Enrichment of mercury

3 Enrichment of Mercury. Due often to very low mercury contents of the samples to be analysed, enrichment procedures are required. Mercury can be extracted with PDDC into MIBK or with dithiazone into chloroform. It can also be electrolysed on the copper or silver cathode. The mercury vapour can be collected in several traps such as various solution traps, gold trap, and active carbon. Adsorption solutions may be nitric acid, bromine water—nitric acid, or potassium permanganate solutions. 

Hydroxylamine hydrochloride, which is used to reduce excess permanganate, can have a substantial influence on mercury at higher concentrations. 

Complexing agents which form stable complexes with mercury may cause 

Sulfur dioxide interferes by absorbing at the mercury line 253.7 nm used for measurements, but SO2 may be adsorbed into NaOH solution. 

The cold vapour technique may be fully automated by using a FIA system, which is discussed in section 6.4,2. 

---

A 35- to 40-fold incorporation (relative to other fractions) of labelled mercury into a nonhistone fraction of rat kidney nuclei has been reported [44]. By using flameless atomic absorption, a 12 to 15-fold enrichment of mercury was found in the euchromatin fraction of mouse liver nuclei [45, 46]. Mercury was not detected in the inactive heterochromatin. 

Paasivirta, J., J. Sarkka, K. Surma-Aho, T. Humppi, T. Kuokkanen, and M. Marttinen. 1983. Food chain enrichment of organochlorine compounds and mercury in clean and polluted lakes of Finland. Chemosphere 12 239-252. 

Fig. 5.10 The mass dependence of the critical temperature of the superconducting/resistive transition in isotopically enriched samples of mercury (Triangles Reynolds, C. A., et al. Phys. Rev. 78, 487 (1950). Circles Maxwell, E., Phys. Rev. 78, 477 (1950))...

Large scale enrichment of lithium for thermonuclear uses took place at the Oak Ridge National Laboratory in the 1950 s. The enrichment primarily employed ion exchange between aqueous/organic solutions and amalgam, commonly mercury-based (Palko et al. 1976). Electrochemical separation has also been employed for such operations (Umeda et al. 2001). These practices have not been taken up in academic laboratories in the intervening years, partly as they tend to be most effective only with relatively pure starting materials, partly because of the difference in scales involved. Enrichment factors of Li of 1-7% are typical for these techniques (Symons 1985). 

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. 

Because of the complex cycling of MMHg in the ocean, carnivorous fish at the top of the food chain could be naturally enriched in mercury. But mercury levels in seabird feathers show significant increases over time, suggesting that anthropogenic emissions have similarly caused an increase in fish tissues. 

Research indicates that a significant fraction (50-90% ) of mercury is volatilized and lost during coal combustion (10, 11, 12) and that many of the potentially hazardous trace elements appear concentrated upon finer particulate emissions (13, 14). Several investigators have observed enrichment of these hazardous elements upon particulates in urban areas... 

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). 

In 1953, Billings et al. (17) studied the water vapor reaction with a lssHg source. The experiments were carried out in a flow system with nitrogen as carrier gas. The mercury oxide formed was found to be enriched in mHg, relative to its natural abundance. Similarly, with a -"-Hg lam)), an enriclnnent in 2,2Hg was observed (18). The isotopic analysis of mercury product in these studies was made by interferometry. 

The importance of gas phase exchange reactions of the type HgA + AHg A1 IgA + Hg should also be determined. This could be assessed from the effect which the change of the isotopic composition of mercury vapor in the. absorbing enclosure lias upon the values of product enrichments. 

Dai, S., Zeng, R. and Sun, Y. (2006) Enrichment of arsenic, antimony, mercury, and thallium in a Late Permian anthracite from Xingren, Guizhou, southwest China. International Journal of Coal Geology, 66(3), 217-26. 

European Standard. 1998. Water quality. Determination of mercury. Enrichment methods by amalgamation. EN 12338. European Committee for Standardization, Brussels, Belgium. 

Plate tectonic activity, which is responsible on Earth for subduction zones, spreading centres and obducted ophiolites, as well as associated ore deposits of Cu, Cr and Ni described in 8.6, appears to have been less significant on other terrestrial planets. As a result, local enrichments of these and other transition elements (apart from Fe and Ti) are probably absent on the Moon, Mercury, Venus, Mars and the asteroids. Since Fe and Ti minerals are predominant on terrestrial planets, electronic spectra of Fe2+ and Fe3+ in silicates and oxides influenced by Ti4+ and Ti3+ are expected to dominate remote-sensed spectra of their surfaces. 

Some elements appear in plant and animal products at relatively constant levels, but in a number of cases an abundance of a certain element in the environment may result in a greatly increased level of that mineral in plant or animal products. Enrichment of elements in a biological chain may occur note, for instance, the high mercury levels reported in some large predatory fish species such as swordfish and tuna. 

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... 

The method of isotope ratio has been employed predominantly in assays of volatile compounds of lead, tin, and selenium. The applicability of the method of isotope dilution depends on the availability of isotopically enriched standard forms. To date, it has been utilized for assaying methyl derivatives of mercury and butyl derivatives of tin. The effectiveness of the former method, which is more widespread, is dependent to a large extent on the quality of the module connecting the gas chromatograph to the ICP MS spectrometer [138]. 

In this chapter we summarize what we know about the chemical composition of Mercury, with emphasis on assessing the amount of FeO in the bulk planet. FeO is a particularly useful quantity to evaluate the extent to which Mercury is enriched in refractory elements, because its concentration increases with decreasing temperature in a cooling gas of solar composition (e.g., Goettel, 1988). We then examine models for the composition of Mercury and outline tests that future orbital missions to Mercury will be able to make. 

---