Mudd reported in 2001 that the technique of in situ leach (ISL) uranium mining is well established in the USA, as well as being used extensively in Eastern Europe and the former Soviet Union. The method is being proposed and tested on uranium deposits in Australia, with sulfuric acid chemistry and no restoration of groundwater following mining.
Test sites in the USA were required to restore groundwater to ascertain the extent of impacts and compare costs to alkaline ISL mines. The problems encountered include expensive and difficult restoration, gypsum precipitation, higher salinity and some heavy metals and radionuclides after restoration. One of the most critical issues is whether natural attenuation is capable of restoring groundwater quality and geochemical conditions in an acid leached aquifer zone. The history of acid ISL sites in the USA and Australia are presented in this study, with a particular focus on the demonstration of restoration of groundwater impacts.
The unconventional mining technique of in situ leach
(ISL) is now the primary producer of refined uranium in the United States, with a market share of around 95% in the mid 1990s (DoE 1999). The ISL technique, also known as 'solution mining', appears set to assume a new part of Australia's uranium industry. It is an historical curiosity as to where the conceptual processes for ISL were first conceived and applied. The Chinese were apparently the first to use solution mining to produce copper as early as 907 A.D., with references to the technology dating back to 177 B .. c. (Morris 1984). During the 1890s, the Frasch process for mining elemental sulfur was invented, and ISL mining of gold was first suggested by the Russians (Morris 1984).
The first trials of uranium ISL were developed in the USA and the Soviet Union in the early 1960s. It is uncertain who developed the first projects or if they originated separately (Mudd 1998). By the mid-1970s, there were uranium ISL mines across the world as alternative, potentially low cost producers
(Larson 1981).
In the USA, ISL mines generally used alkaline chemistry with only a few sites trialling acid chemistry. In contrast, Soviet mines generally used acid with only a few sites using alkaline reagents. In Australia during the early 1980s, two ISL projects at Beverley and Honeymoon in South Australia proposed acid while a third at Manyingee in Western Australia trialled alkaline chemistry. The Honeymoon site undertook an acid ISL trial in late 1982.
The environmental regulation of mining generally requires the restoration of affected groundwater to be returned to its pre-mining quality or use category. In countries controlled by the Soviet block, the need for restoration of contaminated groundwater following mining was ignored during operation, and the problems and magnitude of groundwater contamination, which are now coming to light in the 1990s, can only be described as extreme (Mudd 1998, 2001).
Indeed, the use of alkaline chemistry in the USA has been related to the need to restore affected groundwater and that alkaline mine sites are considered to be easier to restore (Tweeton and Peterson 1981; Mudd 1998). In direct contrast, Australian ISL projects - historically and currently - proposed not to restore affected groundwater after acid ISL mining.
The resurfacing of the Australian acid ISL uranium mine proposals in 1996 (because of a change in federal government and uranium policy), the lack of acid ISL mines in the USA, the research coming to light through the International Atomic Energy Agency (IAEA) and others of the extent of impacts from acid ISL mines in the Soviet block, led to a detailed review of ISL uranium mining.
Also see: See Part 2: Critical Review of Acid In Situ Leach Uranium Mining - Part 2, Soviet Block and Asia:
https://www.i2mconsultants.com/downloads/corp/s002540100405.pdf
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