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Title: Microwave-assisted sample preparation of coal and coal fly ash for subsequent metal determination

Abstract

The aim of this paper is to review microwave-assisted digestion of coal and coal fly ash. A brief description of microwave heating principles is presented. Microwave-assisted digestion appears currently to be the most popular preparation technique, possibly due to the comparatively rapid sample preparation and the reduction of contamination, compared to the conventional hot-plate digestion methods.

Authors:
 [1]
  1. Inst. of Chemical Processing of Coal, Zabrze (Poland)
Publication Date:
OSTI Identifier:
20862081
Resource Type:
Journal Article
Resource Relation:
Journal Name: Analytical Letters; Journal Volume: 40; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; COAL; FLY ASH; SAMPLE PREPARATION; MICROWAVE HEATING; DIGESTION; CHEMICAL ANALYSIS; ELEMENTS; TRACE AMOUNTS

Citation Formats

Srogi, K. Microwave-assisted sample preparation of coal and coal fly ash for subsequent metal determination. United States: N. p., 2007. Web. doi:10.1080/00032710600867713.
Srogi, K. Microwave-assisted sample preparation of coal and coal fly ash for subsequent metal determination. United States. doi:10.1080/00032710600867713.
Srogi, K. Mon . "Microwave-assisted sample preparation of coal and coal fly ash for subsequent metal determination". United States. doi:10.1080/00032710600867713.
@article{osti_20862081,
title = {Microwave-assisted sample preparation of coal and coal fly ash for subsequent metal determination},
author = {Srogi, K.},
abstractNote = {The aim of this paper is to review microwave-assisted digestion of coal and coal fly ash. A brief description of microwave heating principles is presented. Microwave-assisted digestion appears currently to be the most popular preparation technique, possibly due to the comparatively rapid sample preparation and the reduction of contamination, compared to the conventional hot-plate digestion methods.},
doi = {10.1080/00032710600867713},
journal = {Analytical Letters},
number = 2,
volume = 40,
place = {United States},
year = {Mon Jan 15 00:00:00 EST 2007},
month = {Mon Jan 15 00:00:00 EST 2007}
}
  • Using the amorphous aluminosilicate of coal fly ash (FA), Na-A zeolite was synthesized. The FA particles mechanically treated with ball mill were added into a tube made of cellulose filter paper, and they were pretreated with a NaOH solution by refluxing under microwave (MW) irradiation for 60 min. The amorphous aluminosilicate of FA was dissolved during the pretreatment. After pretreatment, the tube was removed and NaAlO{sub 2} solution was added to the residual solution to control the SiO{sub 2}/Al{sub 2}O{sub 3} molar ratio of the solution ranging from 0.5 to 4.0. The precipitates thus formed were aged by refluxing undermore » MW irradiation for 60 min. After aging, white precipitates were yielded over the whole SiO{sub 2}/Al{sub 2}O{sub 3} range. At SiO{sub 2}/Al{sub 2}O{sub 3} = 0.51.0, the materials were identified as Na-A zeolite with a little amount of hydroxysodalite. The amorphous aluminosilicate emerged slightly at SiO{sub 2}/Al{sub 2}O{sub 3} = 2.0. The diffraction peaks of Na-A zeolite and hydroxysodalite disappeared at SiO{sub 2}/Al{sub 2}O{sub 3} = 4.0. The cation exchange capacity of Na-A zeolite formed at SiO{sub 2}/Al{sub 2}O{sub 3} = 0.5 and 1.0 was 4.32 and 4.70 meq.gP{sup -1}, respectively. The results obtained led to the conclusion that Na-A zeolite can be synthesized from milled FA for 120 min under MW irradiation.« less
  • An automated fluidic instrument is described that rapidly determines the total 99Tc content of aged nuclear waste samples, where the matrix is chemically and radiologically complex and the existing speciation of the 99Tc is variable. The monitor links microwave-assisted sample preparation with an automated anion exchange column separation and detection using a flow-through solid scintillator detector. The sample preparation steps acidify the sample, decompose organics, and convert all Tc species to the pertechnetate anion. The column-based anion exchange procedure separates the pertechnetate from the complex sample matrix, so that radiometric detection can provide accurate measurement of 99Tc. We developed amore » preprogrammed spike addition procedure to automatically determine matrix-matched calibration. The overall measurement efficiency that is determined simultaneously provides a self-diagnostic parameter for the radiochemical separation and overall instrument function. Continuous, automated operation was demonstrated over the course of 54 h, which resulted in the analysis of 215 samples plus 54 hly spike-addition samples, with consistent overall measurement efficiency for the operation of the monitor. A sample can be processed and measured automatically in just 12.5 min with a detection limit of 23.5 Bq/mL of 99Tc in low activity waste (0.495 mL sample volume), with better than 10% RSD precision at concentrations above the quantification limit. This rapid automated analysis method was developed to support nuclear waste processing operations planned for the Hanford nuclear site.« less
  • As compared to a commercial absorbent prepared from Ca(OH){sub 2}, gypsum (CaSO{sub 4}) and coal fly ash, an absorbent prepared by use of CaO in place of Ca(OH){sub 2}, exhibited a higher activity for dry-type flue gas desulfurization. The order of the addition of the raw materials in the slaking procedure has an effect on the activity of the resulting absorbent. The activity of the absorbent increased further upon hydrothermal treatment following the kneading procedure. The period of hydrothermal treatment was reduced to 3 h to attain the activity which exceeds 20% of the activity of the commercial absorbent whichmore » requires an optimum hydrothermal treatment period of 10 h. The activity enhancement by use of CaO is considered to result from exothermic heat of slaking CaO. At a high temperature, the reaction of CaO with a SiO{sub 2} component included in the coal fly ash facilitates the formation of calcium silicate. The formation of calcium silicate was suppressed by the existence of CaSO{sub 4} in the slaking procedure.« less
  • A 2 level full factorial design of experiment was used to evaluate the significance of four sorbent preparation variables towards the structural properties of sorbent prepared from coal fly ash, calcium oxide (CaO) and calcium sulfate (CaSO{sub 4}) for flue gas desulfurization. The structural properties studied were BET specific surface area and average pore size of the sorbent while the experimental sorbent preparation variables studied were hydration period (x{sub 1}), ratio of CaO to fly ash (x{sub 2}), amount of CaSO{sub 4} (x{sub 3}), and drying temperature (x{sub 4}). The surface area and average pore diameter of the sorbent obtainedmore » in this work range from 12.9 to 92.7 m{sup 2}g and 48.4 to 159.5 nm, respectively. The results revealed that there were significant influence of all the variables studied on the average pore diameter of the sorbent while only variables x{sub 1} x{sub 2}, and x(3) had significant influence on the surface area of the sorbent. X-ray diffraction (XRD) analysis revealed that the main phases detected in the sorbent was calcium alumino silicate hydrate compound. Scanning electron microscope (SEM) analysis showed that the sorbent consists of irregular shape particles that have a high structural porosity.« less
  • A two-step optimization strategy was employed to optimize the surface area of sorbent prepared from coal fly ash, calcium oxide (CaO) and calcium sulfate (CaSO{sub 4}) for flue gas desulfurization. In the first step, a 3 level full factorial design of experiment was used to develop a regression model equation to correlate the significant experimental sorbent preparation variables to the surface area of the resulting sorbent. The three experimental sorbent preparation variables studied are hydration period (x{sub 1}), ratio of CaO to fly ash (x{sub 2}) and amount of CaSO{sub 4} (x{sub 3}). In the subsequent step, response surface methodologymore » was used to identify the experimental sorbent preparation variables that maximize the surface area of the sorbent. Through this two-step optimization strategy, it was found that at a hydration period of 10 hrs and drying temperature of 100{sup o}C, optimum surface area of 67.0 m{sup 2}/g could be attained by using 5 grams of CaO, 13.7 grams of fly ash, and 7.4 grams of CaSO{sub 4} in the preparation mixture. The prediction was verified with experimental runs.« less