untitled ISSN 215 Applicat uranyl p Ewelina G Maria Curie Skło * Corresponding Tel.: +48.81.537 ARTICLE IN DOI: 10.5155/e Received: 23 Oc Received in rev Accepted: 05 De Published onlin Printed: 31 Mar KEYWORDS Uranium Bentonite Phosphates Job method Sorption spectr Uranyl phospha 1. Introduct Due to i surface comp demand for effectively b the aqueous as well as in different me exchange, so tion‐filtration dialysis, sorp of the mater on the sur ferrihydrite 13]. Our aim the stoichiom It is commo continuous v method, is formed in th complexes. T measured fe absorbance teristic meta 53‐2249 (Print) tion of th phosphate Grabias, Agn łodowska University g author at: Maria 75729. Fax: +48.81. FORMATION eurjchem.7.1.42‐48 ctober 2015 vised form: 05 Dece ecember 2015 ne: 31 March 2016 rch 2016 S ra ate complexes tion ts practical im plexes has been the introducti bind uranium io environment. U groundwater n ethods used fo olvent extracti n, reverse osm ption plays a pr rials used. Pho rface of differ and silica, evid m is to present a metry of surfac on knowledge i variation meth a simple tool he equilibrium The main assu eature of a c in a solution, al/ligand ratio, / ISSN 2153‐225 ht Europ e de Job m e complex ieszka Głady y, Faculty of Chemi Curie Skłodowska U 5333348. E‐mail ad 8.1348 ember 2015 mportance, the p n extensively st ion of new so ons and preve Uranium is foun near uranium m or uranium re ion, membrane mosis, hyperfilt rominent role o sphate comple rent sorbents dently improve a new method o e complexes ba in coordination hod, alternative for the evalu phase, i.e. aque umption of this complex, for e has a maxima when the con European Journ Europ 57 (Online)  20 ttp://dx.doi.org pean Jo Journal web method in xes sorbe ysz‐Płaska, istry, 20‐031 Lublin University, Faculty ddress: majdan.ma ABSTRACT For the first stoichiometry UO2(CH3COO) appearance o [U(VI)]/[P(V) XPS data, th (UO2)3(PO4)2⋅4 participation complexes is bentonite in t Cite this: Eur. problem of ura tudied [1]. Ther rbents, which nt their emissi nd in nuclear w mines [2]. Amon emoval, such a e filtration, coa tration and el owing to the low exes of U(VI) fo such as alu e U(VI) sorptio of characterizat ased on the sor n chemistry tha ely called the d uation of comp eous or non‐aq s method is tha example its U al value at a ch centrations of al of Chemistry 7 pean Journal of C 016 Atlanta Pub /10.5155/eurjch ournal bpage: www. n the eval ed on bent Agnieszka L n, PL MC Skłodowsk of Chemistry, 20‐0 arek8@gmail.com ( time, the contin y of uranyl )2⋅2H2O in the pr of maxima in th ]s = 1.4, 3.3, 3.6 hat the UO2HPO 4H2O complex of (UO2)3(OH)5 suggested, bas he presence of p . J. Chem. 2016, anium re is a could ion to wastes ng the as ion agula‐ ectro‐ w cost ormed umina, on [3‐ tion of rption. at the de Job plexes ueous at the UV‐VIS harac‐ metal and sum of t was con cha reac [U(V pha valu of a liga pos this ray sorp con allo sho com imp Iden exp defi 7 (1) (2016) 42‐ Chemistry lishing House LL hem.7.1.42‐48.1 of Che .eurjchem.co uation of tonite Lipke, Stanis kiej 3, Poland 031 Lublin, PL MC S (M. Majdan). nuous variation phosphate com resence of Na2H he sorption pea 6 and 1.2, 1.7. It O4 complex is is precipitated 5+ and (UO2)4(O sed on the deco phosphates. 