Mercury, recovery of, from

Many mercury compounds are labile and easily decomposed by light, heat, and reducing agents. In the presence of organic compounds of weak reducing activity, such as amines (qv), aldehydes (qv), and ketones (qv), compounds of lower oxidation state and mercury metal are often formed. Only a few mercury compounds, eg, mercuric bromide/77< 5 7-/7, mercurous chloride, mercuric s A ide[1344-48-5] and mercurous iodide [15385-57-6] are volatile and capable of purification by sublimation. This innate lack of stabiUty in mercury compounds makes the recovery of mercury from various wastes that accumulate with the production of compounds of economic and commercial importance relatively easy (see Recycling). 

Environmental Factors. The control, recovery, and disposal of mercury-bearing waste products are as important to the mercurials industry as the manufacturing process. The difficulties involved in removing mercury from waste-product streams and the problems of recovery or disposal have resulted in a substantial reduction in the number of manufacturers of mercury compounds as well as in the variety of mercury compounds being manufactured. Moreover, the manufacturing process used for a mercury compound may not necessarily be the most efficient or economical. Rather, the choice may depend on the nature of the by-products, the toxic hazard of the process, and the ease of recovery of the mercury from the waste-product stream. 

Special Industries Certain industrial units, such as secondary lead and nickel-chromium smelters and mercury recovery furnaces, and other units that process wastes from metals recovery normally do not meet the conditions required for being considered as legitimately burned for metals recovery. U.S. EPA revised the BIF standards to conditionally exclude those wastes that are processed for metals recovery, but do not meet the criteria. Waste streams in these units must contain recoverable levels of metals and the waste must not contain more than 500 mg/L of the toxic organics listed in Part 261 to be considered for this conditional exemption. 

The objectives sought to be achieved through disposal of refrigeration and air conditioning waste appliances are (a) separate disposal of the CFCs from the circulation system and the insulating material (b) further stripping of hazardous substances (e.g., mercury switches) and (c) recovery of ferrous metals, the priority in metal recycling. 

Jang M, Hong SM, Park JK (2005) Characterization and recovery of mercury from spent fluorescent lamps. Waste Manag 25 5-14... 

Figure 11 Proposed reaction schemes for the recovery of indium (a) and mercury (b) from waste materials using HN(SPPh2)2-I2 as oxidising reagent56,57...

Land use/land cover influences on the estimated time to recovery of inland lakes from mercury enrichment... 

Electrolytic Recovery of Mercury Metal from a Mercuric Chloride-Containing Waste... 

Electrolytic methods have been applied to the treatment of other metal waste streams generated in the electroplating or metal finishing industries. Pollution engineering processes have been designed and implemented for the removal of hexavalent chromium, trivalent chromium, nickle, copper, zinc and cadmium.Besides the Edwards patent, there seems to be no documentation of electrolytic methods for removal and recovery of mercury metal from waste streams. 

One other method of recovering mercury from the vapor phase is to extract mercury using a suitable solvent (e.g. toluene or chloroform) in a scrubber, e.g. a packed tower. The mercury in the solvent can be reprocessed commercially. But, the poor solubility of mercury in such solvents warrants consumption of huge quantities of solvent thus limiting the use of a packed tower process for mercury recovery. It is therefore apparent that a preconcentration step must be used to facilitate the removal and recovery of mercury from the air phase. 

A biological process for detoxification of mercury in polluted water and sludges has been developed. Recovery of elemental mercury from the vapor phase for reuse is being studied and preliminary results show promise for the process. A full-scale process is under investigation for field/commercial application. 

To recover gold from electronics, see J. W. Hill and T. A. Lear, Recovery of Gold from Electronic Scrap, J. Chem. Ed. 1988,65, 802. To remove Hg from gold, soak it in a 1 1 mixture of 0.01 M (NH4)2S208 and 0.01 M HNOj [T. Nomura and M. Fujisawa, Electrolytic Determination of Mercury(II) in Water with a Piezoelectric Quartz Crystal, Anal. Chim. Acta 1986, 182, 267]. 

The overall mercury recovery in the process is 67 15%. The precision of the method is about 20%, and the detection limit is about 0.01 ppm mercury for a 1-g sample of coal. Reliability of the method was determined by the accurate analysis of two coal samples used in the Bureau of Mines study of the problems involved in determining mercury in coal (9) and then by the agreement within experimental error of the results from the 11 Bureau of Mines round-robin coal samples and their probable mercury contents (4). 

Grau, J.M. and Bisang, J.M., Removal and recovery of mercury from chloride solutions by contact deposition of iron felt, /. Chem. Tech. Biotechnol., 62, 153-158, 1995. 

Kuwae et al. [138] have described a rapid determination of mercury in soils by high-frequency induction heating (rf) followed by cold vapour atomic absorption spectrometry. The mercury released from the sample is absorbed in stannous chloride-hydroxylamine prior to atomic absorption spectrometry. Recovery of 99.4 to 99.8% mercury was obtained by this method from portions of sample containing between 0.025-0.15 p,g of mercury. 

Recoveries of mercury ranged from 83% at the 1 pg mercury level to 96.1% at the 100 pg mercury level in turf, 94% at the 0.5 pg mercury level to 99.5% at the 4 pg mercury level in cracked whole barley, and 101% at the 0.1 pg mercury level to 94% at the 0.5 pg mercury level in wheat. For five-gram barley samples containing less than 5 pg mercury, the standard deviation of a sample determination was 0.12. 

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