Extraction selenium

The sludge which separates from the oxidation process contains sulphates of lead and calcium, and forms a source of the former metal, which is often an important by-product from the selenium extraction. 

M. Demovics, Z. Stefanka, P. Fodor, Improving selenium extraction by sequential enzymatic processes for Se-speciation of selenium-enriched Agaricus bisporus, Anal. Bioanal. Chem., 372 (2002), 473D480. 

Potin-Gautier, M., Gilon, N., Astruc, M., De Gregori, I., Pinochet, H. Comparison of selenium extraction procedures for its speciation in biological materials. Int. J. Environ. Anal. Chem. 67, 15-25 (1997)... 

Numbers in parentheses represent the percentage of selenium extracted by aqueous solution. 

Crews HM, Clarke PA, Lewis DJ, Owen LM, Srutt PR and Izquierdo A (1996) Gastrointestinal extracts of cooked cod by High performance liquid chromatography-inductivdy coupled plasma mass spectrometry and electrospray mass spectrometry. J Anal At Spectrom 11 1177-1182. Dernovics M, Stefanka ZS and Fodor P (2002) Improving selenium extraction by sequential enzymatic processes for Se-speciation of selenium enriched Agaricus bisporus. Anal Bioanal Chem 372 473-480. 

Typically, the emulsion globules are 0.1-2 mm in diameter, and the encapsulated, aqueous droplets are 0.1-5 fim in diameter. A typical emulsion formulation for selenium extraction would consist of a high concentration of aqueous solution of NaCl dispersed in a low volatility, non-polar hydrocarbon like kerosene, and stabilized with an oil-soluble surfactant. The organic phase also contains a complexing agent for the selenium compounds. In the ELM process, a selenium anion first diffuses to the surface of the oil globule where, depending on the ionic... 

Equilibrium Partition Coefficients. Equilibrium solvent extraction experiments are a convenient way to screen various complexing agents for suitability as selenium extractants and to assess the potential for competition from innocuous ions like sulfate. The solvent extraction experiments allow the determination of reaction equilibrium constants and distribution or partition coefficients of the selenium species between the organic (membrane) phase and the aqueous (internal or external) phase. The equilibrium constant (K ) and distribution coefficient (K ) for the reaction of selenite with the complexing agent are defined in the equations given below,... 

Emulsion swelling can also adversely affect ELM performance. Some degree of swelling is inevitable in the ELM process. Swelling is only a problem if it unacceptably reduces the driving force for the selenium extraction, unacceptably dilutes the internal-phase selenium concentration, creates handling problems, or leads to emulsion breakage. 

On the other hand, wet chlorination of refinery slimes has proven to be a rapid and simple method of obtaining high extractions of selenium from slimes. A simple wet chlorination flow sheet is shown in Figure 3. Slimes chlorination per se is not a simple deselenization operation, but rather a process wherein virtually all the constituents of slimes which form soluble chlorides report as a complex solution of mixed chlorides. Thus the use of wet chlorination requires a complete change in the process to recover the metal values in slimes. The first plant to use wet chlorination of slimes was started by Kennecott (Salt Lake City, Utah) in 1995. 

Organ oselenium compounds, such as phosphine selenides, are being evaluated in solvent extraction systems for silver and gold (63). Also, potential pharmaceuticals containing selenium have been prepared (64). 

J. E. Hoffmann, "Recovery of Selenium from Electrolytic Copper Refinery Slimes," in V. Kudryk, D. A. Corrigan, and W. W. Liang, eds.. Precious Metals Mining Extraction and Processing H, TMS, Warrendale, Pa., 1983. 

A solution of 1.0 g of 3,17-androstandione in 50 ml of methanol and containing 1 g of selenium dioxide, was allowed to remain in an ice-chest overnight. The formed 3,3-dimethoxy-androstan-17-one was not separated. 1 g of solid potassium hydroxide and 2.5 g of sodium borohydride in 2.5 ml of water were added and the mixture allowed to react at room temperature for 24 hours. The solution was then poured into a large excess of water, extracted... 

