Praseodymium Without a Licence: Recovery of the Nd/Pr Pair from Magnet Leachates, Magnet-Plant Effluent and Phosphogypsum by Deep-Vacuum Phase Separation

Abstract

Praseodymium is almost never sold as praseodymium. It leaves the refinery bound to neodymium as the NdPr alloy known as didymium, because praseodymium and neodymium are adjacent lanthanides whose separation factor in solvent extraction is close to unity, and splitting them demands hundreds to thousands of counter-current stages. That single fact — not ore, not geology — is the structure of the market. Whoever holds the Nd/Pr separation train holds the permanent-magnet industry. Approximately 85% of neodymium mining and approximately 90% of world NdFeB magnet output sit in one jurisdiction. The NdPr oxide benchmark reached USD 133.02/kg on 1 July 2026, a 21.4% rise in a single month from a trough near USD 90/kg on 1 June; praseodymium metal traded at USD 245.40/kg in 2026, up 112.65% year on year. On 22 June 2026 ten United States entities including MP Materials and USA Rare Earth were added to Chinese export-control lists, and MOFCOM Announcement No. 26 of 2026, effective 1 July, established a formal reporting and reward mechanism for suspected export-control violations. This paper argues that the praseodymium bottleneck is a separation bottleneck sitting downstream of feedstock that is already dissolved. Three aqueous streams carry the Nd/Pr pair today and are managed as waste or as low-value scrap: the acid leachate of end-of-life NdFeB magnets, which are dissolved rather than crushed in the recycling route and hold roughly 225 kg of neodymium and 55 kg of praseodymium per tonne of scrap, with worldwide end-of-life magnet recycling still under 1%; the wash waters and grinding effluent of magnet manufacture, carrying up to 10% of magnet mass; and phosphogypsum, a world flow of approximately 250 Mt/year at roughly 0.3% REO containing on the order of 30,000 t of praseodymium annually, with approximately 1.5 billion tonnes already stacked in the United States alone. We describe the application of ARBOK Zero Waste Discharge (ZWD) — deep-vacuum phase separation at approximately 1 kPa and 6–40 °C — to these streams. The process takes the liquor whole, returns clean water at up to 100% of intake, removes the entire dissolved load as dry separated salt fractions at 10–15% moisture, separates the acid from the metal value in the same pass, and delivers a rare-earth concentrate to a compact second-stage refining unit producing individual oxides including the Nd/Pr split. Specific energy is under 1 kWh/m³, with no membranes, no reagents and no consumables. We set out the process rationale, the mass balance per tonne of magnet scrap entering the leach — approximately USD 37,000 of contained value at 2026 prices taken 20% below prevailing levels — the siting logic, and the strategic consequence: the step that constitutes the actual monopoly is small enough to install at national scale.