7(1), 42‐48 d ligand change m is kept consta the method of s investigated. ncentrations P( anges, the obse ch their char VI)]/[P(V)]s rat ase. The occurre ues of [U(VI)]/[ at least two su ands. A full ch ssible if differe s reason, we ap photoelectron ption products ntinuous variati ow its future a ould remember mplexes forme portant step in ntification of perimental data ining the forma ‐48 LC ‐ All rights re 1348 emistry m the stoich sław Pikus a Skłodowskiej 3, Pola n method was a mplexes sorbed HPO4⋅7H2O from aks of U(VI) an is suggested, ba located on al in the interla H)7+ species in onvolution of s e continuously ant [14]. In the continuous va When the sum (V) is fixed b erved sorption racteristic max tios for their c ence of U(VI) a [P(V)]s would r urface complex aracterization ent, complemen pplied X‐ray pow spectroscopy ( obtained. We b ion method in pplication in s that evaluatio ed, measured the recognition this stoichiom a to the differ ation constants served ‐ Printed y hiometry and Marek M and. applied for the d on bentoni 0.001 mol/L so nd P(V) ions at ased on complem uminols (Al‐O amellar space o the formation orption spectra y and at the sa present work, ariation in a so m of U(VI) and but their mutu ns of U(VI) an ximum values concentrations nd P(V) peaks result only from xes of U(VI) w of the comple ntary methods wder diffraction (XPS) methods believe that the relation to ura systems with o n of the stoich directly, is t n of a complex metry based rent sophistica of surface comp d in the USA y of Majdan * evaluation of th ite. Sorption olutions led to th t molar ratios mentary XRD an OH) whereas th of bentonite. Th of U(VI) surfa a of U(VI) on th ame time their the availability orption system phosphate ion ual proportion d P(V) should at particular in the sorbent at the different m the formation with phosphate exes formed is are used. For n (XRD) and X‐ to describe the e success of the nyl ions would other ions. One hiometry of the the first, very xation scenario. on the fit of ated equations plexes is risky. he of he of nd he he ce he r y m n n d r t t n e s r ‐ e e d e e y . f s Grabias et al. / European Journal of Chemistry 7 (1) (2016) 42‐48 43 2. Experimental 2.1. Reagents Sodium bentonite was prepared from the product delivered by Sigma‐Aldrich, by equilibration of 5 g bentonite with 100 cm3 of NaCl (Sigma‐Aldrich, 99.99% purity) solution (1 mol/L) through 24 h. The sodium form of bentonite was washed several times by water to remove the rest of sodium chloride. The presence of chlorides in washing solution was checked argentometrically. After filtration the solid residue was dried in air. 2.2. Equilibrium sorption data The sorption isotherms of U(VI) were determined by contacting a 0.1 g sample of Na‐clay with 100 cm3 of a UO2(CH3COO)2 ⋅2H2O + Na2HPO4⋅7H2O solution (Lachema, n.p., Brno, p.a., Sigma‐Aldrich) at concentrations of 0.0001‐0.0010 mol/L for U(VI) and P(V), respectively. The sum of U(V) and P(V) concentrations was always 0.001 mol/L. The pH of the mixture was controlled by 0.1 mol/L acetate buffer (CH3COOH + CH3COONa). The following parameters were maintained: a mechanical shaker WU‐4, shaking speed 170 oscillations/min, shaking time 6 h, and temperature 22 °C. After shaking, the samples were left to stand for 12 h and were then passed through filter paper (Filtrak 390, Polish Chemical Reagents) and centrifuged at 10,000 rpm for 15 min (Med. Instruments). The initial and the equilibrium concentrations of U(VI) in the aqueous phase were determined by the Arsenazo(III) method [15], whereas the equilibrium concentrations of phosphate ions P(V) in the aqueous phase were measured spectrophotometrically by the phosphomolybdic method [15]. The concentrations of U(VI) and P(V) ions in the bentonite phase (cs) in mol/g were calculated from the relationship: cs = (c0−ceq)V/m (1) where cs, c0, and ceq denote the concentrations of U(VI) and P(V) ions in the sorbent phase, the initial solution, and the equilibrium solution, respectively. The symbols V and m designate the volume of solution in dm3 and mass in g, respectively. 