2014-J Hardzard Mater-Sr selectivity in sodium nonatitanate Na4Ti9O20

2014-J Hardzard Mater-Sr selectivity in sodium nonatitanate Na4Ti9O20
2014-J Hardzard Mater-Sr selectivity in sodium nonatitanate Na4Ti9O20

Journal of Hazardous Materials 283(2015)432–438

Contents lists available at ScienceDirect

Journal of Hazardous

Materials

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /j h a z m a

t

Strontium selectivity in sodium nonatitanate Na 4Ti 9O 20·x H 2O

Arnaud Villard ?,Bertrand Siboulet,Guillaume Toquer,Aurélie Merceille,

Agnès Grandjean,Jean-Franc

?ois Dufrêche ??Institut de Chimie Séparative de Marcoule,UMR 5257,CEA-UM2-CNRS-ENSCM,Site de Marcoule,BP 17171,F-30207Bagnols-sur-Cèze,France

h i g h l i g h t s

?Equilibrium constant exchange is cal-culated from the sodium-strontium

exchange.

?Two free parameters models for the solid activity have been checked.?Short-range forces on solid govern the extraction.

?The solid imposes the exchange.

g r a p h i c a l

a b s t r a c

t

a r t i c l e

i n f o

Article history:

Received 16June 2014

Received in revised form 4September 2014Accepted 6September 2014Available online 2October 2014

Keywords:

Sodium nonatitanate Strontium adsorption Decontamination

Free energy calculation

a b s t r a c t

We study the extraction of strontium by sodium nonatitanate powder from nitrate strontium and acetate sodium mixture.Experiments show that adsorption is quantitative.The excess Gibbs free energy has been modeled by various models (ideal,2D Coulomb,regular solution model)for the solid phase.We ?nd that the free energy of the solid phase is controlled by short-range interactions rather than long-ranged Coulombic forces.The selectivity is the consequence of a competition between the liquid and solid phases:both phases prefer strontium rather than sodium but the solid contribution is predominant.

?2014Elsevier B.V.All rights reserved.

1.Introduction

Nuclear industry produces a wide range of radioactive solutions requiring effective and selective processes to decontaminate them.The two main methods used in nuclear industry are the evaporation and the chemical treatments.The evaporation method allows processing a huge amount of solution which is not suitable for highly concentrated solutions.For this case,a co-precipitation process is based on in situ precipitation of solid particles to extract selectively pollutant.The strontium,90Sr,is one of the

?Corresponding author.Tel.:+33466796961.??Corresponding author.Tel.:+33466339206.

E-mail addresses:arnaud.villard@univ-montp2.fr (A.Villard),jean-francois.dufreche@univ-montp2.fr (J.-F.Dufrêche).

most abundant radioactive contaminant and most radio-toxic for the environment and human health found as nuclear ?ssion product.Indeed,this element has a speci?c af?nity for bones since strontium and calcium are alkaline earth elements with the same charge and almost the same size.

There are various methods for removing strontium from liq-uid waste using co-precipitation or adsorption processes.For example,decontamination processes using organic extractants [1–4],adsorption onto resin [5–8]have been proposed but they have strong drawbacks due to their low thermal and radiation stability.The current industrial process in ‘La Hague’(French full reprocessing plant)consists in the co-precipitation of radio-strontium by sulphate barium.However,this process gen-erates a large quantity of sludge to be con?ned due to their radioactivity.So alternative processes based on adsorption pro-cesses are investigated.For example,clays [9–12],hybrid materials

https://www.360docs.net/doc/d416120626.html,/10.1016/j.jhazmat.2014.09.0390304-3894/?2014Elsevier B.V.All rights reserved.

A.Villard et al./Journal of Hazardous Materials283(2015)432–438433

[13–16],hydrous metal oxides[17–20],zeolites[21–24]or titanate and silicotitanate[25–31]are widely studied.Among them,sodium nonatitanate presents a selectivity towards strontium with also a suitable radiation resistance.The goal of the present study is to analyze and model some experimental data concerning the sodium nonatitanate extractive properties in aqueous solution containing strontium nitrate and sodium acetate.This latter has been chosen in order to be close to the industrial solution.

Sodium nonatitanate powder materials have recently been syn-thesized using hydrothermal process at different temperature,and then characterized by various techniques(XRD,TGA and chemical analysis),by hydrothermal process at different temperatures[32]. Depending on the synthesis temperature,two structures appear. Below200?C,the ionic exchange is rather complete and upper 200?C,the exchange rate is limited at62%.At low temperature, they are two diffusion limiting steps,diffusion and intra-particle diffusion,whereas at high temperature there exists only an intra-particle diffusion step.

The temperature impacts therefore directly the extraction prop-erties[33].Even if the sodium nonatitanate synthesized at100?C has the best decontamination performances,the strontium quan-tity adsorbed is closely related to the sodium concentrations. Moreover,this exchange is speci?cally due to an ionic exchange (two sodium atoms for one strontium atom).The pH has also an in?uence on the adsorption rate of the strontium.Indeed when the pH is low,the adsorption rate is minimal whereas this rate is maximum for a pH above eight[33].

