At a number of places on the east and west coasts of Australia, parts or all of the sandy beaches and/or associated dunes contain concentrations of heavy minerals. These are called mineral sands deposits.
Heavy minerals in such deposits are ilmenite (FeTiO3), zircon (ZrSiO4) and rutile (TiO2) — a minor one is monazite (a rare earth element, thorium phosphate/silicate). They are called heavy minerals because their densities (between 4 and 5.5) are greater than quartz (density of 2.65), the main constituent of most sand.
Mineral sands deposits occur along the coast of eastern Australia from central New South Wales (NSW) to Cape York in Queensland. Large, relic (old) beach deposits are found as far inland as Ouyen in Victoria ( Wemen, Bondi, Kulwin deposits) and south-western NSW ( Gingko, Snapper deposits). In Western Australia (WA), deposits are distributed from the southern tip of the State to Geraldton and are located at the present coastline or as relic deposits up to 35 kilometres inland.
Heavy minerals originally occur as traces (generally less than 0.1 per cent) in igneous rocks such as granite, pegmatite and basalt. Highly metamorphosed (heated and pressured) rocks provide the best source of titanium heavy minerals. If these rocks are weathered and eroded, resistant components (eg quartz and heavy minerals) separate from the less resistant minerals.
As the heavy minerals are washed down to the sea they may accumulate as placer deposits (like alluvial gold) in river channels or along coastal shorelines. In the beach intertidal zone, sand washed up on the beach drops out as wave impacts slows. As waves wash back, some of the lighter sand is carried back into the sea, leaving the heavy minerals behind on the beach. This constant wave action leads to a concentration of the heavier minerals. These minerals are covered by the lighter sand material blown over the dunes at the back of the beach forming heavy mineral sand deposits at the front of the dunes.
Australia’s mineral sands resources are assessed each year by Geoscience Australia (http://www.ga.gov.au/pdf/RR0112.pdf). Australia is rich in mineral sands resources but because they are mainly located at or near the coast their mining competes with other land uses such as national parks, urban or tourist development and recreation. Allocation of land to other uses has rendered some mineral sands resources inaccessible to exploration or mining. Some 19%, 26% and 30% of Australia’s economic resources of ilmenite, rutile and zircon are unavailable. Areas quarantined from mining and now largely incorporated into national parks include- Moreton, Bribie and Fraser Island; Cooloola sand mass north of Noosa; Byfield sand mass and Shoalwater Bay area in Queensland; and Yuraygir, Bundjalung, Hat Head and Myall Lakes National Parks in New South Wales.
Throughout the late 1990s, a large number of coarse-grained strandlines have been identified in the Murray Basin, which occurs within New South Wales, Victoria and South Australia. Over 100 million tonnes of heavy mineral sand concentrates have been outlined. Large resources of fine-grained mineral sands deposits (referred to as WIM-type deposits) occur in the Horsham region of Victoria.
Australia is a world leader in production of mineral sands and has the world’s largest economic demonstrated resources of ilmenite, rutile and zircon with 29%, 44% and 40%, respectively. It produces up to 55 per cent of the world's rutile, 39% of the world's zircon, and about 30 per cent of the world's ilmenite. The other major producers are South Africa (Richards Bay deposit), the United States (Florida), Canada (ilmenite sources from hard rock) and India.
Most of Australia's rutile and synthetic rutile and about 40 per cent of the ilmenite exports are to the USA, the UK, Japan, Spain and the Netherlands for processing into white, titanium dioxide pigment and titanium metal. Australia produces 4% of the world's total pigment production of about 4 Mt and no titanium metal. Zircon is mainly exported to Italy, Netherlands, Japan and the USA.
Mineral sands were first mined in Australia in the 1930s at Byron Bay, on the north coast of NSW. By the late 1940s, rutile and zircon mining started in Queensland and further south in NSW. Mining of ilmenite began in the mid-1950s near Bunbury in south-west WA.
The ilmenite-rich deposits of WA, such as at Eneabba, produce six to nine times more ilmenite and more than twice as much zircon as the east coast deposits. However, WA rutile production is about half that from east coast deposits. Mining has commenced in the Murray Basin. Mineral sands have also been mined on a small scale in Tasmania at Naracoopa, King Island (rutile and zircon), and in South Australia at Kangaroo Island.
Initially, only mineral-rich sand seams were mined. Such seams are now uncommon and lower-grade dune material is worked by a dredge floating on an artificial pond that lifts the ore from the bottom of the pond through a large suction pipe.
