Development of Advanced Cleaning Technology for Hazardous Heavy Metals in Coal

针对煤和煤灰中有害重金属的测定方法的发展以及去除和淋溶行为的研究。本研究取得的主要结果如下：1.针对煤和粉煤灰中的各种元素，建立了测定方法。确定了微波处理酸解的最佳条件。对于挥发性元素，如Hg和F，氧瓶燃烧法也是成功的。采用冷原子吸收法测定汞，氢化物发生法测定砷和硒，离子选择电极法测定氟，ICP-AES法测定其它元素.研究了煤中各种元素在稀酸溶液和螯合剂溶液中的浸出行为。在重金属中，Mn是容易浸出的，而Cu，Pb和Zn也有相当大的浸出。元素的浸出量与其在煤中的含量几乎成正比。元素在稀酸溶液中的浸出趋势与在螯合剂溶液中的浸出趋势相似.为了有效地脱除煤中的汞，提出了在300-400℃的氮气流下加热煤（温和热解）的方法。有些煤的汞去除率很高，超过80%，而有些煤的汞去除率很低。不同煤种对汞的去除效果不同，主要是由于煤中汞的赋存状态不同.研究表明，飞灰中砷、B、硒等有害元素易溶出。粉煤灰经水热处理后，砷被有效地从灰中去除。该工艺得到的废水处理与吸附剂，铝负载Shirasu沸石，这是新制备的，导致从废水中有效地去除砷。

About the hazardous heavy metals in coal and coal ash, the development of measurement methods and the studies on the removal and leaching behaviors were carried out. The results obtained in this study are as follows.1. For the various elements in coal and coal fly ash, the measurement methods were established. The optimum conditions for the acid-decomposition by use of microwave processor were assessed. For volatile elements, such as Hg and F, the oxygen flask combustion method was also successful. The decomposition solutions obtained were analyzed, and the cold vapor AAS for Hg, hydride generation AAS for As and Se, ion-selective electrode for F, and ICP-AES for other elements were applied.2. The leaching behavior of various elements from coal to diluted acid solutions and chelating agent solutions was examined. Among heavy metals, Mn was easy to leach, while Cu, Pb, and Zn were also considerably leached. The leaching amount of element was almost proportional to its content in coal. The tendency of element leaching into diluted acid solutions was similar to that into chelating agent solutions.3. For the effective removal of Hg from coal, the heating of coal under nitrogen flow at 300-400℃ (mild pyrolysis) was proposed. Some coals showed high Hg removals of over 80%, whereas the Hg removal of some coals was very low. The difference in the Hg removal efficiency among coals was ascribed to that in the mode of occurrence of Hg in coal.4. It was proved that some hazardous elements, such as As, B, and Se, were easy to leach out from coal fly ash. When fly ash was subjected to a hydrothermal treatment, As was effectively removed from the ash. The wastewater obtained by the process was treated with an adsorbent, Al-loaded Shirasu zeolite, which had been newly prepared, resulting in the efficient removal of As from the wastewater.