The experiments with radioactive species are sensitive due to the radiation and to reduce the number of experiments,it is necessary to develop a predictive model.Predictive model should be based on a knowledge of the microscopic and macro-scopic phenomena,the former ones still needing much efforts. We propose,as a?rst attempt,an investigation on the adsorption mechanisms through some simple free parameter models.These models aim at improving activity coef?cients determination,both for the solution and the solid(sodium nonatitanate).They also include the solid characterization[32]via various techniques(i.e. XRD,TGA,elementary chemical analysis)and take into account the description of the initial conditions of the solution.The equilib-rium constant of the exchange reaction has been calculated from these models.The different models used allow to discriminate and understand which phenomena drive the extraction.

2.Methods

2.1.Experimental

2.1.1.Synthesis

Sodium nonatitanate powder samples have been synthesized in three steps according to hydrothermal methods[26,32,34,35]: 2.5g of titanium iso-propoxide(Sigma–Aldrich,purity97%)was ?rst added to2g of deionized water and2.73g of50%wt of sodium hydroxide(Sigma–Aldrich,purity>98%).This mixture was then inserted in a Te?on pot at100?C during24h for an hydrothermal treatment.After this thermal treatment,the resulting gel was next washed three times with deionized water to remove some excess NaOH and centrifuged at4500rpm for5min.The gel was then dried at80?C during one day.

2.1.2.Sample characterization

The sodium nonatitanate powder was characterized by the fol-lowing techniques:

–In order to characterize and check the purity powder,X-Ray Diffraction(XRD)has been performed at room temperature with

a Bruker?D8advance diffractometer in Bragg-Brentano geome-try with Ni-?ltered and Cu-K?radiation,between2?=5?and80?, step size0.01?and one second per step.

–The water amount inside the solid was estimated from Thermo-Gravimetric Analysis(TGA)by a Setaram instrumentation with SetSys Evolution instrument on approximately20–50mg of solid samples at heating rate of10?C min?1.The analysis was per-formed from room temperature to1000?C.

–The elementary analysis of powder was performed by inductively coupled plasma atomic emission spectrometry(Thermo Scien-ti?c).Before the analysis,the powder samples were dissolved in acid media.

–The quantity of strontium adsorbed was determined by mea-suring the strontium concentration in solution before and after contact with sodium nonatitanate powder.This analysis has been performed with a Dionex capillary ionic chromatography with methylsufonic acid as an eluent.We have used the IonPac CS16 column with a diameter of0.4mm and a length of250mm.

2.1.

3.Sorption experiments

In this paper,we will focus on two speci?c experiments per-formed from sodium nonatitanate already reported in[32,33].

The?rst set of experiments,is performed in order to obtain the equilibrium constant.In these experiments,the solid activity coef?cients have been neglected by using a solution containing strontium at a very low concentration(trace level).These kind of concentrations have been measured with radioactive strontium (90Sr)by scintillation(Packard,Tri-carb2750TR/LL).A solution of66660±6600Bq L?1,namely13.0±1.3ng L?1,was prepared by dissolving and diluting up to obtain the suitable concentration with a pure radioactive strontium nitrate salt.This solution was added to various sodium acetate concentration solutions,ranging from 0.1to1mol L?1.A second set of experiments has been performed in order to obtain the adsorption isotherm.The initial solution has been obtained by dissolving strontium nitrate and sodium acetate dissolved into deionized water.Sodium acetate has been used both to have an alkaline solution and to buffer the solution at pH≈8 [33].The different solutions were prepared by keeping the cationic charge number?xed at10?2mol L?1(Eq.(1)):

[Na+]+2[Sr2+]=10?2mol L?1(1) Each sample of this set of experiments has been prepared with 10mg of powder added to20mL of initial solution in a vial which was then shacked during one day.

2.2.Modeling

2.2.1.Chemical equilibrium

Initially,the strontium is exclusively in solution,whereas sodium is in the two phases(solid and solution phases).The exchange between two sodium from the solid and one strontium from the solution reads:

2Na++Sr2+ 2Na++Sr2+(2) This also can be written via the mass action law:

K0eq=

a2

Na+

a

Sr2+

a

Sr2+

a Na+2

=[Na

+]2[Sr]

[Sr2+][Na+]

2

2

Na+

Sr2+

Sr2+

Na+2

(3)

where K0eq is the equilibrium constant,a X and a X are respectively cations activities in solution and in solid. X and X are the corre-sponding activity coef?cients.

2.2.2.Aqueous phase

The decoupling between the standard term and the activity term depends on the frame of the reference for the activity scales[36].For

434 A.Villard et al./Journal of Hazardous Materials283(2015)

432–438

Fig.1.Diffractogram of the sodium nonatitanate synthesized at100?C in hydro-thermal conditions.The?rst peak corresponds to the inter-layer distance.

any solute,the considered standard state is a solution concentration of1mol L?1and the particles are non-interacting(in?nite dilution).

