WO2014071966A1

WO2014071966A1 - Layered titanates of unsaturated amines

Info

Publication number: WO2014071966A1
Application number: PCT/EP2012/004691
Authority: WO
Inventors: Sergey Britvin; Wulf Depmeier
Original assignee: Christian Albrechts Universitaet Kiel
Current assignee: Christian Albrechts Universitaet Kiel
Priority date: 2012-11-12
Filing date: 2012-11-12
Publication date: 2014-05-15
Anticipated expiration: 2015-05-12

Abstract

The present invention relates to layered titanates for fixation and immobilization of radioactive iodine- 129 and iodine- 13. The chemical composition of the new titanates is as follows: k(U)⋅mA_1-2O⋅(Ti_1-qM_q)(O_2-wOH_xF_y)_2-z⋅nH₂O wherein k, m, q, w, x, y and z are coefficients ranging from 0.01 to 0.5; n is an integer, wherein 0 ≤ n ≤ 5 U is an chemically bounded, unsaturated amine A is at least one cation of valence 1 to 3 M is at least one metal having valence 1 to 7.

Description

Layered titanates of unsaturated amines

The invention relates to a new family of layered titanates, a method for producing these titanates, and using these new titanates for capture of gaseous (vaporous) iodine, in particular for fixation and immobilization of radioactive iodine- 129 and iodine-131 from gaseous products of nuclear fission.

REFERENCES

Van der Schaaf, B. Zirconium in Nuclear Applications. ASTM STP 551, American Society for Testing Materials, 1974.

Harris, J.T., and Miller, D.W. Radiological Effluents Released by U.S. Commercial Nuclear Power Plants from 1995-2005. Health Physics 2008, v. 95, 734-743.

Muramatsu, Y., Yoshida, S., Fehn, U., Amachi, S., and Ohmomo, Y. Studies with natural and anthropogenic iodine isotopes: iodine distribution and cycling in the global environment. J. Environ. Radioactivity 2004, 74, 221-232.

Williams, D. Cancer after nuclear fallout: lessons from the Chernobyl accident. Nature Reviews Cancer 2002, 7, 543-548. BACKGROUND OF THE INVENTION

Radioactive iodine, 1-131 and 1-129, constitute a significant part of spent nuclear fuel accounting for -15% of uranium-235 fission products (van der Schaaf 1974, p. 479). Iodine-131 is a highly active isotope. Its significance as long-term environmental contaminant is negligible because of very short half-live decay period, 8.02 days. However, due to high beta-decay activity of iodine-131, the emissions of this isotope are rather dangerous on short-time scale resulting in thyroid gland cancer (Williams 2002). The second isotope, iodine- 129, has a half-live of 15.7 million years and belongs to the most important long-live radioactive products of uranium-235 fission. Each irradiated 3 -kg U0₂ fuel rod, after a burn-up of 30MWd/kg and immediate stop of nuclear chain reaction, contains about 0.5 g of iodine- 129. Iodine reacts with another fission product, radioactive cesium- 137 forming stable water-soluble cesium iodide, Csl. The latter, however, is decomposed in the hot fuel due to radiolysis, resulting in liberation of elemental iodine. It is known that elemental iodine is highly volatile substance: its boiling point is 185.5 °C; partial vapor pressure is 0.31 and 1 15.8 mmHg at 25 and 100 °C, respectively. As a consequence, radioactive iodine is concentrated in gas phase of nuclear fission wastes. This is especially essential in case of subsequent acid processing of spent nuclear fuel, and then concentrated nitric acid is used for dissolution of irradiated fuel rods. Formation and release of iodine- 129 into the atmosphere is considered among the most significant long-term problems related to disposal of spent nuclear fuel. There are a few issued patents related to fixation of radioactive iodine from liquid fission wastes (aqueous solutions): U.S. patents 4,229,317 and 4,461 ,71 1. There are numerous patents claiming methods for gaseous iodine scavenging, those include: fixation by charcoal (US 3,240,555; US 3,429,103); by silver-exchanged zeolites beds (US 4,088,737; US 4,447,353; US 4,913,850; US 5,075,084); by electrolytic trapping (US 4,004,993); by metal- impregnated sorbents (US 4,382,879); by passing iodine-containing gases through alkali solutions (US 4,204,911); by freeze vacuum drying (US 5,252,258); by apatite matrix (US 5,71 1,016); by water (US 4,180,476); by nitric acid (US 3,752,876); by polymer coatings (US 3,730,833). However, the known methods do not provide efficient iodine scavenging. It is known that significant amounts of iodine- 129 are still released into the atmosphere as by-product of the normal nuclear cycle (Harris & Miller 2008). Recently, an adsorbent for fixation of gaseous iodine was disclosed in patent

