Extraction Studies of Phosphoric Acid Tributyl Ester from Nitric Acid

Article pubs.acs.org/jced

Extraction Studies of Phosphoric Acid Tributyl Ester from Nitric Acid Solutions Using Dodecane in the Presence of Inextractable Metal Nitrates Shaila Lalkuwar Bajoria,† Virendra Kisan Rathod,*,† N.K. Pandey,‡ U. Kamachi Mudali,‡ and R. Natarajan‡ †

Department of Chemical Engineering, Institute of Chemical Technology, N.P. Marg, Matunga, Mumbai 400019, India RR & DD, Reprocessing Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamilnadu 603102, India

‡

ABSTRACT: Sodium nitrate and calcium nitrate are not extracted by phosphoric acid tributyl ester (TBP) in the plutonium uranium extraction (PUREX) process. The effect of these inextractable metal nitrates on the solubility and distribution data of TBP has been studied. The solubility of TBP in water in the presence of different concentrations of sodium nitrate is determined, and salting coefficient of TBP is calculated. It has been observed that the solubility of TBP in nitric acid decreases in the presence of both inextractable nitrates, that is, sodium nitrate and calcium nitrate. The effect of inextractable metal nitrates on the equilibrium data for the TBP−dodecane−nitric acid system has been studied. The distribution coefficient value of TBP is greater in the presence of sodium nitrate solutions as compared with calcium nitrate solutions due to more salting out of TBP. Because sodium nitrate is a better salting agent than calcium nitrate, the variation in the concentration of nitric acid at equilibrium was more in sodium nitrate solutions in comparison with that in calcium nitrate solutions. The data obtained will be useful in separating dissolved TBP from acidic waste for safe disposal of nuclear waste.

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TBP in kerosene as an extractant.8 Baldwin and Higgins have carried out distribution studies of TBP using different polar solvents, hydrocarbons, and hydroxylated solvents.9 The distribution of electrolytes between water and TBP and all interactions involved in it have also been studied.10 Higgins et al. have studied the effect of various electrolytes and temperature on the solubility of TBP in water and calculated the activity coefficient of TBP.4 The distribution of nitric acid between TBP and water for the TBP−nitric acid−water system has also been studied.11−13 Burger and Forsman have measured the solubility of TBP in water and nitric acid in the presence of inert diluents and also reported that solubility of TBP decreases in the aqueous solutions in the presence of salts like UO2(NO3)2.14 Kuno et al. have investigated the solubility of TBP in the aqueous solutions of plutonium nitrate and in HRLW of PUREX nuclear fuel reprocessing.3 Kumar et al. have proposed an extended Setschenow model for the predicting the solubility of water in (5 to 100) % TBP/diluent/nitric acid/ water biphasic system at 298.15 K and also the temperature dependency on the solubility.15 Hipfner and Tuck have determined the interfacial permeability coefficient k for the transfer of water across the water/TBP interface as a function of both the aqueous electrolyte concentration and the initial water concentration in the TBP.16 All of these above authors

INTRODUCTION Phosphoric acid tributyl ester (TBP) diluted with an inert nparaffin mixture is widely used as an extractant for the reprocessing of irradiated fuels for many years.1 The plutonium uranium extraction (PUREX) process involves the use of 30 % TBP in paraffinic diluent like dodecane for the separation of uranium and plutonium from the aqueous nitric acid solutions.2 Various metal elements are also present in the highly radioactive liquid waste solution (HRLW) in nitrate form.3 The solubility of TBP in the aqueous solution decreases when inorganic solutes are added to these solutions. The salting out of TBP takes place in the presence of these inorganic nitrates in the aqueous phase.4 During the solvent extraction process, some amount of TBP gets transferred to the aqueous acidic solutions containing dissolved metal nitrates, which leads to many environmental problems. Separation of TBP from aqueous solutions in the presence of these inorganic nitrates is of direct interest in the reprocessing process for safe disposal of nuclear waste. Investigators have done various studies related to solubility and equilibrium data for TBP in the presence of nitric acid, water, and inorganic salts. The extraction of nitric acid by TBP for the system TBP−nitric acid−diluent has been studied, and the thermodynamic equilibrium constant for nitric acid has been calculated.5,6 Alcock et al. have measured the solubility of TBP in the presence of nitric acid and sodium nitrate.7 Alcock et al. have also extracted zirconium from the aqueous solutions of nitric acid, sodium nitrate, and uranium nitrate by using 19% © XXXX American Chemical Society

