The US Nuclear Regulatory Commission says In-situ recovery (ISR) has never contaminated the drinking water supply in the US since its inception about 50 years ago.
The International Atomic Energy Agency (IAEA) says ISR mining has become a standard uranium production method following early experimentation and use in the 1960s.
ISR for copper was introduced in the 1970s, and several successful natural tests and mines were conducted. ISR for gold, copper, nickel, rare earth elements, and scandium has been successfully developed over recent years.
The IAEA said ISR uranium mining technology was developed independently in the USSR and the USA in the late 1950s to early 1960s.
It was developed in both countries using similar engineering and technological approaches.
However, the Soviets adopted the acid leach system, while the US specialists employed an alkaline, primarily carbonate-based, system.
According to the agency, ISR allows the extraction of mineralisation with minimal disturbance to the existing natural conditions.
In contrast to underground and open pit mining, there are no large open pits, no rock dumps and tailings storage, no dewatering of aquifers, and much smaller volumes of mining and hydrometallurgical effluents that could contaminate the surface, air and water supply sources; and no exhaust pollution.
According to the IAEA, ISL has become a standard uranium mining production method, although, in the past, it was applied mainly in Bulgaria, the Czech Republic, Kazakhstan, Ukraine, and Uzbekistan.
Recently, the agency says, it has been used in Australia, China, and the USA with minor operations and experiments elsewhere.
The IAEA says ISL mining is expected to remain a significant uranium production method for at least the medium term.
The agency further says there has been continual development and improvement of ISL techniques, particularly in the two decades since it published the Manual of Acid In Situ Leach Uranium Mining Technology in 2001.
A 2019 study titled Groundwater Restoration Following in-situ Recovery (ISR) Mining of Uranium by Omar Ruiz et al. states that nearly all US domestic uranium production is currently from ISR.
The study published in Science Direct notes that in 2015, total US production was 3.3 M lbs of U3O8 from one underground mine and six ISL mines.
What is ISL?
ISL is defined as the extraction of uranium from the host sandstone.
Generally, sedimentary formations are dominated by highly permeable sandstone by chemical solutions and uranium recovery at the surface.
ISL extraction is conducted by injecting a suitable leach solution into the ore zone below the water table, oxidising complexing and mobilising the uranium, and recovering the pregnant (loaded) solutions through production wells.
A well-defined system of injection and extraction wells (wellfields) equipped with filter (screen) sections covering the uranium ore horizon is operated to reach optimum penetration of the leach solution to the uranium ore.
The geometry of wellfield patterns and the spacing between injection and extraction wells must be adjusted to orebody characteristics to establish a stable hydrological pumping regime at a suitable flow rate.
To avoid or minimise the migration of mining fluid into the environment, a bleed from the lixiviant cycle ranging up to a few per cent is usually applied. A network of additional wells around the mining zone monitors and controls wellfield performance within the mining horizon and neighbouring formations. Acid and alkaline leach technologies employ acid and alkaline-based leaching systems, respectively.
Dilute sulphuric acid is commonly used for the former, and carbonate or bicarbonate-based leach solutions are used for the latter.
Oxygen or hydrogen peroxide is typically added to maintain the solid oxidising conditions required to ooxidisetetravalent uranium in ore minerals to its hexavalent stage, thus forming uranyl ions that undergo complexation either with sulphate or carbonate ions.
After recovery of the anionic uranyl (sulphate or carbonate) complexes from the pregnant lixiviant, either by ion exchange, which is predominantly applied, or solvent extraction, barren lixiviant is refortified by dosing the above chemicals in a controlled manner, thus forming a continuous lixiviant recycle.
The total amount of mining fluid (lixiviant) in the lixiviant cycle for a given wellfield operation is mainly determined by the (practical) pore volume available for fluid transport in the mineralised aquifer.
Why use ISR?
ISR is a minimally invasive, environmentally friendly, and economically competitive way of extracting minerals from the ground that has proven to be a successful method of extracting uranium.
Due to its cost efficiency, it is economically viable to extract lower-grade uranium deposits that may not justify the cost of conventional open pit or underground mining.
In addition to significantly lower capital and operating costs, ISR operates without the open pits, waste dumps, or tailings associated with conventional mining and milling, making extraction more environmentally responsible while resulting in a faster and more cost-efficient permitting, development and remediation process.
ISR extraction can extract the uranium while leaving the surface intact, and when reclamation is completed, it is returned to its original state and used.
Since its first appearance in the 1960s, ISR technology has progressed considerably to the point where the process is a controllable, safe, and benign method of uranium production that is heavily regulated, especially in the United States.
In the United States, many companies will use a lixiviant that combines oxygen and sodium bicarbonate in the native groundwater, extracting uranium at a near-neutral pH and significantly less environmental impact.
Environmental friendly
According to EnviroCopper, ISR has a lower visual and minimal environmental impact of mineral extraction than open-cut and underground mining.
ISR operations do not require blasting and movement of waste rock, therefore creating little or no noise, no dust and leaving no large tailings dams or large open pits.
Because of this, access to land may not be restricted; cropping, grazing and foot traffic can co-exist, with the land being returned to its pre-mining use quicker than conventional mining.
ISR is known as “invisible” mining due to its shallow visual impact. This has significant benefits in areas of competing land use like farming, tourism, and urbanisation.
Since ISR does not involve earth or rock movement, blasting or extensive excavations, it produces negligible dust and noise, enabling it to be carried out in areas of competing land use.
There is no longer a need for it to be farming or mining; ISR infrastructure may not need to interfere with land access. At the end of operation everything is removed and the area can be returned to its pre-mining use quickly and effectively.
*various sources
