Di(2-ethylhexyl) Phosphoric Acid Molecules Research Articles

Solvent extraction of vanadium with D2EHPA from aqueous leachate of stone coal after low–temperature sulfation roasting

The solvent extraction of vanadium from aqueous solution after the leaching of stone coal vanadium ore following low–temperature sulfation roasting was enabled by di-(2-ethylhexyl)phosphoric acid (D2EHPA). Firstly, the effects of main factors on vanadium extraction and iron removal were investigated. Secondly, density function theory (DFT) simulations using the DMol3 module (GGA/PW91) were conducted to elucidate the interactions between D2EHPA and vanadium, which concluded that the phosphoric acid oxygen atom formed a coordination bond with vanadium atoms to achieve the solvent extraction of vanadium. D2EHPA molecules also dimerized to form a cyclic chelate complex with vanadium, which contributed to the solvent extraction of vanadium. Lastly, the solution chemical behavior of the vanadium in the organic phase after extraction with D2EHPA was analyzed. After reduction and neutralization pretreatments, VV (VO2+) was reduced to VIV (VO2+), which could be more strongly coordinated by D2EHPA over the pH range of 1–4.03, while FeIII was reduced to FeII, which was not coordinated as strongly by D2EHPA, minimizing the amount of iron extracted from the aqueous leachate into the organic phase by D2EHPA. The vanadium extraction efficiency increased as the initial pH of the leachate increased, but the formation of VOSO4 at pH > 2.5 hampered the extraction of vanadium.

Synergetic facilitated transport of nickel via supported liquid membrane process by a mixture of Di (2-ethylhexyl) phosphoric acid and n-octanol: Kinetic permeation study and approach for a green process

This work addresses the synergistic removal of nickel from the electroplating wastewater using a supported liquid membrane (SLM) process. The supported liquid membrane formulation consisting of Di-2-ethylhexyl phosphoric acid (D2EHPA), n-octanol, kerosene, and sulfuric acid as a carrier, synergist, diluent, and stripping agent, respectively. The effects of several significant parameters namely D2EHPA, n-octanol, and sulfuric acid concentrations as well as feed and stripping phases flow rates were investigated. Results revealed that n-octanol as a synergist significantly affected the removal efficiency of nickel since it can modify the D2EHPA molecules in the membrane phase. Besides, a kinetic model for the nickel ion transport across SLM revealed that the transport resistances due to the diffusion across the membrane (Δorg), transport resistances due to the diffusion through the aqueous boundary layer (Δaq), thickness of the aqueous diffusion layer (daq), and diffusion coefficient of the nickel-carrier complex across the membrane (Dorg) were found to be 2.90 × 105 sm−1, 1.94 × 104 sm−1, 1.24 × 10−5 m and 7.20 × 10−10 m2s−1, respectively. Interestingly, an approach to a green process by incorporating palm oil as a diluent showed that it is feasible to be applied and offers a green SLM process in the future.

Effect of di-(2-ethylhexyl)phosphoric acid on microstructure, cloud point and uranyl ion binding competence of Triton X-100 micelles

The incorporation of an extracting agent di-(2-ethylhexyl)phosphoric acid (D2EHPA) into non-ionic surfactant, Triton X-100 (TX-100) micelles was investigated by monitoring the microstructural changes using light scattering (LS) and small angle neutron scattering (SANS) techniques. Dynamic light scattering (DLS) studies indicate a gradual increase in the apparent diffusion coefficient (Da) of the micelles upon addition of D2EHPA, suggesting the incorporation of D2EHPA molecules into TX-100 micelles. Quantitative analysis of the SANS data for D2EHPA containing micelles indicates that the effective surface charge on the micelles increases with increasing concentration of D2EHPA, while the dimensions of the micelles remain almost same. Thus, the observed increase in Da of the micelles is attributed to the changes in the intermicellar interactions. The increase in repulsive interaction with addition of D2EHPA is also evident from an increase in the cloud point of the micellar solutions. The microstructural and cloud point changes occurred in D2EHPA containing micelles in the presence of an inorganic salt, sodium chloride (NaCl) further support the inclusion of D2EHPA molecules into TX-100 micelles. The binding of uranyl ions (UO22+) to TX-100–D2EHPA mixed micelles was ensured by monitoring a decrease in the intermicellar repulsion upon addition of uranyl nitrate hexahydrate and a subsequent decrease in the cloud point of the micelles. A red-shift in the absorption peaks of uranyl nitrate hexahydrate in the presence of TX-100–D2EHPA mixed micelles also confirms the binding of UO22+ to mixed micelles. The quantitative estimation of UO22+ bound to TX-100–D2EHPA mixed micelles was carried by cloud point extraction (CPE) method followed by spectrophotometric determination.

