Mineral sand particulate processing Cross-reference to related applications This application claims priority to Australian patent application no.2021221762 (filed on 25 August 2021) and Australian provisional patent application no.2022901205 (filed on 6 May 2022). The entire contents of each of AU2021221762 and AU2022901205 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 – ZrSiO ₄ ) 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, 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 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 ³⁺ or Ti ₂ O 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. 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 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 WO2016/127209 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: ^ reacting the mineral sand particulate with an excess of a pyrosulfate 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 excess of pyrosulfate may be an excess by weight or molar excess relative to the mineral sand particulate. In embodiments, the reaction of the mineral sand particulate and the pyrosulfate is conducted under an atmosphere of sulfur trioxide (SO ₃ ). In another 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 selected from: 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 and combinations thereof to form a reaction mixture 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 to a temperature of at least about 900°C. In a further aspect, there is provided a sodium zirconium sulfate characterised by an empirical formula of Na ₂ Zr(SO ₄ ) ₃ . In a further aspect, there is provided a sodium zirconium sulfate characterised by an empirical formula of Na ₈ Zr(SO ₄ ) ₆ . 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 radioactive impurities selected from uranium, thorium and a combination thereof, wherein the ratio by weight of zirconium to silicon (Zr:Si) in the composition is from about 1.3:1 to about 2:1. In another aspect, there is provided a composition comprising, or consisting of, zircon, zirconia (ZrO ₂ ), and silicon dioxide (SiO ₂ ), wherein the composition comprises not more than 500 ppm radioactive impurities selected from uranium, thorium and a combination thereof, wherein the ratio by weight of zirconium to silicon (Zr:Si) in the composition is from about 1.3:1 to about 2:1. 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 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. Figure 8A shows an XRD pattern obtained on a sample of sodium zirconium sulfate phase and sodium pyrosulfate obtained from a process run at 700°C. Figure 8B shows an XRD pattern obtained on a purified sample of sodium zirconium sulfate phase. Figure 9 shows a schematic of a lid for the vessel shown in figures 6 and 7. Figure 10 illustrates a composite reactor. 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. 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 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 pyrosulfate 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 pyrosulfate resulted in the extraction of undesirable contaminants into a water soluble sulfate 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 (along with the radioactive products of their radioactive decay) than other conventional methods. Uranium and thorium, in particular, are widely regarded as difficult to extract from some minerals, eg zircon, using conventional techniques. The product of the pyrosulfate impurity extraction includes a mixture of zircon, zirconia and silica. This reaction product surprisingly provides desirable properties in terms of colour profile when it is used as an opacifier or frit, for example when included in glazes for ceramics, such as tiles. 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 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, along with radioactive products of their radioactive decay). In some embodiments, the process removes uranium and/or thorium from the mineral sand particulate. In some embodiments, the mineral sand particulate comprises zircon. In such embodiments, a mineral sand particulate comprising zircon may be referred to herein as “a zircon particulate”. 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 may comprise any mineral or contaminant of mineral sand ore described herein. In some embodiments, the contaminants comprise uranium, thorium, radioactive products of the radioactive decay of uranium and/or 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 combination 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- 10wt% 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. In some 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). Without wishing to be bound by theory, it is believed that the pyrosulfate degrades portions of the zircon crystal lattice containing contaminant (as these portions are less crystaline – hence stable – than the more pure zircon crystal phases, thus releasing the contaminant from the zircon and converting the contaminant into aqueous leachable sulfates. Accordingly, it will be understood that reaction of the zircon particulate may comprise the partial decomposition of a zircon crystaline phase by the pyrosulfate. The zircon crystalline phase decomposed by the zircon provides sulfated forms of the minerals present, and upon completion of the reaction the contaminant is extracted in the aqueous extraction step, while some of the zircon reciprocates as zirconia (ZrO ₂ ) and silica (SiO ₂ ). It will therefore be appreciated that the zircon particulate may comprise undamaged zircon (in a highly ordered crystalline phase) along with damaged zircon (which may comprise contaminant incorporated into the crystal lattice, which will typically be less ordered than the undamaged zircon phase). The reaction product may therefore be enriched in undamaged zircon. 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 particulate may comprise the radioactive elements between any of these amounts. These radioactive elements may be a contaminant removed by the process. The content of the radioactive elements may be characterised by the uranium and thorium content, however in embodiments the radioactive elements may also include any daughter products of the radioactive decay of uranium and/or thorium. 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 have a minimum particle size (d50) of at least about 20µm, 25µm, 30µm, 40µm, 50µm, 60µm, 70µm, 80µm, 90µm,100µm, 110µm or 120µm, The mineral sand particulate may have a maximum d50 of not more than about 50µm, 60µm, 70µm, 80µm, 90µm,100µm, 110µm, 120µm, 130µm, 140µm, 150µm, 160µm, 170µm, 180µm, 190µm, 200µm, 210µm, 220µm, 230µm, 240µm, 250µm, 260µm, 270µm, 280µm, 290µm or 3000µm. 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 20-300µm, about 30-60µm or 100-150µm. Pyrosulfate-mediated reaction The process comprises reacting the mineral sand particulate with a pyrosulfate at a temperature of at least about 400°C to provide a reaction product. Pyrosulfate Pyrosulfate (S ₂ O ₇ ^2- ) is known to be a highly aggressive corrosion reagent, particularly in the temperature range of 600-750°C, and is sometimes referred to as Type II Hot Corrosion. Pyrosulfate formation in marine jet turbines has been described as a product of sulfur in the fuel combining with sodium chloride (NaCl) in the sea air and resulting in corrosion pitting of the turbine blades. Pyrosulfate has also been described as forming in the burning of Kraft liquor from the pulp and paper industry resulting in corrosion of the reactors. In some texts, sodium pyrosulfate is considered a means for facilitating the sulfation of metals. Despite these descriptions of low concentrations of pyrosulfate being produced, the reaction conditions required to provide sufficient pyrosulfate for the reaction with the mineral sand particulate are non-trivial. Typically, the mineral sand particulate is reacted with an excess of the pyrosulfate. The excess may be an excess by weight or a molar excess. In some embodiments, the excess of pyrosulfate is an excess relative to the contaminant to be removed by the process. In some embodiments, the excess is an excess of the pyrosulfate relative to the mineral sand particulate. In embodiments where the mineral sand particulate is a zircon particulate, the excess of pyrosulfate may be an excess relative to the zircon contained in the zircon particulate. Molar excesses and excess by weight can be interchanged depending on the molecular weight of the pyrosulfate. In some embodiments, the minimum molar excess of the pyrosulfate may be at least about 1.01 molar equivalents, about 1.05 