New rare earth langbeinite phosphosilicates KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) for lanthanide comprising nuclear waste storage

Accepted Manuscript New rare earth langbeinite phosphosilicates KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) for lanthanide comprising nuclear waste storage Sathasivam Pratheep Kumar, Buvaneswari Gopal PII:

S0925-8388(15)31344-X

DOI:

10.1016/j.jallcom.2015.10.088

Reference:

JALCOM 35643

To appear in:

Journal of Alloys and Compounds

Received Date: 11 June 2015 Revised Date:

22 September 2015

Accepted Date: 12 October 2015

Please cite this article as: S.P. Kumar, B. Gopal, New rare earth langbeinite phosphosilicates KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) for lanthanide comprising nuclear waste storage, Journal of Alloys and Compounds (2015), doi: 10.1016/j.jallcom.2015.10.088. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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New rare earth langbeinite phosphosilicates KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) for lanthanide comprising nuclear waste storage Sathasivam Pratheep Kumar a, b, * and Buvaneswari Gopala a

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Materials Chemistry Division, School of Advanced Sciences, VIT University, Vellore632 014, Tamil Nadu, India. b National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan.

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Abstract

In contrast to the existing cubic langbeinite phosphates and sulphates, orthorhombic

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langbeinite phosphosilicates of the chemical formula KBaYMP2SiO12 (M: Zr, Sn), KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) and the wasteform KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 have been synthesized by solution method. Powder X-ray diffraction analysis affirmed that the compounds were phase pure and

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crystallized in an orthorhombic structure with P212121 space group. Spectral analysis of the wasteform revealed the phase stability, thermal stability and chemical durability of the langbeinite structure. Chemical durability of the powder wasteform has been studied

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by a dynamic Soxhlet test. Elemental analysis of the leachates showed that the normalized mass losses of barium, zirconium and silicon were in the order of 10-3-10-2

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g/m2, 10-5-10-4 g/m2 and 10-2-10-1 g/m2 respectively. Normalized mass losses of lanthanides, potassium and phosphorous were found to be below the instrumental detection limits.

Key words: Langbeinite phosphosilicate, X-ray diffraction, Infrared spectra, Thermal analysis, Chemical durability

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*Corresponding author E-mail: [email protected]

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Present address: National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan. Fax: +81-29-859-2401; Tel: +81-29-859-2000 ex. 3795;

1. Introduction

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Encapsulation of high level nuclear waste (HLW), which is generated from the spent

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nuclear fuel reprocessing, into a thermodynamically stable and radiation resistant solid matrix is an important issue for the department of nuclear energy. In this contest, many host matrices related to glass, glass-ceramic, synroc and phosphate ceramics have been investigated in the past three decades [1-7]. Among the studied host ceramic matrices, single phasic phosphates have paid much attention due to their thermodynamic, radiation

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and chemical stabilities [7, 8]. Similarly, silicate based materials like aluminosilicate [9], zircon [10] and britholite [11] have also been found to be a candidate materials for the immobilization of minor actinides and lanthanides.

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Compounds of langbeinite structure are of particular interest due to their

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interesting properties such as optical, magnetic, ferroelectric and phase transitions [1215]. The crystal structure of langbeinite (A2B2(XO4)3) is built with the nine coordinated sites (A cations), octahedral sites (B cations) and tetrahedral sites (XO4 oxyanion). The three dimensional (3D) network structure is closely related to the nasicon-type and garnet-type structures [16]. Studies reveal that langbeinite compounds are exist in cubic and orthorhombic structure with the space group of P213 and P212121 respectively [17]. A

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large number of ionic substitutions into the 3D structure have been reported by many authors [18-33]. Langbeinite phosphates such as KCsFeZrP3O12 [18], KSrFe2(PO4)3 [19],

