AU725713B2 - Separation of zircon from alumino-silicates - Google Patents

Description

*i I

AUSTRALIA

Patents Act 1990 P/00/011 Regulation 3.2

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT /f Invention Title: SEPARATION OF ZIRCON FROM

ALUMINO-SILICATES

Applicant: K.M.C.C. WESTERN AUSTRALIA PTY LTD and YALGOO MINERALS PTY LTD The following statement is a full description of this invention, including the best method of performing it known to me: SEPARATION OF ZIRCON FROM ALUMINO-SILICATES This invention relates to the separation of zircon from alumino-silicates.

The invention finds particularly useful application in the beneficiation of mineral sands, that is the separation of various components of mineral sands from each other and the concentration of the valuable components. Typically such mineral sands contain ilmenite, rutile, zircon, leucoxene and alumino-silicates such as kyanite. It will be convenient to describe this invention with reference to this example application but it is to be clearly understood that this invention is capable of broader application.

Ilmenite and rutile containing mineral sands are processed into titanium dioxide pigment which is the premier white pigment used around the world in the paper and paint industries. The mineral sands typically also contain other valuable minerals such as zircon and leucoxene. The first step in the overall processing of mineral sands comprises separating the valuable components, eg. ilmenite, rutile, leucoxene and zircon from each other and from the tailings which include alumino-silicates. This is done by means of a series of wet gravity, magnetic *o 20 and electrostatic separation processes.

A schematic flow sheet of a typical plant for performing this beneficiation of minerals sands is illustrated in Fig. 1. The first step in the process is the separation of the mineral sands into conductive and non-conductive 25 components. This is carried out in banks of electrostatic separators, typically having both high tension roll separators and/or electrostatic plate separators.

The non-conductive components are then passed through a wet gravity separator such as a spiral concentrator, a wet table or a jig to separate the zircon which has significant value from gangue minerals including alumino- 30 silicates such as kyanite, and quartz which form the tailings.

JB C:\WINWORD\JENNY\NODELETE\PO3207.DOC The wet gravity separation relies on the difference in specific gravity between zircon and the alumino-silicates such as quartz and kyanite to effect the separation.

Naturally the larger the difference in specific gravity between zircon and the gangue mineral components, the greater will be the efficiency of the separation. Many of the unwanted components have a specific gravity of about 3 or less, while zircon has a specific gravity of about 4.6. However one of the major alumino-silicate contaminants namely kyanite has a specific gravity of about 3.6 to 3.7. This is substantially closer to the specific gravity of zircon and tends to detract from the efficient separation of zircon and kyanite.

The potential efficiency of the wet gravity separation is measured by the relative specific gravity ratio which is calculated as follows: 9 9 .Relative specific gravity ratio (SGzircon-SGwater) (SGkyanite-SGwater) Thus the relative gravity ratio is calculated by subtracting the density of the wet separation medium, namely water, from the density of the mineral.

Further magnetic electrostatic separation is conducted on the concentrated valuable mineral streams to remove remaining conductive or magnetic contaminating minerals from the zircon mineral. These contaminating minerals include (but are not limited to) rutile, leucoxene, staurolite, monazite minerals which are misplaced or sent into this section of the processing circuit. Some aluminosilicate minerals (including remaining kyanite mineral) are not removed by these magnetic or electrostatic machines due to their conductive and magnetic nature being similar to that of the zircon mineral non-magnetic and non-conductive).

As the product specification for high grade zircon product is specific and only small amounts of kyanite are permitted in zircon product (not more than 0.42 wt% A120 3 the zircon/tailings split is arranged accordingly and is very conservative. As a result valuable zircon product is currently being lost in the tailings. As zircon represents MR C:\WINWORD\MARY\NODELETE\MMHNODLE42830.DOC significant value it would clearly be highly advantageous if the amount of zircon being lost in the tailings could be reduced.

An A1 2 0 3 -SiO2 phase diagram is annexed hereto as Figure 2. This diagram is typical of those shown in various publications detailing the A1203-SiO 2 system. The kyanite form of alumino-silicate has a composition of about 50 Mol% SiO2 and Mol% A1203. The phase change which occurs when kyanite is calcined at a temperature in the region of 1300°C to 14000C can be traced on the phase diagram.

