Mercury, traces

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. 

In analogy to sample introduction by hydride generation, mercury trace analysis is possible by reducing Hg compounds to the metal using the cold vapour technique or the determination of iodine at the ultratrace level (after oxidation with 70 % perchloric acid of iodide to iodine) via the gas phase. 

Mateo MD, Forteza R, Cerda V, et al. 1988. Comparative study of a kinetic - thermometric method and the atomic-absorption cold-vapour technique for determination of mercury traces and ultra-traces. Thermochimica Acta 128 21-30. 

Scholz, F., Nitschke, L. and Henrion, G. (1987) Determination of mercury traces by differential-pulse stripping voltammetry after sorption of mercury vapour on a gold-plated electrode. Anal. Chim. Acta, 199,167-171. 

Babko-Malyi, S., Battleson, D, Ray, L, Buckley, W.P., Reynolds, J. (2000), Mercury Removal from Combustion Elue Gases by the Plasma-Enhanced Electrostatic Precipitator, Air Quality II Mercury Trace Elements, and Particular Matter Conference, Proceedings, McLean, VA. 

Sondreal, E.A., Benson, S.A., and Pavlish, J.H. 2006. Status of research on air quality Mercury, trace elements, and particulate matter. Fuel Processing Technology, 65/66 5-22. 

Phenylmercuric acetate Helisoma campanulata 4.75 Inorganic mercury (98) Ethyl mercury (2) Methyl mercury (trace) 0.59 Fang (1973)... 

Foley GJ, McKay D. Science program being undertaken in North Dakota. In Proceedings of the air quality II mercury, trace elements and particulate matter... 

Senior CL, Helble JJ, Sarofim AF, Emissions of mercury, trace elements, and fine particles from stationaiy combustion sources. Fuel Process. Technol. 2000, 65, 263-288. 

Cuiiie JE, DeBerry DW, Blythe GM. Enhanced mercury control by wet FGD systems, Proceedings of the International conference on Air Quality VI Mercury, trace elements, SO3, Particulate Matter, and Greenhouse Gases, 2007, Arlington, VA, Sept 24-27. 

Sipos L, Valenta P, Numberg HW, Branica M (1977) Applications of polarography and voltammetry to marine and aquatic chemistry. A new voltammetric method for study of mercury traces in sea and inland waters. J Electroanal Chem 77 263-266... 

When constructing a manometer of the type shown in Fig. 12(c), it is impor tant to apply a very high vacuum (e.g., with a Hy-Vac pump) to the manometer while the mercury in the left-hand (sealed) limb is heated until it boils unless this is done, traces of air will remain in this limb and cause inaccurate readings. During a distillation, the tap I should be kept closed except when a pressure reading is being taken if it is left open indefinitely, a sudden default by the distillation apparatus or by the pump may cause the mercury in the sealed limb of G to fly back and fracture the top of the limb. 

The drying agent was filtered off on a sintered-glass funnel and rinsed with some THF. The solution was transferred into a 500-ml wide-necked flask and concentrated in a water-pump vacuum. In order to remove the last traces of THF and some water the flask was connected directly (without a column) to a condenser and a receiver, cooled at -190°. The flask was evacuated by means of a mercury pump (p < 0.1 mmHg) and heated for 1.5 h at 85°C. The greater part of the mono-... 

Another area where controlled-potential coulometry has found application is in nuclear chemistry, in which elements such as uranium and polonium can be determined at trace levels. Eor example, microgram quantities of uranium in a medium of H2SO4 can be determined by reducing U(VI) to U(IV) at a mercury working electrode. 

Anodic stripping voltammetry at a mercury film electrode can be used to determine whether an individual has recently fired a gun by looking for traces of antimony in residue collected from the individual s hands, fn a typical analysis a sample is collected with a cotton-tipped swab that had been wetted with 5% v/v HNO3. When returned to the lab, the swab is placed in a vial containing 5.00 mb of 4 M HCl that is 0.02 M in hydrazine sulfate. After allowing the swab to soak overnight,... 

Acetic acid, fp 16.635°C ((1), bp 117.87°C at 101.3 kPa (2), is a clear, colorless Hquid. Water is the chief impurity in acetic acid although other materials such as acetaldehyde, acetic anhydride, formic acid, biacetyl, methyl acetate, ethyl acetoacetate, iron, and mercury are also sometimes found. Water significantly lowers the freezing point of glacial acetic acid as do acetic anhydride and methyl acetate (3). The presence of acetaldehyde [75-07-0] or formic acid [64-18-6] is commonly revealed by permanganate tests biacetyl [431-03-8] and iron are indicated by color. Ethyl acetoacetate [141-97-9] may cause slight color in acetic acid and is often mistaken for formic acid because it reduces mercuric chloride to calomel. Traces of mercury provoke catastrophic corrosion of aluminum metal, often employed in shipping the acid. 

Loaded Adsorbents. Where highly efficient removal of a trace impurity is required it is sometimes effective to use an adsorbent preloaded with a reactant rather than rely on the forces of adsorption. Examples include the use of 2eohtes preloaded with bromine to trap traces of olefins as their more easily condensible bromides 2eohtes preloaded with iodine to trap mercury vapor, and activated carbon loaded with cupric chloride for removal of mercaptans. 

The mercury cell operates efficiently because of the higher overpotential of hydrogen on mercury to achieve the preferential formation of sodium amalgam. Certain trace elements, such as vanadium, can lower the hydrogen overpotential, however, resulting in the release of hydrogen in potentially dangerous amounts. 

Removal of brine contaminants accounts for a significant portion of overall chlor—alkali production cost, especially for the membrane process. Moreover, part or all of the depleted brine from mercury and membrane cells must first be dechlorinated to recover the dissolved chlorine and to prevent corrosion during further processing. In a typical membrane plant, HCl is added to Hberate chlorine, then a vacuum is appHed to recover it. A reducing agent such as sodium sulfite is added to remove the final traces because chlorine would adversely react with the ion-exchange resins used later in the process. Dechlorinated brine is then resaturated with soHd salt for further use. 

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