysulfate, sulphuric acid or a sulfate salt of sodium, potassium, lithium, ammonium.

4. A composition of any one of claims 1-3 comprising 60-100wt% zircon, 0-15wt% zirconia and 0-25wt% silicon dioxide, and not more than 500 ppm uranium and thorium.

5. A composition comprising zircon, zirconia and silicon dioxide, and not more than 500 ppm uranium and thorium.

2021107693 11 Nov 2021 1/5

FIGURE 2 FIGURE 1