EP 2045007. The adsorbent is represented by spherical hydroxide-based particles, including transition metal hydroxides and layered double hydroxides. The authors of the cited patent report on high adsorption capacity of the disclosed hydroxides attaining 2.06 mmol of iodine per 1 g of the adsorbent (that corresponds to ~ 25 wt.% of iodine). The disadvantage of the disclosed method is that the adsorption process requires continuous helium gas flow; the latter is expensive and therefore considerably increases total technological costs. Yet another disadvantage of the disclosed method is that the process of iodine adsorption requires a relatively high temperature of 200 °C.

It is known that iodine- 129 easily circulates in the environment with atmospheric and marine flows (Muramatsu et al. 2004). Like non-radioactive iodine and iodine-131 (Williams 2002), 1-129 has a tendency to accumulate in the human body; the selective target for such accumulation is thyroid gland. As a consequence of above mentioned considerations, a development of effective scavengers for gaseous iodine is still greatly appreciated from a medical and ecological point of view. The objective of the invention is thus to provide compounds which can be used as effective scavengers for gaseous iodine, in particular for radioactive iodine- 129 from gaseous wastes of nuclear plants.

This object is solved by the subject matter as defined in the claims. The present invention relates to new titanates. The chemical compositions of the new titanates can be defined in terms of the mole ratios of the constituents as follows:

A:(U)-mA_1-20-(Ti_1-qM_q)(0_2-wO¾F^)_2-z-nH₂0 where (U) denotes an unsaturated amine, preferably allylamine (3-amino-l-propene, CH₂=CHCH₂NH₂) or propargylamine (3-amino-l-propine, CH≡CCH₂NH₂). In the present formula, k,m,q,w,x,y,z are coefficients ranging from 0.01 to 0.5; 0 < n < 5. Cation A is at least one cation of valence 1 to 3, preferably from the group: H, Li, Na, K, Rb, Cs, Tl, Ni?₄ (ammonium or its organic derivatives where R = H, alkyl, alkenyl, alkinyl or aryl), Nft₃0/? (hydroxylammonium or its organic derivatives where R = H, alkyl, alkenyl, alkinyl or aryl), N₂ ?₄ (hydrazinium or its organic derivatives where R = H, alkyl, alkenyl, alkinyl or aryl), H₃0 (hydronium), Ag, Au, Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg, Hg, Sn, Pb, Ca, Sr, Ba. A may also represent an organic or elementoorganic cation. Metal M is at least one element having valence 1 to 7 substituting for titanium, preferably from the group: Li, Mg, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Ru, Rh, Pd, Os, Ir, Pt. Unsaturated amine (e.g. allylamine or propargylamine), titanium and oxygen are essential constituents of the new titanates.

New titanates contain 1-20 wt.%, preferably 5-15 wt.% of unsaturated amine, and the Ti0₂ content ranges from 50-95 wt.%, preferably 65-80 wt.%.

The disclosed new titanates combine the following properties:

1) Layered titanate structure;

2) Nanometer size of particles;

3) Incorporation of chemically bound unsaturated amines;

4) Chemical stability;

5) Thermal stability;

6) Ability to react with gaseous iodine forming stable iodine-bearing

compounds;

7) Ability to adsorb gaseous iodine in air atmosphere;

8) Ability to adsorb iodine at near-ambient temperature (~ 60 °C).