In summary kyanite undergoes crystalline transformation to mullite and silica.

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4 o MR C:\WINWORD\MARY\NODELETE\MMHNODEL\42830.DOC -4- Mullite has a specific gravity of 3.16 g/cm 3 and silica has a specific gravity of 2.3 2.7 g/cm 3 According to a first aspect of the invention there is provided a process for treating zircon and kyanite containing mineral sands, the process including, inducing the kyanite to undergo a phase change to another form of aluminosilicate and/or silica having a lower specific gravity than kyanite thereby to increase the difference in specific gravity between zircon and the other components of the mineral sands.

Advantageously the process includes the further step of separating the zircon from the other components in a wet gravity separation process.

Thus by causing or inducing the kyanite to undergo a phase change which converts it to another alumino-silicate form and/or silica which lowers its specific gravity, the specific gravity differential between the zircon and kyanite is increased which effectively improves the efficiency of separation of these components in a wet gravity separator.

20 Under equilibrium temperature conditions, kyanite starts to transform to other alumino-silicate forms at around 1100 0 C and this transformation is complete at .around 14000C. The products of this decomposition are mullite (3AI 2 0 3 .2SiO 2 and silica (SiO 2 This decomposition is accompanied by a decrease in mineral density which can be quite significant, 3.6-3.7 g/cm 3 (kyanite) to 3.16 g/cm 3 25 (mullite). By converting all of the kyanite in the mineral sands to mullite the relative gravity ratio of zircon to kyanite can be increased from 1.38 to 1.71.

o Preferably the step of inducing the kyanite to undergo a phase change includes heating the mineral sands to a temperature of at least 10600C until the kyanite 30 changes to another form of alumino-silicate and/or silica. Advantageously the step of heating the mineral sands comprises calcining mineral sands at a JB C:\WINWORDJENNY\NODELETE\PO3207.DOC temperature of at least 1300°C for at least one hour. The structure of the zircon is not appreciably changed by the heat treatment.

In one embodiment the mineral sands are calcined in a rotating drum kiln. Typically the rotating drum kiln is arranged to slope down from an inlet located towards one end thereof to an outlet located towards an opposed end thereof, so as to progressively advance the particulate material through the kiln from the inlet to the outer.

In another embodiment the mineral sands are calcined in a fluidised bed.

Optionally the mineral sands are calcined in a reducing atmosphere.

The magnetic susceptibility of kyanite is increased by calcining under reducing 15 conditions. This may allow further removal of kyanite from zircon by magnetic separation methods.

Typically the step of separating the zircon from the other components is carried out in a spiral concentrator, a wet table, or a Kelsey centrifugal jig.

According to a second aspect of this invention there is provided a process for the beneficiation of particulate mineral sands, including: passing electrically non-conductive components of the mineral sands such as zircon and alumino-silicate tailings including kyanite through a wet gravity separator to separate the zircon from the alumino-silicate tailings including kyanite; and calcining at least the alumino-silicate tailings to convert the kyanite into other forms of alumino-silicate and/or silica having a lower specific gravity than kyanite to make it more susceptible to separation from zircon in a wet gravity separator.

MR C \WINW0RD\MARY\NODELETE\MMHNODEL\423ODOC -6- Typically, the process also includes the step of passing the particulate mineral sands through an electrostatic separator prior to said step of passing the non-conductive components through a wet gravity separator, to separate electrically conductive components such as ilmenite, leucoxene and rutile from the electrically non-conductive components.

In one embodiment the alumino-silicate tailings issuing from the wet gravity separator are subjected to said step of calcining, and the tailing issuing from said calcination step are passed through a further wet gravity separator to separate any zircon remaining in the alumino-silicate tailings from the remainder of the alumino-silicate tailings.

In an alternative embodiment all the electrically non-conductive components of the mineral sands issuing from the electrostatic separator are subjected to said step of calcining, prior to being passed through the wet gravity separator.

In a further embodiment all of the mineral sands to be beneficiated are subjected to said step of calcining before said mineral sands are passed through the electrostatic separator.

