Enrichment selenium

Figure 4 Te NMR spectrum of the ternary sulfur-selenium-tellurium melt containing 1.5 mol% of both Se-enriched selenium and Te-enriched tellurium (enrichment 92%). The spectral assignments and the identification of the molecular species were made on the basis of combined information from the natural abundance and from the Se- and Te-emiched samples taking the known trends in the Se and Te chemical shifts into accoimt. (Reprinted with permission from Ref. 26. 1993 American Chemical Society)...

We also developed a number of other useful new fluorinating reagents. They ineluded a convenient in situ form of sulfur tetrafluoride in pyridinium polyhydrogen fluoride, selenium tetrafluoride, and ey-anurie fluoride. We introdueed uranium hexafluoride (UFg), depleted from the U-235 isotope, which is an abundant by-product of enrichment plants, as an effective fluorinating agent. 

Production and Economic Aspects. Thallium is obtained commercially as a by-product in the roasting of zinc, copper, and lead ores. The thallium is collected in the flue dust in the form of oxide or sulfate with other by-product metals, eg, cadmium, indium, germanium, selenium, and tellurium. The thallium content of the flue dust is low and further enrichment steps are required. If the thallium compounds present are soluble, ie, as oxides or sulfates, direct leaching with water or dilute acid separates them from the other insoluble metals. Otherwise, the thallium compound is solubilized with oxidizing roasts, by sulfatization, or by treatment with alkaU. The thallium precipitates from these solutions as thaUium(I) chloride [7791 -12-0]. Electrolysis of the thaUium(I) sulfate [7446-18-6] solution affords thallium metal in high purity (5,6). The sulfate solution must be acidified with sulfuric acid to avoid cathodic separation of zinc and anodic deposition of thaUium(III) oxide [1314-32-5]. The metal deposited on the cathode is removed, kneaded into lumps, and dried. It is then compressed into blocks, melted under hydrogen, and cast into sticks. 

Significant depletion of In, enrichment in iodine and simultaneous reduction of selenium to Se° was observed by XPS for n-CuInSe2 photoelectrode surfaces in an I2—1 —Cu+—HI electrolyte [129]. Over a distance of 100 A the composition of the surface layer gradually changes to that of the substrate. With the help of UPS analysis the surface film, assumed to be CuISe3, was characterized as p-type semiconductor [130],... 

Unlike selenium there is no required biological role for tellurium in bacteria or plants that has been determined however, this may ultimately not be the whole story.111 Selenium was only viewed as a toxic metalloid with no necessary role for metabolism until at least the 1950s see above. While tellurite is less soluble than tellurate in aqueous solution, in general tellurite is probably more toxic to most organisms.190 The non Te-resistant wild type E. coli bacterium (Gramnegative) has MICs of 1 to 3 ppm for tellurite and tellurate.144,191,192 Tellurite is used to enrich and select for Staphylococcus aureus.169,193,194... 

Ip C, Lisk DJ. 1994. Enrichment of selenium in album vegetables for cancer prevention. Carcinogenesis 15 1881-1885. 

Ip C, Lisk DJ and Stoewasand GS. 1992. Mammary cancer prevention by regular garlic and selenium enriched garlic. Nutr Cancer 17 279-286. 

Whanger PD, Ip C, Polan CE, Uden PC and Welbaum G. 2000. Tumorigenesis, metabolism, speciation, bioavailability, and tissue deposition of selenium in selenium-enriched ramps (Allium tricoccum). J Agric Food Chem 48(11) 5723-5730. 

Figure 1. Bio geochemical sub-region and provinces enriched by selenium. 1—sub-region with Se content in soil from 0.2 to 0.5 ppm and in plant species from 0.08 to 0.5 ppm 2—Ulug-Hemsk and Turan-Uluks biogeochemical provinces with Se content in soil as much as 03-6.0ppm and in plant species from 0.1 to 13.1 ppm by dry weight (Ermakov, 1993).

