AU776607B2 - Separation of zircon from alumino-silicates - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicants: K.M.C.C. Western Australia Pty Ltd and Yalgoo Minerals Pty Ltd Actual Inventor(s):

DAVID

C. *c Address for tN, ANDREW STRUTHERS, ANNETTE ELLIOTT PI mLLIPS oRMGNDE FITZPATRICK Patent and Trade Mark Atorncys z 367 Collins Street ev/ 7 Ml..bourne 3000 AUSTRALIA el-. 'c.

rco o w Invention Title: -71 SEPARATION OF ZIRCON FROM ALUMINO-SILICATES Our Ref: 628551 POF Code: 285937/324034, 324042 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 2 SEPARATION OF ZIRCON FROM ALUMINOSILICATES This application is an application for Patent of Addition to Patent No. 725713, the entire disclosure of which is incorporated herein by reference.

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 i!menite nrti!e, zircon, !eucoxene and a!umino-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 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 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 aluminosilicates such as kyanite, and quartz which form the tailings.

wMARYUMMHNODELETE828SS1.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: 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 electrostatic magnetic separation is conducted on the concentrated valuable mineral streams to remove remaining conductive or magnetic S. 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 alumino-silicate 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% A1 2 0 3 the zircon/tailings split is arranged accordingly and is very conservative. As a result valuable zircon product is currently being lost in the wMARYUWMHNOOELETEW52BS1 .doc tailings. As zircon represents 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 -SiO 2 phase diagram is annexed hereto as Figure 2. This diagram is typical of those shown in various publications detailing the A1 2 0 3 -SiO 2 system.

The kyanite form of alumino-silicate has a composition of about 50 Mol% SiO 2 and 50 Mol% A1 2 0 3 The phase change which occurs when kyanite is calcined at a temperature in the region of 1300 0 C to 1400 0 C can be traced on the phase diagram. In summary kyanite undergoes crystalline transformation to mullite and silica.

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 Australian Patent No. 725713 discloses an inventive process for treating zircon and kyanite containing mineral sands, the process including, inducing the kyanite to undergo a phase 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. Advantageously the process includes the further step of separating the zircon from the other components in a wet gravity separation process.

i According to the present 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, said process including the further step of separating zircon from the other components using one or more dry classification techniques.

Accordingly, the present inventors have made a modification to the inventive process of AU 725713. In the modified process, zircon is separated from the other components of the mineral sands by one or more dry separation wMARYMMHNODELETE828551.doC techniques, such as dry gravity separation, possibly in combination with a dry screening process. Accordingly, the inventors have discovered that the lowering of specific gravity of kyanite by the phase change to aluminosilicate and/or silica not only improves the degree of separation of kyanite from zircon using wet classification techniques but also improves separation using dry classification techniques. Examples of suitable dry classification techniques include air tables, air screens, air slides and conventional dry screening techniques.

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 dry gravity separator. The reduction in specific gravity of the kyanite mineral is accompanied by an increase in particle size due to swelling of the mineral grains. This increase in kyanite particle size also acts to improve the separation efficiency of the zircon and kyanite by processes which exploit differences in particle sizes.

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 1400 0 C. 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 (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.

Preferably the 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. Advantageously the step of heating the mineral sands comprises calcining mineral sands at a temperature of at least 1300 0 C for at least one hour. The structure of the zircon is not appreciably changed by the heat treatment.

w MARYMMHNOOELETi2851 .do 6 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 outlet.

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 conditions. This may allow further removal of kyanite from zircon by magnetic separation methods.

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 using dry classification techniques.

Typically, the wet gravity separator is selected from a spiral concentrator, a wet table and a Kelsey centrifugal jig.

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.

.MARYMKMHNODELETE28551.doc 7 In one embodiment the alumino-silicate tailings issuing from the wet gravity separator are subjected to said step of calcining, and the minerals issuing from said calcination step are subjected to dry classification techniques 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 subjected to dry classification techniques.

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.

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: dry classification apparatus; 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 dry classification apparatus 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 dry gravity separation of zircon from alumino-silicate which is enhanced by said :lower specific gravity.

Preferably the calcining means is a rotating drum kiln. Altematively the calcining means is a fluidised bed.

Advantageously the apparatus includes at least one electrostatic separator for separating electrically conductive components of the mineral sands such as MARYAMHNODELETE828551.doC 8 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.

The apparatus may further include a wet gravity separator. The wet gravity separator may be positioned downstream of said at least one electrostatic separator.

