When valuable metals are present together in a complex aqueous stream, the challenge is not simply extraction. The real challenge is selective separation.

Uranium may coexist with thorium and rare earth elements. Scandium can occur alongside other metals in mineral-derived solutions. Gallium and indium may also be present at relatively low concentrations in complex process liquors. In these systems, the choice of extractant can have a direct impact on distribution behavior, phase separation, stripping and overall process efficiency.

Bis(sec-octyl)methylphosphonate, commercially known as P350, is a neutral organophosphorus extractant that has been studied and applied in solvent-extraction and separation systems for rare metals and actinide-related elements.

P350 at a Glance

The chemical is identified by CAS No. 76341-63-4.

Common names include:

Bis(sec-octyl)methylphosphonate

P350

Methyl phosphonic acid di(sec-octyl) ester

Methyl diheptylphosphonate

Di(1-methylheptyl) methylphosphonate

Bis(1-methylheptyl) methylphosphonate

Its molecular formula is C17H37O3P, with a molecular weight of approximately 320.45 g/mol. Chemical databases and technical literature identify P350 as a neutral phosphonate-type extractant.

The long alkyl groups provide strong hydrophobic character, allowing the extractant to remain predominantly in the organic phase during liquid-liquid extraction.

Why P350 Is Valuable in Solvent Extraction

P350 belongs to the family of neutral organophosphorus extractants.

Its phosphonate oxygen atoms can participate in coordination with suitable metal-containing species. During solvent extraction, the target species can form an extractable neutral complex and transfer from the aqueous phase into an organic phase containing P350.

This makes the material particularly interesting for systems where the extraction behavior of different metal ions changes significantly with:

Acid concentration

Anion composition

Metal oxidation state

Extractant concentration

Organic diluent

Phase ratio

Temperature

Stripping conditions

In other words, P350 is not simply a chemical that “captures metals.” Its performance depends on the entire extraction system.

This distinction is important when designing an industrial separation process.

Uranium and Thorium: One of the Most Important P350 Applications

Among the best-documented applications of P350, uranium and thorium separation is particularly significant.

Research and technical literature describe P350 as a neutral phosphonate extractant with strong extraction behavior toward uranium and useful separation characteristics in uranium/thorium systems. A recent Inorganic Chemistry Frontiers study specifically describes P350 as showing excellent performance in the separation of thorium and uranium, while also highlighting the practical challenge of stripping uranium from the loaded organic phase.

Chinese process literature has also reported P350-based extraction systems for separating uranium, iron, thorium and rare earth elements from chloride solutions. One reported process uses P350 to extract uranium and iron while leaving thorium and rare earth elements preferentially in the raffinate, followed by washing and stripping operations.

This illustrates an important principle:

Extraction selectivity and stripping performance must be considered together.

A high distribution ratio alone does not necessarily mean that an extractant is ideal for a complete industrial flowsheet.

Rare Earth and Scandium Separation

P350 has also been investigated for rare-earth solvent extraction.

Technical literature describes di(1-methylheptyl)methylphosphonate (P350) as an important neutral organophosphorus extractant in rare-earth separation. Its application has included the separation and purification of rare-earth elements as well as research involving scandium.

Older patent literature on scandium recovery also describes P350 as a neutral complexing extractant and discusses differences in extraction behavior among iron, uranium, scandium, thorium and rare-earth elements under different acid systems.

Therefore, P350 can be considered a useful option for specialized rare-metal separation research and hydrometallurgical process development, provided that the extraction conditions are optimized for the specific feed solution.

Gallium, Indium and Other Valuable Metals

Commercial and technical descriptions of P350 also associate the extractant with the separation and recovery of metals such as gallium, indium and scandium, in addition to uranium and thorium.

The underlying reason is its ability to interact with metal-containing species in suitable acidic or salt-containing systems.

However, extraction performance can vary substantially from one metal and aqueous composition to another. Therefore, statements such as “P350 extracts all rare metals efficiently” would be misleading.

For process engineers, a better approach is to evaluate:

target metal → competing ions → aqueous chemistry → extraction coefficient → separation factor → stripping efficiency

This process-oriented evaluation is much more meaningful than relying on the extractant name alone.

P350 in Nuclear Fuel and Nuclear-Material Processing Research

Because of its uranium and thorium extraction characteristics, P350 has also been investigated in nuclear-material separation and analytical applications.

Literature reports the use of P350 in uranium/thorium separation, extraction chromatography and related analytical procedures. One published study used P350 as a stationary phase for concentrating uranium and thorium from ore-related solutions and subsequently separating them through controlled elution.

More recent research has continued to examine P350 in uranium-processing chemistry, including methods for improving uranium stripping from the organic phase after extraction.

For this reason, P350 is relevant not only to conventional hydrometallurgy but also to specialized nuclear chemistry and separation research.

What Makes P350 Interesting for Process Developers?

From a process-development perspective, three characteristics deserve particular attention.

1. Neutral extractant chemistry

P350 operates as a neutral organophosphorus extractant, providing a different extraction mechanism from acidic organophosphorus reagents.

2. Strong organic-phase compatibility

Its long hydrocarbon substituents contribute to low water solubility and good compatibility with organic diluents used in liquid-liquid extraction systems.

3. Tunable separation behavior

The extraction behavior of P350 changes with the aqueous chemistry. This can be advantageous when engineers need to exploit differences between uranium, thorium, rare earths or other metal ions.

These characteristics explain why P350 continues to appear in research and process literature decades after its original development.

Selecting P350 for Industrial Applications

For companies purchasing Bis(sec-octyl)methylphosphonate CAS 76341-63-4, product identity is only the first checkpoint.

A professional procurement evaluation should include:

CAS and chemical identity
Confirm CAS 76341-63-4, formula C17H37O3P and molecular weight around 320.45 g/mol.

Purity and composition
For solvent extraction, consistent chemical composition can be critical because changes in extractant quality may influence distribution ratios and phase behavior.

Batch documentation
A current COA, specification and SDS should be available for technical qualification.

Storage and handling
Storage conditions should follow the supplier’s current SDS and product specification.

Scale-up capability
A supplier should ideally be able to support the transition from laboratory evaluation to pilot and larger-volume procurement.

P350 Supply from SHLZ Pharma

SHLZ Pharma lists Bis(sec-octyl)methylphosphonate CAS No. 76341-63-4 as part of its specialty chemical portfolio. The company focuses on research, development and supply of pharmaceutical and specialty chemical products.

For buyers developing rare-metal extraction, hydrometallurgical separation or nuclear-material processing systems, the most appropriate approach is to qualify P350 against the actual aqueous feed and process conditions rather than relying solely on generic extraction claims.

Conclusion

Bis(sec-octyl)methylphosphonate (P350), CAS 76341-63-4, is a specialized neutral organophosphorus extractant with established relevance to rare-earth and rare-metal separation, uranium/thorium extraction, scandium-related separation studies, and nuclear-material processing research.

Its applications in gallium, indium and other metal recovery systems further demonstrate the versatility of P350 as a process reagent.

For industrial users, however, the real performance of P350 depends on the complete solvent-extraction system. Metal distribution, selectivity, phase behavior, stripping efficiency and long-term batch consistency should all be evaluated before scale-up.