Mechanism of the extraction of Molybdenum(VI) from diluted HCl and HNO<sub>3</sub> solutions with di(2-ethylhexyl)phosphoric acid

The mechanism of extraction of Mo (VI) from diluted HCl and HNO3 solutions with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-hexane has been investigated. The mechanism of extraction from both acids at pH 1.0 – 6.0 was found to be majorly by cation exchange of MoO22+ for H+ of the extractant (H2R2), while at lower pH value, it was observed to be by neutral, unstable isopoly acid, H4Mo8O26 or nMoO3.2H2O and MoO22+. The extraction efficiency was maximal at pH 1.0 for both acids, E% = 84.8 and 80.0 for HCl and HNO3 media respectively. From the method of slope analysis, the number of D2EHPA molecules associated with MoO22+ was found to be two at pH = 1.0.Keywords: Extractant, cation exchange, isopoly acid, slope analysis.

Surface Modification of Amberlite XAD‐4 Resin with D2EHPA by a Two‐Step, Solvent–Nonsolvent Procedure and the Application on the Selective Separation of Lead and Copper Ions

Di(2‐ethylhexyl)phosphoric acid (D2EHPA) has the tendency to adsorb at interfaces in an oriented fashion due to the amphiphilic structure. The study of the surface tension shows that the adsorption of D2EHPA at interface can lower the surface tension of ethanol solution. The amount of adsorption is affected by the pH and ionic strength of the solution. Being a small surface‐active molecule, a monolayer of D2EHPA molecules can be immobilized on the surface of nonpolar Amberlite XAD‐4 resin by a two‐step, organic solvent–nonorganic solvent process. The amount of immobilized D2EHPA is as high as 1.02 (mol/kg of resin). The electron spectroscopy for chemical analysis (ESCA) results show that the immobilized D2EHPA undergoes reorientation by further exposing the phosphoric acid group to the water phase. Since the hydrophobic alkyl chains of D2EHPA physically entangle with the surface polymer chains of Amberlite XAD‐4, the immobilized extractant has good stability on the resin surface. This D2EHPA‐modified Amberlite XAD‐4 can be used for the separation of lead and copper ions as an ion‐exchange resin. Ion‐exchange isotherm experiments show that D2EHPA‐modified resin has higher Pb ion affinity than Cu ion. This new type of D2EHPA‐modified resin shows better Pb and Cu ions separation than analogous D2EHPA‐impregnated resin [extractant‐impregnated resin (EIR)] and solvent extraction system. The selective separation results using series contacts of solution mixtures with resins further demonstrated the feasibility of using D2EHPA‐modified Amberlite XAD‐4 resin for the separation of Pb/Cu mixed ion solution. After only six batches of contacts, the relative ion concentration of Cu ion increases from 50% to more than 99%, while the relative ion concentration of Pb ion decreases from 50% to less than 1%. The Cu recovery rate is more than 75%, comparing to 54% in the EIR system.

