D2EHPA

Organophosphorus cation-exchange extractant for liquid–liquid solvent extraction (SX) of zinc, manganese, cobalt-circuit impurities, vanadium, uranium and rare earth elements. Supplied in high-purity SX grade (≥95.0% active acid, mono-ester ≤1.0%) and technical grade (93.0–95.0%) for hydrometallurgical refineries, black-mass battery recycling circuits and REE fractionation plants.

Synonyms: DEHPA, HDEHP, bis(2-ethylhexyl) hydrogen phosphate, bis(2-ethylhexyl) phosphate, di-2-ethylhexyl phosphoric acid, diisooctyl acid phosphate.

Technical Specifications

Specialty REE separation grade: SX-grade base with tightened mono-ester, Fe and neutral-organic limits, specified per separation flowsheet. Batch values are reported on each Certificate of Analysis.

Extraction Mechanism & Equilibrium Chemistry

Cation exchange via the hydrogen-bonded dimer

In non-polar aliphatic diluents D2EHPA exists predominantly as the hydrogen-bonded dimer (HA)₂. Divalent and trivalent metal ions are extracted by proton exchange, releasing acid into the aqueous phase:

Because every metal equivalent loaded releases one H⁺, the distribution ratio D = [M]_org/[M]_aq is strongly pH-dependent: at constant extractant concentration, log D rises with a slope of ≈ n per pH unit. Each metal therefore has a characteristic pH₅₀ (pH at 50% extraction), and selectivity between two metals is controlled by the gap between their extraction isotherms. In practice, raffinate acidification is offset by pre-neutralization (saponification) of the organic with NaOH or NH₃, or by inter-stage pH control.

Extraction sequence (sulfate media, increasing pH)

Windows are indicative for ~20% v/v D2EHPA in aliphatic kerosene at 25–40 °C; actual pH₅₀ values shift with extractant concentration, saponification degree, temperature, ionic strength and organic loading.

Selectivity coefficients

• Zn/Fe(II): high separation factor when iron is maintained as Fe²⁺; Fe(III) must be controlled because it out-competes Zn.
• Zn/Ni, Zn/Co, Mn/Ni: wide isotherm gaps enable clean impurity removal from Co/Ni liquors.
• Co/Ni: moderate separation factor (order of 10¹ at ambient temperature, improving at elevated temperature). For bulk Co/Ni separation, D2EHPA is normally deployed upstream for Zn/Mn/Ca/Cu removal, followed by a phosphinic acid extractant.
• Rare earths: extraction increases with atomic number across the lanthanide series (La → Lu), with Y falling among the heavy REE (near Ho/Er). Average adjacent-element separation factors of ~2.5 allow multistage countercurrent fractionation.

Stripping

Stripping reverses the equilibrium with high acid concentration:

• Zn: spent electrolyte (≈150–200 g/L H₂SO₄) yields advance electrolyte for electrowinning.
• Mn, Co, Ca, Cu: dilute H₂SO₄ or HCl (≈0.5–2 M).
• REE: HCl or HNO₃, acid strength rising with atomic number; heavy REE (Tm–Lu) require the strongest acid.
• Fe(III): ≥6 M HCl or reductive stripping on an organic bleed stream to restore extractant capacity.

Industrial Process Applications

Zinc hydrometallurgy

Selective transfer of Zn²⁺ from pregnant leach solutions (PLS) produced by atmospheric or pressure sulfuric acid leaching of oxide ores, secondary dusts (EAF dust) and residues. Typical organic: 20–40% v/v D2EHPA in aliphatic kerosene. Extraction at pH 1.5–2.5, scrubbing with acidified water or dilute zinc sulfate to remove co-loaded Ca, Mn and entrained aqueous, then stripping with spent electrolyte to generate high-purity advance electrolyte for SHG zinc electrowinning.

Lithium-ion battery recycling (black mass)

Following sulfuric acid–reductive leaching of black mass, D2EHPA removes Mn, Zn, Cu, Al, Fe and Ca from the Co/Ni/Li liquor. Manganese is extracted at pH ≈3–3.5 ahead of cobalt; staged pH control with a saponified organic minimizes Co losses to the Mn product. The purified raffinate feeds Co/Ni separation and lithium recovery.

