**Author details**

Davis et al. [44] used the generalized composite model with variations of defining equilibria

HCO3

Waite et al. [58] investigated U(VI) adsorption onto ferrihydrite as a function of U(VI) concen-

octahedron edge and the uranyl ion. The U-interacting surface reactions without CO2

ground electrolyte. Aluminol surface sites were dominant with adsorption of UO2

]UO<sup>2</sup> + 2H+

2− + 2H+

McKinley et al. [46] observed U(VI) hydrolysis and adsorption onto smectite (SWy-1) at three ionic strengths over a pH range of 4.0–8.5. At low ionic strength, U(VI) adsorption decreased from pH 4 to pH 7, whereas at higher ionic strengths, U(VI) adsorption increased with increasing pH, an attribute attributed to uranyl hydrolysis and cation exchange involving the back-

similar experimental conditions to investigate U(VI) adsorption onto ferruginous beidellite (smectite family) over a pH range from 4.0 to 10.0. The adsorption envelopes for both Al (gibbsite) and Si (silica) began near pH 4 and declined near pH 5.5. With the U(VI) concen-

HUO2

constraints, in general, the adsorption species dominance was (1) SO<sup>2</sup>

)3− (pH ≈ 8) and (6) SO<sup>2</sup>

**Table 12.** Surface reactions on surface adsorption modeling (Herbelin and Westall [74]).

2+ = [FeO<sup>2</sup>

UO2 CO3

surface complexes (weak and strong ≡FeOH), they hypothesized that UO<sup>2</sup>

K = −6.28 for the weak site. The U-interacting surface reactions with CO<sup>2</sup>

]UO<sup>2</sup> CO3

2+ onto mixed mineralogy samples from the Koongarra

partial pressures. Given the different model equilibrium

3− (pH 7.5–8.7), (4) SO<sup>2</sup>

) formed inner sphere mononuclear, bidentate complexes involving the Fe

was important in alkaline pH on SiOH edge sites. Turner et al. [49] employed

) and silica (α-SiO<sup>2</sup>

at 10−7 mol U/L, the model predicted the U aqueous species to be

2+ initial equilibration concentration was 3.9 ×

(pH ≈ 6), where S is the surface site.

with log K = −2.57 for the strong site and log

with log K = 3.67 for the strong site and log

. Using the diffuse double layer model with two site

UO2

UO2

HCO3

(pH 5.2–5.6), (2)

and at higher pH

participation were

1− (pH 6.5–

partici-

2+, whereas

) equilibrations under

to model adsorption scenarios of UO2

(HCO3

tration and the partial pressure of CO2

10−6 mole U/L with variable CO2

UO2

(CO3

] + UO<sup>2</sup>

K = −0.42 for the weak site.

tration established at UO2

pation were [≡Fe(OH)<sup>2</sup>

SO<sup>2</sup> UO2 CO3

7.8), (5) SO<sup>2</sup>

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> + UO2

S(OH)<sup>2</sup> ± UO<sup>2</sup>

where S(OH)<sup>2</sup>

2+ = SO<sup>2</sup>

2+ = SO<sup>2</sup> UO2 2+ + 2H+

2+ + H2

2+ + H2

2+ + H2

2+ + 2H2

2+ + 2H2

2+ + 2H2

2+ + 2H2

HUO2

CO3 = SO<sup>2</sup>

CO3 = SO<sup>2</sup>

CO3 = SO<sup>2</sup>

CO3 = SO<sup>2</sup>

CO3 = SO<sup>2</sup>

CO3 = SO<sup>2</sup>

CO3 = SO<sup>2</sup>

is the surface site.

2+ + H+

134 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

UO2 H2

UO2 HCO3

UO2 CO3 2− + 4H+

UO2 H2 CO3 HCO3

UO2 (H2 CO3 )2 2− + 4H+

UO2 CO3 HCO3

UO2 (CO3 )2 4− ± 6H<sup>+</sup>

CO3 + 2H+

<sup>−</sup> + 3H+

<sup>−</sup> + 3H+

<sup>−</sup> + 5H<sup>+</sup>

levels, UO2

[≡Fe(OH)<sup>2</sup>

(UO2 )3 (OH)<sup>5</sup> +

W2 (Australia) U-impacted samples. The UO2

2− (pH 8.3–8.5), (3) SO<sup>2</sup>

] + UO<sup>2</sup>

2+ + CO2 = [FeO<sup>2</sup>

a composite model based on gibbsite (α-Al(OH)<sup>3</sup>

Michael Thomas Aide

Address all correspondence to: mtaide@semo.edu

Department of Agriculture, Southeast Missouri State University, Cape Girardeau, Missouri, USA