Received: September 5, 2012 Accepted: October 26, 2012

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dx.doi.org/10.1021/je300963c | J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

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by dissolving 100 g of sodium nitrate in 1 L of nitric acid. The concentration of nitric acid in the aqueous phase was also varied from (0.214 to 2.437) mol·kg−1. The organic phase used was containing different percentages of TBP in dodecane ranging from (0.019 to 17.445) mol·kg−1. The partition study was performed by equilibrating the organic and aqueous phases in 1:1 ratio on a magnetic stirrer for 3 h at 303.15 K and then allowing the phases to separate overnight at 303.15 K for complete separation before analysis. The same procedure was repeated for calcium nitrate also. TBP dissolved in the organic phase was analyzed on gas chromatography (GC) using a flame ionization detector (FID) while TBP present in the aqueous phase was analyzed on HPLC) using a refractive index (RI) detector. The analysis procedure is described in detail in Bajoria et al.17 Each sample was analyzed thrice to check the reproducibility. The deviation in the results obtained was precise within ± 2 %. Distribution of Nitric Acid. It is reported that at equilibrium, not only TBP but also nitric acid distributes itself between the organic and the aqueous phase.17 The distribution coefficient Kd of nitric acid is the ratio of concentration of nitric acid in the organic phase to that in the aqueous phase. Kd changes as the concentration of nitric acid varies during this study and hence Kd has been calculated by determining the concentration of nitric acid present in both the phases. The concentration of nitric acid in the aqueous phase was determined by titration method. The nitric acid transferred in the organic phase was measured by back extraction method. 5 mL of the organic phase containing dissolved nitric acid was tumbled with 5 mL of deionized water on a magnetic stirrer for 1 h at 303.15 K. After phase separation, the concentration of nitric in deionized water was determined using the titration method with NaOH solution as a base and phenolphthalein as an indicator. The color change at the end point observed was from colorless to pale pink. All samples were titrated thrice with NaOH to check reproducibility. The uncertainty reported in results was ≤ 0.1 %.

have mainly focused on the solubility of TBP in water or in the presence of metal nitrate in water. However, literature on the separation of TBP from aqueous nitric acid solution in the presence of different inextractable metal nitrates is not available. Hence, it is informative to know the effect of these inextractable metal nitrates on the solubility of TBP in the aqueous solutions. The equilibrium study for TBP−dodecane−nitric acid system in the presence of inextractable metal nitrates will be useful for separation of TBP from different nitric acid solutions using dodecane as the solvent. The objective of the present work is to study the effect of inextractable metal nitrates like sodium nitrate and calcium nitrate on the solubility of TBP in water and nitric acid. The effect of sodium nitrate and calcium nitrate on the equilibrium data of the TBP−dodecane−nitric acid system has also been investigated. The variation in the concentration of nitric acid has also been studied during equilibrium study. The distribution coefficient Kd of nitric acid has been calculated by determining the concentration of nitric acid present in both phases at equilibrium.

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EXPERIMENTAL PROCEDURES Materials. TBP, nitric acid, dodecane, acetonitrile, sodium nitrate, calcium nitrate, and sodium hydroxide were the chemicals used in the present study. All reagents used were of analytical grade. Table 1 lists a summary of chemicals used in this work and their details. Table 1. Sample Description Table substance

source

initial mass fraction purity

TBP dodecane nitric acid acetonitrile sodium nitrate calcium nitrate

Prabhat Chemicals Prabhat Chemicals Prabhat Chemicals HiMedia Laboratories SD Fine Chemicals SD Fine Chemicals

0.970 0.950 0.700 0.997 0.990 0.990

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Solubility Study. The solubility of TBP was measured in water in the presence of sodium nitrate at 303.15 K. The concentration of sodium nitrate in water was varied from (38.1 to 42.5) mol·kg−1. The solubility study was performed by equilibrating 25 mL of pure TBP with 25 mL of these sodium nitrate solutions for 3 h on a magnetic stirrer. The solutions were then transferred to the separating funnel to stand overnight at 303.15 K to attain complete separation. Samples were removed from the aqueous (lower) layer using a warmed and thoroughly cleaned 10 mL pipet. The amount of TBP in the aqueous phase was determined on the high-performance liquid chromatography (HPLC) as described in detail in Bajoria et al.17 All samples were analyzed three times to check the reproducibility of the results. The solubility values obtained were precise within ± 2 %. The solubility of TBP in 2.437 m HNO3 in the presence of metal nitrates was also determined. The amount of dissolved sodium nitrate was varied from (10 to 100) g in 1 L of 2.437 m HNO3 solution. The equilibration, separation, and analysis technique was same as described above. Similar experimentations were performed for the determination of solubility of TBP in the presence of calcium nitrate. Equilibrium Study. The equilibrium study was carried out for the TBP−dodecane−nitric acid system containing dissolved inextractable metal nitrates. The aqueous phase was prepared

