氫氧化鈣與氯化鈣反應產物之生成及穩定化研究

Abstract

中文摘要 垃圾焚化處理所產生的飛灰含有高含量氯鹽以及微量的重金屬與毒性氯化有機物，屬於有害廢棄物。本研究探討飛灰中主要之氯鹽CaClOH之生成及其特性，並探討其高溫反應，以找出去除或穩定氯鹽的方法，期能解決焚化飛灰中氯鹽含量過高之問題，以利焚化飛灰能達到無害化和資源化。本研究以自行合成之CaClOH，探討其熱分解反應，以及其與CO2、H2O、O2等氣體和NaOH、mullite、coal fly ash等固體之高溫反應。 於室溫下氫氧化鈣和含有結晶水的氯化鈣混合很快生成CaClOH。CaClOH於550℃以上會分解為氧化鈣及氯化鈣。CaClOH碳酸化後會生成碳酸鈣及氯化鈣，400℃以下反應不顯著，500℃以上反應速率很快，一小時碳酸鈣莫耳分率不受溫度和CO2濃度影響，可達0.43。在600℃以上，預先煅燒再碳酸化會降低一小時碳酸鈣莫耳分率，其原因是CaCl2之燒結和CaCl2/CaCO3的熔解。碳酸化後固體中的氯化鈣可用水洗將之洗出。氯化鈣亦可在溫度高於氯化鈣熔點(772℃)下，與含有水氣、氧氣及二氧化碳之氣體，反應生成氧化鈣或碳酸鈣；水氣的反應性優於氧氣。CaClOH在高溫(500℃-700℃)下會與氫氧化鈉、模來石及燃煤飛灰反應，降低固體之CaCl2含量，避免高溫固體冷卻後凝結固化。

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.