Attached to the back of the dredge is a barge-mounted primary concentrator that separates the heavy minerals from the sand tailings (waste). As the dredge mines slowly forward the tailings are pumped from the concentrator to the back of the pond, progressively filling the mined area.
Some higher-grade deposits containing moderately indurated (hard) material or layers are mined using a variety of equipment such as self-loading scrapers, bucket-wheel excavators, bulldozers and front-end loaders.
The mined, heavy mineral concentrates are sent to 'dry' mills and the inPidual minerals are separated using their different magnetic and electrical properties at various elevated temperatures. Separation equipment includes high-tension (electrical), high intensity magnetic and electrostatic plate separators.
Careful environmental rehabilitation of mined areas is carried out progressively as the dredge moves forward. Backfill tailings are shaped to approximate the original landform, then the original topsoil and any overburden is replaced and the area is revegetated, either with local flora or pasture grasses. Environmental monitoring continues as the vegetation matures and the area is eventually rehabilitated, as near as possible, to its previous land use, usually natural bushland or farmland.
Public consultation takes place during the approval process prior to consent being given to the mine establishment.
Processing
Ilmenite is upgraded to synthetic rutile (>90 per cent TiO2) by removing contained iron at plants located at Capel, Geraldton and Muchea, all in WA. The technology used is called the Becher process and was developed by a joint industry and government initiative in Australia in the early 1960s.
In the Becher process ilmenite concentrate containing 55-65 per cent TiO2 (the rest is mainly iron oxide) is fed to a rotary kiln to reduce the iron oxide to metallic iron. Ilmenite grains are converted to porous synthetic rutile grains with metallic iron and other impurity inclusions. The iron is precipitated as hydrated iron oxide from the synthetic rutile grains and a mild acid treatment is used to dissolve the impurities and any residual iron. The grains of synthetic rutile are washed, dried and transported to titanium dioxide pigment manufacturing plants either in Australia or overseas for further processing.
A important change to the Becker process at the Geraldton plant has been the development of the SREP (Synthetic Rutile Enhancement Process) process. This process uses various leaching methods to reduce the level of radioactivity in the synthetic rutile product to internationally acceptable levels.
Ilmenite from North Stradbroke Island is unsuitable for end users because of high chromium content. At Pinkenba, in east Brisbane, the chromium is reduced high tension electromagnetics to an acceptable level of less than 0.4 per cent Cr2O3.
White titanium dioxide pigment is manufactured in WA. At Kwinana and Kemerton in WA, plants using the chlorination process produce white pigment by calcining a mixture of synthetic rutile, coke and chlorine to form gaseous titanium tetrachloride (TiCl4). Ilmenite cannot be used as a raw material in the chlorination process as its titanium content is too low. The titanium tetrachloride is condensed to a liquid and most of the impurities separate as solids. It is then reheated to a gas and mixed with hot oxygen to form very fine crystalline rutile (raw white pigment). The displaced chlorine gas is recycled to the start of the process. The properties of the raw pigment produced from both pigment processes are enhanced for different uses by coating the crystals with white hydrous oxides of silica, alumina, titania or zirconia.
Almost all rutile and ilmenite is processed into non-toxic white titanium dioxide pigment for use in the manufacture of paints, plastics, paper, ink, rubber, textiles, cosmetics, leather and ceramics. Titanium dioxide pigment has excellent brightness and high opacity for good hiding power (e.g. in paint for covering undercoats) and has replaced lead carbonate pigments. Rutile is also used to produce light, strong, corrosion-resistant titanium metal for use in aircraft, spacecraft, motor vehicles, desalination plants and surgical implants. Rutile is used in fibreglass, chemicals and as a coating on welding rods. Ilmenite is used as a fluxing agent in blast furnace feeds and as a sand-blasting abrasive.
Zircon is used in foundry sand moulds, and zircon sand or powder is used for glazes on pottery and other ceramic surfaces and in the production of various refractory metals. Heat-resistant zirconia (ZrO2) is used in a fused form to line ladles holding molten steel, in molten metal moulds, and as small beads for abrasives. Zircon is the major source of zirconium, a corrosion-resistant metal that is used in nuclear reactors and chemical processing equipment. Research and development continues into the use of zirconium ceramics to improve diesel engines, and in the metal extrusion industry where heat resistance and strength are required.
Monazite is a major source of certain rare earth elements and thorium. Rare earth elements are used in high-strength permanent magnets, catalysts, ceramics and colour television tubes. Thorium is used in incandescent gas mantles and as fuel for a few nuclear reactors.
