Development of Advanced Cleaning Technology for Hazardous Heavy Metals in Coal

针对煤和灰渣中的有害重金属，开展了测定方法的发展和去除、浸出行为的研究。本研究取得的研究结果如下。建立了煤和飞灰中各种元素的测定方法。确定了微波酸解的最佳条件。对于汞和氟等挥发性元素，氧瓶燃烧法也是成功的。采用冷原子吸收法测定汞，氢化物发生原子吸收法测定砷和硒，离子选择电极测定氟，电感耦合等离子体原子发射光谱仪测定其他元素。考察了煤中各元素在稀酸溶液和络合剂溶液中的浸出行为。在重金属中，锰容易淋失，而铜、铅、锌也有较大的淋溶。元素的浸出量与煤中元素的含量几乎成正比。元素在稀酸溶液中的浸出趋势与在络合剂溶液中的趋势相似。为了有效地脱除煤中的汞，提出了在300~400℃的氮气流量下加热煤(温和热解)。有些煤的汞脱除率高达80%以上，而有些煤的汞脱除率很低。煤中汞的赋存状态不同，可归因于煤中汞脱除效率的差异。研究表明，燃煤飞灰中的As、B、Se等有害元素易被浸出。当飞灰经过水热处理时，砷被有效地从火山灰中去除。用新制备的载铝Shirasu沸石对废水进行处理，有效地去除了废水中的砷。

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.