molar equivalents, about 1.1 molar equivalents, about 1.5 molar equivalents, about 5 molar equivalents, about 10 molar equivalents, about 25 molar equivalents, about 50 molar equivalents, about 100 molar equivalents, about 150 molar equivalents, about 200 molar equivalents, about 250 molar equivalents, about 300 molar equivalents, about 350 molar equivalents or about 400 molar equivalents. The maximum molar excess of pyrosulfate may be not more than about 5000 molar equivalents, 4500 molar equivalents, 4000 molar equivalents, 3500 molar equivalents, 3000 molar equivalents, 2500 molar equivalents, 2000 molar equivalents, 1500 molar equivalents, 1000 molar equivalents, 500 molar equivalents, 450 molar equivalents or 400 molar equivalents. The molar excess of pyrosulfate may be from any of these minimum amounts to any of these maximum amounts provided the minimum is less than the maximum. For example, the molar excess of pyrosulfate may be from about 300 molar equivalents to about 500 molar equivalents. These molar excesses may be relative to the contaminant, relative to the mineral sand particulate or, for embodiments wherein the mineral sand particulate is a zircon particulate, relative to the zircon. In some embodiments, the minimum excess by weight of the pyrosulfate relative to the mineral sand particulate may be at least about 101wt%, about 110wt%, about 150 wt%, about 200 wt%, about 250 wt%, about 300 wt%, about 350 wt% or about 400 wt%. The maximum excess by weight of pyrosulfate relative to mineral sand particulate may be not more than about 5000 wt%, 4500 wt%, 4000 wt%, 3500 wt%, 3000 wt%, 2500 wt%, 2000 wt%, 1500 wt%, 1000 wt%, 500 wt%, 450 wt% or 400 wt%. The excess by weight of pyrosulfate may be from any of these minimum amounts to any of these maximum amounts provided the minimum is less than the maximum. For example, the excess by weight of pyrosulfate relative to the weight of the mineral sand particulate may be from about 300 wt% to about 500 wt%. Any means of providing the pyrosulfate for this reaction may be employed. In embodiments, the pyrosulfate may be supplied directly, for example the pyrosulfate may be generated in a first step before being combined with the mineral sand particulate. However typically, the processes comprise combining the mineral sand particulate with a pyrosulfate precursor, preferably a pyrosulfate precursor that when exposed to the reaction conditions (elevated temperature and atmosphere of SO ₃ ) will form the pyrosulfate in situ. The nature of the pyrosulfate precursor will dictate the counterion for the pyrosulfate present in the rection, however typically the pyrosulfate counterion may formally be selected from sodium, potassium and lithium, or a combination thereof. Suitable pyrosulfate precursors include sodium, potassium and lithium salts of sulfate, bisulfate, hydroxide, chloride, and carbonate. In some embodiments, the pyrosulfate precursor 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 pyrosulfate precursor may be selected from any of these potential precursors, preferably sodium sulfate and/or sodium bisulfate. The pyrosulfate precursor is typically provided in an excess by weight compared with the mineral sand particulate. The pyrosulfate precursor 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 pyrosulfate precursor 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 pyrosulfate precursor 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 pyrosulfate precursor 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 pyrosulfate precursor is provided in an excess amount, it may be preferable to recover the pyrosulfate precursor by separating it from the reaction product. The recovered pyrosulfate precursor may be reused in subsequent reacting steps. Accordingly, in some embodiments, the processes comprise recycling the pyrosulfate precursor. 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 pyrosulfate precursor causing it to precipitate out of solution. In some embodiments, the pyrosulfate precursor may be separated from the reaction product prior to cooling the reaction product. This separation may be aided as at the reaction temperatures the pyrosulfate precursor is typically in a liquid state. The liquid pyrosulfate precursor may therefore be removed from the reaction product by, for example, decantation. The pyrosulfate precursor may advantageously spontaneously form pyrosulfate when subjected to the reaction conditions. For example, the sulfation of sodium sulfate (melting point = 884 °C) has been found to be very rapid and the conversion to pyrosulfate is largely complete at about 400°C with the resulting product being a molten liquid. In some embodiments, the process comprises a step of combining the mineral sand particulate and a pyrosulfate precursor. The mineral sand particulate and the pyrosulfate precursor may be combined by any suitable means, and include addition of the pyrosulfate precursor to the mineral sand particulate, addition of the mineral sand particulate to the pyrosulfate precursor or adding both substantially simultaneously to a container. Once combined the pyrosulfate precursor and the mineral sand particulate may optionally be mixed to form a substantially homogeneous composition. Typically the mineral sand particulate and the pyrosulfate precursor are combined prior to the heating step. In some embodiments, the mineral sand particulate is combined with the pyrosulfate or the pyrosulfate precursor that has been recycled from the process. Sulfur trioxide The mineral sand particulate and the pyrosulfate may be reacted under an atmosphere of sulfur trioxide. The SO ₃ may assist in preventing decomposition of pyrosulfate, particularly at lower temperatures (for example during the period when the reaction is being heated to the temperature). Further, in embodiments where the pyrosulfate is provided from a pyrosulfate precursor, the SO ₃ atmosphere advantageously may assist sulfation of the pyrosulfate precursor to provide the pyrosulfate reactant. In some embodiments, the SO ₃ atmosphere is maintained at a pressure greater than 1 atm. This positive pressure of sulfur trioxide may assist impede the decomposition of pyrosulfate, which is known to proceed rapidly at temperatures above 550°C. For example, it has been found that an atmosphere comprising 37-90% SO ₃ with the balance being SO ₂ and O ₂ is effective when operating at a system pressure of 0.5kPa above 1atm. Accordingly, in some embodiments when operated at a pressure greater than 1atm, the minimum pressure of the SO ₃ 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 SO ₃ atmosphere is limited by the vessel containing the atmosphere and the rate of SO ₃ generation being provided to the vessel. In some embodiments, the maximum pressure of the SO ₃ 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 SO ₃ 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 SO ₃ 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 SO ₃ atmosphere may have a pressure below 1atm. In these embodiments, the minimum pressure of the SO ₃ atmosphere may be at least about 0.5atm, 0.6katm, 0.7atm, 0.8atm, 0.9atm, 0.95atm. The SO ₃ atmosphere may be between any of these minimum pressures to about 1atm, for example from about 0.5atm to about 1atm. The SO ₃ 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 an oxysulfates (eg TiOSO ₄ ), sulphuric acid, and sulfate salts. Accordingly, in some embodiments, the SO ₃ 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 SO ₃ precursor is TiOSO ₄ . TiOSO ₄ decomposes to titanium oxide (TiO ₂ ) and SO ₃ at temperatures from about 500°C. Alternatively or additionally, sulfur trioxide may be provided by reacting sulfur dioxide (SO ₂ ) and oxygen (O ₂ ) 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 O ₅ ) and other oxidation catalysts. SO ₂ may be provided by burning sulfur (S). In some embodiments, the temperature of the SO ₃ gas stream may be modified (ie heated or cooled) prior to forming the SO ₃ atmosphere. Depending on how the SO ₃ is generated, the SO ₃ atmosphere may comprise other gases. In some embodiments, the SO ₃ atmosphere may comprise nitrogen (N ₂ ) and/or sulfur dioxide gases or a combination thereof. Nitrogen can be separated from SO ₃ by cooling the gas stream to condense the SO ₃ (eg to below the boiling point of SO ₃ , which is about 45°C) and then re- vaporising the liquid SO ₃ into a vessel free of N ₂ . Accordingly, in some embodiments, the SO ₃ 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. When employed, the sulfur trioxide atmosphere may be any atmosphere comprising SO ₃ of sufficient