When the solute concentration in water is relatively low(typi-cally10?2mol L?1),the Debye–Hückel approximation(DH)is cho-sen[37].Thus,the activity coef?cients are given by this equation:

ln i=?

z2

i

e2

8 ε0εr k B T

?(4)

with z i the charge of ion i,e the elementary charge,ε0εr the water permittivity,k B the Boltzmann constant,T the absolute temperature and?the inverse Debye length:

?2=4 L B

j

C j z2j(5)

where C j is the concentration of ion j in particle m?3and L B is the Bjerrum length:

L B=

e2

4 ε0εr k B T

(6)

When the solute concentration is high(>10?2mol L?1), Mean Spherical Approximation(MSA)model is used instead of Debye–Hückel model[38–42].This solution model will be devel-oped more precisely into a next paper.

2.2.

3.Solid phase

For the solid phase,the standard state selected for the cation corresponds to a pure sodium nonatitanate(Na4Ti9O20).If other cations(such as H+,Sr2+)are present inside the titanate struc-ture,they are considered as in?nitely dilute toward the standard concentration of1mol g?1of pure sodium nonatitanate.

The solid has been reported to be a multi-layer material [34,43–45].From Fig.1the inter-layer distance is estimated at9.5?A. Considering the thick of the titanium oxide octahedral layer(≈6?A), the space for aqueous part is typically one water molecule diame-ter.Consequently,sodium nonatitanate solid has been modeled as a lamellar system with a mono-layer of hydrated sodium interleaved between two layers of titanium oxide.

Three models have been studied:ideal model,2D Coulomb gas model and regular solution model.

In the?rst model,the ideal one,all the solid activity coef?cients are supposed to be equal to one.

For the second model,the2D Coulomb gas one,is rigorously valid if the main physical interaction between the ions is the elec-trostatic force,similar to the original DH approach in the case of electrolyte solutions.Here,ions in the solid(i.e.Na+for pure Na4Ti9O20)are assumed to be charged point particles(on the TiO2 layers)dispersed in a non-polarizable background.This continuous model has already been extensively studied[46–48]thanks to inte-gral equations on DH approximation and Monte Carlo simulation.

The simulations performed by[47]give a very good approxima-tion,the excess Helmholtz energy(A ex),namely the difference from the standard state,of the2D Coulomb gas in the?uid domain can be approximated as

A ex

Nk B T

=? (7)

where N is the number of particles(here ions within the solid),the parameter?has been reported to be equal to?1.04704from[47] and the screening parameter, ,is

= 2L B

N S(8) where is the charge(in unit of e)of the Coulomb gas,N S is the sur-facic concentration of particles(particles m?2)and L B is the Bjerrum

length in the solid(Eq.(6))withεr

solid

the dielectric constant of the water molecules in this con?ned space between the TiO2layers. For the hydrate ions con?ned between two TiO2layers,theεr

solid

is lower than theεr in the bulk solution and it has been assumed to be15for the hydrate sodium in the sodium nonatitanate[49].In the case of mixtures, can be simply generalised by:

=

L B

i

N S

i

2

i

i

N S

i

(9)

Thus,the activity coef?cients of the i species with a surfacic concentration N S

i

and charge i are obtained by differentiating Eq.

(7)with respect to N.We obtain then:

ln i=?L B

?

?

j

N j

S

k

x k z2

k

2

+z2

i

?

1

2

+z2

i

N?

1

S

?

?

(10) where x k=N k/

i

N i is the particle fraction and N?

1

is the initial num-ber of cation(here Na+)within the solid.

The third model,the regular solution one,allows to evaluate the short range interactions.The regular solution model can also lead to the expression of the activity coef?cient.For a binary mixture with i and j species[50]:

ln i= x2j(11)

where x j represents the molar fraction and the parameter the interaction coef?cient between two ions,which has been?tted from the experimental data.

This model is a simple model for?rst short range interactions. Contrary to the2D Coulomb gas model,it is valid when the inter-actions between the ions are predominantly short ranged and modeled by a very simple mean?eld network model.

Thus the two last models are available to explain the mean inter-actions inside the solid.

3.Results and discussion

3.1.Characterization of powder samples

From the elementary and the TGA analysis,the chemical com-position of the powder has been measured as:Na4.2Ti9O20.1,12.4 H2O.The chemical composition is close to the theoretical compo-sition of a pure sodium nonatitanate reported by[27].From this result,the Cation Exchange Capacity(CEC)has been calculated to be3.9×10?3mol g?1.

XRD measurement from Bragg’s law gives an inter-layer distance equal to9.5?A(Fig.1)which is in agreement with [26,34,35,51].Fig.2shows a transmission electronic microscope

A.Villard et al./Journal of Hazardous Materials 283(2015)432–438

435

Fig.2.Transmission Electronic Microscopy picture of sodium nonatitanate.The

alternations of the dark and light fringe are characteristic of a multi-layer

material.

Fig.3.Scanning Electronic Microscopy picture of sodium nonatitanate.

(TEM)picture of the material.An alternation of dark and bright fringes indicates a multi-layer material.The inter-layer distance observed is in agreement with the XRD results and also with the structure suggested by [27].Fig.3shows the morphology of the powder that is constituted of grains.The average size of grains is close to one micrometer.

