Hydroxyapatite [HAP, Ca10(PO4)6(OH)2], is well documented as a metals sequestration medium. Here, the surface of HAP was amended to enhance these properties. Surface-amended HAP was tested on two aqueous contaminants�As, a metalloid in its arsenite and arsenate oxoanionic forms, and U(VI), a cationic metal. In one test, the surface was amended with either ferric or ferrous iron, forming amorphous phases of iron phosphates. In another test, the HAP surface was amended by creating a vanadate-substituted near-surface rind. Unamended HAP was tested as a control medium. A series of flow-through and batch laboratory-based experiments were conducted to test the As or U removal efficacy of the amended and unamended materials. The material surface areas were analyzed using the BET method. Resulting solutions were analyzed via ICP-MS to determine As/U removal. Solid-phase analyses were performed using TGA, SEM-EDS, TEM, and XRD to determine the resulting surface chemistry and crystallinity for both the iron- and vanadate-amended surfaces and those resulting from As and U solution interactions. Arsenite removal increased with increasing As(III) concentration with iron-modified HAP. Removal ranged from 8% at 52 �M initial As(III) concentration to 28% at 3.8 mM initial As(III) concentration on ferric-amended HAP. Arsenate removal also increased with iron-modified HAP but decreased with increasing As(V) concentration. Removal ranged from 10% at 6.0 mM initial As(V) concentration to 82% at 12 �M initial As(V) concentration on ferric-amended HAP. Removal trended similarly with ferrous-amended HAP. Thermodynamic modeling showed increased removal of U(VI) is favorable with the vanadate-amended HAP, providing phosphate for potential uranyl phosphate precipitation, as well as vanadate for precipitation of uranyl vanadate or mixed vanadate-phosphates which are significantly more stable than uranyl phosphates alone. Laboratory-based experiments tested relative uptake rates as well as conversion percentages and rates from sorbed U(VI) to precipitates between unamended and amended HAP.

Improving oxoanionic metalloid and cationic metal remediation of hydroxyapatite via surface modification

247th National Meeting (2014)

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