concentration for the process of removing contaminants described herein. In some embodiments, the SO ₃ atmosphere contains a concentration of SO ₃ sufficient to form and maintain the presence of pyrosulfate in the reaction. The minimum concentration of SO ₃ in the SO ₃ 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 SO ₃ in the SO ₃ atmosphere is limited only by how it is generated. For example, the maximum concentration of SO ₃ in the SO ₃ 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 SO ₃ atmosphere may comprise SO ₃ 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 SO ₃ in the SO ₃ atmosphere may be from about 5% to about 100%, or about 37% to about 90%. In any of these embodiments, the remainder of the SO ₃ atmosphere may comprise N ₂ , SO ₂ and O ₂ , preferably SO ₂ and O ₂ . The concentration of each of these gasses is not particularly limited and is typically dictated by the SO ₃ generation technique employed. In some embodiments, the SO ₃ atmosphere consists essentially of SO ₃ , SO ₂ and O ₂ . Such atmospheres may comprise minor amounts (eg less than about 5%) of gaseous reaction byproducts or minor amounts of atmospheric gases due to imperfections in reactor seals. In some embodiments, SO ₃ is recovered following cooling of the reaction product, and recycled with optional addition of make-up SO ₃ to offset any losses. The SO ₂ and O ₂ resulting from any decomposition of the SO ₃ during the reaction may additionally or alternatively be recycled through the catalyst for conversion to SO ₃ . Recovery and recycling of SO ₃ may be achieved by recirculating SO ₃ into a reaction chamber, or collection of SO ₃ following the reacting step (eg by condensing the SO ₃ in a condensing tower, which also preferably may allow separation of any other gases, such as nitrogen, present in the SO ₃ atmosphere) and gasification of the condensed liquid SO ₃ prior to recycling to the reactor. Reaction temperature The reaction of the mineral sand particulate and the pyrosulfate is carried out at an elevated temperature of at least about 400 °C. The reaction of the mineral sand particulate and the pyrosulfate may preferably be carried out at a temperature sufficient to at least partially dissociate the pyrosulfate. Under the reaction conditions pyrosulfate begins to dissociate at temperatures around 250°C and has been identified albeit in smaller amounts at temperatures towards the upper end of the ranges described herein. However, sufficient dissociation occurs at temperatures from around 400-450°C for the desired reaction to proceed. In some embodiments, the minimum temperature of the reacting step may be at least about 400°C, 450°C, 500°C, 600°C, 650°C, 675°C, 700°C, 750°C, 800°C, 850°C, 900°C, 925°C or 950°C. The maximum temperature for the reacting step may be not more than about 1250°C, 1200°C, 1100°C, 1050°C, 1000°C, 950°C, 850°C, 800°C or 750°C. 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 reacting the mineral sand particulate with the pyrosulfate at 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 these embodiments wherein the mineral sand particulate comprises zircon and the pyrosulfate is generated from sodium sulfate, the reaction product may comprise a sodium zirconium sulfate phase. This sodium zirconium sulfate phase is described in more detail below. The sodium zirconium sulfate phase is water soluble, and this phase may be extracted in the aqueous extractant. However, this phase may be a useful form/source for the zirconium chemical market, despite its formation corresponding to a lower zircon content in the reaction product. In some embodiments, the process comprises reacting the mineral sand particulate with the pyrosulfate at 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 carrying out the pyrosulfate reaction at higher temperatures, the yield of zirconium in the reaction product is improved. In some embodiments, the process comprises reacting the mineral sand particulate with the pyrosulfate to a first temperature from about 400 °C to about 750 °C or about 450 °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 mineral sand particulate and pyrosulfate to a lower temperature, such as a temperature associated with Variant A embodiments. Heating the mineral sand particulate and the pyrosulfate to the first temperature typically produces the sodium zirconium sulfate intermediate phase within the reaction product, and heating to the second temperature typically results in complete decomposition of the intermediate phase. In some embodiments, the first temperature is achieved by adopting a suitable heating rate that maintains the reaction mixture (eg comprising the mineral sand particulate and the pyrosulfate) 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 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 pyrosulfate is generated from sodium sulfate and the mineral sand particulate comprises zircon, heating sodium sulfate to temperatures of at least about 700 °C leaves the sulfate phases other than the sodium sulfate in the liquid state, with the unreacted zircon remaining as a solid within the melt. Where the process involves heating to about 900-950°C, the pyrosulfate decomposes to SO ₃ gas and sodium sulfate in the absence of SO ₃ in the gas phase (otherwise it remains as pyrosulfate), and it is believed that the sodium zirconium sulfate intermediate phase decomposes to zirconia, sodium sulfate and SO3 gas, while the sodium sulfate remains in a liquid form. In some embodiments of processes involving heating to a temperature of at least about 900°C, the processes may comprise replacing the SO ₃ atmosphere with an atmosphere comprising N ₂ , for example air, or N ₂ only, or a mixture of N ₂ and O ₂ . Typically the atmosphere comprising N ₂ is a dry atmosphere, ie a substantially anhydrous atmosphere. The SO ₃ atmosphere 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 the SO ₃ 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 pyrosulfate precursor (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 unstable SO ₃ precursor and/or pyrosulfate precursor 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, source of pyrosulfate, source of SO3, 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 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 850-1000°C), 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 750 °C and heating to a second temperature from about 850 °C to about 1000 °C, the first temperature may be maintained for at least about 10m, 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 reaction of the mineral sand particulate with the pyrosulfate, 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, 50°C, 40°C, 30°C, 25°C or 20°C. After cooling the reaction product, the process comprises extracting 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 sulfate 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, pyrosulfate precursor if present) and typically provides a solid phase 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 sulfate (formed from decomposition of pyrosulfate or excess pyrosulfate precursor present in the reaction) 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 HCl, 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 sulfates formed in the pyrosulfate reaction and it may further comprise pyrosulfate precursor. 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 an excess of a pyrosulfate at a temperature of at least about 650 °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. 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 pyrosulfate at a temperature of at least about 650 °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. In these embodiments, the zircon particulate may be reacted with an excess of the pyrosulfate, wherein the excess is relative to the zircon content of the mineral sand particulate. The excess is preferably an excess by weight relative to the zircon present in the mineral sand particulate. 