In situ leach
In-situ leach works by artificially dissolving minerals occurring naturally in the solid state.
[2] Unlike open-pit and underground mining, in-situ leaching does not rely on burial depth as a criterion but is based on the properties of the uranium deposit.
In 2010, Uranium Energy Corporation began in-situ leach operations at their Palangana project in Duval County, Texas.
Ores most amenable to leaching include the copper carbonates malachite and azurite, the oxide tenorite, and the silicate chrysocolla.
The ores with the highest sulfide contents, such as bornite and chalcopyrite will require more oxidants and will dissolve more slowly.
A three-year pilot program was undertaken in the 1970s to in-situ leach gold ore at the Ajax mine in the Cripple Creek district in the US, using a chloride and iodide solution.
According to the World Nuclear Organization:In the USA legislation requires that the water quality in the effected aquifer be restored so as to enable its pre-mining use.
Often it needs to be treated by reverse osmosis, giving rise to a problem in disposing of the concentrated brine stream from this.
The usual radiation safeguards are applied at an ISL Uranium mining operation, despite the fact that most of the orebody's radioactivity remains well underground and there is hence minimal increase in radon release and no ore dust.
Therefore, nearly no experience exists with groundwater restoration after acid in- situ leaching, the scheme that was applied in most instances in Eastern Europe.
[16] [17] In USA, the Pawnee, Lamprecht, and Zamzow ISL Sites in Texas were restored using steps 1 and 2 of the above listed treatment scheme.
[citation needed] A study published by the U.S. Geological Survey in 2009 found that "To date, no remediation of an ISR operation in the United States has successfully returned the aquifer to baseline conditions.
Speaking at an EPA Region 8 workshop, on September 29, 2010, Ardyth Simmons, PhD, Los Alamos National Laboratory (Los Alamos, NM) on the subject "Establishing Baseline and Comparison to Restoration Values at Uranium In-Situ Recovery Sites" stated "These results indicated that it may be unrealistic for ISR operations to restore aquifers to the mean, because in some cases, this means that there would have to be less uranium present than there was pre-mining.
In a February, 2012 letter the EPA states, "Because the ISL process affects groundwater quality, the EPA’s Office of Radiation and Indoor Air requested advice from the Science Advisory Board (SAB) on issues related to design and implementation of groundwater monitoring at ISL mining sites."
The SAB also reviews the advantages and disadvantages of alternative statistical techniques to determine whether post-operational groundwater quality has returned to near pre-mining conditions and whether mine operation can be predicted not to adversely impact groundwater quality after site closure acceptance.