RESULTS AND DISCUSSION Effect of Inextractable Nitrate on Solubility of TBP in Water. The presence of sodium nitrate has affected the solubility of TBP in water. It has been observed that the solubility of TBP decreases with the increase in the concentration of sodium nitrate from (38.1 to 42.5) mol·kg−1 in water. The salting coefficient and activity coefficient for TBP in different concentration of sodium nitrate have been calculated using the Setschenow equation, and the values obtained are summarized in Table 2. It has been found that the salting coefficient and activity coefficient values increase with the concentration of sodium nitrate in water. Sodium nitrate is an electrolyte that acts as a salting agent by limiting the solubility of TBP in water. Higgins et al. have also observed similar salting out of TBP in the presence of different electrolytes. Metal nitrates exert pressure on the water and thereby affect the solubility of TBP.4 Schulz et al. have also stated that the solubility of TBP in the aqueous phase decreases when inorganic solutes are added to water.2 Sodium nitrate affects the hydration sphere of water and increases the disorder in the water system, thereby reducing the solubility of TBP in water. Burger and Forsman have also mentioned in their report that the presence of salts in the aqueous phase decreases the solubility of TBP.14 B



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Table 2. Salting Coefficient of TBP in the Presence of Sodium Nitrate in Water conc. of NaNO3 in water

solubility of TBP, S

mol·kg−1

10−5 mol·kg−1

activity coefficient γ = So/S

salting coefficient, ks

38.1 38.4 39.1 39.9 40.7 41.6 42.5

138.07 121.05 90.10 68.44 49.49 36.34 24.37

1.10 1.26 1.69 2.22 3.07 4.18 6.24

0.14 0.20 0.23 0.23 0.24 0.25 0.27

Effect of Inextractable Nitrate on Solubility of TBP in Nitric Acid. It has been found that the presence of inextractable metal nitrates like sodium nitrate and calcium nitrate in nitric acid affects the solubility of TBP in the aqueous acidic solutions. As the amount of these dissolved nitrates increases from 10 to 100 g in the nitric acid solution, the solubility of TBP in nitric acid decreases, as shown in Figure 1.

Figure 2. Effect of inextractable metal nitrates on distribution coefficient of TBP in 0.214 m HNO3. Symbols: ●, 0.214 m HNO3; ■, NaNO3; ▲, Ca(NO3)2.

Figure 3. Effect of inextractable metal nitrates on distribution coefficient of TBP in 0.737 m HNO3. Symbols: ●, 0.737 m HNO3; ■, NaNO3; ▲, Ca(NO3)2.

Figure 1. Effect of inextractable metal nitrates on the solubility of TBP in nitric acid. Symbols: ●, NaNO3; ■, Ca(NO3)2.

It has also been observed that the decrease in solubility is greater in the presence of sodium nitrate as compared with calcium nitrate. The salting-out effect depends on ionic radius and ionic strength of the electrolyte.2 Because sodium nitrate has a smaller ionic radius and a lower ionic strength compared with calcium nitrate, it is easily soluble in nitric acid and exerts greater pressure on nitric acid, thereby reducing the solubility of TBP in nitric acid. Hence, TBP salted out more in sodium nitrate solutions as compared with calcium nitrate solutions. Equilibrium Study in Presence of Inextractable Metal Nitrates. Equilibrium curves have been generated for TBP− dodecane−nitric acid system in the presence of inextractable metal nitrates. The effect of TBP, dodecane, and nitric acid on the distribution of TBP between the two phases in the presence of inextractable metal nitrates like sodium nitrate and calcium nitrate has been studied, and the results obtained are compared with those obtained previously by Bajoria et al. in the absence of any metal nitrates.17 It has been observed from Figures 2−4 that the distribution coefficient Kd of TBP increases with the increase in TBP concentration from (0.019 to 17.445) mol·kg−1 in the organic phase. The results obtained are in concordance with that