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 pyrosulfate under an atmosphere of sulfur trioxide at a temperature of at least about 650 °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 pyrosulfate may be conveniently provided by forming an intimate mixture of the mineral sand particulate with a pyrosulfate precursor prior to the reacting step. In these embodiments, preferred pyrosulfate precursors include sodium sulfate and sodium bisulfate. In other embodiments, the zircon-containing mineral sand particulate is reacted with the pyrosulfate at a temperature from about 650°C to about 750°C. In these embodiments, the reaction product comprises a sodium zirconium sulfate intermediate phase. In some embodiments, following optional cooling, the reaction product is further heated to a temperature from about 850 °C to about 1000 °C, which typically results in decomposition of the sodium zirconium sulfate intermediate phase. In some embodiments, the zircon-containing mineral sand particulate is reacted with the pyrosulfate at 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 of zircon in the reaction product. The raw product from the sulfation reactor consists of a mixture of upgraded zircon, sodium pyrosulfate, sodium sulfate, sodium zirconium sulfate as well as sulfate salts of trace elements such as U, Th, Sc, rare earth and other forms of zirconium and silicon, such as oxides and hydrates. In embodiments where the temperature of the pyrosulfate reaction was about 700°C, when the raw product is discharged from the reactor some of the products are in a solid form (zircon, silica, sodium sulfate) suspended in a liquid phase (sodium zirconium sulfate, sodium pyrosulfate). In embodiments where the temperature of the pyrosulfate reaction was about 950°C, when the raw product is discharged from the reactor, some of the products are in a solid form (zircon, zirconia, silica) suspended in a liquid phase (sodium sulfate and/or sodium pyrosulfate). Sodium zirconium sulfate Analysis of the reaction product following reactions at lower temperatures (Variant A, preferably about 700 °C) showed the presence of a sodium zirconium sulfate phase. This phase is postulated as being characterised by an empirical formula of Na ₂ Zr(SO ₄ ) ₃ . However, at least one species identified in the phase is characterised by an empirical formula of Na ₈ Zr(SO ₄ ) ₆ . The relative atomic abundance for species within the sodium zirconium phase may be determined by EPMA. In some embodiments, the sodium zirconium sulfate is characterised by the XRD pattern shown in Figure 8A and/or Figure 8B. In some embodiments, the sodium zirconium sulfate is characterised by one or more characteristic peaks shown in the XRD pattern shown in Figures 8A and/or 8B. The sodium zirconium sulfate phase is water soluble and is able to be separated from the reaction product by aqueous extraction (such as the methods of extraction or leaching described herein). Further, upon heating to temperatures of about 900-950°C, the sodium zirconium sulfate phase decomposes and may form sodium sulfate, SO ₃ gas and zirconia. 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 (ZrO ₂ ) and silicon dioxide (SiO ₂ ). 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 ZrO ₂ :SiO ₂ 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 higher SiO 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 relatively high SiO ₂ content in these compositions may suggest that the SiO ₂ from the dissolved zircon may be reciprocating as a distinct SiO ₂ phase hosted within/on the original zircon grain. The zirconium to silicon (Zr:Si) ratio (reported typically as ZrO ₂ :SiO ₂ ratio) may be determined by XRF. ZrO ₂ :SiO ₂ ratios describe the ratio of Zr to Si in all mineral forms present in a sample, including an ore. Therefore, any ZrO ₂ :SiO ₂ ratio described herein may be considered equivalent to the ratio of zirconium to silicon (Zr:Si) in a composition. Accordingly, the compositions of the invention comprising zircon, zirconia and silica and less than 500ppm of radioactive impurities selected from uranium, thorium and combinations thereof have a Zr:Si ratio of about 1.3:1 to about 2:1. In some embodiments, the product composition may comprise a minimum concentration of zircon of at least about 60wt%, 61wt%, 62wt%, 63wt%, 64wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt%, 97wt%, 98wt%, 99wt% or 100wt%. The maximum concentration of zircon may be not more than 100wt%, 99wt%, 98wt%, 97wt%, 96wt%, 95wt%, 94wt%, 93wt%, 92wt%, 91wt%, 90wt%, 85wt%, 80wt%, 75wt%, 70wt%, or 65wt%. The composition may comprise zircon from any of these minimum concentrations to any of these maximum concentrations provided the minimum is less than the maximum. For example, the composition may comprise ziron in a concentration from about 60wt% to about 100wt% or from about 61wt% to about 99wt%. In some embodiments, the product composition comprises zirconia. The composition may comprise a minimum concentration of zirconia of at least about 0wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt% or 14wt%. The maximum concentration of zirconia may be not more than 15wt%, 14wt%, 13wt%, 12wt%, 11wt%, 10wt%, 9wt%, 8wt%, 7wt%, 6wt%, 5wt%, 4wt%, 3wt%, 2wt%, 1wt%, or 0.5wt%. The composition may comprise zirconia from any of these minimum concentrations to any of these maximum concentrations provided the minimum is less than the maximum. For example, the composition may comprise zironia in a concentration from about 0wt% to about 15wt% or from about 0.5wt% to about 10wt%. In some embodiments, the product composition comprises silica. The composition may comprise a minimum concentration of silica of at least about 0wt%, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 2.5wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt%, 20wt%, 21wt%, 22wt%, 23wt% or 24wt%. The maximum concentration of silica may be not more than 25wt%, 24wt%, 23wt%, 22wt%, 21wt%, 20wt%, 19wt%, 18wt%, 17wt%, 16wt%, 15wt%, 14wt%, 13wt%, 12wt%, 11wt%, 10wt%, 9wt%, 8wt%, 7wt%, 6wt%, 5wt%, 4wt%, 3wt%, 2wt%, 1wt%, or 0.5wt%. The composition may comprise silica from any of these minimum concentrations to any of these maximum concentrations provided the minimum is less than the maximum. For example, the composition may comprise silica in a concentration from about 0wt% to about 25wt% or from about 0.5wt% to about 10wt%. The reaction product may provide a product composition comprising: . 60-100wt% zircon, . 0-15wt% zirconia . 0-25wt% silicon dioxide . not more than 500 ppm uranium and thorium, and . a Zr:Si ratio of about 1.3:1 to about 2:1. 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, and a Zr:Si ratio of about 1.3:1 to about 2:1. These compositions possess a Zr:Si ratio from 1.3:1 to about 2:1. The Zr:Si ratio may be any ratio between these limits. For example, the Zr:Si ratio may be about 1.3:1, about 1.4:1, about 1.5:1 about 1.52:1, about 1.6:1, about 1.7:1, about 1.753:1, about 1.8:1, about 1.9:1, about 1.99:1, about 1.999:1 or about 2:1. The composition may have a Zr:Si ratio from any one of these values to any other one of these values, or between any suitable values from 1.3:1 to 2:1. In some embodiments, the processes described herein provide a mineral composition comprising a mixture of zircon, zirconia and silicon dioxide, with a Zr:Si ratio of about 1.3:1 to about 2:1. This combination is not typically 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 of radioactive elements selected from uranium, thorium and a combination thereof, and the composition has a Zr:Si ratio of about 1.3:1 to about 2:1. The radioactive elements present in these compositions may also include radioactive daughter products of the radioactive decay of uranium and/or thorium. 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. Accordingly, also provided herein is a use of a composition described herein or produced by the processes described herein as an opacifier for a ceramic. Also provided is a use of a composition described herein or produced by the processes described herein in a glaze for a ceramic. Also provided is a use of a composition described herein or produced by the processes described herein as a frit for a ceramic glaze. Also provided is a ceramic glaze comprising a composition described herein or produced by the processes described herein. The ceramic glaze may comprise any other suitable components known to be used in ceramic glazes. Also provided is a frit comprising a composition described herein or produced by the processes described herein. Also provided is an opacifier comprising a composition described herein or produced by the processes described herein. Also provided is a glazed ceramic product (such as a tile) comprising a composition described herein. Typically a glaze on at least a portion of a surface of the glazed ceramic product comprises the composition. Reactor(s) for the pyrosulfate purification processes The processes described herein are effective to reduce the concentration of uranium and thorium in a mineral sand particulate by reaction with a highly corrosive reagent – pyrosulfate – preferably while blanketed in a highly corrosive atmosphere – SO ₃ atmosphere. Another aspect provides an apparatus for refining a mineral sand particulate, the apparatus