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KSrSc2(PO4)3:Ce3+/Eu2+/Tb3+ [12], K2MIII2(MVIO4)(PO4)2; MIII: Fe, Sc; MVI: Mo, W [13], K2GdZr(PO4)3 [20], K2AlM(PO4)3; M: Sn, Ti [21, 22], K2YHf(PO4)3 [23],

K2FeZr(PO4)3 [24], K2LnZr(PO4)3; Ln: Ce-Yb, Y [25], Na2MTi(PO4)3; M: Fe, Cr [26],

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K2M0.5Ti1.5(PO4)3; M: Mn, Co [27], K2MTi(PO4)3; M: Er, Yb or Y [28], KBaM2(PO4)3; M: Fe, Cr [29], Cs2Ni2(MoO4)3 [30], Rb3Yb2(PO4)3 [31], Rb2YbTi(PO4)3 [32],

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Cs1+xLnxZr2-x(PO4)3; Ln: Sm-Lu [33] have been found to be crystallize in a high temperature cubic structure with P213 space group. However, few sulphates and vanadates (M+2Mn2(SO4)3; M+ = K, NH4, Tl and MBaCr2(VO4)3; M = Li, Na or Ag) were identified as low temperature orthorhombic phases with P212121 space group [17, 34].

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Langbeinite structure is considered for the fixation of high level nuclear waste because of (i) the large cavity which forms due to the interconnection of octahedral and tetrahedral groups is capable of accommodating bigger ions [30, 33], (ii) the structural

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stability towards a wide range of ionic substitutions [35] and (iii) the leach resistance under dynamic conditions [36]. Although, phosphate, silicate, titanate and

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phosphosilicate based wasteforms with different structures are available in the literature, a wasteform of langbeinite phosphosilicate has not been reported. Therefore, the current work aims to fabricate a wasteform with langbeinite structure to immobilize selected lanthanides along with the zirconium ion. Hence, we have synthesized new langbeinite phosphosilicates of the chemical formula KBaYMP2SiO12 (M: Zr, Sn), KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) and the wasteform

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KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12. The phase stability and chemical durability of the wasteform have been investigated and the results are discussed in this paper.

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2. Experimental Section 2.1. Materials

(COOK)2.H2O (99.5%, CDH, India), BaNO3 (99.5%, S.D.Fine Chemicals, India),

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REE2O3 [REE = La, Ce, Nd, Sm, Eu, Gd, Dy and Y] (99.9%, Sigma Aldrich, India),

ZrOCl2.8H2O (Loba Chemie, India), SnCl4.5H2O (98%, Sigma Aldrich, India), H3PO4

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(88%, S.D.Fine Chemicals, India) and Si(OC2H5)4 (98%, Sigma Aldrich, India).

2.2. Synthesis of KBaYMP2SiO12 (M: Zr, Sn), KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) and the wasteform KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12

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Stoichiometric amount of potassium chloride, zirconyl chloride/ stannic chloride and phosphoric acid were dissolved separately in each 10 ml of deionized water. Yttrium oxide and tetraethyl orthosilicate (TEOS) were dissolved in 10 ml of 1:1 nitric acid and

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10 ml of ethanol respectively. The solutions were mixed in the following order with constant stirring on a magnetic stirrer. First potassium chloride solution was added into

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the zirconyl chloride/tin chloride solution. To this mixture barium nitrate followed by yttrium nitrate solutions were added. To the above metal nitrate mixture, phosphoric acid and TEOS solutions were added drop wise one after the other. The resultant homogeneous precipitated solution was further stirred for 20 minutes and dried at 80 ºC in a hot air over for 24 h. The dried precursor was calcined at 600 °C, 900 °C, 1100 °C and 1200 °C for 24 h at each stage with intermittent grinding to attain the homogeneous

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product. Similar procedure was followed to synthesis KBaREEZrP2SiO12 (REE: La, Nd, Sm, Eu, Gd, Dy) and the wasteform KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12. Rare earth

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oxides were dissolved in 10 ml of 1:1 nitric acid and used.