3.2.Equilibrium constant

In the below mentioned study [32],experiments were con-ducted in order to determine the equilibrium constant,K eq .This latter was determined from the trace concentrations,namely at very low strontium concentration.This ?rst set of experiments has been conducted with a strontium concentration below 1.410?10mol L ?1,obtained with radioactive strontium (90Sr).The

Table 1

Ionic diameter used for the liquid activity coef?cients calculated with MSA [38,52].

Ion

Diameter (?A)

Na +

3.05CH 3COO ?

4.8Sr 2+

5.26NO ?

3

3.78

maximum 90Sr adsorbed on solid is very low compared to the total CEC (3.9×10?3mol g ?1).The reference of the solid is chosen to be the pure sodium nonatitanate,as mentioned above.We consider the pure sodium nonatitante as a reference for the solid activity coef?cients and we assume that the solid state is not altered at this very low strontium concentration.In this way, Sr 2+= Na +=1.From this approximation,the equilibrium constant (Eq.(3))is writ-ten as:

K eq

=[Na +]2[Sr 2+][Sr 2+][Na +]2 2Na + Sr 2+

=K D

[Na +]2

2Na

+[Na +]

2(12)

where K D is the distribution coef?cient de?ned as K D =

a Sr 2+a Sr 2+

=

[Sr 2+][Sr 2+] Sr 2+

(13)

For the liquid state,different experiments have been performed by varying the sodium concentration in solution [32].In this latter paper,we have used the simplest model by considering that the activity coef?cients of sodium and strontium in the liquid state are equal to one.

From Eqs.(3)and (13),the slope can be expressed as:

ln 10[K D ]=ln 10K eq +2ln 10[CEC]?2ln 10[a Na +]

(14)

From the decadic logarithm slope of the distribution coef?cient as a function of the decadic logarithm of the sodium concentration,the equilibrium constant has been estimated.The linear coef?-cient has been set to ?2because it corresponds to the number of the sodium exchanged for strontium,which replaces it in order to maintain electro-neutrality.

However,the experiments were conducted up to one molar in sodium acetate and at this high concentration,the activity coef?cients are not equal to one.We have therefore to con-sider several models for the evolution of activity coef?cients.The Debye–Hückel theory is valid up to 10?2mol L ?1while the Mean Spherical Approximate (MSA)theory is valid up to 1mol L ?1.In order to calculate the solution activity coef?cients of the ?rst set of experiments,low concentration in strontium and high concentra-tion in sodium,the MSA theory has been used.This theory requires the hydrate ionic diameters of the solution which are available in the literature [52,38]and are summarized in Table 1.When the strontium concentration is very low,the strontium activity has been imposed by the high sodium concentration.Therefore the strontium solution activity coef?cient have not to be neglected.Fig.4represents the decadic logarithm of the distribution coef?cient as a function of the decadic logarithm of the sodium concentration in solution.The red diamonds represent the exper-imental values with the ideal model,activity coef?cients in liquid phase are equal to 1,and the blue diamonds are the experimental values with the activity coef?cients in the liquid phase calculated through the MSA theory.The solid line represents the ?t of the experimental values with a slope coef?cient set at ?2,as mentioned above.

In the ideal case (red diamond),the equilibrium constant has been estimated at K eq =2.28×107,corresponding approximately to an exchange free energy equal to ?44kJ mol ?1.

436

A.Villard et al./Journal of Hazardous Materials 283(2015)432–438

Fig.4.Distribution coef?cient,K D ,of experimental points measured with radioac-tive strontium as a function of molarity with activity coef?cients by MSA theory,,or equal to one,[33].The K d represents the ration of solid strontium concentration (in mol per gram of solid)to aqueous strontium concentration (in mol per liter).(For interpretation of the references to color in this ?gure legend,the reader is referred to the web version of this article.)

From the same argument,the equilibrium constant of the real solution (blue diamond),modeled with MSA,has been estimated to be K eq =2.24×108,which gives the exchange free energy approxi-mately equal to ?47kJ mol ?1.The equilibrium constant calculated with the MSA correction is the same order of size magnitude but the reaction is slightly more energetic.This high value of the constant con?rms that the solid is more selective for the strontium than for the sodium [33,25].

3.3.Solid activity coef?cients

In order to model the strontium adsorption as a function of the initial strontium concentration,we have used the second set of experiments,namely at constant cationic charge number.The solid activity model has been ?tted with respect to the experimental data.From the experimental data,an apparent equilibrium con-stant is calculated by taking into account the real liquid phase (Eq.(15)).This latter has been calculated as following:

K App

=[Na +]2

[Sr 2+

][Sr 2+][Na +]

2 2

Na + Sr 2+

(15)

The liquid activity coef?cients have been obtained by the

Debye–Hückel theory.The excess exchange energy,between the ideal solid state and the real solid state,can therefore be expressed from Eqs.(3)and (15)into the Eq.(16).

