Mineral Sand Deposits
Adapted to HTML from
Nuclear Issues Briefing Paper 25
courtesy Uranium Information Centre Ltd.
to Earth Science Australia
Main Products and Uses
Industry Response to Radioactivity
Australia is a major producer of mineral sands containing titanium minerals and zircon. A valuable by-product of this is monazite containing thorium, which is radioactive. Monazite is a minor constituent of many mineral sands deposits. Appropriate occupational health provisions ensure safety in handling materials containing thorium.
Australia has extensive deposits of mineral sands which comprise:
titanium minerals (rutile and ilmenite)
monazite - a rare earth phosphate containing a variety of valuable rare earth oxides (particularly cerium) and thorium oxide xenotime, containing yttrium.
These mineral sands have been mined since 1934 and Australia has a major share of the world market for both titanium minerals and zircon. It supplies about 11% of the international requirement for rare earth ores such as monazite.
Most of Australia's
occur on the east coast of Australia between Sydney and Fraser Island
on the southern section of the west coast.
While the main products of mineral sands mining are titanium oxide and zircon, monazite is also a significant component. In some deposits xenotime also occurs. In the past these were often returned with the tailings, but today they are often processed to rare earth oxides containing thorium which are used in:
Televisions - for luminescence and colour
Electronics - for a variety of components including high-performance magnets (cerium)
Robots - electric stepping motors
Computers - monitor luminescence, electronic components and bubble memory systems
Lighting - energy efficient lanthanum lamps
Medicine - X-ray screens, fibre optics, pain-killing elements
Chemistry - catalysts
Ceramics - pigment.
Products from monazite are also used in metallurgy, flints, ferro-alloys, glass polishing, jewellery, fuel cells, refractories, lamp mantles (thorium) and welding electrodes.
Yttrium from xenotime has been used in the most effective superconductors.Radioactivity
The occupational health issue of specific relevance to the mineral sands industry is radiation. Western Australian mineral sands deposits contain up to 10% heavy minerals, of which 1-3% is monazite. This in turn typically contains 5-7% of radioactive thorium and 0.1 - 0.3% of uranium, which is barely radioactive.
In ore, or general heavy mineral concentrate, the radiation levels are too low for radioactive classifications. However, when the radioactive material is concentrated in the process of separation and production of monazite the radiation levels are increased, creating the need for special controls to protect some "designated" employees in dry separation plants.
In the past, occupational exposure to radiation levels of 50 mSv/yr, then the limit, were not uncommon.
Dust control is the most important objective in radiation safety for the titanium minerals industry. The most significant potential radiation problem is inhaled thorium in mineral sands dust.
This contrasts with other industries where the focus for radiation protection has been direct gamma radiation from materials in rock. Exposure to gamma radiation still needs to be controlled in the mineral sands industry, due principally to uranium and thorium in zircon. However, safety programs are targeting alpha radiation arising from airborne dust which may be inhaled.
The more precise identification of airborne radiation in mineral sands dry separation plants led to the introduction of voluntary codes of practice in 1980. These codes were incorporated into protective legislation in 1982. The method of calculating permissible exposure levels was changed in 1984 and again in 1986. The result was an effective six-fold reduction in radiation exposure limits.
Engineering programs to reduce airborne dust in the dry separation plant. Research programs to improve industry and community knowledge about airborne radiation.
Collectively, the WA companies have spent more than $30 million on engineering programs to improve dust control measures. As a result, average radiation levels have been reduced by more than 70 per cent. Protective masks are no longer required for most plant operators. All new plant is designed to incorporate efficient dust control equipment.
Titanium minerals production is managed under the Code of Practice for Mining and Milling of Radioactive Ores. The current radiation levels are well below the recently set Commonwealth Radiation Protection Code limit of 20 millisieverts per year occupational exposure. Current performance data indicates that Australian producers have no difficulty meeting the new standards. Australia is the first titanium minerals producing country to adopt the new standard of 20 millisieverts per year.
New South Wales and Queensland producers are required to meet the same standards as Western Australian miners. However, the limited monazite content of most east coast deposits means that radiation levels in New South Wales and Queensland dry plants have always been well below occupational health limits.
The main focus of research relating to occupational health in the mineral sands industry is thorium, particularly its biological behaviour. Research will aim to discover more about the amount of thorium which is retained in the body and its potential effects.
Prepared from Australian Titanium Minerals Industry and CRA information.
Australian Rare Earth Newsletter may contain further relevant information.