2.3. X‐ray diffraction data The samples for X‐ray powder diffraction analysis were obtained by shaking 0.1 g Na‐bentonite with 100 cm3 of a mixture of UO2(CH3COO)2⋅2H2O and Na2HPO4⋅7H2O at their constant sum concentration of 0.002 mol/L and a variable [U(VI)]/[P(V)] molar ratio of 0.4‐18. After 6 h, the mixture was centrifuged, and the solid residue was dried in the air. The XRD spectra were registered using the Empyrean apparatus (Panalytical Co.) with CuKα radiation (λ = 1.54178 Å) obtained using a focusing mirror and generated by a Cu anode device operating at 40 kV and 40 mA in conjunction with a one‐dimensional line positional detector. The ICDD diffraction database was used for the identification of peaks in the spectrum. 2.4. X‐ray photoelectron spectroscopy data The samples for the analysis of X‐ray photoelectron spectroscopy spectra were prepared by shaking 1.5 g of Na‐ bentonite with 100 cm3 of a 0.002 mol/L UO2(CH3COO)2⋅2H2O solution or with a mixture of 0.002 mol/L of UO2(CH3COO)2 and Na2HPO4⋅7H2O (0.002 mol/L) at pH = 4 or 7 (symbols of samples: U4, UP4, U7, UP7). After 6 h, the mixtures were centrifuged, and the solid residue was dried in the air. The same procedure was applied for the samples with different proportions of U(VI) and P(V) in the initial solution. The concentration of U(VI) was 0.002 mol/L, whereas the concentration of P(V) changed according to the series 0.0002, 0.001, 0.002, 0.005 mol/L. The symbols of the respective samples were: UP0.0002, UP0.001, UP0.002, and UP0.005. The U4f XPS spectra were recorded on an ESCA apparatus with a multidetection electron analyzer Scienta R4000 (produced by VG Scienta) in the fixed analyzer transmission mode. An unmonochromatized AlK source (1253.6 eV) with a voltage of 12 kV and an emission current of 30 mA was employed. Powdered samples were placed on a molybdenium sample holder and submitted to a vacuum of 5 × 10−9 mbar. The U4f spectra were fitted, using CASA XPS software, with a Gaussian‐Lorentzian peak shape after subtraction of the background with a Shirley baseline; the uranium 4f spin‐orbit coupling was maintained at 10.8 eV, and the component ratio (U4f5/2)/(U4f7/2) was constrained to 0.75. The typical error associated with binding energies was +/− 0.3 eV. 3. Results and discussion 3.1. Sorption isotherms Sorption isotherms of U(VI) and P(V) ions on bentonite in the presence of phosphate are given in Figure 1. There is an evident improvement in U(VI) and P(V) sorption in the bi‐ component system compared with the mono‐component systems. It seems, however, that P(V) peaks refer to the similar complexes independent of the pH. Their position is located at initial solution c0 = 0.0005 mol/L. The U(VI) peak has changed its position from c0 = 0.0006 to 0.0008 mol/L. The enhance‐ ment of the U(VI) peak (when the bi‐component system is compared with the mono‐component ones) is easily recog‐ nizable for pH = 4.7 and is significantly weakened for pH = 6.6. The positions of the maxima of U(VI) and P(V) sorption are shown in Figure 2. At pH = 4.7, the sorption maximum for U(VI) appears at the molar ratio of U(VI)/P(V) = 1.4, whereas for pH = 5.4 and 6.6 at the molar ratios of 3.3 and 3.6, respectively. It is interesting that the peaks related to P(V) sorption appear at U(VI)/P(V) = 1.2, 1.2, 1.7 for pH = 4.7, 5.4 and 6.6, respectively . It is rather certain that at