S* According to a third aspect of this invention there is provided an apparatus for the beneficiation of zircon- and kyanite-containing mineral sands material, including: a wet gravity separator; and 25 calcining means; wherein the calcining means is operable to calcine the mineral sands material at a temperature and for a period of time sufficient to convert the kyanite into other forms of alumino-silicate and/or silica, said forms having a lower specific gravity than kyanite, and wherein the wet gravity separator is adapted to receive, from the calcining means, mineral sands material calcined to convert the kyanite into said other forms of alumino-silicate and/or silica and is operable to achieve a wet gravity separation of zircon from alumino-silicate which is enhanced by said M lower specific gravity.

W:\mary\MMHNODEL\42830-97.doc 6a Preferably the calcining means is a rotating drum kiln. Alternatively the calcining means is a fluidised bed.

a 0 a a.

a a a a a U a a a a a a a W:\maryWMMHNODEL\4283G-97.dOc Advantageously the apparatus includes at least one electrostatic separator for separating electrically conductive components of the mineral sands such as ilmenite, leucoxene, and rutile from electrically non-conductive components including said zircon and alumino-silicate tailings.

Typically the apparatus includes a plurality of said electrostatic separators including both electrostatic plate separators and high tension roll separators.

Typically the wet gravity separator is a spiral concentrator, a wet table or a Kelsey centrifugal jig.

In one embodiment the calcining means is positioned downstream of the wet gravity separator.

In an alternative embodiment the calcining means is positioned downstream of said electrostatic separator and upstream of said wet gravity separator.

In a further alternative embodiment the calcining means is positioned upstream of said electrostatic separator.

An advantage of the present invention is the recovery of a greater proportion of S"zircon contained in mineral sands. A further advantage is the creation of a potential new calcined aluminosilicate product.

A process for separating zircon from kyanite containing mineral sands in accordance with this invention may manifest itself in a variety of process configurations. It will be convenient to hereinafter describe two particular configurations in detail with reference to the accompanying drawings. It is to be understood however that the specific nature of these embodiments does not supersede the generality of the preceding description. In the drawings: Figure 1 is a schematic flow sheet of a typical process for beneficiating rutile containing mineral sands; MR C:\WINWORD\MARY\NODELETE\MMHNODEL\42830.DOC 8 Figure 2 is a phase diagram of the A1 2 03-SiO2 system; Figure 3 is a schematic flow sheet of a process for beneficiating mineral sands in accordance with a first embodiment of this invention; and Figure 4 is a schematic flow sheet of apparatus for beneficiating mineral sands in accordance with a second embodiment.

Figure 5 is a graph showing the effect of temperature and time on the extent of transformation of kyanite to mullite.

from a mine are dried and then passed through a series of electrostatic separation stages 2. These separate the mineral into electrically conductive components 3 containing Ilmenite, leucoxene and rutile and non-conductive components 4 containing zircon and alumino-silicate tailings including kyanite quartz and silica.

Typically the electrostatic separation stages consist of a number of individual electrostatic separation units. These units can be either electrostatic plate separators or high tension roll separators and would be well known to persons skilled in the art and accordingly will not be described in further detail here.

The non-conductive components are then passed into a screening circuit where they are separated into a coarse and a fine fraction. The details of the screening circuit do not affect the scope of the invention and the invention should accordingly not be limited by this detail.

The screened mineral is then passed into a wet gravity circuit separator 5 which relies on exploiting the difference in specific gravity of respective minerals (i.e.

zircon and alumino-silicates such as kyanite) to perform the separation. Typically the gravity separator 5 is selected from a number of different types of separator including but not limited to spiral trough concentrator, wet table concentrator or MR CAkWINWORD\MAR'MJODELETE\MMHNODEL\4283.DOC Kelsey centrifugal jig concentrator. Preferably, the gravity separator 5 is a spiral concentrator.

A spiral concentrator comprises a spirally extending open topped channel. When viewed in cross-section the channel is deeper towards the radially inner edge thereof and shallower towards the outer edge thereof. Particulate minerals to be processed are fed into the top of the spiral. As the minerals flow down the channel, the components of relatively higher density, e.g. zircon, tend towards the radially inner edge of the channel and components of relatively lower density, e.g. silica and quartz tend towards the radially outer edge of the channel. A plurality of openings are located at spaced intervals along the length of the channel to permit the high io o density components to exit the channel. By contrast the lower specific gravity components travel down the full length of the spiral channel and are discharged at the bottom. The structure and function of spiral concentrators would be well known toto 15 to persons skilled in the art and shall not be described in further detail.

