title: The effect of silica fume on biodegradation of cement paste and its capacity to immobilize strontium during exposure to microbial sulfur oxidation.
abstract: The disposal of low-level radioactive waste containing isotopes such as strontium by immobilization in cement paste has become common practice. However, the stability of cement paste in the environment may be impaired by sulfuric acid produced by sulfur-oxidizing bacteria. Since biodegradation rates in the environment of most radioactive waste burial sites are too low to be measured, determination of the degradation kinetics of cement paste is a difficult task. This study reports on the development of an accelerated biodegradation system for cement pastes in which the cement paste is exposed to a continuous culture of the sulfur-oxidizing bacterium Halothiobacillus neapolitanus. This system facilitated detection of the biodegradation processes in cement paste after as short a time as 15 days. A comparison of the durability of a cement paste blended with silica fume with that of unblended cement paste showed that the silica fume induced an increase in the leaching of Ca(+2) and Si and enhanced weight loss, indicating rapid deterioration in the structural integrity of the cement paste. The leaching of Sr(+2) from the silica fume amended cement paste was slightly reduced as compared with the non amended cement paste, indicating an increase in immobilization of strontium. Nevertheless, our findings do not support the use of silica fume as a suitable additive for immobilization of low-level radioactive waste.
authors.affiliation: Department of Biotechnology Engineering, Ben Gurion University of the Negev, P. O. Box 653, Beer Sheva 84100, Israel.
authors.forename: Merav
authors.initials: M
authors.lastname: Fisher
authors.forename: Gabi
authors.initials: G
authors.lastname: Bar-Nes
authors.forename: Yehuda
authors.initials: Y
authors.lastname: Zeiri
authors.forename: Alex
authors.initials: A
authors.lastname: Sivan
mesh_terms: D001673:Biodegradation, Environmental; D018441:Biofilms; D044222:Halothiobacillus / Q000187:drug effects* / Q000378:metabolism*; D008855:Microscopy, Electron, Scanning; D010084:Oxidation-Reduction; D012822:Silicon Dioxide / Q000494:pharmacology*; D013324:Strontium; D013457:Sulfur Compounds / Q000378:metabolism*; D013464:Sulfuric Acids / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology
chemical_list: D013457:Sulfur Compounds; D013464:Sulfuric Acids; D012822:Silicon Dioxide; C033158:sulfuric acid; D013324:Strontium