Strontium Immobilization by Fibrous Cerium(IV) Bis(monohydrogenphosphate) under Hydrothermal Conditions

Abstract

The uptake of strontium ions from an aqueous solution by fibrous cerium(IV) bis(monohydrogenphosphate) has been studied from the viewpoints of the immobilization of strontium in radioactive waste by a batchwise operation in the temperature range from 25 to 250 °C. Strontium ions can be exchanged below 100 °C following an ion-exchange reaction between hydrogen ions of the phosphate groups. In contrast, strontium ions can be effectively immobilized under hydrothermal conditions accompanied by a structural change of the exchanger, where divalent strontium ions are incorporated into the monazite-like compound to compensate tetravalent cerium ions in trivalent cerium orthophosphate system. This phenomenon is peculiar to alkaline earth metal ions, since the monazite-like compounds were obtained in the presence of Ca2+ and Ba2+, while this phenomenon was absent in the presence of Cu2+ or Ni2+.

First rare-earth phosphate aerogel: sol–gel synthesis of monolithic ceric hydrogen phosphate aerogel

“…In the diffractograms of these samples, at 2 ~8°, one can observe a pronounced broadened maximum, which may indicate the existence of short-range order in ceriumcontaining hydrogen orthophosphate gels with a characteristic distance of ~1.1 nm. The presence of this peak for cerium-phosphate gels has also been reported previously [40,45]. Hayashi et al [46] presumed that the presence of this peak is due to the layered structure of the gels allowing them to be intercalated with e.g.…”

1D Ceric Hydrogen Phosphate Aerogels: Noncarbonaceous Ultraflyweight Monolithic Aerogels

“…According to the X-ray diffraction (XRD) data, the aerogels had a nearly amorphous structure, with the most intense peak at 7.8°2θ corresponding to an interplanar distance of 1.1 nm (Figure S1). In a number of previous works, similar diffraction patterns have been observed for poorly crystalline materials based on fibrous cerium­(IV) phosphates; − the presence of a broad peak at low 2θ angles was assigned to the layered structure of the materials. A detailed analysis of the XRD data (Figure S1) showed the presence of low intensity peaks that can be attributed to a rhabdophane structure (CePO 4 · x H 2 O).…”

Meet the Cerium(IV) Phosphate Sisters: CeIV(OH)PO4 and CeIV2O(PO4)2

“…In 1975, Herman and Clearfield [18] suggested the existence of af amily of cerium(IV) basic hydrogenphosphates with the general formula Ce(OH) x (PO 4 ) x (HPO 4 ) 2À2x .T he limiting member of this family (x = 1) should be ceric basic phosphate, Ce(OH)(PO 4 ), however,a ccording to Herman and Clearfield, [18] the compositiono ft his compound corresponds to the formula Ce(OH) 0.7 (PO 4 ) 1.1 .A ni denticalc ompoundw as apparently obtained by Hayashi et al [19] At the same time, in the later works of Nazaraly et al, [20] it was shown that the composition of the compound Ce(OH) 1.62 (NH 4 HPO 4 ) 0.35 (H 2 PO 4 ) 0.68 (PO 4 ) 0.45 •0.6 H 2 O, determined by Herman and Clearfield, [18] was erroneous, which casts doubt on the other conclusions of these authors' work. [18] It is worth noting that the existence of Ce(OH)PO 4 was also assumed by Lebedev and Rudenko [21] and Tananaev et al [22] Hayashi et al [23] synthesized crystallinec erium(IV) hydroxidophosphate with the compositionCe(HPO 4 )(PO 4 ) 0.5 (OH) 0.5 ,but Nazaraly et al [24] reliably provedt hat this compound's composition is actually Ce(PO 4 )(HPO 4 ) 0.5 (H 2 O) 0.5 .…”

“…The limiting member of this family ( x= 1) should be ceric basic phosphate, Ce(OH)(PO 4 ), however, according to Herman and Clearfield, the composition of this compound corresponds to the formula Ce(OH) 0.7 (PO 4 ) 1.1 . An identical compound was apparently obtained by Hayashi et al . At the same time, in the later works of Nazaraly et al., it was shown that the composition of the compound Ce(OH) 1.62 (NH 4 HPO 4 ) 0.35 (H 2 PO 4 ) 0.68 (PO 4 ) 0.45 ⋅ 0.6 H 2 O, determined by Herman and Clearfield, was erroneous, which casts doubt on the other conclusions of these authors’ work .…”