In situ leach

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Remains of an abandoned piping system used for uranium in-situ leaching in Straz pod Ralskem, Czech Republic Ralsko uran.JPG
Remains of an abandoned piping system used for uranium in-situ leaching in Stráž pod Ralskem, Czech Republic

In-situ leaching (ISL), also called in-situ recovery (ISR) or solution mining, is a mining process used to recover minerals such as copper and uranium through boreholes drilled into a deposit, in situ . In-situ leach works by artificially dissolving minerals occurring naturally in the solid state.

Contents

The process initially involves the drilling of boreholes into the ore deposit. Explosive or hydraulic fracturing can be used to create open pathways in the deposit for the solution to penetrate. Leaching solution is pumped into the deposit where it comes in contact with the ore. The solution bearing the dissolved ore content is then pumped to the surface and processed. This process allows the extraction of metals and salts from an ore body without the need for conventional mining involving drill-and-blast, open-cut or underground mining.

Process

In-situ leach mining involves pumping of a lixiviant into the ore body via a borehole, which circulates through the porous rock dissolving the ore and is extracted via a second borehole.

The lixiviant varies according to the ore deposit: for salt deposits the leachate can be fresh water into which salts can readily dissolve. For copper, acids are generally needed to enhance solubility of the ore minerals within the solution. For uranium ores, the lixiviant may be acid or sodium bicarbonate.

Minerals

Potash and soluble salts

In-situ leach is widely used to extract deposits of water-soluble salts such as potash (sylvite and carnallite), rock salt (halite), sodium chloride, and sodium sulfate. It has been used in the US state of Colorado to extract nahcolite (sodium bicarbonate). [1] In-situ leaching is often used for deposits that are too deep, or beds that are too thin, for conventional Underground Mining.

Uranium

Diagram of in-situ leaching for uranium (US NRC) NRC Uranium In Situ Leach.png
Diagram of in-situ leaching for uranium (US NRC)

In-situ leach for uranium has expanded rapidly since the 1990s, and is now the predominant method for mining uranium, accounting for 45 percent of the uranium mined worldwide in 2012. [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-situ leaching techniques are systematically categorized based on the primary components of the leaching solution, encompassing acid leaching, alkaline leaching, neutral leaching and bioleaching. [3]

Acid leaching is applicable to low-carbonate uranium deposits, with U(VI) dissolving in acid solution while U(IV) dissolving in acid solution with oxidizing agent; Alkaline leaching is effective for high-carbonate uranium deposits but unsuitable for high-pyrite deposits, with U(VI) dissolving in alkaline solution while U(IV) dissolving in alkaline solution with oxidizing agent; Neutral leaching, including CO2-O2 leaching and weak acid leaching, is widely applicable; and Bioleaching is also widely applicable, especially ideal for pyrite-rich uranium deposits. [3]

ISL of uranium ores started in the United States and the Soviet Union in the early 1960s. The first uranium ISL in the US was in the Shirley Basin in the state of Wyoming, which operated from 1961-1970 using sulfuric acid. Since 1970, all commercial-scale ISL mines in the US have used carbonate solutions. [4] [5]

ISL mining in Australia uses acid solutions. [6]

Ion exchange resin beads Ion exchange resin beads.jpg
Ion exchange resin beads

In-situ recovery involves the extraction of uranium-bearing water (grading as low as 0.05%, or 500 ppm, U3O8). The extracted uranium solution is then filtered through resin beads. [5] Through an ion exchange process, the resin beads attract uranium from the solution. Uranium loaded resins are then transported to a processing plant, where U3O8 is separated from the resin beads and yellowcake is produced. The resin beads can then be returned to the ion exchange facility where they are reused.

At the end of 2008 there were four [7] in-situ leaching uranium mines operating in the United States, operated by Cameco, Mestena and Uranium Resources, Inc., all using sodium bicarbonate. ISL produces 90% of the uranium mined in the US. In 2010, Uranium Energy Corporation began in-situ leach operations at their Palangana project in Duval County, Texas. In July 2012 Cameco delayed development of their Kintyre project, due to challenging project economics based on $45.00 U3O8. One ISR reclamation project was also in operation as of 2009. [8]

Significant ISL mines are operating in Kazakhstan and Australia.

A drum of yellowcake LEUPowder.jpg
A drum of yellowcake

Examples of in-situ uranium mines include:

Rhenium

There are technologies for the associated extraction of rhenium from productive solutions of underground leaching of uranium ores. [10]

Copper

In-situ leaching of copper was done by the Chinese by 907 AD, and perhaps as early as 177 BC. [4] Copper is usually leached using acid (sulfuric acid or hydrochloric acid), then recovered from solution by solvent extraction electrowinning (SX-EW) or by chemical precipitation.

