Trace metals in coal

Group 3 elements which are not mostly vaporized in the boiler (1423 K) V, Cr, Mn, Co, Ni Referring to the classification, we investigated the temperature dependency of release of trace metals in coal combustion. We already reported the behavior of these three types of elements during high temperature coal processing and reported elsewhere . So in this paper, we investigated the effect of atmosphere for the emission behavior of trace elements. 

Temperature dependency of release of trace metals in coal combustion... 

We compared and discussed about the release behavior of trace metals from coal under the condition of coal combustion, pyrolysis and steam gasification. Under the condition of combustion, the residual fraction of Zn and Sb was grater than in case of pyrolysis and the residual fraction of Se was smaller. Because a part of trace metals in coal was oxidized during combustion. Moreover the release of Se and Sb was promoted when steam existed in atmosphere, and the release of Hg was suppressed. 

The Clean Air Act of 1970 declared beryllium, mercury, and asbestos as hazardous elements. Of the three, mercury is of particular interest to coal technologists. Other elements that exist as trace metals in coal and are suspected to be potentially detrimental to the environment include Pb, As, Sb, Zn, Se, Mo, Co, Li, V, Cr, Mn, Ni, etc. It is not the purpose of this book to create villains out of these elements, but to illustrate analytical techniques to determine how and in what amounts they are released in coal conversion processes. 

Fate of trace metals in coal preparation and conversion processes... 

Within this context, the quantitation and speciation of organically bound trace metals in coal liquefaction soluble products presents a real challenge. Quantitative trace element methods in the solid state on liquefaction... 

Based on thermodynamic property of each element, the behavior of trace metals in the coal combustion process was generally classified into 3 groups as follows ... 

As a result, it was found that the release of trace metals was affected by temperature, and atmosphere. The volatility of chemical form of trace metals in raw coal and the chemical change of trace metals during high temperature heat processing were very important for the... 

TDF mixture was distinctly richer in S03, Zn, Ge, and As than the fly ash from pure coal. Most pronounced are the changes in the contents of S03 and Zn, which increased by factors of more than 2 and 16, respectively (Fig. 6). This result can be explained by the average concentrations of these volatile components in the two fuels used in the test bum the coal + TDF blend contains 2.1 wt% S and 183 ppm Zn, whereas the pure coal only contains 1.5 wt% S (Table 4) and 36 ppm Zn (Giere, unpublished data). The levels of most other analysed trace metals in the bulk fly ash decreased with the addition of TDF. For the bottom ash, many of... 

The modern investigations of trace elements in coals were pioneered by Goldschmidt, who developed the technique of quantitative chemical analysis by optical emission spectroscopy and applied it to coal ash. In these earliest works, Goldschmidt (31) was concerned with the chemical combinations of the trace elements in coals. In addition to identifying trace elements in inorganic combinations with the minerals in coal, he postulated the presence of metal organic complexes and attributed the observed concentrations of vanadium, molybdenum, and nickel to the presence of such complexes in coal. 

Kotz etal. (1972, Decomposition of biological materials for the determination of extremely low contents of trace elements in limited amounts with nitric acid under pressure in a Teflon tube) Hartstein et al. (1973, Novel wet-digestion procedure for trace-metal analysis of coal by atomic absorption) Jackson etal. (1978), Automated digestion and extraction apparatus for use in the determination of trace metals in foodstuffs) Campos etal. (1990, Combustion and volatilization of solid samples for direct atomic absorption spectrometry using silica or nickel tube furnace atomizers) Erber et al. (1994, The Wickbold combustion method for the determination of mercury under statistical aspects) and Woit-tiez and Sloof (1994, Sampling and sample preparation). 

Vanadium and nickel were the only metals increasing in concentration as a consequence of cofiring petroleum coke, as expected. Table 2.13 documents the concentrations of trace metals in the petroleum coke fired at BGS, relative to the coal and urban wood waste Bred at that... 

In reality, however, CWS represents a family of fuels. They are variable based upon the sources of fine coal, the size fractions of the fine coal, the extent of coal processing, the density of the slurry, and related factors. If produced from coal pond fines these fuels can be high in ash and high in certain trace metals. In order to consider these opportunity fuels, this chapter first considers the basic published properties and then examines case studies of CWS production and utilization. Following the consideration of CWS, the chapter discusses analogous fuels and then the direct use of waste coal products in electricity generating stations. 

Exact concentrations of trace metals in CWS fuels will vary dramatically depending upon the coal being cleaned, the cleaning process employed, and whether the fines are further cleaned before being used in a CWS formulation. Metals with high organic affinity or organic association such as beryllium, boron, titanium, and vanadium [29] may not report preferentially with the fines, and may not increase in... 

Trace metals in herbaceous crops are typically a consequence of fertilizer practices, and economic activities in the area. Commercial fertilizers can contain as much as 4,570 mg/kg Cr, 430 mg/kg Pb, and 3,000 mg/kg Zh [42, 43]. Further, the presence of a large source of airborne metals (e.g., a metals smelter) can cause elevated levels of trace metals in herbaceous biomass. Significantly it is the arsenic concentration that can cause poisoning of the SCR catalyst, along with the possibility of catalyst blinding from the alkali metals. The arsenic concentrations in herbaceous biomass ash are typically lower than those associated with western low rank coals and lignites [42]. 

Zinc, like most metals, is found in all natural waters and soils as well as the atmosphere and is an important trace element in plant and animal life (see Mineral nutrients). Rocks of various kinds contain 20—200 ppm zinc and normal soils 10—30 ppm (average ca 50 ppm) in uncontaminated areas. The average zinc content of coal is 33 ppm. Seawater contains 1—27 )-lg/L (median ca 8 p.g/L), and uncontaminated freshwater usually <10 / g/L. 

Concern over the release of hazardous trace elements from the burning of coal has been highlighted by the 1990 Clean Air Act Amendments. Most toxic elements are associated with ash-forming minerals in coal (5). As shown in Table 1, levels of many of these toxic metals can be significantly reduced by physical coal cleaning (6). 

Although the petrochemical and metals industries were the primai y focus of the toxic air pollutants legislation, approximately forty of these substances have been detected in fossil power plant flue gas. Mercury, which is found in trace amounts in fossil fuels such as coal and oil, is liberated during the combustion process and these emissions may be regulated in the future. EPA issued an Information Collection Request (ICR) that required all coal-fired plants to analyze their feed coal for mercury and chlorine. Since these data will be used in making a regulatory decision on mercury near the end ot the year 2000, it is critical that the power industry provide the most accurate data possible. 

Hopkins, W.A., M.T. Mendonca, C.L. Rowe, and J.D. Congdon. 1998. Elevated trace metal concentrations in southern toads, Bufo terrestris, exposed to coal combustion waste. Arch. Environ. Contam. Toxicol. 35 325-329. 

Coal ash was converted to a low-carbon vitreous slag, impervious to leaching and valued as an aggregate in construction or as grit for abrasives and roofing materials trace metals from petroleum coke were also encased in an inert vitreous slag. 

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