ReviewIn situ recovery, an alternative to conventional methods of mining: Exploration, resource estimation, environmental issues, project evaluation and economics
Graphical abstract
Introduction
Globally, the mining industry faces a number of challenges, including:
- •
increasingly rapid depletion of low-cost, high profit, deposits, mined by conventional methods;
- •
increasing costs of mining and processing;
- •
accumulation of tailings, requiring expensive management and ongoing monitoring;
- •
reduced and variable commodity prices (Bloomberg Commodity Index, 2015); and,
- •
consequently, reduced profitability and return on investment.
Innovation and new approaches to the extraction of minerals provide answers to these challenges.
In situ recovery (ISR) is the one of the most effective methods to address the costs of mining. The key feature of ISR is transferring a significant proportion of the hydrometallurgical processing the mineralised bodies to the subsurface to directly obtain solutions of metals of interest.
ISR technology has been in existence for 65 years, but was only widely developed for uranium production in South Kazakhstan last the last 10–15 years with strong improvements in experience in applying ISR. This technology has been used for copper for 40 years, but the first experience was not entirely positive. Copper and gold mines have operated successfully over the last 10-15 years in Russia building on the uranium ISR experience. At Dalur, a uranium mine in Russia, a plant is under construction to extract scandium and rare earths as by-products from the uranium pregnant solutions. It is the authors' opinion that the growing experience in ISR technology will allow the technique to be adopted more widely.
The evaluation of the suitability of deposits for ISR requires different and/or modified approaches compared to traditional mining/extraction techniques. Furthermore, some deposits that are currently uneconomic to extract using traditional mining methods may be a profitable as ISR operations.
An important reason for the slow uptake of ISR technology is the lack of experience and expertise in ISR, and the need for a somewhat more complex approach for resource estimation for deposits to use ISR.
This article is aims to highlight key features of current ISR practice, based on modern technologies and in challenging economic conditions.
Section snippets
What is in situ recovery?
Conventional mining in open pit and underground mines involves removing ore (and waste) from the ground, and then processing it to extract the metals of interest.
In situ recovery (ISR), also known as in situ leaching (ISL), use solutions that are pumped through the mineralized body in situ (underground) to recover metals by leaching. In situ mining according to Bates and Jackson (1987), a definition endorsed by The National Academy of Sciences (2002), is the “removal of the valuable components
History of ISR
In situ recovery (ISR)2 uranium mining technology was developed independently in both the USSR and in 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 (IAEA, 2001) (Fig. 2).
The first field tests of acid ISR technology for extracting uranium
In situ recovery of metals other than uranium
Research has shown that there are thermodynamic conditions suitable for leaching a broad spectrum of elements using solutions based on sulphuric acid or other solvents, with or without additional oxidants: copper, gold, silver, zinc, cadmium, lead, manganese, lithium, molybdenum, selenium, vanadium, scandium, yttrium, rare earth elements, indium, beryllium, chromium, gallium, nickel, and cobalt (Laverov et al., 1998, O’Gorman et al., 2004).
Copper is the most popular commodity (after uranium)
Geological features of deposits suitable for mining by in situ recovery
ISR can allow profitable exploitation of deposits with low grades of metals and/or small resources unsuitable for conventional mining.
There are two critical parameters that must be met for a deposit amenable to ISR:
- •
mineralisation must be located in permeable environment; and,
- •
the lixiviant should be suitable for selective leaching of a specific component from the deposit.
Permeability is the most critical parameter for ISR (Table 2). The lixiviant must be able to move between injection and
Environmental aspects of ISR
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;
- •
much smaller volumes of mining and hydrometallurgical effluents (that could contaminate the surface, air and water supply sources); and,
- •
no exhaust pollution (International Atomic Energy Agency (IAEA), 2001, O’Gorman et al., 2004).
As a result, the impact of
Economic attributes and advantages of ISR
The uranium industry shows that ISR is the cheapest source of uranium. The production cost (OpEx) of uranium is less than US$40 per pound U3O8 at the most of the deposits operated by ISR (Fig. 9). These deposits are profitable while uranium prices are low. The underground mines at Olympic Dam in South Australia that produces uranium as by-product, and at McArthur River in Canada with extremely high uranium grades (≈ 15%) compete with ISR deposits for low production costs.
Capital investments
Special requirements for exploration, mineral resource estimation and development of ISR projects
Exploration, estimation and development of ISR projects has some features along with the usual requirements to mining projects. Particular features of resource estimation and development of ISR projects are described in this section.
Projects for ISR should be checked for compliance with the criteria shown in the Table 2 from the earliest stages of evaluation and exploration (Table 7). Hydrogeological investigations are strongly recommended beginning with the evaluation stage. Filtration
Conclusions
In situ recovery (ISR) is the one of the most effective methods available to reduce the cost of production for certain deposits or parts of deposits. One feature of ISR is transferring part of hydrometallurgical processing to mineralised bodies below the surface and directly obtaining solutions of metals.
Uranium industry is the first experience of absolutely successful using ISR for mining. Uranium production share by ISR in the World reached 51% in 2014. Experience of ISR in the uranium
References (31)
- et al.
A practical approach to determine permeability from wireline measurements
SPE Int.
(2007) Prepared by: The Joint Ore Reserves Committee of the Australasian Institute of Mining and Metallurgy
(2012)Tables and Charts
(2015)Worldwide ISL Uranium Mining Outlook. URAM 2014
(2014)- et al.
Geological 3D Modelling and Resource Estimation of Budenovskoye Uranium Deposit (Kazakhstan)
(2014) History of the San Manuel-Kalamazoo Mine, Pinal County, Arizona
(2014)- et al.
Prediction, Research, Exploration and Resource Estimation of Uranium Deposits for in Situ Recovery (in Russian)
(1997) CIM Definition Standards for Mineral Resources and Mineral Reserves, 2010
(2010)- et al.(2009)
Pilot test of in situ leaching of nickel from silicate ores
Globe
Manual of Acid in Situ Leach Uranium Mining Technology
Beyond the three Mines - in Situ Uranium Leaching Proposals in South Australia
In Situ Leaching of Ores. Moscow
A Research Report for Friends of the Earth (Fitzroy) with the Australian Conversation Foundation
Cited by (118)
Green recovery of rare earth elements under sustainability and low carbon: A review of current challenges and opportunities
2024, Separation and Purification TechnologyIndirect in situ bioleaching is an emerging tool for accessing deeply buried metal reserves, but can the process be managed? – A case study of copper leaching at 1 km depth
2023, Environmental Technology and Innovation
- 1
More accurately is hydraulic conductivity or permeability coefficient, m/day.