2.3. Dissolution test

Dissolution test of the powder wasteform KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 has been

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carried out by a Soxhlet method for a period of one month as described in our previous studies [37, 38]. To brief, the 1200 ºC sintered pellets were crushed in an agate mortar

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and sieved in 85-100 mesh brass sieves to collect uniform sized powders. 1 g of washed and dried powder was used for the test. The leachant (deionized water) was heated to boil at 90 ±5 °C, vaporized and condensed through the condenser to fall the droplets on the sample. The flow rate of fresh leachant was maintained at the rate of 1.0 L/day. 20 ml of

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the leachate was collected after every 24 h interval for elemental analysis and the same volume of fresh leachant was replaced to maintain the constant volume. The collected leachate was analyzed by Inductively Coupled Plasma-Optical Emission Spectroscopy

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(ICP-OES). The BET surface area of the wasteform was found to be 0.4677 m2/g. From the ICP-OES results, normalized elemental mass loss (expressed in g/m2) and the

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corresponding normalized leach rate (expressed in g/m2/day) of molybdenum were determined by considering the following equation [39]

Where Ci = analyzed concentration of ith component in g/ml, V = volume of the leachant in ml, S = surface area of the sample, t = time in days and fi = mass fraction of the ith component in the original sample (unitless).

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2.4. Characterization The synthesized products were characterized by powder X-ray diffraction (XRD) method (CuKα, Bruker, D8 Advanced) at room temperature. The unit cell parameters and cell

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volume were calculated by least square refinement method. Fourier Transformed Infrared Spectra (FTIR) was recorded by JASCO, FT-IR/4100 spectrometer using KBr pellet technique in the frequency range of 400-4000 cm-1. Scanning Electron Microscopic

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(SEM) images were recorded using FEI Quanta FEG 200 attached with EDS. Thermal

analysis was performed on TA instruments Model SDT Q600 in the temperature range

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RT – 1000 °C. Surface area for the powder sample was measured using BET technique on Micromeritics, ASAP 2020 V3.00H. Inductively Coupled Plasma Optical Emission Spectroscopic (ICP-OES) analysis was performed using Perkin Elmer, Optima 5300 DV

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ICP-OES.

3. Results and Discussion

3.1. Spectral analysis of KBaYZrP2SiO12 and KBaYSnP2SiO12

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3.1.1. Powder XRD

The powder XRD patterns of KBaYZrP2SiO12 (KYZP) and KBaYSnP2SiO12 (KYSP)

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recorded at room temperature are shown in Fig. 1. The XRD patterns of both compounds were indexed based on the orthorhombic langbeinite K2Ca2S3O12 (ICDD card No: 740404) and identified as single phasic. Generally, phosphates and sulphates of langbeinites were crystallized in cubic structure whereas vanadates of the formula MBaCr2(VO4)3 (M = Li, Na or Ag) (rV = 0.355 Å (td)) preferred an orthorhombic symmetry [34]. The evolution of orthorhombic structure can be explained based on the size of ions substituted

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in the tetrahedral site. Survey of langbeinite compounds indicates that most of the sulphates (rS = 0.12 Å (td)) and phosphates (rP = 0.17 Å (td)) crystallize in cubic structure [40, 25]. Comparing the room temperature structures of K2Mg2(SO4)3 and K2Ca2(SO4)3, it

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is noted that the presence of bigger Ca2+ ion results in symmetry reduction. In the current systems 1/3rd of ‘PO4’ tetrahedra were replaced by a bigger ‘SiO4’ tetrahedra (rSi = 0.26 Å (td)) [41]. Further, crystallographically, Speer and Salje demonstrated that the driving

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force behind the structural transformation is a slight rotation of SO4 tetrahedra [17]. Thus, it is presumed that the average size effect of the tetrahedra influences the structure and

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resulted in an orthorhombic symmetry for the compounds.