Ores most amenable to leaching include the copper carbonates malachite and azurite, the oxide tenorite, and the silicate chrysocolla. Other copper minerals, such as the oxide cuprite and the sulfide chalcocite may require addition of oxidizing agents such as ferric sulfate and oxygen to the leachate before the minerals are dissolved. The ores with the highest sulfide contents, such as bornite and chalcopyrite will require more oxidants and will dissolve more slowly. Sometimes oxidation is sped up by the bacteria Thiobacillus ferrooxidans , which feeds on sulfide compounds.

Copper ISL is often done by stope leaching, in which broken low-grade ore is leached in a current or former conventional underground mine. The leaching may take place in backfilled stopes or caved areas. In 1994, stope leaching of copper was reported at 16 mines in the US.

Recovery well at former San Manuel operation. Recovery Well.jpg
Recovery well at former San Manuel operation.

At the San Manuel Mine [11] in the US state of Arizona, ISL was initially used by collecting the resultant solution underground but in 1995 this was converted to a well-to-well recovery method which was the first large scale implementation of that method. This well-to-well method has been proposed for other copper deposits in Arizona.

Gold

In-situ leaching has not been used on a commercial scale for gold mining. 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. After obtaining poor results, perhaps because of the complex telluride ore, the test was halted. [12]

Environmental concerns

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. Usually this is potable water or stock water (usually less than 500 ppm total dissolved solids), and while not all chemical characteristics can be returned to those pre-mining, the water must be usable for the same purposes as before. 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. Employees are monitored for alpha radiation contamination and personal dosimeters are worn to measure exposure to gamma radiation. Routine monitoring of air, dust and surface contamination are undertaken. [13]

The advantages of this technology are:

After termination of an in-situ leaching operation, the waste slurries produced must be safely disposed, and the aquifer, contaminated from the leaching activities, must be restored. Groundwater restoration is a very tedious process that is not yet fully understood.[ citation needed ]

The best results have been obtained with the following treatment scheme, consisting of a series of different steps: [14] [15]

But, even with this treatment scheme, various problems remain unresolved:[ citation needed ]

Most restoration experiments reported refer to the alkaline leaching scheme, since this scheme is the only one used in Western world commercial in-situ operations. Therefore, nearly no experience exists with groundwater restoration after acid in- situ leaching, the scheme that was applied in most instances in Eastern Europe. The only Western in-situ leaching site restored after sulfuric acid leaching so far, is the small pilot scale facility Nine Mile Lake near Casper, Wyoming (USA). The results can therefore not simply be transferred to production scale facilities. The restoration scheme applied included the first two steps mentioned above. It turned out that a water volume of more than 20 times the pore volume of the leaching zone had to be pumped, and still several parameters did not reach background levels. Moreover, the restoration required about the same time as used for the leaching period. [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. [18] Relaxed groundwater restoration standards have been granted at these and other sites, since the restoration criteria could not be met.[ 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." [19]

Baseline conditions include commercial quantities of radioactive U3O8. Efficient in-situ recovery reduces U3O8 values of the aquifer. 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. Pursuing more conservative concentrations results in a considerable amount of water usage, and many of these aquifers were not suitable for drinking water before mining initiated." [20]

The EPA is considering the need to update the environmental protection standards for uranium mining because current regulations, promulgated in response to the Uranium Mill Tailings Radiation Control Act of 1978, do not address the relatively recent process of in-situ leaching (ISL) of uranium from underground ore bodies. 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 makes recommendations concerning monitoring to characterize baseline groundwater quality prior to the start of mining operations, monitoring to detect any leachate excursions during mining, and monitoring to determine when groundwater quality has stabilized after mining operations have been completed. 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. [21]

See also

Related Research Articles

Gold cyanidation is a hydrometallurgical technique for extracting gold from low-grade ore by converting the gold to a water-soluble coordination complex. It is the most commonly used leaching process for gold extraction. Cyanidation is also widely used in the extraction of silver, usually after froth flotation.

<span class="mw-page-title-main">Yellowcake</span> Uranium concentrate powder

Yellowcake is a type of powdered uranium concentrate obtained from leach solutions, in an intermediate step in the processing of uranium ores. It is a step in the processing of uranium after it has been mined but before fuel fabrication or uranium enrichment. Yellowcake concentrates are prepared by various extraction and refining methods, depending on the types of ores. Typically, yellowcakes are obtained through the milling and chemical processing of uranium ore, forming a coarse powder that has a pungent odor, is insoluble in water, and contains about 80% uranium oxide, which melts at approximately 2880 °C.

