Some thermodynamic aspects of dissolution of solid solutions of hydroxylapatites of phosphorus and arsenic

Narasaraju, T. S. B.; S., U.

doi:10.1139/v79-431

Cited by 5 publications

(14 citation statements)

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“…[5] The reflection peaks of HAP and AsHAP were slightly different from each other. The reflections of the Ca 5 (P x As 1-x O 4 ) 3 (OH) solid solutions shifted gradually to a higher-angle direction when the mole fraction of Ca 5 (AsO 4 ) 3 (OH) of the solids decreased.…”

Section: àmentioning

confidence: 94%

“…[5] It is also obvious that there was a steep increase in the amount of dissolved calcium, phosphate and arsenate and the accompanying decrease in solution pH between x ¼ 0.43 (AsPHA-4) and x ¼ 0.71 (AsPHA-7) with peak values at x ¼ 0.54 (AsPHA-5) or x ¼ 0.63 (AsPHA-6) for the aqueous dissolution of the Ca 5 (P x As 1Àx O 4 ) 3 (OH) solid solutions. This phenomenon was also observed by other researchers.…”

Section: Evolution Of Aqueous Compositionmentioning

confidence: 99%

“…[2,3] Hydroxylapatite shows a high capacity for substitutions of Ca and PO 4 3À by other cations and anions due to its crystal structure and chemical composition, [4] significant among which from the point of view of arsenic poisoning being the substitution of PO 4 3À by AsO 4 3À resulting in the formation of its isomorph, arsenate hydroxylapatite (AsHAP). [5][6][7] Arsenic toxicity is a global health problem affecting many millions of people. [8] Occurrences of dissolved arsenic in surface and ground waters and observed adverse health effects have emphasised the need for better understanding of reactions that govern arsenic mobility in the environment.…”

Section: Introductionmentioning

confidence: 99%

“…[15] Some synthesis experiments at ambient temperatures were conducted to evaluate the conditions of formation and solubilities of different calcium arsenates. [11,16,17] Hydroxylapatite (HAP) is one of the most stable forms of calcium phosphate and exhibits a low solubility (K sp ¼ 10 À53.02 -10 À53.51 ); however, the solubility of AsHAP [Ca 5 (AsO 4 ) 3 (OH)] is significantly greater than that of HAP, [11,[18][19][20][21][22] which suggested that phosphate substitution in the arsenate compound could significantly reduce their solubilities. [21][22][23][24] The thermodynamic properties of solid solutions have a vital influence on the transport and fate of toxic metals in the environment.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, there are insufficient data upon which to assess the true environmental risk of arsenic posed by these minerals. [5] In the present study, a series of the Ca 5 (P x As 1Àx O 4 ) 3 (OH) solid solutions (AsPHA) with different P/(PþAs) atomic ratios were prepared by a precipitation method. The resulting solid solution particles were characterised by various techniques.…”

Section: Introductionmentioning

confidence: 99%

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Dissolution and solubility of the arsenate - phosphate hydroxylapatite solid solution [Ca5(PxAs1 - xO4)3(OH)] at 25°C

et al. 2011

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Environmental context. Apatites form a large family of minerals and compounds that can incorporate a variety of ions, including arsenate that can substitute for phosphate. Apatites may therefore control the concentration of arsenic in some aqueous environments. This manuscript describes the synthesis and characterisation of the arsenate-phosphate hydroxylapatite solid solution and the solid solution-aqueous solution interaction.Abstract. Nine different members of the arsenate-phosphate hydroxylapatite solid solution [Ca 5 (P x As 1Àx O 4 ) 3 (OH)] were prepared and characterised by various techniques, and then dissolution of the synthetic solids was studied at 258C and pH 2 in a series of batch experiments. The concentrations of aqueous arsenate species increased rapidly at the beginning of the dissolution and reached a steady-state after 480 h. The concentrations of aqueous phosphate species increased very fast initially and reached a peak value within the first hour of dissolution and then declined slowly with time and remained constant after 240-360 h. The solubility of the Ca 5 (P x As 1Àx O 4 ) 3 (OH) solid solution increased and its stability decreased with an increase in the mole fraction of Ca 5 (AsO 4 ) 3 (OH). The dissolution followed or slightly overshot the Lippmann solutus curve, then approached the solutus curve. The Ca 5 (AsO 4 ) 3 (OH)-poor solid solution was in equilibrium with the arsenate-rich aqueous solution.