In order to find the effect of zirconium ion replacement with tin ion, the unit cell parameters and cell volumes were calculated by least square refinement method. The corresponding values are compared in Table 1. The cell parameter values indicate that

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‘a’, ‘b’ and the cell volume of KYSP were decreased slightly compared to the phase KYZP. This indicate that the fraction of MO6 octahedra shrinks by replacing the bigger

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ZrO6 octahedra (rZr = 0.72 Å) with the smaller SnO6 octahedra (rSn = 0.69 Å) ion.

3.1.2. FT-IR and SEM study

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The FT-IR spectra of both compounds are shown in Fig. 2. Identification of the vibrational modes of (P-O) and (Si-O) was found to be difficult due to the similar absorption frequency of ‘PO4’ and ‘SiO4’ tetrahedral groups [42]. For the compound KYZP, the asymmetric and stretching vibrational modes of (P-O) were observed at 1054 cm-1, 1014 cm-1 and 919 cm-1 respectively. However, the stretching bands for (Si-O) were not identified, which could be due to the overlapping of both (P-O) and (Si-O) vibrational

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bands. The asymmetric and symmetric bending vibrational modes of (P-O) were noticed at 553 cm-1, 580 cm-1 and 497 cm-1 respectively. In the case of KYSP compound, the stretching and bending vibrational modes of (P-O) were observed at 1220 cm-1,1087 cm-1

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and 577 cm-1, 524 cm-1 respectively. Similarly, the stretching and bending vibrational

modes of (Si-O) were noticed at 1006 cm-1 and 787 cm-1, 458 cm-1 respectively. Overall, a comparative FT-IR spectra of KYZP and KYSP show that the substitution of ‘Sn’ ion for

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‘Zr’ ion lead to broadening of vibrational bands and a shift in their positions.

Surface morphology of the phases was observed by scanning electron microscope.

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A significant difference in the particles shape was noticed between the samples KYZP and KYSP. Figure 4 shows the lower and higher magnified SEM images of KYZP and KYSP. In the case of KYZP, appearance of uniformly distributed hexagonal particles was noticed. When zirconium ion was replaced with tin ion, the particles were transformed

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from hexagonal shape to rod shape. Furthermore, the particles size in both the compounds was found to be in the range of nanoscale. The diameter of hexagonal shaped particles (KYZP) and rod shaped particles (KYSP) was in the range of 39-120 nm and

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35-145 nm respectively. The morphological change indicates that the small variation in ionic radii (rZr = 0.72 Å; rSn = 0.69 Å) could make a large difference in the surface

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structures.

3.2. Lanthanide incorporation Since zirconium is one of the major radionuclide in most of the HLW, the ‘Zr’ containing phase KBaYZrP2SiO12 has been chosen for the incorporation of lanthanides. The yttrium ion was replaced by the rare earth ions to obtain KBaREE3+ZrP2SiO12 where REE3+ = La,

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Nd, Sm, Eu, Gd and Dy compounds. The powder XRD patterns (Fig. 4) were indexed based on the orthorhombic langbeinite K2Ca2S3O12 (ICDD No: 74-0404) and identified them as phase pure. For comparison, the powder XRD pattern of KYZP is given at the

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base in Fig. 4. Compared to the powder XRD pattern of KYZP (Fig. 4a), lanthanide substituted phases (Figs. 4b to 4g) show peak shifts towards lower angle due to the

replacement of yttrium ion by rare earth ions. The calculated unit cell parameters and cell

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volume of the compounds are given in Table 2. Though the cell parameters show

difference in their values due to the substitution of various rare earth cations, the size

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effect was not gradual for the compounds. To understand this complex behavior of lattice parameter changes, a detailed structural investigation of these compounds is needed. Since the FT-IR spectra of KBaREE3+ZrP2SiO12 where REE3+ = La, Nd, Sm, Eu, Gd and Dy compounds were identical to the FT-IR spectrum of KYZP, the characteristic

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stretching and bending vibrational mode values of PO4 and SiO4 tetrahedra are summarized in Table 3. The spectral data show variations in peak positions with the

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replacement of yttrium ion by the rare earth ions.

