Phosphates and polyphosphates of the rare-earth elements—I

Buyers, A.G.; Giesbrecht, Ernesto; Audrieth, L. F.

doi:10.1016/0022-1902(57)80054-2

Cited by 24 publications

(5 citation statements)

References 5 publications

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“…3 Lanthanide orthophosphates, LnPO 4 , are normally prepared by high-temperature synthesis at temperatures up to 1300 C. [3][4][5][6][7][8][9][10][11][12] This reaction can take up to two days for completion. Aqueous methods generally yield hydrated phosphates, [13][14][15][16][17][18][19][20][21][22][23][24][25] and in order to obtain monazite (for La-Gd) or xenotime (for Tb-Lu) type phases, further heating up to 1300 C is required. 3,[16][17][18][19][28][29][30][31][32] A glycothermal synthesis in 1,4-butanediol has also been reported.…”

Section: Introductionmentioning

confidence: 99%

Formation of lanthanide phosphates in molten salts and evaluation for nuclear waste treatment

Volkovich

Griffiths

Thied

2003

Phys. Chem. Chem. Phys.

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The formation of phosphates of the lighter lanthanides (Ln ¼ La, Ce, Pr, Nd, Sm, Eu, Gd, Tb and Dy) by reaction with alkali metal phosphates has been studied in a LiCl-KCl eutectic melt between 450 and 650 C and in a NaCl-KCl equimolar melt at 750 C and under an inert atmosphere. Alkali metal ortho-, meta-and pyrophosphate precursors have been employed. The reaction results in the formation of single lanthanide or double alkali metal-lanthanide orthophosphates, the former favoured in LiCl-KCl melts and the latter in NaCl-KCl melts. The mean crystallite size of precipitated phosphates was evaluated from X-ray powder diffraction patterns, and found to be within 300-450 A ˚. Increasing the melt temperature results in increasing the crystallite size of phosphate phases. This technique offers an attractive means of removing lanthanide fission products from chloride melts arising from pyrochemical reprocessing of spent nuclear fuels. LiCl-KCl based melts are recommended because the bulk of phosphate waste precipitated is smaller since normal rather than double phosphates are formed therein.

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Section: Introductionmentioning

confidence: 99%

Formation of lanthanide phosphates in molten salts and evaluation for nuclear waste treatment

Volkovich

Griffiths

Thied

2003

Phys. Chem. Chem. Phys.

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“…The decreased surfactant adsorption from pH 4.0-6.0 was probably produced by the decreased positive charge on the precipitate as La3+ and LaF2+ (Figure 1) were reduced. Studies by Buyers and Andrieth (1950) showed that H + adsorption was probably not significant at pH 54.5, but H + adsorption might have influenced the charge above pH 4.5.…”

Section: Discussion Of Flotation Resultsmentioning

confidence: 99%

Precipitate coflotation of orthophosphate and fluoride

1972

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Orthophosphate and fluoride are simultaneously precipitated from aqueous solution, 5.26 X 10-3 M. in each, by La (111). The precipitates are cofloated by the anionic surfactant sodium laurylsulfate, with optimum flotation at pH 4.0 and a stoichiometric lanthanum concentration based on LaP04 and LaF3. Over pH 3.5 to 6.0, better than 95% flotation of the total orthophosphate and precipitated fluoride that are present can be floated at a molar sodium laurylsulfate to orthophosphate plus fluoride ratio of 0.023.At lower sodium laurylsulfate concentrations, the flotation decreases at pH 3.5 and 6.0 compared to pH 4.0-5.0; at pH 4.0, an increase in the La(II1) concentration decreases the flotation. SCOPEThe removal of a soluble ionic species from aqueous solution followed by concentration in a foam or froth can be accomplished by precipitating the ion, then by adding a surface-active agent to act as a collector-frother, and then by aerating the suspension and floating the precipitate-surfactant particulates to the surface of the suspension. The initial charge of the precipitate has a significant effect on the adsorption (or exchange) of the surfactant on the particles, with the change established either by desorption of one of the ionic species of the solid or by adsorption of ions from solution onto the surface of the crystal. The constituent ions of the precipitate present in solution are preferentially adsorbed over other ions. The surfactant, added as a collector-frother in a flotation process, serves three or more functions: the adsorption (or exchange) of the surfactant on the surfaces of the particles makes the precipitate suitable for gas bubble attachment (the surfactant may also promote aggregation of the precipitate, becoming incorporated in the precipitate structure); interaction between surfactant adsorbed on the particles and "free" surfactant adsorbed at the gas-liquid, bubble interfaces produces bubble attachment to the particles; and "free" surfactant acts as a frother, producing a stable foam, which may be further by the presence Of particulates.The objective of this work is to investigate experimentally the simultaneous precipitation of orthophosphate and fluoride by lanthanum (La (111)) over an acidic pH range (pH 3.5 to 6.0), followed by coflotation of LaPOl plus LaF3 (plus crystals containing both orthophosphate and fluoride) with a single surfactant. The effects of pH, lanthanum concentration, and surfactant concentration are discussed in terms of flotation results, in terms of calculated and experimentally-measured solution concentrations of the ionic species of significance, and in terms of the characteristics of the precipitate particles. Lanthanum has been reported as an orthophosphate precipitant superior to A1 (111), Fe (111), and Ca (11) salts (Recht et al., 1971;Leckie and Stumm, 1970; Yuan and Hsu, 1970). In particular, at the same cation to orthophosphate ratios, La (111) has yielded lower soluble orthophosphate concentrations (by as much as three orders of magnitude) over a broader pH ...

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“…The similarity of behaviour of La and Ce is not surprising since the stability constants for the various complexes and solids of b o t h R E E are v e r y s i m i l a r . P h o s p h a t e precipitation of REE from aqueous solution has been documented by Buyers et al (1957) and Kanapilly (1980). In nature, REE often occur as p h o s p h a t e m i n e r a l s such as m o n a z i t e and xenotime, whose solubilities are low enough that they persist as c o m m o n c o m p o n e n t s of heavy beach sands (Jonasson et al, 1985).…”

Section: Rare Earth Species In Solutions 253mentioning

confidence: 99%

Use of GEOCHEM-PC to predict rare earth element (REE) species in nutrient solutions

1993

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The interpretation of results of some experiments examining effects of rare earth elements (REE) on plant growth may have been complicated by rare earth phosphate precipitation. Simulations were undertaken using the computer model GEOCHEM-PC to define REE solubility limits and predict REE species in low and high ionic strength nutrient solutions. In low ionic strength solutions containing 5 ~tM P, lanthanum phosphate (LaPO~) precipitation is predicted to occur at solution pH>4.0, reaching a maximum (>95% of total) at pH 5.5. In high ionic strength solutions (1000 ~tM P) over 95% of the La is predicted to precipitate as phosphate at pH>4.0. The predicted behaviour of cerium (Ce) was closely similar to that for La. At pH 5.5, the concentration of REE species in solution can be increased only after virtually all the P has been precipitated. Consequently, it is important to consider REE-P interactions in nutrient solutions when investigating REE effects on plant growth.

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Phosphates and polyphosphates of the rare-earth elements—I

Cited by 24 publications

References 5 publications

Formation of lanthanide phosphates in molten salts and evaluation for nuclear waste treatment

Formation of lanthanide phosphates in molten salts and evaluation for nuclear waste treatment

Precipitate coflotation of orthophosphate and fluoride

Use of GEOCHEM-PC to predict rare earth element (REE) species in nutrient solutions

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