Typically the dry classification apparatus is an Air table (or Bed Type Pneumatic Concentrator), Air Screen or Air Slide which may be used in conjunction with conventional dry screening. Descriptions of these apparatus are provided below.

Air tables, or Bed Type Pneumatic Concentrators typically include a porous supporting surface for particulate material and the surface is inclined from a feed end to a discharge end. Air is blown upwardly through the bed of particulate material and flows through the interstices between the mineral particles, creating flow of the material bed mass. The air flow causes segregation of the material bed, with the denser and coarser fraction tending to migrate towards the base of the bed and lighter, finer fraction migrating towards :the upper surface of the bed. The respective fractions are then laterally separated, such as by pulsing or shaking the bed and/or adjusting air flow rates through the length of the bed and/or use of longitudinal riffles, together with possible adjustment of the cross bed inclination. This results in the coarser/heavier fraction concentrating towards one lateral side of the bed and :the finer/lighter fraction concentrating towards the other side.

Air screens rely upon the simple impulse of an air stream across a stream of falling particles. The finer/lighter particles are deflected more by the air stream than the coarser/heavier particles, thereby effecting separation.

wMARY%*AKNOOELETE~fi~.dx While the above dry gravity separators are generally an effective means of classifying particles, fine heavy particles will tend to mix with coarse light particles. In order to separate these fractions, conventional dry screening is preferably also employed after the dry gravity separation.

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 the dry 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 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; Figure 2 is a phase diagram of the A1 2 0 3 -SiO 2 system; Figure 3 is a schematic flow sheet of a process for beneficiating mineral sands •in accordance with a first embodiment described in parent case AU 725713; WMARYMRMNODELETE%88G1.*c Figure 4 is a schematic flow sheet of apparatus for beneficiating mineral sands in accordance with a second embodiment described in parent case AU 725713; Figure 5 is a graph showing the effect of temperature and time on the extent of transformation of kyanite to mullite.

Figure 6 is a schematic flow sheet of a process for beneficiating mineral sands in accordance with the present invention.

Figure 7 shows typical release curves for the dry gravity separation of calcined and uncalcined minerals.

Referring to Figure 1, which illustrates a known prior art process, wet mineral sands 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 exploits the difference in specific gravity of respective minerals zircon and I 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 w.UARYMMHNODLETMC825 IoC 11 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 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 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 functioning 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 S: 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 a S' 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 .MARYM ,,oMaETE'4sML.dOC 12 weight percent). 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 conductive minerals (predominantly rutile) and magnetic minerals (monazite, leucoxene, tourmaline, staurolite etc.).

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 described in AU 725713. 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 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 S. 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.

e The sands 4 are calcined in the kiln 9 at 1300 1400°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 wMARYUJMHNOOELETE8251 .doc 13 The phase changes in the kyanite can be traced on the A1 2 0 3 -SiO 2 equilibrium phase diagram illustrated in Figure 2. Kyanite has a composition of 50 mol A1 2 0 3 and 50 mol SiO 2 As the kyanite is heated from 800 0 C to 1050 0 C it 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 alumino-silicates 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 described in AU 725713. 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 *s 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

S

be used as a product grade material or disposed of as a conventional tailings stream.

S

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.

wMARY\MMHNOOELETE128S51doc 14 As a result the energy required to perform the calcination is substantially lower with the attendant cost savings.

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 wt% corundum. The squares indicate no decomposition of kyanite, open circles ***indicate partial decomposition and closed circles indicate complete 20 decomposition. Figure 5 shows that the required treatment time to gain 100% transformation of kyanite mineral to mullite changed from 2 minutes at 1450 0

C

o*oo to 180 minutes at 1325 0 C. 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 o. the rate of transformation.

Laboratory scale test work was conducted 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.

-ARYMMYVX4NOMELE7TVJQ5c' The treated portions of samples 1 and 2 were heated to a temperature greater than 1300 0 C for 1 hour in a muffle furnace. The minerals were contained in a crucible 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 I 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 wMARYWkMXNOOELETFE82B55.dOC 16 approximately 0.12 to 0.18. As discussed in the initial part of the specification, this is substantially more favourable for wet gravity separation.

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.

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 20 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 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 wMARYMMHNOCELETE\28B5I.doc 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.