3.3. Phase stability and chemical durability of the wasteform

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3.3.1. Powder XRD and FT-IR

The wasteform KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 has been synthesized as described in section 2.2 to incorporate lanthanide ions along with zirconium into langbeinite structure. Powder XRD pattern of the wasteform (Fig. 6b) confirmed the single phasic orthorhombic structure similar to the parent compound KYZP (Fig. 6a). A simultaneous fixation of La, Nd, Sm and Eu ions by the partial replacement of yttrium ion led to appear

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few extra reflections (Fig. 6b) in the powder XRD pattern of the wasteform. However, the extra reflections were also attributed to the orthorhombic langbeinite structure (ICDD card No: 74-0404). When Gd and Dy ions were tried to incorporate in the wasteform by

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further reducing the yttrium percentage, a segregation of the phase was noticed.

FT-IR spectra of the wasteform and KYZP are compared in Figure 7. The

wasteform show stretching and bending vibrational modes of (P-O) and (Si-O) similar to

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the parent phase KYZP. However, a significant reduction in the intensity of vibrational

lanthanides in place of yttrium ion.

3.3.2. TGA and SEM-EDX

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frequencies was observed in the wasteform due to the incorporation of selected

Thermal stability of the wasteform has been tested as it is an important parameter to

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assess the wasteform. Figure 8 shows the thermogravimetric profile analyzed between room temperature and 1000 °C. The absence of any weight loss in the TGA curve proves that the wasteform is stable up to 1000 °C, which is acceptable for practical applications.

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Scanning electron micrographs of the wasteform are shown in Fig. 8. The lower magnified image (Fig. 8a) shows that the smaller particles were deposited on a larger

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particle. Also, it was found that the larger particles were agglomerated each other. Figure 8b indicates that the size of deposited smaller particles were in the range of 100-250 nm. This size difference of the particles could be due to the substitution of rare earth ions. To confirm the effect of lanthanide ions addition, the SEM image of the wasteform was compared with the SEM image of KYZP (Figs. 3a and 3b). This comparison reveals that the particles were transformed from well distributed hexagonal particles into an

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agglomerated hexagonal particles with the substitution of La, Nd, Sm and Eu for yttrium ion in the compound KYZP. The presence of incorporated elements in the wasteform was

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confirmed by the EDX spectrum (Fig. 8c).

3.3.3. Chemical durability

Chemical durability of the wasteform was studied as described in section 2.3. Analysis of

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the leachates by ICP-OES showed only the leaching of Ba, Zr and Si ions. The

concentration of all other ions was found to be below the instrumental detection limit.

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The instrumental detection limit values for K, Y, La, Nd, Sm, Eu and P are 0.001, 0.004, 0.01, 0.09, 0.04, 0.002 and 0.08 ppm respectively. Normalized mass loss and leach rate of the elements Ba, Zr and Si were calculated as described in section 2.3 and the values are given in Table 4.

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The normalized mass loss of barium increased linearly with time whereas it was almost plateaued for zirconium after 15 days of the experiment. The normalized mass loss of silicon was only observed for initial 7 days and it was below the instrumental

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detection limit during later days. Figure 9 shows the leach rates of barium and zirconium from the wasteform. The leach rate of Ba, Zr and Si was found to be in the order of 10-4

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g/m2/d, 10-6-10-5 g/m2/d and 10-4-10-2 g/m2/d respectively. The negligible leaching of potassium could be attributed to the encapsulation of monovalent ion in the closed cavity of the three dimensional structure. However, the leach resistance of rare earth elements and phosphorous could be due to the differences in the metal-oxide bond strength, solubility and mobility of the ions. It is worth mention that the leaching behavior of lanthanides is similar to our recently investigated monazite and apatite wasteforms [37,

