Technetium Reduction and Permanent Sequestration by Abiotic and Biotic Formation of Low-Solubility Sulfide Mineral Phases

doi:10.2172/1225844

GSTDTAP > 地球科学

DOI	10.2172/1225844
报告编号	None
来源ID	OSTI ID: 1225844
	Technetium Reduction and Permanent Sequestration by Abiotic and Biotic Formation of Low-Solubility Sulfide Mineral Phases
	Tratnyek, Paul G.; Tebo, Bradley M.; Fan, Dimin; Anitori, Roberto; Szecsody, Jim; Jansik, Danielle
	2015-11-14
出版年	2015
页数	103
语种	英语
国家	美国
领域	地球科学
英文摘要	One way to minimize the mobility of the Tc^VII oxyanion pertechnetate (TcO₄^-) is to effect reduction under sulfidogenic conditions (generated abiotically by Fe₀ or biotically) to form TcS_x, which is significantly slower to oxidize than Tc^IVO₂. In sediment systems, TcS_x and other precipitates may oxidize more slowly due to oxygen diffusion limitations to these low permeability precipitate zones. In addition, the TcO₄^- reduction rate may be more rapid in the presence of sediment because of additional reductive surface phases. This project aims to provide a fundamental understanding of the feasibility of immobilization of TcO₄^- as TcS_x in the vadose zone or groundwater by application nano zero-valent iron (nZVI), and sulfide or sulfate. Biotic batch experiments have used the sulfate-reducing bacterium (SRB) Desulfotomaculum reducens. The iron sulfide mineral mackinawite was generated under these conditions, while vivianite was formed in nZVI only controls. The sulfide/bacteria-containing system consistently reduced aqueous pertechnetate rapidly (> 95% in the first hour), a rate similar to that for the sulfide-free, nZVI only system. Reduced Tc (aged for 3 months) generated in both SRB/nZVI systems was highly resistant to reoxidation. In reduced samples, Tc was found associated with solid phases containing Fe and S (D. reducens/nZVI) or Fe (nZVI only). Experiments using D. reducens without nZVI provided some additional insights. Firstly, stationary phase cultures were able to slowly reduce pertechnetate. Secondly, addition of pertechnetate at the beginning of cell growth (lag phase) resulted in a faster rate of Tc reduction, possibly indicating a direct (e.g. enzymatic) role for D. reducens in Tc reduction. Abiotic batch experiments were conducted with Na₂S as the sulfide source. Pertechnetate reduction was rapid in the presence of sulfide and nZVI, although the rate was suppressed at the higher S/Fe ratios tested. This suppression appeared to be due to the formation of Tc-containing colloids. As with the biotic experiments, pertechnetate reduced under sulfidic conditions was highly resistant to reoxidation. The microscopic morphology of abiotically-transformed nZVI particles varied significantly with those in the biotic experiment, although mackinawite was formed in both systems (as indicated by ÎźXRD and MĂśssbauer spectroscopy). Preliminary XAS analysis pointed to a mixture of Tc-O and Tc-S binding in the abiotic sulfide/nZVI system, while the major reduced solids under non-sulfidic conditions were TcO₂â˘nH₂O. The presence of sediment and advective flow to the TcO₄^-/nZVI/sulfide system results in additional processes occurring. Although the natural Hanford sediment used has sufficient available ferrous iron to slowly reduce TcO₄^-, under anaerobic conditions, that rate is orders of magnitude slower than reduction by nZVI/sulfide. Batch and 1-D column experiments showed that the TcO₄^- reduction rate increased with the sediment surface area (with the same nZVI mass). As in batch systems, column studies showed that the presence of sulfide with TcO₄^- at low (2-5 mM) concentrations increased the TcO₄^- reduction rate and high (10-30 mM) sulfide decreased the rate. This change is attributed to the formation of sulfide precipitates on the nZVI and sediment surfaces. Injection of low and high sulfide (i.e. pretreatment) prior to TcO₄^-/sulfide injection also greatly decreased the TcO₄^- reduction rate, likely decreasing the generation of ferrous iron from the nZVI. Although the high sulfide systems have slower Tc reduction rates, 190 times more Tc mass precipitated than in the low sulfide systems and the highest fraction of Tc mass remained immobilized.
英文关键词	Pertechnetate, Technetium Sulfide, Sequestration, Reduction, Oxidation, Zerovalent Iron, nZVI, Sulfidation, TEM, XAS, XPS, ÎźXRD, MĂśssbauer, Remediation
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来源平台	US Department of Energy (DOE)
引用统计
文献类型	科技报告
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/7055
专题	地球科学
推荐引用方式 GB/T 7714	Tratnyek, Paul G.,Tebo, Bradley M.,Fan, Dimin,et al. Technetium Reduction and Permanent Sequestration by Abiotic and Biotic Formation of Low-Solubility Sulfide Mineral Phases,2015.