A process for the gravimetric determination of mixtures of selenium and tellurium is also described. Selenium and tellurium occur in practice either as the impure elements or as selenides or tellurides. They may be brought into solution by mixing intimately with 2 parts of sodium carbonate and 1 part of potassium nitrate in a nickel crucible, covering with a layer of the mixture, and then heating gradually to fusion. The cold melt is extracted with water, and filtered. The elements are then determined in the filtrate. 

A novel TLC spectrofluorometric method for identification and determination of selenium in different food samples of animal and vegetable origin has been proposed [30]. The procedure involves the digestion of food sample (1 to 5 g) in the presence of cone. HNO3 (5 ml), 70% HCIO4 (10 ml), and FIjO (10 ml) in a 250-ml Kjeldahl flask reduction of Se(VI) into Se(IV) complexation of the isolated selenium with 23-diaminonaphthene (DAN) extraction of the resultant Se—DAN complex with cyclohexane and spectrofluorometric determination followed by confirmation of the presence of Se in the sample by TLC using thin layers of MN-300 cellulose powder. 

Selenium(IV) reacts with substituted 1,2-diaminobenzene or 2,3-diamlnonaphthalene in acidic solution to form stable cyclic derivatives which can t>e extracted into an organic solvent and analyzed by gas or liquid chromatography [682,683]. With chloro-, bromo-, or nitro-substituents the plazselenols can be determined with an electron-capture detector at the low picogram level. Se(VI) does not form piazselenol derivatives so the reaction with diaminobenzene can be used to determine the concentration of Se(IV) and Se(VI). Selenium(VI) may be redu to Se(IV) with... 

V. H. Aprahamian and D. G. Demopoulos, The Solution Chemistry and Solvent Extraction Behaviour of copper, iron, nickel, zinc, lead, tin, Ag, arsenic, antimony, bismuth, selenium and tellurium in Acid Chloride Solutions Reviewed from the Standpoint of PGM Refining, Mineral Processing and Extractive Metallurgy Review, Vol. 14, p. 143,1995. 

The ability of metal ions to form complexes with formazans is utilized to determine these ions either directly (for low valent reducing ions) or indirectly in the presence of a reducing agent. Among others, molybdenum(VI) and vanadium(V) have been determined using this method.442,443 Indirect methods have been reported for the analyses of substances that do not reduce tetrazolium salts. Examples include arsenic in nickel ores436 and traces of selenium.437 A method for the extraction and analysis of a number of metal ternary ion association complexes has been described.444 - 448... 

Plant groups such as Brassica have members with the ability to extract selenium from soil. Brassica juncea, in particular, has been the focus of much research due to its relatively large biomass... 

A waste is toxic under 40 CFR Part 261 if the extract from a sample of the waste exceeds specified limits for any one of eight elements and five pesticides (arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, endrin, methoxychlor, toxaphene, 2,4-D and 2,4,5-TP Silvex using extraction procedure (EP) toxicity test methods. Note that this narrow definition of toxicity relates to whether a waste is defined as hazardous for regulatory purposes in the context of this chapter, toxicity has a broader meaning because most deep-well-injected wastes have properties that can be toxic to living organisms. 

Water soluble Se in the North West region varied from 0.0002-0.0429 mg/kg. Water soluble Se accounted for 2.13-6.34% of the total Se in the soils of North China. Selenium is an essential element to animals and humans. When water soluble Se in soils is less than 0.003 mg/kg, Se deficiency in animal and human beings may occur. EDTA-extractable Se in the alkali desert soils of North China was in the range of 0.011-0.090 mg/kg this was about 5-11% of the total Se in the soils. Selenium deficiency was mostly found in the Loess Plateau and Tibet region. NH4OAc-cxtractable Ni in soils from Beijing was 0.29 mg/kg. 

Jump R.K., Sabey B.R. Soil test extractants for predicting selenium in plants. In Selenium in Agriculture and the Environment, L.M. Jacobs, ed. Madison, IL Soil Science of America, Inc. 1989. 

Tertiary phosphine selenides have been prepared either by direct fusion of the tertiary phosphine with elemental selenium1 or by refluxing the phosphine with selenium in an inert solvent.2 In the case of a solid phosphine, such preparations often require numerous and time-consuming extractions to obtain the pure phosphine selenide. 

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