least two different complexes are present in the sorbent phase, i.e. ones with a higher and ones with a lower content of U(VI) ions. The formation of (UO2)3(OH)5+ and (UO2)4(OH)7+ is well‐ documented [16]. They can locate on silanols Si‐OH or aluminols Al‐OH. The role of phosphate ions in the whole complexation scenario is, however, problematic. The precipi‐ tation of (UO2)3(PO4)2⋅4H2O in the bentonite interlayer space results in a sorption maximum at [U(VI)/P(V)]s = 1.4. Some kind of interaction of (UO2)3(OH)5+ and (UO2)4(OH)7+ cations, present in the equilibrium aqueous phase (Figure 3), with HPO42− ions and at the same time with silanols or aluminols would lead to the appearance of surface complexes with U(VI)/P(V)s = 3.3 and 3.6. Phosphate ions probably play a bridging role between oligomeric uranyl hydroxy complexes. The whole complexation process is, however, more complicated. It is rather certain that phosphate ions sorb on the surface of bentonite via an exchange reaction [11]: HPO42− + Al‐OH ⇌ Al‐(HPO4)− + OH− (2) As a consequence, uranyl ions would locate on the aluminum‐ phosphate complex, forming Al‐(HPO4)UO2+ species at a molar ratio of U(VI)/P(V) = 1, which may explain the position of the observed peaks of P(V) sorption for pH = 4.7 and 5.4 at [U(VI)/P(V)]s = 1.2. An alternative complexation reaction involves the sorption of uranyl ions on aluminols with subsequent coordination of phosphate ions: UO22+ + Al‐OH ⇌ Al‐O(UO2)+ + H+ (3) Al‐O(UO2)+ + HPO42− ⇌ Al‐O(UO2) HPO4− (4) 44 Figure 1. The monocomponen CH3COONa was The loca silanols Si reaction (2), basicity of al In turn, t pH = 6.6 (wh monocompo of some kind species whic analysis of th The sorp Fit Programm well‐known procedure [1 characterizat of the metho bands arou absorption b absorption b where the ra presented in about the p distributed sorption isother nt system, P(V) alo s used at pH 6.6; cs ation of the ura ‐OH is rather , is preferred f luminols compa the lack of U(VI hen the bicomp nent ones) pro d of U(VI)‐phosp ch do not con he U(VI) sorptio ption peaks of U me (AISN Softw second deriv 17], which is ve tion of differen od is based on und discrete e band is random band can be mo andom variable n this work, a probability of in the [U(VI)/ G ms of U(VI) ions one; C ‐ a bicompo ‐ concentration of Figure 2. Sorption anyl phosphate r minimized, s for aluminols o ared to silanols. I) distinct sorp ponent mixture ovides evidence phate complexe ntain phosphate on isotherms is U(VI) were deco ware Inc., Versi vative method ry often applied nt spectra. The the distributio energies. The mly distributed delled with a G is energy. Acco crude approxim U(VI) sorptio /P(V)]s ratio, w Grabias et al. / Eu on bentonite in onent system, U(VI f U(VI) and P(V) in n of U(VI) and P(V) complex on su since the exc owing to the h . tion enhancem e is compared e for the coexis es with U(VI) su es. A more de given in Figure onvoluted using on v4), based o and the Gau d in spectrosco general assum on of the absor probability o d in energy, an Gaussian distrib ording to the m mation can be on being rand which allows uropean Journal the presence of I) + P(V); In all sys the sorbent phase ) ions vs. molar rat urface hange higher ment at to the stence urface etailed e 4. g Peak on the ussian py for mption rption of an nd an bution, method made domly U(VI) sorp usin cs = whe corr U(V spe obs 0.89 stoi and the only pho (UO com frac corr for of a of Chemistry 7 (1 phosphate ions stems, 0.1 mol/L ac e, c0 ‐ initial concen tio [U(VI)]/[P(V)]s ption peaks to ng the following a0×exp[‐1/2×( ere