We can see that Se deficit is often monitored in the biogeochemical food webs in the Chita region, Russia, and Latvia and the Se enrichment in the Fergana valley of Uzbekistan. The Se deficit is also connected with the lower values of Cb in the first two regions in comparison with the latter, where selenium is more mobile due to... 

He, S. H., Teixeira, M., LeGall, J., Patil, D. S., Moura, L, Moura, J. J., DerVartanian, D. V., Huynh, B. H. and Peck, H. D. Jr (1989b) EPR studies with 02-enriched (NiFeSe) hydrogenase of Desulfovibrio baculatus. Evidence for a selenium ligand to the active site nickel. J. Biol. Chem., 264, 2678-82. 

Results of the second experiment (Table 3) show that Se-enriched broccoli sprouts have properties similar to enriched broccoli florets that contain SeMSC as the predominant form of Se (13). Consumption of Se from high-Se broccoli sprouts, as compared to Se from selenite, resulted in a significant decrease in the number of aberrant crypts. Additional experimentation is needed to determine whether the decrease in carcinogenesis is a result primarily of the presence of SeMSC, and if there is a correlation between SeMSC content in enriched plants and the reduction of carcinogenesis. If such a correlation is established, then the SeMSC content of various enriched plants could be used to screen for the greatest efficacy in tumor reduction. Se-enriched broccoli appears to be similar to enriched broccoli florets, for which the predominant form of selenium was also shown to be SeMSC (13). 

In summary, coal-fired power plants appear not to be the major source of most enriched elements on particles In urban areas, despite the great attention devoted to mechanisms by which those elements become preferentially attached to fine particles (e.g.. Refs. 18, 34). However, the detailed studies of processes In coal-fired plants are of considerable value, as the fundamentals should be applicable to other kinds of combustion sources. Furthermore, It may be necessary to use this fundamental approach to develop methods for predicting the source compositions for coal-fired power plants that have not been measured. Selenium Is much... 

Solely on the basis of volatility profiles, fossil fuel burning is expected preferentially to transfer As, Hg, Cd, Sn, Sb, Pb, Zn, Tl, Ag, and Bi to the atmosphere (1). In a study designed to detect fallout from a major coal burner equipped with a precipitator, Klein and Russell (27) showed that Ag, Cd, Co, Cr, Fe, Hg, Ni, Ti, and Zn were deposited in the surrounding soil (115 sq mi), and with the exception of mercury, enrichment correlated with the respective metal concentrations in the coal. Mercury was more widely disseminated to the environment. Previous work has indicated that mercury exists primarily in the volatile phase of the flue gas and consequently as much as 90% bypasses the electrostatic precipitation control device (2). Bolton and co-workers have evidence that selenium and arsenic may present a similar problem (see Chapter 13). 

Nicotinic acid and nicotinamide, members of the vitamin B group and used as additives for flour and bread enrichment, and as animal feed additive among other applications, are made to the extent of 24 million pounds (nearly 11 million kilograms) per year throughout the world. Nicotinic acid (pyridine-3-caiboxylic acid), also called niacin, has many uses. See also Niacin. Nicotinic acid is made by the oxidation of 3-picolme or 2-mcthyl-5-cthylpyridine (the isocinchomcnc acid produced is partially deearboxylated). Alternatively, quinoline (the intermediate quinolinic acid) is partially deearboxylated with sulfuric add in the presence of selenium dioxide at about 300° C or with nitric acid, or by electrochemical oxidation. Nicotinic acid also can be made from 3-picoline by catalytic ammoxidation to 3-cyanopyridine, followed by hydrolysis. 

Gonz lez, A.Z.I., Krachler, M., Cheburkin, A.K. and Shotyk, W. (2006) Spatial distribution of natural enrichments of arsenic, selenium, and uranium in a minerotrophic peatland, Gola di Lago, Canton Ticino, Switzerland. Environmental Science and Technology, 40(21), 6568-74. 

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