Sequential differential-precipitation process for rare-earth pair separation

Rare-earth element (REE) refining is bottlenecked at the separation stage. Adjacent lanthanides — Nd and Pr, Dy and Tb, La and Ce, Sm and Eu, Y and the heavy rare earths — sit within nanometers of each other on the periodic table, which means their ionic radii and coordination chemistries differ only slightly. The industrial response to this has been solvent-extraction (SX) cascades: long trains of organic-solvent mixer-settlers that separate one ionic species at a time, requiring tens to hundreds of stages, organic diluents, acidic stripping solutions, and continuous recycling of enormous solvent inventories. SX works, but it is capital-intensive, operationally complex, hazardous, and difficult to deploy at small or mid-scale where feedstocks are irregular — exactly the feedstock profile of magnet recycling, secondary recovery, and diversified refinery feed. This asset covers a cascade of precipitation stages engineered to exploit the differential solubility products (Ksp) of specific rare-earth counter-anion pairs as a function of pH and redox potential. Rather than a single bulk precipitation step (which co-precipitates the adjacent elements and is already well-documented in the prior art), the process sequences at least three pH- and redox-adjusted stages — each matched to a specific anion system — to achieve meaningful per-stage separation factors between adjacent REE pairs. The five chemically distinct pairs covered are: Nd/Pr separated via oxalate precipitation; Dy/Tb via fluoride; La/Ce via ceric sulfate (exploiting Ce's accessible +4 oxidation state); Sm/Eu via reductive carbonate (exploiting Eu's accessible +2 state); and Y together with the heavy rare earths via double-sulfate crystallization. By pairing each separation with the anion chemistry that maximally leverages the Ksp divergence between those two elements, thermodynamic modelling gives upper-bound per-stage separation factors of 1.5 for adjacent pairs and 3.0 for non-adjacent pairs — not SX performance; whether this yields industrially meaningful enrichment on a simpler, lower-capital platform is untested. The timing argument for this technology is structural. REE supply chains are under sustained regulatory and geopolitical pressure; the Inflation Reduction Act and its equivalents in the EU and Japan are actively driving investment in domestic and allied separation capacity. The refining bottleneck is real: mining output and magnet-recycling recovery are both outpacing available separation capacity outside of China. SX capacity takes years and hundreds of millions of dollars to build. A precipitation-based alternative that could, if bench purity is confirmed, reach commercially usable purity in a modular plant — particularly for magnet-grade Nd/Pr and Dy/Tb streams — would address an immediate gap; purity and capital cost are not yet computed or measured.

This is a process asset, not a new solid-state material, so conventional lattice-dynamics computational validation (phonon dispersion, MLIP consensus on dynamic stability) does not apply. The computational underpinning is instead thermodynamic: Pourbaix diagram analysis (potential-pH equilibrium maps) and solubility-product differential modeling, both carried out as part of the broader Lattice Graph workflow designated WE21 and WE21A for rare-earth crossover analysis. Pourbaix diagrams for the relevant rare-earth systems map the regions in potential-pH space where each oxidation state and each anion-complex phase (oxide, hydroxide, oxalate, fluoride, sulfate, carbonate) is thermodynamically stable. For the pair-separation concept to work, there must exist accessible windows in potential-pH space where one member of a pair preferentially precipitates while the other remains in solution — these windows are the "crossover" regions identified in WE21/WE21A. The five pair-anion combinations were selected because they correspond to five distinct Pourbaix-crossover mechanisms. Nd/Pr oxalate: both form insoluble trivalent oxalates, but the Ksp ratio is exploitable with precise pH control and oxalate concentration. Dy/Tb fluoride: the fluoride system amplifies the Ksp difference between adjacent heavy rare earths more than hydroxide or carbonate. La/Ce ceric sulfate: Ce can be oxidized to Ce(IV) by controlled oxidants (e.g., ozone, peroxodisulfate), forming ceric sulfate double-salt precipitates at potentials and pH values where La remains as La(III) in solution — a redox-assisted separation that achieves separation factors unavailable to any purely pH-driven hydroxide precipitation. Sm/Eu reductive carbonate: Eu is the only lanthanide with a readily accessible +2 state under mild reductants; Eu(II) carbonate precipitates at pH conditions where Sm(III) remains soluble. Y/heavy-RE double-sulfate: the double-sulfate system (RE₂(SO₄)₃·Na₂SO₄·nH₂O) has long been known to preferentially co-precipitate the light rare earths plus La and Ce while leaving Y and the heavier lanthanides in the supernatant; this process harnesses that selectivity as a dedicated separation stage. Solubility-product differential modeling quantifies what the Pourbaix diagrams indicate qualitatively. For each pair, the modeling estimates the theoretical concentration ratio achievable in the precipitate versus the supernatant as a function of pH, temperature, ionic strength, and counter-anion concentration, generating design guidance for operating windows that hit the target separation factors. The claimed per-stage separation factor of ≥1.5 for adjacent pairs and ≥3 for non-adjacent pairs is drawn from those computed windows, which are thermodynamic upper bounds that a real stage may fall short of, so these values are not guaranteed process performance. The process is intended to operate in at least three sequential stages, with the specific sequence and anion chemistry at each stage tailored to the feed composition — a leachate from magnet scrap will be predominantly Nd/Pr and Dy/Tb, while a bastnasite-derived stream will have higher La/Ce/Pr ratios, requiring a different stage ordering and potentially different anion systems at the front end. What the computational work does not yet provide is experimental validation on a real, complex leachate. Synthetic single-element and binary solutions are tractable, and the Pourbaix modeling captures equilibrium behavior well. Industrial leachates from magnet recycling or mixed-RE feeds contain iron, cobalt, boron, and other transition metals that can co-precipitate, block ligand sites, or alter ionic strength in ways that shift operating windows. A bench-scale multi-stage cascade run on real leachate is the explicit next validation gate — without it, the computed separation factors are thermodynamic upper bounds, not guaranteed process performance. This is candidly acknowledged in the development roadmap.