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38]. Further, the leach rate of phosphorus from langbeinite structure is several order lower (BDL) than the apatite structure (LRP: 10-4-10-3 g/m2/d) [38]. Phase stability of the wasteform after leach test was investigated by the powder

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XRD. Figure 10 shows the powder XRD patterns of the wasteform before and after leach test. From the results, it was noticed that the wasteform is stable ever after one month

continuous exposure with water. However, the crystallinity of the wasteform after the test

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was affected as it can be seen from the x-ray diffraction pattern (Fig. 10b). Thus, the

preliminary results on the phase stability towards ionic substitution, thermal stability and

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chemical durability study indicate that langbeinite structure could be considered as a suitable candidate for the fixation of lanthanide comprising high level nuclear waste.

4. Conclusions

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In summary, we have synthesized a series of novel langbeinite phosphosilicates and the wasteform by solution method and characterized them by several spectroscopic analysis. All the compounds were identified as single phasic orthorhombic structure with P212121

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space group. Electron micrographs of KBaYZrP2SiO12 and KBaYSnP2SiO12 displayed a remarkable difference in the particles shape. A distributed crystalline hexagonal and rod

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shaped particles were obtained for the compounds KBaYZrP2SiO12 and KBaYSnP2SiO12 respectively. Dissolution test of the langbeinite wasteform resulted negligible leaching of lanthanides. However, leach rates of barium, zirconium and silicon elements were found to be in the order of 10-4 g/m2/d, 10-6-10-5 g/m2/d and 10-4-10-2 g/m2/d respectively.

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Acknowledgement The authors thank VIT University for providing all required facilities to carry out the

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experiments.

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[32] J.C.M. Gustafsson, S.T. Norberg, G. Svensson, J. Albertsson, Acta Crystallogr., Sect. C: Cryst. Struct. Commun. C61 (2005) i9-i13.

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[33] I.V. Ogorodnyk, V.N. Baumer, I.V. Zatovsky, N.S. Slobodyanik, O.V. Shishkin, K.V. Domasevitch, Acta Crystallogr., Sect. B: Struct. Sci. B63 (2007) 819-827. [34] M.A. Nabar, D.S. Phanasoaonkar, Spectrochim. Acta 37A (1981) 279-281.

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[35] A.I. Orlova, A.K. Koryttseva, E.E. Loginova, Radiochemistry 53 (2011) 51-62. [36] A.R. Zaripov, V.A. Orlova, V.I. Petkov, O.M. Slyunchev, D.D. Galuzin, S.I.

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Rovnyi, Russ. J. Inorg. Chem. 54 (2009) 45-51. [37] S.P. Kumar, G. Buvaneswari, J. Nuc. Mater. 458 (2015) 224-232. [38] S.P. Kumar, G. Buvaneswari, Mater. Res. Bull. 48 (2013) 324-332. [39] O. Terra, N. Clavier, N. Dacheux, R. Podor, New J. Chem. 27 (2003) 957-967. [40] R.G. Brown, S.D. Ross, Spectrochim. Acta. 26A (1970) 1149-1153. [41] R.D. Shannon, Acta Crystallogr. Sect. A. 32 (1976) 751-757.

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[42] K. Boughzala, E.B. Salem, A.B. Chrifa, E. Gaudin, K. Bouzouita, Mater. Res. Bull.

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Table 1. Lattice parameter of KBaYZrP2SiO12 and KBaYSnP2SiO12 Compounds

Volume (Å3)

Lattice parameter (Å) b

c

KBaYZrP2SiO12

10.30 (5)

10.82 (7)

10.20 (9)

1138

KBaYSnP2SiO12

10.28 (5)

10.22 (7)

10.54 (4)

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Table 2. Comparison of unit cell parameters of KBaREE3+ZrP2SiO12

Volume (Å3)

Lattice parameter (Å)

a

b

c

10.30 (5)

10.82 (7)

10.20 (9)

1138

10.25 (5)

10.46 (6)

10.93 (9)

1173

KBaNdZrP2SiO12

10.76 (1)

