Molybdenum Solvent Extraction (Organic Phase) Storage & Tank Compatibility

Storing Molybdenum Solvent Extraction (Organic Phase)? Start Here

Molybdenum solvent extraction (SX) is a hydrometallurgical purification step that recovers and concentrates molybdenum(VI) from acidic leach or process liquors. The working fluid is not a single compound but an engineered organic phase: an amine extractant (commonly a tertiary or secondary trialkylamine) dissolved in an aliphatic kerosene diluent, with a phase modifier such as tributyl phosphate or a long-chain alcohol added to prevent third-phase formation. In the mixer-settlers this organic is repeatedly contacted with the aqueous feed, becoming the "loaded organic" before molybdenum is stripped back into an alkaline solution. Because the bulk of the fluid is a flammable petroleum diluent carrying organic extractants, materials of construction (MOC) are governed by hydrocarbon resistance and flammability — not by aqueous corrosion alone. Choosing the wrong tank material leads to swelling, permeation, and seal failure, so the organic circuit relies on lined steel, FRP, or stainless rather than commodity plastic.

Is Polyethylene (HDPE / XLPE) Safe for the SX Organic Phase?

No — polyethylene is not recommended for the molybdenum SX organic phase. The fluid is dominated by an aliphatic kerosene diluent plus organic modifiers (TBP or alcohols) and dissolved amine extractant. While HDPE shrugs off brief splashes of fuels, continuous contact with kerosene-grade aliphatic hydrocarbons and organic solvents causes polyethylene to absorb the solvent, swell, soften, and lose mechanical strength, and lets vapors permeate the wall. Crosslinked polyethylene (XLPE) is more rigid but is subject to the same permeation and swelling and is likewise not rated for sustained hydrocarbon-solvent storage. For the organic circuit, specify lined carbon steel, FRP (vinyl ester or dual-laminate), or stainless steel with PTFE/FKM (Viton) seals. Polyethylene should only be considered for separate aqueous duties (e.g., dilute aqueous strip make-up) and only after confirming the actual chemistry against a current SDS and the resin maker's resistance chart.

Material compatibility at a glance

This is a non-aqueous hydrocarbon process stream, not a water-based chemical. The kerosene diluent and organic modifiers permeate and swell polyethylene, so HDPE/XLPE tanks are unsuitable for the loaded/stripped organic phase. Standard materials of construction are lined carbon steel, FRP (vinyl ester or dual-laminate), or stainless steel, with PTFE/FKM seals. Polyethylene may still serve adjacent aqueous duties only after independent verification.

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 liquid (H226): the kerosene diluent has a flash point near 38-65°C; keep away from heat, sparks, and open flame, and bond/ground transfer equipment.
• Aspiration hazard (H304): may be fatal if swallowed and entering the airways — do NOT induce vomiting; this is the most serious acute hazard of hydrocarbon diluents.
• Vapor and respiratory effects (H336): vapors may cause drowsiness or dizziness; provide local exhaust ventilation in mixer-settler areas.
• Skin and eye irritation (H315): prolonged contact degreases and irritates skin; wear chemical-resistant nitrile/Viton gloves, goggles, and apron.
• Acidic aqueous carryover: entrained feed/raffinate can be strongly acidic and chloride-bearing — protect against trace acid corrosion and crud build-up.
• Static and crud control: manage organic-aqueous interface crud, secondary containment, and vapor accumulation; values above are representative and must be confirmed against the project SDS.

Common questions

Can I store the molybdenum SX organic phase in an HDPE or XLPE tank?

No. The organic phase is a kerosene-diluent solvent stream that permeates and swells polyethylene under continuous contact. Use lined carbon steel, FRP (vinyl ester or dual-laminate), or stainless steel with PTFE/FKM seals instead.

Why is polyethylene fine for some fuels but not for this?

Polyethylene tolerates brief splashes of fuels, but the SX organic is in sustained contact and also contains organic modifiers and extractants. Long-term aliphatic-hydrocarbon and solvent exposure causes absorption, swelling, softening, and permeation, which commodity poly tanks are not rated to withstand.

What tank material is recommended for the SX circuit?

Industry practice for the organic mixer-settlers and storage is lined carbon steel, FRP, or stainless steel. Match the FRP resin and any elastomer seals (PTFE or FKM/Viton) to your specific diluent and confirm against a current SDS.

Is the contacted aqueous (feed/raffinate) side different?

Yes. The aqueous leach liquor and raffinate are typically acidic and may carry chloride; those streams have their own MOC considerations (lined steel or FRP). Polyethylene for any aqueous duty must be verified independently against the actual chemistry.