Figure 4. Effect of inextractable metal nitrates on the distribution coefficient of TBP in 2.437 m HNO3. Symbols: ●, 2.437 m HNO3; ■, NaNO3; ▲, Ca(NO3)2.

reported by Bajoria et al.17 Kd of TBP is the ratio of concentration of TBP in the organic phase to that in the aqueous phase. As the concentration of TBP increases in the C



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organic phase, a greater amount of TBP is transferred into the aqueous phase and distribution coefficient Kd of TBP increases. It has been reported that Kd depends upon the concentration of TBP in both the phases and is a function of TBP concentration in the organic phase.2,17 Thus, Kd values were found to be increased with the concentration of TBP in the organic phase, but the solubility of TBP in the aqueous phase is less in the presence of these inextractable metal nitrates due to salting out of TBP, and thus the ratio of concentration of TBP in the organic phase to that in the aqueous phase increases, resulting in higher distribution coefficient Kd values in the presence of sodium nitrate and calcium nitrate solutions. Figures 5−7 also demonstrate that the solubility of TBP in the aqueous phase decreases with dodecane concentration in Figure 7. Effect of dodecane on solubility of TBP in 2.437 m HNO3 in the presence of inextractable metal nitrates. Symbols: ●, 2.437 m HNO3; ■, NaNO3; ▲, Ca(NO3)2.

equilibrium curves generated for TBP at different concentrations of nitric acid in the presence of sodium nitrate is as shown in Figure 8. Similarly, the equilibrium curve for TBP in

Figure 5. Effect of dodecane on the solubility of TBP in 0.214 m HNO3 in the presence of inextractable metal nitrates. Symbols: ●, 0.214 m HNO3; ■, NaNO3; ▲, Ca(NO3)2.

Figure 8. Equilibrium curve for TBP−dodecane−nitric acid system in presence of sodium nitrate. Symbols: ●, 0.214 m HNO3; ■, 0.737 m HNO3; ▲, 2.437 m HNO3.

the presence of calcium nitrate at different nitric acid concentration is shown in Figure 9. It has been observed that the solubility of TBP decreases with increase in the concentration of nitric acid in the presence of sodium nitrate and calcium nitrate solutions in the aqueous phase. Bajoria et al. have also obtained similar results. They have reported that solubility of TBP in the aqueous phase decreases with the concentration of nitric acid, as nitric acid also restricts the solubility of TBP in the aqueous phase.17 Sodium nitrate and calcium nitrate are salting agents that reduce the solubility of TBP in the aqueous phase and thus increase the distribution coefficient of TBP. Kuno et al. have also reported similar salting out of TBP in the presence of electrolytes like plutonium nitrate, ferric nitrate, and zirconium nitrate. They have also observed variation in the solubility of TBP in the aqueous phase in the presence of plutonium nitrate solution at different nitric acid concentrations.3 Sodium nitrate and calcium nitrate do not form solvates with TBP like other metal nitrates. Hence, they are inextractable metal nitrates.2 When these inextractable nitrates are present in the nitric acid solutions, TBP alone would be extracted into the organic phase and not any complex of TBP with nitrates. Thus, extraction of

Figure 6. Effect of dodecane on solubility of TBP in 0.737 m HNO3 in the presence of inextractable metal nitrates. Symbols: ●, 0.737 m HNO3; ■, NaNO3; ▲, Ca(NO3)2.

the organic phase as dodecane is the diluent that limits the solubility of TBP in the aqueous phase.17 The reduction in the solubility of TBP in the aqueous phase is more in the presence of the inextractable metal nitrates, as sodium nitrate and calcium nitrate are salting agents that restrict the solubility of TBP. The effect of nitric acid on the distribution of TBP between the organic and the aqueous phase has also been examined. The D



