Estimation of Chemical Forms of Heavy Metals in Fly Ash

了解城市生活垃圾焚烧飞灰中重金属的化学形态和浓度，对于对其进行解毒和再利用，或弄清其上二恶英的从头合成等复杂反应机理是非常重要的。采用X射线光电子能谱(XPS)、X射线衍射法、顺序萃取法和热力学方法对重金属的化学形态进行了评价。通过对飞灰中锌、铜、铅、镉的毒性和浓度的测定，发现用X射线衍射法测定飞灰中重金属的含量不能有效地判断飞灰中重金属的化学形态。利用X射线光电子能谱(XPS)对多种飞灰中重金属的化学形态进行了评价，因为重金属集中在飞灰表面，XPS的强度较高。为了掌握重金属与飞灰中重金属的组成之间的关系，采用顺序萃取法。将每次分析的结果合并在一起，得出飞灰中主要的锌化合物是2ZnCO3 3Zn(OH)2、ZnSO4 7H2O和ZnO。干法烟气处理飞灰中镉的化学形态(Cd(OH)_2，CDO)与湿法烟气处理(Cd(OH)_2，Cd_2O_2)中镉的化学形态不同，分别采用XPS和顺序萃取法可以确定飞灰中重金属的化学形态，但两者相结合可提高估算的准确性。

It is very important to know chemical forms and concentration of heavy metals in fly ash from municipal solid waste incinerator in order to detoxify and reuse it or clarify complex reaction mechanism such as de novo synthesis for dioxin on it. Chemical forms of heavy metals were estimated using X-ray Photoelectron Spectroscopy (XPS), X-ray diffraction, sequential extraction procedure and thermo-dynamics study. Zinc, copper, lead and cadmium were measured for its toxicity and concentration in fly ash.The application of X-ray diffraction analysis for heavy metals in fly ash was not effective to estimate chemical forms. Chemical forms of heavy metals in many kinds of fly ash were estimated by XPS, because heavy metals concentrated onto its surface and higher intensity was obtained for XPS.Sequential extraction procedure was used for the purpose of grasping the relationship between heavy metals and the composition in fly ash keeping heavy metals.Putting the results by each analysis together, the dominant zinc compounds in fly ash were 2ZnCO_3 3Zn(OH)_2, ZnSO_4 7H_2O and ZnO.Many compounds such as PbCl_2, PbCO_3, PbO, etc., were estimated and it is impossible to determine a dominant form in it. The dominant copper compound was CuO.Chemical form of cadmium in fly ash of dry process flue-gas treatment (Cd(OH)_2, CdO) was different from that of wet process flue-gas treatment (CdSO_4, CdCl_2).Estimation of chemical form of heavy metals in fly ash is possible by XPS and sequential extraction procedure respectively, but it is considered to be able to increase the exactitude of estimation by the combination of both methods.