Mercury chloralkali industry

A mixture of hydrogen and chlorine gas, eventually in combination with air, can be very explosive if one of the components exceeds certain limits. In chlorine production plants, based on the electrolysis of sodium chloride solutions, there is always a production of hydrogen. It is, therefore, essential to be aware of the actual hydrogen content of chlorine gas process streams at any time. There are several places in the chlorine production process where the hydrogen content in the chlorine gas can accumulate above the explosion limits. Within the chloralkali industry, mainly two types of processes are used for the production of chlorine—the mercury- and the membrane-based electrolysis of sodium chloride solutions (brine). 

The ozone concentration in the atmosphere is only a few pphm. In certain chemical plants as in electrolytic mercury cell houses in the chloralkali industry, the ozone concentration is higher. Although the atmospheric ozone level is low, it reacts with rubber double bonds rapidly and causes cracking of rubber products. Especially when rubber is under stress (stretching and bending as in the case of flexible cell covers), the crack development is faster. Neoprene products resist thousands of parts per hundred million of ozone for hours without surface cracking. This nature of neoprene is quite suitable for cell house application in chlor-alkali industries. Natural rubber will crack within minutes when subjected to ozone concentration of only 50 pphm. 

Several industrial processes use mercury in large amounts, and the resulting potential for spills and loss to the environment is great. One of the largest is the chloralkali industry, in which mercury is used as an electrode for the electrolysis of brine to form chlorine gas and sodium hydroxide ... 

Occupational exposure to inorganic mercury is quite common, and occurs in the dental and chloralkali industries, as well as in thermometer factories, and in mercury mines. Approximately 70,000 workers in the United States are regularly exposed to mercury [16]. Measurements of mercury in blood and urine are useful in quantifying the magnitude of exposure (see section about biological monitoring below). In most instances there is a linear relationship between ambient air and urine concentration of mercury, where the urine... 

Sallsten G, BarregSrd L, Jarvholm B. Mercury In the Swedish chloralkali industri - an evaluation of the exposure and preventive measures over 40 years. Ann Occup Hyg 1990 34 205-14. 

A needed study is a longitudinal epidemiology study that tracked daily individual exposure levels in chloralkali industry workers, fluorescent lightbulb manufacturers, or other mercury utilizing industries, and associated these exposure levels with weekly urine and blood samples for a period of 1-2 years. Neurobehavioral testing (using tests from ATSDR s recommended test battery for adults) should be used... 

Ellingsen DG, Andersen A, Nordgagen NP, et al. 1993. Incidence of cancer and mortality among workers exposed to mercury vapour in the Norwegian chloralkali industry. Brit J Ind Med 50 875-880. 

Mercury compounds continue to have numerous commercial uses. Besides its use as a preservative, mercury is used in the manufacture of many technical and medical instruments including blood pressure measurement devices, manometers, thermometers, and barometers. Mercury is also used in production of certain types of fluorescent lamps and in the chloralkali industry, where chlorine and caustic soda are produced using brine electrolysis in mercury cells. Metallic mercury is used in the production of precious metals such as gold and silver. As part of the production process, metallic mercury can be used to concentrate gold from... 

In 2000, 45 Mt of CI2 was manufactured by the chloralkali process this represents 95% of the global supply. The main producers are the US, Western Europe and Japan. Whereas the Japanese chloralkali industry operates almost entirely with the membrane cell, the US favours use of the diaphragm cell, and just over half of the Western European industry retains use of the mercury cell. On environmental grounds, the chloralkali industry is being pressured to replace mercury and diaphragm cells by the membrane cell. This is not the only environmental concern facing the industry demand for CI2 has fallen in the pulp and paper industry and in the production of chlorofluorocarbons, the latter being phased out as a result of the Montreal Protocol for the Protection... 

Ellingsen D, Andersen A, Nordhagen HP, Eeskind j and Kjuus H (1992) Cancer incidence and mortality among workers exposed to mercury in the Norwefian chloralkali industry. 8th International Symposium on Epidemiology in Occupational Health, Paris, France, September 10-12, 1991. Rev. Epidemiol Sante Publique 40 (Suppl. 1) 93-S94. 

For many years, cells with mercury cathodes were used in the chloralkali industry. Mercury is not very reactive or soluble and was thought to be harmless in the environment. Then some individuals who ate fish from mercury-contaminated waters became seriously ill. This event brought to light the fact that aquatic microorganisms convert metallic mercury to a toxic, water-soluble compound that enters the food chain (Section 15.6). 

In the profiles of the core from the industrial area, mercury displays the highest accumulation. Mercury in this area, close to the industrial district, has probably derived from a large chloralkali plant which has employed mercury cathodes since the fifties. Whereas, at present, very severe measures are taken to prevent mercury spills into the Lagoon, in the past, polluted waters and solid materials were discharged almost untreated. In the most superficial strata a marked decrease in the accumulations is, in fact, recorded. Lead and Cd accumulations are lower here by a factor of 5-10. The presence of cadmium in the sediments of the Lagoon has been referred to sphalerite (ZnS) processing on the basis of a strict concomitant... 

Mercury is one of the most toxic water contaminants, and its discharges from chloralkali. paper and pulp, oil refining, pla.stic, and battery manufacturing industries [212] need to be controlled. It can exist in aqueous solution as the free metal, as Hg(l), or as Hg(Il) [32], the latter being favored in well-aerated water (see Fig. A2). 

Based on samples from museum collections, it was demonstrated that mercury content in feathers from fish-eating birds were comparatively low in the years 1815 through 1940. However, since 1940, or the advent of the chlo-ralkali industry (wherein mercury is used as a catalyst in the process to produce sodium hydroxide and chlorine gas from sodium chloride and water, with significant loss of mercury to the biosphere), mercury concentrations in feathers were eight times higher on average. Mercury levels were also elevated in feathers and tissues of aquatic and fish-eating birds from the vicinity of chloralkali plants these increased levels of mercury were detectable up to 300 km from the chloralkali plant. 

In aquatic environments where point sources of industrial contamination have been identified, the elimination of mercury discharges has usually improved environmental quality. Such improvement has been reported for Minamata Bay for sediments in Saguenay Fjord, Quebec, when chloralkali wastes were limited for fish residues in Lake St. Clair, Canada, after two chloralkali plants were closed and in various sections of Europe and North America when industrial discharges were eliminated. 

Occupational exposure to mercury vapor occurs in a variety of industries such as chloralkali plants, thermometer factories, gold extraction process, and mercury mining. Dentists and dental assistants are also exposed to mercury vapor during insertion, polishing, and removal of amalgam fillings. 

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