Effect of Reaction Pathway on the Extent and Mechanism of Uranium(VI) Immobilization with Calcium and Phosphate

Abstract

Phosphate addition to subsurface environments contaminated with uranium can be used as an in situ remediation approach. Batch experiments were conducted to evaluate the dependence of the extent and mechanism of uranium uptake on the pathway for reaction with calcium phosphates. At pH 4.0 and 6.0 uranium uptake from solution occurred via autunite (Ca(UO2)2(PO4)2) precipitation irrespective of the starting forms of calcium and phosphate. At pH 7.5, a condition at which calcium phosphate solids could form, the uptake mechanism depended on the nature of the calcium and phosphate as determined by X-ray absorption spectroscopy and laser-induced fluorescence spectroscopy. When dissolved uranium, calcium, and phosphate were added simultaneously, uranium was structurally incorporated into a newly formed amorphous calcium phosphate solid. Adsorption was the dominant removal mechanism for uranium contacted with preformed amorphous calcium phosphate solids. When U(VI) was added to a suspension containing amorphous calcium phosphate solids as well as dissolved calcium and phosphate, then removal occurred through precipitation (57 ± 4%) of autunite and adsorption (43 ± 4%) onto calcium phosphate. Dissolved uranium, calcium, and phosphate concentrations with saturation index calculations helped identify removal mechanisms and determine thermodynamically favorable solid phases.

Uranium removal from mining water using Cu substituted hydroxyapatite

“…High costs associated with pumpand-treat remediation strategies and toughening of regulatory requirements regarding sewage discharge have prompted research into more effective methods 1,2 . In this field, new methods involving hydroxyapatite (Hap) amendments to immobilize U(VI) as a nonlabile uranyl phosphate phase have been extensively studied [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] . The rationale for using these methods is the is the less soluble one (Erreur !…”

“…However, the precipitation of U-phosphate phases of the autunite group is not the only mechanism of immobilization observed when using Hap as reactive material to remove uranium from contaminated solutions. Surface complexation, ion exchange [5][6][7][8]12 and surface mineralization 28 can occur depending on the composition of the solution and the total uranium concentration,. The fluor-apatite structure can also accommodate hexavalent uranium by substitution in the Ca1 site 29 .…”

Multifunctional Inorganic‐Organic U‐MOF Materials with Nitrogen Heterocyclic Carboxylate: Synthesis, Structure and Properties

“…It has been an active area of exploration on uranyl complexes since the suitable starting materials were discovered. [1,2] The uranium, as a good candidate element for mixed organicinorganic extended networks complexes has novel chemical compositions and physicochemical properties, [3][4][5][6][7] such as biomedical imaging, [8,9] luminescence sensors [10] and sensors over light-emitting devices (LEDs, OLEDs). [11,12] ion exchange, [13] proton conductivity, [14] intercalation chemistry, [15] photochemistry, [16] nonlinear optics, [17] selective oxidation catalysis, nuclear power, [18] X-ray attenuation and detection [19,20] and so on.…”

Comparative analysis of uranium bioassociation with halophilic bacteria and archaea

“…In addition to microbially induced reduction, the formation of insoluble minerals by microorganisms (biomineralization) is another possible retention process. The formation of uranyl phosphate minerals has been commonly observed [ 25 – 27 ].…”