Mineral sands deposits are typically formed as a result of coastal marine sedimentary processes and are found in unconsolidated fossil shorelines up to hundreds of kilometres inland from present coastlines.

A link exists between marine erosion and mineral sand deposits where wave and current action creates conditions in which lighter sand particles are transported more readily than heavier mineral sands particles, creating a build up of mineral sands. Mineral sands are supplied to the coast through rivers draining the hardrock hinterland. The size of mineral sand deposits vary, but are typically 100 or 200 metres wide, 5 to 20 me res thick and 2 to 20 kilometres long.

Most mineral sand deposits were formed between 1.8 and 12 million years ago. During this period immense changes in the sea levels resulted in repeated reworking of sediments deposited by rivers in coastal shorelines. The composition of mineral sand deposits reflects the type of rocks from which the sands containing the heavy minerals derive.

The mineral sands industry consists of two core product streams:
•Titanium dioxide minerals - in the form of rutile, ilmenite and leucoxene. Ilmenite is also used to manufacture titanium slag and synthetic rutile products; and
•Zircon

Mineral sands deposits are characterised by their grade (the percentage of HM found in a deposit) and their assemblage (the relative proportion of valuable HM components of ilmenite, rutile and zircon). The typical composition of a mineral sands deposit has a HM grade ranging from 0.5 per cent to above 20 per cent. The differing grades and assemblage characteristics can influence the relative cost and value stream of product produced from any specific deposit.

Mining commences with land clearing activity, where any millable timber is harvested, and the rest is used for fencing, firewood or chipped for use in dust suppression or rehabilitation. Topsoil and subsoil is stripped and stockpiled separately from the underlying overburden material.

The inherent seed bank is maintained to prevent potential sterilisation from saline soils. Overburden is removed and stockpiled for replacement at the end of the mine life. In previously mined areas it may be placed in adjacent previously mined pits or voids, or on sand tailings.

Iluka’s operations currently use dry mining techniques. These techniques vary across sites although, in all cases, the ore is deposited into a hopper, usually adjacent to the active mining area. The ore is fed to the hopper by front-end loaders, dozers, self-elevating scrapers, or trucks. Where appropriate, a consistent grade and quality of the mined ore is blended prior to being fed into the hopper.

If scrapers or dozers are being used, ore is mined from the top of the face to the toe of the face and across the face. If trucks are being used, ore is transported to a pad adjacent to the hopper and then a front end loader is employed to blend the ore, bucket by bucket.

The valuable mineral sands are only a small proportion of the total ore removed from the mining area, being mixed with clays, silts, quartz sand and rock.

Depending on the type of waste material associated with the ore, the primary separation may vary but, in general:
• material in the ore that is 150 millimetres (“mm”) or greater is screened out using vibrating grizzlies and returned to the mining pit;
• the mixture of mineral sand, quartz sand, clays, silts, and rock (less than 150mm) is passed through a rotating screen (trommel) where the clays, sand and silt are washed away from the rock;
• if the clay content is high or forms balls entrapping the mineral sand, it is passed through a similar rotating screen (a scrubber) prior to entering the trommel. In the scrubber the ore is subjected to high pressure water sprays. These break up the clay balls releasing the mineral sand.

The mineral sand, silt and clay mixture, now in a slurry form, is pumped to the wet concentrator.

Wet concentration is used to produce a high grade heavy mineral concentrate, containing titanium dioxide (rutile, ilmenite) and zircon, as well as other heavy minerals. As part of this process, ore is washed through a series of spiral separators that use gravity to separate the heavy mineral sands from the lighter quartz and clay. Attritioning and secondary concentration is also carried out to assist in upgrading the heavy mineral content of the mined ore.

Iluka’s concentrators vary in size from 200 to 1,200 tonnes per hour. The land-based concentrators are a modular design making them easy to assemble and disassemble to move around a site or to other sites.

