Iron (Fe) is one of the most abundant rock-forming elements, constituting about 5% of the Earth's crust. It is the fourth most abundant element after oxygen, silicon and aluminium, and after aluminium, the most abundant and widely distributed metal. Iron is indispensable to modern civilisation and people have been skilled in its use for more than 3,000 years. However, its use only became widespread in the 14th century, when smelting furnaces (the forerunner of blast furnaces) began to replace forges.
Iron ore, the raw material from which iron is smelted, provides the foundation for one of Australia's major export industries. In 2002 91.5% of Australia's iron ore production of 182.7 million tonnes was exported. Australia is the world's largest iron ore exporter and, as a producer, ranks third (with 17%) after China (21%) and Brazil (20%). The value of Australia's iron ore exports was $5.2 billion.
Australia has been self-sufficient in iron and steel production for many years, but despite its large resources and output of iron ore, it is not a large producer in terms of world steel output, which exceeds 800 million tonnes a year.
Most iron ores mined today comprise the iron oxide minerals hematite, Fe2O3 (70% Fe); goethite, Fe2O3s H2O, (63% Fe); limonite, a mixture of hydrated iron oxides (up to 60% Fe); and magnetite, Fe3O4 (72% Fe).
Most of the world's important iron ore resources occur in iron-rich sedimentary rocks known as banded iron formations (BIFs) that are almost exclusively of Precambrian age (i.e. greater than 600 million years old). BIFs occur on all continents. In many instances they are mined as iron ores, but most importantly they are the source rocks for most of the large high-grade concentrations of iron ore currently mined throughout the world.
In the Hamersley Province in the Pilbara district of Western Australia there are three main types of deposit: iron oxide enrichments within BIFs; iron oxides deposited along ancient, mainly Tertiary age river channels (palaeochannels); and iron oxide deposits formed from the erosion of existing orebodies (detrital iron ore deposits).
The BIF enrichment deposits comprising hematite and hematite goethite are the most important in regard to resources and production. The iron content of these ores varies widely, but most deposits need to have an average grade of more than 60% Fe for mining to be commercially viable. Those produced for export generally exceed 62% Fe.
The palaeochannel deposits comprised of pisolitic limonite are the next in importance and are prized for their low impurities such as phosphorus. They are not as rich in iron as the BIF enrichment ores. Those mined usually contain 57-59% Fe.
Detrital iron ore deposits, including scree and canga deposits, are found downhill of the BIF enrichment deposits from which they have been eroded. They are usually easily recovered and have a grade of between 40-55% Fe. BIF enrichment deposits also occur elsewhere in Western Australia in the Pilbara (e.g. Yarrie), and the Yilgarn Block (e.g. Koolyanobbing) and in South Australia (e.g. Iron Duke, Middleback Range).
Numerous magnetite deposits of igneous origin or association occur in most States and uneconomic sedimentary sideritic (those containing the mineral siderite, FeCO3) iron ore deposits occur in Queensland and the Northern Territory.
Although iron ore resources occur in all the Australian States and Territories, almost 90% of identified resources (totalling 31.5 billion tonnes) occur in Western Australia, including about 80% in the Hamersley Province, one of the world's major iron ore provinces.
In 2002 Australia's economic demonstrated resources (i.e. those that have been sufficiently tested by drilling and that could be economically extracted at current prices with existing technology) totalled 13.0 billion tonnes and ranked Australia fourth (with 9%) behind those in the Ukraine (21%), Russia (17%) and China (14%).
As with most iron ore mines throughout the world, all the major Australian iron ore mines are open cut. The ores from the major mines in Western Australia's Pilbara region are hauled from working faces to crushing and screening plants using trucks that can carry over 200 tonnes. The ore is then transported for further treatment and blending to port sites in trains consisting of up to three locomotives and 250 wagons. Trains of this size are up to 3 kilometres long and contain loads in excess of 25,000 tonnes. There are three major Pilbara iron ore producers: BHPBilliton Iron Ore Pty Ltd and Rio Tinto Ltd.
BHPBilliton Iron Ore manages the Mount Newman Joint Venture ( Mount Whaleback plus three other nearby mines); the Yandi Joint Venture ( Yandi /Marillana Creek mine); and the Mount Goldsworthy Joint Venture ( Yarrie mine); and the Mining Area C Joint Venture (C Deposit mine). It also owns the Jimblebar mine. The Mount Whaleback mine, 5.5 kilometres in length, has a width of up to 2 kilometres and will be mined until it reaches a depth of 0.5 kilometres. Products from these mines are transported by rail to Port Hedland for export and shipment to Australian steelworks. Most products are further crushed, screened and blended at the port.
Hamersley Iron Pty Ltd (100% Rio Tinto) operates the Mount Tom Price, Brockman No 2, Paraburdoo, Channar, Marandoo and Yandicoogina (or HIYandi) mines. The lump and fines ore products from the mines (lump ore size is 6.3 to 31.5 millimetres; maximum size of fines is 6.3 millimetres) are transported by rail to the port of Dampier for blending and rescreening before export.