The new titanates can be used in a wide area of applications as convenient solid source of carrier-bound unsaturated amines. In particular, they can be used as high- capacity adsorbents for elemental iodine vapors, including radioactive iodine- 129 and iodine-131. The advantage of using new titanates as iodine adsorbents is their ability to adsorb iodine in air atmosphere at near-ambient temperature, and high thermal stability of adsorption products.

SHORT DESCRIPTION OF THE FIGURES shows examples of typical particle morphology and particle size of new layered titanates: (a) propargylamine titanate; (b) allylamine titanate. TEM bright field images.

Fig. 2 shows typical X-ray powder diffraction patterns of new layered

titanates: (a) propargylamine titanate; (b) allylamine titanate. Note strong reflections at 13-14A characteristic of interlayer -spacings.

Fig. 3 shows infrared spectra of as-synthesized and iodinated layered

titanates: (a) allylamine titanate, as-synthesized; (b) allylamine titanate, iodinated; (c) propargylamine titanate, as-synthesized; (d) propargylamine titanate, iodinated; (e) propargylamine, free base; (f) allylamine, free base. shows TG and DTA curves (recorded in air) of layered allylamine titanate. Note pyrolytic decomposition of titanate occurs from -250 to -700 °C.

Fig. 5 shows TG and DTA curves (recorded in air) of layered

propargylamine titanate. Note pyrolytic decomposition of titanate occurs from -180 to -650 °C. Fig. 6 shows TG and DTA curves (recorded in air) of iodinated layered allylamine titanate. Note that iodine release occurs from -250 to ~420°C. Fig. 7 shows TG and DTA curves (recorded in air) of iodinated layered propargylamine titanate. Note that iodine release occurs from -250 to -370 °C.

Fig. 8 shows TEM EDX analysis spectra of samples of as-synthesized and iodinated allylamine titanate annealed at different temperatures (in air), (a) as-synthesized substance; (b) iodinated and annealed at 100 °C; (c) iodinated and annealed at 160 °C; (d) iodinated and annealed at 245 °C; (e) iodinated and annealed at 420 °C. Note the energy bands corresponding to iodine (iodine Z-series, -3.9 and -4.2 KeV).

Fig. 9 shows TEM EDX analysis spectra of samples of as-synthesized and iodinated propargylamine titanate annealed at different temperatures (in air), (a) as-synthesized substance; (b) iodinated and annealed at 100 °C; (c) iodinated and annealed at 190 °C; (d) iodinated and annealed at 245 °C; (e) iodinated and annealed at 370 °C. Note the energy bands corresponding to iodine (iodine -series, -3.9 and -4.2 KeV).

Fig. 1 (a,b) shows the typical platy habit of the new titanates. The new titanates have particle sizes from 5 to 500 nm, depending on thermal and chemical conditions of the synthesis. In case of the platy particles shown in Figs. 1 a,b, the typical width of the leaflets is 30-100 nm and the typical thickness is 3-20 nm. The new titanates may have platy, lamellar (nano-plates, nano-sheets, nano-lamella, nano-flakes), tubular (nano-tubes, nano-scrolls), fibrous (nano-rods, nano-needles, nano-whiskers) or isometric morphology. The habit of the titanate particles depends on the thermal and chemical conditions of their synthesis.

The X-ray powder diffraction patterns of the new titanates are characterized by the presence of a significant reflection at d = 13-14 A corresponding to the interlayer spacing of titanates. (Table 1, Fig. 2). The relative intensities of the X-ray reflections may change to a certain degree with changing morphology of the titanate particles.