including: a batch-processing vessel of silicon carbide or completely or substantially lined with silicon carbide, the vessel for containing the mineral sand particulate and a pyrosulfate, the vessel being adapted to contain an atmosphere comprising sulfur trioxide (eg any SO ₃ atmosphere described herein); and an indirect heat source for indirect heating of 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. The gas inlet port may be spaced from the gas outlet port, whereby the gas inlet port projects into the vessel. The spacing of the gas inlet port from the gas outlet port may be in a direction along a central axis of the vessel or parallel to a central axis of the vessel, e.g. offset from the central axis. The central axis of the vessel may be understood as the central longitudinal axis of a cylindrical vessel. The central axis of the vessel may correspond to the rotational axis of a rotating vessel. Preferably, the gas inlet port projects further into the vessel than the gas outlet port. For instance, the gas outlet port may be provided in a wall or lid of the vessel. The gas inlet port may be provided in the form of a lance. The lance may be comprised of silicon carbide (SiC) or siliconised silicon carbide (SiSiC). The gas inlet port may be arranged project into the mineral sand particulate mixture. Preferably, the vessel is also provided with one or more ports for introduction of the mineral sand particulate and/or other reactants such as the pyrosulfate precursor. Optionally a port is provided for the extraction of the products. 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). The chamber may be 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 reagent 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 a closed vessel within the chamber. 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. When the vessel is a rotatable vessel, the gas inlet port and the gas outlet port may be concentrically arranged. For instance, the gas inlet port may be centrally arranged relative to an outer annular gas outlet port. In such an arrangement, the gas inlet port may extend further into the vessel compared to the gas outlet port. There will be understood that “gas inlet port” is a reference to gas being delivered to the vessel, whereas “gas outlet port” is a reference to gas being extracted from the vessel. Heating is typically electric heating, usually electrical resistance elements but also induction coils may be provided, or indirect flame or fired, whereby the hot combustion gas would be on the outside of the containment vessel/reactor. The indirect heat source should have the capability for the vessel and/or the contents thereof to reach 950°C, and/or any of the process temperatures mentioned elsewhere. The SO ₃ may be generated within the chamber or external to the chamber. The SO ₃ may be generated within the vessel or external to the vessel. In addition to the vessel, the heating chamber may accommodate an SO ₃ precursor. The heating chamber may be shaped and/or sized to accommodate the vessel with the SO3 precursor distributed around the vessel. The apparatus may be fluidly connected with an SO ₃ generator. Or in other words, the apparatus may be in gas phase connection with an SO ₃ generator. The vessel may be directly fluidly connected with the sulphur trioxide generator. The apparatus may also be in fluid/gas communication with an SO ₃ and/or SO ₂ analyser. 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 the SO ₃ and/or SO _2. 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 to SO ₃ and/or SO ₂ data from the analyser. The control system may control the fluid connection between the SO ₃ generator and the apparatus, depending upon the SO ₃ and/or SO ₂ data. The control system may also ensure maintenance of the desired partial pressure range of sulfur trioxide and/or the desired gaseous composition range of SO ₃ and other gases such as SO ₂ and O _2. 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 and/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 and/or refractory 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. The vessel itself is silicon carbide (SiC) or completely or substantially lined with silicon carbide (SiC). The preferred ceramic is siliconized SiC (SiSiC). Siliconized SiC also called silicon bonded SiC. It is a SiC to which Si metal powder is added during the ceramic shape forming stage. When the shape is fired (~1500°C) the Si metal melts and files the pores of the SiC matrix giving a dense impermeable structure. The vessel and/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 reactant 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(es). The heating, preferably electric, such as induction 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. As SO ₃ rapidly forms sulfuric acid on contact with moisture, preferably the apparatus/vessel is retained in an anhydrous state. 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. In accordance with a further aspect of the present invention, there is provided a composite reactor for refining a mineral sand particulate, the apparatus including: a first vessel for containing a pyrosulfate precursor, the vessel being adapted to contain an atmosphere comprising sulfur trioxide; a second vessel for containing the mineral sand particulate, the vessel being adapted to contain an atmosphere comprising sulfur trioxide; wherein the first and second vessels are fluidly connected for the transfer of heated liquid pyrosulphate from the first vessel to the second vessel; one or more heating devices for heating the first vessel and/or the contents of the first vessel to a temperature of at least 250°C, and for heating the second vessel and/or the contents thereof to a temperature of at least about 400°C. In accordance with yet another aspect of the present invention, there is provided an apparatus for refining a mineral sand particulate, the apparatus including: a first substantially closed vessel of a ceramic material or lined with a ceramic material, the closed vessel for containing a pyrosulfate precursor, or a salt selected from: 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 and combinations thereof, the vessel comprising one or more ports for introduction and removal of reactant gas; a second 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 at least removal of reactant gas; wherein the first and second vessels are fluidly connected for the transfer of heated liquid pyrosulphate from the first vessel to the second vessel; one or more heating devices for heating the first vessel and/or the contents thereof to a temperature of at least 250°C, and for heating the second vessel and/or the contents thereof to a temperature of at least about 400°C. Considering the composite apparatus aspects set out above, the fluid connection between the first and second vessels may be by way of a conduit adapted for the transfer of heated liquid pyrosulfate. Suitably, the fluid connection incorporates refractory material considering the hot corrosive nature of the heated liquid pyrosulfate. The first and/or second vessel may be comprised of silicon carbide or completely or substantially lined with silicon carbide. As such, the first and/or second vessel may be adapted to contain an atmosphere comprising sulfur trioxide (eg any SO ₃ atmosphere described herein). The first vessel may be housed within a first reactor having a dedicated delivery port for the pyrosulfate precursor material which may be in the form of solid granular/power sodium sulphate. Additionally, the first reactor may incorporate a dedicated heating device. The heating device (preferably indirect) should have the capability for the first vessel and/or the contents thereof to reach 250°C. Accordingly, the first reactor may be in the form of a furnace with an indirect heat source for the first vessel or the contents thereof. The first vessel suitably provides containment of the sulphur trioxide atmosphere/reactant gas atmosphere. Additionally, delivery and extraction ports may be provided for delivery of sulphur trioxide or alternative reactant gas. Such ports may be provided in the first vessel or the reactor housing. Likewise, the second vessel may be housed within a second reactor with the fluidic connection provided to feed the pyrosulfate as a hot liquid to the second vessel. Additionally, the second reactor may incorporate a dedicated heating device. The heating device (preferably indirect) should have the capability for the second vessel and/or the contents thereof to reach 400°C. Accordingly, the second reactor may be in the form of