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Materials Used for General Radiation Detection
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
The hexagonal form of mercuric sulphide (HgS) has received considerable attention as a room-temperature replacement for HgI2, in view of its high density (8.2 g cm–3), favourable bandgap (2.1 eV) and relative chemical stability. HgS can assume two different crystalline forms, – α-HgS, which crystallizes in a trigonal type, hexagonal structure, and β-HgS, which crystallizes in a zincblende type, cubic structure. Alpha-HgS is more commonly recognized as the mineral cinnabar, which happens to be the main commercial source of the metal mercury. It is also widely used as the high-grade paint pigment, vermillion. Recently, it has been explored for acousto-optical [160], infrared sensing [161] and photoelectronic applications [162-164]. Beta-HgS (also known as metacinnabar) is generally considered a semimetal but has recently been shown to be a strong topological insulator [165]. As a bulk material, it has potential for use in low-power consumption electronic devices [165] and in its nano-particle form, in solid-state solar cell and photo-electrochemical cell applications [164]. Interestingly, metacinnabar is the compound form that mercury evolves into in aged amalgam dental fillings.
Removal of Inorganic Contaminants
Published in Samuel D. Faust, Osman M. Aly, Chemistry of Water Treatment, 2018
The MCL for mercury in drinking water is 0.002 mg/L.1 There are very few historical data on the occurrence of Hg in ground, surface, and finished waters in the United States. This is due mainly to the cumbersome analytical techniques for Hg in water. Mercury contents of <0.5 to 6.8 μg/L were reported for several surface waters in the United States.2 Of the several mercury-bearing minerals in nature, only a few exist abundantly. The most common are the sulfides [cinnabar and metacinnabar (HgS)] and native mercury. In aqueous systems, mercury can exist in one of three oxidation states: as the free metal, Hg0, as the mercurous ion, Hg22+ or as the mercuric ion, Hg2+. Mercury readily forms complexes with many inorganic anions and organic constituents, for which the methylation reactions have been documented.2 An important characteristic of Hg is its tendency to adsorb and adhere to various types of surfaces. This, of course, has immediate application to water treatment.
Hg, 80]
Published in Alina Kabata-Pendias, Barbara Szteke, Trace Elements in Abiotic and Biotic Environments, 2015
Alina Kabata-Pendias, Barbara Szteke
Mercury occurs mainly at +2 oxidation stage, but may also have valences from +1 to +3. It easily forms amalgams with noble metals. It may also be methylated by microorganisms in various natural environments and reveals a chalcophillic character, and thus combine readily with sulfur. Its main mineral, of commercial importance, is cinnabar (metacinnabar), HgS. Calomel (mercurous chloride), Hg2Cl2, is rarely found in nature. Sulfide (e.g., schuetteite, Hg3SO4O2), selenide, telluride, and so on of Hg may occur in various ore deposits. There are several Hg host minerals such as amphiboles, sphere, sphalerite, and other sulfides. The most important geochemical features of Hg are as follows: (1) affinity to form strong bonds with S; (2) formation of organomercury compounds; (3) formation of gaseous compounds; (4) volatility of metallic form; and (5) low affinity for oxygen bound to carbon. The characteristics of Hg in the environment are its number of chemical and physical forms, such as Hg0, HgCl2, HgO, HgS, CH3HgCl, and (CH3)2Hg. All these compounds behave differently in various ecosystems. Some of the mercuric salts are soluble in water, whereas organomercuries are neither soluble nor do they react with weak acid and bases.
Mercury methylation by anaerobic microorganisms: A review
Published in Critical Reviews in Environmental Science and Technology, 2019
Ming Ma, Hongxia Du, Dingyong Wang
If neutrally charged Hg(II) complexes are confirmed to enter the cell through passive diffusion, then the chemical form of Hg(II) in the extracellular environment, namely the forms of Hg(II) and their chemical stability is an important determinant of its bioavailability (Hsu-Kim et al., 2013). Mercury exists as liquid metal at room temperature, and the natural forms of Hg(II) compounds are Hg sulfides, such as cinnabar and metacinnabar. It is thus clear that Hg(II) can easily react with sulfur-containing molecules, especially reduced sulfur, to form insoluble precipitates or water-soluble complexes. The most commonly used model for simulating the bioavailability of Hg in anaerobic aquatic water speculates that Hg(II) is mainly taken up by microorganisms via passive diffusion (Benoit et al., 2001a, 2001b). In this case, it is speculated that neutral, uncharged, small, and soluble Hg(II) compounds such as Hg(HS)2° and HgS0(aq) could be passively taken up by anaerobic Hg-methylating microorganisms (Hsu-Kim et al., 2013) due to their strong affinity with reduced sulfur (Dyrssen & Wedborg, 1991) and their ability to passively diffuse through cell membranes (Benoit et al., 2001b), while other forms such as HgHS+, HgHS2− and Hg-DOM could not be passively diffused into cells (Hsu-Kim et al., 2013). When the soluble Hg(II) reaches a chemical equilibrium state in the water, various Hg-sulfide complexes gradually dissolve and are the main form of soluble Hg(II) in water (Dyrssen & Wedborg, 1991). Thus, the net yield of MeHg is associated with the amount of neutral Hg-sulfide complexes (Benoit, Gilmour, et al., 1999; Hsu-Kim et al., 2013). The reasons perhaps are that the structure of bacterial cell membrane is a lipid bilayer inlaid with a variety of proteins, which has selective permeability. The inner layer of bacterial cell membrane is made up of two fatty acids which are strong hydrophobic or lipophilic. Consequently, if Hg(II) can transport into the cytoplasm by passive diffusion, the Hg(II) complexes must be uncharged so as to dissolve in the cell membrane. In addition, the Hg(II) complexes must also be small molecules, such as O2, CO2, and H2O, so that they can pass through the cell membrane without the help of transporters. This explanation confirms again that the uncharged small molecule compounds HgS0(aq) and Hg(HS)2° are more likely to pass through the inner membrane and carry out subsequent biochemical reactions.