Neodymium / Praseodymium (NdPr) Separation Process Stream Storage & Tank Compatibility

Storing Neodymium / Praseodymium (NdPr) Separation Process Stream? Start Here

Neodymium and praseodymium are adjacent light rare-earth elements that are notoriously difficult to separate because their chemistry is nearly identical. Industry separates them by liquid-liquid solvent extraction: a strongly acidic aqueous chloride feed containing dissolved Nd and Pr chlorides is contacted, stage after stage, with an organic phase — an organophosphorus extractant such as PC88A or P507 dissolved in a kerosene-type diluent. The process generates several distinct storable liquors: the chloride feed, the raffinate, scrub solutions, and a hydrochloric-acid strip liquor that carries the purified metal. These streams supply magnet-grade neodymium for permanent magnets in EV motors and wind turbines. Materials of construction matter because the streams split into two very different chemical worlds — a corrosive acidic water phase and a hydrocarbon solvent phase — and no single tank material is ideal for both. Selecting the right tank per stream prevents corrosion of the aqueous side and solvent attack on the organic side.

Is polyethylene (HDPE / XLPE) the right tank? Yes — for the aqueous streams

For the high-volume acidic aqueous chloride and HCl process streams (feed, raffinate, scrub, and strip liquor), polyethylene is an excellent and standard choice. HDPE is rated compatible with hydrochloric acid at all concentrations to roughly 37% and at moderate temperatures, and dissolved rare-earth chlorides do not change that picture. XLPE is widely used for acid-chloride service as well, though for high-purity strong-HCl duty some tank makers prefer HDPE — confirm the rating against your specific free-acid level and temperature.

The exception is the organic extractant phase. The kerosene-type diluent contains hydrocarbons — and any aromatic content will swell and stress-crack polyethylene over time, so HDPE/XLPE is not recommended for the organic inventory. Store that smaller stream in lined steel, FRP, or a fluoropolymer-lined vessel. In short: poly for the acidic water streams, lined steel/FRP for the solvent. Always match the tank to the individual stream and verify against the supplier SDS and a current polyethylene chemical-resistance chart.

Material compatibility at a glance

Storage strategy follows the phase: the acidic aqueous chloride / HCl process streams (feed, raffinate, scrub, strip liquor) are a textbook polyethylene duty — HDPE or XLPE tanks handle them well, the same way they handle hydrochloric acid up to ~37%. The separate organic extractant phase (organophosphorus reagent in a kerosene-type diluent) is NOT a polyethylene application; it requires lined steel, FRP, or fluoropolymer. Most operators store the high-volume aqueous streams in poly and keep the smaller organic inventory in lined steel.

Ratings: S suitable · C conditional / limited · U unsuitable. Verify against the cited resistance charts and your concentration/temperature before specifying.

The safety that actually matters

• Acidic chloride and HCl strip streams cause severe skin and eye burns — use chemical splash goggles, face shield, and acid-resistant gloves and apron.
• HCl vapor and mist irritate the respiratory tract; provide local exhaust ventilation and avoid breathing mist.
• The organic extractant / kerosene-diluent phase is combustible — keep away from ignition sources, ground and bond transfer equipment, and store it separately from the aqueous phase.
• Acidic chloride streams are corrosive to many metals (H290) and can pit stainless steel — verify drip trays, fittings, and secondary containment are compatible.
• Provide chemically compatible secondary containment sized to the largest tank, and keep separation of the aqueous and organic inventories.
• Hazard ratings are representative and SDS-dependent — obtain and follow the supplier/operator Safety Data Sheet for each specific process stream before storage or handling.

Common questions

Can I store the NdPr separation feed liquor in a polyethylene tank?

Yes. The acidic aqueous chloride feed, raffinate, scrub, and HCl strip liquors are well suited to HDPE (and generally XLPE) tanks — the same materials used for hydrochloric acid up to about 37%. The dissolved rare-earth chlorides do not change polyethylene compatibility. Always confirm against your free-acid concentration and temperature.

Why can't I put the organic extractant phase in the same poly tank?

The organic phase is an organophosphorus extractant dissolved in a kerosene-type diluent. Hydrocarbon diluents — especially any aromatic content — swell and stress-crack polyethylene over time. Store the organic inventory in lined steel, FRP, or a fluoropolymer-lined vessel, kept separate from the aqueous streams.

Is stainless steel a good choice for these streams?

Use caution. The acidic chloride / HCl aqueous phase poses chloride pitting and stress-corrosion-cracking risk even for 316 stainless. Lined steel, FRP, or polyethylene are safer for the aqueous side; lined steel or FRP is typical for the organic side.

What NFPA and GHS ratings apply?

Ratings are representative and stream-specific. The acidic aqueous phase is corrosive and non-flammable (representative NFPA Health 3, Flammability 0). The organic diluent phase is combustible and rates separately. Treat all values as SDS-dependent and confirm against the supplier Safety Data Sheet.