Removal of Mercury

This secondary reaction starts at about 180°C, but the mass must be heated to 350—400°C to bring the reaction to completion and produce a nitrate-free product. The off-gases are extremely corrosive and poisonous, and considerable attention and expense is required for equipment maintenance and caustic-wash absorption towers. Treatment of the alkaline wash Hquor for removal of mercury is required both for economic reasons and to comply with governmental regulations pertaining to mercury ia plant effluents. 

Soluble sulfides such as sodium sulfide, potassium sulfide, and calcium polysulfides have been used to precipitate mercury salts from alkaline solutions. When this procedure is used, exercise of caution is requked to maintain the pH within a given alkaline range so as to prevent evolution of H2S. Because the solubiUty of mercuric sulfide in water is 12.5 flg/L at 18°C or 10.7 ppb of mercury, use of this method for removal of mercury is adequate for most purposes. However, the presence of excess alkah, such as sodium hydroxide or sodium sulfide, increases the solubiUty of mercuric sulfide as shown ... 

Problems of removal of mercury from aqueous effluents are more comphcated in plants that manufacture a variety of inorganic and organic mercury compounds it is generally best to separate the effluent streams of inorganic and organic mercurials. When phenyhnercuric acetate is precipitated from its solution in acetic acid by addition of water, the filtrate is collected and reused for the next precipitation. This type of recycling is necessary not only for economic reasons but also to minimise recovery operations. 

The most popiilar dry scrubbing systems for incinerators have involved the spray drying of hme slurries, followed by dry coUection in electrostatic precipitators or fabric filters. Moller and Christiansen [Air Poll. Cout. Assoc. 84-9.5 (1984)] published data on early European technology. Moller et al. [U.S. Patent no. 4,889,698 (1989)] describe the newer extension of that technology to include both spray-dryer absorption and dry scrubbing with powdered, activated carbon injection. They claim greatly improved removal of mercury, dioxins, and NOx. 

Sulfide ores usually contain small amounts of mercury, arsenic, selenium, and tellurium, and these impurities volatilize during the ore treatment. All the volatilized impurities, with the exception of mercury, are collected in the dust recovery systems. On account of its being present in low concentrations, mercury is not removed by such a system and passes out with the exit gases. The problem of mercury contamination is particularly pertinent to zinc plants since the sulfidic ores of zinc contain traces of mercury (20-300 ppm). The mercury traces in zinc sulfide concentrates volatilize during roasting and contaminate the sulfuric acid that is made from the sulfur dioxide produced. If the acid is then used to produce phosphatic fertilizers, this may lead to mercury entering the food chain as a contaminant. Several processes have been developed for the removal of mercury, but these are not yet widely adopted. 

Removal of Mercury from Coil Coating Wastewater by Granular Activated Carbon Filtration... 

Because of the removal of mercury from the alkaline MnOz cell, there has been a re-formulation in the anode paste. Because of this change, theses cells... 

Fig. 39. Removal of mercury fulminate from the reaction flask to a rubber bucket, according to Budnikov et al. [61].

Hansen, C. L., G. Zwolinski, D. Martin, and J. W. Williams. 1984. Bacterial removal of mercury from sewage. Biotech. Bioeng. 26 1330-1333. 

Crosslinked polymers of vinyl-substituted imidazolecarboxylic acids have been studied as chelating resins for heavy metal ions (78MI11101). For example, polymer (75) displays stabilities and capacities in the order Cu2+ > Ni2+ > Cd2+ > Zn2+ > Mg2+ which is similar to that observed with other amino acid chelating resins. The unusual feature of the polymer, however, is that exceptionally strong complexing abilities are maintained even in strongly acidic media. Polymer (75) also displayed potential utility for the removal of mercury(II) ions from aqueous media. 

In order to gain a better understanding of the usefulness of phase diagrams, consider a cylinder in which temperature can be controlled and volume varied by injection or removal of mercury as shown in Figure 2-2. Figure 2-2A shows that a pure substance has been trapped in the... 

If the same process is followed for a temperature above the critical temperature, for instance, line 45 on Figure 2-3, the removal of mercury will cause pressure to decrease. However, there will not be a sudden change in the density of the substance. The vapor-pressure line will not be crossed. There is no abrupt phase change. 

