Mercury recovery

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. 

Scenario 1 The first phase of the roll out would be of around 3 years (2013-2016). It would cover mainly the class I cities.2 It is desired that the collection and recycling program uses the best demonstrated available technology (BDAT) option which are - DTCs to collect and crush lamps without releasing mercury in transit and recycling facility having mercury recovery facility. 

Cappon and Crispin-Smith [59] have described a method for the extraction, clean-up and gas chromatographic determination of alkyl and aryl mercury compounds in sediments. The organomercury compounds are converted to their chloroderivatives and solvent extracted. Inorganic mercury is then isolated as methylmercury upon reaction with tetramethyltin. The initial extract is subjected to a thiosulphate clean-up and the organomercury species are isolated as their bromoderivatives. Total mercury recovery was in the range 75-90% and down to lpg kg-1 of specific compounds can be determined. 

NFS claims that DeHg technology offers a low-temperature alternative to other mercury recovery processes. They claim that the final waste form generated by processing passes Toxicity Characteristic Leaching Procedure (TCLP) criteria for disposal, and that centrifuge testing has proven that no free liquid mercury remains in the treated product. 

Mercury Recovery Services, Inc. (MRS), has developed the Mercury Removal/Recovery Process (MRRP) to treat media contaminated with mercury. The ex situ process uses medium-temperature thermal desorption to remove the mercury from contaminated wastes. Process wastes are heated in a two-step process to recover metallic mercury in a 99% pure form. MRS claims MRRP can be applied to soils, activated carbon, mixed waste, catalysts, electrical equipment, batteries, lamps, fluorescent bulbs, mercurous and mercuric compounds, mercury-contaminated waste liquids, and debris. 

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. 

In our laboratory research efforts are directed towards development of a mercury recovery process based on adsorption/desorption mechanisms. The schematic diagram of the process is shown in Figures 3 and 4. 

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). 

Various atomic absorption spectrophotometric procedures have been described for the determination of mercury in soils. Methods based on attacking the mercury in soil samples with mineral acids and permanganate have been shown to give low mercury recoveries. In recent years methods based on decomposition of the sample by heating have gained favour in that they obviate any tendency to produce low results. 

Mercury Recovery.. The methods would be costly if the mercury could not be recovered and reworked. Details of a simple procedure for recovering the mercury by converting the mercuric bromide to the oxide and heating the oxide have been published.41... 

Sample Encapsulation. The popular polyethylene snap-cap, heat-sealed vials, used in the initial phases of the work, were found to be unsatisfactory because of post-irradiation losses of mercury and had to be replaced by quartz vials. Since 197Hg has a convenient half-life, initially no special attempts were made to count the samples immediately after arrival from the reactor facilities, and they were processed whenever time and sample scheduling permitted. The first set of data, obtained five days after irradiation, indicated that the petroleum stocks spiked with mercury had lost 50-60% of their 197Hg activity when compared with aqueous standards the latter showed only the expected decrease in activity caused by decay. A second set of the same samples was irradiated and counted the same day in this case the mercury recovery was more nearly quantitative. Repeated experiments showed that if the samples were irradiated in polyethylene and counted within four to eight hours, excellent recoveries of mercury were obtained (Table 3.VI). Subsequent... 

Samples are placed in an ultrasonic bath for 1 h immediately prior to analysis. This step was recommended to us by the NIC representative to increase mercury recovery in a sample. Ice chips are added to the ultrasonic bath to prevent the temperature from rising more Aan 3°C above ambient laboratory temperature. 

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