Chemical separation Contaminants

Wegeng mentions the use of micro reactors for the cleanup of environmental contamination [1]. In particular, he refers to downwell groundwater cleanup by micro-chemical separations and conversions such as destruction of organics. 

Flotation. In many cases, contaminants adsorbed on the surface of clay particles, or contaminants occurring in soil as discriminate particles, have different surface properties to clean soil particles. By adding special chemical substances, the formation of a hydrophobic surface on the contaminated particles is possible. Pulp aeration results in the attachment of hydrophobic contaminated particles to the surface of the small bubbles that are formed. In this way, selective flotation of these particles is achieved. Contrary to the gravimetric separation methods, flotation offers the possibility to separate contaminated and noncontaminated particles of the same grain size and density but with different surface properties. 

As liquid chromatography plays a dominant role in chemical separations, advancements in the field of LC-NMR and the availability of commercial LC-NMR instrumentation in several formats has contributed to the widespread acceptance of hyphenated NMR techniques. The different methods for sampling and data acquisition, as well as selected applications will be discussed in this section. LC-NMR has found a wide range of applications including structure elucidation of natural products, studies of drug metabolism, transformation of environmental contaminants, structure determination of pharmaceutical impurities, and analysis of biofiuids such as urine and blood plasma. Readers interested in an in-depth treatment of this topic are referred to the recent book on this subject [25]. 

Chemical separation techniques can be used to reduce spectral interferences and concentrate the analyte. These techniques include solvent extraction(39) and hydride generation(39, 46, 47). At Imperial College, the hydride generation technique is being used on a daily basis(46) for the analysis of soils, sediments, waters, herbage, and animal tissue. The solvent extraction technique is ideally suited for automated systems where the increased manipulation is carried out automatically, and a labor intensive step and sources of contamination are avoided. 

The liquid waste must be pumpable. Contaminants must be in particulate form, or it must be possible to precipitate dissolved contaminants such as metal ions chemically. Separation must provide an advantage. The EPOC microfiltration technology does not remove volatile organic compounds (VOCs) from liquids. The unit s operation is affected by cold weather. 

The Snrbec-ART Environmental, L.L.C. (Snrbec), soil washing technology is a process based on mining and mineral processing principles that incorporates physical and chemical separation techniqnes (D12463A, p. 3). The technology separates and treats oversized fractions and sand fractions so that they can be placed back on the site as clean backfill. Contaminants are concentrated in the fines, and this fraction can be managed separately for further treatment or disposal. 

Much of the effort on environmental chemicals that contaminate food has concentrated on a small range of chlorinated chemicals. In addition to the chlorinated PCDDs, PCDFs and PCBs already mentioned, other chlorinated compounds can be separated into two groups chlorinated aromatic compounds and chlorinated aliphatic compounds. Although there is a number of organochlorine pesticides that are persistent in the environment, these will not be considered here, as they comprise an extensive field of study in their own right. 

Actinides found as environmental contamination in mosses collected from a bog in the eastern Italian Alps were analyzed after their chemical separation by extraction chromatography (deposited on steel targets) with respect to isotope ratios and their concentration was determined by LA-ICP-MS. Moss samples were contaminated with a variety of actinide isotopes. The detection limits for actinides were determined as 3.6-7.2 x 10 gg for " Am and respectively. The Pu/ Pu isotope ratio (0.212 0.003) was almost constant within experimental error for all samples investigated. Pu contamination in moss samples was mainly the result of global fallout after nuclear weapons tests. " Am was found at the 2x 10 " gg level. This example demonstrates that mosses can be used as bioindicators for environmental contamination. ... 

Mass spectrometry of zinc Isotopes has been realized using either chelates on a solids probe(10,11,17) or thermal Ionization of purified solutions(12). Both of these approaches require a chemical separation of all of the metals and this separation must be accomplished In an environment free of contamination from the metal(s) of Interest In the part-per blllion range (19). Neutron activation also requires a set of separation steps. In this case the requirement for a contamination-free environment Is the same but the chemical separation Is mainly to remove sodium and chlorine (2). 

Calcium-41 Ca-41 is produced by neutron activation of natural Ca-40. It has been found to exceed the GQ by a factor of 2 in both graphite fuel struts and desiccant from HNA (3 streams). The reported desiccant value is an upper limit probably based on trace contamination by graphite dust. In decommissioning wastes, activation of the concrete bioshield would also be expected to produce Ca-41 but these wastes streams are regarded as low level wastes in the NIREX inventory and hence GQ values do not apply. Measurements of Ca-41 can be obtained after chemical separation of Ca, which is done routinely for Ca-45 measurements. After any Ca-45 (t 14 =163 days) has decayed away, it can be measured by liquid scintillation counting. Procurement of direct standards from NPL would be required. In fresh samples, if the Ca-45 has been measured, then the Ca-41 could be estimated by comparison of activation... 

Gleason KJ, Yu J, Bunge AL, and Wright JD. Removal of selenium from contaminated waters using emulsion liquid membranes. In Bartsch RA, Way JD, eds. Chemical Separations with Liquid Membranes, Washington, DC American Chemical Society, ACS symposium series 642, 1996 342-360. 

Neutron activation analysis without chemical separation is possible when the contaminating element and the principal constituent have... 

One more separation technique that deserves some discussion is the scrubber. Scrubbers are the most mature technology from the chemical separation industry that usually employs liquid-gas interaction to achieve the contaminant removal. While they can be very selective due to the liquid-stripping agent, they are complicated systems that use specialty chemicals and require multiple steps to transfer the contaminant from gas phase to liquid, then from liquid back to gas phase, which is ultimately vented. For very large, stationary installations, scrubbers are usually the technology of choice because of their performance they can routinely achieve 99.99% removal efficiency, durability, and robustness. However, scale-down is not... 

Other NAA methods involve the chemical separation of interfering ions (Blotcky et al., 1976) in these the short half-life (2.24 minutes) of AI makes post-irradiation separations a problem. Pre-irradiation separation techniques have potential problems of contamination and losses during the separation phase. 

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