Environmental heterogeneity

Burford, M.D., S.B. Hawthorne, and D.J. Miller. 1993. Extraction rates of spiked vs. native PAHs from heterogeneous environmental samples using supercritical fluid extraction and sonication in methylene chloride. Anal. Chem. 65 1497-1505. 

Westall, J.C. et al., Models for association of metal ions with heterogeneous environmental sorbents. 1. Complexation of Co(II) by leonardite humic acid as a function of pH and NaC104 concentration, Environ. Sci. Technol., 29, 951, 1995. 

Westall, J. C., Jones, J. D., Turner, G. D., and Zachara, J. L. (1995) Models for Association of Metal Ions with Heterogeneous Environmental Sorbents, Environ. Sci. and Techn. 29, 951-959. 

J. J. Langenfeld, S. B. Hawthorne, D. J. Miller, Kinetic study of supercrititcal fluid extraction of organic contaminants from heterogeneous environmental samples with carbon dioxide and elevated temperature, Anal. Chem., 67 (1995), 1727-1739. 

The commonly used methods for the extraction of PAHs from sample matrices are Soxhlet extraction, sonication, or partitioning with a suitable solvent or a solvent mixture. Dichloromethane, cyclohexane, benzene, and methanol have been widely used as solvents (see Table 6- 2). Supercritical fluid extraction (SFE) of heterogeneous environmental samples with carbon dioxide in the presence of a modifier, such as 5-10% methanol or dichloromethane is preferable to the conventional extraction method because SFE is much less time consuming and has comparable or better PAH extraction recovery than the conventional methods (Burford et al. 1993 Dankers et al. 1993 Hawthorne et al. 1993 Hill and Hill 1993). 

Much of the literature on heavy-metal-bearing soils and sediments has been devoted to the speciation of anthropogenic metal(oid)s in contaminated matrices, but few papers focus on their crystal chemistry when they are present in trace amounts. This section reviews this topic and supplements and enhances the existing literature by describing the forms of arsenic, selenium, nickel, and zinc in two natural soils. It also attempts to illustrate with one example (Zn) how the novel synergistic use of pSXRF, pSXRD, and pEXAFS provides a quantitative analytical tool to speciate dilute multi-component metals in heterogeneous environmental materials. 

Di Monte R, Kaspar J Heterogeneous environmental catalysis—a gende art Ce02-Zr02 mixed oxides as a case history, Catal Today 100(1-2) 27-35, 2005a. 

In general, heterogeneous catalysts are preferred to homogeneous catalysts because the separation and recycling of homogeneous catalysts often can be very difficult. Loss of homogeneous catalyst not only creates a direct expense through loss of material but also creates an environmental problem. 

The two different, but related, eonsiderations in waste disposal are hazard eontrol and loss prevention in the treatment and disposal operations, and the eontrol of environmental hazards. With gas and liquid streams the eontrol of on-site hazards arising from the ehemieal properties and proeessing operations generally follows the prineiples summarized in earlier ehapters. The measures neeessary with solid wastes may, however, differ, partieularly if they are heterogeneous in nature and disposed of on land. 

Thus in all corrosion reactions one (or more) of the reaction products will be an oxidised form of the metal, aquo cations (e.g. Fe (aq.), Fe (aq.)), aquo anions (e.g. HFeO aq.), Fe04"(aq.)), or solid compounds (e.g. Fe(OH)2, Fej04, Fe3 04-H2 0, Fe203-H20), while the other reaction product (or products) will be the reduced form of the non-metal. Corrosion may be regarded, therefore, as a heterogeneous redox reaction at a metal/non-metal interface in which the metal is oxidised and the non-metal is reduced. In the interaction of a metal with a specific non-metal (or non-metals) under specific environmental conditions, the chemical nature of the non-metal, the chemical and physical properties of the reaction products, and the environmental conditions (temperature, pressure, velocity, viscosity, etc.) will clearly be important in determining the form, extent and rate of the reaction. 

Heterogeneous catalysts have been used industrially for well over 100 years. Amongst the first processes was the catalytic hydrogenation of oils and fats to produce margarine using finely divided nickel. It is quite likely that when this process was first operated in the late nineteenth century unhealthy amounts of nickel remained in the product. The issue of leaching and the avoidance of trace catalyst residues are still important aspects of research from both economic and environmental points of view. 

Atmospheric aerosols have a direct impact on earth s radiation balance, fog formation and cloud physics, and visibility degradation as well as human health effect[l]. Both natural and anthropogenic sources contribute to the formation of ambient aerosol, which are composed mostly of sulfates, nitrates and ammoniums in either pure or mixed forms[2]. These inorganic salt aerosols are hygroscopic by nature and exhibit the properties of deliquescence and efflorescence in humid air. That is, relative humidity(RH) history and chemical composition determine whether atmospheric aerosols are liquid or solid. Aerosol physical state affects climate and environmental phenomena such as radiative transfer, visibility, and heterogeneous chemistry. Here we present a mathematical model that considers the relative humidity history and chemical composition dependence of deliquescence and efflorescence for describing the dynamic and transport behavior of ambient aerosols[3]. 

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