Main XRD reflections of the new titanates (see Fig.

d, A Wo*

13-14 VS-S

3.2-3.5 VS-S

1.86-1.89 VS-S

1.46-1.49 VS-S

* VS - very strong reflection, S - strong reflection

The infrared absorption spectra of the new titanates (Fig. 3 a,c) contain strong broad bands from 400 to 1000 cm^"1 attributed to stretching vibrations of Ti-0 bonds in the (Ti0₆) octahedra within titanate layers. The multiple bands in the region from 1000 to 1700 cm^"1 are attributed to internal vibration modes of the title amines. The IR-spectrum of allylamine titanate (Fig. 3a) has a duplet at 1645 and 1615 cm^"1 which can be interpreted as overlapping of stretching vibrations of C=C bond in allylamine and bending vibrations of molecular water. The IR-spectrum of propargylamine titanate (Fig. 3c) contains a sharp band at 2130 cm^"1 which clearly indicates the presence of the C≡C bond attributed to propargylamine. Note that exact positions of the bands in the IR-spectra of new titanates differ from those in the spectra of corresponding free unsaturated amines (Fig. 3). This indicates that the new substances are the compounds of corresponding amines rather than mixtures of titanium oxides with free amine bases.

It is known that both allylamine and propargylamine are very unstable compounds. They have low boiling points (53 °C for allylamine; 83 °C for propargylamine); very low flash points (-29 °C for allylamine; 6 °C for allylamine); they are easily oxidized on air (this especially relates to propargylamine); they easily polymerize. In addition, both title amines are strong lacrimators. Contrary to that, the new layered titanates are stable solid substances; they are not lacrimators and they are resistant to thermal decomposition. The thermal decomposition of the new titanates on air is illustrated by Fig. 4 (allylamine titanate) and Fig. 5

(propargylamine titanate). The pyrolysis of allylamine titanate occurs from -200 to ~700 °C; the pyrolysis of propargylamine titanate occurs from -170 to ~700 °C. The final product of thermal decomposition of both titanates is pure titanium dioxide (rutile, anatase or their mixtures).

It is important that the obtained iodinated titanates are thermally stable compounds. Thermogravimeteric analyses (carried out in air) show that iodine release occurs in the range of 250-420 °C (for iodinated allylamine titanate, Fig. 6) and 250-370 °C (for iodinated propargylamine titanate, Fig. 7). The iodine content of iodinated titanates was traced by their stepwise annealing in air followed by chemical analysis (titrimeteric) of annealing products. The EDX spectra of annealing products (Fig. 8,9) clearly show that iodine is retained in the composition of iodinated titanates until 370-420 °C.

As a consequence of thermal stability of the disclosed compounds, the title titanates can be used as effective and stable scavengers for gaseous iodine, in particular for scavenging of radioactive iodine- 129 from gaseous products of nuclear fission. The fixed iodine can be easily re-extracted by simple heating of the iodinated titanates to about 500 °C (Fig. 6,7).

The new layered titanates easily react with elemental gaseous iodine. They are capable to fix up as much as 10 wt.% of gaseous iodine within 1 hour of reaction time, at 60 °C. The infrared spectra of the resultant iodinated titanates (Fig. 3 b,d) are similar, but different from IR-spectra of corresponding parent titanates. This indicates that not a simple sorption but a chemical reaction occurs between the titanates and gaseous iodine. In case of propargylamine titanate, a clear evidence of such chemical reaction is illustrated by disappearing of the IR-absorption band at 2130 cm^"1. This band is characteristic for an acetylenic C≡C bond. It is very sharp in the spectrum of propargylamine titanate (Fig. 3c), but absent in the spectrum of the iodinated propargylamine titanate (Fig. 3d). This implies the absence of a triple bond in the iodinated titanate.

The new layered titanates contain chemically bound unsaturated amines (allylamine or propargylamine) and possess the ability to adsorb iodine directly from the gaseous phase. The capacity of new titanates with respect to iodine scavenging is up to 10-12 wt.%, recalculated on elemental iodine. Both the layered titanates and products of their iodination are thermally stable substances (decomposition in air above 200 °C). Thus, the new layered titanates can be used as effective scavengers of iodine from gaseous wastes of nuclear plants.