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0.00 0.00 0.00 0.00 0.17 0.33 3.67 0.33 0.83 0.00 0.67 2.33 2.437 2.437 2.437 2.432 2.428 2.335 2.428 2.414 2.437 2.437 2.418 2.372 0.0141 0.0282 0.0636 0.1242 0.1852 0.2795 0.4044 0.5200 0.6525 0.7678 0.8926 0.9557 2.418 2.400 2.353 2.270 2.187 1.980 1.918 1.769 1.639 1.512 1.361 1.254 2.50 6.00 7.50 5.00 9.50 12.50 18.00 17.50 19.00 23.00 25.00 25.50 0.718 0.691 0.679 0.698 0.664 0.641 0.599 0.603 0.592 0.561 0.546 0.543 0.004 0.007 0.018 0.035 0.053 0.074 0.106 0.139 0.171 0.192 0.214 0.225 0.714 0.683 0.660 0.660 0.607 0.561 0.486 0.456 0.412 0.360 0.323 0.309 0.00 3.33 1.00 2.33 6.67 9.67 11.67 18.67 20.67 24.33 29.00 31.00 0.214 0.207 0.212 0.209 0.200 0.193 0.189 0.174 0.169 0.161 0.151 0.147

total conc. of HNO3 (m)

0.737 m HNO3

conc. of HNO3 in org. phase (m) conc. of HNO3 in aq. phase (m) deviation in Conc. of HNO3 (%) total conc. of HNO3 (m)

0.214 0.207 0.207 0.200 0.185 0.171 0.156 0.135 0.121 0.106 0.092 0.085 0.019 0.039 0.120 0.204 0.431 0.973 1.677 2.627 3.979 6.057 9.661 17.445

0.214 m HNO3

conc. of HNOmol· in org. phase (m) conc. of HNO3 in aq. phase (m) conc. of TBP in dodecane (mol·kg−1)

TBP−dodecane−HNO3−NaNO3 system

Table 3. Equilibrium Concentration of Nitric Acid in Both Phases in Presence of Sodium Nitrate Solutions

TBP into the organic phase by dodecane is fast because there is no competition for complex formation during extraction. Hesford and Mckay have also mentioned a similar type of extraction in their work. They observed that the extraction of extractable nitrates by TBP increases in the presence of inextractable metal nitrates because of lack of competition for complex formation and salting-out effect of inextractable nitrates.18 Alcock et al. has investigated the salting-out effect of TBP in the presence of nitric acid and sodium nitrate and found that TBP salted out more in sodium nitrate as compared with nitric acid because nitric acid is an extractable but sodium nitrate is inextractable electrolyte by TBP.7 Figures 2−4 clearly elucidate the lower distribution coefficient value of TBP in the presence of calcium nitrate for the TBP−nitric acid−dodecane system as compared with sodium nitrate. The pressure exerted by inextractable metal nitrates to salt out TBP depends on their ionic radius and ionic strength.2 The small ionic radius and low ionic strength of sodium nitrate as compared with calcium nitrate has resulted in lower solubility of TBP in the aqueous phase and higher distribution coefficient value of TBP. Distribution of Nitric Acid. The extraction of nitric acid into the organic phase from aqueous phase takes place in the presence of TBP.2,5,6,11−13 The equilibrium concentration of nitric acid in both of the phases along with the total concentration of nitric acid after extraction and deviation in the concentration of nitric acid measured is mentioned in Tables 3 and 4. The presence of nitric acid in the solution in the free and complex formed with TBP is basically the reason behind this deviation in the total concentration of nitric acid before and after extraction.11 The distribution coefficient Kd value of nitric acid was calculated by measuring the amount of nitric acid in aqueous and organic phases in the presence of inextractable metal nitrates like sodium nitrate and calcium nitrate, and the results obtained are summarized in Tables 5 and 6. The distribution study was carried out for three different concentrations of nitric acid, that is, (0.214, 0.737, and 2.437) m HNO3. It has been found that the extraction of nitric acid by TBP increases with the concentration of nitric acid in the aqueous phase and hence distribution coefficient Kd of nitric acid increases. The result obtained is in agreement with that reported by Bajoria et al.17

deviation in conc. of HNO3 (%)

Figure 9. Equilibrium curve for TBP−dodecane−nitric acid system in presence of calcium nitrate. Symbols: ●, 0.214 m HNO3; ■, 0.737 m HNO3; ▲, 2.437 m HNO3.

