Trace metals volatilization

Liquid fuels for ground-based gas turbines are best defined today by ASTM Specification D2880. Table 4 Hsts the detailed requirements for five grades which cover the volatility range from naphtha to residual fuel. The grades differ primarily in basic properties related to volatility eg, distillation, flash point, and density of No. 1 GT and No. 2 GT fuels correspond to similar properties of kerosene and diesel fuel respectively. These properties are not limited for No. 0 GT fuel, which allows naphthas and wide-cut distillates. For heavier fuels. No. 3 GT and No. 4 GT, the properties that must be limited are viscosity and trace metals. 

Isopiestic or isothermal distillation. This technique can be useful for the preparation of metal-free solutions of volatile acids and bases for use in trace metal studies. The procedure involves placing two beakers, one of distilled water and the other of a solution of the material to be purified, in a desiccator. The desiccator is sealed and left to stand at room temperature for several days. The volatile components distribute themselves between the two beakers whereas the non-volatile contaminants remain in the original beaker. This technique has afforded metal-free pure solutions of ammonia, hydrochloric acid and hydrogen fluoride. 

Despite the difficulties, there have been many efforts in recent years to evaluate trace metal concentrations in natural systems and to compare trace metal release and transport rates from natural and anthropogenic sources. There is no single parameter that can summarize such comparisons. Frequently, a comparison is made between the composition of atmospheric particles and that of average crustal material to indicate whether certain elements are enriched in the atmospheric particulates. If so, some explanation is sought for the enrichment. Usually, the contribution of seaspray to the enrichment is estimated, and any enrichment unaccounted for is attributed to other natural inputs (volcanoes, low-temperature volatilization processes, etc.) or anthropogenic sources. 

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... 

Nearly every area of measurement science can boast of progress in measuring ever-smaller quantities of chemicals, but several stand out in their stunning trace-analysis capabilities. Trace-metal analysis has come to be dominated by methods that volatilize the sample and then either measure its spectroscopic emission or absorption, or measure the masses of the gaseous metal ions using mass spectrometry. Volatilization is accomplished by various thermal means that include flames, furnaces, and inductively coupled or microwave plasmas. The com-... 

Further research in the library and discussion with other chemists in the company leads you to a new mechanism autooxidative degradation. Fatty chemicals are known to undergo such degradation with the formation of a series of compounds, some of which are volatile and potentially explosive (Table 21.1). These reactions would occur more readily at elevated temperatures and in the presence of trace metals, such as iron, cobalt, and nickel. 

Coke which is low in sulfur and metal content is valued as a fuel, as a raw material for the manufacture of electrodes, and in graphite production. To produce high-purity coke, all traces of volatile matter must be removed from coke. A calcination process is utilized for this purpose. This process requires the coke to be heated to temperatures of 2,000°F (1,093.3°C) or higher. The pure coke is valued as raw material for the manufacture of electrolytic cell anodes and as a pure carbon source. 

S02, NOx, and C02), and volatile trace metals to the atmosphere during the combustion process. 

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 stability of the inorganic sulfides appears to be a major factor in the disposition of trace metals in the feed. As examples, lead, tin, cadmium and nickel can be largely recovered as the sulfides in most energy conversion processes, although many forms of these materials are volatile. ... 

Numerous applications concern the mass spectrometric analysis of quite different gases and highly volatile compounds. For example, the determination of trace metal impurities in ethylene gas for... 

This technique can be useful for the preparation of metal-free solutions of volatile acids and bases for use in trace metal studies. The procedure involves placing two beakers, one of distilled water and the other of a solution of... 

Partly because of this concern, the Wisconsin Department of Natural Resources, in cooperation with the Electric Power Research Institute, initiated an extensive study of Hg cycling in seepage lakes of north-central Wisconsin (14). The mercury in temperate lakes (MTL) study used clean sampling and subnanogram analytical techniques for trace metals (10, 17) to quantify Hg in various lake compartments (gaseous phase, dissolved lake water, seston, sediment, and biota) and to estimate major Hg fluxes (atmospheric inputs, volatilization, incorporation into seston, sedimentation, and sediment release) in seven seepage lake systems. 

Long, E.R., MacDonald, D.D., Cubbage, J.C. and Ingersoll, C.G. (1998) Predicting the toxicity of sediment associated trace metals with simultaneously extracted trace metal acid-volatile sulfide concentrations and dry weight-normalized concentrations a critical comparison, Environmental Toxicology and Chemistry 17 (5), 972-974. 

As(V), and Hg(II) versus MMHg (monomethyl-Hg)], solubility [e.g., Fe(II) versus Fe(III) and Mn(II) versus Mn(IV)], the difference in volatility [Hg(0) versus Hg(II)], and bioavailability (e.g., labile-bound metal complex/strongly bound metal complex). It is therefore a challenge to identify and quantify the major species of elements such as Cr, Fe, Mn, As, and Fig in aquatic systems. Table 7.1 gives an overview of the levels of common trace metals in various aquatic systems. 

Precleaning of material, sampling, and filtration in the field are not very different from the procedures used for the other trace metals described above, except that for Hg borosilicate glass bottles can also be used, and that samples collected for volatile, metallic mercury Hg(0) and dimethylmer-cury (DMHg) species are not filtered. When filtration cannot be carried out in the field, samples should be kept unpreserved, cold, and in the dark. More specific information about our techniques can be found in Baeyens80 and Leermakers et al.47,84... 

Dry ashing is simple and inexpensive. Large numbers of samples can be treated at the same time and the quantity of the sample is not limited. Usually the sample is heated in a crucible of platinum, silica or pyrex to a relatively high temperature, between 400°C and 700°C, in a muffle furnace. Dry ashing is not recommended for samples with trace metal contents unless special furnaces, and very accurate temperature control methods are employed. The more volatile metals such as lead, mercury, and cadmium may be partially lost at even low temperatures. 

Closed systems minimise consumption of reagents and avoid losses of volatile elements. Decomposition vessels should have low trace metal contents and be of extremely pure quartz and PTFE and should be carefully purified prior to use in ultrapure acids or acid vapour (Tschopel et al., 1980) and elemental blanks should be determined for each decomposition vessel. Matusiewicz (1991) has described the special advantages and problems associated with acid vapour-phase digestion procedures. 

The acidification of seawater samples is required for the storage of seawater in order to prevent the precipitation, adsorption of trace metals on the container walls or volatilization loss from solution. Generally, nitric acid is added to seawater to bring the pH of the solutions to below 1.5. The addition of acids immediately after collection on board ship may be preferable for sample storage rather than addition before analysis in the laboratory. 

Although more widely applicable to organic chemicals, the matrix of some inorganic chemicals may be reduced or modified by heating to an elevated temperature. Care must be exercised not to lose volatile trace metals such as arsenic, cadmium and zinc mercury will almost invariably be lost to some extent. Matrices which might be amenable to this treatment include ammonium salts, sulphates, nitrates and the salts of organic acids such as the oxalates. 

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