In-Situ Leaching

In-situ leaching is the main way rare earths are mined from ion-adsorption clays. A salt solution, the lixiviant, is injected into the ground, where it trades places with rare earth ions held on clay, and the rare earth-bearing "pregnant" solution is collected at the surface. The International Energy Agency calls it the dominant extraction method for these deposits, mined primarily in southern China and Myanmar (IEA, May 2026). Chinese Academy of Sciences researchers wrote in 2024 that ion-adsorption deposits supply more than 95% of global heavy rare earth demand (Wang et al., The Innovation, May 2024).

How in-situ leaching of rare earth clays works

In ion-adsorption clays, weathering of granite and other igneous rock leaves rare earth ions adsorbed on clay minerals so they can be recovered by low-temperature ion-exchange leaching. The IEA says operators typically inject ammonium sulfate or magnesium sulfate into the ore body and pump the dissolved rare earths to the surface. The IEA counts this step as mining that produces mixed rare earth compounds for separation (IEA).

MCRE Resources says that at its Kenering mine in Malaysia it pumps native groundwater fortified with ammonium sulfate through the orebody from injection holes. Collection tunnels, diversion holes and drains gather the pregnant solution, which a hydrometallurgical plant turns into lanthanide carbonate (MCRE).

In-situ leaching compared with heap and tank leaching

Ion-adsorption mining has gone through three generations: pond leaching, heap leaching and in-situ leaching (Wang et al.). Pond leaching moved excavated topsoil into a tank and sprayed it with sodium chloride and oxalic acid; heap leaching soaked a mound of ore with ammonium sulfate and oxalic acid. Both destroyed vegetation and caused soil erosion, and China's 2012 entry conditions for the rare earth industry prohibited both for heavy rare earth production (Chen et al., Fundamental Research, 2025). The IEA notes that ion-adsorption clays may also be scrubbed and then tank leached or processed by ion exchange (IEA).

In-situ leaching avoids excavation and creates less solid waste, and nearly all ion-adsorption deposits are now mined this way. It brought new problems, though: ammonia nitrogen in water and soil, release of harmful elements, and landslides. Wang and colleagues cite reports that 7 to 15 metric tons of ammonium salts are injected for each metric ton of rare earth oxide (Wang et al.).

Environmental damage documented in Ganzhou

Much of the extraction in southern Jiangxi's Ganzhou region uses in-situ leaching with large amounts of ammonium sulfate, a 2025 study says (Wang Y. et al., Microorganisms, 2025). At one Ganzhou site, 12 years after mining ended, tailings had a mean pH of 3.90. Ammonia nitrogen in the soil was 12 to 40 times higher than in the ore soil before mining, which the authors traced to residual leaching agents (Zhang et al., Environmental Pollution, December 2020).

Ground stability is a wider risk in ion-adsorption mining. In a 2020 laboratory study, Wuhan Institute of Technology researchers wrote that improper lixiviant injection can swell clay minerals in the ore body, causing landslides and other geological disasters (Chen Z. et al., Frontiers in Chemistry, December 2020).

Is China moving away from ammonium sulfate?

Wang and colleagues wrote in 2024 that ammonium salt-based mining techniques have been prohibited since 2018 (Wang et al.). Later sources still describe ammonium sulfate in use: the 2025 Ganzhou study does, and the IEA in 2026 lists ammonium sulfate or magnesium sulfate as typical reagents and names ammonium sulfate recycling as a way to cut emissions (IEA). One Chinese research team has suggested magnesium sulfate as a substitute to cut ammonia nitrogen pollution (Chen et al.), and laboratory work has found magnesium salts recover rare earths while limiting clay swelling (Chen Z. et al.).

Projects using or testing in-situ leaching outside China (as of October 2026)

• MCRE Resources, Kenering, Malaysia. REEx reported in November 2025 that Malaysia suspended MCRE's operations after the Perak River turned blue, and that the Natural Resources and Environment Ministry found the operation's effluent matched the river's discoloration (REEx, November 2025). Southern Alliance Mining, which owns 40% of MCRE, said the suspension orders were issued over erosion and sedimentation control, including run-off discharge above permitted limits, as well as workflow, reporting and other non-compliances. It said the orders were lifted on January 15, 2026, operations resumed, and the orders were entirely unrelated to the river incident (Southern Alliance Mining, January 16, 2026).
• Brazilian Critical Minerals, Ema, Brazil. BCM is developing its Ema ion-adsorption clay project in Amazonas using in-situ recovery with magnesium sulfate to make a mixed rare earth carbonate. The state regulator approved magnesium sulfate injection for pilot testing in April 2025; as of October 15, 2026, the development environmental license was pending (BCM, October 15, 2026).
• Cobra Resources, Boland, Australia. At the Boland project in South Australia, Cobra believes the rare earths sit in permeable paleochannel sediments that may suit in-situ recovery, which would circulate lixiviant through a confined aquifer, REEx reported in June 2026 (REEx, June 2026). Cobra's July 2026 update targets a small-scale production plant at the existing Boland wellfield in the first half of 2027, and its consultants have begun the engagement process to secure permit approvals for that demonstration (Cobra RNS via Investegate, July 29, 2026). Cobra's July 2026 update said the consultancy ERM was completing a maiden mineral resource estimate (Cobra RNS via Investegate, July 29, 2026); Cobra had not published it as of October 21, 2026 (Cobra RNS list via Investegate). In June 2026 REEx noted no declared reserve, feasibility study or commercial field trial (REEx).

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