a0, amplitud In other word respond to spe VI) surface com ectra can be use served in the U 9, 1.31 and 1.85 ichiometries 1.6 d 6.6, respective equilibria defi y at pH = 4.7. osphate and O2)4(OH)7+ oligo mplexes with ctional numb respond to the example, the st a mixture of 1 an 1) (2016) 42‐48 (A ‐ a monocomp cetate buffer was u ntration of U(VI) an in the sorbent pha o be modelled g relationship: (([U(VI)]/[P(V)] de; a1, center; a2 ds, the maxim ecific [U(VI)/P mplexes. For th ed without exag (VI) sorption sp 5 at pH = 4.7. O 61, 3.83; 1.93 a ely. For this re ined by equatio For all the pH the participa omeric species phosphate io ers character e occurrence of toichiometry 1. nd 2 stoichiome ponent system, U used at pH = 4.7, 5 nd P(V) in the aque ase. with a Gaussia ]s‐a1)/a2)2] 2, width (standa ma on the sorp (V)]s values ch his reason, the ggeration. Thre pectra for the s nly two peaks r and 3.5 are visi ason it can be ons (2‐4) exist Hs, the precipita ation of (UO s in the format ons is unques rizing the s f different surfa 3 relates to the etry’s. U(VI) alone; B ‐ a 5.4 and 0.05 mol/L eous phase). an distribution (5) ard deviation). ption isotherm haracteristic of term sorption ee peaks can be stoichiometries referring to the ible at pH = 5.4 concluded that t unequivocally ation of uranyl 2)3(OH)5+ and tion of surface stionable. The stoichiometries ace complexes, predominance a L n m f n e s e 4 t y l d e e s , e Figure 3. Molar (based on Med excluded from aqueous phase, Figure 4. Sorpt deconvolution, Finally, intensifies f system is com The value of relationship:  s s m c c I where cs and with phosp obtained for were found i r fractions of diffe dusa software [16] calculation; TOT , pCO2‐ partial press tion spectra of U(V bottom‐ the best f it is worth for different p mpared with th f intensification : d cs(m) refer to t phates and w the same initia in the band of d Grabias et a rent U(VI) comple ]; species formed T‐ overall concent sure of CO2 in air). VI) at different pH v fit of cs with the exp examining ho pH values whe he monocompon n I was evaluat the sorption of without phosp al concentration dependence: I vs al. / European Jo exes in the aqueous in the sorbent ph tration of species values (top‐ result perimental points) ow U(VI) sor en the bicomp nent ones (Figu ted according t f U(VI) in the sy phates, respect n of U(VI). Two s. [U(VI)]/[P(V) ournal of Chemist s phase ase are in the ts of the ). rption ponent ure 5). to the (5) ystem tively, peaks )]s, for [U(V lead UO2 com 5.4, 2.82 (UO high (UO mec sorb [U(V furt dire and Figu of p with 3.2. U(V vici pho pro disa resp 2 = 0.25 (UO try 7 (1) (2016) 4 VI)]/[P(V)]s = 1 ds to the conc 2HPO4 comple mpared with th , three peaks w 2; this means O2)3(PO4)2⋅4H2O her complexes O2)4(OH)7+ spe chanisms of U bent phase. At VI)]/[P(V)]s = ther shift of t ection of comm d HPO42‐ ions on ure 5. Intensificati hosphates (top‐ r h the experimental . X‐ray diffract The XRD spec VI) ions and ph inity of bentoni osphate comple obably, from p appears at [U(V pectively. Apar = 12‐28 °, is vis 5 to 1.50, wh O2)3(PO4)2⋅4H2O 42‐48 1.04 and 1.29, r clusion that at ex for benton he other forms were observed a that, at this a O in the bentoni with the parti ecies prevaile (VI) ion transf pH = 6.6, U(VI 1.83, 2.91, whi the surface com mon sorption o n the surface of on of U(VI) sorpti esults of the deco points). tion spectra ctra of the ben osphates are g te peak appear ex of U(VI) at precipitated u VI)]/[P(V)]s = 4 t from that, a g ible for the mol hich also orig O. respectively, at t this pH the