Alternatively the wet gravity separator might be a wet table. The structure and to 0functioning of wet tables would be well known to persons skilled in the art and shall not be described in further detail.

Further alternatively the wet gravity separator might be a Kelsey jig. The Kelsey jig is a relatively new apparatus in which a mix of high and low specific gravity minerals are passed over a bed of material of intermediate specific gravity under high centrifugal acceleration. High specific gravity minerals eg zircon pass through the bed and low specific gravity minerals eg kyanite and silica pass over the bed to a tailings stream. The Kelsey jig would be well known to persons skilled in the art and will not be described in further detail.

Zircon 6 is recovered as a product from the gravity separator 5 and the aluminosilicates, such as kyanite and quartz are rejected as tailings. The separator 5 is designed to have a conservative specific gravity split because the product zircon 6 is required to be substantially free of kyanite (not more than 0.42 weight percent).

MR CAXWINWORD\MARY\NODELETE\MMHNODEL\42830.DOC Thus some zircon value is lost in the tailings which is a major limitation or shortcoming of the prior art apparatus illustrated in Figure 1.

The wet concentrate from the wet gravity separation containing predominantly zircon mineral is then dried and passed through a further series of electrostatic and magnetic separation stages. These stages remove remaining amounts of magnetic minerals (monazite, leucoxene, tourmaline, staurolite etc.) and conductive minerals (predominantly rutile). This allows a product grade zircon mineral to be manufactured.

Three embodiments of apparatus and processes in accordance with the invention are discussed below. Figure 3 illustrates apparatus in accordance with one embodiment of the invention. Unless otherwise indicated, the same reference numerals will be used to refer to the same components as in Figure 1.

The major difference between the Figure 1 apparatus and the Figure 3 apparatus is II* I the treatment of non-conductive components between the electrostatic separator 2 and the wet gravity separator The components 4 are fed into a kiln 9. The kiln 9 is in the form of a rotating drum having an inlet at one end thereof and an outlet at an opposed end thereof. The kiln 9 is arranged to slope downwardly from the inlet to the outlet so as to progressively advance the sands 4 from the inlet to the outlet. Typically the residence time of the sands 4 within the kiln 9 would be about 1 hour.

The sands 4 are calcined in the kiln 9 at 1300 1400 0 C for about one hour which causes the kyanite to decompose into mullite and silica. Mullite and silica have specific gravities in the range of 3.1 g/cm 3 3.3 g/cm 3 Thus the specific gravity of what was kyanite is effectively reduced from 3.7 g/cm 3 to 3.1-3.3 g/cm 3 The phase changes in the kyanite can be traced on the A120 3 -SiO2 equilibrium phase diagram illustrated in Figure 2. Kyanite has a composition of 50% A1 2 0 3 and Si02. As the temperature of the kyanite is increased from 800 0 C to 1050 0 C it MR C:\WINWOROkMARY\NODELETE\MMHNODEL\4283.DOC 11 passes through the phase boundary illustrated in the phase diagram and the transformation to mullite and silica commences. With sufficient time all the kyanite will be transformed into mullite and silica. When the mineral is cooled it remains as mullite and silica.

Calcined material issuing from the rotating kiln 9 is then passed into wet spiral concentrators 5 to separate the zircon from the alumino-silicates. Product zircon passes out of the separator outlets for high density components, and aluminosilicates are discharged separately at the bottom of the spiral. The transformation of the kyanite (to lower density alumina-silicate) in the minerals passed through the wet gravity separator improves the efficiency of the wet gravity separation and thereby the level of recovery of zircon as a product.

Figure 4 illustrates apparatus in accordance with a second embodiment of the invention. Unless otherwise indicated the same reference numerals refer to the same components as in Figure 3.

The major difference between the Figure 4 embodiment and the Figure 3 embodiment lies in the location within the circuit flow diagram of the calcination step. In this embodiment the calcination process treats the combined tailings °stream 7 from the existing wet gravity separation process. The calcined mineral is then passed to an additional gravity separation process using established prior art wet gravity separation techniques. The zircon product from this wet gravity separation can then be either added to the existing zircon products or recycled to an earlier processing stage (as shown in Figure The alumino silicate material from this wet gravity separation (calcined kyanite) would either be used as a product grade material or disposed of as a conventional tailings stream.