a furnace with an indirect heat source for the second vessel or the contents thereof. The second vessel suitably provides containment of the sulphur trioxide atmosphere/reactant gas atmosphere. The sulphur trioxide atmosphere may exist due to decomposition of the pyrosulfate (which may occur above 950°C) or alternatively may be provided by delivery of sulphur trioxide to the second vessel or the second reactor. The latter may maintain a positive pressure of sulphur trioxide to hinder the decomposition of pyrosulfate at lower temperatures. Additionally, delivery and extraction ports may be provided for delivery of sulphur trioxide or alternative reactant gas. Such ports may be provided in the first vessel or the reactor housing. Given the corrosion potential of the reaction and the high temperatures involved, the inventors have developed several alternative batch reactors including: 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 pyrosulfate precursor (such as sodium sulfate), and positioned within the reactor chamber 10. A SO ₃ precursor (eg TiOSO ₄ ) is distributed within the reactor chamber around the crucible. The SO ₃ precursor undergoes thermal decomposition and provides the SO ₃ atmosphere 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, the SO ₃ atmosphere may be vented and stored for later use, for example to provide the SO ₃ 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 (furnace). 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 of approximately 5 L capacity. Furnace 100 is heatable to the desired reaction temperature of 700/950°C. Rotating pot 200 is capable of containing the mineral sand particulate combined with a pyrosulfate precursor. Rotating pot 200 comprises silicon carbide coatings on all surfaces. The furnace further comprises a gas inlet in communication with an SO ₃ generator 300. SO ₃ generator system 300 comprises a SO ₂ source in the form of SO ₂ tank 301, an O ₂ source in the form of O ₂ tank 302 and one or more SO ₃ generators 310, 320. The SO ₃ generators 310 may be provided in any suitable form. In Figure 2, the SO ₃ generators comprise a first SO ₃ generator 310 comprising a tube furnace charged with a vanadium oxide catalyst and a second SO ₃ generator 320 also comprising a tube furnace charged with a vanadium oxide catalyst, wherein the first and second SO ₃ generators are separated by an interstage cooler 330. The interstage cooler assists increase conversion of SO ₂ to SO ₃ by preventing excessive heating by the exothermic reaction of SO ₂ and O ₂ over catalyst, which may provide sufficient energy for SO ₃ to convert back to SO ₂ and O ₂ . The SO ₃ generator system 300 is in gaseous communication with internal atmosphere of furnace 100. The rotating pot furnace also optionally comprises an SO ₃ /SO ₂ analyser system 400 to analyse the gases entering the furnace 100. SO3/SO2 analyser system 400 is adapted to receive a gas stream from the SO ₃ generator system before entering furnace 100. Furnace 100 and SO ₃ /SO ₂ analyser 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 exhausted SO ₃ , which may be recycled in future reaction runs. In use, rotating pot 200 is charged with mineral sand particulate and pyrosulfate precursor, and then sealed or closed. The sealed/closed rotating pot is inserted into the furnace 100. The SO ₂ and O ₂ are discharged from tanks 301 and 302 and pass through SO ₃ generator 310, intercooler 330 and SO ₃ generator 320 operating at elevated temperature sufficient for vanadium oxide catalyzed SO ₃ formation. The output from the SO ₃ generator system is analysed by the SO ₃ /SO ₂ analyser and when the SO ₃ concentration is sufficiently high, the rotating pot 200 is charged with SO ₃ produced in the SO ₃ generator 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. The SO ₃ generator 320 remains in operation through the course of the reaction continuously supplying SO ₃ to the rotating pot 200 and passing through the furnace to the exhaust or scrubber. At the conclusion of the reaction, the SO ₃ generator 320 is turned off and remaining SO ₃ atmosphere 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 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 metal housing 206. Gasket 207 used in the trial was off the shelf, although found to have a short lifespan. The outer housing 206 affords the rotating connection described below such that the pot 200 can be sealed. The provision of the inner vessel 201 and the outer metal housing 206 arose because of the difficulty in making attachments to the inner ceramic vessel and the need to rotatably mount the pot 200 within the furnace, and make appropriate gaseous connections as described below. 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 accommodates 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 conduit assembly may comprise a metal, although a corrosion resistant or refractory material is preferred. “Refractory” is used to refer to a means of protecting mechanical components from high temperatures and also in some instances to provide a wear /erosion protection. The pot 200 is rotationally mounted on laterally spaced ceramic rollers 209, only one of which is shown in Figure 4. The rollers 209 are either fused silica or silicon carbide. 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 sulfur trioxide, and optionally sulfur dioxide and O ₂ to the 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 an annulus radially outward from the gas introduction pipe 216. The gas introduction pipe 216 extends further into the pot/vessel than the exhaust takeoff 218. The manifold 214 allows for rotation of the pot and vessel while maintaining the gas introduction pipe 216 and the exhaust takeoff 218 which are static. During operation, according to the processes described above, sulfur trioxide, sulfur dioxide, oxygen, nitrogen and/or air enter through gas introduction pipe 216 and are exhausted through exhaust conduit 218. Typically, sulfur trioxide and/or sulfur 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 217 is provided on exhaust conduit 218 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. Given that the furnace must cool down before disassembly thereof, the reaction product will be “frozen” in the form of a salt. Therefore, it is either necessary to break the salt into fragments before removal. Alternatively, water can be poured into dissolve the salt so that it can be poured out of the vessel. Figures 6, 7 and 9 illustrates another form of the vessel 300 for disposal within a furnace such as induction furnace 301. The vessel 300 is in the form of a hollow cylindrical vessel constructed of a ceramic such as silicon carbide, or more specifically, siliconised silicon carbide (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 (e.g. SiSiC), for the introduction of reactant gas. The lance 306 is in the form of an elongate cylindrical tube having a longitudinal axis which is 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, as best shown in Figure 9, the vessel 300 has a lid 340 also comprised of a ceramic such as silicon carbide (e.g.Siliconised SiC) or metal with refractory coating. This refractory coating is a castable high alumina low cement refractory. The lid 340 comprises one or more ports, for example, for the introduction of reactants (via feed port 350) and/or charging with gas (e.g. through lance 306) and discharging gas (through exhaust port 342). The lid 340 may also comprise an aperture (lance port 344) for allowing the lance 306 to enter the vessel 300. Additionally, the lid may include observation and sampling port 346, two thermocouple ports 348 sized to suit thermocouple sheath OD. 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. The vessel 300 sits within an electric furnace 301 for heating the contents of the vessel 300. The vessel has a 40L capacity and can produce up to 10 kg of upgraded zircon. More specifically, the outer wall of the furnace 301 is made up of clamshell shaped walls (each in the form of a half annulus, both making up a full annulus). The walls have an outer metal casing within which insulation is provided as is known in the art. Between the inner surface of the walls of the furnace 301, heating elements (happen to be SiC but could be any other type of electrical heating element) are provided in the gas space between the vessel 304 and the insulation. The heating elements have electrical connections which project through the walls. The heating elements may extend in an upright manner on the inner surface of the walls. 