Wet concentration produces a high grade heavy mineral concentrate, maximising the content of valuable mineral sand whilst minimising the amount of non valuable mineral (gangue).

The slurry of mineral sands, silts and clays is further screened at a smaller aperture to remove such gangue material as fine rock, tree roots, other organic matter and fine clay balls. It is imperative that this material is removed before passing into the next stage of the concentrator as much of the equipment used has fine apertures, pipes and cutters which could become blocked.

The slurry is pumped to a bank (or banks) of hydrocyclones. These remove very fine, predominantly clay and silt particles.

The underflow from the hydrocyclones is fed to a constant density (“CD”) tank. This is then pumped, at a constant density and feed rate (to optimise performance), to the distributors above the primary spirals in the wet concentrator.

The slurry then passes to the spiral banks where separation of heavy mineral from the quartz sand occurs through gravity separation. The spiral troughs are angled and the heavy mineral sand moves to the inside and the lighter gangue minerals to the outside of the trough as the slurry travels down the spiral. Repulpers on the spirals aid in the recovery process.

Iluka concentrators consist of the following spiral stages:
1. primary or rougher
2. middlings
3. cleaners
4. recleaner and/or upgrade and finally
5. scavenger

Heavy mineral concentrate from each stage passes on to the next upgrading stage to be further concentrated, middlings are usually recirculated, and tails scavenged to collect any left-over valuable heavy mineral.

Heavy mineral concentrate is stockpiled on site before being transported to the secondary concentrator or dry separation plant. It is stockpiled using dewatering cones or cyclone stackers. The concentrate is allowed to drain to minimise moisture before transportation.

The fine clay and silt minerals, previously separated by the hydrocyclones are mixed with flocculant, thickened in high rate thickeners, remixed with the quartz sand residue and pumped to the mining void. Alternatively, the thickener underflow is pumped to solar evaporation dams to dry. The dried clay is reclaimed by machine and returned to the mining pit or mixed with soil to enhance the rehabilitation process.

Sand residue is pumped to the mining pit and discharged via a monitor or cyclone stackers. The sand is re-contoured before overburden and topsoil replacement, ready for rehabilitation.

The return water from the cyclone stackers and solar evaporation dams is recycled to a clean water dam from which process water is drawn.

Attritioning is carried out on heavy mineral concentrate to clean the mineral surface. It increases separation efficiencies in electrostatic separation performed during dry separation. This is done by agitating the mineral slurry vigorously causing the mineral particles to collide together and scrub the surfaces. Chemicals are occasionally added to aid this process.

Secondary concentration uses an up-current classifier to remove fine quartz and non valuable heavy minerals from the wet concentrator heavy mineral concentrate to achieve a heavy mineral content of approximately 98 per cent.

Following wet processing the heavy mineral concentrate undergoes a number of dry processing stages to separate the valuable minerals. The design of each flow sheet will differ depending on the mineral assemblage.

Dry mill processing relies upon the unique physical properties of each mineral to separate the gangue minerals from the valuable heavy minerals.

Rare earth drum and roll magnets remove most of the ilmenite as it is the most magnetic of the minerals in the dry mill feed.

Electrostatic separation, using high tension roll and plate electrostatic machines, separate the non-conductive minerals such as zircon, kyanite, staurolite, quartz and monazite from conductive minerals such as rutile, leucoxene and residual ilmenite.

The conductive minerals are further cleaned by
•electrostatic separation to remove residual non-conductive contaminants to marketable levels; and
• magnetic separation to separate rutile, leucoxene and residual ilmenite into rutile, Hyti and ilmenite products.

The non-conductive minerals pass through a wet gravity circuit to separate the light quartz, kyanite and staurolite from the heavier zircon.

The zircon concentrate is dried and cleaned by further
• electrostatic separation to reduce the titanium dioxide content to below 0.15 per cent; and
• magnetic separation to remove weakly magnetic monazite and residual staurolite.