0.000 0.000 0.005 0.009 0.014 0.022 0.032 0.038 0.048 0.054 0.059 0.062

total conc. of HNO3 (m) conc. of HNO3 in org. phase (m) conc. of HNO3 in aq. phase (m)

2.437 m HNO3


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Table 4. Equilibrium Concentration of Nitric Acid in Both Phases in the Presence of Calcium Nitrate Solutions TBP−dodecane−HNO3−Ca(NO3)2 system 0.737 m HNO3

0.214 m HNO3 conc. of TBP in dodecane (mol·kg−1)

conc. of HNO3 in aq. phase (m)

conc. of HNO3 in org. phase (m)


0.019 0.039 0.120 0.204 0.431 0.973 1.677 2.627 3.979 6.057 9.661 17.445

0.214 0.207 0.207 0.200 0.185 0.171 0.156 0.135 0.121 0.106 0.092 0.085

0.000 0.000 0.004 0.007 0.012 0.017 0.023 0.028 0.034 0.039 0.049 0.052

0.214 0.207 0.211 0.207 0.197 0.188 0.179 0.163 0.155 0.146 0.141 0.138


conc. of HNO3 in aq. phase (m)



0.00 0.33 1.67 3.33 7.17 12.00 16.00 23.67 27.33 31.67 33.67 35.33

0.722 0.698 0.683 0.675 0.622 0.584 0.561 0.509 0.456 0.412 0.360 0.338

0.003 0.005 0.014 0.028 0.042 0.064 0.085 0.106 0.135 0.156 0.203 0.214

0.725 0.705 0.698 0.706 0.668 0.653 0.653 0.622 0.599 0.577 0.573 0.561

Kd values 0.214

0.737

mol·kg−1

m

m

m

0.019 0.039 0.120 0.204 0.431 0.973 1.677 2.627 3.979 6.057 9.661 17.445

0.000 0.000 0.024 0.046 0.077 0.129 0.205 0.284 0.400 0.513 0.638 0.725

0.005 0.011 0.028 0.056 0.090 0.136 0.224 0.310 0.421 0.520 0.667 0.733

0.007 0.015 0.031 0.062 0.095 0.156 0.230 0.316 0.422 0.531 0.674 0.776





1.60 4.20 5.00 4.00 9.00 11.00 11.00 15.00 18.00 21.00 21.50 23.00

2.418 2.390 2.344 2.252 2.160 2.025 1.892 1.760 1.631 1.503 1.336 1.213

0.011 0.025 0.042 0.089 0.142 0.211 0.285 0.360 0.471 0.584 0.737 0.811

2.432 2.423 2.400 2.367 2.344 2.293 2.249 2.206 2.206 2.206 2.206 2.156

0.17 0.50 1.33 2.50 3.33 5.17 6.77 8.33 8.33 8.33 8.33 10.17

acid into the organic phase increases and thus distribution coefficient values increase with the presence of these inextractable metal nitrates in the aqueous phase. Sodium nitrate and calcium nitrate are inextractable metal nitrates, and their presence in the aqueous phase along with nitric acid eliminates any competition for complex formation with TBP.7,18 Hence, extraction of nitric acid takes place easily by TBP in their presence. Because sodium nitrate is a better salting agent than calcium nitrate, the distribution coefficient Kd values for nitric acid are also high in the presence of sodium nitrate as compared with calcium nitrate, as illustrated in Figures 10−12.

Table 5. Distribution Coefficient of Nitric Acid in the Presence of Sodium Nitrate Solutions conc. of TBP in org. phase

2.437 m HNO3 conc. of HNO3 in aq. phase (m)

2.437

Table 6. Distribution Coefficient of Nitric Acid in the Presence of Calcium Nitrate Solutions Kd values conc. of TBP in org. phase mol·kg

−1

0.019 0.039 0.120 0.204 0.431 0.973 1.677 2.627 3.979 6.057 9.661 17.445

0.214

0.737

2.437

m

m

m

0.000 0.000 0.017 0.036 0.065 0.100 0.145 0.205 0.820 0.367 0.531 0.617

0.004 0.008 0.022 0.043 0.071 0.113 0.156 0.214 0.302 0.386 0.570 0.638

0.005 0.012 0.021 0.045 0.074 0.116 0.165 0.222 0.310 0.410 0.571 0.684

Figure 10. Effect of inextractable metal nitrates on distribution coefficient of 0.214 m HNO3. Symbols: ●, 0.214 m HNO3; ■, NaNO3; ▲, Ca(NO3)2.

