P204 metals extractant

P204

Di-(2-ethylhexyl)phosphoric acid  (DEHPA or HDEHP) 

CAS: 298-07-7  

EINECS: 206-056-4

Chemical formula: C16H35O4P

Molar mass: 322.43 g/mol

Density: 0.972 g/ml

Melting point: -50°C

Boiling point: 393°C

Content: 95.64%

P204, also known as Di-(2-ethylhexyl)phosphoric acid (D2EHPA), is an organic extractant commonly used in the solvent extraction of metal ions in hydrometallurgical processes. It is a phosphoric acid ester that is highly effective in selectively extracting a variety of metals, particularly divalent metal ions like copper, nickel, uranium, and rare earth elements. Here’s a more detailed explanation of P204/D2EHPA as a metal extractant:

1. Chemical Structure and Properties

• Chemical Formula: C??H??O?P

• IUPAC Name: 1,3-Bis(2-ethylhexyl)phosphoric acid

• Molecular Structure:

• The structure consists of two 2-ethylhexyl groups attached to a phosphoric acid backbone, forming an ester group. This functional group allows D2EHPA to interact with metal ions in aqueous solutions.

• 2. Mechanism of Metal Extraction

P204/D2EHPA works by interacting with metal ions through a ligand exchange mechanism. In the extraction process, the metal ion (typically in its divalent form, such as Cu2?, Ni2?, or UO?2?) reacts with the phosphoric acid ester groups to form a complex. The metal-D2EHPA complex is then transferred from the aqueous phase to the organic phase (usually containing kerosene or other hydrocarbons as the solvent).

• pH Dependence: The extraction is generally pH-dependent. For most metal ions, extraction is most efficient in acidic conditions where D2EHPA remains protonated (as D2EHPA-H), facilitating its ability to bind to the metal ions.

3. Applications in Metal Extraction

P204/D2EHPA is used in a variety of hydrometallurgical applications for extracting valuable metals, particularly:

• Copper Extraction:

• D2EHPA is commonly used in copper solvent extraction (SX) processes, where it extracts copper from acidic leach solutions (e.g., from heap leaching or tank leaching of copper ores).

• The extracted copper is then stripped from the organic phase using a more concentrated acid solution, such as sulfuric acid, to obtain a purified copper solution.

• Uranium Recovery:

• In uranium mining, particularly in acidic uranium-bearing ores, D2EHPA is effective in extracting uranium from the aqueous phase. Uranium forms complexes with D2EHPA, which can be separated and stripped from the organic phase for further processing.

• Nickel Extraction:

• D2EHPA is also used in nickel extraction from acidic solutions, such as those derived from laterite ores. Nickel is extracted and separated from other metals, often using a combination of D2EHPA and other extractants.

• Rare Earth Elements (REEs):

• D2EHPA plays a significant role in the separation and extraction of rare earth elements, which are critical in industries like electronics, renewable energy, and electric vehicles.

• Separation of Other Metals:

• D2EHPA can also be used for the extraction and separation of metals like zinc, cobalt, manganese, and precious metals (e.g., gold and platinum), depending on the specific industrial needs.

4. Advantages of P204 (D2EHPA)

• High Selectivity: D2EHPA is highly selective for divalent metal ions, allowing efficient separation of metals like copper, nickel, uranium, and others, even from complex mixtures.

• Efficiency in Acidic Conditions: The extractant works well in mildly acidic to moderately acidic environments, which are common in many industrial hydrometallurgical processes.

• Reusability: After metal extraction, the organic phase containing D2EHPA can be stripped and reused, making the process cost-effective.

• Versatility: It is compatible with a wide range of solvents, making it adaptable to different extraction systems, such as mixer-settlers, counter-current decantation (CCD), and continuous contactors.

5. Challenges and Limitations

• Emulsions Formation: One of the potential challenges with D2EHPA is the formation of emulsions during extraction, especially when there is an excess of the extractant or high agitation. This can hinder phase separation and reduce extraction efficiency.

• Solvent Loss: Organic solvents containing D2EHPA can sometimes degrade or be lost, requiring replenishment or recycling, which can add to operational costs.

• Environmental Concerns: While D2EHPA itself is not highly toxic, the organic solvents used in conjunction with it (e.g., kerosene, xylene) can pose environmental risks if not properly handled. Adequate waste management and solvent recovery systems are necessary to mitigate these concerns.

• Cost of Extraction: While D2EHPA is effective, the cost of the extractant and its solvents can be relatively high, particularly in large-scale operations where significant quantities of solvent are required.

6. Stripping and Recovery

After the metal is extracted into the organic phase, it is typically stripped back into the aqueous phase. This step is necessary to recover the metal from the organic phase and regenerate the extractant for further use.

• Copper: For copper, a sulfuric acid solution is commonly used for stripping, which releases the copper ions from the D2EHPA complex.

• Uranium: For uranium, hydrochloric acid or sulfuric acid is typically used to strip uranium from the organic phase.

• Nickel and Other Metals: Stripping agents vary depending on the metal being extracted. Nickel, for example, may require different acid solutions based on the specific chemistry of the system.

7. Environmental and Safety Considerations

• Toxicity and Handling: While D2EHPA itself is not highly toxic, the organic solvents used in its formulation can be harmful if not handled properly. Appropriate personal protective equipment (PPE) should be used during handling, and systems should be in place to mitigate exposure to fumes and spills.

• Waste Treatment: Disposal of waste materials from solvent extraction processes, including spent solvents and metal-laden aqueous phases, must comply with environmental regulations to minimize pollution and toxic runoff.

• Regulatory Compliance: Solvent extraction processes must adhere to local and international environmental and safety regulations. This includes managing the disposal of both organic solvents and aqueous waste.

8. Conclusion

P204 (Di-(2-ethylhexyl)phosphoric acid) is a highly effective extractant used in various hydrometallurgical processes for the separation and recovery of metal ions, particularly copper, uranium, nickel, and rare earth elements. Its ability to form stable complexes with metal ions in mildly acidic conditions makes it a versatile and valuable reagent in the mining and refining industries. However, challenges such as emulsion formation, solvent losses, and environmental concerns must be managed carefully to ensure efficient and sustainable extraction processes.

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