Selective Extraction of Americium(III) over Macroscopic Concentration of Lanthanides(III) by Synergistic System of TPEN and D2EHPA in 1‐Octanol

The synergistic extraction with N,N,N′,N′‐tetrakis(2‐methylpyridyl)‐ethylenediamine (TPEN) and di(2‐ethylhexyl)phosphoric acid (D2EHPA) in 1‐octanol demonstrates good selectivity for Am(III) over Ln(III) in solutions containing macroscopic concentrations of the latter. The maximum apparent separation factor, which is defined as the ratio of the distribution ratio of Am(III) to that of Eu(III), is ca. 80 at the molar ratio of D2EHPA to TPEN, 2.0. This ratio corresponds to the result of the spectrophotometric titration, which indicates that TPEN and D2EHPA associate in 1‐octanol and two D2EHPA molecules coordinate to Eu(III)–TPEN complex, [Eu(TPEN)]3+. In the present study, association of D2EHPA and TPEN is one of the most important factors for the synergistic extraction and the complexation of TPEN and D2EHPA with Eu(III).

Mechanism of rate enhancement in the extraction of Zn(II) by di(2-ethylhexyl)phosphoric acid in the presence of sodium lauryl sulphate micelles

The effect of a sodium lauryl sulphate (NaLS) micellar phase on the rate of Zn(II) extraction from a sulphate medium by a 0.01 M solution of di(2-ethyl-hexyl)phosphoric acid (DEHPA) in dodecane was investigated in a constant area stirred cell. The concentration of NaLS was varied between 5.1×10 −5 and 7.7×10 −3 M. Below the critical micellar concentration (CMC) the presence of the surfactant decreased the extraction flux, whereas substantial flux enhancements were observed above the CMC reaching an enhancement ratio of 10 at a concentration of 4.6×10 −3 M. Solubilization of DEHPA in the Zn-free micellar aqueous phase at different concentrations of NaLS was investigated using Fourier transform infra-red spectroscopy. Solubility increased with NaLS concentration, reaching a maximum at the highest NaLS used, rendering a calculated concentration of DEHPA in the aqueous phase of 0.8×10 −3 M. As DEHPA is practically insoluble in water it was concluded that DEHPA molecules were incorporated in the micellar interface, thus producing a substantial enlargement of the reaction site for the interfacial Zn complexation reaction, together with a reaction rate enhancement due to micellar catalysis. It is proposed that the main mechanism of flux enhancement is the additional production of Zn complex at the micellar interface, coupled with a high rate of complex transfer to the organic phase due to micellar interaction with the system interface. The effect of the negative electrical charge at both the interface and the micellar interface is also discussed.

Distribution Behavior of L-Phenylalanine by Extraction with Di(2-Ethylhexyl) Phosphoric Acid

In the separation processes of amino acids, zwitterionic species are prevented from being exchanged because of the spatial proximity of two opposite charges on the molecule. There would be a high chemicals cost due to the need to change the solution pH. It is therefore desirable to develop a novel recovery technology for amino acids in the middle pH range. A series of extraction equilibrium experiments for L-phenylalanine (L-phe) with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-octane was carried out. The effects of L-phe concentration, D2EHPA concentration, and pH on the distribution ratio were discussed in detail. The infrared spectrogram of the organic-phase-loaded solute illustrated that the pH condition had little effect on the structure of the complex. There are proton-transfer and ion-exchange reactions in the extraction. One L-phe molecule is extracted by forming a complex with two dimeric D2EHPA molecules. An expression of the equilibrium distribution was proposed.

Distribution Behavior of Amino Acid by Extraction with Di(2-ethylhexyl) Phosphoric Acid

The distribution equilibrium of l-tryptophan (l-Trp) by extraction with di(2-ethylhexyl) phosphoric acid (D2EHPA) dissolved in n-hexane was studied. The effects of L-Trp and D2EHPA concentrations, pH, and ionic strength, particularly of L-Trp loading in the organic phase, on extraction equilibrium were examined in detail. When the amino acid loading ratio (the molar concentration ratio of the equilibrium amino acid in the organic phase to the initial dimeric D2EHPA) was less than 3 × 10−3, one L-Trp molecule was extracted by forming a complex with four monomeric D2EHPA molecules, and the extraction equilibrium constant (K e) was determined to be 0.045 dm3/mol. Above this loading ratio the equilibrium formula did not hold, and the apparent equilibrium constant (K a) increased significantly with increasing loading ratio. The phenomenon was explained by taking into account two parallel reactions in which fewer D2EHPA molecules, two and one respectively, were needed to extract one l-Trp molecule.