Robe River Mining Company (53% Rio Tinto) mines pisolitic limonite ore deposits at Deepdale J along the Robe River. The ore is railed to Cape Lambert for crushing and screening and export as fines (limonite fines, including those from HIYandi above have a maximum size of 9.5 millimetres). Robe River also mines marra mamba ore at the West Angelas operation and rails the products to Cape Lambert for export.
Other locally significant iron ore mines in Australia include the Portman Ltd mine at Koolyanobbing, which rails products for export to the port of Esperance in WA. Portman also have a mine on Cockatoo Island in north west WA. At Tallering Peak in the mid-west of WA Mount Gibson Iron Ltd commenced mining hematite ore during 2003. In South Australia hematite ore is extracted at three mines in the Middleback Ranges by OneSteel Ltd and used in iron and steelmaking at Whyalla. In Tasmania, magnetite ore mined at Savage River by Australian Bulk Minerals is crushed, ground and concentrated, then pumped 85 kilometres as a slurry to Port Latta via a pipeline where pellets are produced for shipment.
As at December 2003 iron ore projects that are either under construction, committed or proposed include Mt Gibson, Fortescue, Hope Downs, Mt Jackson and Windarling, Koolan Island, Mt Nicholas, Koolanooka, Iron Magnet and Eastern Range.
In various parts of Australia other iron ore deposits are mined on a small scale (50,000 - 100,000 tonnes a year), mainly for coalwashing, mineral separation, cement manufacture, gas and water purification, fluxing and the manufacture of pigments.
Concentration includes all the processes that will increase (upgrade) the iron content of an ore by removing impurities. Beneficiation, a slightly broader term, includes these processes as well as those that make an ore more usable by improving its physical properties (e.g. pelletising and sintering). Many of the iron ore mines employ some form of beneficiation to improve the grade and properties of their products. At Mount Tom Price, Paraburdoo and Mount Whaleback major concentrators have been constructed which enable low grade iron ores, including ores which have been contaminated with shale, to be mined and after upgrading, sold as high grade products. The operation of the concentrators has also increased the iron ore resources available at these mines.
Pelletising is a treatment process used for very fine or powdery ores. Pellets are an ideal blast furnace feed because they are hard and of regular size and shape. In Australia, concentrates pumped from Savage River are pelletised at Port Latta for shipment to domestic and overseas markets, and fine Middleback Range ores are pelletised prior to smelting in the Whyalla blast furnace.
Sintering is a process used to agglomerate iron ore fines in preparation for blast-furnace smelting, and is usually carried out at iron and steelmaking centres. It involves the incorporation of crushed limestone, coke and other additives available from iron and steelmaking operations. These additives include wastes extracted from furnace exhaust gases, scale produced during rolling mill operations, and coke fines produced during coke screening.
Pig iron is an intermediate step in the production of steel and is produced by smelting iron ore (commonly in lump, pellet or sinter form) in blast furnaces. Blast furnaces are located at Port Kembla and Whyalla. The removal, by oxidation, of impurities in pig iron such as silicon, phosphorus and sulphur and the reduction in the carbon content, result in the production of steel.
Steel is produced at Port Kembla, Whyalla, Sydney, Mayfield and Laverton North. At Sydney (Rooty Hill), Mayfield and Laverton North, steel is produced entirely from the remelting of scrap iron and steel in electric arc furnaces (EAF).
BHPBilliton produces a direct reduced iron (DRI) product from its hot briquetted iron plant near Port Hedland, WA. In DRI plants the iron ore is reduced to a product with over a 90% iron content which is then used as a feedstock for the production of steel in EAF. HIsmelt Corporation Pty Ltd are constructing a DRI plant at Kwinana in WA. A number of other consortiums are also examining the construction of DRI plants including Ausmelt Ltd who own a DRI demonstration plant in Whyalla, SA.
Although iron in cast form has many specific uses (e.g. pipes, fittings, engine blocks) its main use is to make steel. Steel is the most useful metal known. Steel is strong, durable and extremely versatile. The many different kinds of steel consist almost entirely of iron with the addition of small amounts of carbon (usually less than 1%) and of other metals to form different alloys (e.g. stainless steel). Pure iron is quite soft, but adding a small amount of carbon makes it significantly harder and stronger. Most of the additional elements in steel are added deliberately in the steelmaking process (e.g. chromium, manganese, nickel, molybdenum). By changing the proportions of these additional elements, it is possible to make steels suitable for a great variety of uses.
Steel's desirable properties, and its relatively low cost, make it the main structural metal in engineering and building projects, accounting for about 90% of all metal used each year. About 60% of iron and steel products are used in transportation and construction, 20% in machinery manufacture, and most of the remainder in cans and containers, in the oil and gas industries, and in various appliances and other equipment.
