Dysprosium / Terbium Separation Process Stream (Solvent Extraction) Storage & Tank Compatibility

Storing Dysprosium / Terbium Separation Process Stream (Solvent Extraction)? Start Here

The dysprosium/terbium separation stream is not a single chemical but a working solvent-extraction (SX) process liquor. Because dysprosium and terbium are chemically adjacent heavy rare earths, they are split in multi-stage mixer-settler trains rather than by simple precipitation. An organic phase - an organophosphorus extractant such as HEHEHP (P507) or D2EHPA dissolved in a sulfonated kerosene-type hydrocarbon diluent - is contacted countercurrently against an acidic aqueous chloride feed containing the dissolved rare-earth chlorides in dilute hydrochloric acid. The two phases are nearly immiscible; metals shuttle between them stage by stage, and loaded organic is stripped back with strong HCl. The result is a system that combines a flammable, swelling petroleum solvent with a corrosive, low-pH chloride brine. That dual nature is exactly why material of construction matters: a tank that handles the brine fine can still fail against the hydrocarbon, which is the dominant compatibility driver here.

Is Polyethylene (HDPE / XLPE) Compatible with the Dy/Tb Extraction Stream?

No - not for the real-world stream. Standard high-density and cross-linked polyethylene rate as unsuitable (U) for this service because the organic phase is built on a kerosene-type hydrocarbon diluent. Long-chain petroleum solvents swell polyethylene and slowly permeate the wall over continuous storage, which softens the tank, distorts dimensions and embrittles welds - the same reason poly is not used for diesel, kerosene or solvent-borne product tanks. It is true that polyethylene would happily hold the bare acidic rare-earth chloride raffinate on its own (an aqueous salt in dilute acid), so a poly tank can have a role for purely aqueous side-streams. But for the organic extract, the mixed two-phase liquor, or any vessel that sees the diluent, the honest answer is to step up to 316L stainless, lined steel, or vinyl-ester FRP with PTFE/PVDF and FKM seals. Do not default to a polyethylene tank for the SX circuit.

Material compatibility at a glance

Treat this as a petroleum-solvent service, not an aqueous-salt service. The controlling factor is the kerosene-type hydrocarbon diluent in the organic extract, which rules out standard polyethylene tanks. Specify 316L stainless steel, lined steel, or properly engineered vinyl-ester FRP for tanks, mixer-settlers and settlers, with PTFE/PVDF and FKM (Viton) for linings, gaskets and seals. Carbon steel is acceptable only for the organic side or behind a liner; the acidic, low-pH chloride aqueous phase corrodes bare steel and can pit lesser stainless grades.

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

• Flammable/combustible organic diluent: the kerosene-type solvent gives off ignitable vapor (GHS H226). Keep away from heat, sparks, and open flame; bond and ground during transfer; provide adequate ventilation (representative, SDS-dependent).
• Aspiration hazard: the hydrocarbon phase may be fatal if swallowed and drawn into the lungs (H304). Never siphon by mouth; if swallowed do not induce vomiting and seek medical attention.
• Corrosive acidic aqueous phase: the low-pH rare-earth chloride / HCl liquor causes severe skin burns and eye damage (H314 / H319) and may corrode metals (H290). Wear splash goggles, face shield, acid-resistant gloves and apron.
• Respiratory and skin irritation (H335 / H315) from organophosphorus extractant mist and acid aerosol; minimize aerosol during pumping and mixing.
• Environmentally hazardous: toxic to aquatic life with long lasting effects (H411). Bund all tankage, prevent any release of organic or aqueous phase to drains or surface water, and capture spills with inert absorbent.
• Provide eyewash and safety shower at point of use; on contact, flush eyes and skin with water for at least 15 minutes and obtain medical care.

Common questions

Can I store the dysprosium/terbium extraction stream in a polyethylene tank?

Not for the organic or mixed phase. The kerosene-type hydrocarbon diluent swells and permeates HDPE and XLPE over time, so polyethylene rates as unsuitable for the SX circuit. Use 316L stainless, lined steel, or vinyl-ester FRP. A poly tank could hold only a bare aqueous chloride side-stream, never the solvent-bearing liquor.

Why is polyethylene fine for many rare-earth salts but not for this stream?

Aqueous rare-earth chloride or nitrate salt solutions are compatible with polyethylene. This stream is different because it includes a petroleum-solvent organic phase (kerosene-type diluent). Hydrocarbon solvents, not the dissolved metals, are what attack polyethylene, which shifts the correct tank choice to metal or lined/FRP construction.

What tank and seal materials are recommended for the SX circuit?

316L stainless steel, lined carbon steel, or properly specified vinyl-ester FRP for tanks, mixer-settlers and settlers, with PTFE or PVDF linings and FKM (Viton) gaskets and seals. Avoid EPDM and natural rubber, which swell in the hydrocarbon diluent, and avoid bare carbon steel on the acidic aqueous side.

What are the main hazards to plan for?

Two combined hazard sets: a flammable/combustible, aspiration-hazardous hydrocarbon organic phase, and a corrosive, low-pH chloride aqueous phase. Plan for ignition control and bonding/grounding on the solvent side, acid splash PPE and corrosion-resistant metallurgy on the aqueous side, and full containment because the stream is toxic to aquatic life. Exact ratings are SDS-dependent.