TABLE 2 SAMPLE 1: Recovery in Zircon Stream Schultz Zr02 A1 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 Zr0 2 A1 2 0 3 Efficiency Untreated mineral 23.2 11.5 11.8 Heat treated mineral 57.9 8.4 49.4 The recovery of rutile to the stream of conductive as opposed to non-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, 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.

wM*RYWAMHNOELETE2851I.doc 18 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.

Example The following is a description of an embodiment of the process of the present invention with reference to Figures 6 and 7 of the accompanying drawings.

Approximately 1 tonne of a mixed tailings feed 10 was subjected to wet gravity separation (12) in rougher (12a), cleaner (12b). scavenger (12c) and mids (12d) spiral stages. The offstreams from the rougher (12a), cleaner (12b) and scavenger (12c) spiral stages are collected in pump sump 13 and then pumped to the mids (12d) spiral separator. The wet gravity separation resulted in removal of quartz from the mixed tailings feed, leaving a mineral concentrate (16) and quartz rich tails The respective compositions of the feed material concentrate (16) and tails (14) are provided in Table 3.

wrMARY\MMHNOOELETEM82851doc 9* 19 TABLE 3 Wt(kg) Wt% Ilmenite Rutile Leucoxene Zircon Monazite Staurolite Kyanite Tourmaline Spinel Goethite Corundum Quartz Other Feed 1061 1.00 0.53 1.51 0.05 11.73 0.04 10.98 39.57 3.33 3.72 0.00 1.11 26.23 1.24 Concentrate: Grade 465.5 43.9% 0.7% 3.0% 0.0% 24.7% 0.1% 13.3% 47.5% 0.8% 5.3% 0.0% 2.3% 1.0% Recovery 43.9% 62.1% 86.2% 0.0% 92.3% 85.7% 53.1% 52.6% 10.0% 62.5% 0.0% 90.5% 1.7% 52.7% Tails: Grade 595.5 56.1% 0.4% 0.4% 0.1% 1.6% 0.0% 9.2% 33.4% 5.3% 2.5% 0.0% 0.2% 45.9% Recovery 56.1% 37.9% 13.8% 100% 7.7% 14.3% 46.9% 47.4% 90.0% 37.5% 0.0% 9.5% 98.3% 47.3% w.MARY'IMHNOELETEa2851 .d0oc Table 3 demonstrates that a large proportion (approximately 98%) of quartz was removed from the feed material to tails while the majority of zircon (approximately 92%) was retained in the concentrate. Furthermore, approximately 47% of the kyanite was rejected to tails 14 also.

The concentrate 16 was fed to a drier 18 and the dried concentrate was passed to a magnetic separator 20, which could be selected from a number of types induced roll, semi lift, permaroll etc., all of which would be understood by a person skilled in the art. Magnetic material 22 was removed from the concentrate and also rejected to tails Removal of the strong and slightly magnetic materials is beneficial in that it reduces the tonnage of material to be subsequently calcined as well as precluding the significant detrimental effect that magnetic minerals can have on the calcination process.

Non-magnetic minerals (24) are passed through an electrostatic separator (26), selected from any of a number of known separation devices which exploit differences in the electrical characteristics of minerals to effect separation of those minerals. An example of a separation device is an UltraStat high tension separator. However, the invention is not limited to a particular type of separation device. Non-conductive materials (28) (predominantly quartz) are passed to tails 14. Conductive materials (30) (predominantly TiO 2 containing) are also removed to tails Removal of both conductive and non-conductive materials further reduces calcination tonnage and removes minerals problematic to the calcination process.

The middling fraction which typically contains the majority of zircon and kyanite minerals, is fed to the calcination furnace Calcination was conducted at 1400°C for a residence time of 20 minutes, under essentially S"similar conditions as described previously in relation to the embodiments of AU i 30 725713.

The calcined material (36) is fed to a sinter screening step (38) and then to a combination of dry separation techniques. Initially, the material is fed to an air table rougher (40) which separates the material into kyanite-derived tails (42), w.MARY'IAMHNODELETE 1 .dDOC 21 zircon rich concentrate (44) and mids The kyanite rich tails (42) are subjected to dry screening (48) and the plus 180 pm fraction (50) is collected as calcined kyanite product The minus 180 pm fraction is passed to another air table (54) for further classification of fine and mid fractions. The zircon rich concentrate (44) is subjected to dry screening The minus 350 pm fraction (58) is collected as zircon product whereas the plus 350 pm fraction (62) is passed to another air table (64) for classification of coarse and mid fractions.

