Oxide volatilization

Human-made sources cover a wide spectrum of chemical and physical activities and are the major contributors to urban air pollution. Air pollutants in the United States pour out from over 10 million vehicles, the refuse of over 250 million people, the generation of billions of kilowatts of electricity, and the production of innumerable products demanded by eveiyday living. Hundreds of millions of tons of air pollutants are generated annu ly in the United States alone. The five main classes of pollutants are particulates, sulfur dioxide, nitrogen oxides, volatile organic compounds, and carbon monoxide. Total emissions in the United States are summarized by source categoiy for the year 1993 in Table 25-10. 

Source category Particulate (PM-10) Sulfur dioxide Nitrogen oxides Volatile organic compounds Carbon monoxide... 

Organic compounds released from plant roots have been categorized according to (a) their chemical properties, such as stability (e.g., hydrolysis and oxidation), volatility, molecular weight, solubility in water, etc. (Chap. 2) (b) the modality of their release (exudates, secreted, or lysates) (c) the way of utilization... 

Root products may be classified into types on the basis of their (1) chemical properties, such as composition, solubility, stability (e.g., hydrolysis, oxidation), volatility, molecular weight etc. (2) site of origin and (3) e.stablished, not just perceived, functions. The chemical properties determine in turn their biological activity and how the compounds will behave in soils their persistence in soil is very much an outcome of their chemical behavior, particularly sorption and their biodegradability. 

WASP/TOXIWASP/WASTOX. The Water Quality Analysis Simulation Program (WASP, 3)is a generalized finite-difference code designed to accept user-specified kinetic models as subroutines. It can be applied to one, two, and three-dimensional descriptions of water bodies, and process models can be structured to include linear and non-linear kinetics. Two versions of WASP designed specifically for synthetic organic chemicals exist at this time. TOXIWASP (54) was developed at the Athens Environmental Research Laboratory of U.S. E.P.A. WASTOX (55) was developed at HydroQual, with participation from the group responsible for WASP. Both codes include process models for hydrolysis, biolysis, oxidations, volatilization, and photolysis. Both treat sorption/desorption as local equilibria. These codes allow the user to specify either constant or time-variable transport and reaction processes. 

CADRE A process for removing and oxidizing volatile organic compounds from gas streams. The compounds are adsorbed on a fixed bed of carbon and then desorbed by a stream of hot air or inert gas. Developed by Vard International, a division of Calgon Carbon Corporation. 

SWITGTHERM A catalytic process for oxidizing volatile organic compounds (VOCs). It involves regenerative heat exchange, which permits autothermal operation at VOC concentrations in the range 250 to 650 ppm. Developed in Poland and now used in over 100 installations there. 

Platinum loadings, reducing, 19 628 Platinum metals plating, 9 822-823 Platinum oxides, volatilized, 17.T80 Platinum-palladium thermocouple, 24 461 Platinum reforming catalysts, rhenium and, 21 695-696... 

The Biocube aerobic biofilter is an ex situ off-gas filtration system that is commercially available. The technology utilizes microbes to biologically oxidize volatile organic compounds (VOCs) and complex odors. It can be used in conjunction with vapor-vacuum-extraction (VVE), a process that draws gases from subsurface soil. These gases often require further treatment before being released into the atmosphere. Biocube has been field tested and has been implemented at over 100 sites for the treatment of hydrocarbon vapors. The technology has also been successfully used for odor control at a variety of sites. In addition, the Biocube system can treat odor and VOC emissions simultaneously. The units are modular, so additional stacks can be added as needed for increased flow and/or removal rates. 

The PO WW ER system was developed by Wheelabrator Clean Air Systems, Inc., a subsidiary of U.S. Filter Corporation, to reduce the volume of aqueous waste and catalytically oxidize volatile contaminants. PO WW ER is used to treat complex industrial and hazardous wastewaters containing mixtures of organic, inorganic, and radioactive contaminants. This proprietary, commercial technology combines evaporation with catalytic oxidation to concentrate and remove contaminants, producing a high-quality product water. 

Amine salts have been used to recover molybdenum from solutions arising from a variety of sources. Most of the western world s supply of this metal is derived from molybdenite (MoS2) concentrates obtained as a byproduct of copper production in the USA and Chile. Such concentrates are roasted to molybdenum(VI) oxide (volatile Re207 can often be recovered as a valuable byproduct from the roaster gases) and leached with dilute sulfuric acid to remove the copper from the crude M0O3 product. Some molybdenum also dissolves and can be recovered, for example, by the same technique as that practised at Kennecott s Utah Copper Division smelter,213 i.e. by extraction into a solution of a tertiary amine in kerosene at an aqueous pH value of about 1. 

If carbon monoxide is passed over metallic nickel or iron in a fine state of subdivision produced by reducing their oxides, volatile compounds are formed of the formulx Ni(CO)4, and Fe(CO)5 on exposing the latter to light gold-coloured crystals are formed, of the formula Fe2(CO )7. The nickel carbonyl boils at 43°, and the iron penta-carbonyl at 103° di-ferro-hepta-carbonyl decomposes... 

WOF is characterized sensorially as being "old, stale, rancid, metallic and painty". These flavors are highly related to concentrations of pentanal, hexanal, 2,3-octanedione and total volatiles in chicken, turkey and beef (21) and to twenty-one different oxidative volatiles in pork (22). The compounds were quantitated by the GLC/MS method of Suzuki and Bailey (23) and appear to be excellent markers for WOF. 

It has been observed (a) that aeration plays an important role in prolonging the life of a redox metal stabilized silicone fluid by sweeping away any partially oxidized volatiles to prevent their return to the bulk fluid (b) that aeration is needed to keep some redox antioxidants from... 

Red sohd, oxidized by air to chromimn oxide, volatile (80 °C, 10 mbar), mp... 

In addition to making comparisons with chondrites, the bulk composition of the Earth also has been defined in terms of a model mixture of highly reduced, refractory material combined with a much smaller proportion of a more oxidized volatile-rich component (Wanke, 1981). These models follow on from the ideas behind earlier heterogeneous accretion models. According to these models, the Earth was formed from two components. Component A was highly reduced and free of all elements with equal or higher volatility than sodium. All other elements were in Cl relative abundance. The iron and siderophile elements were in metallic form, as was part of the silicon. Component B was oxidized and contained all elements, including those more volatile than sodium in Cl relative abundance. Iron and all siderophile and lithophile elements were mainly in the form of oxides. 

Ringwood (1979) first proposed these models but the concept was more fully developed by Wanke (1981). In Wanke s model, the Earth accretes by heterogeneous accretion with a mixing ratio A B — 85 15. Most of component B would be added after the Earth had reached about two thirds of its present mass. The oxidized volatile-rich component would be equivalent to Cl carbonaceous chondrites. However, the reduced refractory rich component is hypothetical and never has been identified in terms of meteorite components. 

A model for the total composition of the terrestrial planets involves the mixture between a highly reduced, refractory component and an oxidizing volatile-rich component with characteristics similar to Cl chondrites (Dreibus and Wanke, 1987 Wanke and Dreibus, 1988). The proportions of each are determined by key elemental ratios, and initial inventories of water, noble gases, and other volatiles have been calculated that exceed present abundances, along with inferences regarding subsequent modification. 

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