Influence of in situ Biofilm Coverage on the Radionuclide Adsorption Capacity of Subsurface Granite

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• 作者：Craig Anderson ; Anna-Maria Jakobsson ; Karsten Pedersen
• 刊名：Environmental Science & Technology
• 出版年：2007
• 出版时间：February 1, 2007
• 年：2007
• 卷：41
• 期：3
• 页码：830 - 836
• 全文大小：189K
• 年卷期：v.41,no.3(February 1, 2007)
• ISSN：1520-5851

文摘

Any migration of radionuclides from nuclear wasterepositories is expected to be mitigated by adsorption tothe host rocks surrounding hydraulically conductive fractures.Fluid rock interfaces are considered to be importantbarriers for nuclear waste disposal schemes but theiradsorptive capacity can be affected by the growth ofmicrobial biofilms. This study indicates that biofilms growingon fracture surfaces decrease the rocks adsorptioncapacity for migrating radionuclides except for trivalentspecies. Potential suppression of adsorption by biofilmsshould, therefore, be accounted for in performance safetyassessment models. In this study, the adsorptive capacityof in situ anaerobic biofilms grown 450 m underground oneither glass or granite slides was compared to thecapacity of the same surfaces without biofilms. Surfaceswere exposed to the radiotracers ⁶⁰Co(II), ¹⁴⁷Pm(III),²⁴¹Am(III), ²³⁴Th(IV), and ²³⁷Np(V) for a period of 660 h in apH neutral anaerobic synthetic groundwater. Adsorptionwas investigated at multiple time points over the 660 h usingliquid scintillation and ICP-MS. Results indicate thatthese surfaces adsorb between 0 and 85% of the addedtracers under the conditions of the specific experiments.After 660 h, the distribution coefficients, R (ratio betweenwhat is sorbed and what is left in the aqueous phase),approached 3 × 10⁴ m for ⁶⁰Co, 3 × 10⁵ m for ¹⁴⁷Pm and²⁴¹Am, 1 × 10⁶ m for ²³⁴Th, and 1 × 10³ m for ²³⁷Np. The highestrate of adsorption was during the first 200 h of theadsorption experiments and started to approach equilibriumafter 500 h. Adsorption to colloids and precipitatescontributed to decreases of up to 20% in the available⁶⁰Co, ¹⁴⁷Pm, ²⁴¹Am, and ²³⁷Np in the adsorption systems. Inthe ²³⁴Th system 95% of the aqueous ²³⁴Th was removedby adsorbing to colloids. Although the range of R values foreach surface tested generally overlapped, the biofilmsconsistently demonstrated lower R values except for thetrivalant ¹⁴⁷Pm and ²⁴¹Am adsorption systems.