Mercury recovery tests

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. 

Multicommutation also allows implementation of procedures for assessment of accuracy. For example, the same analyte can be determined by two different methods with the same flow network. In this way, a multicommutated flow manifold was proposed for chloride determination in natural waters with different sample matrices based on the spectrophotometric procedure using mercury(II) thiocyanate and the turbidimetric method using silver nitrate [19]. Moreover, in-line addition/recovery tests were implemented for every assayed sample in order to detect matrix effects. 

The method was tested by tracer experiments on several matrices, including coal and crude oil. Recoveries were quantitative or nearly so (97.8%). The method gave good results for zinc, cadmium, mercury, selenium, and arsenic in NBS orchard leaves and bovine liver and is currently being used to determine these elements in new SRMs. 

A surprising result was the amount of mercury remaining on the bullet after it had passed through a wad of filter paper and the bullet recovery medium. Mercury was also readily detectable in the bullet hole perimeter tests (Table 20.12 and Table 20.13). 

In order to test the NMR-PR approach further, the time course of metabolic urinary changes induced by two renal toxins has been investigated in detail. In this case, toxic lesions were induced in Fisher 344 rats by a single acute dose of the renal cortical toxin mercury(II) chloride and the medullary toxin 2-bromoethanamine. The rat urine was collected for up to 9 days after dosing and was analysed using NMR spectroscopy. The onset, progression and recovery of the lesions were also followed using histopath-... 

A person has the symptoms of chronic mercury poisoning, but there is no logical explanation of where the contamination is occurring. The problem is to determine if the person is in fact being slowly exposed to mercury vapors or a mercury compound. This will be done by testing for Hg in head hair. You are given a sample of hair to determine the Hg in it. However, you have never done this before, and you need a blank, in any case. You obtain some hair from a known healthy person and determine the Hg present. You run two samples one as a blank and the other spiked with 10 ppb Hg to make sure you can detect it. You also run a set of five standards. This allows you to prepare a calibration curve and to determine the % recovery. 

Reticulated vitreous carbon (RVC) cathodes were tested for removing mercury from contaminated brine solutions [28]. Copper foeun cathodes were used for electrolytic recovery of copper [29]. 

Centrifugation of urine decreased the mercury content of the liquid phase (Lindstrom, 1959). Full recovery of mercury added in urine could only be achieved if the specimen was vigorously shaken before analysis. None of the preservatives tested could prevent this loss (Trujillo et al., 1974),... 

In conclusion, considerable discrepancy afflicts reported data on loss of mercury from samples during preparation and digestion. It is, thus, important to adapt the procedure to real samples and to carefully evaluate recovery, matrix effects, and detection limits for these samples. Mostly, such tests are carried out on spiked samples, but a more distinguished approach is to study the recovery through the different steps of the procedure by use of radioactive mercury isotopes. The most reliable data should be those obtained on samples, in which the mercury has been incorporated in vivo (e.g. Clarkson and Greenwood, 1970 LaFleur, 1973 Stein et al., 1974 Iyengar et al., 1978 Stuart, 1978a Semu et al., 1985). 

Figure 2 shows a schematic diagram of a pressure let down system, which conforms to the European Standard ISO 6978 (ASTM 6350) for natural gas sampling. By careful choice of components and temperature of operation it is possible to provide reliable data on the mercury levels present in the natural gas samples. By injecting defined samples of mercury into the sample line prior to the sample collection, it is possible to check the validity of the measurements by testing the spike recovery. Recoveries in the region of 95-105 % will show that there is little, if any, loss with the system, and the analyst can be confident of the levels found in the gas streams. 

In addition to the incomplete oxidation of some chemicals with the reflux methods, laboratory wastes generated from the standard COD tests contain hexavalent chromium, mercury, and silver metals, all of which are classified as hazardous wastes by the US Environmental Protection Agency and their disposal is regulated under Resource Conservation and Recovery Act. Consequently, various modifications of the standard procedures or alternative methods have been reported for the COD test. These include the replacement of hexavalent chromium, mercury, and silver metals microwave digestion automation and online COD measurement and electrochemical oxidation to measure the sample COD. 

Becker prepared a sttlfur derivative by a two step procedure consisting of prereaction of chitosan with glutaraldehyde followed by reaction with a mixture of formaldehyde and thioglycolic add. These sulfur derivatives have been successfully tested for the recovery of mercury and the uptake of predous metals, owing to the chelating affinity of sulfur compounds for metal ions (Becker et al., 2000). Sulfonic groups have been also grafted on chitosan to improve sorption capacity for metal ions on acidic solutions (Weltrowski et al., 1996). 

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