Extraction

Freiser, Henry

doi:10.1021/ac60237a008

Cited by 29 publications

(4 citation statements)

References 39 publications

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“…Le., from r = rp + 1 and the following equation (3) where uwater is the volume of a water molecule in bulk water. By assuming all the water to be accumulated in the pools, the (maximum) values of r can be calculated, which are listed as rCd along the experimentally obtained hydrodynamic radii rh (=Dd2) in Table 2.…”

Section: Lightmentioning

confidence: 99%

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Equilibrium Properties of Crystallites and Reverse Micelles of Sodium Bis(2-ethylhexyl) Phosphate in Benzene

Feng¹,

Schelly²

1995

J. Phys. Chem.

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In sodium bis(Zethylhexy1) phosphate (or NaDEHP)/benzene/H20 temary systems, the apparent hydrodynamic diameter Dh of the surfactant aggregates and the mean aggregation number (n), monomer concentration C , , electrical conductivity K , and absolute viscosity 9 of the solutions are investigated by quasi-elastic light scattering, controlled partial pressure-vapor pressure osmometry (CPP-VPO), conductance, and viscosity measurements, generally as a function of surfactant concentration C, temperature, and water content WO. As a function of water content, the apparent size of the aggregates and the viscosity exhibit a minimum at wo % 3.0; Dh, q, and (n) decrease with increasing temperature while C , shows the opposite trend. The conductivity (in homogeneous electric field) increases nonmonotonically with WO, exhibiting a plateau region for 1.5 5 wo I 4.0. Conductance measurements in inhomogeneous electric field indicate the aggregates present at wo < 3.0 have a permanent dipole moment that diminishes with increasing water content. The results suggest that below the "critical water content" ( W O ,~ x 3.0) the aggregates are rod-shaped, dipolar crystallites (with the same structure as the constituent rods of the hexagonal liquid crystalline solid state of NaDEHP) which successively dissolve with increasing water content. At wo > 3.0, nondipolar, proper reverse micelles exist.The role of water in the formation of reverse micelles is discussed. IntroductionDue to their complexing ability toward metal ions,'-4 dialkylphosphoric acids and their alkaline salts are widely used in extraction processes by the industry. One of the representatives, sodium bis(2-ethylhexyl) phosphate or NaDEHP, has drawn particular attention for its ability to form reverse micelles in nonpolar solvents5 which is believed to be a key for its utility in metal extraction.6As a surfactant, the NaDEHP molecule is structurally related to the classical Aerosol-OT (or AOT, sodium bis(Zethylhexy1) sulfosuccinate), which has identical hydrophobic parts and differs only in its polar head group. The present study was undertaken to investigate the effect of the difference in head group on aggregation and on the properties of reverse micelles formed. Results of quasi-elastic light scattering, controlled partial pressure-vapor pressure osmometry (CPP-VPO),7.8 conductance, and viscosity measurements on the NaDEHP/ benzene/H20 system are reported for a wide range of composition and temperature. It is shown that with increasing water content wo[H20]/[NaDEHP] of the solution structural changes occur in the aggregates. At low water content, the structures are crystalline dipoles. We also comment on recent suggestions by Neuman and co-workers that water acts as an antimicellization agent9.I0 rather than a "gluing" agent"*'2 in the formation of NaDEHP reverse micelle. Experimental SectionMaterials. Bis(2-ethylhexy1)phosphoric acid (HDEHP; ICN Biomedicals) was purified by the Cu(I1) salt precipitation methodI3 as modified by McDowell et a1.14 The purity of the resulti...

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Section: Lightmentioning

confidence: 99%

“…3. The values of the monomer concentration and mean aggregation number calculated from the linear least-squares fitted data obtained in the range of surfactant concentration 0.1 M < C < 0.35 M are listed in Table1as a function of water content and temperature.…”

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confidence: 99%

Equilibrium Properties of Crystallites and Reverse Micelles of Sodium Bis(2-ethylhexyl) Phosphate in Benzene

Feng¹,

Schelly²

1995

J. Phys. Chem.

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“…The extractants are usually surface-active agents and are classified into three groups: acidic, basic and neutral extractants [2]. Alkyl phosphorus acids are the most widely used acidic extractants [2][3][4]. Bis (2-ethylhexyl) phosphoric acid (HDEHP), bis(2-ethylhexyl) phosphinic acid (Cyanex ® 272) and bis(2-ethylhexyl) dithiophosphoric acid are some of the alkyl phosphorus acids extractants which are employed in extraction of metal ions [5].…”

Section: Introductionmentioning

confidence: 99%

Molecular modeling study of the aggregation behavior of nickel(II), cobalt(II), lead(II) and zinc(II) bis(2-ethylhexyl) phosphate complexes

Ibrahim

Neuman

2006

Journal of Colloid and Interface Science

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“…Differential standard concentrations (~g Ni/40 mg cellulose): photocell in darkness ("), 106.7 ( " ) , 83.0 (-0--), 59.3 (-0-), 5.9 (-Q'-). [(1-P)(1-R h )]2/(R h (1-P)+P)…”

Section: ""mentioning

confidence: 99%