Introduction
Uranium (U) is a radioactive metal with a high specific gravity of 18.7. It was discovered in the mineral pitchblende by Martin Klaproth in 1789 and was named after the planet Uranus.
Naturally occurring uranium consists of a mixture of three isotopes in the following proportions: U238 (99.28%), U235 (0.71%) and U234 (0.01%). U235 has an outstanding property in that it is the only naturally-occurring fissionable element. By interaction with neutrons, the nucleus of U235 may be split into two parts. This splitting - termed fission - releases energy and more neutrons, starting a nuclear chain reaction. The large amounts of heat released by this reaction are used in nuclear reactors to generate electricity.
Uranium has two main valencies - U4+ when it occurs in a reducing medium, and U6+ in an oxidising medium, e.g. at the Earth's surface. U6+ is more soluble than U4+ in natural waters. Streams carry a quantity of dissolved uranium depending on the geological characteristics of the region they drain. Sea water averages 0.003 parts per million U. Uranium oxide precipitates from groundwaters containing dissolved uranium when these waters enter a reducing environment.
In terms of abundance in the Earth's crust, uranium is about as common as tin, tungsten and molybdenum.
Naturally occurring uranium consists of a mixture of three isotopes in the following proportions: U238 (99.28%), U235 (0.71%) and U234 (0.01%). U235 has an outstanding property in that it is the only naturally-occurring fissionable element. By interaction with neutrons, the nucleus of U235 may be split into two parts. This splitting - termed fission - releases energy and more neutrons, starting a nuclear chain reaction. The large amounts of heat released by this reaction are used in nuclear reactors to generate electricity.
Uranium has two main valencies - U4+ when it occurs in a reducing medium, and U6+ in an oxidising medium, e.g. at the Earth's surface. U6+ is more soluble than U4+ in natural waters. Streams carry a quantity of dissolved uranium depending on the geological characteristics of the region they drain. Sea water averages 0.003 parts per million U. Uranium oxide precipitates from groundwaters containing dissolved uranium when these waters enter a reducing environment.
In terms of abundance in the Earth's crust, uranium is about as common as tin, tungsten and molybdenum.
Occurence
More than 150 uranium-bearing minerals have been identified. The main primary minerals are uraninite (UO2), pitchblende (a mixed oxide, usually U3O8), brannerite (a complex oxide of uranium, rare-earths, iron and titanium) and coffinite (uranium silicate). Most of the world's uranium is produced from pitchblende ores. The most important secondary minerals are carnotite, autunite, davidite, gummite, torbernite and uranophane.
Australia has some of the largest uranium deposits in the world and major uranium deposits occur in a number of distinct geological settings and rock types.
Australia has some of the largest uranium deposits in the world and major uranium deposits occur in a number of distinct geological settings and rock types.
Australian Resources and Deposits
The earliest uranium deposits mined in Australia were at Radium Hill and Mount Painter in South Australia. These deposits were worked from about 1910 to 1931 for radium, a radioactive daughter product of uranium which was used mainly for medical purposes. Exploration for uranium in Australia began in 1944 at the request of the British Government. The Australian Government offered financial rewards and in 1949 the Rum Jungle deposit was discovered. Subsequently, the Mary Kathleen deposit in Queensland and a number of smaller deposits in the South Alligator Valley of the Northern Territory were discovered. Between 1954 and 1971 the following deposits were mined: Rum Jungle (1954 to 1971), Radium Hill (1954 to 1962), Mary Kathleen (1958 to 1963) and South Alligator Valley (1959 to 1964).
Uranium exploration declined during the late 1950s but increased again in the late 1960s, stimulated by the easing of the government's export embargo and predictions of increased world demand for uranium in the early 1970s for generating electricity in nuclear power stations.
Important deposits were discovered between 1969 and 1973 at Nabarlek, Ranger, Koongarra and Jabiluka in the Alligator Rivers area of the Northern Territory, at Beverley and Honeymoon in the Lake Frome area of South Australia at Yeelirrie and Lake Way in Western Australia. The Olympic Dam deposit in South Australia and the Kintyre deposit in Western Australia were discovered in 1975 and 1985 respectively.
The Mary Kathleen mine recommenced production in 1975 and ceased operations in 1982. A total of 8,894 tonnes U3O8 was produced from Mary Kathleen during its two periods as an operating mine. The Nabarlek deposit was mined and stockpiled in 1979. This stockpiled ore was processed from 1980 to mid-1988 for a total output of 10,858 tonnes U3O8.
Australia currently has three uranium mining operations - Ranger, Olympic Dam and Beverley
Ranger is a large unconformity-related deposit in the Alligator Rivers region of the Northern Territory. The ore is mined by open-cut methods. Production commenced in 1981 from the first ore body which has been mined out and mine production now is from the second ore body. The processing plant (acid leach and solvent extraction) has a production capacity of 5,000 tonnes U3O8 per year. Ranger mine area and the adjoining Jabiluka Mineral Lease are on Aboriginal land and are surrounded by Kakadu National Park.
