Chemical extraction

In addition to the Hquid—Hquid reaction processes, there are many cases in both analytical and industrial chemistry where the main objective of separation is achieved by extraction using a chemical extractant. The technique of dissociation extraction is very valuable for separating mixtures of weakly acidic or basic organic compounds such as 2,4-dichlorophenol [120-83-2] and 2,5-dichlorophenol [583-78-8] which are difficult to separate by... 

Other Metals. Because of the large number of chemical extractants available, virtually any metal can be extracted from its aqueous solution. In many cases extraction has been developed to form part of a viable process (275). A review of more recent developments in metal extraction including those for precious metals and rare earths is also available (262). In China a complex extraction process employing a cascade of 600 mixer—settlers has been developed to treat leach Hquor containing a mixture of rare earths (131). 

Only slightly less accurate ( 0.3—0.5%) and more versatile in scale are other titration techniques. Plutonium maybe oxidized in aqueous solution to PuO " 2 using AgO, and then reduced to Pu" " by a known excess of Fe", which is back-titrated with Ce" ". Pu" " may be titrated complexometricaHy with EDTA and a colorimetric indicator such as Arsenazo(I), even in the presence of a large excess of UO " 2- Solution spectrophotometry (Figs. 4 and 5) can be utilized if the plutonium oxidation state is known or controlled. The spectrophotometric method is very sensitive if a colored complex such as Arsenazo(III) is used. Analytically usehil absorption maxima and molar absorption coefficients ( s) are given in Table 10. Laser photoacoustic spectroscopy has been developed for both elemental analysis and speciation (oxidation state) at concentrations of lO " — 10 M (118). Chemical extraction can also be used to enhance this technique. 

Demand and prices for chemicals from brine has fluctuated in the last 10 years. Table 2 shows a price Hst (73) of some of the main chemicals extracted from brines in 1991. 

Table 2. 1991 Prices for Chemicals Extracted from Brine...

The reliance of fossil fuels has been challenged by lower cost and renewable sources that are more environmentally friendly. The traditional chemical plant has met serious competition from green plants. Many monomers are now made via fermentation, using low-cost sugars as feedstock. Some of the commodity monomers are under siege by chemicals extracted from biomass. Monomer production has been expanded to include many more monomers from nature. 

Chlorinated polyethylene CPEs provide a very wide range of properties from soft/ elastomeric to hard. They have inherent oxygen and ozone resistance, have improved resistance (compared to PEs) to chemical extraction, resist plasticizers, volatility, and weathering. Products do not fog at high temperatures as do PVCs and can be made flame retardant. 

Marigold petals are rich sources of xanthophyUs, mainly lutein esters. To increase the coloring power, chemical extraction of the colorant from flower meal is performed or a new enzymatic procedure is applied. It was shown that treatment with cellulases or mixed saprophyte microorganisms or solid state fermentation improved the xanthophyll extraction yield. ... 

By combining our images of these walls and their constituent polymers during chemical extraction, with data from immunogold labelling of thin-sectioned material, we were able to construct a simple structural model of the primary cell wall of onion (Fig 3). 

Pectins were extracted from isolated cell walls of 5-week-old wheat plants using different methods. Enzymic digestions of the cell walls involved pectinases such as a commercial pectolayse or recombinant endopolygalacturonase [Maness Mort, 1989]. Chemical extractions involved the chelating agent imidazole [Mort et al., 1991] or solvolysis with anhydrous HF at 0 °C in a closed teflon line [Mort et al., 1989] followed by imidazole extraction. 

Gibson, M.J. and Farmer, J.G., Multi-step sequential chemical extraction of heavy metals from urban soils, Environ. Poll. (Ser. B), 11, 117, 1986. 

Despite these shortcomings, common to any chemical extraction procedure, sequential dissolution techniques still furnish more useful information on metal binding, mobility and availability than can be obtained with only a single extractant. 

Below is a review of the chemical extractants and their extraction order, in sequence, in the selective sequential dissolution procedures (Table 4.5). 

The Chemical Extractants for Different Fractions in Solid-phase Components... 

Belzile N., Lecomte P., Tessier A. Testing readsorption of trace elements during partial chemical extractions of bottom sediments. Environ Sci Technol 1989 23 1015-1020. 

Jung J., Logan T.J. Effects of sewage sludge cadmium concentration on chemical extractability and plant uptake. J Environ Qual 1992 21 73-81. 

Ma L.Q., Rao G.N. Effects of phosphate rock on sequential chemical extraction of lead in contaminated soils. J Environ Qual 1997b 26 788-794. 

McGrath S. P., Cegarra J. Chemical extractability of heavy metals during and after long-term applications of sewage sludge to soil. J Soil Sci 1992 43 313-321. 

Wang K, Xing B (2005) Chemical extractions affect the structure and phenanthrene sorption of soilhumin. Environ Sci Technol 39 8333-8304... 

Kelsey JW, Kottler BD, Alexander M (1997) Selective chemical extractants to predict bioavailability of soil-aged organic chemicals. Environ Sci Technol 21 214-217... 

Baier [59]). The advantage of the latter method is that chemical extraction of petroleum from such as sand and water is unnecessary. 

Isobaric interferences (especially those arising from the plasma itself, e.g., ArO+ on Fe) can be eliminated using cool-plasma conditions, sometimes in combination with a shield torch. This option is not suitable for seawater samples because a cool plasma, in the presence of a heavy matrix, cannot fully ionize elements with high first ionization potentials, notably Zn, Cd, and Hg. Protocols have thus been established for analysis of 10-fold diluted seawater on instalments with sufficiently high resolution to separate most of the affected isotopes from their isobaric interferences [1], To circumvent the issue entirely, others have used online chemical extraction to separate analytes of interest... 

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