2023-06-06 デューク大学(Duke)
◆石炭灰は、微粒子や表面に結合した有害元素を含んでおり、異なるサンプルによって漏出の度合いが異なることが分かりました。この研究は、石炭灰の処理や再利用において、その化学的な特性を理解する必要性を示しています。
＜関連情報＞
- https://pratt.duke.edu/about/news/coal-ash-nanostructure
- https://pubs.rsc.org/en/content/articlelanding/2023/en/d2en01056a
石炭フライアッシュ粒子におけるヒ素およびセレン種のナノスケール不均一性：強化分光イメージングとスペシエーション技術を用いた分析 Nanoscale heterogeneity of arsenic and selenium species in coal fly ash particles: analysis using enhanced spectroscopic imaging and speciation techniques
Nelson A. Rivera, Jr, Florence T. Ling, Zehao Jin, Ajith Pattammattel, Hanfei Yan, Yong S. Chu, Catherine A. Peters and Heileen Hsu-Kim
Environmental Science: Nano Published:24 May 2023
DOI:https://doi.org/10.1039/D2EN01056A
Abstract
Coal combustion byproducts are known to be enriched in arsenic (As) and selenium (Se). This enrichment is a concern during the handling, disposal, and reuse of the ash as both elements can be harmful to wildlife and humans if mobilized into water and soils. The leaching potential and bioaccessibility of As and Se in coal fly ash depends on the chemical forms of these elements and their association with the large variety of particles that comprise coal fly ash. The overall goal of this research was to determine nanoscale and microscale solid phase mineral associations and oxidation states of As and Se in fly ash. We utilized nanoscale 2D imaging (30–50 nm spot size) with the Hard X-ray Nanoprobe (HXN) in combination with microprobe X-ray capabilities (∼5 μm resolution) to determine the As and Se elemental associations. Speciation of As and Se was also measured at the nano- to microscale with X-ray absorption spectroscopy. The enhanced resolution of HXN showed As and Se as either diffusely located around or comingled with Ca- and Fe-rich particles. The results also showed nanoparticles of Se attached to the surface of fly ash grains. Overall, a comparison of As and Se species across scales highlights the heterogeneity and complexity of chemical associations for these trace elements of concern in coal fly ash.
Environmental significance
Fly ashes are the waste residuals collected during coal energy production and represent one of the largest industrial waste streams worldwide. The disposal of these residues is a significant challenge due the large volumes produced annually and the enrichment of toxic elements such as arsenic (As) and selenium (Se) in fly ash. This study describes the nanoscale heterogeneity of As and Se, both in distribution and speciation within individual fly ash grains. These insights help explain why the leaching potential of these elements are not easily predicted by elemental content. Rather, the heterogeneous distribution of As and Se in fly ash signifies that both intrinsic properties of the fly ash as well as extrinsic variables related to the leaching environment contribute to As and Se mobilization.