Olympic is the world's largest uranium deposit in terms of total reserves and resources of uranium. Mineralisation occurs in a hematite-rich granite breccia complex and is beneath approximately 300 metres of flat-lying sedimentary rocks of the Stuart Shelf geological province. The mine produces uranium, copper, gold and silver. The ore is mined by large-scale underground method, long-hole open stoping. Production began in 1988.
The operation has annual production capacity of 200,000 tonnes of refined copper and 4,300 tonnes U3O8.
Beverley in the Lake Frome area of South Australia, is the first in situ leach (ISL) uranium mine in Australia. The deposit occurs in unconsolidated sands with inter-bedded clays (Upper Tertiary in age) which were deposited in a confined palaeochannel sequence. Mineralisation is at an average depth of 107 metres below surface. Production commenced in November 2000 and the operation has capacity to produce 1,000 tonnes U3O8 annually. Acid leach solutions and oxygen are used to dissolve uranium in situ, and resin-type ion-exchange techniques are used to recover uranium in the processing plant.
Australia has the world's largest resources of low-cost uranium (recoverable at costs of less than US$40/kg U), with approximately 43% of world resources in this category. Other countries which have large low-cost resources include Kazakhstan (21%), Canada (18%) and South Africa (8%).
Uranium exploration declined during the late 1950s but increased again in the late 1960s, stimulated by the easing of the government's export embargo and predictions of increased world demand for uranium in the early 1970s for generating electricity in nuclear power stations.
Important deposits were discovered between 1969 and 1973 at Nabarlek, Ranger, Koongarra and Jabiluka in the Alligator Rivers area of the Northern Territory, at Beverley and Honeymoon in the Lake Frome area of South Australia at Yeelirrie and Lake Way in Western Australia. The Olympic Dam deposit in South Australia and the Kintyre deposit in Western Australia were discovered in 1975 and 1985 respectively.
The Mary Kathleen mine recommenced production in 1975 and ceased operations in 1982. A total of 8,894 tonnes U3O8 was produced from Mary Kathleen during its two periods as an operating mine. The Nabarlek deposit was mined and stockpiled in 1979. This stockpiled ore was processed from 1980 to mid-1988 for a total output of 10,858 tonnes U3O8.
Australia currently has three uranium mining operations - Ranger, Olympic Dam and Beverley
Ranger is a large unconformity-related deposit in the Alligator Rivers region of the Northern Territory. The ore is mined by open-cut methods. Production commenced in 1981 from the first ore body which has been mined out and mine production now is from the second ore body. The processing plant (acid leach and solvent extraction) has a production capacity of 5,000 tonnes U3O8 per year. Ranger mine area and the adjoining Jabiluka Mineral Lease are on Aboriginal land and are surrounded by Kakadu National Park.
Olympic is the world's largest uranium deposit in terms of total reserves and resources of uranium. Mineralisation occurs in a hematite-rich granite breccia complex and is beneath approximately 300 metres of flat-lying sedimentary rocks of the Stuart Shelf geological province. The mine produces uranium, copper, gold and silver. The ore is mined by large-scale underground method, long-hole open stoping. Production began in 1988.
The operation has annual production capacity of 200,000 tonnes of refined copper and 4,300 tonnes U3O8.
Beverley in the Lake Frome area of South Australia, is the first in situ leach (ISL) uranium mine in Australia. The deposit occurs in unconsolidated sands with inter-bedded clays (Upper Tertiary in age) which were deposited in a confined palaeochannel sequence. Mineralisation is at an average depth of 107 metres below surface. Production commenced in November 2000 and the operation has capacity to produce 1,000 tonnes U3O8 annually. Acid leach solutions and oxygen are used to dissolve uranium in situ, and resin-type ion-exchange techniques are used to recover uranium in the processing plant.
Australia has the world's largest resources of low-cost uranium (recoverable at costs of less than US$40/kg U), with approximately 43% of world resources in this category. Other countries which have large low-cost resources include Kazakhstan (21%), Canada (18%) and South Africa (8%).
New Mine Developments
Jabiluka deposit, in the Alligator Rivers region, is approximately 20km north of the Ranger mine. Both Jabiluka and Ranger are owned by Energy Resources of Australia Ltd (ERA). Jabiluka is one of the world's largest unconformity-related deposits with total resources containing 163,000 tonnes of U3O8.
The Jabiluka project was subjected to an exhaustive three-year environmental impact assessment process. This involved separate assessments of both the options to mill Jabiluka ore at the existing Ranger facility and the option of building a mill on-site at Jabiluka. Both options have received Australian Government environmental clearance, subject to the company complying with certain requirements.