Hydrometallurgy is a technique within the field of extractive metallurgy, the obtaining of metals from their ores. Hydrometallurgy involve the use of aqueous solutions for the recovery of metals from ores, concentrates, and recycled or residual materials. Processing techniques that complement hydrometallurgy are pyrometallurgy, vapour metallurgy, and molten salt electrometallurgy. Hydrometallurgy is typically divided into three general areas:

Uranium(IV) sulfate (U(SO4)2) is a water-soluble salt of uranium. It is a very toxic compound. Uranium sulfate minerals commonly are widespread around uranium bearing mine sites, where they usually form during the evaporation of acid sulfate-rich mine tailings which have been leached by oxygen-bearing waters. Uranium sulfate is a transitional compound in the production of uranium hexafluoride. It was also used to fuel aqueous homogeneous reactors.

<span class="mw-page-title-main">Heap leaching</span> Industrial mining process used to extract precious metals from ore

Heap leaching is an industrial mining process used to extract precious metals, copper, uranium, and other compounds from ore using a series of chemical reactions that absorb specific minerals and re-separate them after their division from other earth materials. Similar to in situ mining, heap leach mining differs in that it places ore on a liner, then adds the chemicals via drip systems to the ore, whereas in situ mining lacks these liners and pulls pregnant solution up to obtain the minerals. Heap leaching is widely used in modern large-scale mining operations as it produces the desired concentrates at a lower cost compared to conventional processing methods such as flotation, agitation, and vat leaching.

<span class="mw-page-title-main">Uranium mining</span> Process of extraction of uranium ore from the ground

Uranium mining is the process of extraction of uranium ore from the ground. Over 50,000 tons of uranium were produced in 2019. Kazakhstan, Canada, and Australia were the top three uranium producers, respectively, and together account for 68% of world production. Other countries producing more than 1,000 tons per year included Namibia, Niger, Russia, Uzbekistan, the United States, and China. Nearly all of the world's mined uranium is used to power nuclear power plants. Historically uranium was also used in applications such as uranium glass or ferrouranium but those applications have declined due to the radioactivity and toxicity of uranium and are nowadays mostly supplied with a plentiful cheap supply of depleted uranium which is also used in uranium ammunition. In addition to being cheaper, depleted uranium is also less radioactive due to a lower content of short-lived 234
U and 235
U than natural uranium.

<span class="mw-page-title-main">Kazatomprom</span> Uranium producer

National Atomic Company Kazatomprom Joint Stock Company (Kazatomprom) (Kazakh: Қазатомөнеркәсіп, romanized: Qazatomónerkásip) is the world’s largest producer and seller of natural uranium, providing over 40% of global primary uranium supply in 2019 from its operations in Kazakhstan. Kazatomprom's uranium is used for the generation of nuclear power around the world.

<span class="mw-page-title-main">Uranium mining in the United States</span> Uranium mining industry in U.S.

Uranium mining in the United States produced 224,331 pounds (101.8 tonnes) of U3O8 in 2023, 15% of the 2018 production of 1,447,945 pounds (656.8 tonnes) of U3O8. The 2023 production represents 0.4% of the uranium fuel requirements of the US's nuclear power reactors for the year. Production came from five in-situ leaching plants, four in Wyoming (Nichols Ranch ISR Project, Lance Project, Lost Creek Project, and Smith Ranch-Highland Operation) and one in Nebraska (Crowe Butte Operation); and from the White Mesa conventional mill in Utah.

<span class="mw-page-title-main">Uranium mining in Colorado</span>

Uranium mining in Colorado, United States, goes back to 1872, when pitchblende ore was taken from gold mines near Central City, Colorado. The Colorado uranium industry has seen booms and busts, but continues to this day. Not counting byproduct uranium from phosphate, Colorado is considered to have the third largest uranium reserves of any US state, behind Wyoming and New Mexico.

<span class="mw-page-title-main">Uranium mining in Wyoming</span>

Uranium mining in Wyoming was formerly a much larger industry than it is today. Wyoming once had many operating uranium mines, and still has the largest known uranium ore reserves of any state in the U.S. At the end of 2008, the state had estimated reserves dependent on price: 539 million pounds of uranium oxide at $50 per pound, and 1,227 million pounds at $100 per pound.

