Mercury chlor-alkali

EEC Directive on mercury (chlor-alkali electrolysis industry)... 

There will be no increase in mercury chlor-alkali production capacity. This is an unequivocal reiteration of a commitment made in 1995. It represents a de facto commitment to phase-out as mercury cellrooms reach the end of their working life. 

Replacement of Mercury Chlor-Alkali Plants with New Membrane Plants in Australia... 

Emissions from mercury ore processing facilities and mercury chlor-alkali plants Emissions from sludge incineration plants, sludge drying plants, or a combination of these that process wastewater treatment plant sludge... 

Decommissioning of Mercury Chlor-Alkali Plants, Env. Prot. 3,2nd ed., Euro Chlor, Brussels (1999). 

Overvoltages for various types of chlor—alkali cells are given in Table 8. A typical example of the overvoltage effect is in the operation of a mercury cell where Hg is used as the cathode material. The overpotential of the H2 evolution reaction on Hg is high hence it is possible to form sodium amalgam without H2 generation, thereby eliminating the need for a separator in the cell. 

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. 

Electrolytic Preparation of Chlorine and Caustic Soda. The preparation of chlorine [7782-50-5] and caustic soda [1310-73-2] is an important use for mercury metal. Since 1989, chlor—alkali production has been responsible for the largest use for mercury in the United States. In this process, mercury is used as a flowing cathode in an electrolytic cell into which a sodium chloride [7647-14-5] solution (brine) is introduced. This brine is then subjected to an electric current, and the aqueous solution of sodium chloride flows between the anode and the mercury, releasing chlorine gas at the anode. The sodium ions form an amalgam with the mercury cathode. Water is added to the amalgam to remove the sodium [7440-23-5] forming hydrogen [1333-74-0] and sodium hydroxide and relatively pure mercury metal, which is recycled into the cell (see Alkali and chlorine products). 

H. Y. Castner (US/UK) and C. Kellner (Vienna) independently developed commercial mercury-cathode cell for chlor-alkali production... 

Markholm mm and Bennett JP (1998) Mercury accumulation in transplanted llypogymniaphy-sodes lichens downwind of Wisconsin chlor-alkali plant. Water, Air Soil Poll 102 427-436. 

The wastewater generated in the membrane cell and other process wastewaters in the cell are generally treated by neutralization.28 Other pollutants similar to those in mercury and diaphragm cells are treated in the same process stated above. Ion exchange and xanthate precipitation methods can be applied in this process to remove the metal pollutants, while incineration can be applied to eliminate some of the hydrocarbons. The use of modified diaphragms that resist corrosion and degradation will help in reducing the amount of lead, asbestos, and chlorinated hydrocarbon in the wastewater stream from the chlor-alkali industry.28... 

Summary of Raw Waste Loadings Found in Verification Sampling of Unit Product of Chlor-Alkali (Mercury Cell and Diaphragm Cell Processes)... 

FIGU RE 22.5 General wastewater treatment process flow diagram at a mercury cell plant for the production of chlor-alkali. 

According to the different sentinel species analyzed, THg levels in specimens collected downstream from the impacted areas are 10-20 times greater than upstream levels. It clearly points out the relevance of chlor-alkali plants in terms of mercury river pollution. 

Keywords Aquatic organisms, Chlor-alkali plants, Crayfish, Fish, Mercury, Methylmercury, Zebra mussel... 

The Hg-electrolysis technology is one of the major point sources of Hg contamination, and its impact on the environment has been studied worldwide [23-26]. Although mercury cell chlor-alkali industry is obsolete in most of the European Union countries [27], in Spain it will be allowed until the end of 2010. 

Finally, it should be mentioned that three out of the eight Spanish chlor-alkali plants operating with the mercury process are located in the Ebro River basin in the cities of Sabinanigo and Monzon - along the tributaries Gallego and Cinca Rivers, respectively - and Flix along the Ebro River (Fig. 1). Indeed, mercury emissions from the Hix and Monzon have already been reported [28]. Therefore, the mid-low Ebro River watershed might be considered as a hot spot of aquatic pollution of mercury in Spain. 

On the other hand, the industrial activity of the other two mercury cell chlor-alkali plants have caused important Hg pollution in Sabinanigo (capacity of 25 x 103 Mg chlorine/year) and Monzon (31 x 103 Mg chlorine/year) (see Fig. 1), two small and industrial cities located in the middle course of the Gallego and Cinca Rivers, respectively, two tributaries of the Ebro River [31]. 

Another well-documented case of feral fish chronically exposed to mercury through the effluent of the chlor-alkali plant is the case of the Cinca tributary [64, 65]. Barbel and bleak were collected upstream (SI) and downstream (S2) a chlor-alkali plant located at Monzon (Fig. 3). It is important to point out that there is no physical barrier between SI and S2 to prevent fish upstream migration of suspicious contaminated fishes from S2. 

In this regard, high liver/muscle ratios of mercury concentration were reported in fish exposed to the effluents from a chlor-alkali plant in a contaminated area [68, 69]. Then, liver of fish downstream from the plant also had very high inorganic mercury to THg ratios [69]. 

Delta irrigation channels (Faria, personal communication) indicate a saline water intrusion in the irrigation channels of the Delta. This saline intrusion may cause a dilution of mercury pollution originated at the chlor-alkali plant, hence resulting in lower average THg concentrations in Delta specimens. 

Biester H, Muller G, Scholer HF (2002) Estimating distribution and retention of mercury in three different soils contaminated by emissions from chlor-alkali plants part I. Sci Total Environ 284 177-189... 

Landis MS, Keeler GJ, Al-Wali KI, Stevens RK (2004) Divalent inorganic reactive gaseous mercury emissions from a mercury cell chlor-alkali plant and its impact on near-field atmospheric dry deposition. Atmos Environ 38 613-622... 

Montuori P, Jover E, Diez S, Ribas-Fito N, Sunyer J, Triassi M, Bayona JM (2006) Mercury speciation in the hair of pre-school children living near a chlor-alkali plant. Sci Total Environ 369 51-58... 

OSPAR (2007) Mercury losses from the chlor-alkali industry (1982-2005). ISBN 978-1-905859-56-6... 

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