**4.8.3 Lead vanado-iodoapatite**

( ) ( ) ( ) ( )

Strontium bromapatite forms softer crystal than fluorapatite or strontium chlorapatite. Since it is not stable under the mercury-vapor discharge in fluorescent lamp (**Section 10.6**), stronti‐

Other bromapatites are Cd5(PO4)3Br (*a* = 9.733 Å, *c* = 6.468 Å and Z = 2), Cd5(AsO4)3Br (*a* = 10.100 Å, *c* = 6.519 Å and Z = 2) and Cd5(VO4)3Br (*a* = 10.173 Å, *c* = 6.532 Å and Z = 2). They can be grown from melt in platinum crucible filled with Cd3(MO4)2 (M = As, V and P) and the excess

Since, the apatite structure is capable of accommodating monovalent anions, strontium iodoapatites were investigated as a potential waste form to immobilize radioactive iodine

Calcium iodoapatite (Ca5(PO4)3I) does not exist as a separate phase but as oxoapatite. Iodooxyapatite (pentadecacalcium iodide oxide nanophosphate, Ca15(PO4)9(I,O)) was synthesized by the flux method (**Section 4.2**). The crystal structure was refined in the space group P63/M with lattice parameters *a* = 9.567 Å, *b* = 20.754 Å and *Z* = 2. Iodo-oxyapatite has typical hexagonal structure but the unit cell is tripled along the hexad (refer to **Footnote 16** in

Strontium iodoapatite (strontium iodoapatite, strontium iodine-apatite) is of academic interest

functions determined for the alkaline earth apatite series preclude the formation of stable iodoapatite because the cationic size of Sr2+ or Ba2+ is too small relating to that of iodide ion which must fit upon the *c*-axis of the structure next to the triads of Sr2+ or Ba2+ at (000), (010), and (001) positions in the lattice. Such crystals relevant to radioactive waste management include fluorapatite, and, in the end, iodoapatite which should be able to immobilize the

<sup>−</sup> ions compared to other halide ions. However, the thermodynamic

<sup>+</sup> (50)

ions, it must be washed thoroughly to obtain pure product.

<sup>2</sup> 3 4 10 4 2 <sup>6</sup> 10 SrBr aq 6 Na PO aq Sr PO Br s

+ ®

um bromapatite cannot be used for the production of lighting phosphor [135].

of CdBr2. All phases belong to the space group of P63/M [142],[143],[186].

( )

220 Apatites and their Synthetic Analogues - Synthesis, Structure, Properties and Applications

18 NaBr aq

A small amount of hydroxylapatite may also be present.

Since the precipitate contains Na+

**4.7.4 Other bromapatites**

**4.8 Iodoapatites**

**4.8.1 Calcium iodoapatite**

**4.8.2 Strontium Iodoapatite**

due to large size of I

radioactive species [135].

**Chapter 1**) and oxide ions along this direction [135].

[135],[192].

The preparation of lead vanado-iodoapatite (Pb10(VO4)6I2) by hot pressing (HP), isostatic hot pressing (HIP) andsealed-tube method (**Section 4.1.1**) weredescribedin literature. Pb10(VO4)6I2 is thermally stable up to about 800 K. The thermal conductivity of hot-pressed sample, with the theoretical density of 82%, increases gradually with increasing temperature from 0.65 W·m −1·K−1 at room temperature to 0.78 W·m−1·K−1 at 523 K. The leaching rate of iodine for apatite was two orders of magnitude higher than that of AgI glass waste form. Despite the high leaching rate (compared to AgI embedded in glass), high chemical stability up to 800 K and acceptable mechanical properties of this apatite suggest that it be a good waste form when embedded in a suitable matrix material [135],[193].

Facile low temperature solid-state synthesis of iodoapatite by high-energy ball milling of PbI2, PbO and V2O5 was described by Lu et al [195]. As-milled iodoapatite is in the form of amor‐ phous matrix embedded with nanocrystals and can be readily crystallized by subsequent thermal annealing at low temperature of 200°C with minimal iodine loss.
