United States Department of Energy

About: United States Department of Energy is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Catalysis & Coal. The organization has 13656 authors who have published 14177 publications receiving 556962 citations. The organization is also known as: DOE & Department of Energy.

Chemistry of aqueous mineral carbonation for carbon sequestration and explanation of experimental results

Abstract: In aqueous mineral carbonation for carbon sequestration, high-pressure CO2 is injected into water or sodium bicarbonate solution mixed with olivine or serpentine to produce magnesium carbonate. Thus, CO2 gas is fixed in a solid carbonate for sequestration. Such reactions are generally slow, and a significant amount of research was conducted to increase the reaction rate. This article is an initial effort using basic thermodynamic analysis to understand this complicated heterogeneous chemical process, and to explain some experimental results. The approach started with decomposing the process into two basic steps: magnesium ion dissolution from the olivine or serpentine, and magnesite precipitation. Thermodynamic calculation then is used to assess two important parameters for each of these two steps: the pH and carbonic ion concentration. The calculations explain the roles of increased CO2 pressure, elevated temperature, and adding sodium bicarbonate for enhancing the carbonation reaction, and these results agreed well with the experimental data. The analysis also indicates that for reaction routes in which leaching magnesium silicate and forming magnesium carbonate occur in the same reactor, lowering the pH helps dissolve magnesium ions from silicate, but it lowers carbonic ion concentration and limits precipitation of magnesite; careful balance of these two steps is critical. Further improvement may be built upon this model. © 2006 American Institute of Chemical Engineers Environ Prog, 2006

Genome dynamics in a natural archaeal population.

Abstract: Evolutionary processes that give rise to, and limit, diversification within strain populations can be deduced from the form and distribution of genomic heterogeneity. The extent of genomic change that distinguishes the acidophilic archaeon Ferroplasma acidarmanus fer1 from an environmental population of the same species from the same site, fer1(env), was determined by comparing the 1.94-megabase (Mb) genome sequence of the isolate with that reconstructed from 8 Mb of environmental sequence data. The fer1(env) composite sequence sampled ≈92% of the isolate genome. Environmental sequence data were also analyzed to reveal genomic heterogeneity within the coexisting, coevolving fer1(env) population. Analyses revealed that transposase movement and the insertion and loss of blocks of novel genes of probable phage origin occur rapidly enough to give rise to heterogeneity in gene content within the local population. Because the environmental DNA was derived from many closely related individuals, it was possible to quantify gene sequence variability within the population. All but a few gene variants show evidence of strong purifying selection. Based on the small number of distinct sequence types and their distribution, we infer that the population is undergoing frequent genetic recombination, resulting in a mosaic genome pool that is shaped by selection. The larger genetic potential of the population relative to individuals within it and the combinatorial process that results in many closely related genome types may provide the basis for adaptation to environmental fluctuations.

Uranium Precipitation in a Permeable Reactive Barrier by Progressive Irreversible Dissolution of Zerovalent Iron

Abstract: A permeable reactive barrier (PRB) containing zerovalent iron [Fe(0)] was installed at a former uranium milling site in Monticello, UT. A large-scale column experiment was conducted at the site to test the feasibility of Fe(0) to treat U prior to installing the PRB. Effluents from the field column experiment had pH values near 7.34, moderate decreases in C(IV) and Ca concentrations, and an elevated Fe concentration (27.1 mg/L). In contrast, groundwater exiting the PRB had a pH value of 9.82, decreases in C(IV) and Ca concentrations, and a low concentration of Fe (0.17 mg/L). A geochemical model was used to explain the chemical changes that occurred in both the field column experiment and the PRB. The model simulated the systems by the progressive irreversible dissolution of Fe(0). Modeling results indicated that a longer residence time in the PRB compared with the shorter residence time in the column contributed to the disparate effluent qualities. Prior to modeling, a controlled laboratory column experim...