E. P. Krasavina

Sorption of cesium, strontium, and yttrium radionuclides from the aqueous phase on layered double hydroxides

Sorption of 137Cs, 85,90Sr, and 90Y from aqueous solutions on the solid phase of layered double hydroxides (LDHs) and layered double oxides (LDOs) of various compositions was studied. On the solid phase of Mg-Al and Cu-Al LDHs and Mg-Al LDO, the Sr and Cs radionuclides are very weakly sorbed from aqueous solutions containing 10−5 M of the corresponding element (Cs+ or Sr2+). Introduction of EDTA ions into Mg-Al LDH increases the distribution coefficients Kd of Sr by a factor of more than 40. After 96-h contact of the solid and liquid phases, Kd of radioactive Sr in sorption from aqueous solution on Mg-Al LDH and Mg-Al LDH-EDTA is 2.4 and 100 ml g−1, respectively. The Sr and Y radionuclides are efficiently sorbed from aqueous solutions containing 10−5 M Sr2+ and Y3+ on the Mg-Nd LDH solid phase. After 5-min contact of the solid and liquid phases, Kd of Sr exceeds 105 ml g−1. For Y, the distribution coefficients equal to 700–800 ml g−1 are attained after 30-min contact of the solid and liquid phases. Aging of the Mg-Nd LDH precipitate does not affect its sorption properties toward Sr and Y radionuclides. With an increase in the Sr(NO3)2 concentration in the solution from 10−5 to 10−1 M, the distribution coefficients Kdz of Sr drastically decrease (virtually to zero) and those of Y change insignificantly.

Sorption of U(VI) from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of 60Co from aqueous solutions of various compositions on layered double hydroxides (LDHs) of Mg, Al, and Nd in carbonate and hydroxide forms and on layered double oxides (LDOs) of Mg and Al was studied. 60Co is poorly sorbed from aqueous nitrate solutions onto LDH-Mg-Al-OH. The 60Co distribution coefficient Kd does not exceed 50 ml g−1 at a phase contact time of 15 min and V/m = 50 ml g−1. At the same time, 60Co is efficiently sorbed from 10−3–10−5 M aqueous Co(NO3)2 solutions onto LDH-Mg-Al and LDH-Mg-Nd with CO32− in the interlayer space. At a phase contact time of 15 min and V/m = 50 ml g−1, Kd exceeds 2 × 104 ml g−1 for LDH-Mg-Nd and does not exceed 5 × 103 ml g−1 for LDH-Mg-Al. The 60Co desorption from LDH-Mg-Nd-CO3 into 0.05–0.2 M solutions of Na2CO3, NaNO3, (NH4)2C2O4, and Na2H2EDTA and into distilled water was studied. Na2H2EDTA is the most efficient desorbing agent. After 15-min contact of LDHMg(60Co)-Nd-CO3 with 0.1 and 0.05 M Na2H2EDTA solutions, the degree of desorption of 60Co is ∼100 and ∼99%, respectively.

Sorption of radioiodine from aqueous solutions on layered double magnesium aluminum hydroxides at 300 K

Sorption of 131I− and 131IO3− from aqueous solutions at 300 K on solid layered double magnesium aluminum hydroxides (Mg-Al-LDH) in the carbonate (Mg-Al-LDH-CO3) and nitrate (Mg-Al-LDH-NO3) forms was studied. The distribution coefficients of 131I− and 131IO3− between solid Mg-Al-LDH-CO3 and an aqueous solution after contact of these phases for 60 min are 38 and 34 ml g−1, respectively. The distribution coefficients of 131I− and 131IO3− between solid Mg-Al-LDH-NO3 and an aqueous solution, measured under the similar conditions, are about 5 ml g−1. After contact of the solid and liquid phases for 14 h, the distribution coefficients of 131I− and 131IO3− between an aqueous phase and solid layered double magnesium aluminum oxides (Mg-Al-LDO) prepared by thermolysis of Mg-Al-LDH are 7999 and 7068 ml g−1, respectively.

