Enrichment cadmium

This practical exercise makes use of an istopically enriched cadmium standard which is available from a number of sources. However, any element with an enriched isotope can be used in place of cadmium, provided that the natural abundance is known. 

Enriched cadmium isotopic standard (Spectrascan Stable Isotope Solution, Teknolab A/S, P.O. Box 131, N-1441 Drobak, Norway). 

J. R. Lakowicz et ah. Time-resolved spectral observations of cadmium-enriched cadmium sulfide nanoparticles and the effects of DNA oligomer binding. Analytical Biochemistry, 280(1), 128-136 (2000). 

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. 

Cadmium and mercury are usually recovered ia separate processes at the ziac plant. The others are shipped as enriched residues to plants that specialize ia their recovery. 

Uranium is not a very rare element. It is widely disseminated in nature with estimates of its average abundance in the Earth s crust varying from 2 to 4 ppm, close to that of molybdenum, tungsten, arsenic, and beryllium, but richer than such metals as bismuth, cadmium, mercury, and silver its crustal abundance is 2.7 ppm. The economically usable tenor of uranium ore deposits is about 0.2%, and hence the concentration factor needed to form economic ore deposits is about 750. In contrast, the enrichment factors needed to form usable ore deposits of common metals such as lead and chromium are as high as 3125 and 1750, respectively. 

Bingham F.T., Page A.L., Mahler R.J., Ganji T.J. Growth and cadmium accumulation of plants grown on a soil treated with a cadmium-enriched sewage sludge. J Environ Qual 1975 4 207-211. 

Mahler R.J., Bingham F.T., Sposito G., Page A.L. Cadmium-enriched sewage sludge application to acid and calcareous soils Relation between treatment, cadmium in saturation extracts, and cadmium uptake. J Environ Qual 1980 9 359-364. 

Mitchell G.A., Bingham F.T., Page A.L. Yield and metal composition of lettuce and wheat grown on soils amended with sewage sludge enriched with cadmium, copper, nickel and zinc. J Environ Qual 1978 7 165-171. 

Handy, R.D. 1992. The assessment of episodic metal pollution. II. The effects of cadmium and copper enriched diets on tissue contaminant analysis in rainbow trout (Oncorhynchus mykiss). Arch. Environ. Contam. Toxicol. 22 82-87. 

Chemical analysis of the Meza River and its tributaries revealed significant heavy metal pollution of the upper Meza River sediments with lead, zinc, and some molybdenum, cadmium and arsenic enrichments. The trend of Cd and As is similar to trend of Pb and Zn, which is in agreement with the fact that Cd and As are associated with Pb and Zn in ore minerals (Strucl, 1984 Fux Gosar, 2007). In the lower Meza valley, these heavy metal concentrations decreased somewhat. 

There are also natural geochemical anomalies where soils are enriched by cadmium, for example, in the central parts of Sweden. Here the cultivation of crops accumulating cadmium (grains, potato, some grasses) is not recommended. In the coastal marine areas the cadmium mobility in soils is stimulated by its complexation with chlorine. 

On a worldwide basis, toxic concentrations of the heavy metals have thus far been limited to industrialized harbors. The only metals that appear to have accumulated to toxic levels on a regional scale are mercury, cadmium, and lead in the Arctic Ocean. This concentration of mercury and lead has been fecilitated by a natural process, called the grasshopper effect, which acts to transport volatile compoimds poleward. This transport plays a major role in redistributing the volatile organic pollutants, such as the PCBs, and, hence, is discussed at further length in Chapter 26.7. The process responsible for the cadmium enrichment in the Arctic appears to involve low-altitude transport of the fine particles that compose Arctic haze. 

Figure 2. Computer plot of a cadmium spectrum spiked with enriched...

