報告書番号

U98068

タイトル（和文）

石炭の生物加工-14- -微生物浮遊選炭による高硫黄炭からの重金属除去-

タイトル（英文）

Bioprocessing of coal -14--Removal of heavy metals from high sulfur coal by microbial flotation-

概要 （図表や脚注は「報告書全文」に掲載しております）

当所では，将来的な高品位炭（低硫黄分，低灰分）の枯渇にともない，使用を余儀なくされると予測される低品位炭の改質を目指して，鉄酸化細菌を用いた微生物浮遊選炭法を提案し，脱灰，脱硫できることを示してきた。一方，石炭中には，灰や硫黄の他に重金属元素が含有しており，低品位炭の改質にあたっては，これら重金属類を除去することも重要な意味を持つと思われる。このような観点から，燃え殻の埋め立て処分の際に規制されている重金属元素（As，Se，Cd，Cr，Pb，Hg）の高硫黄炭（高黄鉄鉱含有量1.4%以上，3炭種）内の局在性を検討した結果，これら元素の多くは，石炭中の鉱物質，特に黄鉄鉱とともに存在していることが明らかとなった。そこで，黄鉄鉱除去能力に長ける微生物浮遊選炭法を適用し，重金属の除去を試みた。その結果，炭種に限らず，石炭の脱灰，脱硫にともない，特に砒素やカドミウムなどの重金属を除去できることが明らかとなった。

概要 （英文）

Low ash and sulfur coals are currently used in Japanese electric power plants. In the near future, high ash and sulfur coal must be utilized. In this case, further clean coal technology would be required for the utilization of the high ash and sulfur coal. More convenient and less expensive technologies would be required for coal cleaning. In order to help the solution for this problem, we have been developing the microbial flotation of coal as a new coal utilization technology. On the conventional flotation, removing of pyritic sulfur in coal was impossible since the surface properties of pyrite as well as are hydrophobic. The microbial flotation can remove the pyrite by changing its surface properties by bacterial adhesion. On the other hand, heavy metals exit in coal, other than ash and sulfur. It is important to reduce experimental pollutants during coal combustion such as these elements. Here, we report on such a method for removing of heavy metals from coal by the microbial flotation. First, we investigated in the specific gravity distribution of heavy metals. Concentration of each element is higher in the higher gravity fraction, so that As, Se, Cd, Hg, Pb associate with pyrite and/or sulfide mineral. These results suggested that it is possible to eliminate these elements by microbial flotation. Since microbial flotation has high ability to remove pyrite from coal, at the same time, heavy metals are also removed. Secondly, high pyritic sulfur coal (Pittsburgh coal, Tenfu coal and Heisaku coal; pyritic sulfur content >=1.4) was subjected to microbial column flotation at laboratory scale experiment. In the absence of bacteria, pyrite rejection of Pittsburgh coal, Tenfu coal and Heisaku coal was 11.8, 36.2 and 55.5%, respectively. The 12.9 to 74.68% of toxic elements (As, Se, Cd, Hg, Pb, Cr) in coal was rejected by conventional flotation. With bacteria, pyrite rejection was increased to 48.9, 61.2 and 64.0%, respectively. At the same time, 31.9 to 87.34% of heavy metals was also rejected. These results showed that microbial flotation was useful method on removing of heavy metals in particular As and Cd from coal.

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