MP Materials Mountain Pass Heavy Rare Earth Separation Facility

The Mountain Pass heavy rare earth separation facility is a new circuit at MP Materials' California mine built to separate dysprosium and terbium from the site's heavy rare earth concentrate. It matters because, by REEx's count, the U.S. produced no commercial-scale heavy rare earth compounds in 2025 and relied on imports for all of them (REEx).

Who runs the facility and where it is

MP Materials operates the Mountain Pass mine and processing site (MP Materials). The site sits in the United States, near Mountain Pass in San Bernardino County, California, on 2,232 acres about 50 miles southwest of Las Vegas (10-K).

MP's filings treat the heavy rare earth plant as its own asset, the "HREE Facility," next to the chlor-alkali plant and recycling work (10-K). REEx tracks the mine and the separations plant, which MP says began operating in 2023, as the Mountain Pass project (10-K).

How the Mountain Pass heavy rare earth separation circuit works

The circuit is a separation step. MP expects it to produce mainly terbium and dysprosium products at first (10-K). After that, MP plans to add other heavy rare earth products, starting with samarium, in line with its agreement with the Department of War (MP Materials). On its August 6, 2026 earnings call, MP said it was planning first samarium production in 2028 (Q2 2026 call).

MP has committed to restart the site's idle chlor-alkali plant to make hydrochloric acid, sodium hydroxide and sodium hypochlorite for its separations (10-K).

Capacity and status (as of August 2026)

In February 2022, the Department of Defense awarded MP a contract through its Industrial Base Analysis and Sustainment program for a commercial-scale heavy rare earth processing plant at Mountain Pass (MP Materials). MP said in November 2025 that the dysprosium-terbium circuit would have a nameplate capacity of 200 metric tons a year (MP Materials).

On the August 6, 2026 call, MP said it had reached mechanical completion of its first heavy rare earth separation circuit in May, was "actively commissioning" the dysprosium-terbium circuit and was preparing to introduce feed imminently. It said it remained on track to produce terbium and dysprosium later in 2026, with the ramp depending on commissioning at scale and on putting quality ahead of quantity (Q2 2026 call).

REEx has cautioned that commissioning activity is different from sustained commercial production. It has also noted that Mountain Pass is richer in light rare earths than heavy ones, and that access to dysprosium- and terbium-bearing feed remains a constraint (REEx).

Where the feed comes from and where the output goes

Since late 2023, MP has produced and stockpiled a heavy rare earth concentrate called SEG+ at Mountain Pass. It holds samarium, europium and gadolinium plus terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and yttrium. The plant will also take third-party feedstock from emerging suppliers (MP Materials), including recycled material (10-K).

On August 6, MP's CEO said the company remained on track to begin shipping product from Mountain Pass to Independence later in 2026 (Q2 2026 call). Independence, in Fort Worth, Texas, began making NdFeB magnets in December 2025 (10-K).

SEG+ also carries gadolinium (REEx). In August 2026, MP said it had signed a long-term offtake to supply separated gadolinium to a new U.S. aerospace and defense customer (MP Materials), and that it was moving ahead with engineering and procurement for a gadolinium separation project (Q2 2026 call).

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