In order to obtain, for example, the cadmium concentration in a fuel by isotope dilution SSMS, cadmium enriched in 106Cd is equilibrated with the cadmium in the sample. The success of the technique depends on establishing isotopic equilibrium between the highly enriched 106Cd and the normal cadmium in the sample. Isotopic and chemical equilibrium is attained by an acid (perchloric acid-nitric acid) reflux digestion and oxidation of the organic matter. Thereafter, any technique that permits the transfer of 0.1-3 ng of cadmium from the solution to the surface of a suitable substrate may be used. In this IDSSMS work, graphite was the substrate for cadmium, lead, and zinc, and copper was used for mercury (5). 

Figure 2 shows a mass spectrum of cadmium spiked with enriched 106Cd. The solid line at position 106 represents the 106Cd spike, and the dashed lines represent the relative abundance for the other cadmium isotopes. The dashed line at juxtaposition at 106 is the relative abundance of 106Cd as it occurs in nature. Table I shows the IBM 1130 computer-programmed output for a typical isotope dilution analysis. The program... 

Andrews (4) showed that fine-grained particulate contaminants (arsenic, cadmium, copper, lead, and zinc in sediment less than 0.016 mm in diameter) decreased downstream from the source and that the distribution could be explained solely by mixing of mill tailings with uncontaminated floodplain sediment. Work by Brook and Moore (5) and Moore et al. (6) showed that the sediments were enriched in arsenic, cadmium, copper, manganese, lead, and zinc. They also found that the contaminants were carried mostly in the reducible and oxidizable phases (operationally defined). 

I. Narin, M. Soylak, Enrichment and determinations of nickel (II), cadmium(II), copper(II), cobalt(II), and lead(II) ions in natural waters, table salts, tea and urine samples as pyrrolydine dithiocarbamate chelates by membrane filtration-flame atomic absorption spectrometry combination, Anal. Chim. Acta, 493 (2003), 205-212. 

Many studies on the direct reaction of methyl chloride with silicon-copper contact mass and other metal promoters added to the silicon-copper contact mass have focused on the reaction mechanisms.7,8 The reaction rate and the selectivity for dimethyldichlorosilane in this direct synthesis are influenced by metal additives, known as promoters, in low concentration. Aluminum, antimony, arsenic, bismuth, mercury, phosphorus, phosphine compounds34 and their metal complexes,35,36 Zinc,37 39 tin38-40 etc. are known to have beneficial effects as promoters for dimethyldichlorosilane formation.7,8 Promoters are not themselves good catalysts for the direct reaction at temperatures < 350 °C,6,8 but require the presence of copper to be effective. When zinc metal or zinc compounds (0.03-0.75 wt%) were added to silicon-copper contact mass, the reaction rate was potentiated and the selectivity of dimethyldichlorosilane was enhanced further.34 These materials are described as structural promoters because they alter the surface enrichment of silicon, increase the electron density of the surface of the catalyst modify the crystal structure of the copper-silicon solid phase, and affect the absorption of methyl chloride on the catalyst surface and the activation energy for the formation of dimethyldichlorosilane.38,39 Cadmium is also a structural promoter for this reaction, but cadmium presents serious toxicity problems in industrial use on a large scale.41,42 Other metals such as arsenic, mercury, etc. are also restricted because of such toxicity problems. In the direct reaction of methyl chloride, tin in... 

Early life forms thriving near thermal vents in waters enriched in heavy metal ions would have had to have been endowed with mechanisms to deal with toxic metal ions and it is conceivable that efflux mechanisms for these metals evolved before or concomitandy with their use as cofactors. In line with such a hypothesis, the CPx-type ATPases encompass a wider spectrum of ion specificities than the non-heavy metal ATPases, now including Cu+, Ag+, Zn +, Cd +, and Pb. It is to be expected that other metal ions will be added to this list. ATPases transporting silver, zinc, cadmium, and lead are involved in bacterial resistance to these toxic metal ions, while copper-transporting ATPases have a role both in copper uptake to meet cellular demands and in copper extrusion when ambient... 

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