TVEX-TBP

TVEX-TBP Uranium Extraction from Dense Pulps by Using... 

FIGURE 8.4 Specific surface area (a), total pore volume (b), and average effective pore radius (c) of TVEX-TBP matrix depending on extractant content. 

Chemical methods based on the study of extractant distribution (TBP) on TVEX-TBP resins were used to demonstrate that TBP is adsorbed by the TVEX porous matrix by physical adsorption. Extractant wash-out from the TVEX matrix is an important characteristic for metal extraction applications of solid adsorbents as TVEX since it may influence the physical-chemical properties of the extraction process. Infrared (IR) spectroscopy analysis of TVEX-TPB resins show the absence of shift for stretching frequency of the P = O group in comparison to the stretching frequency assignment for liquid TBP as an indication that TBP is hold by matrix surface due to physical adsorption as was confirmed from the by enthalpy values of TBP distribution from the TVEX matrix of 45.0 0.5 kJ/mol [10]. 

Equilibrium washout of tri-butylphosphate between the aqueous phase and the TVEX matrix (Figure 8.8) shows S-shaped curves typical for physical adsorption with formation of an extractant polymolecular adsorbed layer. The increase of temperature leads to a decrease of equilibrium distribution (Figure 8.9) due to the decrease of TBP solubility in water with temperature increase. Thus, TBP losses from TVEX matrix are small and are caused by tri-butylphosphate solubility in the aqueous phase, depending on solution acidity, ionic strength, and temperature. For example, during the pilot tests, TBP leakage from TVEX-TBP resins after 100... 

P NMR spectroscopy was used as a nondestructive method to determine TBP activity on TVEX-TBP materials by comparison with activity of TBP in pure samples. The signal width of TBP in TVEX matrix is only 1.5 to 2 times broader as compared with signal width for liquid tri-butylphosphate, indicating the drop-liquid state of extractant (TBP) in matrix pores. TBP signal width increases at extractant partial washout by acetone due to the increase of portion of extractant adsorbed by TVEX matrix the total washout leads to the extractant signal disappearance. However, according to chemical analysis, TVEX matrix still contains 2 to 5% TBP after complete extractant washout. This fact indicates that tri-butylphosphate is dissolved partially in TVEX matrix and acts as plasticizer of styrene-divinylbenzene copolymer. 

FIGURE 8.10 Temperature dependence of H atom longitudinal relaxation time for TVEX-TBP (1-groups CH2 -1, 2, 3 2-groups CH3-4), and TBP (3-gronp CH2-1 4-groups CH2-2, 3 5-group CH3-4). 

Relative Value of Longitudinal Relaxation Time TVEX-TBP/(100%TBP)... 

Activation Energy of Dipole-Dipole E,.(dd) and Spin-Rotational E, Interaction between Carbon Atoms in Extractant Molecules for Liquid TBP and TVEX-TBP... 

Extraction isotherms of nitric, sulphuric, and hydrochloric acids in comparison with solvent extraction data (Figure 8.15) show that extraction capacity of TBP in TVEX resins. An increase of TBP capacity in TVEX-TBP is caused by the extractant state in the polymer matrix. The extraction capacity of mineral acids by TVEX-TBP decreases in the sequence HNO3 > H2SO4 > HCI (Figure 8.15a,b,c), and when compared with TBP solvent extraction performance, the capacity of the impregnated polymers exceeds 1.5 times the capacity of HNO3, 3.5 times that of HCI, and several times that of H2SO4. 

Extraction rates of mineral acids extraction by TVEX-TBP 1-HCl, 2-HNO3,... 

The Sc extraction process by TVEX-TBP and TVEX-DIOMP from hydrochloric, nitric, and sulfuric is endothermic in hydrochloric solutions and exothermic for sulfuric and nitric solutions (Table 8.6). Additionally, the extraction rates showed diffusion coefficients 1 to 2 orders of value higher (K jf of Sc + ions into TVEX granule mVs) than for phosphorus-containing ion-exchange resins. 