The Traditional Aboriginal owners have not granted their approval to develop the deposit. The Jabiluka site currently is in an environmental care-and-maintenance phase. ERA and the Government have given an undertaking to the World Heritage Committee also that Ranger and Jabiluka will not be brought into full production simultaneously.
The Honeymoon deposit south of Lake Frome occurs in coarse-grained sands of Tertiary age and is between 100 metres and 120 metres below surface. It has a roll-front shape and occurs at an oxidation-reduction interface along the lateral margins of a buried palaeochannel. Following an assessment of the Environmental Impact Statement in late 2000, the Environment Minister cleared the way for the Honeymoon in situ leach operation to proceed. Planned production rate is 1,000 tonnes of U3O8 annually.
The Jabiluka project was subjected to an exhaustive three-year environmental impact assessment process. This involved separate assessments of both the options to mill Jabiluka ore at the existing Ranger facility and the option of building a mill on-site at Jabiluka. Both options have received Australian Government environmental clearance, subject to the company complying with certain requirements.
The Traditional Aboriginal owners have not granted their approval to develop the deposit. The Jabiluka site currently is in an environmental care-and-maintenance phase. ERA and the Government have given an undertaking to the World Heritage Committee also that Ranger and Jabiluka will not be brought into full production simultaneously.
The Honeymoon deposit south of Lake Frome occurs in coarse-grained sands of Tertiary age and is between 100 metres and 120 metres below surface. It has a roll-front shape and occurs at an oxidation-reduction interface along the lateral margins of a buried palaeochannel. Following an assessment of the Environmental Impact Statement in late 2000, the Environment Minister cleared the way for the Honeymoon in situ leach operation to proceed. Planned production rate is 1,000 tonnes of U3O8 annually.
Mining and Processing
Uranium is usually mined by either open-cut methods (e.g. Ranger, Nabarlek, Mary Kathleen and Rum Jungle deposits) or underground mining methods (e.g. Olympic Dam, Radium Hill and the South Alligator Valley deposits), depending on the depth at which the orebody occurs. Sandstone-type deposits are usually mined by in situ leaching in which an acidic or alkaline solution is pumped through a permeable orebody to dissolve the uranium. It is then recovered from these solutions in a processing plant (e.g. Beverley and Honeymoon deposits).
Processing
Initially, the uranium ore is crushed and then ground to a fine grain size. Grinding and mixing with water produces a slurry of fine ore particles suspended in water. This slurry is leached with either an acid or an alkali, depending on the metallurgical characteristics of the ore. Leaching causes uranium to dissolve in the solution. Most of the other minerals in the ore remain undissolved, and these solids, called tailings, are then separated from the uranium-rich liquid, usually by allowing them to settle out. The uranium-rich liquid is filtered to remove any remaining solids and the uranium is then recovered by techniques using solvent extraction, ion exchange or direct precipitation. The method used depends on the nature of the particular ore.
Uranium is finally recovered in a chemical precipitate which is filtered and dried to produce a yellow powder known as yellowcake. The yellowcake is heated to about 700°C to produce a dark grey-green uranium oxide powder containing more than 98% U3O8, which is placed into 200 litre steel drums for export.
For ISL operations, uranium is recovered in a processing plant using either ion exchange or solvent extraction technologies.
Uranium is finally recovered in a chemical precipitate which is filtered and dried to produce a yellow powder known as yellowcake. The yellowcake is heated to about 700°C to produce a dark grey-green uranium oxide powder containing more than 98% U3O8, which is placed into 200 litre steel drums for export.
For ISL operations, uranium is recovered in a processing plant using either ion exchange or solvent extraction technologies.
Uses
Uranium has two major peaceful uses as the fuel in nuclear power reactors to generate electricity and in the manufacture of radioisotopes.
Electricity Generation
In a nuclear reactor, the heat released during the fission of U235 is used to produce steam which drives turbines to generate electricity. Approximately 16% of the world's electricity is currently generated by the use of uranium in nuclear reactors. Some 439 nuclear power reactors with a total nett capacity of more than 350 gigawatts (electrical) are operating in 31 countries. A further 34 reactors are under construction worldwide. A total of 16 countries generate more than 25% of their total electricity requirements from nuclear reactors.
Exports of Australian Uranium
Australia has no significant national demand for uranium and all production is exported. Australia applies very stringent conditions to the export of uranium to ensure it is used only for peaceful purposes. These conditions called nuclear safeguards require customer countries to allow international inspectors from the International Atomic Energy Agency to verify that the uranium is not directed into weapons programs. In addition, Australia requires compliance with parallel conditions under treaties it has concluded with end customer countries. This compliance is monitored by the Australian Safeguards and Non-Proliferation Office.
Suggestions for Further Reading
- McKay, A.D., & Miezitis, Y. (2001) Australia's uranium resources, geology and development of deposits. AGSO - Geoscience Australia. Mineral Resource Report 1. (PDF 6.2 MB)
- Uranium Information Centre web site www.uic.com.au
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