ite was the of U(VI) comp at [U(VI)]/[P(V) acidity , the p ite phase and th icipation of (UO d among ov fer from the a ) sorption was ich provides ev mplexation eq of (UO2)3(OH)5+ bentonite. on on bentonite un onvolution, bottom ntonite sample iven in Figure s a distinct pea 2 = 9.9°, ori ranyl phospha 4 and 9 for pH group of peaks lar ratios [U(VI inate from th 45 t pH = 4.7. This affinity of the highest when plexes. At pH = )]s = 0.97, 1.54, precipitation of he formation of O2)3(OH)5+ and er the other aqueous to the intensified for vidence for the uilibria in the +, (UO2)4(OH)7+ nder the influence m‐ the best fit of I es loaded with 6 and 7. In the ak referring to a iginating, most ate; this peak H = 5.4 and 4.7, in the range of )]/[P(V)]s from he precipitated s e n = , f f d r e r e e + e I h e a t k , f m d 46 Fi Fi It is inte observed for ratios, which worth inspe formed in th sorbent pha excess of U evident in th The obse result from t some kind of precipitation 3.3. X‐ray ph When th U4f7/2 XPS components igure 6. XRD spect igure 7. XRD spect eresting that no r the samples h is in disagre cting the mola he U(VI) + P(V se (Figure 8). U(VI) ions, pre he whole pH ran ervations mad the fact that, th f U(VI) surface n of uranyl phos hotoelectron sp e pH was kept a spectra (Figur [18]. The ex G tra of bentonite loa tra of bentonite loa o uranyl phosp with higher [U eement with s ar fractions of t V) mixture for One can obser cipitation of u nge, jointly with e in the sorpti hermodynamica complex is mor sphate. pectra at 4 or 7, the co re 9 and 10) w xperiment was Grabias et al. / Eu aded with U(VI) + aded with U(VI) + phate precipitat U(VI)]/[P(V)]s solubility rules the different sp the system wi rve that for the uranyl phosph h UO2(OH)2⋅2H2 ion experiment ally, the format re favorable tha orresponding U4 were fitted with repeated wit uropean Journal P(V) mixture (pH P(V) mixture (pH tion is molar . It is pecies ith no e high ate is 2O. t may tion of an the 4f5/2, h two th the diff pos Figu the s of Chemistry 7 (1 = 4.7; the numbers = 5.4; the numbers ferent combina sitions of the pa ure 8. Molar fracti system with no sor 1) (2016) 42‐48 s denote the molar s denote the molar tions of U(VI) articular peaks a ons of species form rbent (calculations r ratio [U(VI)]/[P(V r ratio [U(VI)]/[P(V and P(V) conce are given in Tab med in the U(VI) + s based on Medusa V)]s). V)]s). entrations. The ble 1. + P(V) mixture for a freeware [16]). e r Table 1. Peak p during loading Sample U4 U P4 U 7 UP7 UP0.0002 UP0.001 UP0.002 UP0.005 Introduc an enlargem correspondin aluminol site result of positions (in eV) a of bentonite with U Al‐OH 381.8; 4 382.8; 8 381.6; 6 381.9; 8 381.5; 7 381.1; 7 381.7; 7 380.5; 6 ction of phospha ment of the p ng with a U(VI es and decrease minor role o Grabias et a nd areas (in %) in U(VI) and P(V)). 40.2% 3.6% 8.0% 5.9% 8.9% 1.8% 4.5% 8.9% Figure 9. XPS sp Figure 10. XPS s ate to the sorpt peaks: 381.8, I) phosphate c e of the peaks: of silanol sit al. / European Jo n the XPS spectra o Unrecogn 384.4; 16. 384.9; 14. 384.9; 21. 384.4; 28. 384.5; 25. pectra of bentonite spectra of bentonit tion system resu 381.6 eV, pro omplexes sorb 383.3, 383.8 eV tes in phosp ournal of Chemist of U‐loaded benton nized peak .4% .1% .1% .2% .5% e loaded with U(VI te loaded with U(V ults in obably ed on V as a phates imm UO2 (UO bin pH try 7 (1) (2016) 4 nite samples (symb I) and U(VI) + P(V) VI) and U(VI) + P(V mobilization. Th 2HPO4 complex O2)3(PO4)2⋅4H2O ding energy of = 4 (symbol UP 42‐48 bol. pHeq denotes t Si‐OH 383.3; 59.8% 383.8; 32.0% 383.4; 31.1% ) mixture at pH = 4 V) mixture at pH = 7 his may be a re x or a result of O species with s f 382.7 eV, foun P4), correspond he equilibrium pH % % % 4. 