D2EHPA, short for di-(2-ethylhexyl) phosphoric acid (CAS 298-07-7), is one of the most widely used extractants in hydrometallurgy. Mining and refining companies use it in solvent extraction (SX) to separate and purify metals such as zinc, cobalt, rare earths and uranium from leach solutions. This guide explains what D2EHPA is, how it works and where it is used.
What is D2EHPA?
D2EHPA is an organophosphorus acid: a phosphoric acid molecule carrying two branched 2-ethylhexyl groups. Those long hydrocarbon groups make it oil-soluble, so it stays in the organic phase, while its acidic P–OH group can swap its hydrogen ion for a metal ion. That makes it a cation-exchange extractant.
- Chemical name: bis(2-ethylhexyl) hydrogen phosphate
- CAS number: 298-07-7
- Appearance: clear, colourless to pale yellow viscous liquid
- Common names: D2EHPA, DEHPA, HDEHP
How D2EHPA works in solvent extraction
In a typical SX circuit, D2EHPA is dissolved in a kerosene-type diluent, usually at 5–40% by volume, and mixed with the aqueous leach solution. Metal ions move into the organic phase and hydrogen ions are released into the aqueous phase:
M²⁺ (aqueous) + 2 HA (organic) ⇌ MA₂ (organic) + 2 H⁺ (aqueous)
Because the reaction releases acid, pH controls which metals are extracted. At low pH only strongly extracted metals load; as pH rises, more metals follow. Plants use this to separate metals step by step. The loaded organic is then stripped with a stronger acid, usually sulfuric acid, which reverses the reaction and produces a clean, concentrated metal solution. The stripped organic is recycled.
To hold pH steady during extraction, many plants partially neutralise (“saponify”) the organic or the aqueous feed with an alkali such as caustic soda or ammonia.
Main applications
Zinc
D2EHPA is the classic extractant for zinc. It selectively extracts zinc from sulfate leach solutions, leaving many impurities behind, and the stripped solution feeds zinc electrowinning to produce high-purity zinc metal.
Cobalt and nickel refining
In cobalt and nickel circuits, D2EHPA is used mainly for impurity removal. It takes out zinc, manganese, copper, calcium and iron before the cobalt–nickel separation step, which usually uses a phosphinic acid extractant.
Rare earth elements
D2EHPA is one of the main reagents for separating rare earths from each other. Because neighbouring rare earths behave very similarly, plants use many extraction stages in series to split them into individual high-purity products.
Uranium
Combined with a neutral synergist such as TOPO (trioctylphosphine oxide), D2EHPA is used to recover uranium, including from wet-process phosphoric acid. The combination extracts uranium much more strongly than either reagent alone.
Vanadium, indium and other metals
It is also applied to recover vanadium from leach liquors and to purify specialty metals such as indium and gallium.
Common operating issues and how to manage them
- Third-phase formation: at high metal loading, the organic can split into two layers. A phase modifier such as TBP or isodecanol, typically a few percent by volume, prevents this.
- Iron build-up: ferric iron loads strongly and is hard to strip. Many circuits remove iron upstream or use a dedicated strong-acid bleed strip.
- Entrainment losses: fine droplets of organic carried away in the aqueous raffinate waste reagent. Good mixer-settler design and after-settlers reduce losses.
- Crud: solid–liquid emulsions at the interface, usually caused by suspended solids in the feed. Good feed clarification is the best prevention.
Handling and storage
- D2EHPA is corrosive to eyes and skin. Wear chemical goggles, gloves and protective clothing.
- Store it in closed containers in a cool, dry, ventilated area, away from strong oxidisers and bases.
- Stainless steel, HDPE and suitable lined steel tanks are commonly used.
- It is supplied with a Certificate of Analysis and Safety Data Sheet, and should be handled according to the SDS and local regulations.
Buy D2EHPA for your SX circuit
Saeby Chemical supplies D2EHPA for solvent extraction in zinc, cobalt, rare earth and uranium operations, along with other mining and flotation chemicals. Every batch comes with a CoA and SDS. Contact us with your circuit, required volume and delivery location for a quotation.
Related guides: Caustic Soda Flakes vs Pearls vs Liquid · ACH vs Alum for Water Treatment