G excess 2Na →Sr

=?k B T ln

Sr 2+ Na +2

K eq

=k B T ln K App

(16)

The Coulomb 2D model requires the solid speci?c area,developed by the lamellars,in order to calculate the sur-facic concentration.This area cannot be obtained by nitrogen adsorption–desorption measurement.Indeed,the hydrate sodium occupying the space between two sodium nonatitanate layers,avoid the insertion of the nitrogen molecules.A model of the spe-ci?c area has been developed from the chemical composition of the solid based on the hydration number of the sodium in solution.It consists in calculating the surface occupied by the sodium tri-hydrate between the TiO 2layers.The simplest way to place three water molecules around sodium is to form a triangle (Fig.5),

the sodium is placed at the gravity center.From this model,a speci?c area has been calculated at 1050m 2g ?1.

The second model used to estimated the solid activity coef?cient is the regular solution model which requires one parameter called (representing the short range energy).This latter has been ?tted from the experimental data.

Fig.5.Representation of triangular geometry of the sodium hydrate in porous media,the blue and red spheres are water molecules and sodium ions respectively.This geometry give an speci?c surface area of approximately 1050m 2g ?1.(For inter-pretation of the references to color in this ?gure legend,the reader is referred to the web version of this article.)

0.0

5.0×10-4

1.0

×10-3 1.5 ×10

-3

2.0 ×10

-3

Q Ads / mol g

-1

6

8101214ΔG e x c h a n g e / k B T

Experiments 2D Coulomb Regular solution

e x c e s s

Fig.6.The excess exchange Gibbs energy as a function of the adsorption quantity;?are experimental values.The dashed blue line represents the 2D Coulomb model and the solid red line is the regular solution model.The uncertainty,from the com-prehensive expression of the Gibbs energy,is especially high at saturation because of the very small amount of non-ideal part.(For interpretation of the references to color in this ?gure legend,the reader is referred to the web version of this article.)

Fig.6represents the excess exchange Gibbs energy of the solid calculated from experimental data as a function of the adsorbed strontium quantity by the solid.The experimental data have been plotted using the Debye–Hückel model for the liquid phase.The uncertainty has been calculated for each experiments and this latter is more important at the solid saturation.The uncertainty,from the comprehensive expression of the Gibbs energy,is especially high at saturation because of the very small amount of non-ideal part.The dashed blue line represents the predictive data calculated by Coulomb 2D model.The calculated curve decreases slightly linearly while the experimental data increase.The solid red line is the regu-lar solution model with a parameter equals to 2.The solid red line goes quite well through the experimental values which indicates that the short range interactions are dominant.Then,the regu-lar solution model has been chosen to calculate the solid activity coef?cient.

3.4.Model applications

Fig.7represents the quantity of strontium adsorbed by the solid as a function of the decadic logarithm of the initial strontium con-centration in solution.The total charge concentration has been set equal to 10?2mol L ?1.The uncertainty has been evaluated at 10?4mol g ?1.

Up to an initial strontium concentration of 8×10?4mol L ?1,the quantity of strontium adsorbed on the solid can be simply plotted by Q Ads =V 0/m C Sr initial ,where V 0represents the volume of the solution and m is the solid mass.This equation is inde-pendent of the equilibrium constant.From an initial strontium

A.Villard et al./Journal of Hazardous Materials 283(2015)432–438

437

10

-610

-5

10

-4

10

-3Sr

2+

initial concentration / mol L

-1

0.0

5.0 ×10

-4

1.0 ×10

-3

1.5 ×10-3

2.0 ×10

-3

Q A d s / m o l g -1

Experiments

Ideal

Real liquid (DH)Solid + DH

Fig.7.Adsorption quantity as a function of initial strontium concentration with positive charge number is equal to 10?2mol L ?1.The black solid line represents the ideal case when the activities and concentrations are mixed and equal.The red dashed line is the case of the solid activity coef?cients are neglected and the solution activity coef?cients are calculated by DH model.The blue mixed dashed and dotted line is the case of the solid and solution activity coef?cients are calculated by regular solution model and DH model.Experimental data have been extracted from [32].(For interpretation of the references to color in this ?gure legend,the reader is referred to the web version of this article.)

concentration of 10?3mol L ?1,the experimental strontium sorp-tion capacity reaches a plateau corresponding to the solid saturation.

The solid black line has been calculated from the ideal model,the activities coef?cients of the solid and the solution are equal to one.It represents the ideal phases.The ideal curve encompasses all values.

The dashed red line has been calculated by using DH theory in order to calculate the solution activity coef?cients,the solid activ-ity coef?cients are still equal to one.It represents the real liquid phase and the ideal solid phase.This model has been used because the total charge concentration is equal to 10?2mol L ?1.The solid black line and the dashed red line are similar,which means that the solution does not have an important impact on the adsorption at this charge concentration.

The dot-dashed blue line has been calculated with DH theory for the solution activity coef?cients and regular solution for the solid activity coef?cients.This latter represents the real phases.The dot-dashed line reaches the plateau more rapidly than the ideal model or real liquid phases model.It is due to excess term calculated by the regular solution for the solid activity coef?cient.Moreover,there is a little difference between the value of the plateau obtained from the ideal model or the real solution phase model and the real phases,solid and liquid phases,which shows that the extraction is driven by the solid.