7. esponse to the f some kind of surface groups nd for the samp ds strictly with t 47 H of aqueous phase pHeq 5.13 5.34 7.83 7.88 6.36 7.38 7.74 7.81 formation of a f interaction of . The 4f‐orbital ple obtained at the value 382.9 e a f l t 9 48 Grabias et al. / European Journal of Chemistry 7 (1) (2016) 42‐48 eV observed by Drot et al. for U(VI) sorbed on thorium diphosphate/phosphate [19]. The peaks referring to binding energies higher than 384 eV have not been recognized. We can only presume that they relate to U‐O bonds in triuranium heptaoxide U3O7 [20]. In turn, the peak 380.5 eV in the sample with an excess of phosphates, referring to pH = 7.81, can be identified as an uranyl polyhydroxo complex (UO2)x(OH)y2x−y sorbed on surface aluminols [21]. 4. Conclusions The experimental results obtained in this study lead to the following conclusions: 1. The continuous variation method can serve as a preliminary test for the evaluation of the stoichiometry of U(VI)‐P(V) surface complexes. The approximate character of the method is evident for pH = 6.6, when the free U(VI) hydroxy complexes are anchored on the sorbent surface parallel to the uranyl phosphate complexes. This difficulty can be eliminated by analyzing the intensification I of U(VI) sorption when the system with phosphates is compared with that without phosphates. The interaction of (UO2)3(OH)5+ and (UO2)4(OH)7+ species with HPO42‐ ions is evident. 2. Phosphate anions evidently improve the sorption of U(VI) ions on bentonite owing to the formation of ternary complexes among aluminol sites, U(VI) and phosphate anions HPO42−. This fact can be exploited in the construction of engineering barriers used for the isolation of nuclear waste repository sites from the natural environment [22,23]. The stoichiometries of these complexes, i.e. their U(VI)/P(V)s molar ratios, are 1.2, 1.4; 1.2, 3.3; 1.7, 3.6 for pH = 4.7, 5.4 and 6.6, respectively. Deconvolution of the sorptive spectra of U(VI) results in the presumption about the stepwise evolution of the surface complexes formation with pH , where UO2HPO4, (UO2)3(PO4)2⋅4H2O, (UO2)3(OH)5+, (UO2)4(OH)7+ species interact with the surface sites of bentonite. 3. X‐ray photoelectron spectroscopy allows one to diagnose the participation of silanol and aluminol groups in the complexation of U(VI) ions in the absence and presence of phosphates. 4. X‐ray diffraction data confirm the precipitation of (UO2)3(PO4)2⋅4H2O in the interlayer space of bentonite. Acknowledgements The research was carried out with the equipment purchased thanks to the financial support of the European Regional Development Fund in the framework of the Operational Program Development of Eastern Poland 2007‐ 2013 (Contract No. POPW 01.03.00‐06‐009/11‐00), equipping the laboratories of Biology and Biotechnology, Mathematics, Physics and Informatics, and Chemistry for studies of biologically active substances and environmental samples. References [1]. Kremleva, A.; Kruger, S.; Rosch, N. Geochim. Cosmochim. Acta 2011, 75, 706‐718. [2]. The long term stabilization of uranium mill tailings; Final report of a coordinated research project IAEA‐TECDOC‐1403, Vienna, August 2004. [3]. Payne, T. E. Uranium (VI) interactions with mineral surfaces: controlling factors and surface complexation modelling. PhD thesis, University of New South Wales, Sydney, Australia, 1999. 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