Sorption of 137Cs from aqueous solutions onto layered double hydroxides containing the Fe(CN)64− ion in the interlayer space

Sorption of 137Cs from aqueous solution onto layered double hydroxides (LDHs) of the composition LDH-M2+-M3+-Fe(CN)6 (M2+ = Mg, Cu, Ni, Zn; M3+ = Al, Fe) was studied. The LDH-Mg-M3+-Fe(CN)6 solid phases (M3+ = Al, Fe) take up 137Cs from 10−5 M aqueous CsNO3 solutions extremely weakly, whereas the LDH-M2+-M3+-Fe(CN)6 solid phases (M2+ = Cu, Ni, Zn; M3+ = Al, Fe) efficiently take up 137Cs. After 15-min contact of the solid and liquid phases, the apparent distribution coefficient Kd* of 137Cs ranges from ≈3 × 102 to ≈104 mL g−1 for M2+ = Cu, from ≈4 × 103 to ≈2 × 104 mL g−1 for M2+ = Ni, and from ≈5 × 103 to ≈3 × 104 mL g−1 for M2+ = Zn at V/m = 50 mL g−1. As the NaOH concentration in the solution is increased, the sorption performance of the examined LDHs, except LDH-Ni-Al-Fe(CN)6, drastically decreases, which is due to the formation of LDH-M2+-M3+-OH (M2+ = Ni, Zn; M3+ = Al, Fe) having low ability to take up 137Cs.

Effect of complexing anions on sorption of U(VI), 90Sr, and 90Y from aqueous solutions on layered double hydroxides of Mg, Al, and Nd

Sorption of 90Sr and 90Y from aqueous solutions on Mg-Al and Mg-Nd layered double hydroxides (LDHs) in various forms was studied. The distribution coefficients Kd of U(VI) and 90Sr on LDH-Mg-Al-EDTA are 100–120 ml g−1 in 15 min of contact of the solid and liquid phases at V/m = 50 ml g−1. At the same time, under similar conditions, U(VI) and 90Sr are not sorbed from aqueous solutions on LDH-Mg-Al-C2O4. The sorption of U(VI) from aqueous solutions containing H2EDTA2−, C2O42−, and CO32− on LDH-Mg-Nd-CO3 and LDH-Mg-Al-CO3 strongly depends on the concentration of the complexing anions in the solution. In particular, for 10−3 M aqueous UO22+ solutions, with an increase in [C2O42−] from 10−3 to 5 × 10−2 M, Kd of U(VI) decreases from >5 × 103 to 70 ml g−1 for LDH-Mg-Al-CO3 and from 170 to ∼0 ml g−1 for LDH-Mg-Nd-CO3. In the presence of 10−3 to 5 × 10−2 M CO32− in aqueous solution, U(VI) is not noticeably sorbed on LDH-Mg-Nd-CO3 (Kd does not exceed 16 ml g−1 at V/m = 50 ml g−1), and on LDH-Mg-Al-CO3 the sorption sharply decreases (Kd decreases from >5 × 103 to ∼0 ml g−1 at V/m = 50 ml g−1). The presence of complexing anions in the solution does not appreciably affect the 90Sr sorption, but noticeably affects the 90Y sorption. With an increase in their concentration, Kd of 90Y appreciably decreases. The effect exerted by Sr2+ ions on the sorption of microamounts of U(VI) and by UO22+ ions on the sorption of microamounts of 90Sr and 90Y from aqueous solutions on LDH-Mg-Nd-CO3 was also examined.

Sorption of Cs, Sr, and Y radionuclides on mixed layered double hydroxides of Mg, Al, and Nd from the aqueous phase

Sorption of 137Cs, 90Sr, and 90Y radionuclides from aqueous solutions on the solid phase of layered double hydroxides (LDHs) of Mg, Al, and Nd was studied. Sorption of 137Cs from 10−5 M aqueous CsNO3 solutions on the LDH-Mg-Al-Nd solid phase is extremely weak. At the same time, 90Sr and 90Y are efficiently sorbed on the LDH-Mg-Al-Nd solid phase from 10−5 M aqueous Sr(NO3)2 solutions. After 5-min contact of the solid and liquid phases, Kd of 90Sr and 90Y exceeds 103 ml g−1. With an increase in the Nd content in LDHs of mixed composition, their sorption properties toward 90Sr and 90Y are enhanced.

