Formation and Stabilization of the Product of the Reaction of Ca(OH)2 and CaCl2 .
Date Issued
2010
Date
2010
Author(s)
Wang, Wei-Hsun
Abstract
Abstract
Fly ash generated from MSW incinerator, containing high contents of alkali chlorides and trace amounts of heavy metals and toxic organic chlorides, is classified as a hazardous waste. This work is to study the formation and the characteristic of the major alkali chloride in MSW fly ash, CaClOH, and to investigate its high-temperature reactions, with the aim to develop processes which can be used to remove or stabilize the chlorides and thus can enhance the utilization of fly ash. In this study,
CaClOH was prepared and its thermal decomposition and reactions with CO2, H2O, O2, NaOH, mullite and coal fly ash at high temperatures were investigated.
CaClOH was formed rapidly by mixing Ca(OH)2 and CaCl2．2H2O at room temperature . CaClOH decomposed to CaO and CaCl2 at tempera ture≧550℃. CaClOH reacted with CO2 to form CaCO3 and CaCl2 . The carbonation reaction was insignificant below 400℃ and was very rapid above 500℃; in the range of 500-700℃, the ultimate (1h) CaCO3 fraction, independent of temperature and CO2 concentration, was about 0.43. Above 600℃, prior calcination of CaClOH reduced the ultimate CaCO3 fraction due to the sintering of CaCl2 and the melting of CaCl2/CaCO3. CaCO3 and CaCl2 could be easily separated by washing the carbonated sample with water. CaCl2 could be converted to CaO or CaCO3 by reacting with gas mixture containing H2O, O2, and CO2 at temperatures above the melting point of CaCl2 (773℃); H2O had a higher reactivity toward CaCl2 than O2. NaOH, mullite, and coal fly ash could react with CaClOH at high temperatures (500-700℃) and reduce the CaCl2 content of solid, avoiding the solidification of solid particles when they were cooled down from high temperatures.
Subjects
fly ash
carbonation
CaClOH
SDGs
Type
thesis
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