The apparatus in Fig. 9.7.b is the simplest to operate because the entire manometer system, the sample, and its vapor are immersed in the constant-temperature bath. The mercury reservoir permits the removal of mercury from the U-manometer portion of the apparatus, and the material to be measured is then condensed into the terminal bulb. While this material is still condensed and there is a high vacuum in the system, the mercury is reintroduced to the U, thus isolating the sample. The apparatus is immersed in a constant-temperature bath to the level of the wavy lines. With a vacuum on the upper portion of the apparatus the vapor pressures can be measured directly. If vapor pressures beyond the range of the immersible manometer must be measured, the mercury in the... 

Mercury represents a serious environmental risk, and the study of removal of mercury from wastewater has received considerable attention in recent years. Mercury concentration was usually reduced by deposition on a cathode with high surface area. Removal of mercury is studied using extended surface electrolysis which reduces the level of mercury to below acceptable concentrations of 0.01 ppm in wastes by employing a Swiss roll cell with a cadmium-coated, stainless-steel cathode. An industrial cell with a fluidized bed electrode has also been studied. Graphite, as an efficient porous electrode, has been used to remove traces of mercuric ions form aqueous electrolyte solutions. In order to apply the electrochemical method for some effluents, it is necessary to use sodium hypochlorite to convert elemental mercury and less soluble mercury compounds to water-soluble mercuric-chloride complex ions. 

Concentration of Amalgams. Rare earth metal amalgams may be concentrated with respect to their rare metal content by removal of mercury through distillation under reduced pressure. An all-glass distilling apparatus should be used for this purpose, since cork or rubber stoppers will not withstand the temperature required to eliminate much of the mercury. The apparatus depicted in Fig. 2 has been found satisfactory for this purpose. 

Bell and McDowell16 studied the Hg photosensitized oxidation of isobutane using a static system. There was a slow removal of mercury vapor ( = 6 X 10-4 at 30°C. and 2 X 10-4 at 100°C.). The main... 

The reaction mechanism of alkoxymercuration/demercuration of an alkene is similar to other electrophilic additions we have studied. First, the cyclopentene n electrons attack Hg2+ with formation of a mercurinium ion. Next, the nucleophilic alcohol displaces mercury. Markovnikov addition occurs because the carbon bearing the methyl group is better able to stabilize the partial positive charge arising from cleavage of the carbon-mercury bond. The ethoxyl and mercuric groups are trans to each other. Finally, removal of mercury by NaBH4 by a mechanism that is not fully understood results in the formation of 1-ethoxy-1-methylcyclopentane. 

Phytovolatilization involves the use of plants and plant-associated soil microbes to take up contaminants from the soil, transform them into volatile forms, and release them into the atmosphere (Lin, 2008). Phytovolatilization occurs as growing trees and other plants take up water and the organic and inorganic contaminants. Metalloids, such as selenium. As, and tin, can be methylated to volatile compounds or mercury that can be biologically transformed to elemental Hg. Phytovolatilization has been primarily used for the removal of mercury and selenium. 

One point of note is that the use of cold-box technology requires the removal of mercury from the gas streams. A fire at Santos Moomba facility in Australia in early 2004 was thought to be due to a mercury attack on the equipment... 

Mercuriocyclization has also been utilized in order to obtain spiroketals from hemiketals. Thus, treatment of l,10-undecadien-6-one (11) with mercury(II) acetate in water/tetrahydrofuran affords, with total regioselectivity, 2,8-bis[(chloromercurio)mcthyl]-l,7-dioxaspiro[5.5]undccanc as a diastereomeric mixture. The diastereomeric ratio was not reported but depends on the reaction time, owing to the reversibility of oxymercuration-cyclization steps. Reductive removal of mercury by sodium borohydride under phase-transfer conditions gives a good yield of 2,8-dimethyl-l,7-dioxaspiro[5.5]undecane (12) as a diastereomeric mixture101,102. 

Delanghe et al. studied the removal of mercury(II) from contaminated brines using graphite felt cathodes [25]. A 100% current efficiency for mercury removal was obtained at a potential of - 400 mV vs. SCE on a graphite felt 1 cm thick at a flowrate of 1 cm/s. This current efficiency was higher than that obtained on RVC, nickel foam platinum grids, or graphite sphere cathodes. 

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