<span class="mw-page-title-main">Uranium ore</span> Economically recoverable concentrations of uranium within the Earths crust

Uranium ore deposits are economically recoverable concentrations of uranium within Earth's crust. Uranium is one of the most common elements in Earth's crust, being 40 times more common than silver and 500 times more common than gold. It can be found almost everywhere in rock, soil, rivers, and oceans. The challenge for commercial uranium extraction is to find those areas where the concentrations are adequate to form an economically viable deposit. The primary use for uranium obtained from mining is in fuel for nuclear reactors.

Leaching is a process widely used in extractive metallurgy where ore is treated with chemicals to convert the valuable metals within the ore, into soluble salts while the impurity remains insoluble. These can then be washed out and processed to give the pure metal; the materials left over are commonly known as tailings. Compared to pyrometallurgy, leaching is easier to perform, requires less energy and is potentially less harmful as no gaseous pollution occurs. Drawbacks of leaching include its lower efficiency and the often significant quantities of waste effluent and tailings produced, which are usually either highly acidic or alkali as well as toxic.

<span class="mw-page-title-main">Crow Butte</span> Uranium mine in Nebraska, United States

Crow Butte is a uranium mining operation located four miles (6 km) southeast of the city of Crawford in Dawes County, Nebraska, United States. Cameco Corporation owns and operates Crow Butte through its wholly owned subsidiary, Crow Butte Resources, Inc.

Four Mile is Australia's fifth uranium mine. It is sited in the Frome Basin in far north of the state of South Australia, around 600 kilometres (370 mi) north of the state capital, Adelaide. It is 10 kilometres (6 mi) from the existing Beverley uranium mine, where its uranium oxide product is produced. Construction of the mine commenced in late 2013 and the mine was officially opened in June 2014.

<span class="mw-page-title-main">Uranium mining in Namibia</span>

Namibia has one of the richest uranium mineral reserves in the world. There are currently two large operating mines in the Erongo Region and various exploration projects planned to advance to production in the next few years.

The world's largest producer of uranium is Kazakhstan, which in 2019 produced 43% of the world's mining output. Canada was the next largest producer with a 13% share, followed by Australia with 12%. Uranium has been mined in every continent except Antarctica.

The Willow Creek mine is an in-situ leach (ISL) uranium mining project located in Powder River Basin in the state of Wyoming, United States. It comprises the Irigaray central processing plant and wellfields, and the Christensen Ranch ion exchange plant and wellfields.

The Imouraren mine is a large mine located in the northern part of Niger in Agadez Region, about 80 km (50 mi) south of Arlit. Imouraren represents one of the largest uranium reserves in Niger having estimated reserves of 109.1 million tonnes of ore grading 0.06% uranium. It is the site of a uranium mining project involving French company Areva and SOPaMin. The U3O8 ore grade at nearby SOMAIR is 14,000 tons at 0.3%, COMINAK is 29,000 t at 0.4% and Imouraren 120,000t at 0.15%.

<span class="mw-page-title-main">Uranium acid mine drainage</span>

Uranium acid mine drainage refers to acidic water released from a uranium mining site using processes like underground mining and in-situ leaching. Underground, the ores are not as reactive due to isolation from atmospheric oxygen and water. When uranium ores are mined, the ores are crushed into a powdery substance, thus increasing surface area to easily extract uranium. The ores, along with nearby rocks, may also contain sulfides. Once exposed to the atmosphere, the powdered tailings react with atmospheric oxygen and water. After uranium extraction, sulfide minerals in uranium tailings facilitates the release of uranium radionuclides into the environment, which can undergo further radioactive decay while lowering the pH of a solution.

<span class="mw-page-title-main">Greyhawk Mine</span> Abandoned uranium mine in Ontario, Canada

Greyhawk Mine is a decommissioned underground uranium mine located in Faraday Township near Bancroft, Ontario. It operated from 1954 to 1959 and from 1976 to 1982. The mine produced 80,247 tons of uranium ore, of which 0.069% was U3O8 worth $834,899.