The mids (46) are screened with dry screen The plus 250 pm fraction (68) is passed to air table (64) for processing as previously described. The minus 250 p m fraction (70) is passed to air table (54) for processing as previously described.

The use of dry classification techniques after calcination has advantages over wet gravity separation. Dry classification does not require the classified product to be dried prior to shipment, as is the case with wet gravity separation. The drying stage can be expensive in terms of capital and operating costs. The dry classification of calcined material can separate kyanite derived material from zircon as effectively as wet gravity separation, as is evident in Figure 7.

Figure 7 shows typical release curves for the dry gravity separation of calcined and uncalcined minerals. It is a plot of the cumulative recovery of a particular mineral to the concentrate versus the cumulative total recovery of all minerals to the concentrate fraction and shows a comparison of a single pass across an air table for calcined (solid lines) and uncalcined (dashed lines) material.

Additionally in Figure 7 a plot of the calculated Shultz separation effeciency is included. This is calculated by subtracting the cumulative recovery of the undesired mineral (kyanite) in the concentrate fraction from the desired mineral (zircon) recovery. Viewed simply the efficiency is simply a measure of the gap between the zircon and kyanite release curves at any given total mineral cumulative recovery to the concentrate. The higher the value of the calculated separation efficiency, the easier separation of the two minerals can be achieved.

wMARYWWMHNODELETEi828551doc In Figure 7, the peak separation efficiency for raw minerals is achieved at a total mineral recovery of -37% with only -42% of the zircon being recovered to the concentrate. However associated with the zircon approximately 11% of the kyanite is also recovered to the concentrate. By comparison the peak separation efficiency for calcined minerals of 58% is reached at a total mineral recovery of around 55%. Recovery of kyanite at this point is lower at around 7% also.

It is therefore clear that the calcination process improves the peak separation efficiency of the process, improves the total mineral recovery to the concentrate and also improves grade considerations of the products. A significant feature of Figure 7 is that the curves for the zircon mineral are relatively unchanged after calcination. However the release curves for the kyanite minerals are significantly displaced after calcination, reflecting the improved separation efficiency arising from the kyanite transformation into the compounds having reduced specific gravity.

Figure 7 can also be further used to estimate product grade data for the mineral separation at any point in the separation process.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.

°I•.O

wMA*RYWUMNOELETEeB51Moc

Claims (26)

1. 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 and/or particle size between zircon and the other components of the mineral sands, said process including the further step of separating zircon from the other components using one or more dry classification techniques.

2. A process according to claim 1, wherein said one or more dry classification techniques are selected from air tables, air screens, air slides and dry screening techniques.

3. A process according to claim 1 or 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.

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 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. wMARYVMHNODELETEZ8551 .doc 24

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 claim 3, wherein the step of heating the mineral sands comprises calcining mineral sands at a temperature of at least 1400°C for at least 20 minutes.

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 dry classification process.

11. A process for the beneficiation of particulate minerals and according to claim 10, further including the step of passing the particulate mineral sands S 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.

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 subjected to a dry classification process to separate any zircon remaining in the alumino-silicate tailings from 30 the remainder of the alumino-silicate tailings.

13. A process for the beneficiation of particulate mineral sands according to claim 12, wherein all the electrically non-conductive components of the mineral wMARY\MMHNODELETE82S651.doc sands issuing from the electrostatic separator are subjected to said step of calcining, prior to being subjected to dry classification process.

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: dry classification apparatus; 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 dry classification apparatus 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 S 20 dry gravity separation of zircon from alumino-silicate which is enhanced by said lower specific gravity.

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 *foe.: 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. wrMARYMMHNODELETEa28551 .doc 26

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, further including a wet gravity separator, preferably selected from 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 dry gravity separator.

23. Apparatus according to claim 18 or claim 19, wherein said calcining means is positioned upstream of said electrostatic separator. **S

24. A process for treating zircon and kyanite containing mineral sands 20 substantially as herein described with reference to Figs. 6 and 7. 0* 0 0

25. A process for the beneficiation of particulate mineral sands substantially as herein described with reference to Figs. 6 and 7.

26. Apparatus for the beneficiation of particulate mineral sands substantially as herein described with reference to Figs. 6 and 7. DATED: 19 December 2000 30 PHILLIPS ORMONDE FITZPATRICK Patent Attorneys for: K.M.C.C. WESTERN AUSTRALIA PTY. LTD. and YALGOO MINERALS PTY. LTD. w:MARY\MMHNOOELETE82855i.doc