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Section: àmentioning

confidence: 94%

Section: Evolution Of Aqueous Compositionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Dissolution and solubility of the arsenate - phosphate hydroxylapatite solid solution [Ca5(PxAs1 - xO4)3(OH)] at 25°C

et al. 2011

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Characterization, dissolution and solubility of synthetic svabite [Ca5(AsO4)3F] at 25–45°C

et al. 2010

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Svabite is a secondary arsenate mineral, calcium fluoride arsenate [Ca 5 (AsO 4 ) 3 F], in the apatite group of phosphates. Its dissolution and subsequent release of aqueous species play an important role in the cycling of arsenic and fluoride in the environment, but the thermodynamic and kinetic properties of svabite dissolution have never been investigated. In the present study, svabite was prepared by precipitation and characterized by various techniques, and then dissolution of synthetic svabite was studied at 25, 35 and 45°C in a series of batch experiments. In addition, the aqueous concentrations from the batch dissolution were used to calculate the solubility product and free energy of formation of svabite. The results of the X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy analyses indicated that the synthetic, microcrystalline svabite with apatite structure used in the experiments has not changed after dissolution. For the dissolution of svabite [Ca 5 (AsO 4 ) 3 F] in ultrapure water, F -ions were initially found to dissolve preferentially when compared with calcium and arsenate. Preferential dissolution of arsenate when compared with that of calcium was also observed. Dissolution of svabite in aqueous medium appeared to be always non-stoichiometric at the beginning, but when a dissolution equilibrium or steady state was reached at 25 and 35°C, the solid dissolved almost stoichiometrically. The release of calcium, arsenic and fluoride to solution increased with decreasing temperature. The mean K sp value was calculated for Ca 5 (AsO 4 ) 3 F of 10 -39.21 (10 -39.18 * 10 -39.24 ) at 25°C; the free energy of formation DG f o [Ca 5 (AsO 4 ) 3 F] was -5210.46 kJ/mol.

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Synthesis and Characterization of Arsenate/Phosphate Fluorapatite Solid Solutions

Zhu

Chen

Long

et al. 2009

Metall Mater Trans A

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A series of arsenate-substituted fluorapatite (FA) was directly prepared through the aqueous precipitation method. Characterization studies from elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, and scanning electron microscopy (SEM) have confirmed the formation of the arsenate/phosphate fluorapatite solid solutions (AsPFAs), i.e., Ca 5 (P x As 1-x O 4 ) 3 F, which had a single phase of apatite structure. The analysis of the measurements indicated that the unit cell a and c parameters did not vary smoothly with the degree of substitution, as expected by Vegard's law. The morphology was dependent of the arsenate/phosphate ratio. The solids with high As/(P + As) molar ratio of 0.29 to 1.0 were typically needlelike crystals, which developed along the c-axis; all apatites with the As/(P + As) molar ratio of <0.09 were large tabular. The phosphate peaks and the arsenate peaks in the FT-IR spectra were observed for the entire series of substituted apatites. The area of the phosphate peak was gradually suppressed and that of the arsenate peak increased as the proportion of the arsenate increased.

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Some thermodynamic aspects of dissolution of solid solutions of hydroxylapatites of phosphorus and arsenic

Cited by 5 publications

References 0 publications

Dissolution and solubility of the arsenate - phosphate hydroxylapatite solid solution [Ca5(PxAs1 - xO4)3(OH)] at 25°C

Dissolution and solubility of the arsenate - phosphate hydroxylapatite solid solution [Ca5(PxAs1 - xO4)3(OH)] at 25°C

Characterization, dissolution and solubility of synthetic svabite [Ca5(AsO4)3F] at 25–45°C

Synthesis and Characterization of Arsenate/Phosphate Fluorapatite Solid Solutions

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