References

  1. ↑ Hardy, M.; Ramey, M.; Yates, C.; Nielsen, K. (2003). Solution Mining of Nahcolite at the American Soda Project, Piceance Creek, Colorado (PDF). 2003 SME Annual Meeting. Archived from the original (PDF) on 2007-09-28.
  2. ↑ Uranium 2014, International Atomic Energy Agency/OCED Nuclear Energy Agency, 2014.
  3. 1 2 Li, Guihe; Yao, Jia (March 2024). "A Review of In Situ Leaching (ISL) for Uranium Mining". Mining. 4 (1): 120–148. doi: 10.3390/mining4010009 . ISSN   2673-6489.
  4. 1 2 Mudd, Gavin M. (January 2000). Acid In Situ Leach Uranium Mining : 1 - USA and Australia (PDF). Tailings & Mine Waste '00. Fort Collins, CO, USA. Archived from the original (PDF) on 2009-09-13.
  5. 1 2 "In-Situ Recovery (ISR)". enCore Energy. 2023-09-21. Retrieved 2024-07-04.
  6. ↑ Honeymoon Project
  7. ↑ "Domestic Uranium Production Report". Energy Information Administration.
  8. ↑ "U.S. Uranium In-Situ-Leach Plants by Owner, Capacity, and Operating Status at End of the Year". Domestic Uranium Production Report. Energy Information Administration. Archived from the original on 2012-05-24. Retrieved September 19, 2012.
  9. ↑ "Uranium production begins," Mining Engineering, December 2010.
  10. ↑ Rudenko, A. A.; Troshkina, I. D.; Danileyko, V. V.; Barabanov, O. S.; Vatsura, F. Ya (2021-10-13). "Prospects for selective-and-advanced recovery of rhenium from pregnant solutions of in-situ leaching of uranium ores at Dobrovolnoye deposit". Gornye Nauki I Tekhnologii = Mining Science and Technology (Russia). 6 (3): 158–169. doi:10.17073/2500-0632-2021-3-158-169. ISSN   2500-0632. S2CID   241476783.
  11. ↑ Sutton, Gary (2019). "Reconciling Mineral Reserves at the well-to-well in-situ copper leaching operation at San Manuel Mine, Arizona, USA". CIM Geology. 10 3Q2019 (3): 133–141. Bibcode:2019CIMJ...10..133S. doi:10.15834/cimj.2019.9.
  12. ↑ Peter G. Chamberlain and Michael G. Pojar (1984) Gold and silver leaching practices in the United States, US Bureau of Mines, Information Circular 8969, p.24.
  13. ↑ In Situ Leach (ISL) Mining of Uranium , retrieved 2012-10-12
  14. ↑ "Schmidt, C: Groundwater Restoration and Stabilization at the Ruth-ISL Test Site in Wyoming, USA. In: In Situ Leaching of Uranium - Technical, Environmental and Economic Aspects, Proceedings of a Technical Committee Meeting, IAEA- TECDOC-492, Vienna 1989, p.97-126", Vienna, 492: 97–126, 1989
  15. ↑ Catchpole, Glenn; Kirchner, Gerhard: Restoration of Groundwater Contaminated by Alkaline In-Situ Leach of Uranium Mining. In: Merkel, B et al. (Ed.): Uranium Mining and Hydrogeology, GeoCongress 1, Köln 1995, p.81-89, 1995, pp. 81–89
  16. ↑ Nigbor, Michael T; Engelmann, William H; Tweeton, Daryl R: Case History of a Pilot-Scale Acidic In Situ Uranium Leaching Experiment. United States Department of the Interior, Bureau of Mines Report of Investigations RI-8652, Washington D.C., 1982, 81 p, 1982, p. 81
  17. ↑ Engelmann, W H; Phillips, P E; Tweeton, D R; Loest, K W;Nigbor, M T: Restoration of Groundwater Quality Following Pilot-Scale Acidic In-Situ Uranium Leaching at Nine- Mile Lake Site Near Casper, Wyoming. In: Society of Petroleum Engineers Journal, June 1982, p.382-398, 1982, pp. 382–398
  18. ↑ Mays, W M: Restoration of Groundwater at Three In- Situ Uranium Mines in Texas. In: IAEA (Ed.), Uranium in situ leaching. Proceedings of a Technical Committee Meeting held in Vienna, 5-8 October 1992, IAEA-TECDOC-720, Vienna 1993, p.191- 215, 1993, pp. 191–215
  19. ↑ J.K. Otton, S. Hall: In-situ recovery uranium mining in the United States: Overview of production and remediation issues, International Symposium on Uranium Raw Material for the Nuclear Fuel Cycle: Exploration, Mining, Production, Supply and Demand, Economics and Environmental Issues, 2009
  20. ↑ "In-Situ Recovery of Uranium" (PDF). 2010-09-29. Archived from the original (PDF) on 2013-07-28. Retrieved 2012-10-16.
  21. ↑ "Advisory on EPA's Draft Technical Report entitled Considerations Related to Post- Closure Monitoring of Uranium In-Situ Leach/In-Situ Recovery (ISL/ISR) Sites" . Retrieved 2012-10-13.
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