The difference of the standard hydration free energy between one strontium and two sodium,in solution,is equal to 636kJ mol ?1[52].This positive value corresponds to the fact that the solution prefers to contain one strontium rather than two sodium at the standard state.Nevertheless,the sodium extraction in the solid phase occurs,so that the global free energy difference is favorable to the exchange.Therefore,the extraction is controlled by the solid phase.At standard state,the two phases prefer strontium but the predilection is more important for the solid phase.

The three calculated curves (ideal,real liquid phase and real phases models)are located very close to the experimental data.

4.Conclusion

The different analysis have shown that the synthesized mate-rial is a sodium nonatitanate with the chemical stoechiometry

Na 4.2Ti 9O 20.1,12.4H 2O.This solid is a multi-layer material with a strong exchange capacity for the strontium.

An equilibrium constant with the simplest model (i.e.ideal model)has been reported equal to 2.28×107.Taking into account the solution activity coef?cient,the equilibrium constant has been calculated to 2.24×108.This high constant is characteristic of a spontaneous reaction of extraction.

The solid phase has been modeled by two different kinds of mod-els.The ?rst,the 2D Coulomb model,requiring the surface area,represents the electrostatic interactions.The second,the regular solution,requiring a single parameter which has been ?tted from the experimental data,represents the short range interactions.The regular solution model is closer to the experimental value than the 2D Coulomb model.Thus,the free energy of the solid phase is gov-erned by the short range forces and not by the long range Coulombic interactions.

The global extraction curves leads to the estimation of the standard Gibbs energy of the exchange.We show that the two phases prefer strontium,but the solid phase is predominant and it imposes the exchange.

Acknowledgements

Financial supports from the French Ministère de l’Enseignement Supérieur et de la Recherche and the CEA are greatly acknowledged.

References

[1]V.Romanovskiy,I.Smirnov,V.Babain,R.Todd,T.A.Herbst,https://www.360docs.net/doc/d416120626.html,w,K.Brewer,

The universal solvent extraction (UNEX)process.I.Development of the UNEX process solvent for the separation of cesium,strontium,and the actinides from acidic radioactive waste,Solvent Extr.Ion Exch.19(1)(2001)1–21.[2]C.Ozeroglu,G.Kec ?eli,Kinetics of the adsorption of strontium ions by

a crosslinked copolymer containing methacrylic acid functional groups,Radiochim.Acta 95(2007)459–466.

[3]S.Wu,C.Sun,W.Wang,Y.He,S.Hu,C.Zheng,Separation of strontium from asso-ciated elements with selective speci?c resin and extraction chromatography,Chin.Chem.Lett.24(7)(2013)633–635.

[4]P.Dhami,C.Janardanan,P.Jagasia,S.Pahan,S.Tripathi,P.Gandhi,P.Wattal,

Separation and puri?cation of Sr-90from PUREX HLLW using N,N,N ,N -tetra(2-ethylhexyl)diglycolamide,J.Radioanal.Nucl.Chem.296(3)(2013)1341–1347.[5]G.Ye,F.Bai,J.Wei,J.Wang,J.Chen,Novel polysiloxane resin functionalized

with dicyclohexano-18-crown-6(DCH18C6):synthesis,characterization and extraction of Sr(II)in high acidity HNO 3medium,J.Hazard.Mater.225–226(2012)8–14,https://www.360docs.net/doc/d416120626.html,/10.1016/j.jhazmat.2012.04.020.

[6]M.Lee,T.Park,J.Park,K.Song,M.Lee,Radiochemical separation of Pu,U,Am

and Sr isotopes in environmental samples using extraction chromatographic resins,J.Radioanal.Nucl.Chem.295(2)(2013)1419–1422,https://www.360docs.net/doc/d416120626.html,/10.1007/s10967-012-1926-4.

[7]Z.Chen,Y.Wu,Y.Wei,Adsorption characteristics and radiation stabil-ity of a silica-based DtBuCh18C6adsorbent for Sr(II)separation in HNO 3medium,J.Radioanal.Nucl.Chem.299(1)(2014)485–491,https://www.360docs.net/doc/d416120626.html,/10.1007/s10967-013-2750-1.

[8]B.Prelot,I.Ayed,F.Marchandeau,J.Zajac,On the real performance of cation

exchange resins in wastewater treatment under conditions of cation competi-tion:the case of heavy metal pollution,Environ.Sci.Pollut.Res.21(15)(2014)9334–9343,https://www.360docs.net/doc/d416120626.html,/10.1007/s11356-014-2862-3.

[9]E.Bascetin,G.Atun,Adsorptive removal of strontium by binary mineral mixture

of montmorillonite and zeolite,J.Chem.Eng.Data 55(2)(2010)783–788.

[10]G.Bochkarev,G.Pushkareva,Strontium removal from aqueous media by nat-ural and modi?ed sorbents,J.Min.Sci.45(2–3)(2009)290–294.

[11]A.Ararem,O.Bouras,A.Bouzidi,Batch and continuous ?xed-bed column

adsorption of Cs +and Sr 2+onto montmorillonite-iron oxide composite:com-parative and competitive study,J.Radioanal.Nucl.Chem.298(1)(2013)537–545,https://www.360docs.net/doc/d416120626.html,/10.1007/s10967-013-2433-y .