The advantage of the Figure 4 configuration is that the volume of material which has to be calcined is substantially lower than that for the Figure 3 embodiment. As a result the energy required to perform the calcination is substantially lower with the attendant cost savings.

MR C:\WINWORD\MARYWODELETEXMMHNOEL\4263.DOC A further possible configuration (not illustrated) would be to calcine all the mineral sands 1 before they pass into the electrostatic separator 2. This configuration would include calcining the ilmenite and rutile compounds as well. The calcination would be carried out in a reducing atmosphere which would confer the additional benefit of improving the electrical conductivity of rutile and ilmenite which in turn would improve the recovery of ilmenite and rutile in the electrostatic separator.

The influence of temperature on the rate of transformation from kyanite to mullite and silica is significant. To this end experimental tests were carried out to determine the effect of temperature on the transformation extent of the kyanite mineral. The findings are show diagrammatically in Figure 5. With reference to Figure 5, the composition of the raw material before calcination was 55.5 wt% .kyanite, 23.9 wt% zircon, 3.3 wt% rutile, 7.9 wt% quartz and 9.5 wt% corundum.

The squares indicate no decomposition of kyanite, open circles indicate partial decomposition and closed circles indicate complete decomposition. Figure 5 shows that the required treatment time to gain 100% transformation of kyanite mineral to mullite changed from 2 minutes at 14500C to 180 minutes at 1325C. The transformations were determined by X-ray diffraction analysis of the calcined :minerals.

The rate of decomposition of kyanite is also influenced by particle size, i.e. exposed surface area of particles. The larger the surface area, the greater is the rate of transformation.

Some laboratory scale test work was done putting the invention into practice. Two samples, namely sample 1 and sample 2, were taken from appropriate streams at the Tiwest plant. Each of the samples was divided into an untreated portion which was used as reference material and several "treated" portions which were subjected to heat treatment and other analysis.

The treated portions of samples 1 and 2 were heated to a temperature greater than 1300°C for 1 hour in a muffle furnace. The minerals were contained in a crucible MR C:\WINWORD\MARY\NODELETE\MMHNO0EL\42830.DOC

C

13 and a treatment gas was supplied into the bottom of the crucible. Three treatment gases were used, namely neutral (nitrogen), reducing (hydrogen) and oxidising (air).

The specific gravity of the treated samples was measured using a gas Pycnometer and compared with the specific gravity of the untreated sample. The results are summarised in Table 1 below.

TABLE 1 SAMPLE 1: S.G. Inferred Kyanite S.G. Relative S.G.

Untreated mineral 4.03 3.65 1.36 Heat treated mineral 3.84 3.35 1.53 Heat treated mineral 3.83 3.32 1.55 Heat treated mineral 3.84 3.34 1.54 SAMPLE 2: S.G. Inferred Kyanite S.G. Relative S.G.

Untreated mineral 4.31 3.65 1.36 Heat treated mineral 4.20 3.44 1.48 The inferred kyanite specific gravity is the specific gravity calculated for kyanite on the assumption that no compositional change occurs in the sample during the heat treatment and that the other minerals present, e.g. zircon and rutile do not undergo any significant specific gravity change.

As the above results show, the heat treatment reduces the specific gravity of the kyanite by 0.2 to 0.33 g/cm 3 to about 3.34 g/cm 3 As mullite the final decomposition product has a specific gravity of 3.16 g/cm 3 the conversion of kyanite to mullite is of the order of about 66%. The above results also show that the heat treatment increases the relative specific gravity of the minerals by approximately 0.12 to 0.18. As discussed in the initial part of the specification, this is substantially more favourable for wet gravity separation.

MR C:\WINWORD\MARy(tODELETE\MMHNODEL283.DOC 13a The above findings have been confirmed by dense liquid analysis of 100% transformed mineral. The dense liquid analysis was conducted at increments of 0.1 g/cm 3 over the range 3-3.8 g/cm 3 The kyanite mineral prior to calcination was found to report to the 3.6-3.7 specific gravity range fraction. Once calcined the mineral however reported to the 3.0-3.1 and 3.1-3.2 specific gravity ranges. These results are in excellent agreement with published specific gravity data for natural kyanite and mullite respectively.

