Syntheses of Rare Earth Orthophosphates

Abstract

Rare Earth orthophosphates have been synthesized and examined by X-ray diffraction, DTA and TGA. Six types have been found: a) the monazite type RPO4, b) the xenotime type RPO4, c) the hexagonal form RPO4·0.5H2O, d) the weinschenkite type RPO4·2H2O, e) the orthorhombic form DyPO4·1.5H2O and f) the amorphous phosphate.

Crystal Chemistry and Stability of Hydrated Rare-Earth Phosphates Formed at Room Temperature

“…Hikichi et al [14] reported that a churchite structure in DyPO 4 , YPO 4 , and YbPO 4 formed at a pH of 3 at 20 • C; however, Hikichi et al [43] did not identify a churchite structure for YPO 4 at a pH of 3.7 at 50 • C. The present study also did not detect a churchite structure at a pH of 3 at room temperature. The HREPO 4,hyd structure did not match the structure of any RE phosphate minerals, and only a few peaks in the XRD pattern corresponding to the anhydrous tetragonal structure of the xenotime structure appeared in the HREPO 4,hyd patterns.…”

“…The LREPO 4,hyd that formed at room temperature exhibited a rhabdophane structure similar to [40]. In this study, monazite did not form an primary product from solution at room temperature, although Hikichi and Hukuo [41] and Hikichi et al [14] reported that monazite formed from aqueous solutions at 50 • C and pH < 1 within 28 days and at pH 5 after 900 days. Previous studies also reported that monazite was formed at 90 • C from solutions at pH < 1 [40,42], proceeded by the rhabdophane structure losing hydrated waters as a function of the aging time [40].…”

“…The LREPO4,hyd that formed at room temperature exhibited a rhabdophane structure similar to [40]. In this study, monazite did not form an primary product from solution at room temperature, although Hikichi and Hukuo [41] and Hikichi et al [14] reported that …”

“…The structure depends on physico-chemical parameters such as pH, reaction time, and temperature [14][15][16]. Ionic radii also influence the crystal structure and morphology.…”

Coupled redox transformations of catechol and cerium at the surface of a cerium(III) phosphate mineral

“…Cerium phosphate was synthesized by rapidly mixing 0.5 M phosphoric acid and cerium chloride solutions at 20°C, as described elsewhere (Hikichi et al, 1978). Solid samples were separated from the liquor and rinsed with distilled water until the pH of the supernatant solution was 5.7 ± 0.2. pH measurements were conducted before conducting dissolution experiments.…”