[12]A.Seliman,https://www.360docs.net/doc/d416120626.html,sheen,M.Youssief,M.Abo-Aly, F.Shehata,Removal of

some radionuclides from contaminated solution using natural clay:ben-tonite,J.Radioanal.Nucl.Chem.300(3)(2014)969–979,https://www.360docs.net/doc/d416120626.html,/10.1007/s10967-014-3027-z .

[13]Q.Li,H.Liu,M.Guo,B.Qing,X.Ye,Z.Ye,Strontium and calcium ion adsorption

by molecularly imprinted hybrid gel,Chem.Eng.J.157(2–3)(2010)401–407.[14]Z.Cheng,Z.Gao,W.Ma,Q.Sun,B.Wang,X.Wang,Preparation of magnetic

Fe 3O 4particles modi?ed sawdust as the adsorbent to remove strontium ions,Chem.Eng.J.209(2012)451–457,https://www.360docs.net/doc/d416120626.html,/10.1016/j.cej.2012.07.078.[15]T.Wen,X.Wu,M.Liu,Z.Xing,X.Wang, A.-W.Xu,Ef?cient capture

of strontium from aqueous solutions using graphene oxide-hydroxyapatite

438 A.Villard et al./Journal of Hazardous Materials283(2015)432–438

nanocomposites,Dalton Trans.43(20)(2014)7464–7472,http://dx.

https://www.360docs.net/doc/d416120626.html,/10.1039/C3DT53591F.

[16]P.Cakir,S.Inan,Y.Altas,Investigation of strontium and uranium sorption

onto zirconium-antimony oxide/polyacrylonitrile(Zr-Sb oxide/pan)com-posite using experimental design,J.Hazard.Mater.271(2014)108–119, https://www.360docs.net/doc/d416120626.html,/10.1016/j.jhazmat.2014.02.014.

[17]S.Kirillov,T.Lisnycha,O.Pendelyuk,Appraisal of mixed amorphous man-

ganese oxide/titanium oxide sorbents for the removal of90Sr from solutions, with special reference to savannah river site and chernobyl radioactive waste stimulants,Adsorpt.Sci.Technol.24(10)(2006)907–914.

[18]S.Ahmadi,N.Akbari,Z.Shiri-Yekta,M.Mashhadizadeh,A.Pourmatin,Adsorp-

tion of strontium ions from aqueous solution using hydrous,amorphous MnO2-ZrO2composite:a new inorganic ion exchanger,J.Radioanal.Nucl.Chem.299

(3)(2014)1701–1707,https://www.360docs.net/doc/d416120626.html,/10.1007/s10967-013-2852-9.

[19]N.A.Weerasekara,K.-H.Choo,S.-J.Choi,Metal oxide enhanced micro-

?ltration for the selective removal of Co and Sr ions from nuclear laundry wastewater,J.Membr.Sci.447(2013)87–95,https://www.360docs.net/doc/d416120626.html,/

10.1016/j.memsci.2013.06.039.

[20]Q.Li,H.Liu,T.Liu,M.Guo,B.Qing,X.Ye,Z.Wu,Strontium and calcium ion

adsorption by molecularly imprinted hybrid gel,Chem.Eng.J.157(2–3)(2010) 401–407,https://www.360docs.net/doc/d416120626.html,/10.1016/j.cej.2009.11.029.

[21]R.Rahman,H.Ibrahim,M.Hanafy,N.Monem,Assessment of synthetic zeolite

Na A–X as sorbing barrier for strontium in a radioactive disposal facility,Chem.

Eng.J.157(1)(2010)100–112.

[22]H.Mimura,T.Kanno,Distribution and?xation of cesium and strontium in

zeolite A and chabazite,J.Nucl.Sci.Technol.22(4)(1985)284–291.

[23]A.Sachse, A.Merceille,Y.Barre, A.Grandjean, F.Fajula, A.Galarneau,

Macroporous LTA-monoliths for in-?ow removal of radioactive stron-tium from aqueous ef?uents:application to the case of Fukushima, Microporous Mesoporous Mater.164(2012)251–258,https://www.360docs.net/doc/d416120626.html,/

10.1016/j.micromeso.2012.07.019.

[24]H.Faghihian,M.Moayed,A.Firooz,M.Iravani,Evaluation of a new magnetic

zeolite composite for removal of Cs+and Sr2+from aqueous solutions:kinetic, equilibrium and thermodynamic studies,C.R.Chim.17(2)(2014)108–117, https://www.360docs.net/doc/d416120626.html,/10.1016/j.crci.2013.02.006.

[25]S.F.Yates,P.Sylvester,Sodium nonatitanate:a highly selective inorganic ion

exchanger for strontium,Sep.Sci.Technol.36(5–6)(2001)867–883.

[26]E.Behrens,P.Sylvester,A.Clear?eld,Assessment of a sodium nonatitanate and

pharmacosiderite-type ion exchangers for strontium and cesium removal from doe waste simulants,Environ.Sci.Technol.32(1)(1998)101–107.

[27]A.Clear?eld,J.Lehto,Preparation,structure,and ion-exchange properties of

Na4Ti9O20·x H2O,J.Solid State Chem.73(1)(1988)98–106.