Sorption of strontium and yttrium radionuclides from aqueous solutions onto layered double hydroxides of various compositions

New experimental results and published data on sorption of strontium and yttrium radionuclides from aqueous solutions onto layered double hydroxides (LDHs) of various compositions are summarized. The effect of double-charged (Mg2+, Ba2+, Sr2+, Cu2+, Zn2+, Ni2+) and triple-charged (Al3+, Fe3+, Nd3+) cations incorporated in the LDH matrix and of anions incorporated in LDH (CO32−, SO42−, NO3−, OH−, Cl−, C2O42−, H2EDTA2−) on the physicochemical properties of this class of compounds, including the ability to sorb strontium and yttrium radionuclides, is examined.

Removal of 60Co and 137Cs from simulated NPP trap waters

The possibility of removing 60Co and 137Cs from simulated NPP trap waters by sorption and precipitation methods was examined. The use of layered double hydroxides (LDHs) of Mg and Nd, containing CO32− in the interlayer space, for removing 60Co from NPP trap waters is inefficient, especially in the presence of EDTA. After 2 h of contact of the solid and liquid phases, the degree of 60Co sorption does not exceed 12% at V/m = 500 mL g−1. Coprecipitation of 60Co with a complex precipitate of Fe3+ and triethylenediamine (CH2-CH2)3N2 from simulated NPP trap waters containing 0.03 M Co2+ allows ∼85% removal of the radionuclide. The 60CO coprecipitation with KFe[Fe(CN)6] from simulated NPP trap waters does not ensure its efficient removal. The degree of coprecipitation of 60CO with KFe[Fe(CN)6] varies from ∼55 to ∼85%. A procedure was suggested for removing 60Co and 137Cs from aqueous solutions by coprecipitation of the radionuclides with the solid phase of K+, Fe3+, and Ni2+ ferrocyanides formed by adding K4[Fe(CN)6], Fe(NO3)3, and Ni(NO3)2 in succession to the solution. The procedure ensures almost 100% removal of both radionuclides from simulated NPP trap waters.

Sorption of U(VI) onto layered double hydroxides and oxides of Mg and Al, prepared using microwave radiation

Layered double hydroxides of Mg and Al, containing CО32– ions in the interlayer space (LDH-Mg-Al-CО3), and layered double oxides of Mg and Al (LDO-Mg-Al) were prepared using microwave radiation (MWR). The use of MWR allows not only acceleration of the synthesis of both LDH and LDO, but also preparation of compounds with high kinetic characteristics of the U(VI) sorption. The degree of U(VI) sorption (α) from 10–2 M aqueous U(VI) solutions at a sorption time of 4 h and V/m = 50 mL g–1 exceeds 99.0%. In sorption from more concentrated (10–1 M) aqueous U(VI) solutions under similar conditions, α on all the samples does not exceed 37.5%.

New composite materials containing fine particles of D-elements for localization of molecular radioactive iodine in water coolants of nuclear power plants

New composite materials based on KU-2 cation exchanger that contains various compounds of Ni and Zn are developed for localization of I2 in the water coolant of nuclear power plants (NPPs). Composite materials containing nanometer particles of Ni and Zn compounds are able to quickly and efficiently convert I2 into ionic forms in the water coolant of the primary circuit of an NPP. Almost complete conversion of I2 (>99%) in the aqueous phase is achieved after 15 min of contact of the liquid phase and the developed composite material. It is shown that the use of a tandem of the developed composite material and AB-18 anion exchanger makes it possible to isolate I2 in the water coolant of the primary circuit of an NPP almost completely.