The method for the preparation of layered titanates of unsaturated amines disclosed in the present invention comprises mixing, in any sequence, of solutions having the following general composition:

Solution A

The solution contains water and the following essential constituents: a. Any compound of titanium or titanyl (TiO) as source of titanium, preferably halogenides Ti¾ (X=F,Cl,Br,I); titanyl salts TiOX_2/n (X is any anion of valence n); salts or complexes of trivalent titanium Ti³⁺; halogenotitanic acids and their salts A₂/_mTi[Xi_-n(OH)_n]₆ (A is any cation of valence m, X=F,Cl,Br,I, 0 < n < 1); any complex compounds of titanium; any titanoorganic compounds, preferably aryloxides or alkoxides of titanium Ti(OR)_4-nX_n, where R is any organic or metalloorganic radical, preferably methyl (C¾), ethyl (C₂H₅), propyl isomers (C₃H₇), butyl isomers (C₄¾), X=F,Cl,Br,I. Concentration of titanium in solution A is varying in from 0.01 to 6 mole per liter, preferably 0.1-1 mole per liter. b. Any ion forming stable complex ions with titanium, preferably from the group: fluoride ion in form of any compound, preferably as HF (hydrofluoric acid);

fluorides Aⁿ⁺F_n (A is any cation of valence n); hexafluorotitanic acid H₂TiF₆; hexahalogenotitanates A2_/mTi(F_1-nX_n)₆ (A - any cation of valence m,

X=F,Cl,Br,I,OH, 0 < n < 1); hydro fluorides Aⁿ⁺F_n-/wHF (A is any cation of valence n, 0 < m < 4); oxycarboxylic acids or their salts, preferably oxalic, citric, malic, tartaric, tartronic acid or their salts. Concentration of complexing ion in solution A is varying in from 0.01 to 30 mole per liter, preferably 0.1-1 mole per liter. Mole ratio of complexing ion to titanium in solution A ranges from 0.1 to 100, preferably 0.5-10. Complexing ion is an essential modifying constituent in the synthesis of LHT-9. Synthesis without complexing ion yields either amorphous titanium hydroxide or the anatase polymorph of titanium dioxide as it is disclosed in WO2005/051847.

Solution B

Allylamine, propargylamine or an aqueous solution containing title amines or salts of title amines in any soluble form. The aminee concentration in solution B varies in from 0.1 to 30.5 mole per liter, preferably 1-15 mole per liter. Solution B is alkaline (pH >7). The necessary level of alkalinity is achieved by the presence of free unsaturated amine or by adding of any alkali, preferably of aqueous solution of NaOH, KOH or NH₃. Solutions A and B are mixed together in any sequence under following required conditions:

- the resultant reaction mixture should have alkaline reaction (pH >7);

- reaction temperature ranging from -10 to 130°C, preferably at room

temperature;

- in an atmosphere of any gas, preferably in air;

- under vacuum or a gas pressure of at most 100 bar, preferably under atmospheric pressure. The resultant reaction mixture may be optionally thermally treated by the subsequent heating or boiling. The present invention is illustrated below by the way of typical examples. However, the present invention is not limited to concentrations, compositions and synthesis conditions described below. EXAMPLE 1. Preparation of layered titanate of allylamine.

Solution A. 50 mL of 0.5 aqueous solution of hexafluorotitanic acid prepared by dilution of commercial 60 wt/% solution of hexafluorotitanic acid. Solution B. 25 mL of commercial allylamine mixed with 25 mL of distilled water.

Solution A is mixed up with Solution B under vigorous stirring, heated to boiling temperature and boiled for 10 to 20 min. The resulting white slurry is cooled to room temperature, diluted with excess of distilled water, washed a few times with distilled water, filtered off and dried under ambient conditions. Chemical composition (TGA with exhaust gas FTIR screening, wt. %): Ti0₂ 71.5; allylamine 1 1.0; H₂0 to 100 %. Powder XRD pattern of resultant product is consistent with that shown on Fig. 2b. Absorption bands on FTIR spectrum are consistent with those shown on Fig. 3a.

EXAMPLE 2. Preparation of layered titanate of propargylamine.