[28]J.Lehto,A.Clear?eld,The ion exchange of strontium on sodium titanate

Na4Ti9O20·x H2O,J.Radioanal.Nucl.Chem.118(1)(1987)1–13.

[29]K.Popa,C.C.Pavel,Radioactive wastewaters puri?cation using titanosilicates

materials:state of the art and perspectives,Desalination293(2012)78–86. [30]H.Liu,D.Yang,E.R.Waclawik,X.Ke,Z.Zheng,H.Zhu,R.L.Frost,A Raman

spectroscopic study on the active site of sodium cations in the structure of Na2Ti3O7during the adsorption of Sr2+and Ba2+cations,J.Raman Spectrosc.

41(12)(2010)1792–1796,https://www.360docs.net/doc/d416120626.html,/10.1002/jrs.2634.

[31]G.Hyushin,Hydrothermal crystallization of Na2Ti6O13,Na2Ti3O7,and

Na16Ti10O28in the NaOH-TiO2-H2O system at a temperature of500?c and a

pressure of0.1GPa:the structural mechanism of self-assembly of titanates from suprapolyhedral clusters,Crystallogr.Rep.51(4)(2006)715.

[32]A.Merceille,E.Weinzaepfel,Y.Barre,A.Grandjean,Effect of the synthesis tem-

perature of sodium nonatitanate on batch kinetics of strontium-ion adsorption from aqueous solution,Adsorption17(6)(2011)967–975.

[33]A.Merceille,E.Weinzaepfel,Y.Barre,A.Grandjean,The sorption behaviour

of synthetic sodium nonatitanate and zeolite a for removing radioac-tive strontium from aqueous wastes,Sep.Purif.Technol.96(2012) 81–88.

[34]T.Moller,P.Sylvester,T.Adams,Improved separation methods for the recovery

of82Sr from irradiated targets,Appl.Radiat.Isot.64(4)(2006)422–430. [35]G.Graziano,Synthesis,Characterization and Ion Exchange Properties of a

Sodium Nonatitanate,Na4Ti9O20·x H2O,A&M Texas University,1998(Ph.D.the-sis).

[36]IUPAC,Notation for states and processes,signi?cance of the word standard

in chemical thermodynamics,and remarks on commonly tabulated forms of thermodynamic functions,IUPAC54(6)(1982)1239.

[37]P.Debye,E.Hückel,The theory of electrolytes.I.Lowering of freezing point and

related phenomena,Physiol.Zool.24(1923)185.

[38]J.-F.Dufrêche,O.Bernard,S.Durand-Vidal,P.Turq,Analytical theories of trans-

port in concentrated electrolyte solutions from the MSA,J.Phys.Chem.B109

(20)(2005)9873–9884.

[39]J.Barthel,H.Krienke,W.Kunz,Physical Chemistry of Electrolyte Solutions,

Springer,1998.

[40]S.Durand-vidal,J.Simonin,P.Turq,Electrolytes at Interfaces,Kluwer Academic

Publishers,2000.

[41]L.Blum,J.Hoye,Mean spherical model for asymmetric electrolytes.2.Thermo-

dynamic properties and pair correlation-function,J.Phys.Chem.81(13)(1977) 1311–1316.

[42]J.Salacuse,G.STELL,Polydisperse systems–statistical thermodynamics,with

applications to several models including hard and permeable spheres,J.Chem.

Phys.77(7)(1982)3714.

[43]J.Lehto,O.Heinonen,J.Miettinen,Sorption properties of sodium titanate,

Radiochem.Radioanal.Lett.46(6)(1981)381–387.

[44]R.Cahill,A.Clear?eld,C.Andren,Partially crystalline layered sodium titanate,

Patent,WO/1997/014652(041997).

[45]O.Heinonen,J.Lehto,J.Miettinen,Sorption of strontium(II)and radio strontium

ions on sodium titanate,Radiochim.Acta28(2)(1981)93–96.

[46]E.Hauge,P.Hemmer,2-Dimensional coulomb gas,Phys.Norv.5(3–4)(1971)

209.

[47]https://www.360docs.net/doc/d416120626.html,do,Hypernetted-chain solutions for2-dimensional classical electron-gas,

Phys.Rev.B17(7)(1978)2827.

[48]J.Chalupa,Equation of state of a classical electron layer,Phys.Rev.B12(1)

(1975)4–9.

[49]E.de Souza,G.Ceotto,O.Teschke,Dielectric constant measurements of inter-

facial aqueous solutions using atomic force microscopy,J.Mol.Catal.A:Chem.

167(1–2)(2001)235–243.

[50]M.Hillert,L.Staffans,Regular solution model for stoechiometric phases and

ionic melts,Acta Chem.Scand.24(10)(1970)3618–3626.

[51]P.Sylvester,T.Moller,T.Adams,A.Cisar,New ion exchange materials for use

in a82Sr/82Rb generator,Appl.Radiat.Isot.61(6)(2004)1139–1145.

[52]Y.Marcus,Ion Solvation,John Wiley and Sons,1985.

相关主题
相关文档
最新文档