Low-temperature ashing

Dry Mineralisation Dry mineralisation techniques include incineration (ashing), low-temperature mineralisation in oxygen plasma, mineralisation in oxygen, and melting. 

Hunt CD and Shuler TR (1990) Open-vessel, wet-ash, low-temperature digestion of biological materials for inductively-coupled argon plasma spectrometry (ICAP) analysis of boron and other elements. 

Wood wastes have ash compositions that are quite alkaline (Table 6) and that have consequent low ash fusion temperatures (Table 7). When firing soHd ... 

The proposed mechanism by which chlorinated dioxins and furans form has shifted from one of incomplete destmction of the waste to one of low temperature, downstream formation on fly ash particles (33). Two mechanisms are proposed, a de novo synthesis, in which PCDD and PCDF are formed from organic carbon sources and Cl in the presence of metal catalysts, and a more direct synthesis from chlorinated organic precursors, again involving heterogeneous catalysis. Bench-scale tests suggest that the optimum temperature for PCDD and PCDF formation in the presence of fly ash is roughly 300°C. 

For solvent extraction of pentavalent vanadium as a decavanadate anion, the leach solution is acidified to ca pH 3 by addition of sulfuric acid. Vanadium is extracted in about four countercurrent mixer—settler stages by a 3—5 wt % solution of a tertiary alkyl amine in kerosene. The organic solvent is stripped by a soda-ash or ammonium hydroxide solution, and addition of ammoniacal salts to the rich vanadium strip Hquor yields ammonium metavanadate. A small part of the metavanadate is marketed in that form and some is decomposed at a carefully controlled low temperature to make air-dried or fine granular pentoxide, but most is converted to fused pentoxide by thermal decomposition at ca 450°C, melting at 900°C, then chilling and flaking. 

A variety of instmmental techniques may be used to determine mineral content. Typically the coal sample is prepared by low temperature ashing to remove the organic material. Then one or more of the techniques of x-ray diffraction, infrared spectroscopy, differential thermal analysis, electron microscopy, and petrographic analysis may be employed (7). 

Arsine, AsHs, is formed when many As-containing compounds are reduced with nascent hydrogen and its decomposition on a heated glass surface to form a metallic mirror formed the basis of Marsh s test for the element. The low-temperature reduction of AsCls with LiAlH4 in diethyl ether solution gives good yields of the gas as does the dilute acid hydrolysis of many arsenides of electropositive elements (Na, Mg, Zn, etc.). Similar reactions yield stibine, e.g. ... 

Molten salts promote rapid corrosion of many constmctional materials at relatively low temperatures. Low-melting-point salts include sodium salts from saline atmospheres, fireside ash, silicate insulation, contaminants in the feed, etc. Corrosion rates of several mm/year can be observed at temperatures as low as 520°C. High chromium- and nickel-containing alloys up to 50% Cr/50% Ni are employed. 

Solid carbon, however produced, presents a hazard. It may be burnt off at low temperatures, with free access to air, without harm to the crucible, but it should never be ignited strongly. Precipitates in filter paper should be treated in a similar manner strong ignition is only permissible after all the carbon has been removed. Ashing in the presence of carbonaceous matter should not be conducted in a platinum crucible, since metallic elements which may be present will attack the platinum under reducing conditions. 

Nutrient Losses Associated With Biomass Burning. Nutrient losses associated with slash fires occur through volatilization and convective losses of ash. Elements with low temperatures of volatilization (e.g. N, K, S, and some organic forms of P) will be lost in the highest quantities (Table III) (57). Conversely, Ca and Mg have volatilization temperatures higher than that recorded during most vegetation fires. Almost all fire-induced losses of these elements are due to particulate transfer by convective processes. 

The steep dependence on hydrogen content of the tar yields obtained during the low temperature (500°C) fluidized bed carbonization of 14 Australian coals, ranging in rank from 72% to -89% (dry ash-free basis) carbon content, is clearly demonstrated in Fig. 5 (15,16). 

The Effect of Mineral Matters on the Decomposition Ethers. Recently, the effect of mineral matters of coal on the coal liquefaction has received much attention. It was shown that small amounts of FeS or pyrite are responsible for the hydro-genative liquefaction of coal. Therefore, it is interesting to elucidate the effect of mineral matters of coal on the decomposition rate and products of aromatic ethers, and so three diaryl ethers were thermally treated in the presence of coal ash obtained by low temperature combustion of Illinois No.6 coal at about 200°C with ozone containing oxygen. 

The capillaries (Itmn ID and 150 mm length tubular reactors) are heated rapidly (within 5 s) in a fluidized sand bed to the desired reaction temperature. Experimentation with the batch capillary method has revealed that, especially at low temperatures and high feed concentrations, char formation occms. A fluidized-bed reactor might be a good alternative to solve the problems related to this char and ash formation (Kruse et al., 2000). 

Low temperature ashing with radio frequency induced oxygen plasma ... 

Fourier transform infrared (FTIR) spectroscopy of coal low-temperature ashes was applied to the determination of coal mineralogy and the prediction of ash properties during coal combustion. Analytical methods commonly applied to the mineralogy of coal are critically surveyed. Conventional least-squares analysis of spectra was used to determine coal mineralogy on the basis of forty-two reference mineral spectra. The method described showed several limitations. However, partial least-squares and principal component regression calibrations with the FTIR data permitted prediction of all eight ASTM ash fusion temperatures to within 50 to 78 F and four major elemental oxide concentrations to within 0.74 to 1.79 wt % of the ASTM ash (standard errors of prediction). Factor analysis based methods offer considerable potential in mineral-ogical and ash property applications. 

Small Data Set. Low-temperature (plasma) ashes (LTAs) were obtained from ten diverse coal samples (Table I), ranging in rank from lignite to Ivb. Infrared spectra were obtained of duplicate samples of each LTA. A separate set of duplicates generated (for other purposes) for the first four LTAs listed also was analyzed by FTIR. 

Methods. Coals ground to -60 mesh were low-temperature (O2 plasma) ashed in one of three plasma ashers to constant weight for about... 

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