Solution A. 20 mL of 0.5 aqueous solution of hexafluorotitanic acid prepared by dilution of commercial 60 wt/% solution of hexafluorotitanic acid.

Solution B. 10 mL of commercial allylamine mixed with 10 mL of distilled water.

Solution A is mixed up with Solution B under vigorous stirring, heated to boiling temperature and boiled for 10 to 20 min. The resulting yellow- white slurry is cooled to room temperature, diluted with excess of distilled water, washed a few times with distilled water, filtered off and dried under ambient conditions. Chemical composition (TGA with exhaust gas FTIR screening, wt. %): Ti0₂ 70.4; propargylamine 11.3; H₂0 to 100 %. Powder XRD pattern of resultant product is consistent with that shown on Fig. 2a. Absorption bands on FTIR spectrum are consistent with those shown on Fig. 3c. EXAMPLE 3. Adsorption of iodine vapors on layered titanate of allylamine.

1 g of solid iodine was poured into 3 cm Petri dish. The dish was covered with filter paper and placed into another Petri dish (10 cm diameter). A batch (300 mg) of layered titanate of allylamine (Example 1) was subsequently poured onto filter paper covering iodine. The whole assemblage was covered by glass plate and placed into oven maintaining constant temperature of 60 °C. After one hour, the batch of iodine-saturated layered titanate was transferred into uncovered clean 3 cm Petri dish and allowed to stay in air for 1 hour at 100 °C for complete removal of excess iodine. The iodine-saturated layered titanate was found to contain 9.1 wt. % of iodine.

EXAMPLE 4. Adsorption of iodine vapors on layered titanate of

propargylamine. 1 g of solid iodine was poured into 3 cm Petri dish. The dish was covered with filter paper and placed into another Petri dish (10 cm diameter). A batch (300 mg) of layered titanate of propargylamine (Example 2) was subsequently poured onto filter paper covering iodine. The whole assemblage was covered by glass plate and placed into oven maintaining constant temperature of 60 °C. After one hour, the batch of iodine-saturated layered titanate was transferred into uncovered clean 3 cm Petri dish and allowed to stay in air for 1 hour at 100 °C for complete removal of excess iodine. The iodine-saturated layered titanate was found to contain 10.5 wt. % of iodine.

Claims

1. Layered titanate of the formula

k(U)-mA_1-20-(Ti_1-qM_q)(0_2-wOH_xF_y)_2-z-nH₂0 wherein

k,m,q,w,x,y and z are coefficients ranging from 0.01 to 0.5;

n is an integer, wherein 0 < n < 5

U is an chemically bounded, unsaturated amine

A is at least one cation of valence 1 to 3

M is at least one metal having valence 1 to 7

2. Layered titanate according to claim 1 , characterized in that U is selected from the group of allylamine or propargylamine contain 1-20 wt.%, preferably 5-15 wt.% of unsaturated amine

3. Layered titanate according to any one of the preceding claims, characterized in that U is selected from the group of allylamine or propargylamine

4. Layered titanate according to any one of the preceding claims, characterized in that A is selected from the group of H, Li, Na, K, Rb, Cs, Tl, Ag, Au, Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd, Hg, Hg, Sn, Pb, Ca, Sr, Ba, H₃0, NR4, NR₃OR, N₂R, where R = H, alkyl, alkenyl, alkinyl or aryl.

5. Layered titanate according to any one of the preceding claims, characterized in that M is selected from the group of Li, Mg, Al, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Ru, Rh, Pd, Os, Ir, Pt.

6. Layered titanate according to any one of the preceding claims, characterized in that the interlayer spacing is in the range of 1.2 nm to 1.5 nm preferably 1.3 nm to 1.4 nm.

7. Use of the layered titanate according to any one of the preceding claims as an adsorbent for fixation of iodine.

8. Use of the layered titanate according to claim 7, characterized in that the iodine is gaseous.

9. Use of the layered titanate according to claim 7 or 8, characterized in that the iodine is radioactiv.