The addressable market for this technology sits within REE separation and refining, which is a concentrated, globally strategic segment of the specialty-chemicals and critical-minerals value chain. Total rare-earth oxide production runs at roughly 300,000 metric tons per year globally, with the separation and refining step representing the highest-value, highest-complexity portion of that chain. The fraction of that output that requires pair-level separation — particularly Nd/Pr for permanent magnets and Dy/Tb for high-coercivity magnets — is growing as EV adoption, wind turbine deployment, and defense electronics demand accelerates. The global rare-earth separation chemicals and services market has been estimated in the $0.5–1 billion range and is expanding with greenfield refinery investment outside China, though it should be noted these are estimates subject to significant uncertainty given the opaque and government-influenced nature of REE pricing. The primary buyers are REE refiners operating outside established SX infrastructure — in particular, midstream processors attached to magnet-recycling operations, where the feed is a concentrated Nd/Pr/Dy/Tb stream from demagnetized scrap alloy. For these operators, the capital and operational overhead of a full SX train is disproportionate to the scale and variability of their feed. A precipitation-based cascade that can be implemented in standard stirred-tank reactors with conventional pH and oxidation-potential control represents a substantially lower barrier to entry. Secondary customers include junior REE miners seeking to add downstream value without SX-plant capital, and government-backed initiatives building domestic separation capacity on tighter budgets and timelines than SX construction permits. Royalty and licensing logic for a process patent of this type typically attaches to throughput — a per-kilogram-of-separated-RE-oxide royalty or a license tied to plant capacity. Given the modular nature of precipitation, the technology is also amenable to licensing as a process package with engineering design services, which tends to command better per-unit economics than a bare patent license.

scalable precipitation alternative to long SX cascades

specific pair + counter-anion + >=3 sequential stages vs single-stage precipitation

Preliminary screen only. This is not a freedom-to-operate opinion.

The most natural acquirers and licensees are mid-scale REE refiners and magnet-recycling operators who need a credible separation path without the capital commitment of an SX train — particularly those operating in the United States, Europe, Japan, Australia, and Canada where government policy is actively incentivizing domestic REE processing investment. Companies building integrated magnet-recycling facilities (taking demagnetized NdFeB scrap through leaching and separation to mixed-RE oxide or separated oxides) represent the clearest near-term licensee profile: their feedstock is highly concentrated in Nd/Pr and Dy/Tb, exactly the pairs for which the most commercially urgent pair-separation stages (oxalate and fluoride) are claimed. Junior REE miners seeking to add downstream refining value on a limited capital budget are a secondary acquirer profile. Strategic acquirers from the specialty-chemicals or separation-technology sector — companies with precipitation plant expertise or existing REE chemical-supply relationships — could have interest in the IP as a platform to extend their service offering into the domestic separation market. Government technology-transfer programs (DOE critical minerals, EU CRM Alliance programs) are also relevant as potential licensees or joint-development partners, given the policy-driven urgency to demonstrate non-Chinese REE separation pathways at demonstration scale before committing SX capital. The asset is most valuable when paired with experimental bench validation data; a licensee who acquires rights pre-validation carries process risk, but in the current policy environment, process risk is competing with geopolitical supply risk, which changes the buyer's calculus.

The primary technical risk is the gap between thermodynamic Pourbaix modeling and real-leachate cascade performance. Complex feedstocks can behave substantially differently from binary solutions — co-precipitation of iron, cobalt, and boron impurities can degrade product purity or consume reagent, pH and redox control is harder to maintain at stage boundaries in industrial reactors, and the fluoride stage for Dy/Tb carries handling and waste-treatment complications (fluoride effluent management is a non-trivial operational cost). The path to de-risking is straightforward in design if not in execution: a bench-scale cascade study using authentic magnet-recycling leachate, measuring per-stage separation factors by ICP-MS across all five pair systems, with reagent consumption and impurity deportment tracked at each stage. That data package would convert the asset from a computationally supported process concept to a demonstrated process with a provisional engineering basis. The secondary risk is commercial: the market for REE separation technology is relationship-driven, government-influenced, and relatively opaque. The $0.5–1 billion TAM estimate reflects the global opportunity but the accessible fraction is narrower, and incumbent SX operators may compete on licensing their own processes or on building new SX capacity with government support rather than adopting a precipitation alternative. Filing strategy should therefore be coordinated with bench validation timing to ensure experimental support is available for prosecution arguments before the application advances to examination.