An X-ray diffraction analysis was carried out on the samples that were subjected to the heat treatment. The X-ray diffraction trace showed zircon as the major phase.

The trace also showed unreacted kyanite indicating incomplete transformation of *this mineral, as well as decomposition products mullite and silica.

a MR C:\WINWORO\MARY\NODELETE\MMHNODEL2830.DOC -14- An optical microscope analysis was carried out on the samples to show the structural changes in the grains brought about by the heat treatment. The kyanite grains became frosted by the heat treatment and showed significant cracking through the grains. By contrast the shape and structure of the zircon grains was unchanged by the heat treatment, although the treated grains exhibited a cleaner appearance. Overall the heat treatment caused the minerals to change colour from a buff colour to a white or grey colour.

An electron microscope analysis was also carried out to confirm the structural io transformation occurring within the mineral grains during heat treatment. The micrographs showed substantial cleavage cracks caused by expansion of the kyanite mineral grains. Closer imaging showed crystal growth on the mineral surfaces extending into the mineral interiors. The zircon mineral grains did not undergo any observable change as a result of the heat treatment.

Those treated and untreated portions of the two samples were passed across a small wet table to assess the effect of heat treatment upon the efficiency of wet gravity separation. The results showed that the treated minerals were separated more efficiently than untreated minerals. The results indicated that heat treatment would provide at least a 10 to 20% improvement in the efficiency of the wet gravity separation process.

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JB C:\WNWORDUJENNYVNODELETE\PO3207.DOC TABLE 2 SAMPLE 1: Recovery in Zircon Stream Schultz ZrO 2

AI

2 0 3 Efficiency Untreated mineral 45.7 9.2 36.6 Heat treated mineral 69.4 17.0 52.4 SAMPLE 2: Recovery in Zircon Stream Schultz ZrO 2

AI

2 0 3 Efficiency Untreated mineral 23.2 11.5 11.8 Heat treated mineral 57.9 8.4 49.4 a a a a. a

SS

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The recovery of rutile to the stream of conductive as opposed to non- 5 conductive material in an electrostatic separator was also enhanced by the heat treatment. By contrast the recovery of zircon mineral to the conductors was unaffected by the heat treatment.

Of the three atmospheres used for the heat treatment, namely reducing, 0o oxidising, and neutral, the reducing atmosphere gave the best overall improvement in the recovery of rutile.

An advantage of the method described above with reference to Figs 3 and 4 is that it enables the recovery of zircon to be substantially increased which will inevitably lead to better overall plant performance. Further the method can be implemented at reasonable cost by making relatively straight forward modifications to existing plant.

JB C:\WINWORDJENNY\NODELETE\PO3207.DOC -16- A further advantage of calcining kyanite containing mineral sands is that the magnetic susceptibility of the kyanite is increased by calcining under reducing conditions. This creates the potential to also separate the kyanite from other non-magnetic minerals by magnetic separation methods.

It is to be understood that various alterations, modification, and/or additions may be introduced into the constructions and arrangements of the components previously described without departing from the ambit of the invention disclosed herein.

JB C:\WINWORDUENNY\NODELETE\PO3207.DOC

Claims (20)

1. A process for treating zircon and kyanite containing mineral sands, the process including, inducing the kyanite to undergo a phase change to change to another form of alumino-silicate and/or silica having a lower specific gravity than kyanite thereby to increase the difference in specific gravity between zircon and the other components of the mineral sands.

2. A process according to claim 1, including the further step of separating the zircon from the other components in a wet gravity separation process.

3. A process according to claim 2, wherein said step of inducing the kyanite to undergo a phase change includes heating the mineral sands to a temperature of at least 1060 0 C until the kyanite changes to another form of alumino-silicate and/or silica.

4. A process according to claim 3, wherein said step of heating the mineral sands comprises calcining mineral sands at a temperature of at least 1300°C *for at least one hour.

5. A process according to claim 4, wherein the mineral sands are calcined in a rotating drum kiln.

6. A process according to claim 5, wherein the rotating drum kiln is 25 arranged to slope down from an inlet located towards one end thereof to an outlet located towards an opposed end thereof, so as to progressively advance the particulate material through the kiln from the inlet to the outlet.

