Ionic Adsorption Clay

Ionic adsorption clay is a type of rare earth deposit: weathered granite or other igneous rock in which rare earth ions sit loosely attached to clay surfaces. Deposits of this type in southern China are the world's primary source of the heavy rare earths, according to USGS Professional Paper 1802-O. The ionic clays of Myanmar's Kachin State are rich in dysprosium and terbium (REEx).

How ionic adsorption clay deposits form

The U.S. Geological Survey describes three steps in tropical regions with moderate to high rainfall. Groundwater leaches rare earths out of granite bedrock. A thick laterite soil rich in clay develops above the granite. The freed rare earths then become weakly fixed onto clays such as kaolinite and halloysite (USGS). A 2020 study of Chinese and Madagascan samples found them mostly on kaolinite (Borst et al., Nature Communications).

Grades are low. In southern China, rare earth concentrations range from about 300 to 2,000 parts per million, and the richest layer is usually the B horizon, or subsoil, which also holds the most clay. USGS says these clay deposits lack radioactivity (USGS).

Why ionic clay matters for heavy rare earths

The clays are a resource for yttrium (USGS). Estimates of their share differ. The 2020 Borst study put Chinese ion-adsorption deposits at about 35% of China's rare earth production and roughly 80% of global heavy rare earth supply. A 2025 study says the deposits supply over 90% of global medium and heavy rare earth resources (Tao et al., Frontiers in Earth Science).

How rare earths are leached from ionic clay

The rare earths come off the clay after mild acidification with an ammonium sulfate solution (Borst et al.). USGS says easy extraction, heavy rare earth enrichment, low labor costs and a localized lack of environmental protection made such modest grades economic in southern China (USGS).

Chinese mines moved through three methods: pool leaching, heap leaching and in-situ leaching. In-situ leaching, which mainly uses ammonium sulfate, pumps the solution into the ground through injection holes. The authors warn of landslide risk near those holes and of leachate leaking into groundwater (Tao et al.). Borst and co-authors say low-cost in-situ and heap leaching has had a significant environmental impact in China.

Leaching yields a mixed concentrate that still has to be separated; a Brazilian ionic clay mine, for example, produced mixed concentrates with elevated terbium and dysprosium (USGS). As of September 2026, REEx reported that no project outside China had yet proven continuous commercial-scale output of separated dysprosium, terbium and yttrium (REEx).

China and Myanmar supply (as of October 2026)

China's ion-adsorption deposits are spread across seven southeastern provinces (Tao et al.; see South China ion-adsorption clay operations). Beijing tightened regulation of the mining around 2010 as its environmental impacts became clear, and many investors turned to Myanmar (Frontier Myanmar, August 2025).

Most of the Kachin mines sit near the towns of Pangwa and Chipwi. Global Witness reported in May 2024 that China's imports of heavy rare earth oxides from Myanmar rose from 19,500 metric tons in 2021 to 41,700 metric tons in 2023. It described the mining there as largely unregulated and cited water sampling data showing highly acidic streams with elevated arsenic (Global Witness).

After the Kachin Independence Army seized Pangwa in October 2024, China closed its border gates into territory held by the Kachin Independence Organization (KIO) and imports of rare earth concentrates from Myanmar fell by more than 80%. Imports recovered after the KIO reportedly began letting companies export existing stockpiles from March 2025. By May, volumes were similar to a year earlier, per Chinese customs data cited by Frontier Myanmar.

Ionic clay projects outside China (as of October 2026)

• Serra Verde, Goiás, Brazil: USA Rare Earth calls the Pela Ema mine the first operating ionic clay deposit in the Western world (April 2026 release). It closed its acquisition of the Serra Verde group on September 3, 2026 (Form 8-K).
• Caldeira, Minas Gerais, Brazil: Lynas Rare Earths signed a binding deal on October 1, 2026 to acquire Meteoric Resources and its project. The companies call Caldeira the largest known ionic clay JORC resource outside China. On an indicative timetable, they expect implementation by March 2027, subject to shareholder, court and Brazilian regulatory approval (ASX release).
• Makuutu, Uganda: Ionic Rare Earths holds 60% of the project company. It began a strategic review on July 31, 2026, with a mining license application still in progress (September 2026 quarterly).
• Ampasindava, Madagascar: Harena Rare Earths plans heap leaching, washing the rare earths out with seawater and then ammonium sulfate (January 2026 study). It said its exploitation permit was formalized in October 2026 and that it now needs an environmental permit before building a pilot plant, as it works toward production in 2028 (October 2026 release).

Frequently asked questions