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 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 annulus 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 annulus 312 has an annular recess 319 such that the peripheral flange 317 is seated within the annular recess 319. When the tubular extension fastener annulus 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 323 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. As described above, the pyrosulphate can be produced either in situ with the zircon or as an alternative, the pyrosulphate can be produced ex-situ and added to a separate zircon reactor. With the latter alternative in mind, Figure 10 illustrates a composite reactor 360 comprised of two reactors: a first reactor 362 having a vessel 363 therein which is ceramic, or completely or substantially lined with ceramic material; and a second reactor 364 having a vessel 365 therein which is ceramic, or completely or substantially lined with ceramic material. The first reactor vessel 363 is loaded with a pyrosulfate precursor (such as sodium sulfate). A means of introducing the solid granular or powder sodium sulphate may be provided. SO ₃ is fed to the first reactor 362 or an SO ₃ precursor (eg TiOSO ₄ ) is distributed within the reactor chamber around the first reactor vessel 363. The SO ₃ precursor undergoes thermal decomposition and provides the SO ₃ atmosphere within the internal space of the reactor chamber. The reactor chamber is heated to the desired reaction temperature to produce pyrosulfate such as sodium pyrosulfate. The first reactor 362 provides containment of the SO ₃ with appropriate seals and constructed of corrosion-resistant and/or refractory material(s). A means of heating 367 (preferably external), in any of the forms of heating described above, is also provided. The first reactor vessel 363 is also provided with a means of capturing the pyrophosphate as a liquid and transferring that liquid to the second reactor vessel 365, e.g. via a tube 366. The sodium pyrosulfate, in the form of a hot liquid is then fed to the second reactor vessel 365 containing the mineral sand particulate. The reaction proceeds to produce the reaction product as described elsewhere in the specification. A means of heating 367 (preferably external), in any of the forms of heating described above, is also provided. The second reactor 364 may also provide containment of the SO ₃ /gas(es) with appropriate seals and constructed of corrosion- resistant and/or refractory material(s).The second reaction vessel 365 is removed from the second 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. Using this separate preparation of the pyrosulphate may possibly remove the need to add SO ₃ to the second reactor. SO ₃ will be evolved from the pyrosulphate in the second reactor 364 as the temperature is raised to 950° C. However it may be beneficial to maintain a positive pressure of SO ₃ to hinder the decomposition at the lower temperatures. Therefore, SO ₃ may be added to the second reactor 364 in any case. The benefit of the composite reactor 360 is that the pyrosulfate can be made separately, reducing the processing time required in the second reactor 364. Additionally, the first reactor 362 could be used to feed the pyrosulfate to multiple second reactors 364. The separating of the two reactors means that the productivity of the second reactor(s) 364 is improved (i.e. shorter residence time). Examples Example 1: Crucible Scale Roasting of Unmilled Zircon Small scale crucible tests were initially undertaken to test viability of removing 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 generating SO ₃ in situ 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 generating SO ₃ externally 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 H ₂ SO ₄ at 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. Selected examples of both techniques are briefly discussed below. 1.1. In situ SO ₃ Tests 1.1.1. Test 1 10g 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 ₃ Test (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 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 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 SiC pot and the lance assembly fixed to the non-rotating side of the rotating swivel. This arrangement enabled a controlled sulfation gas composition to be maintained within the silicon carbide pot. A sulfur trioxide (SO ₃ ) rich gas mixture together with sulfur dioxide (SO ₂ ) and oxygen (O ₂ ) entered the inner concentric tube and SO ₃ 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. The SO3 rich 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”. SO ₂ and O ₂ flows were controlled through rotameters and passed down through both SO ₃ generators operating at 430°C furnace set-point. Thermocouples monitored both catalyst bed temperatures and exit gas temperatures of both furnaces. The SO ₃ 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 ensure SO ₃ 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 950°C on blended sulfated product; 4. Static sulfation at 700°C, followed immediately by decomposition at 950°C; 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 ZrO ₂ , U and 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 analysis 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 the SO ₃ generators reach 430°C when nitrogen is replaced by SO ₂ and O ₂ flows based on the test conditions. When the temperature reaches 700°C 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 400°C under the same SO ₂ and O ₂ 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 Process variables studied during the dynamic tests included the impact of sulfation temperature, sulfation time, SO ₃ /SO ₂ ratios and sodium sulfate to zircon ratios on ZrO 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 R 2.2 Sulfation at 700°C and Decomposition at 950°C As indicated in the above table a significant amount of ZrO ₂ is leached from the zircon caused by the formation of a soluble sodium zircon sulfate phase (Na ₈ Zr(SO ₄ ) ₆ ) (see XRD patterns shown in Figures 8A and 8B). The sodium zircon sulfate phase was analysed by electron probe micro-analyser (EPMA) and the results are shown in Table 4. Table 4. EPMA results and calculated empirical formula Based on current understanding of the properties of this phase, this phase likely decomposes at temperatures greater than the 700°C sulfation temperature. A number of crucible and leach tests were completed over a range of temperatures and times indicated that a temperature of 950°C for 2 hours was required for complete decomposition of the sodium zircon sulfate phase. 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 lower SO ₃ /SO ₂ gas composition that was used during sulfation. After the 2 hold period, the system was cooled under the same SO ₂ and O ₂ flowrates 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 SO ₃ /SO ₂ gas composition. Similarly the system was cooled under the same SO ₂ and O ₂ flowrates to 400°C then changed to nitrogen purge for 4 hours. Table 5 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 5. 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 the SO ₃ generators reach 430°C when nitrogen is replaced by SO ₂ and O ₂ flows 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. Initially the same SO ₂ and O ₂ flow rates were used during the 2 hour decomposition and subsequent cooling period to 400°C then switched to nitrogen for 4h purge. XRD traces indicated that the Na ₈ Zr(SO ₄ ) ₆ phase had decomposed but sodium pyrosulfate had not fully decomposed to sodium sulfate. XRD patterns for the Na ₈ Zr(SO ₄ ) ₆ phase are shown in Figures 8A and 8B and a representative XRD pattern for a reaction product is shown in Figure 5. The procedure was modified and the SO ₂ and O ₂ flows were changed to 5L/min of nitrogen for the decomposition and subsequent cooling stages. XRD traces confirmed that only zircon and sodium sulfate were present in decomposed sulfated zircon. 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 6 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 6. SO O ^{A id L h d S lf t d} R S lf t d 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 75µm) with 9.9 g of flux (consisting of 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. XRF results report zircon (ZrSiO ₄ ) partitioned between the amounts reported for ZrO ₂ and SiO ₂ . X-Ray Powder Diffraction (XRD). XRD analysis was carried out by first forming a pressed powder sample (milled to 95% passing 75µm) analysed on a Malvern Panalytical CubiX X-Ray Diffractometer with a post-diffraction monochromators and a cobalt X-ray tube. Example 4: Glaze tests This example describes the results of a glaze test comparing properties of a reaction product of the invention with a premium grade zircon. The test samples were analyzed by XRF according to the general protocol described in Example 3, with results shown in Tables 7 and 9. 