7. A process according to claim 5, wherein the mineral sands are calcined in a fluidised bed. W:\mary\MMHNODEL\42830-97.doc -18-

8. A process according to any one of claims 4 to 7, wherein the mineral sands are calcined in a reducing atmosphere.

9. A process according to any one of claims 2 to 8, wherein the step of separating the zircon from the other components is carried out in a spiral concentrator, a wet table, or a Kelsey centrifugal jig. A process for the beneficiation of particulate mineral sands, including: passing electrically non-conductive components of the mineral sands such as zircon and alumino-silicate tailings including kyanite through a wet gravity separator to separate the zircon from the alumino-silicate tailings including kyanite; and calcining at least the alumino-silicate tailings to convert the kyanite into other forms of alumino-silicate and/or silica having a lower specific gravity than kyanite to make it more susceptible of separation from zircon in a wet gravity separator.

11. A process for the beneficiation of particulate minerals and according to claim 10, further including the step of passing the particulate mineral sands 20 through an electrostatic separator prior to said step of passing the non- 'conductive components through a wet gravity separator, to separate electrically conductive components such as ilmenite, leucoxene and rutile from the electrically non-conductive components. 25 12. A process for the beneficiation of particulate mineral sands according to claim 10 or claim 11, wherein the alumino-silicate tailings issuing from the wet gravity separator are subjected to said step of calcining, and wherein the tailings issuing from said calcination step are passed through a further wet gravity separator to separate any zircon remaining in the alumino-silicate tailings from the remainder of the alumino-silicate tailings. JB C:\WINWORD\JENNY\NODELETE\PO3207.DOC -19-

13. A process for the beneficiation of particulate mineral sands according to claim 12, wherein all the electrically non-conductive components of the mineral sands issuing from the electrostatic separator are subjected to said step of calcining, prior to being passed through the wet gravity separator.

14. A process for the beneficiation of particulate mineral sands according to claim 12, wherein all of the mineral sands to be beneficiated are subjected to said step of calcining before said mineral sands are passed through the electrostatic separator. Apparatus for the beneficiation of zircon- and kyanite-containing mineral sands material, including: a wet gravity separator; and calcining means; wherein the calcining means is operable to calcine the mineral sands material at a temperature and for a period of time sufficient to convert the kyanite into other forms of alumino-silicate and/or silica, said forms having a lower specific gravity than kyanite, and wherein the wet gravity separator is adapted to receive, from the calcining 20 means, mineral sands material calcined to convert the kyanite into said other forms of alumino-silicate and/or silica and is operable to achieve a wet gravity separation of zircon from alumino-silicate which is enhanced by said lower specific gravity. *eo. 25 16. Apparatus according to claim 15, wherein said calcining means is a rotating :drum kiln.

17. Apparatus according to claim 15, wherein said calcining means is a fluidised bed.

18. Apparatus according to any one of claims 15 to 17, further including at least one electrostatic separator for separating electrically conductive components of the mineral sands such as ilmenite, leucoxene, and rutile from electrically Snon-conductive components including said zircon and alumino-silicate tailings. W:\maryMMHNODEL\42830-97.doc

19. Apparatus according to claim 18, including a plurality of said electrostatic separators and wherein said electrostatic separators include both electrostatic plate separators and high tension roll separators.

20. Apparatus according to any one of claims 15 to 19, wherein said wet gravity separator is a spiral concentrator, a wet table or a Kelsey centrifugal jig.

21. Apparatus according to any one of claims 15 to 20, wherein said calcining means is positioned downstream of the wet gravity separator.

22. Apparatus according to claim 18 or claim 19, wherein said calcining means is positioned downstream of said electrostatic separator and upstream of said wet gravity separator. 15 23. Apparatus according to claim 18 or claim 19, wherein said calcining 0* *b means is positioned upstream of said electrostatic separator.

24. A process for treating zircon and kyanite containing mineral sands substantially as herein described with reference to Figs. 3 and 4. A process for the beneficiation of particulate mineral sands substantially as herein described with reference to Figs. 3 and 4. 6600

26. Apparatus for the beneficiation of particulate mineral sands substantially 25 as herein described with reference to Figs. 3 and 4. DATED: 24 October, 1997 PHILLIPS ORMONDE FITZPATRICK Attorneys for: TIWEST PTY LTD JB C:\WINWORDUENNY\ODELETE\PO3207.DOC