Appendix 1.1
In Situ Leaching Method of Extracting Uranium
In situ leaching - or ISL for short - has been used successfully in
Europe, Asia and the United States to mine uranium for over 25 years.
Currently 13 per cent of world production is by in situ leaching and
almost all of the US production is by that method, apart from some uranium
produced in by-product operations. The techniques for in situ leaching
have evolved to the point where it is a controllable, safe, environmentally
benign method of mining which can produce uranium with low capital and
operating costs and can operate under strict environmental controls.
. . . ISL is a closed loop mining system, where ground water from the
aquifer is utilised as the transport medium. Uranium is dissolved in
situ within the host formation generally using oxygen as an oxidant
and with either carbonate or sulfate leach chemistry, depending on the
chemistry of the ore and the ground water. Patterns of screened and
cased water bores or wells are used to deliver the reagent stream to
the ore horizon - as shown here - enabling it to contact the uranium
mineralisation whilst passing through the aquifer. Similarly, patterns
of recovery or extraction wells fitted with submersible pumps deliver
the fluid to the surface for processing to recover the dissolved uranium.
After processing, the fluid is returned to the wellfield to continue
the leaching cycle. Thus, ISL takes place on a continuous basis.
Limiting the reagent stream to within the ore body is achieved by careful
wellfield planning, by excess pumping of extraction over injection to
create a zone of depression centred on the mining activity and by routine
monitoring of monitor wells located outside the ore body. ISL operations
have a number of advantages over open pit and underground mining. By
comparison with open cut and underground mining, there is minimal surface
disturbance.
ISL mines consist of wellfields, pipelines, a compact and simple uranium
extraction plant and drying facilities. There are no open pits, shafts
or tunnels, nor grinding, crushing and ancillary features, nor ore and
waste rock heavy earth-moving equipment. The extent and visual impacts
are reduced. There are no tailings. As ore is not crushed or ground,
there are no long-term tailings dams nor waste rock piles. Small evaporation
ponds only are required. Operational surface water and long-term restoration
requirements are significantly reduced. Limited solid wastes can be
easily managed. There is no ore exposure. As ore is left in situ, radon
release is reduced and dust generation is insignificant. Material handling
requirements are safer and underground mining, cooling and ventilation
problems are non-existent.
There is reduced radiation exposure. Reduced dust and absence of exposure
to the ore enables greatly reduced radiation exposure to both workers
and the public at large. The lower impacts require reduced rehabilitation
requirements. Upon completion of mining, wells can be sealed and capped,
process facilities removed and the surface returned to its original
contour and vegetation.
Reduced labour inputs: ISL requires a smaller work force per unit output
and therefore local social impacts are reduced. The technology enables
smaller ore bodies to be mined. The ore bodies may be smaller and lower
in grade, narrow and otherwise uneconomic.
- Description provided by David Brunt, Consultant, Heathgate Resources
Pty Ltd.
Committee Hansard, 24 January 1997, 996-7