Metallurgical emissions

Metallurgical equipment has long been an obvious source of air pollution. The effluents from metallurgical furnaces are submicron-size dusts and fumes and hence are highly visible. The emissions from associated coke ovens are not only visible but odorous as well. 

Emissions from other nonferrous metal facilities are primarily metal fumes or metal oxides of extremely small diameter. Zinc oxide fumes vary from 0.03 to 0.3 jiim and are toxic. Lead and lead oxide fumes are extremely toxic and have been extensively studied. Arsenic, cadmium, bismuth, and other trace metals can be emitted from many metallurgical processes. 

The chemical and metallurgical industries of the world are so varied and extensive that it is impossible to cover all of the processes, emissions, and controls in a single chapter. 

Air Pollution Emissions from Miscellaneous Nonferrous Metallurgical Processes... 

Atomic absorption spectrometry is one of the most widely used techniques for the determination of metals at trace levels in solution. Its popularity as compared with that of flame emission is due to its relative freedom from interferences by inter-element effects and its relative insensitivity to variations in flame temperature. Only for the routine determination of alkali and alkaline earth metals, is flame photometry usually preferred. Over sixty elements can be determined in almost any matrix by atomic absorption. Examples include heavy metals in body fluids, polluted waters, foodstuffs, soft drinks and beer, the analysis of metallurgical and geochemical samples and the determination of many metals in soils, crude oils, petroleum products and plastics. Detection limits generally lie in the range 100-0.1 ppb (Table 8.4) but these can be improved by chemical pre-concentration procedures involving solvent extraction or ion exchange. 

Polycyclic aromatic hydrocarbons (PAHs, sometimes also called polynuclear aromatics, PNA) are a hazardous class of widespread pollutants. The parent structures of the common PAHs are shown in Fig. 4 and the alkylated homologs are generally minor in combustion emissions. PAHs are produced by all natural combustion processes (e.g., wild fires) and from anthropogenic activity such as fossil fuels combustion, biomass burning, chemical manufacturing, petroleum refining, metallurgical processes, coal utilization, tar production, etc. [6,9,15,18, 20,24,131-139]. 

Automatic Atomic Emission Spectroscopy, 2nd edn, Slickers, K., Briihlsche Universitatsdmckerei, Giessen, 1993. A very useful practical guide to arc and spark methods in the metallurgical industry. 

Present atomic emission spectrophotometers allow multi-element analyses to be performed either simultaneously or sequentially. This ability is the result of progress made in optics, excitation sources, detectors and microcomputers. Atomic emission, which was initially used in the metallurgical industry, has now expanded into many areas and competes with atomic absorption. 

Beryllium alloys are usually analyzed by optical emission or atomic absorption spectrophotometry. Low voltage spark emission spectrometry is used for the analysis of most copper—beryllium alloys. Spectral interferences, other inter-element effects, metallurgical effects, and sample inhomogeneity can degrade accuracy and precision and must be considered when constructing a method (17). 

Production of Ions. Several methods are used (11 by bombardment with electrons from a heated filament (2 by application of a strong electrostatic field (field ionization, field desorption) Ot by reaction with an ionized reagent gas (chemical ionization) (4 by direct emission of ions from a solid sample that is deposited on a heated filament (surface ionization) (SI by vaporization from a crucible and subsequent electron bombardment (e.g.. Knudsen cell for high-lcmperalure sludies id solids and (6) by radio-frequency spark bomhardmenl of sample fur parts-per-biliion (ppb) elemental analysis of solids as encountered in metallurgical, semiconductor, ceramics, and geological studies. Ions also are produced by photoion izution and laser ionizalion. 

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