Scandium extraction capacity of TBP and DIOMP in TVEX porous matrix is higher as compared with corresponding solvent extractant capacity [10,19-22]. Isotherms of Sc extraction from hydrochloric solutions by TBP, TBP 50% solution in CCI4 and TVEX-TBP almost coincide (Figure 8.16) at low Sc concentration ... 

FIGURE 8.16 Isotherms of scandium extraction by TBP (1), TVEX-TBP (2), and TBP solution 50% in CC14 (3) from 8 mol/L hydrochloric solution. 

TBP (3.4 to 2.9), 50% TBP solution in CCI4 (2.4 to 2.8), and TVEX-TBP (2.8-1.9) and has fractional value indicating simnltaneous formation of several scandium complexes in organic phase and different ratio between them. In addition, the ASN value depends on the metal concentration in the resin phase and decreases for TVEX-TBP resins and increases for 50% TBP solution in CCI4 with scandium content increase. 

FIGURE 8.21 P(P) and (b) NMR spectra of scandium extract by TVEX-TBP from 6... 

During scandium extraction by TVEX-DIOMP resins an increase of DIOMP capacity in TVEX matrix is observed at lower Sc concentrations as compared with TVEX-TBP due to the higher DIOMP donor abilities in comparison with TBP. 

FIGU RE 8.22 45Sc NMR spectra of TVEX-TBP after different number of extraction-reextraction cycles. 

After 45 extraction cycles, NMR spectrum of TVEX-TBP contains signals related to Sc compounds with TBP and di-butylphosphoric acid (DBP), which is a prodnct of TBP hydrolysis. The narrow signal remaining in TVEX spectrum after Sc reextraction with a chemical shift indicates the absence of Cl-ions in Sc coordination sphere. The small width of the signal indicates high symmetry of the central ion environment as it corresponds to the Sc complex [Sc(DBP)g]. 

After 90 cycles of extraction, the reextraction TVEX-TBP capacity significantly decreases, and the -Sc NMR spectra before and after reextraction do not differ. The nature of the spectrum suggests the formation of linear Sc polymers with TBP hydrolysis products. These compounds with a general composition of [ScCl2(DBP)2(TBP)2]+ are not extracted and accumulate in the resin matrix. 

The nature of changes led to TVEX-TBP aging in a cyclic process of scandium extraction-reextraction from hydrochloric solntions. A decrease in extraction ability is caused by a decrease in TBP content dne to extractant gradnal hydrolysis and... 

Then, scandium extraction from H2SO4 media by both TBP and TVEX-TBP may be presented by the following reactions ... 

The extraction capacity of liquid TBP and TVEX-TBP increases with increase of aqueous phase acidity for 7,9, and 11 mol/1 HCl solutions (Figure 8.23). TBP capacity in TVEX matrix is higher as compared with liquid tri-butylphosphate this difference depends on aqueous phase acidity and becomes maximal (1.5 to 2 times) at 9 mol/L HCl. TVEX-TBP capacity is also higher for Nb extraction for sulfuric media however, dependence of extractant capacity on aqueous phase acidity is dependent on the redox unstability of Nb in sulfuric media [25,26]. 

The process is temperature dependent, and a temperature increase leads to increase of TVEX-TBP capacity for extraction from HCl media and negligibly... 

Isotherms of Ga extraction by TVEX-TBP, TVEX-DIOMP as well as by liquid TBP andDIOMP from 3,5, and 8 mol/L HCl solutions show (Figure 8.25 and Figure 8.26) that extractant equilibrium capacity increases with aqueous phase acidity increase extractant capacity in TVEX matrix is 1.3 to 1.5 times higher as compared with solvent extractant. Enthalpy of gallium extraction from 3 mol/L HCl is -11.7 kJ/mol for TBP and -12.0 kJ/mol for TVEX-TBP. Diffusion coefficient of gallium extraction is 4.210-" mVs for TVEX-TBP (3mol/L HCl) and 5.410-" mVs for TVEX-DIOMP (6 mol/L HCl) [27]. 

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