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CONCLUSIONS The effect of inextractable metal nitrates on the solubility of TBP in water and nitric acid has been successfully studied. The salting coefficient of TBP in water at different sodium nitrate concentrations has also been efficiently calculated. The distribution coefficient of TBP is greater in the presence of sodium nitrate as compared with calcium nitrate. The variation in the concentration of nitric acid at equilibrium is larger in the presence of sodium nitrate than calcium nitrate. All obtained results have conclusively demonstrated that sodium nitrate is a

The distribution coefficient values Kd obtained for nitric acid have been compared with the previously obtained distribution coefficient values of nitric acid in the absence of metal nitrates.17 The results obtained reveal that the transfer of nitric F



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(5) Zongcheng, L.; Tiezhu, B.; Yuxing, S.; Li, Y. G. Determination of the Thermodynamic Equilibrium Constant of the Extraction System HNO3-Tributylphosphate (TBP) − n-C7H16. Fluid Phase Equilib. 1989, 46, 281−293. (6) Davis, W. J. Thermodynamics of Extraction of Nitric Acid by Trin-butyl Phosphate-Hydrocarbon Diluent Solutions I. Distribution Studies with TBP in Amsco 125-82 at Intermediate and Low Acidities. ORNL Report, ORNL-TM-43; Oak Ridge National Laboratory operated by Union Carbide Corporation for U.S. Atomic Energy Commission, 1961; pp 1−31. (7) Alcock, K.; Grimley, S. S.; Helay, T. V.; Kennedy, J.; McKay, H. A. C. The Extraction of Nitrates by Tri-n-butyl Phosphate (TBP). Part 1. The system TBP + Diluent + H2O + HNO3. Trans. Faraday Soc. 1956, 52, 39−47. (8) Alcock, K.; Bedford, F. C.; Hardwick, W. H.; McKay, H. A. C. Tri-n-butyl Phosphate As an Extracting Solvent for Inorganic Nitratesi: Zirconium Nitrate. J. Inorg. Nucl. Chem. 1957, 4, 100− 105. (9) Baldwin, W. H.; Higgins, C. E. Liquid-Liquid Distribution. Tributyl Phosphate between Immiscible Solvents. J. Chem. Eng. Data 1974, 19, 152−154. (10) Higgins, C. E.; Baldwin, W. H.; Soldano, B. A. The Distribution of Monovalent Electrolytes between Water and Tributyl Phosphate. J. Phys. Chem. 1959, 63, 118−123. (11) Collopy, J. J.; Cavendish, J. H. Equilibrium Constants for the System Tri-n-butyl Phosphate- Water- Nitric Acid. J. Phys. Chem. 1960, 64, 1328−1330. (12) Hardy, C. J.; Davis, W.; Mrochek, J. The System: Tri-n-butyl phosphate (TBP)- Nitric Acid- Water- I. Activities of TBP in Equilibrium with Aqueous Nitric Acid and Partial Molar Volumes of the Three Components in the TBP Phase. J. Inorg. Nucl. Chem. 1966, 28, 2001−2014. (13) Tuck, D. G. Solvent Extraction Studies. Part II. the System Nitric Acid−water−tri-n-butyl Phosphate. J. Chem. Soc. 1958, 52, 2783−2789. (14) Burger, L. L.; Forsman, R. C. the Solubility of Tributyl Phosphate in Aqueous Solutions. Hansford Works Report, HW20936: 1−17, 1951. (15) Kumar, S.; Kumar, R.; Koganti, S. B. An Extended Salt-Effect Model for Organic Solubility of Water in a 5−100% tri-n-Butyl Phosphate/Diluent/Nitric Acid/Water Biphasic System at 298.15K. Indian J. Chem. Technol. 2008, 15, 287−290. (16) Hipfner, J. C.; Tuck, D. G. Diffusion in the System Water/Tri-nbutyl Phosphate. Effect of Aqueous Electrolytes, And of Organic Phase Water Concentration. J. Chem. Soc., Faraday Trans. 1974, 70, 528− 534. (17) Bajoria, S. L.; Rathod, V. K.; Pandey, N. K.; Mudali, U. K.; Natarajan, R. Equilibrium Study for the System Tri-n-butyl Phosphate, Normal Paraffin Hydrocarbon, and Nitric Acid. J. Chem. Eng. Data 2011, 56, 2856−2860. (18) Hesford, E.; Mckay, H. A. C. The Extraction of Nitrates by TriN-butyl Phosphate. Part 3. Extraction at Trace Concentrations. Trans. Faraday Soc. 1958, 54, 573−586.



better salting agent for TBP compared with calcium nitrate. This extraction data would be of prime importance in nuclear reprocessing for waste management.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: 91-22-33612020. Fax: 91-22-33611020. Notes

The authors declare no competing financial interest.

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REFERENCES

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Extraction Studies of Phosphoric Acid Tributyl Ester from Nitric Acid

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