Tian Quanzhi, Guo Binglin, Nakama Shingo, Sasaki Keiko
Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishiku, Fukuoka 819-0395, Japan.
ACS Omega. 2018 Oct 11;3(10):13055-13064. doi: 10.1021/acsomega.8b02096. eCollection 2018 Oct 31.
Fly ash usually contains a considerable amount of toxic elements that can be leached into the environment, thereby easily leading to serious contaminations. In this work, the leaching behaviors of poisonous elements including boron (B), phosphorus (P), vanadium (V), chromium (Cr), arsenic (As), selenium (Se), molybdenum (Mo), antimony (Sb), and tungsten (W) from fly ash were explored by sequential extraction. Importantly, the associations of these elements in fly ash were discussed based on their leaching and X-ray absorption near-edge structure (XANES) results. From the XANES results, it was observed that V(IV), Cr(III), As(V), Se(IV), and W(IV) were their main states of existence in fly ash. In terms of leaching results, large amounts of Mo and W were leached into pure water, which indicated their high mobilities. Furthermore, the occurrence of Mo in fly ash was mainly in the form of oxides, and W had complex associations including WX (X can be monovalent anions), its reduction state or association with the elements that can be oxidized, and existence in silicates. B was as easily released into the environment as Mo and W. It can have several associations with the other cations, such as Ca, Na, and Mg, and occurs in silicates. In contrast, most of the Cr and Sb were locked in silicates, indicating that they were very stable in fly ash. In addition, P, V, and As can exist within the structure of silicates as well. However, a considerable amount of them leached in the reduction step with a low pH. Hence, they can be associated with Ca, Na, Mg, or Fe. In terms of Se, oxidation processes played an important role in controlling its leaching because of the oxidation of Se(IV) to Se(VI). Calcium selenite should be the predominant form of Se in fly ash.
粉煤灰通常含有大量可溶出到环境中的有毒元素，从而容易导致严重污染。在本研究中，通过连续提取法探究了硼（B）、磷（P）、钒（V）、铬（Cr）、砷（As）、硒（Se）、钼（Mo）、锑（Sb）和钨（W）等有毒元素从粉煤灰中的溶出行为。重要的是，基于这些元素的溶出和X射线吸收近边结构（XANES）结果，讨论了它们在粉煤灰中的赋存形态。从XANES结果可以看出，V（IV）、Cr（III）、As（V）、Se（IV）和W（IV）是它们在粉煤灰中的主要存在形态。就溶出结果而言，大量的Mo和W溶出到纯水中，这表明它们具有较高的迁移性。此外，Mo在粉煤灰中的赋存形态主要为氧化物，而W具有复杂的赋存形态，包括WX（X可以是一价阴离子）、其还原态或与可氧化元素的结合态以及在硅酸盐中的存在形态。B与Mo和W一样容易释放到环境中。它可以与其他阳离子如Ca、Na和Mg形成多种结合态，并存在于硅酸盐中。相比之下，大部分Cr和Sb被锁定在硅酸盐中，这表明它们在粉煤灰中非常稳定。此外，P、V和As也可以存在于硅酸盐结构中。然而，它们中有相当一部分在低pH值的还原步骤中溶出。因此，它们可能与Ca、Na、Mg或Fe结合。就Se而言，由于Se（IV）氧化为Se（VI），氧化过程在控制其溶出方面起着重要作用。亚硒酸钙应该是粉煤灰中Se的主要存在形式。