4.1 Test compositions 4.1.1 Premium grade zircon The premium grade zircon used in these glaze tests was Zircosil 5 (Z5). Zircosil 5 [CAS no. 14940-68-2] has a nominal average particle size of 5 micron and an average particle diameter (Malvern d50) of 1.5 micron. Zircosil 5 used in this study was obtained from Endeka Ceramics Ltd. Table 7. XRF analysis of zircosil 5 composition A l t ZIRCOSIL 5 4.1.2 Reaction product A mineral sand particulate defined by the XRF analysis – starting material - in Table 9 was treated according to the process described herein. The starting material was subjected to a number of different reaction conditions summarised in Table 8. The mineral sand particulate starting material comprises about 64% Zr content and a combined uranium and thorium content of 1024 ppm. The reaction product comprises about 63% Zr content (Zr:Si ratio of about 1.85:1) and a combined uranium and thorium content of 373 ppm. The process comprised reacting the zircon particulate with a pyrosulfate precursor (sodium sulfate) under an atmosphere of SO ₃ according to similar protocols described in Examples 1 and 2. All processes include a first heating step (Roast) under conditions outlined in Table 8, and some embodiments also include a second heat treatment (Decomposition). The amounts of zircon particulate (Zr), pyrosulfate precursor (Na ₂ SO ₄ ) are included in Table 8. Table 8 also notes the heating rate, the maximum temperature (temperature) and time the maximum temperature was held (time). The reaction product of each of these runs was combined to provide the reaction product used in the glaze tests of this Example.

Table 8. Summary of test conditions to convert starting material to reaction product used in Example 4 CONDITIONS _WEIGHT Table 9. XRF analysis of mineral sand particulate (starting material) and reaction product used in glaze test of example 4 Analyte Starting material Reaction product 4.2 Protocol In general, each sample is milled to 3 different particle sizes (D ₅₀ = 1.07, 1.20 and 1.45). Each milled sample was suspended in an equivalent glaze base solution, coated onto a ceramic tile substrate and fired in a kiln (max temperature 1070°C). Once fired, the colour of each tile is assessed according to Cielab color system. A protocol for these tests is as follows: 1. Zircon Milling 1.1. Weigh 1500g of 3mm Yttrium stabilised Zirconia milling balls into a plastic jar. Using a funnel, with the hose touching the bottom of the jar, transfer the balls into the ceramic milling jars. 1.2. Split out 3 x 50g +/- 0.5g lots of Zircon. Add 50g to each of the 3 ceramic milling jars. 1.3. Add 200mL of deionised water into each milling jar, and cover with an alumina lid. 1.4. Using a drill press fitted with a stirrer rod, mill the samples until an approximate range of particle sizes above and below 1.5µm is attained 1.5. Using a glass beaker and plastic strainer tip decant the milled contents into the strainer. 1.6. Pipette 4ml of zircon slurry into 100mL of a 0.02g/L Calgon solution. Add a stirrer bar into the beaker. 1.7. Place the beaker onto a Sonifier magnetic stirrer, and run at 45% for 5 minutes with the cabinet door latched closed. 1.8. Analyse each milled zircon using a Laser Sizer. 1.9. Dry the Zircon slurry in a microwave and dry for 20 minutes, followed by further drying in an oven for a further 10 minutes. Remove from oven and once cooled transfer contents to a labelled bag and crush contents. 2. Glaze Production 2.1. For each of the different particle size samples, into a 1L round plastic jar add 450g of 10mm zirconia balls, 75g of glass frit, 16.5g of crushed zircon powder, 42g of a 1% CMC/TSPP solution 2.2. For the ZORCOSIL 5 (z5) standard, into one 2L round plastic jar add 1500g of 10mm balls, 250g of glass frit, 55g of z5 and 140g of 1 % CMC/TSPP solution. 2.3. Secure the internal lid with tape and place a grip/glove around each jar. Carry jars to the jar roller located next to the drill presses. Give each jar a shake then roll for 1h (z5) and 25 minutes (particle sized samples). 3. Slipping 3.1. Take 6 bisque tiles and dry in an oven for at least an hour. Remove and cool. 3.2. Take the cooled tiles and label. 3.3. Remove the tape from the jars prepared in step 2, shake then upend contents into a strainer seated in a jug to separate the zircon balls and liquid. 3.4. Agitate the strainers until 200mL of glaze is collected for the z5 standard and 100mL for the particle sized samples. 3.6. Clean the tops of the jugs by removing any glaze residue, gently agitate jugs on an orbital mixer. 3.7. Dampen the tile holder before inserting into a 1.25mm slipping frame. Place a tile into the tile holder and align the frame with a linear actuator. 3.8. Place a slipper onto the tile holder so that it sits ~2mm back from the edge of the tile. Ensure the linear actuator is centred on the slipper 3.9. Pour the Z5 into a well of a slipper to cover the bottom of the slipper reservoir. 3.10. Pour test glaze into a clean well in the slipper to substantially the same level as the Z5 glaze 3.11. Engage the actuator to pass the slipper across 2 adjacent tile and apply glaze to the 2 adjacent tiles - one coated with z5 and a second with test glaze. 3.12. Remove the slipper. Slide the tile holder backwards and remove the glazed tile. 3.13. Repeat steps 3.9 to 3.12 for remaining samples. 3.14. Allow the tiles and glaze to air dry for up to 1 hour before firing. 4. Firing Tiles 4.1. Using a grooved spatula, remove any portion of glaze overhanging the edge of the tile and any residue on the side or bottom of the tile. 4.2. Place tiles within a furnace 4.3. Fire tiles to a maximum temperature of 1070°C over 90 minutes. 4.4. Remove tiles from the furnace and allow the tiles to cool. 5. Colour Measuring 5.1. For each tile, using a white board eraser rub the surface of the glaze to remove any residue/dirt 5.2. Using the BYK Spectro-guide 2 colour reader measure the colour of the glaze in 5 places across the tile, excluding the biscuit 4.3 Results of glaze tests The colour properties of these glazes were compared using the CieLAB colour system. The results are shown in Tables 10 and 11. In Table 10, L, a and b are the components of the CieLAB colour system, wherein: L is black (0) - white (100) so higher is whiter a is red (+ve) to green (-ve) b is yellow(+ve) to blue (-ve). The values reflected in Table 10 for L, a and b were experimentally determined according to CieLAB colour system instructions. The CIELAB colour scale can also be used to express the differences in colour between objects. DL, Da and Db indicate difference along each axis. The total colour difference is often expressed as DE. DE is calculated as square root of the sum of squares of dL, Da and Db. The sign of DE is taken from the sign of the DB value. The calculated DL, Da, Db and DE results are shown in Table 11 based on the measurements described in Table 10. Table 10. Results of glaze tests for premium zircon (Z5 reference glaze) and product of the invention (test sample glaze) SIZING Z5 REFERENCE GLAZE COLOUR TEST SAMPLE GLAZE COLOUR Table 11. DE test results comparing based on raw data presented in Table 10 4.4 Conclusions These results show that the composition of the invention is able to be incorporated effectively in a ceramic glaze. Further, these results suggest that the composition of the invention possesses discernible differences in colour properties to the reference glaze. These differences in glaze properties are considered desirable and were unpredictable prior to testing the compositions of the invention. Typically, more blue (negative DB) is seen as attractive as it enhances white (for example cooler whites, such as arctic/ice whites). The DL at 0.11 suggests that the test glaze is preferred over the standard as it is relatively more towards the whiter end of the black/white scale. The DA of the test glaze is more towards the green (negative value) than the reference. The DB of the test glaze is slightly more towards the blue (negative value) than the reference. Overall, the DE at -0.46 shows a better performance for the test glaze relative to the reference. This difference is approaching the limit believed to be discernible to the naked eye - the eye is thought to be able to discern differences greater than about 0.5 on this scale. 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.