10.40 (5)

10.27 (4)

1151

KBaSmZrP2SiO12

10.86 (4)

10.06 (7)

10.14 (5)

1109

KBaEuZrP2SiO12

10.68 (5)

10.20 (4)

10.38 (8)

1131

KBaGdZrP2SiO12

10.28 (6)

10.22 (4)

10.54 (6)

1109

KBaDyZrP2SiO12

10.26 (4)

10.71 (6)

10.16 (6)

1118

KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12

10.39 (5)

10.28 (4)

10.71 (1)

1145

KBaYZrP2SiO12

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KBaLaZrP2SiO12

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Table 3. Assignment of IR bands of KBaREE3+ZrP2SiO12 PO43-

Compositions

SiO44-

υ2

υ3

υ4

υ1

υ2

υ3

υ4

(cm-1)

(cm-1)

(cm-1)

(cm-1)

(cm-1)

(cm-1)

(cm-1)

(cm-1)

KBaYZrP2SiO12

919

497

1054, 1014

553, 580

-

445

-

770

KBaLaZrP2SiO12

939

494

1024

545, 594

-

458

-

743

KBaNdZrP2SiO12

951

499

1012

558, 586

-

448

-

742

KBaSmZrP2SiO12

936

472

1037

559, 584

-

435

-

736

KBaEuZrP2SiO12

939

482

1024

553, 573

-

431

-

743

KBaGdZrP2SiO12

926

485

1038

550

-

428

-

740

KBaDyZrP2SiO12

926

483

1049

564

-

436

-

731

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Table 4. Normalized mass loss of KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 Normalized Elemental Mass Loss (g/m2) Ba×10-2

Zr×10-4

Si×10-1

0.13 0.24 0.35 0.45 0.62 0.80 0.99 1.13 1.35 1.37 1.56 1.73 1.89 2.08 2.04 1.98

0.78 0.85 1.24 1.16 1.32 1.24 0.93 0.99 1.09 1.09 0.93 0.93 0.78 0.78 0.78 0.62

0.33 1.65 2.52 3.44 0.26 0.07 -

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* K, Y, La, Nd, Sm, Eu, P – Below the detection limit (BDL)

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Figure captions Fig. 1. Powder XRD patterns of a. KBaYZrP2SiO12 and b. KBaYSnP2SiO12 Fig. 2. FTIR spectra of a. KBaYZrP2SiO12 and b. KBaYSnP2SiO12

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Fig. 3. a, b) Lower and higher magnified SEM images of KBaYZrP2SiO12 and c, d) Lower and higher magnified SEM images of KBaYSnP2SiO12

Fig. 4. Powder XRD patterns of KBaREE3+ZrP2SiO12 where REE3+ = a. Y, b. La, c. Nd, d. Sm, e. Eu, f. Gd, g. Dy

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Fig. 5. Powder XRD patterns of a) KBaYZrP2SiO12 and b) KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12

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Fig. 6. FTIR spectra of a) KBaYZrP2SiO12 and b) KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 Fig. 7. TGA curve of KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12

Fig. 8. a, b) Lower and higher magnified SEM images and c) EDX spectrum of KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 Fig. 9. Leach rates of Ba and Zr for KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12

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Fig. 10. Powder XRD patterns of KBaY0.6La0.1Nd0.1Sm0.1Eu0.1ZrP2SiO12 a) before and b) after leaching

10 (111)

20

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50 (452) (136) (632)

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(144) (352)

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(121) (112) (220) (022) (202) (221) (212) (310) (301) (131) (311) (222) (302) (032) (203) (231) (132) (040) (400) (312) (140) (330) (133) (223) (412) (214) (323) (422) (242)

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A series of novel langbeinite phosphosilicates have been synthesized.
New langbeinite wasteform has been fabricated and characterized.
Synthesized phosphosilicates were crystallized in orthorhombic structure.

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Dissolution study of the wasteform revealed negligible leaching of lanthanides.