Estimation of Chemical Forms of Heavy Metals in Fly Ash

为了解垃圾焚烧飞灰中重金属的化学形态和含量，对垃圾焚烧飞灰的无害化处理和资源化利用以及二恶英在飞灰上的从头合成等复杂反应机理进行了研究，采用X射线光电子能谱（XPS）、X射线衍射、连续萃取法和热力学方法对飞灰中重金属的化学形态进行了分析。测定了飞灰中锌、铜、铅和镉的毒性和含量，X射线衍射分析法不能有效地预测飞灰中重金属的化学形态。利用重金属在飞灰表面富集、XPS强度高的特点，采用XPS分析了多种飞灰中重金属的化学形态，并采用连续提取法，研究了飞灰中重金属与其组成的关系，将各分析结果综合起来，飞灰中锌的主要化合物为2ZnCO_33Zn（OH）_2、ZnSO_47H_2O和ZnO，还有PbCl_2、PbCO_3、PbO等化合物，结果表明，干法烟气处理飞灰中镉的存在形态（Cd（OH）_2，CdO）与湿法烟气处理飞灰中镉的存在形态不同（CdSO_4，CdCl_2），分别用XPS法和连续萃取法测定了飞灰中重金属的化学形态，但是认为通过两种方法的组合能够增加估计的精确度。

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.