Radioiodide Sorption to Sediment Minerals
- PDF / 500,849 Bytes
- 7 Pages / 386.64 x 620.1 pts Page_size
- 67 Downloads / 186 Views
Res. Soc. Symp. Proc. Vol. 556
© 1999
Materials Research Society
difference in I and IO3; sorptive behavior is not known but is presumably the result of the "harder" base nature of IO3-, as compared to F, which would favor "hard-hard" interactions with the "hard" acid sites on the mineral surfaces. Iodide sorption to other sediment minerals is generally quite limited. Ticknor and Cho (6) reported no F sorption to calcite or muscovite using a pH 7.7 synthetic groundwater dominated by Ca, Na and Cl. Muramatsu et al. (7) reported essentially no sorption of F from distilled water onto bentonite and Fe2O3 using distilled water. Sazarashi et al. (8) reported no P sorption (F Kd = 0 mL/g) to montmorillonite (10-6 M KI and 5-day contact period). Ticknor et al. (9) reported low F-Kd values for biotite, 0.7 mL/g, and montmorillonite, 1.9 mL/g, when measured in a pH 7.7 synthetic groundwater that was dominated by the Ca, Na, Cl, and S04 ions. De et al. (10) reported either no adsorption or negative adsorption (anion exclusion) for F onto montmorillonite and kaolinite suspension in contact with 3.175 and 2.595 mg/L KI solutions, respectively. Subsurface arid sediments are the most common type of sediments contaminated by radioiodine or at risk to be contaminated by radioiodine by proposed nuclear waste storage (e.g., Hanford Site in Richland, Washington, Idaho National Engineering and Environmental Laboratory in Idaho Falls, Idaho). These sediments tend to contain very low concentrations of organic carbon ( vermiculite > goethite >> montmorillonite. The fact that the surface-area normalized Kd value of the illite remained appreciably greater than the other minerals, suggests that the surface area alone was not responsible for the high P sorption capacity of the illite. The unique mineralogical properties of the illite that permitted it to sorb large amounts of I are not known. A computer-assisted review of the literature revealed that high I-sorption to illite has previously been reported, albeit these reports are few and separated by many years. De et al. (10) reported that illite sorbed -99% of the F initial added as 31.75 mg/L I-(KI) in deionized water. They also reported that I tended to sorb appreciably more to natural sediments with clay fractions dominated by illite rather than sediments dominated by kaolinite or montmorillonite. Unfortunately, the conditions of the experiments conducted by De et al. (10) were not fully described and those that were described were quite different from the conditions of this study. They contacted the illite for only 2 hr with
Eo
2
-
+0
+I
cd
>~
+IcJ
+I +I+1
+1
I
0
0)
~ 1+1 +~0
0
+1
c)
cz
E0+ 0
c'0s 0)- 0
-
-
0000
-
Cls
o
2
-
--
-
M
0
E 0-0
>
0)
c~0,
'i
Cl
-
0clC
M
U
ri U
1062
O0)
)
0
Ticknor et al. (9) reported a low F Kd value of 0.4 ± 2.9 mL/g for a goethite sample acquired from the same location (Biwabik, Minnesota) as the goethite used in this study. The goethite Kd values measured in this study were 0.10 ± 0.03 and 0.07 ± 0.05 mL/
Data Loading...