Rare earth element (REE) fractionation

Multistage countercurrent mixer-settler cascades in chloride or nitrate media separate light, middle and heavy REE groups and purify individual elements including Nd, Tb, Dy and Y. Saponified D2EHPA (typically 0.5–1.5 M in kerosene) maintains stage pH; heavy REE loading is limited by stripping difficulty, which governs extractant concentration and acid selection in the strip section.

Uranium & vanadium recovery

• Uranium from wet-process phosphoric acid: synergistic D2EHPA/TOPO (trioctylphosphine oxide), typically 0.5 M D2EHPA + 0.125 M TOPO (4:1 molar) in kerosene, extracts U(VI) from oxidized ~28–30% P₂O₅ acid; first-cycle reductive stripping with Fe²⁺-bearing phosphoric acid.
• Vanadium: extraction of VO²⁺ [V(IV)] at pH ≈1.8–2.5 after reduction of V(V) and Fe(III), stripping with 1–2 M H₂SO₄; applied to stone-coal, spent-catalyst and vanadium-titanomagnetite leach liquors.

Diluent selection, phase modifiers & crud prevention

• Diluents: low-aromatic aliphatic kerosenes (Escaid™ 110, ShellSol™ D70, Exxsol™ D80) give higher flash point, lower solubility losses and stable dimerization. Aromatic diluents reduce extraction strength and raise odor and flammability concerns.
• Phase modifiers: 2–5% v/v TBP or isodecanol suppresses third-phase formation and gel/emulsion at high saponification degree or high metal loading (notably with Ca, REE and Fe).
• Crud control: clarify PLS to <10–20 mg/L suspended solids; remove colloidal silica; control Fe(III) and gypsum supersaturation; run periodic clay treatment of the organic inventory.
• Phase continuity & entrainment: operate aqueous-continuous where organic loss to raffinate dominates and organic-continuous where aqueous carry-over into loaded organic must be minimized; monitor continuity by conductivity probes; maintain impeller tip speed and O/A recycle to avoid phase inversion.
• Temperature: 25–40 °C typical; higher temperature shortens break time and improves Co/Ni selectivity but increases diluent losses.

Packaging, Storage & Dangerous Goods Transport

Packaging

• 200 kg UN-approved HDPE drums
• 950 kg / 1,000 kg UN-approved IBC totes
• Flexitanks (subject to route and DG acceptance)
• Dedicated stainless-steel ISO tank containers for bulk SX plant fills

Storage & materials of construction

• Compatible: HDPE, PP, PVDF, PTFE/PFA, 316L stainless steel at ambient temperature; titanium or fluoropolymer-lined steel for elevated-temperature service.
• Avoid: unlined carbon steel, aluminum, zinc and galvanized surfaces (acid corrosion, particularly with moisture present).
• Temperature: store at 10–35 °C; viscosity rises steeply in cold climates — provide tank heating or warm-room storage before pumping.
• Atmosphere: keep containers tightly closed; nitrogen blanketing recommended for long-term bulk storage to exclude moisture.
• Segregate from strong bases, oxidizers and reactive metals; store in bunded areas.

Transport classification

EHS, Emergency Response & Regulatory Compliance

First aid

• Skin: remove contaminated clothing; flush with water for at least 15 minutes; seek medical attention.
• Eyes: irrigate immediately with water for at least 15 minutes, holding eyelids open; remove contact lenses if easily done; urgent ophthalmological care.
• Ingestion: rinse mouth; do not induce vomiting; seek immediate medical attention.
• Inhalation (mist/aerosol): move to fresh air; seek medical attention if symptoms persist.

Spill response

• Contain with bunding; absorb with inert material (vermiculite, dry sand, diatomaceous earth).
• Do not use sawdust or combustible absorbents; avoid contact with strong oxidizers and concentrated bases.
• Prevent entry into drains, surface water and soil; collect in labeled acid-resistant containers for licensed disposal.

Personal protective equipment

• Gloves: butyl, Viton™ or neoprene (verify breakthrough time against the SDS)
• Chemical splash goggles plus full face shield
• Acid-resistant apron or coveralls; chemical-resistant boots
• Where mists or heated vapors occur: respirator with combination organic vapor/acid gas